0000950170-24-027955 | 10-K | XBRL Viewer | ALX Oncology Holdings INC

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Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets and liabilities transfers amount	$ 0	$ 0
Fair value assets transferred into level 3	0	0
Fair value assets transferred out of level 3	0	0
Fair value liabilities transferred into level 3	0	0
Fair value liabilities transferred out of level 3	0	0
Accrued interest receivable, investment	$ 1,000,000	$ 1,000,000
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Prepaid Expense and Other Assets, Current	Prepaid Expense and Other Assets, Current
Bank account cash	$ 2,300,000	$ 8,600,000
Allowance for credit losses	0	0
Fair value of securities, continuous unrealized loss position for more than 12 months	5,900,000	0
Impairment losses on available-for-sale investments	0	0
Fair Value on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial liabilities fair value disclosure	$ 0	$ 0

Commitments and Contingencies - Summary of Other Contractual Obligations and Other Commitments from Manufacturing and Service Contracts (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Manufacturing and service contracts, Total	$ 6,736
Manufacturing and service contracts, 2024	6,535
Manufacturing and service contracts, 2025-2026	201
Contractual Obligation, Total	6,736
Contractual Obligation, 2024	6,535
Contractual Obligation, 2025-2026	$ 201

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ (160,805)	$ (123,482)	$ (83,463)
Other comprehensive gain (loss), net of tax:
Unrealized gain (loss) on available-for-sale investments	1,101	(845)
Total comprehensive loss	$ (159,704)	$ (124,327)	$ (83,463)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Acquisition of Assets and Ownership

12 Months Ended

Dec. 31, 2023

Business Combinations [Abstract]

ACQUISITION OF ASSETS AND OWNERSHIP

(3) ACQUISITION OF ASSETS AND OWNERSHIP

On October 4, 2021, the Company entered into a stock purchase agreement with ScalmiBio, Inc., or ScalmiBio, as the Company expands its pipeline with plans to develop new anti-cancer drug candidates based on ScalmiBio’s platform. Under the terms of the stock purchase agreement, the Company made an initial payment to the stockholders of ScalmiBio at closing on October 4, 2021 of approximately $4.5 million in cash, net of certain expenses and adjustments, and made an additional payment of $2.0 million at the one-year anniversary of the transaction on October 4, 2022 to the stockholders of ScalmiBio. This additional payment was recorded as research and development costs within the consolidated statements of operations and consolidated statements of comprehensive loss over the one-year period given the payment was contingent on the majority stockholder remaining employed with the Company through the one-year anniversary of the closing. In addition, the Company has agreed to pay up to $35.0 million, in aggregate, in certain milestones based on the clinical development of the acquired ScalmiBio technology and has also agreed to pay a

low single digit royalty on net sales of any products developed from the ScalmiBio acquired technology for a defined term. The Company has the option to buy-out the royalty payment, prior to the first marketing approval of the developed product.

The Company’s former Chief Executive Officer and current President and Chief Scientific Officer, who is also a director, was also a director of ScalmiBio prior to the acquisition, and owned 31.7% of ScalmiBio stock. As a result, he received or will receive a proportional share of the consideration to ScalmiBio stockholders as described above. He also received approximately $87,000 out of the closing proceeds for the repayment of a note and accrued interest for a loan to ScalmiBio. Given his interest in the ScalmiBio acquisition, the Company’s audit committee approved the acquisition under its related-party transaction policy and the Company’s former Chief Executive Officer recused himself from the negotiation and approval of the transaction.

To determine the accounting for this transaction, an assessment was made as to whether an integrated set of assets and activities should be accounted for as a business combination or an asset acquisition. The guidance requires an initial screen test to determine if substantially all of the fair value of the gross assets acquired is concentrated in a single asset or group of similar assets. If that screen is met, the set is not considered a business. The Company concluded that substantially all of the fair value is concentrated in a group of similar identifiable assets. Pursuant to asset acquisition accounting, acquired IPR&D with no alternative future use is expensed at acquisition. Accordingly, $4.7 million including $0.2 million of legal and other professional fees related to the acquisition, was recognized in “Research and development” expenses in the consolidated statements of operations and consolidated statements of comprehensive loss for the year ended December 31, 2021.

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Shares Available for Grant

The following table provides a summary of shares available for grant under the 2020 Plan:


	Amended and Restated 2020 Equity Incentive Plan
Shares available for grant at December 31, 2022		2,932,309
Authorized		1,634,456
Granted		(3,703,150	)
Canceled/forfeited		441,771
Shares available for grant at December 31, 2023		1,305,386

Summary of Share Option Activity

The following table provides a summary of stock option activity under the 2020 Plan and related information:


	Outstanding Options
	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		6,196,848		$	20.56		7.78	$	19,872
Granted		3,139,800			6.03
Exercised		(54,359	)		4.95
Canceled/forfeited		(297,618	)		25.00
Outstanding at December 31, 2023		8,984,671		$	15.43		7.53	$	59,900
Exercisable at December 31, 2023		4,704,798		$	17.47		6.27	$	30,924

Schedule of Fair Value of Each Option Grant Using Black-Scholes Option-Pricing Model

The fair value of each option grant during the years ended December 31, 2023, 2022 and 2021 was estimated with the following assumptions:


	Year Ended December 31,
	2023	2022	2021
Expected term (in years)	5.3 - 6.1	5.3 - 6.1	5.3 - 6.1
Risk-free interest rate	3.5% - 4.7%	1.6% - 4.4%	0.8% - 1.4%
Expected dividend rate	-	-	-
Expected stock price volatility	83.6% - 88.6%	81.9% - 84.7%	79.7% - 86.9%

Summary of Restricted Stock Unit Activity

The following table provides a summary of restricted stock unit activity under the 2020 Plan and related information:


	Outstanding RSUs
	Number of RSUs			Weighted- Average Grant Date Fair Value		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (in thousands)
Unvested as of December 31, 2022		820,326		$	14.13		1.68	$	9,245
Granted		563,350			5.86
Vested		(289,854	)		13.33
Canceled/forfeited		(144,153	)		12.48
Unvested as of December 31, 2023		949,669		$	9.72		1.57	$	14,141

Summary of Share-Based Compensation Expense

Stock-based compensation expense includes stock options and restricted stock units and has been reported in the Company’s consolidated statements of operations as follows (in thousands):


	Year Ended
	December 31,
	2023		2022		2021
Research and development	$	14,665	$	10,741	$	5,211
General and administrative		11,608		13,098		8,703
Total	$	26,273	$	23,839	$	13,914

Stock-Based Compensation - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 26,273	$ 23,839	$ 13,914
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	14,665	10,741	5,211
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 11,608	$ 13,098	$ 8,703

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Subparagraph (d)(2)
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Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
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-Subparagraph (e)(1)
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Reference 23: http://www.xbrl.org/2003/role/disclosureRef
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Reference 24: http://www.xbrl.org/2003/role/disclosureRef
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Reference 25: http://www.xbrl.org/2003/role/disclosureRef
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Reference 26: http://www.xbrl.org/2003/role/disclosureRef
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Reference 27: http://www.xbrl.org/2003/role/disclosureRef
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Balance Sheet Components - Components of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Accrued contract manufacturing	$ 9,543	$ 5,249
Accrued clinical and nonclinical study costs	8,873	5,485
Accrued compensation and related expenses	6,067	3,708
Accrued property and equipment	179	2,110
Other	2,205	2,050
Total accrued expenses and other current liabilities	$ 26,867	$ 18,602

Term Loan - Schedule of Future Maturities Under the Loan Agreement (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Long-Term Debt, Fiscal Year Maturity [Abstract]
2025	$ 435
2026	5,217
2027	4,948
Total future maturities	10,600
Less: current portion of term loan	0
Total term loan, net of current portion	10,600
Less: unamortized debt issuance costs	(781)
Less: unaccreted final payment costs	(180)
Term loan, non-current, net	$ 9,639	$ 9,389

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Number of Options, Balance	6,196,848
Number of Options, Granted	3,139,800
Number of Options, Exercised	(54,359)
Number of Options, Canceled/forfeited	(297,618)
Number of Options, Balance	8,984,671	6,196,848
Number of Options, Exercisable at December 31, 2023	4,704,798
Weighted Average Exercise Price, Balance	$ 20.56
Weighted Average Exercise Price, Granted	6.03
Weighted Average Exercise Price, Exercised	4.95
Weighted Average Exercise Price, Canceled/forfeited	25
Weighted Average Exercise Price, Balance	15.43	$ 20.56
Weighted Average Exercise Price, Exercisable at December 31, 2023	$ 17.47
Weighted Average Remaining Contractual Life (Years), Outstanding Options	7 years 6 months 10 days	7 years 9 months 10 days
Weighted Average Remaining Contractual Life (Years), Outstanding Options Exercisable	6 years 3 months 7 days
Outstanding Options Aggregate Intrinsic Value, Balance	$ 59,900	$ 19,872
Outstanding Options Aggregate Intrinsic Value, Exercisable	$ 30,924

Acquisition of Assets and Ownership - Additional Information (Details) - ScalmiBio, Inc - USD ($)		12 Months Ended
	Oct. 04, 2021	Dec. 31, 2021	Oct. 04, 2022
Business Acquisition [Line Items]
Business acquisition, initial payment in cash	$ 4,500,000
Retention milestone payment			$ 2,000,000
Business acquisition, date of acquisition	Oct. 04, 2021
Maximum milestones amount payable on clinical development acquired technology	$ 35,000,000
Business acquisition, percentage of voting interests acquired	31.70%		31.70%
Repayment of note and accrued interest	$ 87,000
Acquisition related costs		$ 200,000
Research and Development
Business Acquisition [Line Items]
Acquisition related costs		$ 4,700,000

Income Taxes - Schedule of Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Current provision for income taxes:
Federal	$ 64	$ (21)
Total current	64	(21)
Deferred tax provision:
Provision (benefit) for income taxes	$ 64	$ (21)

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Stock-Based Compensation - Summary of Restricted Stock Unit Activity (Details) - Restricted Stock Units - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSUs, Balance	820,326
Number of RSUs, Granted	563,350
Number of RSUs, Vested	(289,854)
Number of RSUs, Canceled/forfeited	(144,153)
Number of RSUs, Balance	949,669	820,326
Weighted-Average Grant Date Fair Value, Balance	$ 14.13
Weighted-Average Grant Date Fair Value, Granted	5.86	$ 13.55	$ 58.56
Weighted-Average Grant Date Fair Value, Vested	13.33
Weighted-Average Grant Date Fair Value, Canceled/forfeited	12.48
Weighted-Average Grant Date Fair Value, Balance	$ 9.72	$ 14.13
Weighted Average Remaining Contractual Life (Years), Balance	1 year 6 months 25 days	1 year 8 months 4 days
Aggregate Intrinsic Value, Balance	$ 14,141	$ 9,245

Stock-Based Compensation - Additional Information (Details) - USD ($)			1 Months Ended	12 Months Ended
	Jan. 01, 2023	Jan. 01, 2022	Jul. 31, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Apr. 01, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance				12,305,115
Unvested early exercised options				0
Stock-based compensation expenses				$ 26,273,000	$ 23,839,000	$ 13,914,000
Total intrinsic value of options exercised				$ 200,000	$ 1,700,000	$ 48,100,000
Weighted-average grant-date fair value per share				$ 4.44	$ 7.88	$ 42.29
Unrecognized share-based compensation expense				$ 38,900,000
Unrecognized share-based compensation expense, weighted-average period				2 years 10 months 24 days
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance			400,000	1,065,389
Percentage of eligible compensation withheld			15.00%
Share-based compensation, authorized amount			$ 25,000
Share-based compensation, number of shares authorized			3,000
Share-based Compensation, lower of closing price, percentage			85.00%
Maximum percentage of additional shares reserved for future issuance				1.00%
Number of additional shares reserved for future issuance	0	405,871
Number of shares purchased				138,927
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant-date fair value per share, restricted stock units granted				$ 5.86	$ 13.55	$ 58.56
Restricted stock units granted				563,350
Unrecognized share-based compensation expense				$ 8,200,000
Unrecognized share-based compensation expense, weighted-average period				2 years 10 months 24 days
Maximum \| ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares reserved for future issuance				800,000
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of permitted issuance of share option							4,379,139
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance			7,874,862
Share options, maximum term				10 years
Share options, service period				4 years
Maximum percentage of additional shares reserved for future issuance				4.00%
2020 Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares reserved for future issuance				4,000,000
Stock Option Modification
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expenses				$ 0	$ 0

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

FAIR VALUE OF FINANCIAL INSTRUMENTS

(4) FAIR VALUE OF FINANCIAL INSTRUMENTS

The following table presents the Company’s financial assets that are measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2023 and 2022 (in thousands):


	December 31, 2023
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents
Money market funds	Level 1	$	15,591	$	—	$	—		$	15,591
Corporate debt securities	Level 2		4,489		1		—			4,490
Short-term investments
U.S. Treasury securities	Level 1		74,790		80		(20	)		74,850
U.S. government agency securities	Level 2		28,215		—		(38	)		28,177
Corporate debt securities	Level 2		21,881		24		(3	)		21,902
Commercial paper	Level 2		34,967		22		(9	)		34,980
Asset-backed securities	Level 2		423		—		(2	)		421
Long-term investments
U.S. Treasury securities	Level 1		14,737		75		—			14,812
U.S. government agency securities	Level 2		3,009		31		—			3,040
Corporate debt securities	Level 2		17,464		95		—			17,559
Total		$	215,566	$	328	$	(72	)	$	215,822


	December 31, 2022
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents
Money market funds	Level 1	$	36,690	$	—	$	—		$	36,690
U.S. government agency securities	Level 2		3,484		—		—			3,484
Short-term investments
U.S. Treasury securities	Level 1		73,058		3		(438	)		72,623
U.S. government agency securities	Level 2		16,227		36		—			16,263
Corporate debt securities	Level 2		56,318		—		(367	)		55,951
Commercial paper	Level 2		62,087		—		—			62,087
Asset-backed securities	Level 2		10,512		—		(51	)		10,461
Long-term investments
U.S. Treasury securities	Level 1		5,242		2		—			5,244
U.S. government agency securities	Level 2		9,760		—		(15	)		9,745
Asset-backed securities	Level 2		1,725		—		(15	)		1,710
Total		$	275,103	$	41	$	(886	)	$	274,258

The Company did not have any outstanding financial liabilities to be re-measured on a recurring basis as of December 31, 2023 and 2022.

The fair value of cash equivalents and available-for-sale investments by classification included in the consolidated balance sheets was as follows as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Cash and cash equivalents	$	20,081	$	40,174
Short-term investments		160,330		217,385
Long-term investments		35,411		16,699
Total	$	215,822	$	274,258

Cash and cash equivalents in the above table excludes bank account cash of $2.3 million and $8.6 million as of December 31, 2023 and 2022, respectively.

The fair value of cash equivalents and available-for-sale investments by contractual maturity was as follows as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Maturing in one year or less	$	180,411	$	257,559
Maturing after one year through five years		35,411		16,699
Total	$	215,822	$	274,258

The primary objective of the Company’s investment portfolio is to maintain safety of principal, prudent levels of liquidity and acceptable levels of risk. The Company’s investment policy limits investments to certain types of instruments issued by institutions with investment-grade credit ratings, and it places restrictions on maturities and concentration by asset class and issuer.

There were no transfers of assets or liabilities between the fair value measurement levels during the years ended December 31, 2023 and 2022 and there were no financial instruments classified as Level 3 as of December 31, 2023 and 2022.

As of December 31, 2023 and 2022, accrued interest receivable related to the Company’s investments of $1.0 million and $1.0 million, respectively, was included in prepaid expenses and other current assets as well as other assets on the consolidated balance sheets.

