0000950170-24-031516 | 10-K | XBRL Viewer

Balance Sheet Components and Supplemental Disclosures - Schedule of Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Prepaid clinical expenses	$ 1,092	$ 1,741
Prepaid manufacturing expenses	3,877	21,998
Other prepaid expenses or current assets	4,126	5,318
Total	$ 9,095	$ 29,057

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	ATM Offering Member	Common Stock	Common Stock ATM Offering Member	Additional Paid-In Capital	Additional Paid-In Capital ATM Offering Member	Accumulated Other Comprehensive Gain (Loss)	Accumulated Other Comprehensive Gain (Loss) ATM Offering Member	Accumulated Deficit	Accumulated Deficit ATM Offering Member
Balance at Dec. 31, 2021	$ 445,476		$ 54		$ 1,058,399		$ (153)		$ (612,824)
Balance, Shares at Dec. 31, 2021			54,622
Stock-based compensation expense	43,158		$ 0		43,158		0		0
Issuance of common stock upon exercise of stock options	853		$ 1		852		0		0
Issuance of common stock upon exercise of stock options, Shares			464
Issuance of common stock upon 2018 ESPP purchase	438		$ 0		438		0		0
Issuance of common stock upon 2018 ESPP purchase, Shares			104
Issuance of common stock	140,591		$ 30		140,561		0		0
Issuance of common stock, shares			29,882
Issuance of common stock upon vesting of restricted stock units	0		$ 0		0		0		0
Issuance of common stock upon vesting of restricted stock units, Shares			315
Unrealized gain (loss) on marketable securities	(131)		$ 0		0		(131)		0
Net loss	(319,952)		0		0		0		(319,952)
Balance at Dec. 31, 2022	310,433		$ 85		1,243,408		(284)		(932,776)
Balance, Shares at Dec. 31, 2022			85,387
Stock-based compensation expense	41,223		$ 0		41,223		0		0
Issuance of common stock upon exercise of stock options	673		$ 0		673		0		0
Issuance of common stock upon exercise of stock options, Shares			206
Issuance of common stock upon 2018 ESPP purchase	865		$ 0		865		0		0
Issuance of common stock upon 2018 ESPP purchase, Shares			281
Issuance of common stock		$ 990		$ 0		$ 990		$ 0		$ 0
Issuance of common stock, shares				142
Issuance of common stock upon vesting of restricted stock units	0		$ 3		(3)		0		0
Issuance of common stock upon vesting of restricted stock units, Shares			1,734
Unrealized gain (loss) on marketable securities	334		$ 0		0		334		0
Net loss	(185,701)		0		0		0		(185,701)
Balance at Dec. 31, 2023	$ 168,817		$ 88		$ 1,287,156		$ 50		$ (1,118,477)
Balance, Shares at Dec. 31, 2023			87,750

Balance Sheet Components and Supplemental Disclosures

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components and Supplemental Disclosures

5. Balance Sheet Components and Supplemental Disclosures

Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):


	December 31,
	2023		2022
Prepaid clinical expenses	$	1,092	$	1,741
Prepaid manufacturing expenses		3,877		21,998
Other prepaid expenses or current assets		4,126		5,318
Total	$	9,095	$	29,057

The decrease in prepaid manufacturing expenses from December 31, 2022 to December 31, 2023 is primarily due to the timing of manufacturing activities relating to lirentelimab.

Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):


	December 31,
	2023			2022
Laboratory equipment	$	6,993		$	6,473
Furniture and office equipment		3,947			3,947
Leasehold improvements		32,386			32,457
Capitalized software		4,382			4,112
Construction-in-progress or pending installation		69			422
		47,777			47,411
Less accumulated depreciation		(14,408	)		(8,267	)
Property and equipment, net	$	33,369		$	39,144

Depreciation expense for the years ended December 31, 2023 and 2022 was $6.1 million, and $7.1 million, respectively. During the year ended December 31, 2022, gross fixed assets of $5.8 million with accumulated depreciation of $4.6 million were disposed of or sold for $1.2 million in conjunction with exiting the Redwood City facility.

Other Long-Term Assets

Other long-term assets were $6.2 million and $8.2 million as of December 31, 2023 and 2022, respectively. Other long-term assets at December 31, 2023 and 2022 included $0.8 million and $6.6 million, respectively, in advance payments to CDMOs for development and manufacturing services expected to be provided more than one year from the balance sheet date. Other long-term assets as of December 31, 2023 additionally includes $3.9 million of tax credit receivables classified as long-term.

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	December 31,
	2023		2022
Accrued contract research and development expense	$	22,262	$	13,950
Accrued compensation and benefits expense		8,674		7,039
Current portion of operating lease liabilities		3,250		3,161
Other current liabilities		628		1,056
Total	$	34,814	$	25,206

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 66,440	$ 87,217
Restricted cash in other long-term assets	1,472	1,472
Total	$ 67,912	$ 88,689	$ 155,097

Subsequent Events - Additional Information (Details) - Re-organization Plan [Member] - Subsequent Event - USD ($) $ in Millions		3 Months Ended
	Jan. 16, 2024	Mar. 31, 2024
Subsequent Event [Line Items]
Percentage reduction in workforce	50.00%
Severance and transition cost		$ 4

Leases - Summary of Components of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease costs	$ 5,806	$ 5,886
Variable costs	3,627	3,007
Total lease costs	$ 9,433	$ 8,893

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate Intrinsic Value, Exercised	$ 100	$ 1,800
2018 and 2012 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Outstanding, Beginning balance	5,423
Options Outstanding, Granted	3,458
Options Outstanding, Exercised	(206)
Options outstanding, Expired	(267)
Options Outstanding, forfeited	(440)
Options Outstanding, Ending balance	7,968	5,423
Options Outstanding, Options exercisable	4,216
Options Outstanding, Options vested and expected to vest	7,776
Weighted Average Exercise Price, Beginning balance	$ 15.41
Weighted Average Exercise Price, Granted	5.79
Weighted Average Exercise Price, Exercised	3.26
Weighted Average Exercise Price, Forfeited	7.99
Weighted Average Exercise Price, Ending balance	10.85	$ 15.41
Weighted Average Exercise Price, Options exercisable	13.62
Weighted Average Exercise Price, Options vested and expected to vest	$ 10.95
Weighted Average Remaining Years	6 years 10 months 24 days	6 years 4 months 24 days
Weighted Average Remaining Years, Options exercisable	5 years
Weighted Average Remaining Years, Options vested and expected to vest	6 years 10 months 24 days
Aggregate Intrinsic Value, Beginning balance	$ 22,657
Aggregate Intrinsic Value, Ending balance	3,168	$ 22,657
Aggregate Intrinsic Value, Options exercisable	3,165
Aggregate Intrinsic Value, Options vested and expected to vest	$ 3,168
Weighted Average Exercise Price, Expired	$ 48.35

Income Taxes - Summary of Effective Tax Rate Differs From Federal Statutory Tax Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%
Change in deferred tax asset valuation allowance	(24.50%)	(39.10%)
State taxes, net of federal benefit	5.30%	20.30%
Research and development tax credits	3.10%	0.60%
Stock-based compensation	(0.70%)	(0.10%)
Other	(4.20%)	(2.70%)
Effective tax rate	0.00%	0.00%

Investments - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 104,340	$ 192,853
Unrealized Gains	39	3
Unrealized Losses	(25)	(287)
Fair Value	104,354	192,569
Investments \| U.S. treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	96,688	192,853
Unrealized Gains	39	3
Unrealized Losses	(22)	(287)
Fair Value	96,705	$ 192,569
Investments \| U.S. government agency bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	7,652
Unrealized Gains	0
Unrealized Losses	(3)
Fair Value	$ 7,649

- 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/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Defined Contribution Plans - Additional Information (Details) - 401(K) Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Contribution Plan Disclosure [Line Items]
Contributions made by employer	$ 1.0	$ 1.0
Maximum
Defined Contribution Plan Disclosure [Line Items]
Employer contribution matching percentage	4.00%

Income Taxes - Summary of Total Deferred Income Tax Assets, Net of Valuation Allowance (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets
Net operating loss carryforwards	$ 247,208	$ 225,924
Capitalized research expenditures	65,677	48,767
Research and development credits	42,347	35,906
Accruals and reserves	8,182	6,839
Stock-based compensation	5,519	6,341
Lease liability	11,314	13,403
Fixed and intangible assets	295	0
Gross deferred tax assets	380,542	337,180
Less: valuation allowance	(373,957)	(328,553)
Deferred tax assets, net of valuation allowance	6,585	8,627
Deferred tax liabilities
Fixed and intangible assets	(0)	378
Right-of-use asset	6,585	8,249
Gross deferred tax liabilities	6,585	8,627
Net deferred tax assets	$ 0	$ 0

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

6. Leases

Operating Leases

The Company’s lease obligations primarily relate to leased office and laboratory space under noncancelable operating leases. In accordance with ASC 842, the Company has performed an evaluation of its other contracts with vendors and has determined that, except for the leases described below, none of its other contracts contain a lease.

2019 San Carlos Lease

In December 2019, the Company entered into an additional operating lease agreement for approximately 98,000 square feet of office and laboratory space in San Carlos, California (the “2019 San Carlos Lease”). The contractual term of the 2019 San Carlos Lease is 10.25 years from August 2021 until October 2031. The 2019 San Carlos Lease provides rent abatements and includes a one-time option to extend the lease term for five years. This option to extend the lease term was not determined to be reasonably certain and therefore has not been included in the Company’s calculation of the associated operating lease liability under ASC 842.

