SELLAS Life Sciences (SLS) 10-Q 9 Nov 23 2023 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2023	Nov. 08, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-33958
Entity Registrant Name	SELLAS Life Sciences Group, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8099512
Entity Address, Address Line One	7 Times Square, Suite 2503,
Entity Address, City or Town	New York,
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10036
City Area Code	(646)
Local Phone Number	200-5278
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	SLS
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		32,062,258
Entity Central Index Key	0001390478
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 3,969	$ 17,125
Restricted cash and cash equivalents	100	100
Prepaid expenses and other current assets	1,134	531
Total current assets	5,203	17,756
Operating lease right-of-use assets	592	874
Goodwill	1,914	1,914
Deposits and other assets	377	399
Total assets	8,086	20,943
Current liabilities:
Accounts payable	4,340	3,357
Accrued expenses and other current liabilities	6,929	6,286
Operating lease liabilities	466	372
Acquired in-process research and development payable	0	5,500
Total current liabilities	11,735	15,515
Operating lease liabilities, non-current	178	573
Warrant liability	0	4
Total liabilities	11,913	16,092
Commitments and Contingencies
Stockholders’ (deficit) equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; Series A convertible preferred stock, 17,500 shares designated; no shares issued and outstanding at September 30, 2023 and December 31, 2022	0	0
Common stock, $0.0001 par value; 350,000,000 shares authorized, 28,393,958 and 21,005,405 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	3	2
Additional paid-in capital	205,278	184,753
Accumulated deficit	(209,108)	(179,904)
Total stockholders’ (deficit) equity	(3,827)	4,851
Total liabilities and stockholders’ (deficit) equity	$ 8,086	$ 20,943

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	350,000,000	350,000,000
Common stock, shares issued (in shares)	28,393,958	21,005,405
Common stock, shares outstanding (in shares)	28,393,958	21,005,405
Series A Preferred Stock
Preferred stock, shares authorized (in shares)	17,500	17,500

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Licensing revenue	$ 0	$ 0	$ 0	$ 1,000,000
Operating expenses:
Cost of licensing revenue	0	0	0	100,000
Research and development	5,813,000	4,282,000	18,910,000	14,422,000
General and administrative	3,548,000	2,864,000	10,782,000	8,982,000
Acquired in-process research and development	0	0	0	10,000,000
Total operating expenses	9,361,000	7,146,000	29,692,000	33,504,000
Operating loss	(9,361,000)	(7,146,000)	(29,692,000)	(32,504,000)
Non-operating income:
Change in fair value of warrant liability	0	2,000	4,000	39,000
Change in fair value of contingent consideration	0	11,000	0	126,000
Interest income	94,000	111,000	484,000	159,000
Total non-operating income	94,000	124,000	488,000	324,000
Net loss	$ (9,267,000)	$ (7,022,000)	$ (29,204,000)	$ (32,180,000)
Per share information:
Net loss per common share, basic (in dollars per share)	$ (0.33)	$ (0.34)	$ (1.09)	$ (1.70)
Net loss per common share, diluted (in dollars per share)	$ (0.33)	$ (0.34)	$ (1.09)	$ (1.70)
Weighted-average common shares outstanding, basic (in shares)	28,355,427	20,562,351	26,767,914	18,932,571
Weighted-average common shares outstanding, diluted (in shares)	28,355,427	20,562,351	26,767,914	18,932,571

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' (DEFICIT) EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2021		15,895,637
Beginning balance at Dec. 31, 2021	$ 20,347	$ 2	$ 158,948	$ (138,603)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and common stock warrants, net of issuance costs (in shares)		4,629,630
Issuance of common stock and common stock warrants, net of issuance costs	22,946		22,946
Issuance of common stock, net of issuance costs (in shares)		37,891
Issuance of common stock, net of issuance costs	119		119
Issuance of common stock under employee stock purchase plan (in shares)		25,089
Issuance of common stock under employee stock purchase plan	85		85
Stock-based compensation	1,280		1,280
Net loss	(32,180)			(32,180)
Ending balance (in shares) at Sep. 30, 2022		20,588,247
Ending balance at Sep. 30, 2022	12,597	$ 2	183,378	(170,783)
Beginning balance (in shares) at Jun. 30, 2022		20,551,918
Beginning balance at Jun. 30, 2022	19,057	$ 2	182,816	(163,761)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and common stock warrants, net of issuance costs (in shares)		21,602
Issuance of common stock and common stock warrants, net of issuance costs	69		69
Issuance of common stock under employee stock purchase plan (in shares)		14,727
Issuance of common stock under employee stock purchase plan	38		38
Stock-based compensation	455		455
Net loss	(7,022)			(7,022)
Ending balance (in shares) at Sep. 30, 2022		20,588,247
Ending balance at Sep. 30, 2022	$ 12,597	$ 2	183,378	(170,783)
Beginning balance (in shares) at Dec. 31, 2022	21,005,405	21,005,405
Beginning balance at Dec. 31, 2022	$ 4,851	$ 2	184,753	(179,904)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and common stock warrants, net of issuance costs (in shares)		7,220,217
Issuance of common stock and common stock warrants, net of issuance costs	18,554	$ 1	18,553
Issuance of common stock, net of issuance costs (in shares)		76,882
Issuance of common stock, net of issuance costs	268		268
Issuance of common stock under employee stock purchase plan (in shares)		91,454
Issuance of common stock under employee stock purchase plan	107		107
Stock-based compensation	1,597		1,597
Net loss	$ (29,204)			(29,204)
Ending balance (in shares) at Sep. 30, 2023	28,393,958	28,393,958
Ending balance at Sep. 30, 2023	$ (3,827)	$ 3	205,278	(209,108)
Beginning balance (in shares) at Jun. 30, 2023		28,347,920
Beginning balance at Jun. 30, 2023	4,843	$ 3	204,681	(199,841)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock purchase plan (in shares)		46,038
Issuance of common stock under employee stock purchase plan	54		54
Stock-based compensation	543		543
Net loss	$ (9,267)			(9,267)
Ending balance (in shares) at Sep. 30, 2023	28,393,958	28,393,958
Ending balance at Sep. 30, 2023	$ (3,827)	$ 3	$ 205,278	$ (209,108)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss	$ (29,204)	$ (32,180)
Adjustment to reconcile net loss to net cash used in operating activities:
Acquired in-process research and development expense	0	10,000
Non-cash stock-based compensation	1,597	1,280
Non-cash lease expense	367	334
Change in fair value of common stock warrants	(4)	(39)
Change in fair value of contingent consideration	0	(126)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(581)	505
Accounts payable	983	(17)
Accrued expenses and other current liabilities	643	1,930
Operating lease liabilities	(386)	(344)
Net cash used in operating activities	(26,585)	(18,657)
Cash flows from investing activities:
Cash paid for acquisition of in-process research and development	(5,500)	(4,500)
Net cash used in investing activities	(5,500)	(4,500)
Cash flows from financing activities:
Proceeds from issuance of common stock and common stock warrants, net of issuance costs	18,554	22,946
Proceeds from issuance of common stock, net of issuance costs	268	119
Proceeds from employee stock purchases	107	85
Net cash provided by financing activities	18,929	23,150
Net decrease in cash, cash equivalents, restricted cash, and restricted cash equivalents	(13,156)	(7)
Cash, cash equivalents, restricted cash, and restricted cash equivalents at the beginning of period	17,225	21,455
Cash, cash equivalents, restricted cash, and restricted cash equivalents at the end of period	4,069	21,448
Supplemental disclosure of cash flow information:
Cash received during the period for interest	484	159
Supplemental disclosure of non-cash investing and financing activities:
Non-cash acquisition of in-process research and development	0	5,500
Increase in operating lease right-of-use assets and current and non-current operating lease liabilities	$ 0	$ 449