As of December 31, 2023, the unrealized losses for available-for-sale investments were non-credit related and the Company does not intend to sell the investments that were in an unrealized loss position, nor will it be required to sell those investments before recovery of their amortized costs basis, which may be maturity. As of December 31, 2023 and 2022, no allowance for credit losses for the Company’s investments was recorded. As of December 31, 2023 and 2022, securities with a fair value of $5.9 million and zero, respectively, were in a continuous net unrealized loss position for more than 12 months. As of December 31, 2023 and 2022, the Company has not recognized any impairment losses on available-for-sale investments.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Components - Schedule of Components of Other Assets, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Operating lease right-of-use assets	$ 4,847	$ 5,626
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Total other assets	Total other assets
Finance lease right-of-use assets	$ 2,405	$ 298
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Total other assets	Total other assets
Other	$ 200	$ 288
Total other assets	14,894	14,932
Long-term Prepaid Clinical Expenses
Property Plant And Equipment [Line Items]
Long-term prepaid expenses	7,442	7,264
Long-term Prepaid Contract Manufacturing Costs
Property Plant And Equipment [Line Items]
Long-term prepaid expenses	$ 0	$ 1,456

Related-Party Transactions

12 Months Ended

Dec. 31, 2023

RELATED-PARTY TRANSACTIONS

(11) RELATED-PARTY TRANSACTIONS

Tallac Service Agreement

The Company entered into a research and development services agreement, or the Tallac Services Agreement, with Tallac Therapeutics, Inc., or Tallac, effective as of July 1, 2020. The Tallac Services Agreement provides that Tallac will provide certain preclinical research services to the Company for a service fee based on the costs incurred by Tallac plus a mark-up equal to 10.0% of such costs. The Tallac Services Agreement has an initial term of four years and is renewed automatically for additional one year terms thereafter. The Company records the payments for the research and development services as research and development, or R&D, costs within the consolidated statements of operations. For the years ended December 31, 2023, 2022 and 2021, the Company recorded $0.3 million, $0.6 million and $0.8 million, respectively, as R&D costs in relation to the Tallac Services Agreement.

Tallac Collaboration Agreement

On March 4, 2021, the Company entered into a Collaboration Agreement with Tallac, or the Tallac Collaboration Agreement, to jointly develop, manufacture, and commercialize a novel class of cancer immunotherapy. The collaboration builds on the Company’s expertise in developing therapies that block the CD47 checkpoint pathway and expands its immuno-oncology pipeline. The companies will leverage their respective scientific and technical expertise to advance an anti-SIRPα antibody conjugated to a Toll-like receptor 9, or TLR9, agonist for targeted activation of both the innate and adaptive immune systems. The key economic components of the collaboration transaction include that both parties will share equally (a) in the cost and expenses of research and development and (b) any profit or loss.

The Company accounts for R&D costs in accordance with ASC 730, Research and Development, which states R&D costs must be charged to expense as incurred. Accordingly, the Company records its internal and third-party costs associated with the collaboration as R&D expenses as incurred. When the Company is entitled to reimbursement of the R&D expenses that it incurs under the collaboration, the Company records those reimbursable amounts as a reduction to R&D expenses. The Company also records as R&D expenses, the portion of Tallac’s expenses that the Company is obligated to reimburse, in the period when Tallac incurs such expenses. During the years ended December 31, 2023, 2022 and 2021, the Company recorded $1.7 million, $7.8 million and $2.8 million, respectively, as R&D costs in relation to the Tallac Collaboration Agreement.

The Tallac Collaboration Agreement includes the right to set off clause, as such, the Company records the amount due to or reimbursable from Tallac on a net basis. As of December 31, 2023 and 2022, the Company had accrued expenses of $0.5 million and $1.6 million, respectively, related to the Tallac Collaboration Agreement which was presented within the payable and accrued liabilities due to related party on the consolidated balance sheets.

Acquisition of assets and ownership of ScalmiBio

On October 4, 2021, the Company entered into a stock purchase agreement with ScalmiBio. The Company’s former Chief Executive Officer and current Chief Scientific Officer and President, who is also a director, was also a director of ScalmiBio prior to the acquisition, and owned 31.7% of ScalmiBio stock. Refer to Note 3 “Acquisition of assets and ownership” for additional discussion.

On October 4, 2022, the Company made a $2.0 million payment to stockholders of ScalmiBio at the one-year anniversary of the transaction to stockholders of ScalmiBio, including 31.7%, or $0.6 million, to the Company’s former Chief Executive Officer and current Chief Scientific Officer and President. This payment was recorded as R&D costs within the consolidated statements of operations over the one-year period.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating activities
Net loss	$ (160,805)	$ (123,482)	$ (83,463)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	836	342	51
Non-cash lease costs	1,272	1,124	685
Acquired in-process research and development			4,739
Stock-based compensation	26,273	23,839	13,914
Net amortization of premiums and accretion of discounts on investments	(6,487)	(940)
Accretion of term loan discount and issuance costs	250	44
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(1,291)	(1,476)	(1,662)
Other assets	1,366	750	(9,682)
Accounts payable	458	4,506	3,290
Payable and accrued liabilities due to related party	(1,107)	20	1,419
Accrued expenses and other current liabilities	11,224	7,027	3,306
Other non-current liabilities	(2,353)	(977)	(698)
Net cash used in operating activities	(130,364)	(89,223)	(68,101)
Investing activities
Purchase of investments	(246,629)	(376,789)
Maturities of investments	292,560	142,800
Purchase of property and equipment	(1,274)	(1,427)	(666)
Acquisition of in-process research and development			(4,257)
Net cash provided by (used in) investing activities	44,657	(235,416)	(4,923)
Financing activities
Proceeds from equity offerings, net of underwriter discounts ($3.8 million) and issuance costs ($0.6 million)	58,887
Proceeds from exercise of stock options under equity incentive plan	269	567	2,551
Proceeds from issuance of common stock under employee stock purchase plan	523	336	202
Principal payments on finance leases	(388)	(388)	(281)
Proceeds from issuance of term loan, net		10,000
Payments of debt issuance costs		(655)
Net cash provided by financing activities	59,291	9,860	2,472
Net decrease in cash, cash equivalents and restricted cash	(26,416)	(314,779)	(70,552)
Cash, cash equivalents and restricted cash at beginning of year	48,888	363,667	434,219
Cash, cash equivalents and restricted cash at end of period	22,472	48,888	363,667
Supplemental disclosure
Cash paid for interest	1,177	103	11
Cash paid for taxes			274
Supplemental disclosure of non-cash investing and financing activities
Purchase of property and equipment in accounts payable and accrued expenses	1,407	2,145	237
Acquisition of in-process research and development in accounts payable and accrued expenses			482
Right-of-use asset acquired under operating leases		4,613	1,780
Right-of-use asset acquired under finance leases	2,600		776
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents	22,406	48,822	363,667
Restricted cash (included in other assets)	66	66
Total cash and cash equivalents and restricted cash	$ 22,472	$ 48,888	$ 363,667

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended			12 Months Ended
	Jul. 21, 2020	Jul. 20, 2020	Oct. 31, 2023	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2023	Dec. 31, 2022
Class Of Stock [Line Items]
Common stock, shares authorized	1,000,000,000					1,000,000,000	1,000,000,000
Common stock, par value	$ 0.001					$ 0.001	$ 0.001
Preferred stock, par value	$ 0.001
Common stock, shares outstanding						49,951,989	40,861,386
Underwriting discounts and commissions paid						$ 0.6
Pre-funded Warramts
Class Of Stock [Line Items]
Common stock shares, Percentage			9.99%
Excess other percentage			19.99%
Proceeds from offering allocated to pre-funded warrants			$ 7.4
Initial Public Offering \| Common Stock
Class Of Stock [Line Items]
Shares issued	9,775,000
Net proceeds from initial public offering	$ 169.5
Underwriting discounts and commissions paid	13.0
Payment for offering related expense	$ 3.2
Convertible shares converted in to common stock	23,934,533
Follow-on Public Offering \| Common Stock
Class Of Stock [Line Items]
Shares issued					2,737,000
Net proceeds from initial public offering					$ 194.9
Underwriting discounts and commissions paid					12.5
Payment for offering related expense					$ 0.7
Underwritten Follow-on Public Offering
Class Of Stock [Line Items]
Net proceeds received			$ 58.9
Underwritten Follow-on Public Offering \| Common Stock
Class Of Stock [Line Items]
Shares issued			8,663,793
Underwriting discounts and commissions paid			$ 3.8
Payment for offering related expense			$ 0.6
Shares original issue price			$ 6.38
Underwritten Follow-on Public Offering \| Pre-funded Warramts
Class Of Stock [Line Items]
Warrants to purchase of common stock			1,250,000
Shares original issue price			$ 6.379
Common stock exercise price			$ 0.001
Over Allotment Option \| Common Stock
Class Of Stock [Line Items]
Shares issued			1,293,103
At-the-Market Equity Offering \| Common Stock \| Maximum
Class Of Stock [Line Items]
Gross proceeds from issuance of common stock				$ 150.0
Undesignated Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized	100,000,000
Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, cumulative dividends percentage						6.00%
Accrued cumulative dividends on the Series A, Series B and Series C convertible preferred stock		$ 18.0
Cumulative preferred stock dividend convertible shares issued upon conversion		2,564,759
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Shares original issue price						$ 6.58
Series B and C Convertible Preferred Stock
Class Of Stock [Line Items]
Shares original issue price						$ 9.4972

Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Loss per Share

The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):


	Year Ended
	December 31,
	2023			2022			2021
Numerator:
Net loss	$	(160,805	)	$	(123,482	)	$	(83,463	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		42,987,767			40,699,612			40,308,050
Net loss per share, basic and diluted	$	(3.74	)	$	(3.03	)	$	(2.07	)

Summary of Outstanding Potentially Dilutive Securities Were Excluded from Computation of Diluted Net Loss Per Share

The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the years ended December 31, 2023, 2022 and 2021, because including them would have been anti-dilutive:


	Year Ended
	December 31,
	2023		2022		2021
Stock options issued and outstanding		8,984,671		6,196,848		5,128,639
Restricted stock issued and outstanding		949,669		820,326		15,075
Employee Stock Purchase Plan estimated shares issuable		—		—		—
Total		9,934,340		7,017,174		5,143,714

Consolidated Statements of Cash Flows (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Statement of Cash Flows [Abstract]
Underwriter discounts	$ 3.8
Issuance costs	$ 0.6

Insider Trading Arrangements - shares			12 Months Ended
Insider Trading Arrangements - shares	Dec. 06, 2023	Oct. 12, 2023	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted			false
Non-Rule 10b5-1 Arrangement Adopted			false
Rule 10b5-1 Arrangement Terminated			false
Non-Rule 10b5-1 Arrangement Terminated			false
Rekha Hemrajani
Trading Arrangements, by Individual
Name		Rekha Hemrajani
Title		Board of Directors
Rule 10b5-1 Arrangement Adopted		false
Arrangement Duration		488 days
Aggregate Available		50,000
Jaume Pons
Trading Arrangements, by Individual
Name	Jaume Pons
Title	President, Chief Scientific Officer and a member of the Board of Directors
Rule 10b5-1 Arrangement Adopted	false
Arrangement Duration	849 days
Aggregate Available	351,198

Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2023
Basis of Presentation	Basis of Preparation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP, and the applicable rules and regulations of the U.S. Securities and Exchange Commission, or SEC.
Reclassifications	Reclassifications Certain reclassifications have also been made within the consolidated statements of operations for the years ended December 31, 2022 and 2021 to conform to the current year presentation. For the year ended December 31, 2022, the Company reclassified approximately $0.2 million out of other expense, net into a separate interest expense financial statement line item and renamed other expense, net to other income (expense), net. For the year ended December 31, 2021, the Company reclassified less than $0.1 million out of other expense, net into a separate interest income financial statement line item and renamed other expense, net to other income (expense), net. Total loss before income taxes as of December 31, 2022 and 2021 did not change as a result of these reclassifications.
Principles of Consolidation	Principles of Consolidation All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, management evaluates its estimates, including, but not limited to, those related to the estimated useful lives of long-lived assets, clinical and contract manufacturing accruals, fair value of assets and liabilities, fair value of investments, valuation of the Company’s common stock in periods prior to its initial public offering and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company holds its cash and cash equivalents in checking and money market accounts. The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market funds and U.S. government agency securities that are stated at cost, which approximate fair value.
Investments	Investments Investments consist of money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt securities, commercial paper and asset-backed securities. The Company’s investments are classified as available-for-sale and carried at estimated fair values and reported in cash equivalents, short-term investments and long-term investments. Management determines the appropriate classification of the investments at the time they are purchased and evaluates the appropriateness of such classifications at each balance sheet date. Investments with contractual maturities greater than 12 months are considered long-term investments. Management has elected to use transaction settlement date as the purchase date of investments. The Company regularly reviews its investments for declines in estimated fair value below amortized cost. The factors considered in determining whether a credit loss exists include the creditworthiness of the security issuers, the number of investments in an unrealized loss position, the severity and duration of the unrealized losses, and whether it is more likely than not that the Company will be required to sell the investments before the recovery of their amortized cost basis. The cost of investments sold is based on the specific identification method. In circumstances when an unrealized loss is determined to be credit-related, or when the Company intends to sell or is more likely than not required to sell a security before it recovers its amortized cost basis, the difference between the fair value and the amortized cost of the security is recognized within other income (expense), net in the consolidated statements of operations, and an allowance for credit loss is recorded on the consolidated balance sheets. In circumstances when the decline in fair value is non-credit related, the difference is reported in accumulated other comprehensive loss, net of tax as a separate component of consolidated stockholders’ equity.
Concentration Of Credit Risk, Credit Losses And Other Risks And Uncertainties	Concentration of Credit Risk, Credit Losses and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash, cash equivalents, and investments. The primary objectives for the Company’s investment portfolio are the preservation of capital and the maintenance of liquidity. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash, cash equivalents and investments and issuers of investments. The Company manages its credit risk by holding its cash, cash equivalents and investments in large financial institutions within the U.S. In addition, the Company’s investment policy limits investments to certain types of instruments such as money market funds, debt securities issued by the U.S. government and its agencies, corporate debt securities, commercial paper as well as asset-backed securities, and places restrictions on the credit ratings, maturities and concentration by type and issuer. The Company has not experienced any realized losses on its deposits of cash, cash equivalents and investments. The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals or sole-source suppliers. The Company’s product candidates require approvals from the U.S. Food and Drug Administration, or FDA, and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation of property and equipment is provided using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on a straight-line basis over the shorter of the term of the lease, or the useful life of the assets. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the consolidated balance sheets and the resulting gain or loss is reflected in the consolidated statements of operations. Maintenance and repairs are charged to the consolidated statements of operations as incurred.
Leases	Leases On January 1, 2021, the Company adopted Accounting Standards Update No. 2016-02, Leases, Topic 842, or Accounting Standards Codification (ASC) 842, using the alternative modified transition method, which applies the standard as of the adoption date. Results and disclosure requirements for reporting periods beginning after January 1, 2021 are presented under ASC 842. The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, leases are included in operating or finance lease right-of-use, or ROU, assets; current operating or finance lease liabilities; and non-current operating or finance lease liabilities. Lease ROU assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. ROU assets also include any initial direct costs incurred and any lease payments made on or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. The incremental borrowing rate is reevaluated upon a lease modification. The Company considered information available at the adoption date of ASC 842 to determine the incremental borrowing rate for leases in existence as of this date. Lease terms may include options to extend or terminate the lease when the Company is reasonably certain that the option will be exercised. Lease expense for operating leases is recognized on a straight-line basis over the lease term. For finance leases, ROU assets are amortized on a straight-line basis over the shorter of the expected useful life or the lease term, and the carrying amount of the lease liability is adjusted to reflect interest, which is recorded in interest expense. The Company elected to apply each of the practical expedients described in ASC 842 which allow companies (i) not to reassess prior conclusions on whether any expired or existing contracts are or contain a lease, lease classification, and initial direct costs, (ii) combine lease and non-lease components for all underlying assets groups, and (iii) not recognize ROU assets or lease liabilities for short term leases. A short-term lease is a lease that, at the commencement date, has a lease term of 12 months or less and does not include an option to purchase the underlying asset that the lessee is reasonably certain to exercise.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future undiscounted net cash flows which the asset or asset group are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds its fair value. Fair value is determined using various valuation techniques including discounted cash flow models, quoted market values and third-party independent appraisals, as considered necessary. The Company has not recorded impairment of any long-lived assets.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The fair value of the Company’s financial assets and liabilities are determined in accordance with the fair value hierarchy established in ASC 820, Fair Value Measurements and Disclosures. ASC 820 defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy of ASC 820 requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels: Level 1—Observable inputs, such as quoted prices in active markets; Level 2—Inputs, other than the quoted prices in active markets, which are observable either directly or indirectly such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life; and Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. As of December 31, 2023 and 2022, the carrying amount of cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximated their estimated fair value due to their relatively short maturities. The carrying amount of our non-current debt approximates fair value based on Level 2 inputs since the debt carries a variable interest rate that is tied to the current SOFR rate plus a spread. The Company classifies money market funds and U.S. treasury securities as Level 1 within the fair value hierarchy as the fair value is based on quoted prices. The Company classifies its investments in U.S. government agency securities, corporate debt securities, commercial paper, and asset-backed securities as Level 2 within the fair value hierarchy as the fair value is estimated by third-party pricing sources using quoted prices for identical or similar instruments in markets that are not active and industry-standard model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Where applicable, these models project future cash flows and discount the future amounts to a present value using market-based observable inputs obtained from various third-party data providers, including but not limited to benchmark yields, reported trades and broker/dealer quotes. Where applicable the market approach utilizes prices and information from market transactions for similar or identical assets.
Issuance Costs	Issuance Costs Debt issuance costs consist of payments made to secure commitments under certain debt financing arrangements. These amounts are recognized as interest expense over the period of the financing arrangement using the effective interest method. If the financing arrangement is canceled or forfeited, or if the utility of the arrangement to the Company is otherwise compromised, these costs are recognized as interest expense immediately. The Company’s consolidated financial statements present debt issuance costs related to a recognized debt liability as a direct reduction from the carrying amount of that debt liability. Equity issuance costs consist of certain legal, professional accounting and third-party fees directly associated with in-process equity financings. These amounts are capitalized as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the equity financing. In the event an anticipated offering is terminated or significantly delayed, deferred offering costs will be immediately expensed as part of general and administrative expenses. As of December 31, 2023 and 2022, no deferred offering costs were included as prepaid expenses and other current assets on the consolidated balance sheets, and all offering costs were offset against offering proceeds and reclassified to additional paid-in capital on the consolidated balance sheets.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred and consist primarily of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to nonemployees and external entities on behalf of the Company, such as consultants, central laboratories, contractors, collaborators, CMOs and CROs, in connection with our preclinical and clinical development activities and expenses incurred in connection with license agreements. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and recorded in prepaid expenses and other current assets, and then expensed as the related goods are delivered or the services are performed.
Asset Acquisition Including Acquired In-Process Research and Development Expenses	Asset Acquisition including Acquired In-Process Research and Development Expenses When determining whether a transaction gives rise to an acquisition of a business or asset group, the Company applies a screening test to determine whether substantially all of the fair value of the gross assets acquired in the transaction is concentrated in a single identifiable asset or group of similar identifiable assets. If so, then the assets are not considered a business and the transaction is accounted for as an asset acquisition. The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the asset or group of assets, which includes transaction costs. Goodwill is not recognized in asset acquisitions or transactions to license intellectual property. In an asset acquisition, the cost allocated to acquired in-process research and development (IPR&D) with no alternative future use is recognized as an expense on the acquisition date. When a transaction is accounted for as an asset acquisition, an in-process research and development, or IPR&D asset is only capitalized if it has an alternative future use other than in a particular research and development project. Otherwise, amounts allocated to IPR&D that have no alternative use are expensed. Upfront and milestone payments made related to an asset acquisition are accrued for and expensed when the achievement of the milestone is considered probable.
Clinical and Contract Manufacturing Accruals	Clinical and Contract Manufacturing Accruals The Company records accruals for estimated costs of research, preclinical studies and clinical trials, and manufacturing development, which are a significant component of research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations, or CROs, and contract manufacturing organizations, or CMOs. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fees to be paid for such services. To assist in its estimates the Company relies upon the receipt of timely and accurate reporting from its clinical and non-clinical studies and other third-party vendors. The Company makes significant judgments and estimates in determining the accrual balance at the end of each reporting period. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, the Company’s understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in the Company reporting amounts that are too high or too low in any particular period. Through December 31, 2023, there have been no material differences from the Company’s accrued estimated expenses to the actual clinical trial expenses. However, variations in the assumptions used to estimate accruals, including, but not limited to, the number of patients enrolled, the rate of patient enrollment, the actual services performed, and related costs may vary from the Company’s estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial position and results of operations.
Stock-based Compensation Expense	Stock-based Compensation Expense The Company incurs stock-based compensation expense primarily from stock options, restricted stock units, and ESPP purchase rights. The Company estimates the fair value of stock options granted to employees, directors and non-employees and ESPP purchase rights using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of subjective assumptions, including expected volatility, expected dividend yield, expected term, risk-free rate of return and the estimated fair value of the underlying common stock on the date of grant. Prior to the Company’s initial public offering, the fair value of the common stock underlying the stock-based awards was determined on each grant date by the board of directors, with input from management, considering the most recently available third-party valuation of common shares. The grant-date fair value of restricted stock units is the fair value of the underlying stock on the award’s grant date. The Company uses the straight-line method to allocate compensation expense to reporting periods over the requisite service period, which is generally the vesting period. The Company accounts for the effect of forfeitures as they occur.
Segment Reporting	Segment Reporting The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. All of the Company’s long-lived assets are located in the United States.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency of the Company’s operation and each of its subsidiaries is U.S. dollars. All assets and liabilities denominated in a foreign currency are translated into U.S. dollars at the exchange rate prevailing on the balance sheet date. Expenses are translated at the average exchange rates prevailing during the applicable period. Foreign currency transaction gains and losses are included in the consolidated statements of operations and recorded in other income (expense), net, and were immaterial for the years December 31, 2023, 2022 and 2021.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates in effect for the period in which the temporary differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statements of operations and comprehensive loss in the period that includes the enactment date. Deferred income taxes comprise the impact of temporary differences between assets and liabilities recognized for financial reporting purposes and the amounts recognized for income tax reporting purposes, net operating loss carryforwards, and other tax credits measured by applying currently enacted tax laws. A valuation allowance is provided when necessary to reduce deferred tax assets to an amount that is more likely than not to be realized. If the Company determines that it would be able to realize its deferred tax assets in the future in excess of their net recorded amount, it would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit.
Comprehensive Loss	Comprehensive Loss Comprehensive loss consists of net loss and changes in unrealized gains and losses on investments for all periods presented.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and pre-funded warrants outstanding during the period, without consideration for common stock equivalents. Shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing net loss per share because the shares may be issued for little or no consideration, are fully vested, and are exercisable after the original issuance date. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2020, the FASB issued ASU 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40) (ASU 2020-06). ASU 2020-06 eliminates the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. The new guidance also modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted EPS computation. ASU 2020-06 is effective for annual periods beginning after December 15, 2023, including interim periods within those annual periods. Early adoption is permitted. ASU 2020-06 allows companies to adopt the guidance through either a modified retrospective method of transition or a fully retrospective method of transition. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures. In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (ASU 2023-07). The amendments in ASU 2023-07 are intended to improve reportable segment disclosure, primarily through enhanced disclosures about significant segment expenses. ASU 2023-07 is effective for annual periods beginning after December 15, 2023, and interim periods beginning after December 15, 2024. The amendments in this ASU should be applied retrospectively to all prior periods presented in the financial statements. Early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (ASU 2023-09). ASU 2023-09 requires enhanced annual disclosures regarding the rate reconciliation and income taxes paid information. ASU 2023-09 is effective for annual periods beginning after December 15, 2024 and may be adopted on a prospective or retrospective basis. Early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures.

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule Components of Loss Before Income Taxes

The U.S. domestic and international components of pre-tax loss for the years ending December 31, 2023, 2022 and 2021 are as follows (in thousands):


	Year Ended December 31,
	2023			2022			2021
United States	$	(159,766	)	$	(111,360	)	$	(30,565	)
International		(1,039	)		(12,058	)		(52,919	)
Loss before income taxes	$	(160,805	)	$	(123,418	)	$	(83,484	)

Schedule of Income Tax Provision (Benefit)

The federal and state provision (benefit) for income taxes consist of the following (in thousands):


	Year Ended December 31,
	2023		2022		2021
Current provision for income taxes:
Federal	$	—	$	64	$	(21	)
State		—		—		—
International		—		—		—
Total current		—		64		(21	)
Deferred tax provision:
Federal		—		—		—
State		—		—		—
International		—		—		—
Total deferred		—		—		—
Provision (benefit) for income taxes	$	—	$	64	$	(21	)

Schedule of Statutory and Effective Income Tax Rate Reconciliation

A reconciliation of the U.S. federal statutory income tax rate to the effective tax for the years ended December 31, 2023, 2022 and 2021 are as follows (in thousands):


	Year Ended December 31,
	2023			2022			2021
At federal statutory income tax rate	$	(33,769	)	$	(25,918	)	$	(17,532	)
State income taxes		(1,481	)		(2,659	)		(105	)
Stock-based compensation		3,645			2,368			(4,031	)
Research & development credits		(7,185	)		(1,779	)		(2,131	)
Change in valuation allowance		64,486			9,067			11,476
Other		189			36			172
Foreign rate differential		(23	)		18,949			11,032
Prior period true ups		—			—			1,098
Rate benefit of reorganization		(25,862	)		—			—
Provision (benefit) for income taxes	$	—		$	64		$	(21	)

Schedule of Components of Deferred Tax Assets

Significant components of the Company’s deferred tax assets as of December 31, 2023 and 2022 are as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Loss carryforwards	$	26,517		$	16,319
Research & other credits		17,131			8,435
Other		8,076			14
Accrued expenses		1,014			1,860
Stock options		5,157			3,860
Lease liabilities		1,587			1,323
Capitalized R&D		38,425			1,702
Total deferred tax assets		97,907			33,513
Deferred tax liabilities:
Fixed assets		96			215
Lease ROU assets		1,523			1,244
Prepaid expenses		—			252
Total deferred tax liabilities		1,619			1,711
Valuation allowance		(96,288	)		(31,802	)
Net deferred tax assets	$	—		$	—

Summary of Net Operating Loss and Tax Credit Carryforwards

Net operating losses and tax credit carryforwards as of December 31, 2023 are as follows (in thousands):


	Amount		Expiration Years
Net operating losses, federal (post December 31, 2017)	$	93,542	Do Not Expire
Net operating losses, state	$	68,993	2038-2040
Tax credits, federal	$	14,431	2039-2043
Tax credits, state	$	5,918	N/A
Net operating losses, foreign	$	4,896	N/A

Schedule of Unrecognized Tax Benefits

The Company has the following activity relating to unrecognized tax benefits (in thousands):


	Year Ended December 31,
	2023			2022			2021
Balance at beginning of year	$	1,661		$	1,217		$	842
Additions/reversals based on tax positions of prior years		81			13			(69	)
Additions based on tax positions related to the current year		1,409			443			494
Lapses in statutes of limitations		(31	)		(12	)		(50	)
Balance at end of year	$	3,120		$	1,661		$	1,217

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Depreciation	$ 0.8	$ 0.3

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

LEASES

(6) LEASES

In conjunction with the adoption of ASC 842 on January 1, 2021, the Company evaluated its vendor contracts to identify embedded leases, if any, and noted that a pharmaceutical support services agreement entered into in May 2016 included leases under ASC 842 because the Company has the right to direct the use of certain equipment. The embedded leases commenced in September 2020 and were set to expire in August 2023 with no stated option to extend the term. In May 2023, the Company entered into an addendum to extend the existing lease through May 2026 and lease additional number of certain equipment. In October 2023, the Company entered into an additional addendum to lease an additional number of certain equipment through May 2026. The Company classified the leases as finance leases.

In May 2021, the Company entered into a lease agreement for approximately 10,000 square feet of office space located in South San Francisco, California. The lease commenced on June 6, 2021 and expires on August 31, 2026. The lease does not provide an option to extend after it expires. The total lease payments for the life of the lease are approximately $2.0 million. The Company classified the lease as an operating lease.

In February 2022, the Company entered into a lease agreement totaling approximately 11,074 square feet of office and laboratory space located in Palo Alto, California. The lease consists of two premises and expires in February 2030. The lease provides for an option to extend for two years after expiration. The lease for one of the premises commenced in February 2022 and the lease for the second premises commenced in April 2022. The lease provides for an annual base rent of approximately $0.8 million, which increases on an annual basis by 3%. The total lease payments for the life of the lease are approximately $6.9 million. The Company is also responsible for leasehold improvement costs related to the second premises, which totaled to $2.3 million, of which $1.5 million is to be paid with interest at a rate of 7% per annum as additional payments over the life of the lease. The Company classified the lease as an operating lease. Under the terms of the lease agreement, the Company issued a letter of credit to the landlord in the amount of $0.1 million, which is collateralized by a restricted cash deposit of $0.1 million (see Note 5 “Other Assets”).

As of December 31, 2023, the ROU assets recorded for operating leases and finance leases were $4.8 million and $2.4 million, respectively. As of December 31, 2022, the ROU assets recorded for operating leases and finance leases were $5.6 million and $0.3 million, respectively. The amounts were included in the other assets on the consolidated balance sheets.

The following table presents the maturities and balance sheet information of the Company’s operating and finance lease liabilities as of December 31, 2023 (in thousands, except lease term and discount rate):


	December 31, 2023
	Operating Leases			Finance Leases
2024	$	1,267		$	1,056
2025		1,305			1,056
2026		1,187			440
2027		912			—
2028		939			—
Thereafter		1,130			—
Total lease payments		6,740			2,552
Less: imputed interest		(1,482	)		(252	)
Total lease liabilities	$	5,258		$	2,300

Lease liabilities: current (i)	$	847		$	728
Lease liabilities: non-current (ii)		4,411			1,572
Total lease liabilities	$	5,258		$	2,300

Weighted average remaining lease term (in years)		5.4			2.4
Weighted average discount rate		8.7	%		8.5	%

(i)

Current lease liabilities are presented within accrued expenses and other current liabilities on the consolidated balance sheets.

(ii)

Non-current lease liabilities are presented within other non-current liabilities on the consolidated balance sheets.

The following table presents the components of lease costs for the years ended December 31, 2023, 2022, and 2021 (in thousands):


	Year Ended
	December 31,
	2023		2022		2021
Operating lease cost	$	1,263	$	1,159	$	360
Variable lease cost and other, net (i)		461		262		84
Short-term lease cost		17		88		—
Finance lease cost:
Amortization of right-of-use assets		493		447		369
Interest		44		9		13
Total lease costs	$	2,278	$	1,965	$	826

(i)

The variable lease cost and other, net is comprised primarily of common area maintenance charges for the operating lease, which are dependent on usage. These costs are classified as operating lease expense due to the election to not separate lease and non-lease components. These costs were not included within the measurement of the Company’s operating lease ROU assets and operating lease liabilities.