The 2019 San Carlos Lease includes monthly base rent amounts escalating over the term of the lease. In addition, the lessor provided for a TIA of up to $14.4 million, which was fully utilized and are recorded in lease obligations.

On March 27, 2023, the Company entered into an amendment for the 2019 San Carlos Lease, whereby rentable square feet was adjusted to 95,692 square feet and lease payments were reduced by approximately 2.5% per month, effective from January 1, 2022 through the end of the lease term. The Company accounted for these changes as a modification under ASC 842 and the operating right-of-use asset and lease liability were remeasured during the first quarter of 2023 utilizing an estimated incremental borrowing rate of 10.5%. Our estimated incremental borrowing rate was based on our estimated rate of interest for a fully collateralized borrowing over a similar term as the remaining lease payments while incorporating our credit risk. As a result of the modification, the right-of-use asset and lease liability decreased by approximately $5.6 million. No gain or loss was recognized upon the modification.

Classification of Operating Leases

The 2019 San Carlos Lease required security deposits of $1.5 million, which the Company satisfied by establishing letters of credit secured by restricted cash. As of December 31, 2023 and 2022, a security deposit of $1.5 million for the 2019 San Carlos Lease was recorded as restricted cash in other long-term assets on the Company's balance sheets.

Classification of the Company’s operating lease liabilities included in the Company’s balance sheets at December 31, 2023 and 2022 was as follows (in thousands):


	December 31,
	2023		2022
Operating lease liabilities
Current portion included in accrued expenses and other current liabilities	$	3,250	$	3,161
Operating lease liabilities, net of current portion		38,215		45,949
Total operating lease liabilities	$	41,465	$	49,110

The components of lease costs, which are included in operating expenses in the Company’s statements of operations and comprehensive loss were as follows (in thousands):


	Year ended December 31,
	2023		2022
Operating lease costs	$	5,806	$	5,886
Variable costs		3,627		3,007
Total lease costs	$	9,433	$	8,893

Variable costs included in the table above represent amounts the Company pays related to property taxes, insurance, maintenance and repair costs.

Cash paid for amounts included in the measurement of the Company’s operating lease liabilities and presented within cash used in operating activities in the statements of cash flows was $6.7 million and $6.8 million for the years ended December 31, 2023 and 2022.

Cash received for amounts related to tenant improvement allowances from lessors was $0.3 million and $1.3 million for the years ended December 31, 2023 and 2022, respectively.

Operating Lease Obligations

Future lease payments required under operating leases included on the Company’s balance sheet at December 31, 2023 are as follows (in thousands):


Fiscal Year Ending December 31,
2024	$	7,441
2025		7,287
2026		7,506
2027		7,731
2028		7,963
Thereafter		23,871
Total future lease payments		61,799
Less:
Present value adjustment		20,334
Operating lease liabilities	$	41,465

Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, the Company used its incremental borrowing rate based on the information available at the lease commencement date. As of December 31, 2023, the weighted-average remaining lease term of the Company’s leases was 7.8 years and the weighted-average discount rate used to determine the operating lease liabilities included on the balance sheet was 10.5%.

As of December 31, 2023, the Company has not been party to any lease agreements containing material residual value guarantees or material restrictive covenants.

Leases - Summary of Classification of Company's Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Operating lease liabilities
Current portion included in accrued expenses and other current liabilities	$ 3,250	$ 3,161
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities, Current	Accrued Liabilities, Current
Operating lease liabilities, net of current portion	$ 38,215	$ 45,949
Total operating lease liabilities	$ 41,465	$ 49,110

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Presentation

The financial statements have been prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts and disclosures reported in the financial statements and accompanying notes.

Use of Estimates

Management uses significant judgment when making estimates related to stock-based compensation expense, accrued research and development expense, and lease related assets and liabilities. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates under different assumptions or conditions, and those differences could be material to the financial position and results of operations.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to credit risk principally consist of cash, cash equivalents and marketable securities. These financial instruments are held in accounts at a single financial institution that management believes possesses high credit quality. Amounts on deposit with this financial institution have and will continue to exceed federally-insured limits. The Company has not experienced any losses on its cash deposits. Additionally, the Company’s investment policy limits its investments to certain types of securities issued by the United States government and its agencies.

The Company is subject to a number of risks similar to that of other early-stage biopharmaceutical companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of current or future clinical trials, its reliance on third-parties to conduct its clinical trials, the need to obtain regulatory and marketing approvals for its product candidates, competitive developments, the need to successfully commercialize and gain market acceptance of the Company’s product candidates, its right to develop and commercialize its product candidates pursuant to the terms and conditions of the licenses granted to the Company, protection of proprietary technology, the ability to make milestone, royalty or other payments due under licensing agreements, and the need to secure and maintain adequate manufacturing arrangements with third-parties. If the Company does not successfully commercialize or partner its product candidates, it will be unable to generate product revenue or achieve profitability.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the statements of cash flows (in thousands):


	December 31,
	2023		2022
Cash and cash equivalents	$	66,440	$	87,217
Restricted cash in other long-term assets		1,472		1,472
Total	$	67,912	$	88,689

Restricted cash at December 31, 2023 represents $1.5 million of security deposits for the lease of the Company’s facility in San Carlos, California. The security deposit is in the form of a letter of credit secured by restricted cash and is recorded in other long-term assets on the Company's balance sheets.

Investments

The Company invests in marketable securities, primarily securities issued by the U.S. government and its agencies. The Company’s investments are considered available-for-sale and are classified as current assets even when the stated maturities of the underlying securities exceed one year from the date of the current balance sheet being reported. This classification reflects management’s ability and intent to utilize proceeds from the sale of such investments to fund ongoing operations. Unrealized gains and losses are excluded from earnings and are reported as a component of accumulated other comprehensive gain (loss). The cost of securities sold is determined using the specific-identification method. Interest earned and adjustments for the amortization of premiums and discounts on investments are included in interest income on the statements of operations and comprehensive loss. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on investments in marketable securities are included in other expense, net, on the statements of operations and comprehensive loss.

Fair Value Measurements

The Company accounts for fair value of its financial instruments in accordance with Financial Accounting Standards Board (the “FASB”) Accounting Standards Codification (“ASC”) Topic No. 820, Fair Value Measurements (“ASC 820”). ASC 820 establishes a common definition for fair value, establishes a framework for measuring fair value and expands disclosures about such fair value measurements. Additionally, ASC 820 defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.

The Company measures fair value based on a three-level hierarchy of inputs, of which the first two are considered observable and the last unobservable. Unobservable inputs reflect the Company’s own assumptions about current market conditions. The three-level hierarchy of inputs is as follows:

Level 1 – Quoted prices in active markets for identical assets or liabilities.

Level 2 – Inputs other than Level 1 that 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 assets or liabilities.

Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities.

To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The carrying amounts reflected in the Company’s balance sheets for cash and cash equivalents, prepaid expenses and other current assets, other long-term assets, accounts payable, and accrued expenses and other current liabilities approximate fair value, due to their short-term nature. The Company’s investments in marketable securities are measured at fair value in accordance with the levels above.

Property and Equipment, Net

Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the assets. Generally, the useful lives of laboratory equipment and capitalized software are five years, furniture and office equipment are three to five years, and leasehold improvements property and equipment are the shorter of the remaining lease term or the estimated life of the assets.

Any resulting gains or losses on dispositions of property and equipment are included as a component of other income (expense), net, within the Company’s statements of operations and comprehensive loss. Repair and maintenance costs that do not significantly add value to the property and equipment, or prolong its life, are charged to operating expense as incurred.

Operating Leases

The Company accounts for its leases in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 842, “Leases” (“ASC 842”). Right-of-use assets represent the Company’s right to use an underlying asset over the lease term and include any lease payments made prior to the lease commencement date and are reduced by lease incentives. Lease liabilities represent the present value of the total lease payments over the lease term, calculated using the Company’s incremental borrowing rate. In determining the Company’s incremental borrowing rate, consideration is given to the term of the lease and the Company’s credit risk. The Company recognizes options to extend a lease when it is reasonably certain that it will exercise such extension. The Company does not recognize options to terminate a lease when it is reasonably certain that it will not exercise such early termination options. Lease expense is recognized on a straight-line basis over the expected lease term.

Accrued Research and Development Expense

Service agreements with contract development and manufacturing organizations (“CDMOs”), clinical contract research organizations (“CROs”) and clinical investigative sites comprise a significant component of the Company’s research and development activities. External costs for these vendors are recognized as the services are incurred. The Company accrues for expenses resulting from obligations under agreements with its third-parties for which the timing of payments does not match the periods over which the materials or services are provided to the Company. Accruals are recorded based on estimates of services received and efforts expended pursuant to agreements established with CDMOs, clinical CROs, clinical investigative sites and other outside service providers. These estimates are typically based on contracted amounts applied to the proportion of work performed and determined through analysis with internal personnel and external service providers as to the progress or stage of completion of the services.