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Overview SELLAS Life Sciences Group, Inc. is a late-stage clinical biopharmaceutical company focused on novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, galinpepimut-S ("GPS"), is a cancer immunotherapeutic agent licensed from Memorial Sloan Kettering Cancer Center ("MSK") and targets the Wilms Tumor 1 ("WT1") protein, which is present in an array of tumor types. GPS has potential as a monotherapy or in combination with other immunotherapeutic agents to address a broad spectrum of hematologic, or blood, cancers and solid tumor indications. SELLAS' second product candidate is SLS009 (formerly GFH009), a small molecule, highly selective cyclin-dependent kinase 9 ("CDK9") inhibitor, which the Company licensed from GenFleet Therapeutics (Shanghai), Inc. ("GenFleet"), for all therapeutic and diagnostic uses in the world outside of mainland China, Hong Kong, Macau and Taiwan ("SLS009 Territory").

Liquidity

Liquidity	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Liquidity	Liquidity Since inception, the Company has incurred recurring losses and negative cash flows from operations and, as of September 30, 2023, has an accumulated deficit of $209.1 million. During the nine months ended September 30, 2023, the Company incurred a net loss of $29.2 million, and used $26.6 million of cash in operations. The Company expects to continue to generate operating losses and negative cash flows from operations for the next few years and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of the Company's product candidates and the achievement of a level of revenues adequate to support its cost structure. On October 30, 2023, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with a single institutional investor (the "Investor"), pursuant to which the Company agreed to issue and sell, in a registered direct offering by the Company directly to the Investor (the “October 2023 Registered Direct Offering”), 3,100,000 shares of its common stock and 552,300 pre-funded warrants exercisable for shares of common stock, together with accompanying warrants to purchase an aggregate of 3,652,300 shares of common stock. Each share of common stock and accompanying warrant were sold together at a combined purchase price of $1.0952 and each pre-funded warrant and accompanying warrant were sold together at a combined purchase price of $1.0951. The aggregate gross proceeds to the Company from the October 2023 Registered Direct Offering were approximately $4.0 million, before deducting placement agents' fees and related offering expenses. Subsequent to the closing of the October 2023 Registered Direct Offering, all of the pre-funded warrants were exercised into shares of common stock by the Investor. On February 28, 2023, the Company consummated an underwritten public offering (the "February 2023 Offering"), issuing 7,220,217 shares of common stock and accompanying common stock warrants to purchase an aggregate of 7,220,217 shares of common stock. The shares of common stock and accompanying common stock warrants were sold at a combined price of $2.77 per share and accompanying common stock warrant. Each common stock warrant sold with the shares of common stock represents the right to purchase one share of the Company’s common stock at an exercise price of $2.77 per share, which was reduced to an exercise price of $1.35 per share in October 2023, and further reduced to an exercise price of $0.9702 per share in November 2023. The common stock warrants are exercisable immediately and will expire on February 28, 2028, five years from the date of issuance. The net proceeds to the Company from the February 2023 Offering were approximately $18.5 million, after deducting underwriting discounts and commissions, offering expenses, and excluding the exercise of any warrants. On April 16, 2021, the Company entered into a Controlled Equity Offering SM Sales Agreement (the "Sales Agreement") with Cantor Fitzgerald & Co. (the "Agent"). From time to time during the term of the Sales Agreement, subject to certain restrictions, the Company may offer and sell shares of common stock having an aggregate offering price up to a total of $50.0 million in gross proceeds. The Agent will collect a fee equal to 3% of the gross sales price of all shares of common stock sold. Shares of common stock sold under the Sales Agreement are offered and sold pursuant to the Company's registration statement on Form S-3, which was filed with the SEC on April 16, 2021 and declared effective on April 29, 2021. During the nine months ended September 30, 2023, the Company sold a total of 76,882 shares of common stock pursuant to the Sales Agreement at an average price of $3.59 per share for aggregate net proceeds of approximately $0.3 million. Subsequent to September 30, 2023, the Company sold a total of 16,000 shares of common stock pursuant to the Sales Agreement for aggregate net proceeds of approximately $21,000. In December 2020, the Company, together with its wholly-owned subsidiary, SLSG Limited, LLC, entered into an Exclusive License Agreement (the “3DMed License Agreement”) with 3D Medicines Inc. ("3DMed"), pursuant to which the Company granted 3DMed a sublicensable, royalty-bearing license, under certain intellectual property owned or controlled by the Company, to develop, manufacture and have manufactured, and commercialize GPS and heptavalent GPS product candidates for all therapeutic and other diagnostic uses in mainland China, Hong Kong, Macau and Taiwan ("3DMed Territory"). To date, the Company has received $10.5 million in upfront payments and certain technology transfer and regulatory milestones. In November 2022, the Company announced that the Company has agreed with 3DMed for 3DMed to participate in the REGAL study through the inclusion of approximately 20-25 patients from mainland China. Such participation by 3DMed, which the Company expects to occur in the fourth quarter of 2023, subject to any further delays due to supply chain or other operational reasons, will trigger two development milestone payments totaling $13.0 million which has been agreed with 3DMed. A total of $191.5 million in potential future development, regulatory, and sales milestones, not including future royalties, remains under the 3DMed License Agreement as of September 30, 2023, which milestones are all variable in nature and not under the Company's control. As of September 30, 2023, the Company had cash and cash equivalents of approximately $4.0 million and restricted cash and cash equivalents of $0.1 million. In accordance with Accounting Standards Codification ("ASC") 205-40, Presentation of Financial Statements - Going Concern , the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the consolidated financial statements are issued. The Company expects its cash and cash equivalents, together with the net proceeds from the October 2023 Registered Direct Offering, will not be sufficient to fund its current planned operations for at least the next twelve months from the date of issuance of these consolidated financial statements. The $13.0 million of development milestone payments to the Company triggered by 3DMed's participation in the REGAL study through the enrollment of patients in China are variable in nature and not under the Company's control, and therefore cannot be included in the Company's going concern assumption.