The following table presents the supplemental cash flow disclosures for cash paid for the years ended December 31, 2023, 2022, and 2021 (in thousands):


	Year Ended
	December 31,
	2023		2022		2021
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,241	$	933	$	243
Operating cash flows from finance leases	$	20	$	8	$	11
Financing cash flows from finance leases	$	388	$	388	$	281
Right-of-use asset acquired under leases
Operating leases	$	—	$	4,613	$	1,780
Finance leases	$	2,600	$	—	$	776

Balance Sheet Components - Schedule of Components of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,826	$ 4,292
Less: accumulated depreciation	(1,237)	(403)
Property and equipment, net	3,589	3,889
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,513	2,360
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,733	1,422
Computer Hardware and Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	414	344
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 166	$ 166

Income Taxes - Domestic and International Components of Pre-Tax Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
United States	$ (159,766)	$ (111,360)	$ (30,565)
International	(1,039)	(12,058)	(52,919)
Loss before income taxes	$ (160,805)	$ (123,418)	$ (83,484)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(11))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479557/942-235-S99-1

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 940
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-URI https://asc.fasb.org//1943274/2147481913/940-20-25-1

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 22,406	$ 48,822
Short-term investments	160,330	217,385
Prepaid expenses and other current assets	5,923	4,762
Total current assets	188,659	270,969
Property and equipment, net	3,589	3,889
Long-term investments	35,411	16,699
Other assets	14,894	14,932
Total assets	242,553	306,489
Current liabilities:
Accounts payable	8,591	8,073
Payable and accrued liabilities due to related party	$ 543	$ 1,650
Other Liability, Current, Related Party, Type [Extensible Enumeration]	us-gaap:RelatedPartyMember	us-gaap:RelatedPartyMember
Accrued expenses and other current liabilities	$ 26,867	$ 18,602
Total current liabilities	36,001	28,325
Term loan, non-current, net	9,639	9,389
Other non-current liabilities	7,201	5,311
Total liabilities	52,841	43,025
Commitments and contingencies (Note 13)
Stockholders’ equity
Common stock, $0.001 par value; 1,000,000,000 shares authorized as of December 31, 2023 and December 31, 2022; 49,951,989 and 40,861,386 shares issued and outstanding as of December 31, 2023 and December 31, 2022, respectively	50	41
Additional paid-in capital	675,678	589,735
Accumulated other comprehensive loss	256	(845)
Accumulated deficit	(486,272)	(325,467)
Total stockholders’ equity	189,712	263,464
Total liabilities and stockholders’ equity	$ 242,553	$ 306,489

Term Loan

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

TERM LOAN

(7) TERM LOAN

Oxford Finance and Silicon Valley Bank Loan

In October 2022, the Company entered into a loan and security agreement, or the Loan Agreement, with Oxford Finance LLC, Oxford Finance Credit Fund II LP, and Silicon Valley Bank, or Lenders, for a secured term loan facility of up to $100.0 million. Pursuant to the Loan Agreement, the Company drew an initial loan of $10.0 million and has access to draw an additional $40.0 million through the end of 2023. The Loan Agreement provides for an additional $50.0 million over three tranches, with $12.5 million available in each of two tranches based upon the achievement of milestones related to the development of evorpacept and one preclinical product candidate, and $25.0 million at the Lenders’ sole discretion. The proceeds of the loans may be used by the Company for working capital and to fund its general business requirements.

Borrowings under the Loan Agreement bear interest at a floating rate per annum equal to the greater of (i) 1-month term Secured Overnight Financing Rate, or SOFR, and (ii) 2.33%, plus 6.25%. The minimum per annum interest rate is 8.58%. Interest on the term loans is payable monthly in arrears. The Company will begin to make principal payments in equal monthly installments beginning on December 1, 2025. However, if either of the milestone related tranche term loans are funded, then the Company will begin to make principal payments in equal monthly installments beginning on December 1, 2026. The term loans mature on October 1, 2027.

The term loans may be prepaid in full or in part, in increments of $10.0 million, with various prepayment premiums. Upon the earlier prepayment or maturity of any term loan, the Company is required to pay a final payment fee of 6.0% of the original principal amount of such funded term loan. The final payment will be accreted to the final payment amount as interest expense using the effective interest method over the term of the loan through maturity date. The term loans once repaid or prepaid may not be reborrowed. The Company is also obligated to pay other customary fees for a loan facility of this size and type.

The term loans under the Loan Agreement are secured by substantially all of the Company’s assets, except the Company’s intellectual property, which is the subject of a negative pledge, and will be guaranteed by the Company’s future subsidiaries, subject to certain limitations. Upon the outstanding balance of the term loans reaching $75.0 million or greater, the Company’s intellectual property will become collateral. The Company and its subsidiary, ALX Oncology Limited, have guaranteed the obligations under the Loan Agreement. The Loan Agreement contains customary affirmative and negative covenants, including covenants limiting the ability of the Company to, among other things, dispose of assets, effect certain mergers, incur debt, grant liens, pay dividends and distributions on its capital stock, make investments and acquisitions, and enter into transactions with affiliates, in each case subject to customary exceptions for a loan facility of this size and type.

The Loan Agreement contains customary events of default, which include, but are not limited to payment defaults, material misrepresentations, breaches of covenants, cross defaults with certain other material indebtedness, bankruptcy and insolvency events, and judgment defaults. The occurrence of an event of default could result in the acceleration of our obligations under the Loan Agreement, the termination of the Lenders’ commitments, a 5.0% increase in the applicable rate of interest and the exercise by the Lender of other rights and remedies provided for under the Loan Agreement.

The Company received net proceeds from issuance of the term loan of $9.3 million after deducting debt issuance costs of approximately $0.7 million. Debt issuance costs were recorded as debt discount on the term loan, offsetting term loan, non-current on the consolidated balance sheets. The debt discount will be amortized over the term of the loan as interest expense using the effective interest method. During the years ended December 31, 2023 and 2022, interest expense incurred in connection with the Loan Agreement was $1.1 million and $0.2 million respectively. We had no outstanding debt and did not incur interest expense in 2021.

The Company determined that certain loan features were embedded derivatives requiring bifurcation and separate accounting. Those embedded derivatives were bundled together as a single, compound embedded derivative and then bifurcated and accounted for separately from the host contract. As of December 31, 2023, the value of the embedded derivative is not material, but could become material in future periods if an event of default became more probable than is currently estimated. As of December 31, 2023, we were in compliance with all financial reporting covenants under the Loan Agreement.

In March 2023, Silicon Valley Bank (SVB) was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation, or FDIC, to act as receiver. The FDIC created Silicon Valley Bridge Bank, N.A., or SVBB, as successor to SVB. First Citizens BancShares, Inc., or First Citizens Bank, acquired SVBB from the FDIC and operates SVBB as Silicon Valley Bank, a division of First Citizens Bank, or SVB-First Citizens. Under the Loan Agreement, 50% of the funding comes from SVB, one of the three Lenders. Given the SVBB acquisition by First Citizens Bank, SVB-First Citizens will continue to fulfill SVB’s obligations under the Loan Agreement.

In May 2023, we entered into a second amendment to the Loan Agreement. The primary purpose of the second amendment was to reduce the percentage of the amount required to be held in our collateral account with SVB-First Citizens from 100% to not less than 50% of the aggregate dollar value of all our collateral accounts.

In December 2023, we entered into a third amendment to the Loan Agreement. The primary purpose of the third amendment was to (i) extend the draw period for the first tranche loans from December 31, 2023 to June 30, 2024, (ii) add as a condition for the funding of any first tranche loans after the effective date of the amendment, requirement that the Phase 2 portion of the ASPEN-06 study in gastric/GEJ cancer either remains ongoing or the achievement of a milestone related to the development of the ASPEN-06 study, and (iii) add a contingency fee in the amount of $0.6 million to the Lenders if the Company prepays any of the loans under the Loan Agreement other than in connection with refinancing of the Loan Agreement with the Lenders and their affiliates.

As of December 31, 2023, the future maturities under the Loan Agreement are as follows (in thousands):


	December 31, 2023
2024	$	—
2025		435
2026		5,217
2027		4,948
Total future maturities		10,600
Less: current portion of term loan		—
Total term loan, net of current portion		10,600
Less: unamortized debt issuance costs		(781	)
Less: unaccreted final payment costs		(180	)
Term loan, non-current, net	$	9,639

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1,661	$ 1,217	$ 842
Additions/reversals based on tax positions of prior years	81	13	(69)
Additions based on tax positions related to the current year	1,409	443	494
Lapses in statutes of limitations	(31)	(12)	(50)
Balance at end of year	$ 3,120	$ 1,661	$ 1,217

Subsequent Events

12 Months Ended

Dec. 31, 2023

Subsequent Events [Abstract]

SUBSEQUENT EVENTS

(14) SUBSEQUENT EVENTS

In preparing the consolidated financial statements as of December 31, 2023, the Company evaluated subsequent events for recognition and measurement purposes through the filing date of this Annual Report on Form 10-K. The Company concluded that no events or transactions have occurred that require disclosure in the accompanying consolidated financial statements.

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at Dec. 31, 2020	$ 429,845	$ 40	$ 548,327		$ (118,522)
Balance, shares at Dec. 31, 2020		39,844,522
Issuance of common stock under equity incentive plans	2,551	$ 1	2,550
Issuance of common stock under equity incentive plans, shares		734,922
Issuance of common stock under employee stock purchase plan	202		202
Issuance of common stock under employee stock purchase plan, shares		7,623
Stock-based compensation	13,914		13,914
Net Income (Loss)	(83,463)				(83,463)
Balance at Dec. 31, 2021	363,049	$ 41	564,993		(201,985)
Balance, shares at Dec. 31, 2021		40,587,067
Issuance of common stock under equity incentive plans	567		567
Issuance of common stock under equity incentive plans, shares		225,612
Issuance of common stock under employee stock purchase plan	336		336
Issuance of common stock under employee stock purchase plan, shares		48,707
Stock-based compensation	23,839		23,839
Unrealized gain (loss) on available-for-sale investments	(845)			$ (845)
Net Income (Loss)	(123,482)				(123,482)
Balance at Dec. 31, 2022	263,464	$ 41	589,735	(845)	(325,467)
Balance, shares at Dec. 31, 2022		40,861,386
Issuance of common stock and pre-funded warrants in connection with equity offerings, net of underwriter discounts ($3.8 million) and issuance costs ($0.6 million)	58,887	$ 9	58,878
Issuance of common stock and pre-funded warrants in connection with equity offerings, net of underwriter discounts ($3.8 million) and issuance costs ($0.6 million), shares		8,663,793
Issuance of common stock under equity incentive plans	269		269
Issuance of common stock under equity incentive plans, shares		344,213
Issuance of common stock under employee stock purchase plan	523		523
Issuance of common stock under employee stock purchase plan, shares		82,597
Stock-based compensation	26,273		26,273
Unrealized gain (loss) on available-for-sale investments	1,101			1,101
Net Income (Loss)	(160,805)				(160,805)
Balance at Dec. 31, 2023	$ 189,712	$ 50	$ 675,678	$ 256	$ (486,272)
Balance, shares at Dec. 31, 2023		49,951,989

Related-Party Transactions - Additional Information (Details) - USD ($) $ in Thousands			12 Months Ended
	Oct. 04, 2022	Jul. 01, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 04, 2021
Related Party Transaction [Line Items]
Research and development costs			$ 141,795	$ 98,400	$ 60,170
Accrued expenses due			$ 543	$ 1,650
Other Liability, Current, Related Party, Type [Extensible Enumeration]			us-gaap:RelatedPartyMember	us-gaap:RelatedPartyMember
ScalmiBio, Inc
Related Party Transaction [Line Items]
Research and development costs	$ 600
Business acquisition, percentage of voting interests acquired	31.70%					31.70%
Retention milestone payment	$ 2,000
Research and Development Services Agreement \| Tallac Therapeutics
Related Party Transaction [Line Items]
Initial term of agreement with related party		4 years
Markup cost in percentage		10.00%
Agreement automatically renewal additional term unless terminated		1 year
Research and development costs			$ 300	$ 600	800
Collaboration Agreement \| Tallac Therapeutics
Related Party Transaction [Line Items]
Research and development costs			1,700	7,800	$ 2,800
Accrued expenses due			$ 500	$ 1,600
Other Liability, Current, Related Party, Type [Extensible Enumeration]			us-gaap:RelatedPartyMember	us-gaap:RelatedPartyMember

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 141,795	$ 98,400	$ 60,170
General and administrative	28,483	29,036	23,385
Total operating expenses	170,278	127,436	83,555
Loss from operations	(170,278)	(127,436)	(83,555)
Interest income	10,649	4,278	91
Interest expense	(1,565)	(238)	(13)
Other income (expense), net	389	(22)	(7)
Loss before income taxes	(160,805)	(123,418)	(83,484)
Income tax (provision) benefit		(64)	21
Net loss	$ (160,805)	$ (123,482)	$ (83,463)
Net loss per share, basic	$ (3.74)	$ (3.03)	$ (2.07)
Net loss per share, diluted	$ (3.74)	$ (3.03)	$ (2.07)
Weighted-average shares of common stock used to compute net loss per share, basic	42,987,767	40,699,612	40,308,050
Weighted-average shares of common stock used to compute net loss per share, diluted	42,987,767	40,699,612	40,308,050

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Summary of Other Contractual Obligations and Other Commitments from Manufacturing and Service Contracts

We have other contractual obligations and other commitments from manufacturing and service contracts, which are presented as follows as of December 31, 2023 (in thousands):


	December 31, 2023
	Total		2024		2025-2026		2027-2028		Thereafter
Manufacturing and service contracts	$	6,736	$	6,535	$	201			$	—
Total	$	6,736	$	6,535	$	201	$	—	$	—

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

INCOME TAXES

(10) INCOME TAXES

The U.S. domestic and international components of pre-tax loss for the years ending December 31, 2023, 2022 and 2021 are as follows (in thousands):


	Year Ended December 31,
	2023			2022			2021
United States	$	(159,766	)	$	(111,360	)	$	(30,565	)
International		(1,039	)		(12,058	)		(52,919	)
Loss before income taxes	$	(160,805	)	$	(123,418	)	$	(83,484	)

The federal and state provision (benefit) for income taxes consist of the following (in thousands):


	Year Ended December 31,
	2023		2022		2021
Current provision for income taxes:
Federal	$	—	$	64	$	(21	)
State		—		—		—
International		—		—		—
Total current		—		64		(21	)
Deferred tax provision:
Federal		—		—		—
State		—		—		—
International		—		—		—
Total deferred		—		—		—
Provision (benefit) for income taxes	$	—	$	64	$	(21	)

Deferred income taxes reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes, and (b) operating losses and tax credit carryforwards.

A reconciliation of the U.S. federal statutory income tax rate to the effective tax for the years ended December 31, 2023, 2022 and 2021 are as follows (in thousands):


	Year Ended December 31,
	2023			2022			2021
At federal statutory income tax rate	$	(33,769	)	$	(25,918	)	$	(17,532	)
State income taxes		(1,481	)		(2,659	)		(105	)
Stock-based compensation		3,645			2,368			(4,031	)
Research & development credits		(7,185	)		(1,779	)		(2,131	)
Change in valuation allowance		64,486			9,067			11,476
Other		189			36			172
Foreign rate differential		(23	)		18,949			11,032
Prior period true ups		—			—			1,098
Rate benefit of reorganization		(25,862	)		—			—
Provision (benefit) for income taxes	$	—		$	64		$	(21	)

The Company filed a change in tax status for ALX Oncology Limited in 2023. The reorganization resulted in an increase to capitalized R&D and other deferred tax assets, as well as a corresponding increase in valuation allowance.