The Company makes judgements and estimates in determining the accrual balance in each reporting period. In the event advance payments are made to a CDMO, clinical CRO, clinical investigative site or other outside service provider, the payments are recorded within prepaid expenses and other current assets or other long-term assets, as appropriate, and subsequently recognized as research and development expense when the associated services have been performed. As actual costs become known, the Company adjusts its liabilities and assets. Inputs, such as the extent of services received and the duration of services to be performed, may vary from the Company’s estimates, which will result in adjustments to research and development expense in future periods. Changes in these estimates

that result in material changes to the Company’s accruals could materially affect the Company’s results of operations. The Company’s historical estimates have not been materially different from actual amounts recorded.

Research and Development Expense

Research and development costs are expensed as incurred. Research and development costs include, among others, consulting costs, salaries, benefits, travel, stock-based compensation, laboratory supplies and other non-capital equipment utilized for in-house research, allocation of facilities and overhead costs and external costs paid to third-parties that conduct research and development activities on the Company’s behalf. Costs to terminate commitments with third-party suppliers performing research and development activities and amounts incurred in connection with license agreements, including milestone payments, are also included in research and development expense.

Advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and included in prepaid expenses and other current assets or other long-term assets, as appropriate. The deferred amounts are expensed as the related goods are delivered or the services are performed.

Segments

Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker or decision-making group, in deciding how to allocate resources and in assessing performance. The Company’s chief operating decision maker, its Chief Executive Officer, views its operations and manages its business in one operating segment operating exclusively in the United States.

Patent Costs

The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the statements of operations and comprehensive loss.

Stock-Based Compensation

The Company accounts for its stock-based compensation in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based awards issued to employees and nonemployees to be recognized as expense in the statements of operations and comprehensive loss based on their grant date fair values. Stock-based awards issued to nonemployee consultants are accounted for based on the fair value of services to be received or of the intrinsic value of equity instruments to be issued, whichever is more reliably measured. The measurement date for awards issued to nonemployee consultants is the date of grant.

For purposes of determining the estimated fair value of stock options granted to employees and nonemployees, the Company uses the Black-Scholes option pricing model. The Black-Scholes option pricing model requires the input of certain assumptions that involve judgment, for which changes can materially affect the resulting estimates of fair value. The assumptions used to determine the fair value of stock options granted were as follows:

Expected volatility – As there is insufficient trading history for the Company’s common stock, the Company has based its computation of expected volatility on the historical volatility of our stock as well as a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption.

Expected term – The Company determines the expected term in accordance with the “simplified method” described by SEC Staff Accounting Bulletin No. 107, Share-Based Payment, as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term.

Risk-free interest rate – The Company bases the risk-free interest rate on United States Treasury securities with terms consistent to the expected term of the stock option being valued.

Expected dividends – The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock.

The fair value of restricted stock units (“RSUs”) is determined using the quoted market price of the Company’s common stock on the date of grant.

The Company uses historical data to estimate pre-vesting forfeitures and records stock-based compensation expense only for those awards expected to vest. To the extent that actual forfeitures differ from estimates, the difference is recorded as a cumulative adjustment in the period the estimate are revised. The Company expenses the fair value of its stock-based compensation awards to employees and nonemployees on a straight-line basis over the requisite service period, which is generally the vesting period.

The Company recognizes the stock-based compensation expense related to performance-based stock awards or performance-based RSUs ("PSUs") if the performance targets are deemed probable of being achieved. The vesting of PSUs requires that certain performance conditions are achieved during the performance period and is subject to the employee’s continued service requirements.

Income Taxes

The Company accounts for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes the Company expects to pay or have refunded in the current year. The Company’s deferred income tax assets and liabilities are determined based on differences between financial statement reporting and tax basis accounting of assets and liabilities and net operating loss and credit carryforwards, which it measures using the enacted tax rates and laws that will be in effect when such items are expected to reverse. The Company reduces deferred income tax assets, as necessary, by applying a valuation allowance to the extent that it determined it is more likely than not that some or all of our tax benefits will not be realized.

The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company assesses all material positions reflected in our income tax returns, including all significant uncertain positions, for all tax years that are subject to assessment or challenge by relevant taxing authorities. Upon determining the sustainability of its positions, the Company measures the largest amount of benefit possessing greater than fifty percent likelihood of being realized upon ultimate settlement. The Company reassesses such positions at each balance sheet date to determine whether any factors underlying the sustainability assertion have changed and whether or not the amount of the recognized tax benefit is still appropriate.

Comprehensive Loss

Comprehensive loss is defined as the change in stockholders’ equity during a period from transactions and other events and circumstances from non-owner sources. The difference between net loss and comprehensive loss for the years ended December 31, 2023 and 2022 are a result of unrealized gains and losses on the Company’s investments in marketable securities included in current assets on the Company's balance sheets.

Net Loss per Share

The Company calculates basic net loss per share by dividing the net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company calculates diluted net loss per share after giving consideration to all potentially dilutive securities outstanding during the period using the treasury-stock and if-converted methods, except where the effect of including such securities would be anti-dilutive. Because the Company has reported net losses since inception, the effect from potentially dilutive securities would have been anti-dilutive and therefore has been excluded from the calculation of diluted net loss per share.

The Company’s weighted-average shares of common stock outstanding increased from 63.3 million shares of common stock outstanding during the year ended December 31, 2022 to 86.8 million shares of common stock outstanding during the year ended December 31, 2023 primarily as a result of the 29.9 million shares sold as part of an underwritten registered direct offering closed on September 21, 2022 (the “September 2022 Offering”). Refer to Note 8 “Stockholders’ Equity” for additional details related to the offering.

Basic and diluted net loss per share was calculated as follows (in thousands, except per share data):


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(185,701	)	$	(319,952	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		86,798			63,284
Net loss per share, basic and diluted	$	(2.14	)	$	(5.06	)

The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect for the periods indicated (in thousands):


	Year Ended December 31,
	2023		2022
Options to purchase common stock		7,968		5,423
Unvested restricted stock units		5,621		4,478
Unvested performance stock unit		2,845		3,276
Shares issuable under employee stock purchase plans		127		135
Total		16,561		13,312

Foreign Currency Transactions

The Company is party to multiple contract manufacturing and clinical research agreements for which services to be performed are denominated in foreign currencies other than the United States Dollar. The Company records gains and losses attributable to fluctuations in foreign currencies as a component of other income (expense), net, on the statements of operations and comprehensive loss.

Recently Issued and Adopted Accounting Pronouncements

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This ASU requires entities to expand its existing income tax disclosures, specifically related to the rate reconciliation and income taxes paid. This authoritative guidance will be effective for us in fiscal year 2025, with early adoption permitted. The Company is currently evaluating the impact of the ASU, but does not expect any material impacts upon adoption.

Uncertain Tax Positions

The Company accounts for its uncertain tax positions in accordance with FASB ASC Topic No. 740-10, Accounting for Uncertainty in Income Taxes (“ASC 740-10”). Per ASC 740-10, the Company determines its uncertain tax positions based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings is more likely than not to be sustained upon examination by the relevant income tax authorities.

It is the Company’s policy to include penalties and interest expense related to income taxes as a component of the income tax provision as necessary.

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (185,701)	$ (319,952)

- 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

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Granted and ESPP Shares (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	3.88%	2.95%
Expected volatility	99.96%	75.94%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	5 years 11 months 15 days	5 years 10 months 2 days
ESPP Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	5.14%	2.20%
Expected volatility	127.37%	75.83%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	1 year 3 months 25 days	1 year 8 months 1 day

- 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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+ Details

Summary of Significant Accounting Policies - Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	16,561	13,312
Employee Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	7,968	5,423
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	5,621	4,478
Unvested Performance Stock Unit
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	2,845	3,276
Shares Issuable under Employee Stock Purchase Plans
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from calculation of diluted net loss per share due to anti-dilutive effect	127	135

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	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

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Concentration of Credit Risk and Other Risks and Uncertainties

Cash, Cash Equivalents and Restricted Cash


	December 31,
	2023		2022
Cash and cash equivalents	$	66,440	$	87,217
Restricted cash in other long-term assets		1,472		1,472
Total	$	67,912	$	88,689

Investments

Fair Value Measurements

Level 1 – Quoted prices in active markets for identical assets or liabilities.

Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities.

Property and Equipment, Net

Operating Leases

Accrued Research and Development Expense

Research and Development Expense

Segments

Patent Costs

The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the statements of operations and comprehensive loss.

Stock-Based Compensation

Risk-free interest rate – The Company bases the risk-free interest rate on United States Treasury securities with terms consistent to the expected term of the stock option being valued.

Expected dividends – The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock.

The fair value of restricted stock units (“RSUs”) is determined using the quoted market price of the Company’s common stock on the date of grant.