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies The Company's complete summary of significant accounting policies can be found in "Item 8. Financial Statements and Supplementary Data - Note 3. Basis of Presentation and Significant Accounting Policies" in the audited annual consolidated financial statements included in the 2022 Annual Report. The significant accounting policies summarized and included in the 2022 Annual Report have not materially changed, except as set forth below. Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to U.S. GAAP as found in the ASC and Accounting Standards Updates ("ASUs") of the Financial Accounting Standards Board ("FASB"). Principles of Consolidation The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated upon consolidation. Unless the context otherwise indicates, reference in these notes to the "Company" refer to SELLAS Life Sciences Group, Inc., and its wholly owned subsidiaries, SELLAS Life Sciences Group, Ltd., a privately held Bermuda exempted company, SLSG Limited, LLC, Sellas Life Sciences Limited, and Apthera, Inc. The functional currency of the Company's non-U.S. operations is the U.S. dollar. Unaudited Interim Results These consolidated financial statements and accompanying notes should be read in conjunction with the Company's annual consolidated financial statements and the notes thereto included in the 2022 Annual Report. The accompanying consolidated financial statements as of September 30, 2023 and for the three and nine months ended September 30, 2023 and 2022, are unaudited, but include all adjustments, consisting of normal recurring entries, that management believes to be necessary for a fair presentation of the periods presented. Interim results are not necessarily indicative of results for a full year. Balance sheet amounts as of December 31, 2022 have been derived from the audited financial statements as of that date. Reclassification Certain prior year amounts have been reclassified to conform to current year presentation. These reclassifications had no effect on the Company's loss from operations, net loss, and net loss per share. Net Loss Per Share Net loss per share is computed by dividing net loss applicable to common stockholders by the weighted average number of shares of common stock outstanding during each period. Diluted loss per share includes the effect, if any, from the potential exercise or conversion of securities, such as warrants, stock options and unvested restricted stock that would result in the issuance of incremental shares of common stock. In computing the basic and diluted net loss per share, the weighted average number of shares remains the same for both calculations due to the fact that, when a net loss exists, dilutive shares are not included in the calculation as the impact is anti-dilutive. The following potentially dilutive securities outstanding have been excluded from the computation of diluted weighted average shares outstanding, as they would be anti-dilutive (in thousands): Nine Months Ended September 30, 2023 2022 Common stock warrants 12,221 5,148 Stock options 1,643 1,071 Restricted stock units ("RSUs") 433 297 14,297 6,516

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The following tables present information about the Company's assets and liabilities measured at fair value on a recurring basis in the consolidated balance sheets (in thousands): Description September 30, 2023 Quoted Prices In Significant Other Unobservable Assets: Cash equivalents $ 3,006 $ 3,006 $ — $ — Restricted cash equivalents 100 100 — — Total assets measured and recorded at fair value $ 3,106 $ 3,106 $ — $ — Liabilities: Warrant liability $ — $ — $ — $ — Total liabilities measured and recorded at fair value $ — $ — $ — $ — Description December 31, 2022 Quoted Prices In Significant Other Unobservable Assets: Cash equivalents $ 16,609 $ 16,609 $ — $ — Restricted cash equivalents 100 100 — — Total assets measured and recorded at fair value $ 16,709 $ 16,709 $ — $ — Liabilities: Warrant liability $ 4 $ — $ — $ 4 Total liabilities measured and recorded at fair value $ 4 $ — $ — $ 4

Acquired In-Process Research an

Acquired In-Process Research and Development	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Acquired In-Process Research and Development	Acquired In-Process Research and Development Exclusive License Agreement with GenFleet Therapeutics (Shanghai) Inc. On March 31, 2022, the Company entered into an exclusive license agreement with GenFleet pursuant to which GenFleet granted to the Company a sublicensable royalty-bearing license under certain of its intellectual property, to develop, manufacture, and commercialize SLS009 for the treatment, diagnosis or prevention of disease in humans and animals in the SLS009 Territory. In consideration for the exclusive license, the Company agreed to pay to GenFleet (i) an upfront and technology transfer fee of $10.0 million, all of which has been paid as of September 30, 2023, (ii) development and regulatory milestone payments for up to three indications totaling up to $48.0 million in the aggregate upon the achievement of such milestones, and (iii) sales milestone payments totaling up to $92.0 million in the aggregate upon the achievement of certain net sales thresholds in a given calendar year. The Company also agreed to pay GenFleet single-digit tiered royalties based upon a percentage of annual net sales, with the royalty rate escalating based on the level of annual net sales of SLS009 in the SLS009 Territory ranging from the low to high single digits.