Significant components of the Company’s deferred tax assets as of December 31, 2023 and 2022 are as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Loss carryforwards	$	26,517		$	16,319
Research & other credits		17,131			8,435
Other		8,076			14
Accrued expenses		1,014			1,860
Stock options		5,157			3,860
Lease liabilities		1,587			1,323
Capitalized R&D		38,425			1,702
Total deferred tax assets		97,907			33,513
Deferred tax liabilities:
Fixed assets		96			215
Lease ROU assets		1,523			1,244
Prepaid expenses		—			252
Total deferred tax liabilities		1,619			1,711
Valuation allowance		(96,288	)		(31,802	)
Net deferred tax assets	$	—		$	—

ASC 740 requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s recent history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not likely to be realized and, accordingly, has provided a valuation allowance. The valuation allowance increased by approximately $64.5 million and $9.1 million for the years ended December 31, 2023 and 2022, respectively.

The Tax Cuts and Jobs Act eliminated the option to deduct research and development expenditures currently and requires taxpayers to capitalize and amortize them pursuant to Internal Revenue Code Section 174 beginning in 2022.

Net operating losses and tax credit carryforwards as of December 31, 2023 are as follows (in thousands):


	Amount		Expiration Years
Net operating losses, federal (post December 31, 2017)	$	93,542	Do Not Expire
Net operating losses, state	$	68,993	2038-2040
Tax credits, federal	$	14,431	2039-2043
Tax credits, state	$	5,918	N/A
Net operating losses, foreign	$	4,896	N/A

Utilization of the Company’s U.S. net operating loss and credit carryforwards may be subject to substantial annual limitation due to the ownership change limitations provided by the Internal Revenue Code and similar state provisions. Such annual limitation could result in the expiration of the U.S. net operating loss and credit carryforwards before utilization. To date, the Company has not performed an analysis to determine whether there would be a substantial annual limitation due to a change in ownership.

Unrecognized Tax Benefits

The Company recognizes the tax benefit from uncertain tax positions if it is more likely than not that the tax positions will be sustained on examination by the tax authorities, based on the technical merits of the position. The tax benefit is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense. The Company files income tax returns in the U.S. federal and California jurisdiction, which is not currently under exam, and all years since inception are opened to examination.

The unrecognized tax benefits as of December 31, 2023, 2022 and 2021 were $3.1 million, $1.7 million and $1.2 million, respectively. Future changes in the unrecognized tax benefits will not impact the effective tax rate due to the Company’s full valuation allowance.

The Company has the following activity relating to unrecognized tax benefits (in thousands):


	Year Ended December 31,
	2023			2022			2021
Balance at beginning of year	$	1,661		$	1,217		$	842
Additions/reversals based on tax positions of prior years		81			13			(69	)
Additions based on tax positions related to the current year		1,409			443			494
Lapses in statutes of limitations		(31	)		(12	)		(50	)
Balance at end of year	$	3,120		$	1,661		$	1,217

Although it is reasonably possible that certain unrecognized tax benefits may increase or decrease within the next 12 months due to tax examination changes, settlement activities, expirations of statute of limitations or the impact on recognition and measurement considerations related to the results of published tax cases or other similar activities, the Company does not anticipate any significant changes to unrecognized tax benefits over the next 12 months. During the years ended December 31, 2023, 2022 and 2021, no significant interest or penalties were required to be recognized relating to unrecognized tax benefits.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

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+ Details

Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net loss	$ (160,805)	$ (123,482)	$ (83,463)
Denominator:
Weighted-average shares of common stock outstanding, basic	42,987,767	40,699,612	40,308,050
Weighted-average shares of common stock outstanding, diluted	42,987,767	40,699,612	40,308,050
Net loss per share, basic	$ (3.74)	$ (3.03)	$ (2.07)
Net loss per share, diluted	$ (3.74)	$ (3.03)	$ (2.07)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (160,805)	$ (123,482)	$ (83,463)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Deferred tax assets, increase in valuation allowance	$ 64,500,000	$ 9,100,000
Unrecognized tax benefits	3,120,000	1,661,000	$ 1,217,000	$ 842,000
Recognized interest and penalties expense (benefit) related to unrecognized tax benefits	$ 0	$ 0	$ 0

Stockholders' Equity

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

STOCKHOLDERS' EQUITY

(8) STOCKHOLDERS’ EQUITY

On July 21, 2020, the Company’s amended and restated certificate of incorporation became effective, authorizing 1,000,000,000 shares of common stock, $0.001 par value per share, and 100,000,000 shares of undesignated preferred stock, $0.001 par value per share. As of December 31, 2023 and 2022, the Company had 49,951,989 and 40,861,386 shares of common stock outstanding, respectively.

Common Stock

In July 2020, the Company consummated its initial public offering and issued 9,775,000 shares of common stock for net proceeds of approximately $169.5 million, after deducting underwriting discounts and commissions of $13.0 million and offering-related expenses of $3.2 million. Upon the closing of the initial public offering, all shares of convertible preferred stock outstanding and accrued cumulative dividends were automatically converted into 23,934,533 shares of common stock.

In December 2020, the Company consummated its follow-on public offering and issued 2,737,000 shares of common stock for net proceeds of approximately $194.9 million, after deducting underwriting discounts and commissions of $12.5 million and offering-related expenses of $0.7 million.

In October 2023, the Company completed an underwritten follow-on public offering and issued an aggregate of 8,663,793 shares of common stock, including the underwriters’ exercise in full of their overallotment option of 1,293,103 shares of common stock, and, in lieu of common stock to certain investors, pre-funded warrants to purchase 1,250,000 shares of common stock at a public offering price of $6.38 per share and $6.379 per pre-funded warrant. Net proceeds were approximately $58.9 million, after deducting underwriting discounts and commissions of $3.8 million and offering-related expenses of $0.6 million.

Common stock reserved for future issuance as of December 31, 2023 consists of the following:


	December 31, 2023
Stock options issued and outstanding		8,984,671
Stock options authorized for future issuance		1,305,386
Employee Stock Purchase Plan shares authorized for future issuance		1,065,389
Restricted stock issued and outstanding		949,669
Total		12,305,115

At-the-Market Equity Offering

In December 2021, the Company entered into a sales agreement with Cantor Fitzgerald & Co. and Credit Suisse Securities (USA) LLC (Sales Agreement), under which it may offer and sell shares of the Company's common stock, having aggregate gross proceeds of up to $150.0 million, from time to time through them as the Company's sales agents in its at-the-market equity offering program (ATM Offering). In March 2022, the Company filed a Shelf Registration Statement with the SEC. In May 2022, the Company filed an amended Shelf Registration Statement, which was declared effective by the SEC on May 31, 2022. In August 2023, the Company entered into an amendment to the Sales Agreement to include UBS Securities LLC as an additional sales agent and to remove Credit Suisse as a sales agent. No securities have been sold under the ATM Offering as of December 31, 2023.

Pre-Funded Warrants

As part of the October 2023 underwritten public offering, the Company issued pre-funded warrants to certain investors to purchase 1,250,000 shares of common stock in an underwritten public offering at a public offering price of $6.379 per pre-funded warrant. Each pre-funded warrant entitles the holder to purchase one share of common stock at an exercise price of $0.001 per share.

The pre-funded warrants to purchase shares of common stock are exercisable at any time after their original issuance. However, the pre-funded warrants include a separate provision whereby the exercisability of the pre-funded warrants may be limited if, upon exercise, the warrant holder or any of its affiliates would beneficially own more than 9.99% of the Company’s common stock. This threshold is subject to the warrant holder’s rights under the pre-funded warrants to increase or decrease such percentage to any other percentage not in excess of 19.99% upon at least 61 days’ prior notice from the warrant holder to the Company. The pre-funded warrants will expire on the date the warrants are exercised in full.

The pre-funded warrants were classified as equity and accounted for as a component of additional paid-in capital. The pre-funded warrants were classified as equity because they (i) are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, (ii) are immediately exercisable, (iii) do not embody an obligation for the Company to repurchase its shares, (iv) permit the holders to receive a fixed number of shares of common stock upon exercise, (v) are indexed to the Company's common stock and (vi) meet the equity classification criteria. In addition, such pre-funded warrants do not provide any guarantee of value or return. The Company valued the pre-funded warrants at issuance, concluding that their offering price approximated their fair value, and allocated the aggregate net proceeds from the offering proportionately to the common stock and pre-funded warrants, including approximately $7.4 million allocated to the pre-funded warrants and recorded as a component of additional paid-in capital on the consolidated balance sheets.

As of December 31, 2023, no shares underlying the pre-funded warrants had been exercised. All of the outstanding pre-funded warrants are included in the weighted-average number of shares of common stock used to calculate basic net loss per share attributable to common stockholders (see Note 12 “Net Loss Per Share Attributable to Common Stockholders”).

Dividends

Prior to the Company’s initial public offering, cumulative dividends of 6.0% per annum of the original issue price for each convertible preferred stock series were payable when and as declared by the Company’s Board of Directors, or Board of Directors, upon the occurrence of a liquidation event or upon a contingent mandatory conversion of the convertible preferred stock in connection with a qualified initial public offering as described below. The Series A original issue price was $6.58, and the Series B and Series C original issue price was $9.4972. The original issue price was subject to adjustment in the event of any share dividend, share split, combination, consolidation or other recapitalization. The dividends accrued from day to day from the issue date of such preferred stock whether or not declared and were cumulative. In addition, the preferred stockholders participated on an as-converted basis in any dividends payable to common stockholders. As of July 20, 2020, there were approximately $18.0 million of accrued cumulative dividends on the Series A, Series B and Series C convertible preferred stock, which became payable upon the consummation of the Company’s initial public offering and automatically converted into 2,564,759 shares of the Company’s common stock.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (a)
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 2
-Subparagraph (d)
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (a)
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (g)
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 14
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

(13) COMMITMENTS AND CONTINGENCIES

Guarantees and Indemnifications

In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. The Company also has indemnification obligations to its officers and directors for specified events or occurrences, subject to some limits, while they are serving at the Company’s request in such capacities. There have been no claims to date and the Company has director and officer insurance that may enable the Company to recover a portion of any amounts paid for future potential claims. The Company believes the fair value of these indemnification agreements is minimal. Accordingly, the Company has not recorded any liabilities for these agreements as of December 31, 2023.

Contingencies

From time to time, the Company may be a party to various claims in the normal course of business. Legal fees and other costs associated with such actions will be expensed as incurred. The Company will assess, in conjunction with its legal counsel, the need to record a liability for litigation and contingencies. Reserve estimates will be recorded when and if it is determined that a loss related matter is both probable and reasonably estimable. For the years ended December 31, 2023, 2022 and 2021, the Company had no pending or threatened litigation.

License Agreements

In March 2015, the Company entered into a license agreement, or the Stanford Agreement, with the Board of Trustees of the Leland Stanford Junior University, or Stanford, under which the Company obtained a worldwide, royalty-bearing, sublicensable license under certain patents relating to the Company’s current product candidates, to develop, manufacture and commercialize products for use in certain licensed fields, the scope of which would include the application of the licensed intellectual property in oncology. The Company paid Stanford a nonrefundable license royalty and reimbursed Stanford for past patent expenses, together totaling less than $0.1 million, and granted Stanford a specified number of shares of common stock of the Company. The Company is required to make milestone payments up to an aggregate of $5.0 million in respect of a specified number of licensed products that successfully satisfy certain clinical and regulatory milestones. The Company recorded the first milestone payment of $0.2 million during the year ended December 31, 2021. There was no milestone payment recorded for the year ended December 31, 2023.

In June 2016, the Company entered into a license agreement with Selexis SA, or Selexis, under which the Company obtained a worldwide, royalty-bearing, sublicensable license under certain patents, know-how and other intellectual property, to use Selexis generated cell lines to manufacture evorpacept, and to make, use and sell licensed product containing such compound in all fields of use. The Company paid Selexis a nominal one-time fee and will pay Selexis an annual maintenance fee. The Company also agreed to pay Selexis milestone payments up to an aggregate of 1.2 million Swiss Francs in respect of all licensed products developed and/or commercialized under the grant that successfully satisfies certain milestone events. The Company recorded a milestone payment of $0.1 million during the year ended December 31, 2021. There was no milestone payment recorded for the year ended December 31, 2023.

In March 2017, the Company entered into an agreement with Crystal Bioscience Inc. (now a subsidiary of Ligand Pharmaceuticals Incorporated), or Crystal, under which the Company obtained an assignment of certain patents, covering certain SIRPα antibodies. Under this agreement, the Company also received a worldwide, royalty-bearing non-exclusive license, with the right to grant sublicenses through multiple tiers of sublicenses, under certain of Crystal’s background patents and know-how necessary to commercialize the rights under the assigned patents. The Company agreed to pay Crystal milestone payments up to $11.1 million in respect of all licensed products developed under the assigned patents, that successfully satisfy certain clinical and regulatory milestones, each milestone being paid only once for all products. The Company recorded the first milestone payment of $0.3 million during the year ended December 31, 2022. There was no milestone payment recorded for the year ended December 31, 2023.

Other Contractual Obligations and Other Commitments

We have other contractual obligations and other commitments from manufacturing and service contracts, which are presented as follows as of December 31, 2023 (in thousands):


	December 31, 2023
	Total		2024		2025-2026		2027-2028		Thereafter
Manufacturing and service contracts	$	6,736	$	6,535	$	201			$	—
Total	$	6,736	$	6,535	$	201	$	—	$	—

In November 2015, the Company entered into a Master Service Agreement, or the MSA, with KBI Biopharma, Inc. relating to formulation development, process development and current good manufacturing practices, or cGMP, manufacturing of evorpacept for use in clinical trials on a project basis. The MSA had an initial term of three years with successive one-year renewal periods, which was extended an additional eight years until November 2026, is cancellable upon notice and is non-exclusive. Statements of work under the MSA commit the Company to certain future purchase obligations of approximately $1.8 million. In addition, the Company has commitments with two other pharmaceutical contract manufacturers, including certain future purchase obligations of approximately $4.9 million. These amounts are based on non-cancellable commitments and forecasts that include estimates of future market demand, quantity discounts and manufacturing efficiencies that may impact timing of purchase.

The Company enters into contracts in the normal course of business with various third parties for clinical trials, preclinical research studies and testing, manufacturing and other services and products for operating purposes. These contracts generally provide for termination upon notice. Payments due upon cancellation consist only of payments for services provided or expenses incurred, including non-cancellable obligations of our service providers, up to the date of cancellation.