Income Taxes

Comprehensive Loss

Net Loss per Share

Basic and diluted net loss per share was calculated as follows (in thousands, except per share data):


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(185,701	)	$	(319,952	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		86,798			63,284
Net loss per share, basic and diluted	$	(2.14	)	$	(5.06	)


	Year Ended December 31,
	2023		2022
Options to purchase common stock		7,968		5,423
Unvested restricted stock units		5,621		4,478
Unvested performance stock unit		2,845		3,276
Shares issuable under employee stock purchase plans		127		135
Total		16,561		13,312

Foreign Currency Transactions

Recently Issued and Adopted Accounting Pronouncements

Balance Sheet Components and Supplemental Disclosures (Tables)

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):


	December 31,
	2023		2022
Prepaid clinical expenses	$	1,092	$	1,741
Prepaid manufacturing expenses		3,877		21,998
Other prepaid expenses or current assets		4,126		5,318
Total	$	9,095	$	29,057

Schedule of Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):


	December 31,
	2023			2022
Laboratory equipment	$	6,993		$	6,473
Furniture and office equipment		3,947			3,947
Leasehold improvements		32,386			32,457
Capitalized software		4,382			4,112
Construction-in-progress or pending installation		69			422
		47,777			47,411
Less accumulated depreciation		(14,408	)		(8,267	)
Property and equipment, net	$	33,369		$	39,144

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	December 31,
	2023		2022
Accrued contract research and development expense	$	22,262	$	13,950
Accrued compensation and benefits expense		8,674		7,039
Current portion of operating lease liabilities		3,250		3,161
Other current liabilities		628		1,056
Total	$	34,814	$	25,206

Summary of Significant Accounting Policies - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net Income (Loss)	$ (185,701)	$ (319,952)
Denominator:
Weighted-average shares of common stock outstanding, basic	86,798	63,284
Weighted-average shares of common stock outstanding, diluted	86,798	63,284
Net loss per common share, basic	$ (2.14)	$ (5.06)
Net loss per common share, diluted	$ (2.14)	$ (5.06)

- 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

Leases - Additional Information (Details) $ in Millions	1 Months Ended	12 Months Ended
Leases - Additional Information (Details) $ in Millions	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Mar. 27, 2023 USD ($) ft²
Lessee, Lease, Description [Line Items]
Cash paid for amounts included in measurement of operating lease liabilities		$ 6.7	$ 6.8
Cash received for amounts related to tenant improvement allowances from lessors		$ 0.3	1.3
Operating lease, weighted-average remaining lease term		7 years 9 months 18 days
Operating lease, weighted-average discount rate		10.50%
2019 San Carlos Lease Agreement
Lessee, Lease, Description [Line Items]
Operating lease agreement initiation period	2019-12
Base term of lease	10 years 3 months
Lessee operating lease expected termination Period	2031-10
Lease term extension period	5 years
Area of lease \| ft²	98,000			95,692
Percentage of lease payments reduced				2.50%
Incremental borrowing rate				10.50%
Right of use asset and lease liability decreased				$ 5.6
Security deposit in the form of letter of credit secured by restricted cash		$ 1.5	$ 1.5
2019 San Carlos Lease Agreement \| Maximum
Lessee, Lease, Description [Line Items]
Tenant improvement allowance	$ 14.4

Stockholders' Equity

12 Months Ended

Dec. 31, 2023

Stockholders' Equity Note [Abstract]

Stockholders' Equity

8. Stockholders’ Equity

September 2022 Offering

On September 21, 2022, the Company closed an underwritten registered direct offering (the “September 2022 Offering”) under its shelf registration statement on Form S-3 (File No. 333-265085), supplemented by a prospectus supplement filed with the SEC on September 19, 2022 pursuant to Rule 424(b) under the Securities Act of 1933, as amended. In connection with the September 2022 Offering, the Company sold an aggregate of 29,882,000 shares of our common stock, par value $0.001 per share, at an offering price of $5.02 per share. Aggregate net proceeds were approximately $140.6 million, after deducting the underwriting commissions and estimated offering expenses.

“At-the-Market” Equity Offerings

On August 4, 2022, the Company entered into a sales agreement (the “2022 Sales Agreement”) with Cowen and Company, LLC (“Cowen”). Pursuant to Sales Agreement, the Company may sell, from time to time, up to an aggregate of $75.0 million in gross sales proceeds of its common stock through an “at-the-market” offering (“ATM Offering”) as defined under the Securities Act of 1933. The Company will pay a commission equal to 3% of the gross proceeds from the sale of shares of its common stock under the Sales Agreement. The $75.0 million of common stock that may be offered, issued and sold in the ATM Offering is included in the $250.0 million of securities that may be offered, issued and sold by the Company under its registration statement on Form S-3 (File No. 333-265085). The Company expects to use the net proceeds from sales under the 2022 Sales Agreement for general corporate purposes.

During the year ended December 31, 2023, the Company sold 0.1 million shares of its common stock at an average price of $7.20 per share through its ATM Offering, resulting in proceeds of $1.0 million net of commissions, with all sales occurring during the first quarter of 2023. Under its current ATM Offering program, $74.0 million of common stock remain available for future sales as of December 31, 2023; however, the Company is not obligated to make any sales under this program.

- Definition

The entire disclosure for equity.

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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-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
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Balance Sheet Components and Supplemental Disclosures - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued contract research and development expense	$ 22,262	$ 13,950
Accrued compensation and benefits expense	8,674	7,039
Current portion of operating lease liabilities	3,250	3,161
Other current liabilities	628	1,056
Total	$ 34,814	$ 25,206

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 66,440	$ 87,217
Investments	104,354	192,569
Prepaid expenses and other current assets	9,095	29,057
Total current assets	179,889	308,843
Property and equipment, net	33,369	39,144
Operating lease right-of-use assets	24,136	30,225
Other long-term assets	6,216	8,208
Total assets	243,610	386,420
Current liabilities:
Accounts payable	1,764	4,832
Accrued expenses and other current liabilities	34,814	25,206
Total current liabilities	36,578	30,038
Operating lease liabilities, net of current portion	38,215	45,949
Total liabilities	74,793	75,987
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value per share; 20,000 shares authorized as of December 31, 2023 and 2022; no shares issued and outstanding as of December 31, 2023 and 2022	0	0
Common stock, $0.001 par value per share; 200,000 shares authorized as of December 31, 2023 and 2022; 87,750 and 85,387 shares issued and outstanding as of December 31, 2023 and 2022, respectively	88	85
Additional paid-in capital	1,287,156	1,243,408
Accumulated other comprehensive income (loss)	50	(284)
Accumulated deficit	(1,118,477)	(932,776)
Total stockholders’ equity	168,817	310,433
Total liabilities and stockholders’ equity	$ 243,610	$ 386,420

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

9. Stock-Based Compensation

Total stock-based compensation expense recognized is as follows (in thousands):


	Year Ended December 31,
	2023		2022
Research and development	$	17,599	$	17,399
General and administrative		23,624		25,759
Total	$	41,223	$	43,158

No income tax benefits for stock-based compensation expense have been recognized for the years ended December 31, 2023 and 2022, as a result of the Company’s full valuation allowance applied to net deferred tax assets and net operating loss carryforwards.

Equity Incentive Plans

In July 2018, the Board of Directors adopted the 2018 Equity Incentive Plan (the “2018 Plan”). The 2018 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units (“RSUs”), stock appreciation rights, performance-based awards ("PSUs") and other stock-based awards. The number of shares of common stock that may be issued under the 2018 Plan will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019, equal to the least of (i) 5,000,000 shares, (ii) 5% of the outstanding shares of common stock as of the last day of the preceding fiscal year and (iii) such other amount as the Board of Directors may determine. Stock options and RSUs granted under the 2018 Plan generally vest over four years and expire no more than 10 years from the date of grant.

Following the IPO and upon the effectiveness of the 2018 Plan, the Company’s 2012 Equity Incentive Plan, as amended, (the “2012 Plan”), terminated and no further awards will be granted thereunder. All outstanding awards under the 2012 Plan will continue to be governed by their existing terms. Any shares subject to awards granted under the 2012 Plan that, on or after the termination of the 2012 Plan, expire or terminate and shares previously issued

pursuant to awards granted under the 2012 Plan that, on or after the termination of the 2012 Plan, are forfeited or repurchased by the Company will be transferred into the 2018 Plan. As of December 31, 2023, the maximum number of shares that may be added to the 2018 Plan pursuant to the preceding clause is 2,546,977 shares.

Prior to its termination, the 2012 Plan provided for the grant of stock options, stock appreciation rights, restricted stock and restricted stock units to employees, directors and consultants. Stock options granted under the 2012 Plan generally vest over four years and expire no more than 10 years from the date of grant.

As of December 31, 2023, the number of shares available for issuance under the 2018 Plan was 2,036,811.

Stock Options

Stock option activity under the 2018 Plan and the 2012 Plan during the year ended December 31, 2023 is summarized as follows (in thousands, except per share data):


				Weighted-		Weighted-
				Average		Average		Aggregate
	Options			Exercise		Remaining		Intrinsic
	Outstanding			Price		Years		Value
Balance at December 31, 2022		5,423		$	15.41		6.4	$	22,657
Granted		3,458		$	5.79
Exercised		(206	)	$	3.26
Expired		(267	)	$	48.35
Forfeited		(440	)	$	7.99
Balance at December 31, 2023		7,968		$	10.85		6.9	$	3,168
Options exercisable		4,216		$	13.62		5.0	$	3,165
Options vested and expected to vest		7,776		$	10.95		6.9	$	3,168

The following weighted-average assumptions were used to calculate the fair value of stock options granted during the periods indicated:


	Year Ended December 31,
	2023			2022
Risk-free interest rate		3.88	%		2.95	%
Expected volatility		99.96	%		75.94	%
Expected dividend yield		—			—
Expected term (in years)		5.96			5.84

The weighted-average fair value of options granted during the years ended December 31, 2023 and 2022 was $4.61 and $2.76 per share, respectively.

The aggregate fair value of stock options that vested during the years ended December 31, 2023 and 2022 was $6.7 million and $15.2 million, respectively.

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2023 and 2022 was $0.1 million and $1.8 million, respectively.

As of December 31, 2023, total unrecognized stock-based compensation expense relating to unvested stock options was $16.9 million. This amount is expected to be recognized over a weighted-average period of 2.4 years.