Balance Sheet Accounts

Balance Sheet Accounts	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Accounts	Balance Sheet Accounts Prepaid expenses and other current assets consist of the following (in thousands): September 30, 2023 December 31, 2022 Insurance $ 596 $ 219 Clinical development 425 184 Professional fees 113 82 Other — 46 Prepaid expenses and other current assets $ 1,134 $ 531 Accrued expenses and other current liabilities consist of the following (in thousands): September 30, 2023 December 31, 2022 Clinical trial costs $ 4,864 $ 4,509 Compensation and related benefits 1,547 1,439 Professional fees 304 338 Other 214 — Accrued expenses and other current liabilities $ 6,929 $ 6,286

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company has a non-cancelable operating lease for certain executive, administrative, and general business office space for its headquarters in New York, New York, which began on June 5, 2020, was amended in February 2022 to add additional space, and has a term through December 31, 2024. The Company assessed the lease amendment for the additional space and determined it should be accounted for as a separate contract. The weighted average discount rate of the Company's operating leases under FASB Topic ASC 842, Leases ("ASC 842") is approximately 13.95%. As of September 30, 2023, the leases have a remaining term of 1.25 years. Rent expense related to the Company's operating leases was approximately $0.1 million f or each of the three months ended September 30, 2023 and 2022, and $0.4 million and $0.3 million for the nine months ended September 30, 2023 and 2022, respectively. The Company made cash payments related to its operating leases of approximately $0.1 million for each of the three months ended September 30, 2023 and 2022, and $0.4 million and $0.3 million for the nine months ended September 30, 2023 and 2022, respectively. Future minimum lease payments are as follows as of September 30, 2023 (in thousands): Future minimum lease payments: 2023 (remaining) $ 132 2024 533 Total future minimum lease payments 665 Less: imputed interest (21) Current and non-current operating lease liabilities $ 644 Legal Proceedings From time to time, the Company is subject to various pending or threatened legal actions and proceedings, including those that arise in the ordinary course of its business, which may include employment matters, breach of contract disputes and stockholder litigation. Such actions and proceedings are subject to many uncertainties and to outcomes that are not predictable with assurance and that may not be known for extended periods of time. The Company records a liability in its consolidated financial statements for costs related to claims, including future legal costs, settlements and judgments, when the Company has assessed that a loss is probable and an amount can be reasonably estimated. If the reasonable estimate of a probable loss is a range, the Company records the most probable estimate of the loss or the minimum amount when no amount within the range is a better estimate than any other amount. The Company discloses a contingent liability even if the liability is not probable or the amount is not estimable, or both, if there is a reasonable possibility that a material loss may have been incurred. As of September 30, 2023, there was no pending or threatened litigation.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock The Company has authorized up to 5,000,000 shares of preferred stock, $0.0001 par value per share, for issuance. There were no preferred shares outstanding as of September 30, 2023 and December 31, 2022. Common Stock The Company has authorized up to 350,000,000 shares of common stock, $0.0001 par value per share, for issuance. As of September 30, 2023, the Company has shares of common stock reserved for future issuance as follows (in thousands): Warrants outstanding 12,221 Stock options outstanding 1,643 RSUs outstanding 433 Shares reserved for future issuance under the 2023 Amended and Restated Equity Incentive Plan 3,905 Shares reserved for future issuance under the 2021 Employee Stock Purchase Plan 183 Total common stock reserved for future issuance 18,385