Leases - Additional Information (Details) $ in Thousands	1 Months Ended		12 Months Ended
Leases - Additional Information (Details) $ in Thousands	Feb. 28, 2022 USD ($) ft²	May 31, 2021 USD ($) ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Lessee Lease Description [Line Items]
Finance lease, description			In May 2023, the Company entered into an addendum to extend the existing lease through May 2026 and lease additional number of certain equipment. In October 2023, the Company entered into an additional addendum to lease an additional number of certain equipment through May 2026.
Operating lease ROU assets			$ 4,847	$ 5,626
Option to extend term			no
Total lease payment			$ 6,740
Finance lease ROU assets			$ 2,405	$ 298
Office Space at 323 Allerton Avenue, South San Francisco, California
Lessee Lease Description [Line Items]
Lessee, operating lease commencing end date		Jun. 06, 2021
Lessee operating lease expiration date		Aug. 31, 2026
Operating lease ROU assets		$ 2,000
Area of operating lease \| ft²		10,000
Operating lease, description			Company entered into a lease agreement for approximately 10,000 square feet of office space located in South San Francisco, California. The lease commenced on June 6, 2021 and expires on August 31, 2026. The lease does not provide an option to extend after it expires. The total lease payments for the life of the lease are approximately $2.0 million.
Existence of option to extend		false
Option to extend term		no
Office and Laboratory Space Located In Palo Alto, California
Lessee Lease Description [Line Items]
Area of operating lease \| ft²	11,074
Existence of option to extend	true
Lease operating lease expiration period	2030-02
Lessee operating lease renewal term	2 years
Lease operating lease commencement period	2022-02
Lease operating lease commencement period for second premises	2022-04
Annual base rent	$ 800
Percentage of increase of annual rent	3.00%
Lessee operating lease leasehold improvements	$ 2,300
Lessee operating lease leasehold improvements additional payments	$ 1,500
Annual interest rate of additional payments over life of lease	7.00%
Total lease payment	$ 6,900
Letter of credit	100
Restricted cash deposits	$ 100
Option to extend term			The lease provides for an option to extend for two years after expiration

Income Taxes - Schedule of Statutory and Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
At federal statutory income tax rate	$ (33,769)	$ (25,918)	$ (17,532)
State income taxes	(1,481)	(2,659)	(105)
Stock-based compensation	3,645	2,368	(4,031)
Research & development credits	(7,185)	(1,779)	(2,131)
Change in valuation allowance	64,486	9,067	11,476
Other	189	36	172
Foreign rate differential	(23)	18,949	11,032
Prior period true ups			1,098
Rate benefit of reorganization	$ (25,862)
Provision (benefit) for income taxes		$ 64	$ (21)

Balance Sheet Components

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

BALANCE SHEET COMPONENTS

(5) BALANCE SHEET COMPONENTS

Property and Equipment, Net

The following table presents the components of property and equipment, net as of December 31, 2023 and 2022 (in thousands):


	December 31,			December 31,
	2023			2022
Leasehold improvements	$	2,513		$	2,360
Laboratory equipment		1,733			1,422
Computer hardware and software		414			344
Furniture and fixtures		166			166
Property and equipment, gross		4,826			4,292
Less: accumulated depreciation		(1,237	)		(403	)
Property and equipment, net	$	3,589		$	3,889

Depreciation was $0.8 million, $0.3 million, and nominal for years ended December 31, 2023, 2022 and 2021, respectively.

Other Assets

The following table presents the components of other assets, net as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Long-term prepaid clinical expenses	$	7,442	$	7,264
Operating lease right-of-use assets		4,847		5,626
Finance lease right-of-use assets		2,405		298
Long-term prepaid contract manufacturing costs		—		1,456
Other		200		288
Total other assets	$	14,894	$	14,932

Accrued Expenses and Other Current Liabilities

The following table presents the components of accrued expenses and other current liabilities as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Accrued contract manufacturing	$	9,543	$	5,249
Accrued clinical and nonclinical study costs		8,873		5,485
Accrued compensation and related expenses		6,067		3,708
Accrued property and equipment		179		2,110
Other		2,205		2,050
Total accrued expenses and other current liabilities	$	26,867	$	18,602

Stock-Based Compensation - Schedule of Fair Value of Each Option Grant Using Black-Scholes Option-Pricing Model (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	3.50%	1.60%	0.80%
Risk-free interest rate, maximum	4.70%	4.40%	1.40%
Expected dividend rate	0.00%	0.00%	0.00%
Expected stock price volatility, minimum	83.60%	81.90%	79.70%
Expected stock price volatility, maximum	88.60%	84.70%	86.90%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Net Loss Per Share Attributable to Common Stockholders - Summary of Outstanding Potentially Dilutive Securities Were Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	9,934,340	7,017,174	5,143,714
Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	8,984,671	6,196,848	5,128,639
Restricted Stock Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	949,669	820,326	15,075

Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jul. 21, 2020 shares
Significant Accounting Policies [Line Items]
Other income (expense), net	$ 389,000	$ (22,000)	$ (7,000)
Impairment charges	$ 0
Number of operating segment \| Segment	1
Prepaid Expenses and Other Current Assets
Significant Accounting Policies [Line Items]
Deferred offering costs	$ 0	0
Initial Public Offering \| Common Stock
Significant Accounting Policies [Line Items]
Convertible shares converted in to common stock \| shares				23,934,533
Revision of Prior Period, Reclassification, Adjustment
Significant Accounting Policies [Line Items]
Other income (expense), net		200,000	100,000
Interest income		$ 200,000	$ 100,000

Stock-Based Compensation - Summary of Shares Available for Grant (Details) - 2020 Plan	12 Months Ended
	Dec. 31, 2023 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares Available to Grant Balance	2,932,309
Shares Available to Grant, Authorized	1,634,456
Shares Available to Grant, Granted	(3,703,150)
Shares Available to Grant, Canceled/forfeited	441,771
Shares Available to Grant Balance	1,305,386

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Net Loss Per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS

(12) NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS

The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data):


	Year Ended
	December 31,
	2023			2022			2021
Numerator:
Net loss	$	(160,805	)	$	(123,482	)	$	(83,463	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		42,987,767			40,699,612			40,308,050
Net loss per share, basic and diluted	$	(3.74	)	$	(3.03	)	$	(2.07	)

Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods presented as the inclusion of all potential common stock outstanding would have been anti-dilutive.


	Year Ended
	December 31,
	2023		2022		2021
Stock options issued and outstanding		8,984,671		6,196,848		5,128,639
Restricted stock issued and outstanding		949,669		820,326		15,075
Employee Stock Purchase Plan estimated shares issuable		—		—		—
Total		9,934,340		7,017,174		5,143,714

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	49,951,989	40,861,386
Common stock, shares outstanding	49,951,989	40,861,386

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Feb. 29, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Registrant Name	ALX ONCOLOGY HOLDINGS INC
Entity Central Index Key	0001810182
Entity File Number	001-39386
Entity Tax Identification Number	85-0642577
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	323 Allerton Avenue
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	466-7125
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		50,152,082
Entity Public Float			$ 161.4
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	ALXO
Security Exchange Name	NASDAQ
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Document Annual Report	true
Document Transition Report	false
Auditor Name	KPMG LLP
Auditor Firm ID	185
Auditor Location	San Francisco, California
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Certain portions of the registrant’s definitive proxy statement relating to the Company’s 2024 Annual Meeting of Stockholders, to be filed with the Securities and Exchange Commission within 120 days of the registrant’s fiscal year ended December 31, 2023, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated.

Fair Value of Financial Instruments - Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Fair Value	$ 215,822	$ 274,258
Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	215,566	275,103
Unrealized Gains	328	41
Unrealized Losses	(72)	(886)
Fair Value	215,822	274,258
Money Market Funds \| Level 1 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	15,591	36,690
Fair Value	15,591	36,690
Corporate Debt Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	4,489
Unrealized Gains	1
Fair Value	4,490
U.S. Government Agency Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		3,484
Fair Value		3,484
Short Term Investment U.S. Treasury Securities \| Level 1 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	74,790	73,058
Unrealized Gains	80	3
Unrealized Losses	(20)	(438)
Fair Value	74,850	72,623
Short Term Investment U.S. Government Agency Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	28,215	16,227
Unrealized Gains		36
Unrealized Losses	(38)
Fair Value	28,177	16,263
Short Term Investment Corporate Debt Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	21,881	56,318
Unrealized Gains	24
Unrealized Losses	(3)	(367)
Fair Value	21,902	55,951
Short Term Investment Commercial Paper \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	34,967	62,087
Unrealized Gains	22
Unrealized Losses	(9)
Fair Value	34,980	62,087
Short Term Investment Asset-Backed Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	423	10,512
Unrealized Losses	(2)	(51)
Fair Value	421	10,461
Long Term Investment U.S. Treasury Securities \| Level 1 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	14,737	5,242
Unrealized Gains	75	2
Fair Value	14,812	5,244
Long-term Investment U.S. Government Agency Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	3,009	9,760
Unrealized Gains	31
Unrealized Losses		(15)
Fair Value	3,040	9,745
Long Term Investment Asset-Backed Securities \| Level 2 \| Fair Value on Recurring Basis
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	17,464	1,725
Unrealized Gains	95
Unrealized Losses		(15)
Fair Value	$ 17,559	$ 1,710

Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

SIGNIFICANT ACCOUNTING POLICIES

(2) SIGNIFICANT ACCOUNTING POLICIES

Basis of Preparation

These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP, and the applicable rules and regulations of the U.S. Securities and Exchange Commission, or SEC.

Reclassifications

Certain reclassifications have also been made within the consolidated statements of operations for the years ended December 31, 2022 and 2021 to conform to the current year presentation. For the year ended December 31, 2022, the Company reclassified approximately $0.2 million out of other expense, net into a separate interest expense financial statement line item and renamed other expense, net to other income (expense), net. For the year ended December 31, 2021, the Company reclassified less than $0.1 million out of other expense, net into a separate interest income financial statement line item and renamed other expense, net to other income (expense), net. Total loss before income taxes as of December 31, 2022 and 2021 did not change as a result of these reclassifications.

Principles of Consolidation

All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, management evaluates its estimates, including, but not limited to, those related to the estimated useful lives of long-lived assets, clinical and contract manufacturing accruals, fair value of assets and liabilities, fair value of investments, valuation of the Company’s common stock in periods prior to its initial public offering and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company holds its cash and cash equivalents in checking and money market accounts. The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market funds and U.S. government agency securities that are stated at cost, which approximate fair value.

Investments

Investments consist of money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt securities, commercial paper and asset-backed securities. The Company’s investments are classified as available-for-sale and carried at estimated fair values and reported in cash equivalents, short-term investments and long-term investments. Management determines the appropriate classification of the investments at the time they are purchased and evaluates the appropriateness of such classifications at each balance sheet date. Investments with contractual maturities greater than 12 months are considered long-term investments. Management has elected to use transaction settlement date as the purchase date of investments.

The Company regularly reviews its investments for declines in estimated fair value below amortized cost. The factors considered in determining whether a credit loss exists include the creditworthiness of the security issuers, the number of investments in an unrealized loss position, the severity and duration of the unrealized losses, and whether it is more likely than not that the Company will be required to sell the investments before the recovery of their amortized cost basis. The cost of investments sold is based on the specific identification method. In circumstances when an unrealized loss is determined to be credit-related, or when the Company intends to sell or is more likely than not required to sell a security before it recovers its amortized cost basis, the difference between the fair value and the amortized cost of the security is recognized within other income (expense), net in the consolidated statements of operations, and an allowance for credit loss is recorded on the consolidated balance sheets. In circumstances when the decline in fair value is non-credit related, the difference is reported in accumulated other comprehensive loss, net of tax as a separate component of consolidated stockholders’ equity.

Concentration of Credit Risk, Credit Losses and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash, cash equivalents, and investments. The primary objectives for the Company’s investment portfolio are the preservation of capital and the maintenance of liquidity. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash, cash equivalents and investments and issuers of investments. The Company manages its credit risk by holding its cash, cash equivalents and investments in large financial institutions within the U.S. In addition, the Company’s investment policy limits investments to certain types of instruments such as money market funds, debt securities issued by the U.S. government and its agencies, corporate debt securities, commercial paper as well as asset-backed securities, and places restrictions on the credit ratings, maturities and concentration by type and issuer. The Company has not experienced any realized losses on its deposits of cash, cash equivalents and investments.

The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals or sole-source suppliers.

The Company’s product candidates require approvals from the U.S. Food and Drug Administration, or FDA, and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation of property and equipment is provided using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on a straight-line basis over the shorter of the term of the lease, or the useful life of the assets. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the consolidated balance sheets and the resulting gain or loss is reflected in the consolidated statements of operations. Maintenance and repairs are charged to the consolidated statements of operations as incurred.

Leases

On January 1, 2021, the Company adopted Accounting Standards Update No. 2016-02, Leases, Topic 842, or Accounting Standards Codification (ASC) 842, using the alternative modified transition method, which applies the standard as of the adoption date. Results and disclosure requirements for reporting periods beginning after January 1, 2021 are presented under ASC 842.

The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, leases are included in operating or finance lease right-of-use, or ROU, assets; current operating or finance lease liabilities; and non-current operating or finance lease liabilities.

Lease ROU assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the commencement date. ROU assets also include any initial direct costs incurred and any lease payments made on or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. The incremental borrowing rate is reevaluated upon a lease modification. The Company considered information available at the adoption date of ASC 842 to determine the incremental borrowing rate for leases in existence as of this date. Lease terms may include options to extend or terminate the lease when the Company is reasonably certain that the option will be exercised. Lease expense for operating leases is recognized on a straight-line basis over the lease term. For finance leases, ROU assets are amortized on a straight-line basis over the shorter of the expected useful life or the lease term, and the carrying amount of the lease liability is adjusted to reflect interest, which is recorded in interest expense.

The Company elected to apply each of the practical expedients described in ASC 842 which allow companies (i) not to reassess prior conclusions on whether any expired or existing contracts are or contain a lease, lease classification, and initial direct costs, (ii) combine lease and non-lease components for all underlying assets groups, and (iii) not recognize ROU assets or lease liabilities for short term leases. A short-term lease is a lease that, at the commencement date, has a lease term of 12 months or less and does not include an option to purchase the underlying asset that the lessee is reasonably certain to exercise.

Impairment of Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future undiscounted net cash flows which the asset or asset group are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds its fair value. Fair value is determined using various valuation techniques including discounted cash flow models, quoted market values and third-party independent appraisals, as considered necessary. The Company has not recorded impairment of any long-lived assets.

Fair Value of Financial Instruments

The fair value of the Company’s financial assets and liabilities are determined in accordance with the fair value hierarchy established in ASC 820, Fair Value Measurements and Disclosures. ASC 820 defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy of ASC 820 requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels:

Level 1—Observable inputs, such as quoted prices in active markets;

Level 2—Inputs, other than the quoted prices in active markets, which are observable either directly or indirectly such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life; and

Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.

As of December 31, 2023 and 2022, the carrying amount of cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximated their estimated fair value due to their relatively short maturities. The carrying amount of our non-current debt approximates fair value based on Level 2 inputs since the debt carries a variable interest rate that is tied to the current SOFR rate plus a spread.

The Company classifies money market funds and U.S. treasury securities as Level 1 within the fair value hierarchy as the fair value is based on quoted prices. The Company classifies its investments in U.S. government agency securities, corporate debt securities, commercial paper, and asset-backed securities as Level 2 within the fair value hierarchy as the fair value is estimated by third-party pricing sources using quoted prices for identical or similar instruments in markets that are not active and industry-standard model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Where applicable, these models project future cash flows and discount the future amounts to a present value using market-based observable inputs obtained from various third-party data providers, including but not limited to benchmark yields, reported trades and broker/dealer quotes. Where applicable the market approach utilizes prices and information from market transactions for similar or identical assets.

Issuance Costs

Debt issuance costs consist of payments made to secure commitments under certain debt financing arrangements. These amounts are recognized as interest expense over the period of the financing arrangement using the effective interest method. If the financing arrangement is canceled or forfeited, or if the utility of the arrangement to the Company is otherwise compromised, these costs are recognized as interest expense immediately. The Company’s consolidated financial statements present debt issuance costs related to a recognized debt liability as a direct reduction from the carrying amount of that debt liability.

Equity issuance costs consist of certain legal, professional accounting and third-party fees directly associated with in-process equity financings. These amounts are capitalized as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the equity financing. In the event an anticipated offering is terminated or significantly delayed, deferred offering costs will be immediately expensed as part of general and administrative expenses. As of December 31, 2023 and 2022, no deferred offering costs were included as prepaid expenses and other current assets on the consolidated balance sheets, and all offering costs were offset against offering proceeds and reclassified to additional paid-in capital on the consolidated balance sheets.

Research and Development Costs

Research and development costs are expensed as incurred and consist primarily of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to nonemployees and external entities on behalf of the Company, such as consultants, central laboratories, contractors, collaborators, CMOs and CROs, in connection with our preclinical and clinical development activities and expenses incurred in connection with license agreements. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and recorded in prepaid expenses and other current assets, and then expensed as the related goods are delivered or the services are performed.