Time-based Restricted Stock Units

Each time-based restricted stock unit (“RSU”) represents one equivalent share of our common stock to be awarded after satisfying the applicable continued service-based vesting criteria over a specified period. The fair value for these RSUs is based on the closing price of our common stock on the date of grant. The RSUs do not entitle

participants to the rights of holders of common stock, such as voting rights, until the shares are issued. RSUs that are expected to vest are net of estimated future forfeitures.

RSU activity under the 2018 Plan is summarized as follows (in thousands, except per share data):


				Weighted-
				Average
	Number			Grant Date
	of Shares			Fair Value
Balance at December 31, 2022		4,478		$	16.90
Granted		3,860		$	6.52
Vested		(1,734	)	$	18.29
Forfeited		(983	)	$	12.23
Balance at December 31, 2023		5,621		$	10.16

The weighted-average fair value of RSUs granted during the years ended December 31, 2023 and 2022 was $6.52 and $5.38, respectively.

As of December 31, 2023, total unrecognized stock-based compensation expense relating to unvested RSUs was $48.4 million and the weighted-average remaining vesting period was 2.3 years.

The aggregate intrinsic value of RSUs is calculated as the closing price per share of the Company’s common stock on the last trading day of the fiscal period, multiplied by the number of RSUs expected to vest as of December 31, 2023. As of December 31, 2023, the aggregate intrinsic value of RSUs was $15.3 million.

Performance-based Restricted Stock Units

During the year ended December 31, 2023, no restricted stock units with performance-based vesting (“PSUs”) from the 2018 Plan were granted, however, 2.8 million PSUs were outstanding as of December 31, 2023. Each PSU represents one equivalent share of our common stock to be awarded upon vesting at the end of the performance periods, if specific performance goals set by the Board of Directors are achieved. No PSUs will vest if the performance goals are not met. The fair value of these PSUs is based on the closing price of our common stock on the date of grant. The Company assesses the probability of achieving the performance goals on a quarterly basis. Changes in our assessment of the probability results in adjustments to stock-based compensation, which may include either a cumulative catch-up of expense or a reduction of expense depending on whether the likelihood of vesting has increased or decreased, that is recognized in the period such determination is made. The PSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. PSUs that are expected to vest are net of estimated future forfeitures.

The following table summarizes the PSUs activity for the year ended December 31, 2023 (in thousands, except per share data):


				Weighted-
				Average
	Number			Grant Date
	of Shares			Fair Value
Balance at December 31, 2022		3,276		$	6.21
Granted		—		$	—
Forfeited		(431	)	$	5.58
Balance at December 31, 2023		2,845		$	6.30

No stock-based compensation expense related to the PSUs has been recognized during the years ended December 31, 2023 and 2022 as the achievement of the performance conditions were not deemed probable and the remaining vesting period is undeterminable. As of December 31, 2023, total unrecognized compensation expense relating to PSUs was $17.9 million and the aggregate intrinsic value of PSUs at December 31, 2023 was $7.8 million.

Employee Stock Purchase Plan

In July 2018, the Company’s Board of Directors and stockholders approved the 2018 Employee Stock Purchase Plan (the “2018 ESPP”). The number of shares of common stock that may be issued under the 2018 ESPP shall automatically increase on each January 1, beginning with the fiscal year ending December 31, 2019, equal to the least of (i) 1,000,000 shares, (ii) 1% of the outstanding shares of common stock as of the last day of the immediately preceding fiscal year and (iii) such other amount determined by the 2018 ESPP administrator. As of December 31, 2023, the number of shares available for issuance under the 2018 ESPP was 2,781,902.

Under the 2018 ESPP, employees may purchase shares of the Company’s common stock at a price per share equal to 85% of the lower of the fair market value of the common stock on the first trading day of the offering period or on the exercise date. The 2018 ESPP provides for consecutive, overlapping 24-month offering periods, each of which will include purchase periods. The first offering period commenced on July 18, 2018.

During the years ended December 31, 2023 and 2022, stock-based compensation related to the 2018 ESPP was $0.8 million and $0.8 million, respectively.

The following weighted-average assumptions were used to calculate the fair value of ESPP shares during the periods indicated:


	Year Ended December 31,
	2023			2022
Risk-free interest rate		5.14	%		2.20	%
Expected volatility		127.37	%		75.83	%
Expected dividend yield		—			—
Expected term (in years)		1.32			1.67

As of December 31, 2023, total unrecognized compensation expense relating to shares to be purchased under the 2018 ESPP was $0.3 million and the weighted-average remaining vesting period was 1.1 years.

Investments (Tables)

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Investments

The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s investments by major security type are summarized in the table below (in thousands):


	December 31, 2023
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Available-for-sale securities
U.S. treasuries classified as investments	$	96,688	$	39	$	(22	)	$	96,705
U.S. government agency bonds		7,652		—		(3	)		7,649
Total available-for-sale securities	$	104,340	$	39	$	(25	)	$	104,354


	December 31, 2022
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Available-for-sale securities
U.S. treasuries classified as investments	$	192,853	$	3	$	(287	)	$	192,569
Total available-for-sale securities	$	192,853	$	3	$	(287	)	$	192,569

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Common Stock
Stock issuance costs	$ 9,417

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating expenses
Research and development	$ 150,908	$ 265,081
General and administrative	45,148	57,348
Total operating expenses	196,056	322,429
Loss from operations	(196,056)	(322,429)
Interest income	10,347	3,673
Other income (expense), net	8	(1,196)
Net loss	(185,701)	(319,952)
Unrealized gain (loss) on marketable securities	334	(131)
Comprehensive loss	$ (185,367)	$ (320,083)
Net loss per common share:
Net loss per common share, basic	$ (2.14)	$ (5.06)
Net loss per common share, diluted	$ (2.14)	$ (5.06)
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted-average shares of common stock outstanding, basic	86,798	63,284
Weighted-average shares of common stock outstanding, diluted	86,798	63,284

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 104,354	$ 192,569
Fair Value, Measurements, Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	67,070	86,270
Short-term marketable securities	104,354	192,569
Total cash equivalents and short-term marketable securities	171,424	278,839
Fair Value, Measurements, Recurring Basis \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	67,070	86,270
Short-term marketable securities	104,354	192,569
Total cash equivalents and short-term marketable securities	171,424	278,839
Fair Value, Measurements, Recurring Basis \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term marketable securities	0	0
Total cash equivalents and short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis \| Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term marketable securities	0	0
Total cash equivalents and short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	67,070	86,270
Fair Value, Measurements, Recurring Basis \| Money market funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	67,070	86,270
Fair Value, Measurements, Recurring Basis \| Money market funds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring Basis \| Money market funds \| Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring Basis \| U.S. treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	96,705	192,569
Fair Value, Measurements, Recurring Basis \| U.S. treasuries \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	96,705	192,569
Fair Value, Measurements, Recurring Basis \| U.S. treasuries \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	0	0
Fair Value, Measurements, Recurring Basis \| U.S. treasuries \| Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	0	$ 0
Fair Value, Measurements, Recurring Basis \| U.S. government agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	7,649
Fair Value, Measurements, Recurring Basis \| U.S. government agency bonds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	7,649
Fair Value, Measurements, Recurring Basis \| U.S. government agency bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	0
Fair Value, Measurements, Recurring Basis \| U.S. government agency bonds \| Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term marketable securities	$ 0

Subsequent Events

12 Months Ended

Dec. 31, 2023

Subsequent Events [Abstract]

Subsequent Events

12. Subsequent Events

On January 16, 2024, the Company announced that due to unfavorable clinical trial results associated with the use of lirentelimab in its Phase 2 atopic dermatitis and Phase 2b chronic spontaneous urticaria trials, that the Company will halt lirentelimab-related activities across clinical, manufacturing, research and administrative functions. Accordingly, the Company’s Board of Directors approved the 2024 Reorganization Plan to reduce operating costs and better align our workforce with the new clinical development plans of our business. Under the 2024 Reorganization Plan, the Company’s workforce will be reduced by approximately 50% primarily during the first quarter of 2024.

The Company expects to record approximately $4 million in severance costs during the first quarter of 2024 associated with the workforce reduction.

Organization and Business

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization and Business

1. Organization and Business

Allakos Inc. (“Allakos” or the “Company”) was incorporated in the state of Delaware in March 2012. Allakos is a clinical stage biopharmaceutical company focused on developing therapeutics which target immunomodulatory receptors present on immune effector cells involved in allergic, inflammatory and proliferative diseases. Our most advanced product candidate is AK006 which targets mast cells. Inappropriately activated mast cells have been identified as key drivers in a number of severe diseases affecting the gastrointestinal tract, eyes, skin, lungs and other organs. The Company’s primary activities to date have included establishing its facilities, recruiting personnel, conducting research and development of its product candidates and raising capital. The Company’s operations are located in San Carlos, California.

Liquidity Matters

Since inception, the Company has incurred net losses and negative cash flows from operations. During the year ended December 31, 2023, the Company incurred a net loss of $185.7 million and used $116.5 million of cash in operations. As of December 31, 2023, the Company had an accumulated deficit of $1,118.5 million and does not expect to experience positive cash flows from operating activities in the foreseeable future. The Company has financed its operations to date primarily through the sale of common stock. Management expects to incur additional operating losses in the future as the Company continues to further develop, seek regulatory approval for and, if approved, commence commercialization of its product candidates.