Warrants to Acquire Shares of C

Warrants to Acquire Shares of Common Stock	9 Months Ended
	Sep. 30, 2023
Warrants and Rights Note Disclosure [Abstract]
Warrants to Acquire Shares of Common Stock	Warrants to Acquire Shares of Common Stock Warrants Outstanding The following is a summary of the activity of the Company's warrants to acquire shares of common stock for the nine months ended September 30, 2023 (in thousands): Warrant Issuance Outstanding, December 31, 2022 Granted Expired Outstanding, September 30, 2023 Exercise Price per Share Expiration Warrants classified as equity: February 2023 Offering — 7,220 — 7,220 $ 2.77 February 2028 April 2022 Offering 4,630 — — 4,630 $ 4.08 April 2027 January 2020 Offering 309 — — 309 $ 3.93 July 2025 July 2020 PIPE Offering 25 — — 25 $ 3.30 August 2025 Other 164 — (133) 31 $ 7.50 March 2024 - June 2024 5,128 7,220 (133) 12,215 Warrants classified as liability 13 — (7) 6 $ 7.50 November 2023 5,141 7,220 (140) 12,221 The exercise price per share of the common stock warrants issued in the February 2023 Offering was reduced to $1.35 per share in October 2023 upon the issuance of shares of common stock sold pursuant to the Sales Agreement, and was subsequently reduced to $0.9702 per share in November 2023 upon the closing of the October 2023 Registered Direct Offering due to the issuance of warrants at an exercise price of $0.9702 per share. Warrants to acquire shares of common stock primarily consist of equity-classified warrants. In addition, warrants to acquire shares of common stock that may require the Company to settle in cash are liability-classified warrants. Warrants Classified as Equity The warrants to acquire shares of common stock issued during the February 2023 Offering were recorded as equity upon issuance. During its evaluation of equity classification of these warrants, the Company considered the conditions as prescribed within ASC 815-40, Derivatives and Hedging, Contracts in an Entity’s own Equity (“ASC 815-40”). The conditions within ASC 815-40 are not subject to a probability assessment. The warrants to acquire shares of common stock do not fall under the liability criteria within ASC 480, Distinguishing Liabilities from Equity , as they are not puttable and do not represent an instrument that has a redeemable underlying security. The warrants do meet the definition of a derivative instrument under ASC 815 but are eligible for the scope exception as they are indexed to the Company’s own stock and would be classified in permanent equity if freestanding. On February 28, 2023, in connection with closing of the February 2023 Offering, the Company entered into amendments to an aggregate of 3,438,851 warrants, which had been previously issued by the Company in an underwritten public offering that closed on April 5, 2022 (the "April 2022 Offering"), to reduce the exercise price of such warrants from $5.40 to $3.62, the average closing price of the Company’s common stock, as reported on the Nasdaq Capital Market, for the five trading days immediately preceding the pricing of the February 2023 Offering. The Company accounted for the amendment as a cost to issue equity with the incremental fair value of approximately $0.3 million recognized as an offset to the proceeds received. However, there was no net impact to the consolidated statements of stockholders' equity because the warrants are equity classified. In November 2023, in connection with the closing of the October 2023 Registered Direct Offering, the Company entered into an amendment to reduce the exercise price of warrants to purchase up to 887,000 shares of the Company’s common stock which were issued in the April 2022 Offering and held by the purchaser in the October 2023 Registered Direct Offering to $0.9702 per share, and amended the termination date of such warrants to November 2, 2028. Warrants Classified as Liabilities Liability-classified warrants consist of warrants to acquire common stock issued in connection with certain previous equity financings. These warrants may be settled in cash and were determined not to be indexed to the Company’s common stock. The estimated fair value of outstanding warrants accounted for as liabilities is determined at each balance sheet date. Any decrease or increase in the estimated fair value of the warrant liability since the most recent balance sheet date is recorded in the consolidated statement of operations as change in fair value of warrant liability. The fair value of the warrants is estimated using a Black-Scholes pricing model with the following inputs: September 30, 2023 December 31, 2022 Risk free interest rate 5.55 % 4.75 % Volatility 77.15 % 120.60 % Expected term (years) 0.09 0.75 Expected dividend yield — % — % Strike price $ 7.50 $ 7.50 The expected volatility assumptions are based on the Company's implied volatility in combination with the implied volatilities of similar publicly traded entities. The expected life assumption is based on the remaining contractual terms of the warrants. The risk-free rate is based on the zero-coupon rates in effect at the time of valuation. The dividend yield used in the pricing model is zero, because the Company has no present intention to pay cash dividends. The changes in fair value of the warrant liability for the nine months ended September 30, 2023 were as follows (in thousands): Warrant liability, December 31, 2022 $ 4 Change in fair value of warrants (4) Warrant liability, September 30, 2023 $ —