Asset Acquisition including Acquired In-Process Research and Development Expenses

When determining whether a transaction gives rise to an acquisition of a business or asset group, the Company applies a screening test to determine whether substantially all of the fair value of the gross assets acquired in the transaction is concentrated in a single identifiable asset or group of similar identifiable assets. If so, then the assets are not considered a business and the transaction is accounted for as an asset acquisition.

The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the asset or group of assets, which includes transaction costs. Goodwill is not recognized in asset acquisitions or transactions to license intellectual property. In an asset acquisition, the cost allocated to acquired in-process research and development (IPR&D) with no alternative future use is recognized as an expense on the acquisition date.

When a transaction is accounted for as an asset acquisition, an in-process research and development, or IPR&D asset is only capitalized if it has an alternative future use other than in a particular research and development project. Otherwise, amounts allocated to IPR&D that have no alternative use are expensed.

Upfront and milestone payments made related to an asset acquisition are accrued for and expensed when the achievement of the milestone is considered probable.

Clinical and Contract Manufacturing Accruals

The Company records accruals for estimated costs of research, preclinical studies and clinical trials, and manufacturing development, which are a significant component of research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations, or CROs, and contract manufacturing organizations, or CMOs. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fees to be paid for such services. To assist in its estimates the Company relies upon the receipt of timely and accurate reporting from its clinical and non-clinical studies and other third-party vendors.

The Company makes significant judgments and estimates in determining the accrual balance at the end of each reporting period. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, the Company’s understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in the Company reporting amounts that are too high or too low in any particular period. Through December 31, 2023, there have been no material differences from the Company’s accrued estimated expenses to the actual clinical trial expenses. However, variations in the assumptions used to estimate accruals, including, but not limited to, the number of patients enrolled, the rate of patient enrollment, the actual services performed, and related costs may vary from the Company’s estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial position and results of operations.

Stock-based Compensation Expense

The Company incurs stock-based compensation expense primarily from stock options, restricted stock units, and ESPP purchase rights.

The Company estimates the fair value of stock options granted to employees, directors and non-employees and ESPP purchase rights using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of subjective assumptions, including expected volatility, expected dividend yield, expected term, risk-free rate of return and the estimated fair value of the underlying common stock on the date of grant. Prior to the Company’s initial public offering, the fair value of the common stock underlying the stock-based awards was determined on each grant date by the board of directors, with input from management, considering the most recently available third-party valuation of common shares. The grant-date fair value of restricted stock units is the fair value of the underlying stock on the award’s grant date. The Company uses the straight-line method to allocate compensation expense to reporting periods over the requisite service period, which is generally the vesting period. The Company accounts for the effect of forfeitures as they occur.

Segment Reporting

The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. All of the Company’s long-lived assets are located in the United States.

Foreign Currency Transactions

The functional currency of the Company’s operation and each of its subsidiaries is U.S. dollars. All assets and liabilities denominated in a foreign currency are translated into U.S. dollars at the exchange rate prevailing on the balance sheet date. Expenses are translated at the average exchange rates prevailing during the applicable period. Foreign currency transaction gains and losses are included in the consolidated statements of operations and recorded in other income (expense), net, and were immaterial for the years December 31, 2023, 2022 and 2021.

Income Taxes

The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates in effect for the period in which the temporary differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statements of operations and comprehensive loss in the period that includes the enactment date.

Deferred income taxes comprise the impact of temporary differences between assets and liabilities recognized for financial reporting purposes and the amounts recognized for income tax reporting purposes, net operating loss carryforwards, and other tax credits measured by applying currently enacted tax laws. A valuation allowance is provided when necessary to reduce deferred tax assets to an amount that is more likely than not to be realized. If the Company determines that it would be able to realize its deferred tax assets in the future in excess of their net recorded amount, it would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit.

Comprehensive Loss

Comprehensive loss consists of net loss and changes in unrealized gains and losses on investments for all periods presented.

Net Loss Per Share Attributable to Common Stockholders

Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and pre-funded warrants outstanding during the period, without consideration for common stock equivalents. Shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing net loss per share because the shares may be issued for little or no consideration, are fully vested, and are exercisable after the original issuance date. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.

Recent Accounting Pronouncements

In August 2020, the FASB issued ASU 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40) (ASU 2020-06). ASU 2020-06 eliminates the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. The new guidance also modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted EPS computation. ASU 2020-06 is effective for annual periods beginning after December 15, 2023, including interim periods within those annual periods. Early adoption is permitted. ASU 2020-06 allows companies to adopt the guidance through either a modified retrospective method of transition or a fully retrospective method of transition. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures.

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (ASU 2023-07). The amendments in ASU 2023-07 are intended to improve reportable segment disclosure, primarily through enhanced disclosures about significant segment expenses. ASU 2023-07 is effective for annual periods beginning after December 15, 2023, and interim periods beginning after December 15, 2024. The amendments in this ASU should be applied retrospectively to all prior periods presented in the financial statements. Early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (ASU 2023-09). ASU 2023-09 requires enhanced annual disclosures regarding the rate reconciliation and income taxes paid information. ASU 2023-09 is effective for annual periods beginning after December 15, 2024 and may be adopted on a prospective or retrospective basis. Early adoption is permitted. The Company is evaluating the impact of this guidance on its consolidated financial statements and related disclosures.

Stockholders' Equity - Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2023 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	12,305,115
Stock Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuance	8,984,671
Stock Options Authorized for Future Issuance
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,305,386
Employee Stock Purchase Plan Shares Authorized for Future Issuance
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,065,389
Restricted Stock Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuance	949,669

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 505
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-Name Accounting Standards Codification
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-Paragraph 13
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Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Schedule of Components of Property and Equipment

The following table presents the components of property and equipment, net as of December 31, 2023 and 2022 (in thousands):


	December 31,			December 31,
	2023			2022
Leasehold improvements	$	2,513		$	2,360
Laboratory equipment		1,733			1,422
Computer hardware and software		414			344
Furniture and fixtures		166			166
Property and equipment, gross		4,826			4,292
Less: accumulated depreciation		(1,237	)		(403	)
Property and equipment, net	$	3,589		$	3,889

Schedule of Components of Other Assets, Net

The following table presents the components of other assets, net as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Long-term prepaid clinical expenses	$	7,442	$	7,264
Operating lease right-of-use assets		4,847		5,626
Finance lease right-of-use assets		2,405		298
Long-term prepaid contract manufacturing costs		—		1,456
Other		200		288
Total other assets	$	14,894	$	14,932

Components of Accrued Expenses and Other Current Liabilities

The following table presents the components of accrued expenses and other current liabilities as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Accrued contract manufacturing	$	9,543	$	5,249
Accrued clinical and nonclinical study costs		8,873		5,485
Accrued compensation and related expenses		6,067		3,708
Accrued property and equipment		179		2,110
Other		2,205		2,050
Total accrued expenses and other current liabilities	$	26,867	$	18,602

Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Statement of Stockholders' Equity [Abstract]
Underwriter discounts	$ 3.8
Issuance costs	$ 0.6

Organization

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

ORGANIZATION

(1) ORGANIZATION

Organization

ALX Oncology Holdings Inc., or the Company, was formed as a Delaware corporation on April 1, 2020, or Inception. The Company was formed for the purpose of completing the Company’s initial public offering of its common stock and related transactions in order to carry on the business of ALX Oncology Limited. The Company is a clinical-stage immuno-oncology company focused on helping patients fight cancer by developing therapies that block the CD47 checkpoint pathway and bridge the innate and adaptive immune system.

ALX Oncology Holdings Inc. is incorporated in Delaware. ALX Oncology Limited, incorporated in Ireland, is a wholly-owned subsidiary of ALX Oncology Holdings Inc. ALX Oncology Inc., incorporated in Delaware, is a wholly-owned subsidiary of ALX Oncology Limited. Alexo International Holdings Limited, incorporated in Malta, is a wholly-owned subsidiary of ALX Oncology Inc. All the companies are collectively known as the Subsidiaries.

As of December 31, 2023, the Company has devoted substantially all of its efforts to the formation and financing of the Company, as well as product development, and has not realized product revenues from its planned principal operations. The Company does not have manufacturing facilities and all manufacturing related activities are contracted out to third-party service providers.

Management expects to incur additional losses in the future to conduct product candidate research and development and to conduct pre-commercialization activities and recognizes that the Company will likely raise additional capital to fully implement its business plan. The Company intends to raise such capital through the sale of additional equity, debt financings and/or strategic alliances with third parties. However, there can be no assurance that the Company will be successful in acquiring additional funding at levels sufficient to fund its operations or on terms acceptable to the Company. If the Company is unsuccessful in its efforts to raise additional financing, the Company could be required to significantly reduce operating expenses and delay, reduce the scope of or eliminate some of its development programs or its future commercialization efforts, out-license intellectual property rights to its product candidates and sell unsecured assets, or a combination of the above, any of which may have a material adverse effect on the Company’s business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all. The Company believes that the existing capital resources will be sufficient to fund the projected operating requirements for at least the next twelve months.

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Financial Assets Measured at Fair Value on Recurring Basis


	December 31, 2023
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents
Money market funds	Level 1	$	15,591	$	—	$	—		$	15,591
Corporate debt securities	Level 2		4,489		1		—			4,490
Short-term investments
U.S. Treasury securities	Level 1		74,790		80		(20	)		74,850
U.S. government agency securities	Level 2		28,215		—		(38	)		28,177
Corporate debt securities	Level 2		21,881		24		(3	)		21,902
Commercial paper	Level 2		34,967		22		(9	)		34,980
Asset-backed securities	Level 2		423		—		(2	)		421
Long-term investments
U.S. Treasury securities	Level 1		14,737		75		—			14,812
U.S. government agency securities	Level 2		3,009		31		—			3,040
Corporate debt securities	Level 2		17,464		95		—			17,559
Total		$	215,566	$	328	$	(72	)	$	215,822


	December 31, 2022
	Fair Value Hierarchy Level	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents
Money market funds	Level 1	$	36,690	$	—	$	—		$	36,690
U.S. government agency securities	Level 2		3,484		—		—			3,484
Short-term investments
U.S. Treasury securities	Level 1		73,058		3		(438	)		72,623
U.S. government agency securities	Level 2		16,227		36		—			16,263
Corporate debt securities	Level 2		56,318		—		(367	)		55,951
Commercial paper	Level 2		62,087		—		—			62,087
Asset-backed securities	Level 2		10,512		—		(51	)		10,461
Long-term investments
U.S. Treasury securities	Level 1		5,242		2		—			5,244
U.S. government agency securities	Level 2		9,760		—		(15	)		9,745
Asset-backed securities	Level 2		1,725		—		(15	)		1,710
Total		$	275,103	$	41	$	(886	)	$	274,258

Schedule of Fair Value of Available for Sale Investments by Classification

The fair value of cash equivalents and available-for-sale investments by classification included in the consolidated balance sheets was as follows as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Cash and cash equivalents	$	20,081	$	40,174
Short-term investments		160,330		217,385
Long-term investments		35,411		16,699
Total	$	215,822	$	274,258

Schedule of Fair Value of Available-for-Sale Investments by Contractual Maturity

The fair value of cash equivalents and available-for-sale investments by contractual maturity was as follows as of December 31, 2023 and 2022 (in thousands):


	December 31,		December 31,
	2023		2022
Maturing in one year or less	$	180,411	$	257,559
Maturing after one year through five years		35,411		16,699
Total	$	215,822	$	274,258

Commitments and Contingencies - Additional Information (Details)	1 Months Ended	12 Months Ended
	Nov. 30, 2015 USD ($)	Dec. 31, 2023 USD ($) Litigation	Dec. 31, 2022 USD ($) Litigation	Dec. 31, 2021 USD ($) Litigation
Commitments And Contingencies [Line Items]
Guarantee obligations		$ 6,736,000
Number of pending or threatened litigation \| Litigation		0	0	0
Future purchase obligations		$ 6,736,000
Master Service Agreement
Commitments And Contingencies [Line Items]
Initial term of agreement	3 years
Renewal periods of agreement	1 year
Future purchase obligations	$ 1,800,000
Other Pharmaceutical Manufacturing Contract
Commitments And Contingencies [Line Items]
Future purchase obligations		4,900,000
Indemnification Agreement
Commitments And Contingencies [Line Items]
Guarantee obligations		0
Stanford Junior University \| Exclusive Equity Agreement
Commitments And Contingencies [Line Items]
Nonrefundable license royalty and patent expenses				$ 100,000
Clinical and regulatory milestones payments				5,000,000
Milestone payments related to clinical and regulatory		0		200,000
Selexis SA \| Commercial License Agreement
Commitments And Contingencies [Line Items]
Clinical and regulatory milestones payments				1,200,000
Milestone payments related to clinical and regulatory		$ 0		$ 100,000
Crystal Bioscience Inc \| Commercial Antibody Agreement
Commitments And Contingencies [Line Items]
Clinical and regulatory milestones payments			$ 11,100,000
Milestone payments related to clinical and regulatory			$ 300,000

Income Taxes - Significant Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Loss carryforwards	$ 26,517	$ 16,319
Research & other credits	17,131	8,435
Other	8,076	14
Accrued expenses	1,014	1,860
Stock options	5,157	3,860
Lease liabilities	1,587	1,323
Capitalized R&D	38,425	1,702
Total deferred tax assets	97,907	33,513
Deferred tax liabilities:
Fixed assets	96	215
Lease ROU assets	1,523	1,244
Prepaid expenses		252
Total deferred tax liabilities	1,619	1,711
Valuation allowance	(96,288)	(31,802)
Net deferred tax assets	$ 0	$ 0

Leases - Schedule of Maturities of Operating and Finance Lease Liabilities (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2024	$ 1,267
2025	1,305
2026	1,187
2027	912
2028	939
Thereafter	1,130
Total lease payments	6,740
Less: imputed interest	(1,482)
Operating lease liabilities	5,258
Lease liabilities: current	$ 847
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Lease liabilities: non-current	$ 4,411
Operating lease, liability, noncurrent, statement of financial position [extensible list]	Other non-current liabilities
Total lease liabilities	$ 5,258
Weighted average remaining lease term (in years)	5 years 4 months 24 days
Weighted average discount rate	8.70%
Finance Lease, Liability, Payment, Due [Abstract]
2024	$ 1,056
2025	1,056
2026	440
Total lease payments	2,552
Less: imputed interest	(252)
Finance lease liabilities	2,300
Finance lease liabilities, current	$ 728
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Finance lease liability, noncurrent	$ 1,572
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Noncurrent
Total lease liabilities	$ 2,300
Weighted average remaining lease term (in years)	2 years 4 months 24 days
Weighted average discount rate	8.50%

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Schedule of Maturities of Operating and Finance Lease Liabilities


	December 31, 2023
	Operating Leases			Finance Leases
2024	$	1,267		$	1,056
2025		1,305			1,056
2026		1,187			440
2027		912			—
2028		939			—
Thereafter		1,130			—
Total lease payments		6,740			2,552
Less: imputed interest		(1,482	)		(252	)
Total lease liabilities	$	5,258		$	2,300

Lease liabilities: current (i)	$	847		$	728
Lease liabilities: non-current (ii)		4,411			1,572
Total lease liabilities	$	5,258		$	2,300

Weighted average remaining lease term (in years)		5.4			2.4
Weighted average discount rate		8.7	%		8.5	%

(i)

Current lease liabilities are presented within accrued expenses and other current liabilities on the consolidated balance sheets.

(ii)

Non-current lease liabilities are presented within other non-current liabilities on the consolidated balance sheets.