Due to the clinical study results released in January 2024, our Board of Directors approved a reorganization plan to reduce operating costs and better align our workforce with our current clinical development plans of our business (the “2024 Reorganization Plan”). Refer to Note 12 “Subsequent Events” for additional details.

The Company had $170.8 million of cash, cash equivalents and marketable securities at December 31, 2023. Management believes that this amount is sufficient to fund the Company’s operations for at least the next 12 months from the issuance date of these financial statements.

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The Company is subject to income taxes in the United States and certain states in which it operates, and it uses estimates in determining its provisions for income taxes. Significant management judgement is required in determining the Company's provision for income taxes, deferred tax assets and liabilities and valuation allowances recorded against net deferred tax assets in accordance with U.S. GAAP. These estimates and judgements occur in the calculation of tax credits, benefits, and deductions, and in the calculation of certain tax assets and liabilities, which arise from certain temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant changes to these estimates may result in an increase or decrease to the Company's tax provision in the current or subsequent period.

The Internal Revenue Code of 1986, as amended (the “Code”), provides for a limitation of the annual use of net operating losses (“NOLs”) and other tax attributes (such as research and development tax credit carryforwards) following certain ownership changes defined by the Code that could limit the Company’s ability to utilize these carryforwards in the future. The Company may have had one or more ownership changes in the past, and it may experience ownership changes in the future. Accordingly, the Company's ability to utilize its NOLs and certain other tax attributes could be severely limited or eliminated.

Total deferred income tax assets, net of valuation allowance, at December 31, 2023 and 2022 were as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets
Net operating loss carryforwards	$	247,208		$	225,924
Capitalized research expenditures		65,677			48,767
Research and development credits		42,347			35,906
Accruals and reserves		8,182			6,839
Stock-based compensation		5,519			6,341
Lease liability		11,314			13,403
Fixed and intangible assets		295			—
Gross deferred tax assets		380,542			337,180
Less: valuation allowance		(373,957	)		(328,553	)
Deferred tax assets, net of valuation allowance		6,585			8,627
Deferred tax liabilities
Fixed and intangible assets		—			378
Right-of-use asset		6,585			8,249
Gross deferred tax liabilities		6,585			8,627
Net deferred tax assets	$	—		$	—

Management has evaluated the positive and negative evidence surrounding the realizability of its deferred tax assets and has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $374.0 million and $328.6 million has been established at December 31, 2023 and 2022, respectively. The change in the valuation allowance was $45.4 million and $125.0 million for the years ended December 31, 2023 and 2022, respectively. The Company has incurred NOL since inception. As of December 31, 2023, the Company had federal and state NOL carryforwards of $893.7 million and $847.2 million, respectively. Federal NOL carryforwards of $831.8 million, which were generated after December 31, 2017, do not expire. The remaining $61.8 million of Federal NOL carryforwards expire beginning in 2032. As of December 31, 2023, the Company had federal and California research and other tax credit carryforwards of $48.1 million and $11.2 million, respectively. The federal tax credits expire beginning in 2033. The California tax credits can be carried forward indefinitely.

In accordance with the Tax Cuts and Jobs Act of 2017, research and experimental expenditures are required to be capitalized beginning in 2022 and amortized over a period of 5 years for domestic expenses and 15 years for foreign expenses.

The effective tax rate for the years ended December 31, 2023 and 2022 is different from the federal statutory rate primarily due to the valuation allowance against deferred tax assets as a result of insufficient income. The Company’s effective tax rate differs from the federal statutory tax rate as follows:


	Year Ended December 31,
	2023			2022
Federal statutory tax rate		21.0	%		21.0	%
Change in deferred tax asset valuation allowance		(24.5	)%		(39.1	)%
State taxes, net of federal benefit		5.3	%		20.3	%
Research and development tax credits		3.1	%		0.6	%
Stock-based compensation		(0.7	)%		(0.1	)%
Other		(4.2	)%		(2.7	)%
Effective tax rate		—	%		—	%

Uncertain Tax Positions

A reconciliation of the beginning and ending amount of unrecognized benefits is as follows (in thousands):


	Year Ended December 31,
	2023		2022
Balance at the beginning of the year	$	13,175	$	11,953
Increase related to current year tax positions		1,736		2,317
Increase related to prior year tax positions		101		—
Decrease related to prior year tax positions		—		(1,095	)
Balance at the end of the year	$	15,012	$	13,175

The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. During the years ended December 31, 2023 and 2022, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next twelve months.

The Company files income tax returns in the U.S. federal and multiple state tax jurisdictions.

The U.S. Internal Revenue Service (“IRS”) examined the Company’s federal corporate income tax return for the year ended December 31, 2018. The examination was completed in April 2022 and did not require any material adjustments. The federal and state income tax returns from inception to December 31, 2023 remain subject to examination.

It is the Company’s policy to include penalties and interest expense related to income taxes as a component of the income tax provision as necessary. Management determined that no accrual for interest and penalties was required at December 31, 2023 and 2022. Since the Company is in a loss carryforward position, it is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available.

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

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(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

The Company measures and reports certain financial instruments as assets and liabilities at fair value on a recurring basis. The Company’s financial assets measured at fair value on a recurring basis were as follows (in thousands):


	December 31, 2023
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	67,070	$	—	$	—	$	67,070
Total cash equivalents		67,070		—		—		67,070
Short-term marketable securities
U.S. treasuries		96,705		—		—		96,705
U.S. government agency bonds		7,649		—		—		7,649
Total short-term marketable securities		104,354		—		—		104,354
Total cash equivalents and short-term marketable securities	$	171,424	$	—	$	—	$	171,424


	December 31, 2022
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	86,270	$	—	$	—	$	86,270
Total cash equivalents		86,270		—		—		86,270
Short-term marketable securities
U.S. treasuries		192,569		—		—		192,569
Total short-term marketable securities		192,569		—		—		192,569
Total cash equivalents and short-term marketable securities	$	278,839	$	—	$	—	$	278,839

Leases - Summary of Future Lease Payments Required Under Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract]
2024	$ 7,441
2025	7,287
2026	7,506
2027	7,731
2028	7,963
Thereafter	23,871
Total future lease payments	61,799
Present value adjustment	20,334
Operating lease liabilities	$ 41,465	$ 49,110

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. Commitments and Contingencies

As of December 31, 2023, the Company’s commitments include an estimated $6.0 million of noncancellable purchase commitments, including commitments with contract manufacturers for which the Company has not received the goods or services.

Additionally, the Company enters into contracts in the normal course of business with clinical CROs, clinical investigative sites and other counterparties assisting with our preclinical studies and clinical trials. Such contracts are generally cancellable, with varying provisions regarding termination. In the event of a contract being terminated, the Company would only be obligated for services received as of the effective date of the termination, along with cancellation fees, as applicable.

Indemnification Agreements

The Company has entered into indemnification agreements with certain directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. To date, no such matters have arisen and the Company does not believe that the outcome of any claims under indemnification arrangements will have a material adverse effect on its financial positions, results of operations or cash flows. Accordingly, the Company has not recorded a liability related to such indemnifications at December 31, 2023.

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Balance at the beginning of the year	$ 13,175	$ 11,953
Increase related to current year tax positions	1,736	2,317
Increase related to prior year tax positions	101	0
Decrease related to prior year tax positions	0	(1,095)
Balance at the end of the year	$ 15,012	$ 13,175

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Transfers of assets between level 1 to level 2	$ 0	$ 0
Transfers of assets between level 2 to level 1	0	0
Transfers of liabilities between level 1 to level 2	0	0
Fair Value Liabilities Level 2To Level 1 Transfers Amount 1	0	0
Transfers of assets into level 3	0	0
Transfers of assets out of level 3	0	0
Transfers of liabilities into level 3	0	0
Transfers of liabilities out of level 3	$ 0	$ 0

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance	$ 373,957,000	$ 328,553,000
Increase in valuation allowance	45,400,000	125,000,000
Federal NOL carryforwards	893,700,000
State NOL carryforwards	847,200,000
Accrual for interest and penalties	0	0
Research and development credits	$ 42,347,000	$ 35,906,000
Federal
Income Tax Disclosure [Line Items]
NOL carryforwards, expiration year	2032
Research and development expenditures amortization period	5 years
Research and development credits	$ 48,100,000
Research and development tax credit carryforwards, expiration year	2033
Federal \| Generated After December 31, 2017
Income Tax Disclosure [Line Items]
Federal NOL carryforwards	$ 831,800,000
Federal \| 2032 Expiration Period
Income Tax Disclosure [Line Items]
Federal NOL carryforwards	61,800,000
State
Income Tax Disclosure [Line Items]
Research and development credits	$ 11,200,000
Foreign
Income Tax Disclosure [Line Items]
Research and development expenditures amortization period	15 years

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company’s balance sheets and which, in aggregate, represent the amounts reported in the statements of cash flows (in thousands):


	December 31,
	2023		2022
Cash and cash equivalents	$	66,440	$	87,217
Restricted cash in other long-term assets		1,472		1,472
Total	$	67,912	$	88,689

Calculation of Basic and Diluted Net Loss per Share

Basic and diluted net loss per share was calculated as follows (in thousands, except per share data):


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(185,701	)	$	(319,952	)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted		86,798			63,284
Net loss per share, basic and diluted	$	(2.14	)	$	(5.06	)