Licensing Revenue

Licensing Revenue	9 Months Ended
	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Licensing Revenue	Licensing Revenue Exclusive License Agreement with 3D Medicines Inc. In December 2020, the Company, together with its wholly-owned subsidiary, SLSG Limited, LLC, entered into an Exclusive License Agreement (the “3DMed License Agreement”) with 3D Medicines Inc. ("3DMed"), pursuant to which the Company granted 3DMed a sublicensable royalty-bearing license under certain intellectual property owned or controlled by the Company, to develop, manufacture and have manufactured, and commercialize GPS and heptavalent GPS (referred to as GPS Plus) product candidates ("GPS Licensed Products") for all therapeutic and other diagnostic uses in mainland China, Hong Kong, Macau and Taiwan ("3DMed Territory"). The license is exclusive, except with respect to certain know-how that has been non-exclusively licensed to the Company and is sublicensed to 3DMed on a non-exclusive basis. The Company has retained development, manufacturing and commercialization rights with respect to the GPS Licensed Products in the rest of the world. In partial consideration for the rights granted by the Company, 3DMed agreed to pay the Company (i) a one-time upfront cash payment of $7.5 million, and (ii) milestone payments totaling up to $194.5 million in the aggregate upon the achievement of certain technology transfer, development and regulatory milestones, as well as sales milestones based on certain net sales thresholds of GPS Licensed Products in the 3DMed Territory in a given calendar year. 3DMed also agreed to pay tiered royalties based upon a percentage of annual net sales of GPS Licensed Products in the 3DMed Territory ranging from the high single digits to the low double digits. Revenue Recognition At the inception of the 3DMed License Agreement, the Company recognized an initial transaction price of $9.5 million as licensing revenue, which included the $7.5 million upfront fee as well as $2.0 million in development milestones that were assessed as probable of being achieved, while the remaining milestones were variable consideration subject to constraint at inception. In the first quarter of 2022, an additional $1.0 million in licensing revenue was recognized upon approval by China’s National Medical Products Administration (“NMPA”) for a small Phase 1 clinical trial investigating safety of GPS in China. There is $191.5 million in potential future development, regulatory, and sales milestones, not including future royalties, remaining under the 3DMed License Agreement as of September 30, 2023, which milestones are variable in nature and not under the Company's control. At the end of each reporting period, the Company reevaluates the probability of achievement of the future development, regulatory, and sales milestones subject to constraint and, if necessary, will adjust its estimate of the overall transaction price. Any such adjustments will be recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. For the sales-based royalties, the Company will recognize revenue when the related sales occur. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements. There was no licensing revenue recognized during each of the three months ended September 30, 2023 and 2022. There was no licensing revenue recognized during the nine months ended September 30, 2023, and $1.0 million licensing revenue recognized during the nine months ended September 30, 2022 related to the IND approval by the NMPA.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2017 Equity Incentive Plan On December 29, 2017, the 2017 Equity Incentive Plan was approved by the stockholders of the Company, which currently allows for issuance of up to approximately 22,000 shares of common stock underlying stock options granted prior to September 10, 2019. The 2017 Equity Incentive Plan was terminated upon the approval of the 2019 Incentive Plan subject to outstanding stock options granted under the 2017 Equity Incentive Plan that remain exercisable through maturity for the Company's employees and directors. 2023 Amended and Restated Equity Incentive Plan On September 10, 2019, the 2019 Equity Incentive Plan ("2019 Equity Plan") was approved by the stockholders of the Company, which currently allows for issuance of up to approximately 6,036,000 shares of common stock in connection with the grant of stock-based awards, including stock options, restricted stock, restricted stock units, stock appreciation rights and other types of awards as deemed appropriate. The number of shares reserved for issuance under the 2019 Equity Plan automatically increased on January 1 of each year, for a period of four years, which commenced on January 1, 2020 and ended on (and including) January 1, 2023, by an amount equal to the lesser of (i) 5% of the total number of shares of common stock outstanding at the end of the prior fiscal year; and (ii) an amount determined by the board of directors or authorized committee. On June 20, 2023, an amendment to the 2019 Equity Plan was approved by the stockholders of the Company, which amended and restated the 2019 Equity Plan (as amended and restated, the "2023 Amended and Restated Equity Incentive Plan") to increase the number of shares of common stock authorized for issuance under the 2019 Equity Plan by 3,000,000 shares. As of September 30, 2023, approximately 3,905,000 shares of common stock were reserved for future grants under the 2023 Amended and Restated Equity Incentive Plan. The following table summarizes the components of stock-based compensation expense in the consolidated statements of operations for the three and nine months ended September 30, 2023 and 2022, respectively (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Research and development $ 93 $ 72 $ 281 $ 197 General and administrative 450 383 1,316 1,083 Total stock-based compensation $ 543 $ 455 $ 1,597 $ 1,280 Options to Purchase Shares of Common Stock The following table summarizes stock option activity of the Company for the nine months ended September 30, 2023: Total Weighted Weighted Average Remaining Contractual Term (In Years) Aggregate Outstanding at December 31, 2022 1,040 $ 7.57 $ 91 Granted 682 3.20 Canceled (79) 5.28 Outstanding at September 30, 2023 1,643 $ 5.87 8.40 $ 3 Options exercisable at September 30, 2023 586 $ 9.08 7.49 $ — The aggregate intrinsic values of outstanding and exercisable stock options at September 30, 2023 were calculated based on the closing price of the Company’s common stock as reported on the Nasdaq Capital Market on September 29, 2023 of $1.64 per share. The aggregate intrinsic value equals the positive difference between the closing fair market value of the Company’s common stock and the exercise price of the underlying stock options. The Company uses the Black-Scholes option-pricing model to determine the fair value of all its stock options granted. The weighted average assumptions used during the three and nine months ended September 30, 2023 and 2022, respectively, were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Risk free interest rate n/a 3.00 % 3.78 % 1.95 % Volatility n/a 138.57 % 127.77 % 131.54 % Expected lives (years) n/a 6.03 6.20 6.18 Expected dividend yield n/a — % — % — % There were no options granted during the three months ended September 30, 2023. The weighted-average grant date fair value of options granted during the three months ended September 30, 2022 was $2.78. The weighted-average grant date fair value of options granted during the nine months ended September 30, 2023 and 2022 was $2.88 and $4.52, respectively. The Company’s expected common stock price volatility assumption is based upon the Company's own implied volatility in combination with the implied volatility of a basket of comparable companies. The expected life assumptions for employee grants were based upon the simplified method, which averages the contractual term of the Company’s options of ten years with the average vesting term of four years for an average of approximately six years. The expected life assumptions for non-employees were based upon the contractual term of the option. The dividend yield assumption is zero because the Company has never paid cash dividends and presently has no intention to do so. The risk-free interest rate used for each grant was also based upon prevailing short-term interest rates. The Company accounts for forfeitures as they occur. As of September 30, 2023, there was $3.4 million of unrecognized compensation cost related to outstanding stock options that is expected to be recognized as a component of the Company’s operating expenses over a weighted-average period of 2.53 years. Time-vested RSUs and RSUs with Performance Conditions The following table summarizes RSU activity of the Company for the nine months ended September 30, 2023: Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2022 255 $ 3.25 Granted 195 $ 3.34 Canceled (17) $ 3.76 Unvested at September 30, 2023 433 $ 3.27 As of September 30, 2023, there was $1.1 million of unrecognized compensation cost related to outstanding RSUs that is expected to be recognized as a component of the Company's operating expenses over a weighted-average period of 2.36 years. No RSUs vested during the nine months ended September 30, 2023. 2021 Employee Stock Purchase Plan On April 22, 2021, the Board of Directors adopted the 2021 Employee Stock Purchase Plan ("2021 ESPP") which was approved by the Company's stockholders on June 8, 2021 and authorized the issuance of up to 300,000 shares of common stock pursuant to the 2021 ESPP. The 2021 ESPP allows employees to contribute up to 20% of their cash earnings, subject to a maximum of $25,000 per year under Internal Revenue Service rules, to be used to purchase shares of the Company’s common stock on semi-annual purchase dates. The 2021 ESPP allows eligible employees to purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value of the common stock at the beginning or end of each six-month offering period during the term of the 2021 ESPP. During the three and nine months ended September 30, 2023, 46,038 and 91,454 shares of common stock, respectively, were purchased by employees under the 2021 ESPP for proceeds of approximately $54,000 and $107,000, respectively. There are currently 183,457 shares of common stock reserved for issuance under the 2021 ESPP as of September 30, 2023.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsThe Company evaluated all events or transactions that occurred after September 30, 2023 up through the date these consolidated financial statements were issued. Other than as disclosed elsewhere in the notes to the consolidated financial statements, the Company did not have any material subsequent events.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”). Any reference in these notes to applicable
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated upon consolidation. Unless the context otherwise indicates, reference in these notes to the "Company" refer to SELLAS Life Sciences Group, Inc., and its wholly owned subsidiaries, SELLAS Life Sciences Group, Ltd., a privately held Bermuda exempted company, SLSG Limited, LLC, Sellas Life Sciences Limited, and Apthera, Inc.
Reclassification	Reclassification Certain prior year amounts have been reclassified to conform to current year presentation. These reclassifications had no effect on the Company's loss from operations, net loss, and net loss per share.
Net Loss Per Share	Net Loss Per Share Net loss per share is computed by dividing net loss applicable to common stockholders by the weighted average number of shares of common stock outstanding during each period. Diluted loss per share includes the effect, if any, from the potential exercise or conversion of securities, such as warrants, stock options and unvested restricted stock that would result in the issuance of incremental shares of common stock. In computing the basic and diluted net loss per share, the weighted average number of shares remains the same for both calculations due to the fact that, when a net loss exists, dilutive shares are not included in the calculation as the impact is anti-dilutive.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following potentially dilutive securities outstanding have been excluded from the computation of diluted weighted average shares outstanding, as they would be anti-dilutive (in thousands): Nine Months Ended September 30, 2023 2022 Common stock warrants 12,221 5,148 Stock options 1,643 1,071 Restricted stock units ("RSUs") 433 297 14,297 6,516