Components of Lease Costs

The following table presents the components of lease costs for the years ended December 31, 2023, 2022, and 2021 (in thousands):


	Year Ended
	December 31,
	2023		2022		2021
Operating lease cost	$	1,263	$	1,159	$	360
Variable lease cost and other, net (i)		461		262		84
Short-term lease cost		17		88		—
Finance lease cost:
Amortization of right-of-use assets		493		447		369
Interest		44		9		13
Total lease costs	$	2,278	$	1,965	$	826

(i)

Supplemental Cash Flow Disclosures for Cash Paid for Leases

The following table presents the supplemental cash flow disclosures for cash paid for the years ended December 31, 2023, 2022, and 2021 (in thousands):


	Year Ended
	December 31,
	2023		2022		2021
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,241	$	933	$	243
Operating cash flows from finance leases	$	20	$	8	$	11
Financing cash flows from finance leases	$	388	$	388	$	281
Right-of-use asset acquired under leases
Operating leases	$	—	$	4,613	$	1,780
Finance leases	$	2,600	$	—	$	776

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

STOCK-BASED COMPENSATION

(9) STOCK-BASED COMPENSATION

Equity Incentive Plans

2020 Equity Incentive Plan

On April 1, 2020, the Board of Directors approved a new equity incentive plan, or the 2020 Equity Incentive Plan, that replaced the Company’s existing equity compensation plan, 2015 Share Award Scheme. The 2020 Equity Incentive Plan permitted the issuance of up to 4,379,139 shares of the Company’s common stock pursuant to awards granted under it, and authorized the award of stock options, restricted stock awards, stock appreciation rights and restricted stock units to employees, directors, and consultants.

Amended and Restated 2020 Equity Incentive Plan

In July 2020, the Company adopted the Amended and Restated 2020 Equity Incentive Plan, or the 2020 Plan. The 2020 Plan replaced the Company’s 2020 Equity Incentive Plan and a total of 7,874,862 shares were reserved under the 2020 Plan. Unless the Board of Directors provides otherwise, beginning on January 1, 2021, the maximum number of shares which shall be made available for issuance under the 2020 Plan will automatically increase on the first day in January of each calendar year (i.e., the first day of our fiscal year) by an amount equal to the least of:

•

4,000,000 shares;

•

four percent of the outstanding shares of our common stock on the last day of our immediately preceding fiscal year; or

•

such number of shares as our board of directors may determine no later than the last day of our immediately preceding fiscal year.

The terms of the stock option agreements, including vesting requirements, are determined by the Board of Directors, subject to the provisions of the 2020 Plan. The term of the options generally expire, upon the earliest of (i) termination of continuous service for cause (ii) three months after the termination of continuous service for reasons other than cause, death or disability (iii) twelve months after the termination of continuous service due to disability (iv) eighteen months after the employee’s death if the employee died during the period of continuous service (v) expiration date in the grant notice or (vi) the day before the tenth anniversary of the date of grant. The per share exercise price of the incentive stock options must equal at least the fair market value of a share underlying such options on the date of grant.

All awards that are canceled, forfeited or expired are returned to the 2020 Plan and are available for grant in conjunction with the issuance of new awards. Stock options granted are exercisable over a maximum term of 10 years from the date of grant and generally vest over an agreed service period, usually four years. Certain stock options granted under the 2020 Plan provide option holders the right to elect to exercise unvested options in exchange for common stock. Such unvested common stock is subject to a repurchase right held by the Company at the original issuance price in the event the optionee’s service to the Company is terminated either voluntarily or involuntarily. The right lapses as the underlying repurchase right expires. These repurchase terms are considered to be a forfeiture provision. The cash received from employees for exercise of unvested options is treated as a refundable deposit and is classified as a liability on the consolidated balance sheets. At December 31, 2023, there was no such unvested early exercised options and related liability.

Shares Available for Grant

The following table provides a summary of shares available for grant under the 2020 Plan:


	Amended and Restated 2020 Equity Incentive Plan
Shares available for grant at December 31, 2022		2,932,309
Authorized		1,634,456
Granted		(3,703,150	)
Canceled/forfeited		441,771
Shares available for grant at December 31, 2023		1,305,386

Stock Option Modification

There were no significant stock option modifications for the years ended December 31, 2023 and 2022.

Employee Stock Purchase Plan

In July 2020, the Board of Directors and stockholders approved the ALX Oncology Holdings Inc. 2020 Employee Stock Purchase Plan, or the ESPP. The ESPP allows eligible employees to have up to 15 percent of their eligible compensation withheld and used to purchase common stock, subject to a maximum of $25,000 worth of stock purchased in a calendar year or no more than 3,000 shares in an offering period, whichever is less. An offering period consists of a six-month purchase period, with a look back feature to our stock price at the commencement of the offering period. Eligible employees can purchase the Company’s common stock at the end of the offering period at 85% of the lower of the closing price of our common stock on The Nasdaq Global Select Market on the first and last day of the offering period.

The initial number of shares of common stock available for issuance under the ESPP was 400,000. Unless the Board of Directors provides otherwise, beginning on January 1, 2021, the maximum number of shares which shall be made available for sale under the ESPP will automatically increase on the first day in January of each calendar year (i.e., the first day of our fiscal year) during the term of the ESPP by an amount equal to the least of:

•

800,000 shares;

•

one percent of the outstanding shares of our common stock on the last day of our immediately preceding fiscal year; or

•

such number of shares as our board of directors may determine no later than the last day of our immediately preceding fiscal year.

Accordingly, on January 1, 2023 and 2022, the number of shares available under the ESPP was increased by zero and 405,871 shares respectively. As of December 31, 2023, 138,927 shares of common stock have been purchased under the ESPP, and the number of shares of common stock available for issuance under the ESPP was 1,065,389.

Stock Option Activity

The following table provides a summary of stock option activity under the 2020 Plan and related information:


	Outstanding Options
	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		6,196,848		$	20.56		7.78	$	19,872
Granted		3,139,800			6.03
Exercised		(54,359	)		4.95
Canceled/forfeited		(297,618	)		25.00
Outstanding at December 31, 2023		8,984,671		$	15.43		7.53	$	59,900
Exercisable at December 31, 2023		4,704,798		$	17.47		6.27	$	30,924

The aggregate intrinsic values represent the total pre-tax intrinsic value, of options outstanding and exercisable calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock as of December 31, 2023 and 2022. The total intrinsic value of options exercised during the years ended December 31, 2023, 2022 and 2021 were $0.2 million, $1.7 million and $48.1 million, respectively.

Stock Option Valuation Assumptions

The Company uses the Black-Scholes option pricing model to determine the estimated fair value of stock options at the date of the grant, and stock-based compensation is adjusted for actual forfeitures as they occur. The fair value of each option grant during the years ended December 31, 2023, 2022 and 2021 was estimated with the following assumptions:


	Year Ended December 31,
	2023	2022	2021
Expected term (in years)	5.3 - 6.1	5.3 - 6.1	5.3 - 6.1
Risk-free interest rate	3.5% - 4.7%	1.6% - 4.4%	0.8% - 1.4%
Expected dividend rate	-	-	-
Expected stock price volatility	83.6% - 88.6%	81.9% - 84.7%	79.7% - 86.9%

Expected Term. The expected term of the options represents the average period the stock options are expected to remain outstanding. As the Company does not have sufficient historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior, the expected term of options granted is derived from the average midpoint between the weighted average vesting and the contractual term, also known as the simplified method.

Risk-Free Interest Rate. The risk-free interest rate is based on the yield of U.S. Treasury notes as of the grant date with terms commensurate with the expected term of the option.

Dividend Yield. The expected dividends assumption is based on the Company’s expectation of not paying dividends in the foreseeable future.

Volatility. Since the Company does not have sufficient trading history for its common stock, the expected volatility is based on a combination of the historical volatilities of the common shares of comparable publicly traded companies as well as the historical volatilities of the Company’s common shares. The Company selected companies with comparable characteristics, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the Company’s share-based awards.

Fair Value. Historically, for all periods prior to our initial public offering, the fair value of the shares of common stock underlying our stock option was determined by the Company’s board of directors. Because there was no public market for the Company’s common stock, the board of directors determined fair value of the common stock at the time of grant of the options by considering a number of objective and subjective factors including important developments in the Company’s operations, valuations performed by an independent third party, sales of convertible preferred stock, actual operating results and financial performance, the conditions in the biotechnology industry and the economy in general, the stock price performance and volatility of comparable public companies, and the lack of liquidity of the Company’s common stock, among other factors the board of directors deemed relevant to such determination. Since the completion of our initial public offering, the fair value of each share of common stock underlying stock option grants is based on the closing price of our common stock on the Nasdaq Global Select Market as reported on the date of grant.

Restricted Stock Unit Activity

The following table provides a summary of restricted stock unit activity under the 2020 Plan and related information:


	Outstanding RSUs
	Number of RSUs			Weighted- Average Grant Date Fair Value		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (in thousands)
Unvested as of December 31, 2022		820,326		$	14.13		1.68	$	9,245
Granted		563,350			5.86
Vested		(289,854	)		13.33
Canceled/forfeited		(144,153	)		12.48
Unvested as of December 31, 2023		949,669		$	9.72		1.57	$	14,141

Stock-based Compensation Expenses

Stock options granted are measured based on the grant-date fair value estimated using the Black-Scholes option pricing model. The grant-date fair value of restricted stock units is the fair value of the underlying stock on the award’s grant date. Compensation expense is recognized over the vesting period of the applicable awards on a straight-line basis. The weighted-average grant date fair value per share for stock options granted during the years ended December 31, 2023, 2022 and 2021 was $4.44, $7.88 and $42.29, respectively. The weighted-average grant date fair value per share for restricted stock units granted during the years ended December 31, 2023, 2022 and 2021 was $5.86, $13.55 and $58.56, respectively.

Stock-based compensation expense includes stock options and restricted stock units and has been reported in the Company’s consolidated statements of operations as follows (in thousands):


	Year Ended
	December 31,
	2023		2022		2021
Research and development	$	14,665	$	10,741	$	5,211
General and administrative		11,608		13,098		8,703
Total	$	26,273	$	23,839	$	13,914

As of December 31, 2023, there was unrecognized share-based compensation expense of $38.9 million, related to unvested stock options which the Company expects to recognize over a weighted-average period of 2.9 years. There was unrecognized share-based compensation expense of $8.2 million, related to unvested restricted stock units which the Company expects to recognize over a weighted-average period of 2.9 years.

Leases - Components of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease cost	$ 1,263	$ 1,159	$ 360
Variable lease cost and other, net	461	262	84
Short-term lease cost	17	88
Finance lease cost, Amortization of right-of-use assets	493	447	369
Finance lease cost, Interest	44	9	13
Total lease costs	$ 2,278	$ 1,965	$ 826

Term Loan - Additional Information (Details)	1 Months Ended			12 Months Ended
Term Loan - Additional Information (Details)	May 31, 2023	Mar. 31, 2023	Oct. 31, 2022 USD ($)	Dec. 31, 2023 USD ($) Lenders	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Issuance of term loan					$ 10,000,000
Oxford-SVB Loan Agreement
Debt Instrument [Line Items]
Issuance of term loan			$ 9,300,000
Draw an additional loan			$ 50,000,000
Interest rate terms			Borrowings under the Loan Agreement bear interest at a floating rate per annum equal to the greater of (i) 1-month term Secured Overnight Financing Rate, or SOFR, and (ii) 2.33%, plus 6.25%. The minimum per annum interest rate is 8.58%.
Maturity date			Oct. 01, 2027
Incremental prepayment amount			$ 10,000,000
Percentage of fee amount paid upon final payment			6.00%
Debt default rate			5.00%
Interest expense				$ 1,100,000	$ 200,000
deduction of debt issuance costs			$ 700,000
Number of lenders \| Lenders				3
Contingency fee				$ 600,000
Oxford-SVB Loan Agreement \| Term Loan
Debt Instrument [Line Items]
Interest expense						$ 0
Outstanding debt						$ 0
Oxford-SVB Loan Agreement \| Fixed Rate
Debt Instrument [Line Items]
Basis spread rate			6.25%
Oxford-SVB Loan Agreement \| Base Rate
Debt Instrument [Line Items]
Basis spread rate			8.58%
Oxford-SVB Loan Agreement \| Tranche A
Debt Instrument [Line Items]
Issuance of term loan			$ 10,000,000
Draw an additional loan			40,000,000
Oxford-SVB Loan Agreement \| Tranche B
Debt Instrument [Line Items]
Available borrowing capacity upon achievement of milestones			12,500,000
Oxford-SVB Loan Agreement \| Tranche C
Debt Instrument [Line Items]
Available borrowing capacity upon achievement of milestones			12,500,000
Oxford-SVB Loan Agreement \| Tranche D
Debt Instrument [Line Items]
Available borrowing capacity at lender's discretion			25,000,000
Oxford-SVB Loan Agreement \| Maximum \| Secured Term Loan Facility
Debt Instrument [Line Items]
Term loan, principal amount			$ 100,000,000
Oxford-SVB Loan Agreement \| Minimum
Debt Instrument [Line Items]
Basis spread rate			2.33%
Oxford-SVB Loan Agreement \| Minimum \| Term Loan \| Intellectual Property
Debt Instrument [Line Items]
Outstanding balance of loan threshold at which Intellectual Property becomes collateral			$ 75,000,000
Silicon Valley Bank
Debt Instrument [Line Items]
Loan Agreement with Lenders		50.00%
Silicon Valley Bank \| Maximum
Debt Instrument [Line Items]
Percentage of loan agreement amount to be held in collateral account	100.00%
Silicon Valley Bank \| Minimum
Debt Instrument [Line Items]
Percentage of loan agreement amount to be held in collateral account	50.00%

Term Loan (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Schedule of Future Maturities Under the Loan Agreement

As of December 31, 2023, the future maturities under the Loan Agreement are as follows (in thousands):


	December 31, 2023
2024	$	—
2025		435
2026		5,217
2027		4,948
Total future maturities		10,600
Less: current portion of term loan		—
Total term loan, net of current portion		10,600
Less: unamortized debt issuance costs		(781	)
Less: unaccreted final payment costs		(180	)
Term loan, non-current, net	$	9,639

Fair Value of Financial Instruments - Schedule of Fair Value of Available-for-sale Investments by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale, Fair Value, Fiscal Year Maturity [Abstract]
Maturing in one year or less	$ 180,411	$ 257,559
Maturing after one year through five years	35,411	16,699
Total available-for-sale investments	$ 215,822	$ 274,258

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance as of December 31, 2023 consists of the following:


	December 31, 2023
Stock options issued and outstanding		8,984,671
Stock options authorized for future issuance		1,305,386
Employee Stock Purchase Plan shares authorized for future issuance		1,065,389
Restricted stock issued and outstanding		949,669
Total		12,305,115

Leases - Supplemental Cash Flow Disclosures for Cash Paid for Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating cash flows from operating leases	$ 1,241	$ 933	$ 243
Operating cash flows from finance leases	20	8	11
Financing cash flows from finance leases	388	388	281
Right-of-use asset acquired under leases
Operating leases		$ 4,613	1,780
Finance leases	$ 2,600		$ 776

Fair Value of Financial Instruments - Schedule of Fair Value of Available for Sale Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total available-for-sale investments	$ 215,822	$ 274,258
Cash and Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale	20,081	40,174
Short-term Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short term investments available for sale	160,330	217,385
Long-term Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long term investments available for sale	$ 35,411	$ 16,699

Income Taxes - Schedule of Net Operating Losses and Tax Credit Carryforwards (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Federal
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses	$ 93,542
Tax credits	$ 14,431
Federal \| Minimum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Tax credits, Expiration Years	2039
Federal \| Maximum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Tax credits, Expiration Years	2043
State
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses	$ 68,993
Tax credits	$ 5,918
State \| Minimum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses, Expiration Years	2038
State \| Maximum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses, Expiration Years	2040
Foreign
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses	$ 4,896