Summary of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share


	Year Ended December 31,
	2023		2022
Options to purchase common stock		7,968		5,423
Unvested restricted stock units		5,621		4,478
Unvested performance stock unit		2,845		3,276
Shares issuable under employee stock purchase plans		127		135
Total		16,561		13,312

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	87,750,000	85,387,000
Common stock, shares outstanding	87,750,000	85,387,000

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
Trading Symbol	ALLK
Entity Registrant Name	Allakos Inc.
Entity Central Index Key	0001564824
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 287.5
Entity Common Stock, Shares Outstanding		87,873,995
ICFR Auditor Attestation Flag	false
Entity File Number	001-38582
Entity Tax Identification Number	45-4798831
Entity Address, Address Line One	825 Industrial Road
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	San Carlos
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94070
City Area Code	650
Local Phone Number	597-5002
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ
Document Annual Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	San Mateo, California
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the registrant’s 2024 Annual Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s 2023 fiscal year ended December 31, 2023.
Document Financial Statement Error Correction [Flag]	false

Investments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities in an unrealized loss position, fair value	$ 53,700	$ 162,600
Available for sale securities gross realized gains or losses on sale or maturity	$ 0	$ 0
Maximum
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, remaining maturity period	1 year

- 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

Investments

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Investments

4. Investments

All investments were considered available-for-sale at December 31, 2023 and 2022. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s investments by major security type are summarized in the table below (in thousands):


	December 31, 2023
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Available-for-sale securities
U.S. treasuries classified as investments	$	96,688	$	39	$	(22	)	$	96,705
U.S. government agency bonds		7,652		—		(3	)		7,649
Total available-for-sale securities	$	104,340	$	39	$	(25	)	$	104,354


	December 31, 2022
	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Available-for-sale securities
U.S. treasuries classified as investments	$	192,853	$	3	$	(287	)	$	192,569
Total available-for-sale securities	$	192,853	$	3	$	(287	)	$	192,569

The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. As of December 31, 2023 and 2022, the aggregate fair value of securities held by the Company in an unrealized loss position for less than twelve months was $53.7 million and $162.6 million, respectively. All of these securities had remaining maturities of less than one year. The Company has the intent and ability to hold such securities until recovery and has determined that there has been no material change to their credit risk. As a result, the Company determined it did not hold any investments with a credit loss at December 31, 2023 and 2022.

There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities during the years ended December 31, 2023 and 2022, and as a result, there were no material reclassifications out of accumulated other comprehensive gain (loss) for the same periods.

Stock-Based Compensation - Summary of RSU Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Time-based Restricted Stock Units
Number of Shares
Balance at December 31, 2021	4,478
Granted	3,860
Vested	(1,734)
Forfeited	(983)
Balance at December 31, 2022	5,621	4,478
Weighted-Average Grant Date Fair Value
Balance at December 31, 2021	$ 16.90
Granted	6.52	$ 5.38
Vested	18.29
Forfeited	12.23
Balance at December 31, 2022	$ 10.16	$ 16.90
Performance-based Restricted Stock Units
Number of Shares
Balance at December 31, 2021	3,276
Granted	0
Forfeited	(431)
Balance at December 31, 2022	2,845	3,276
Weighted-Average Grant Date Fair Value
Balance at December 31, 2021	$ 6.21
Granted	0
Forfeited	5.58
Balance at December 31, 2022	$ 6.30	$ 6.21

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Summary of Total Stock-Based Compensation Expense Recognized

Total stock-based compensation expense recognized is as follows (in thousands):


	Year Ended December 31,
	2023		2022
Research and development	$	17,599	$	17,399
General and administrative		23,624		25,759
Total	$	41,223	$	43,158

Summary of Stock Option Activity

Stock option activity under the 2018 Plan and the 2012 Plan during the year ended December 31, 2023 is summarized as follows (in thousands, except per share data):


				Weighted-		Weighted-
				Average		Average		Aggregate
	Options			Exercise		Remaining		Intrinsic
	Outstanding			Price		Years		Value
Balance at December 31, 2022		5,423		$	15.41		6.4	$	22,657
Granted		3,458		$	5.79
Exercised		(206	)	$	3.26
Expired		(267	)	$	48.35
Forfeited		(440	)	$	7.99
Balance at December 31, 2023		7,968		$	10.85		6.9	$	3,168
Options exercisable		4,216		$	13.62		5.0	$	3,165
Options vested and expected to vest		7,776		$	10.95		6.9	$	3,168

Summary of Weighted-Average Assumptions Used to Calculate Fair Value of Stock Options Granted

The following weighted-average assumptions were used to calculate the fair value of stock options granted during the periods indicated:


	Year Ended December 31,
	2023			2022
Risk-free interest rate		3.88	%		2.95	%
Expected volatility		99.96	%		75.94	%
Expected dividend yield		—			—
Expected term (in years)		5.96			5.84

Summary of Weighted-Average Assumptions Used to Calculate Fair Value of ESPP Shares

The following weighted-average assumptions were used to calculate the fair value of ESPP shares during the periods indicated:


	Year Ended December 31,
	2023			2022
Risk-free interest rate		5.14	%		2.20	%
Expected volatility		127.37	%		75.83	%
Expected dividend yield		—			—
Expected term (in years)		1.32			1.67

Time-based Restricted Stock Units

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Summary of Restricted Stock Units

RSU activity under the 2018 Plan is summarized as follows (in thousands, except per share data):


				Weighted-
				Average
	Number			Grant Date
	of Shares			Fair Value
Balance at December 31, 2022		4,478		$	16.90
Granted		3,860		$	6.52
Vested		(1,734	)	$	18.29
Forfeited		(983	)	$	12.23
Balance at December 31, 2023		5,621		$	10.16

Performance-based Restricted Stock Units

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Summary of Restricted Stock Units

The following table summarizes the PSUs activity for the year ended December 31, 2023 (in thousands, except per share data):


				Weighted-
				Average
	Number			Grant Date
	of Shares			Fair Value
Balance at December 31, 2022		3,276		$	6.21
Granted		—		$	—
Forfeited		(431	)	$	5.58
Balance at December 31, 2023		2,845		$	6.30

- 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

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities
Net Income (Loss)	$ (185,701)	$ (319,952)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	41,223	43,158
Net amortization (accretion) of premiums and discounts on marketable securities	(5,250)	588
Depreciation and amortization	6,141	7,071
Noncash lease expense	1,491	2,904
Gain on lease modification	0	0
Loss on disposal of property and equipment	3	28
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	19,994	(2,431)
Other long-term assets	1,992	(574)
Accounts payable	(2,845)	(8,765)
Accrued expenses and other current liabilities	9,907	1,152
Operating lease liabilities, net of current portion	(3,435)	(3,150)
Net cash used in operating activities	(116,480)	(279,971)
Cash flows from investing activities
Purchases of marketable securities	(169,233)	(228,144)
Proceeds from maturities of marketable securities	263,000	287,000
Proceeds from sale of marketable securities	0	19,989
Purchases of property and equipment	(592)	(8,333)
Proceeds from sale of property and equipment	0	1,169
Net cash provided by investing activities	93,175	71,681
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	990	140,591
Proceeds from exercise of stock options, net of repurchases	673	853
Proceeds from issuance of common stock under 2018 ESPP	865	438
Net cash provided by financing activities	2,528	141,882
Net increase (decrease) in cash, cash equivalents and restricted cash	(20,777)	(66,408)
Cash, cash equivalents and restricted cash, beginning of period	88,689	155,097
Cash, cash equivalents and restricted cash, end of period	67,912	88,689
Supplemental disclosures
Right-of-use assets obtained in exchange for lease obligations	665	1,422
Noncash adjustments to right-of-use assets	5,307	0
Changes of property and equipment in accounts payable and accruals	$ (223)	$ (4,021)

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements


	December 31, 2023
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	67,070	$	—	$	—	$	67,070
Total cash equivalents		67,070		—		—		67,070
Short-term marketable securities
U.S. treasuries		96,705		—		—		96,705
U.S. government agency bonds		7,649		—		—		7,649
Total short-term marketable securities		104,354		—		—		104,354
Total cash equivalents and short-term marketable securities	$	171,424	$	—	$	—	$	171,424


	December 31, 2022
	Level 1		Level 2		Level 3		Total
Cash equivalents
Money market funds	$	86,270	$	—	$	—	$	86,270
Total cash equivalents		86,270		—		—		86,270
Short-term marketable securities
U.S. treasuries		192,569		—		—		192,569
Total short-term marketable securities		192,569		—		—		192,569
Total cash equivalents and short-term marketable securities	$	278,839	$	—	$	—	$	278,839

The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between levels during the years ended December 31, 2023 and 2022.