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	The following tables present information about the Company's assets and liabilities measured at fair value on a recurring basis in the consolidated balance sheets (in thousands): Description September 30, 2023 Quoted Prices In Significant Other Unobservable Assets: Cash equivalents $ 3,006 $ 3,006 $ — $ — Restricted cash equivalents 100 100 — — Total assets measured and recorded at fair value $ 3,106 $ 3,106 $ — $ — Liabilities: Warrant liability $ — $ — $ — $ — Total liabilities measured and recorded at fair value $ — $ — $ — $ — Description December 31, 2022 Quoted Prices In Significant Other Unobservable Assets: Cash equivalents $ 16,609 $ 16,609 $ — $ — Restricted cash equivalents 100 100 — — Total assets measured and recorded at fair value $ 16,709 $ 16,709 $ — $ — Liabilities: Warrant liability $ 4 $ — $ — $ 4 Total liabilities measured and recorded at fair value $ 4 $ — $ — $ 4

Balance Sheet Accounts (Tables)

Balance Sheet Accounts (Tables)	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): September 30, 2023 December 31, 2022 Insurance $ 596 $ 219 Clinical development 425 184 Professional fees 113 82 Other — 46 Prepaid expenses and other current assets $ 1,134 $ 531
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): September 30, 2023 December 31, 2022 Clinical trial costs $ 4,864 $ 4,509 Compensation and related benefits 1,547 1,439 Professional fees 304 338 Other 214 — Accrued expenses and other current liabilities $ 6,929 $ 6,286

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments	Future minimum lease payments are as follows as of September 30, 2023 (in thousands): Future minimum lease payments: 2023 (remaining) $ 132 2024 533 Total future minimum lease payments 665 Less: imputed interest (21) Current and non-current operating lease liabilities $ 644

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	As of September 30, 2023, the Company has shares of common stock reserved for future issuance as follows (in thousands): Warrants outstanding 12,221 Stock options outstanding 1,643 RSUs outstanding 433 Shares reserved for future issuance under the 2023 Amended and Restated Equity Incentive Plan 3,905 Shares reserved for future issuance under the 2021 Employee Stock Purchase Plan 183 Total common stock reserved for future issuance 18,385

Warrants to Acquire Shares of_2

Warrants to Acquire Shares of Common Stock (Tables)	9 Months Ended
	Sep. 30, 2023
Warrants and Rights Note Disclosure [Abstract]
Schedule of Warrant Activity	The following is a summary of the activity of the Company's warrants to acquire shares of common stock for the nine months ended September 30, 2023 (in thousands): Warrant Issuance Outstanding, December 31, 2022 Granted Expired Outstanding, September 30, 2023 Exercise Price per Share Expiration Warrants classified as equity: February 2023 Offering — 7,220 — 7,220 $ 2.77 February 2028 April 2022 Offering 4,630 — — 4,630 $ 4.08 April 2027 January 2020 Offering 309 — — 309 $ 3.93 July 2025 July 2020 PIPE Offering 25 — — 25 $ 3.30 August 2025 Other 164 — (133) 31 $ 7.50 March 2024 - June 2024 5,128 7,220 (133) 12,215 Warrants classified as liability 13 — (7) 6 $ 7.50 November 2023 5,141 7,220 (140) 12,221
Schedule of Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model	The fair value of the warrants is estimated using a Black-Scholes pricing model with the following inputs: September 30, 2023 December 31, 2022 Risk free interest rate 5.55 % 4.75 % Volatility 77.15 % 120.60 % Expected term (years) 0.09 0.75 Expected dividend yield — % — % Strike price $ 7.50 $ 7.50
Schedule of Changes in Fair Value of Warrant Liability	The changes in fair value of the warrant liability for the nine months ended September 30, 2023 were as follows (in thousands): Warrant liability, December 31, 2022 $ 4 Change in fair value of warrants (4) Warrant liability, September 30, 2023 $ —