- 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

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Summary of Classification of Company's Operating Lease Liabilities

Classification of the Company’s operating lease liabilities included in the Company’s balance sheets at December 31, 2023 and 2022 was as follows (in thousands):


	December 31,
	2023		2022
Operating lease liabilities
Current portion included in accrued expenses and other current liabilities	$	3,250	$	3,161
Operating lease liabilities, net of current portion		38,215		45,949
Total operating lease liabilities	$	41,465	$	49,110

Summary of Components of Lease Costs

The components of lease costs, which are included in operating expenses in the Company’s statements of operations and comprehensive loss were as follows (in thousands):


	Year ended December 31,
	2023		2022
Operating lease costs	$	5,806	$	5,886
Variable costs		3,627		3,007
Total lease costs	$	9,433	$	8,893

Summary of Future Lease Payments Required Under Operating Leases

Future lease payments required under operating leases included on the Company’s balance sheet at December 31, 2023 are as follows (in thousands):


Fiscal Year Ending December 31,
2024	$	7,441
2025		7,287
2026		7,506
2027		7,731
2028		7,963
Thereafter		23,871
Total future lease payments		61,799
Less:
Present value adjustment		20,334
Operating lease liabilities	$	41,465

Commitments and Contingencies - Additional Information (Details) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Loss Contingencies [Line Items]
Noncancellable purchase commitments	$ 6,000
Common stock, shares issued	87,750	85,387
Indemnification Guarantee
Loss Contingencies [Line Items]
Liability related to indemnifications	$ 0

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Summary of Total Deferred Income Tax Assets, Net of Valuation Allowance

Total deferred income tax assets, net of valuation allowance, at December 31, 2023 and 2022 were as follows (in thousands):


	December 31,
	2023			2022
Deferred tax assets
Net operating loss carryforwards	$	247,208		$	225,924
Capitalized research expenditures		65,677			48,767
Research and development credits		42,347			35,906
Accruals and reserves		8,182			6,839
Stock-based compensation		5,519			6,341
Lease liability		11,314			13,403
Fixed and intangible assets		295			—
Gross deferred tax assets		380,542			337,180
Less: valuation allowance		(373,957	)		(328,553	)
Deferred tax assets, net of valuation allowance		6,585			8,627
Deferred tax liabilities
Fixed and intangible assets		—			378
Right-of-use asset		6,585			8,249
Gross deferred tax liabilities		6,585			8,627
Net deferred tax assets	$	—		$	—

Summary of Effective Tax Rate Differs From Federal Statutory Tax Rate

The Company’s effective tax rate differs from the federal statutory tax rate as follows:


	Year Ended December 31,
	2023			2022
Federal statutory tax rate		21.0	%		21.0	%
Change in deferred tax asset valuation allowance		(24.5	)%		(39.1	)%
State taxes, net of federal benefit		5.3	%		20.3	%
Research and development tax credits		3.1	%		0.6	%
Stock-based compensation		(0.7	)%		(0.1	)%
Other		(4.2	)%		(2.7	)%
Effective tax rate		—	%		—	%

Reconciliation of Beginning and Ending Amount of Unrecognized Benefits

A reconciliation of the beginning and ending amount of unrecognized benefits is as follows (in thousands):


	Year Ended December 31,
	2023		2022
Balance at the beginning of the year	$	13,175	$	11,953
Increase related to current year tax positions		1,736		2,317
Increase related to prior year tax positions		101		—
Decrease related to prior year tax positions		—		(1,095	)
Balance at the end of the year	$	15,012	$	13,175

Defined Contribution Plans

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Defined Contribution Plans

11. Defined Contribution Plans

In January 2018, the Company established a defined contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) plan”). The 401(k) plan covers all employees who meet defined minimum age and service requirements. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under U.S. federal tax regulations. The Company makes matching contributions of up to 4% of the eligible employees’ compensation to the 401(k) plan. During the years ended December 31, 2023 and 2022, the Company made contributions to the 401(k) plan of $1.0 million and $1.0 million, respectively.

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Sep. 21, 2022	Aug. 04, 2022	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Common stock, par value			$ 0.001	$ 0.001
Aggregate net proceeds			$ 990	$ 140,591
September 2022 Offering
Class of Stock [Line Items]
Sale of shares of common stock	29,882,000
Common stock, par value	$ 0.001
Sale of stock, average price per share	$ 5.02
Aggregate net proceeds	$ 140,600
At-the-Market Equity Offering
Class of Stock [Line Items]
Sale of stock, average price per share			$ 7.2
Aggregate amount available to be sold under sales agreement		$ 75,000
Commission rate		3.00%
Amount of securities offered under S-3 registartion statement		$ 250,000
Proceeds from sale of common stock, net of commission			$ 1,000
Common stock sold (in Shares)			100,000
Common stock available for sale			$ 74,000

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tax benefits for stock-based compensation expense recognized		$ 0	$ 0
Weighted-average fair value of options granted		$ 4.61	$ 2.76
Aggregate fair value of stock options vested		$ 6,700,000	$ 15,200,000
Aggregate intrinsic value of stock options exercised		100,000	1,800,000
Total unrecognized stock-based compensation expense relating to unvested stock options		$ 16,900,000
Weighted-average recognition period		2 years 4 months 24 days
Total stock-based compensation expense		$ 41,223,000	$ 43,158,000
Time-based Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average recognition period		2 years 3 months 18 days
Shares of restricted common stock unvested		5,621,000	4,478,000
Description of terms of award		Each time-based restricted stock unit (“RSU”) represents one equivalent share of our common stock to be awarded after satisfying the applicable continued service-based vesting criteria over a specified period. The fair value for these RSUs is based on the closing price of our common stock on the date of grant. The RSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. RSUs that are expected to vest are net of estimated future forfeitures.
Weighted-average fair value of RSUs granted		$ 6.52	$ 5.38
Total unrecognized stock-based compensation expense		$ 48,400,000
Aggregate intrinsic value		$ 15,300,000
Performance-based Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of restricted common stock unvested		2,845,000	3,276,000
Description of terms of award		During the year ended December 31, 2023, no restricted stock units with performance-based vesting (“PSUs”) from the 2018 Plan were granted, however, 2.8 million PSUs were outstanding as of December 31, 2023. Each PSU represents one equivalent share of our common stock to be awarded upon vesting at the end of the performance periods, if specific performance goals set by the Board of Directors are achieved. No PSUs will vest if the performance goals are not met. The fair value of these PSUs is based on the closing price of our common stock on the date of grant. The Company assesses the probability of achieving the performance goals on a quarterly basis. Changes in our assessment of the probability results in adjustments to stock-based compensation, which may include either a cumulative catch-up of expense or a reduction of expense depending on whether the likelihood of vesting has increased or decreased, that is recognized in the period such determination is made. The PSUs do not entitle participants to the rights of holders of common stock, such as voting rights, until the shares are issued. PSUs that are expected to vest are net of estimated future forfeitures.
Weighted-average fair value of RSUs granted		$ 0
Total unrecognized stock-based compensation expense		$ 17,900,000
Aggregate intrinsic value		7,800,000
Total stock-based compensation expense		$ 0	$ 0
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of common stock shares reserved for issuance per year	1,000,000
Percentage increase in shares reserved for issuance per year	1.00%
Number of shares available for issuance		2,781,902
Weighted-average recognition period		1 year 1 month 6 days
Total unrecognized stock-based compensation expense		$ 300,000
Price as a percentage of fair market value of common stock	85.00%
Consecutive overlapping offering period	24 months
First offering period commence date	Jul. 18, 2018
Total stock-based compensation expense		$ 800,000	$ 800,000
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of common stock shares reserved for issuance per year	5,000,000
Percentage increase in shares reserved for issuance per year	5.00%
Award vesting period	4 years
Maximum number of additional shares authorized to be added to the Plan		2,546,977
Number of shares available for issuance		2,036,811
2018 Equity Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option expiration period	10 years
2012 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period	4 years
2012 Equity Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option expiration period	10 years

Organization and Business - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net Income (Loss)	$ (185,701)	$ (319,952)
Cash used in operations	(116,480)	(279,971)
Accumulated deficit	(1,118,477)	$ (932,776)
Cash, cash equivalents and marketable securities	$ 170,800

- Definition

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

+ References

+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Balance Sheet Components and Supplemental Disclosures - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Line Items]
Depreciation and amortization	$ 6,141	$ 7,071
Other long-term assets	6,216	8,208
Accumulated depreciation	14,408	8,267
Tax credits receivable	3,900
Redwood City Facility
Balance Sheet Related Disclosures [Line Items]
Fixed assets disposed, gross		5,800
Accumulated depreciation		4,600
Proceeds from sales and disposal of fixed assets		1,200
CDMO
Balance Sheet Related Disclosures [Line Items]
Advance payments to CDMOs for development and manufacturing services	$ 800	$ 6,600

Summary of Significant Accounting Policies - Additional Information (Details) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Segment shares	Dec. 31, 2022 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Restricted cash in other long term assets, deposit for lease facility \| $	$ 1,472	$ 1,472
Number of operating segments \| Segment	1
Expected dividend yield	0.00%	0.00%
Weighted-average shares of common stock outstanding, basic	86,798	63,284
Weighted-average shares of common stock outstanding, diluted	86,798	63,284
Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember
Laboratory Equipment and Capitalized Software
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	5 years
Furniture and Office Equipment \| Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	3 years
Furniture and Office Equipment \| Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Useful life	5 years
Registered Direct Offering
Summary Of Significant Accounting Policies [Line Items]
Sale of shares of common stock	29,900

Stock-Based Compensation - Summary of Total Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 41,223	$ 43,158
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	17,599	17,399
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 23,624	$ 25,759

Balance Sheet Components and Supplemental Disclosures - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 47,777	$ 47,411
Less accumulated depreciation	(14,408)	(8,267)
Property and equipment, net	33,369	39,144
Laboratory Equipment and Capitalized Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,993	6,473
Furniture And Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,947	3,947
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	32,386	32,457
Capitalized Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,382	4,112
Construction In Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross		$ 422
Construction-in-progress or pending installation
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 69