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Allocated Stock-based Compensation Expense	The following table summarizes the components of stock-based compensation expense in the consolidated statements of operations for the three and nine months ended September 30, 2023 and 2022, respectively (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Research and development $ 93 $ 72 $ 281 $ 197 General and administrative 450 383 1,316 1,083 Total stock-based compensation $ 543 $ 455 $ 1,597 $ 1,280
Schedule of Stock Option Activity	The following table summarizes stock option activity of the Company for the nine months ended September 30, 2023: Total Weighted Weighted Average Remaining Contractual Term (In Years) Aggregate Outstanding at December 31, 2022 1,040 $ 7.57 $ 91 Granted 682 3.20 Canceled (79) 5.28 Outstanding at September 30, 2023 1,643 $ 5.87 8.40 $ 3 Options exercisable at September 30, 2023 586 $ 9.08 7.49 $ —
Schedule of Assumptions for Option Grants Issued	The Company uses the Black-Scholes option-pricing model to determine the fair value of all its stock options granted. The weighted average assumptions used during the three and nine months ended September 30, 2023 and 2022, respectively, were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Risk free interest rate n/a 3.00 % 3.78 % 1.95 % Volatility n/a 138.57 % 127.77 % 131.54 % Expected lives (years) n/a 6.03 6.20 6.18 Expected dividend yield n/a — % — % — %
Schedule of RSU Activity	The following table summarizes RSU activity of the Company for the nine months ended September 30, 2023: Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2022 255 $ 3.25 Granted 195 $ 3.34 Canceled (17) $ 3.76 Unvested at September 30, 2023 433 $ 3.27

Liquidity (Details)

Liquidity (Details) $ / shares in Units, $ in Thousands					1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares	Feb. 28, 2023 USD ($) $ / shares shares	Apr. 16, 2021 USD ($)	Nov. 09, 2023 USD ($) $ / shares shares	Nov. 30, 2022 patient	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($)	Oct. 31, 2023 $ / shares	Dec. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accumulated deficit		$ 209,108					$ 209,108		$ 209,108			$ 179,904
Net loss							9,267	$ 7,022	29,204	$ 32,180
Net cash used in operating activities									26,585	$ 18,657
Upfront fee and milestone payments									10,500
Milestone payment received									13,000
Potential milestone payments to be received		191,500
Cash and cash equivalents		3,969					3,969		3,969			17,125
Restricted cash and cash equivalents		$ 100					$ 100		$ 100			$ 100
Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of patients | patient						20
Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of patients | patient						25
Underwriting Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of shares of stock (in shares) | shares			7,220,217
Common stock to be called by warrants (in shares) | shares			7,220,217
Offering price (in dollars per share) | $ / shares			$ 2.77
Net proceeds of common stock			$ 18,500
Exercise price (in dollars per share) | $ / shares			$ 2.77
Number of securities called by each warrant | shares			1
Expiration term			5 years
Underwriting Agreement | Subsequent Event
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Exercise price (in dollars per share) | $ / shares					$ 0.9702						$ 1.35
Sales Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of shares of stock (in shares) | shares									76,882
Net proceeds of common stock									$ 300
Sale of shares, common stock gross proceeds				$ 50,000
Percentage gross proceeds from the sale of shares (as a percent)				3%
Stock price per share (in dollars per share) | $ / shares		$ 3.59					$ 3.59		$ 3.59
Sales Agreement | Subsequent Event
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of shares of stock (in shares) | shares					16,000
Net proceeds of common stock					$ 21
Securities Purchase Agreement | Subsequent Event
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of shares of stock (in shares) | shares	3,100,000
Offering price (in dollars per share) | $ / shares	$ 1.0952
Securities Purchase Agreement | Subsequent Event | Pre-Funded Warrants
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of shares of stock (in shares) | shares	3,652,300
Common stock to be called by warrants (in shares) | shares	552,300
Offering price (in dollars per share) | $ / shares	$ 1.0951
Net proceeds of common stock	$ 4,000

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	14,297	6,516
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	12,221	5,148
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	1,643	1,071
Restricted stock units ("RSUs")
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	433	297

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Liabilities:
Warrant liability	$ 0	$ 4
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	3,006	16,609
Restricted cash equivalents	100	100
Total assets measured and recorded at fair value	3,106	16,709
Liabilities:
Warrant liability	0	4
Total liabilities measured and recorded at fair value	0	4
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets (Level 1)
Assets:
Cash equivalents	3,006	16,609
Restricted cash equivalents	100	100
Total assets measured and recorded at fair value	3,106	16,709
Liabilities:
Warrant liability	0	0
Total liabilities measured and recorded at fair value	0	0
Fair Value, Measurements, Recurring | Significant Other Observable  Inputs (Level 2)
Assets:
Cash equivalents	0	0
Restricted cash equivalents	0	0
Total assets measured and recorded at fair value	0	0
Liabilities:
Warrant liability	0	0
Total liabilities measured and recorded at fair value	0	0
Fair Value, Measurements, Recurring | Unobservable  Inputs (Level 3)
Assets:
Cash equivalents	0	0
Restricted cash equivalents	0	0
Total assets measured and recorded at fair value	0	0
Liabilities:
Warrant liability	0	4
Total liabilities measured and recorded at fair value	$ 0	$ 4

Acquired In-Process Research _2

Acquired In-Process Research and Development (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Acquired in-process research and development expense		$ 0	$ 0	$ 0	$ 10,000
Cash payments				5,500	4,500
GenFleet Therapeutics (Shanghai) Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront fee	$ 10,000
Eligible payment from collaboration for development and regulatory milestone achievement under collaborations agreement	48,000
Maximum amount eligible for milestones under collaborations agreement	$ 92,000
Acquired in-process research and development expense					$ 10,000
Cash payments		$ 3,000		$ 5,500

Balance Sheet Accounts - Schedu

Balance Sheet Accounts - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Insurance	$ 596	$ 219
Clinical development	425	184
Professional fees	113	82
Other	0	46
Prepaid expenses and other current assets	$ 1,134	$ 531

Balance Sheet Accounts - Sche_2

Balance Sheet Accounts - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Clinical trial costs	$ 4,864	$ 4,509
Compensation and related benefits	1,547	1,439
Professional fees	304	338
Other	214	0
Accrued expenses and other current liabilities	$ 6,929	$ 6,286

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Operating lease, discount rate (as a percent)	13.95%		13.95%
Operating lease, remaining term			1 year 3 months
Rent expense	$ 0.1	$ 0.1	$ 0.4	$ 0.3
Cash payments related to operating lease	$ 0.1	$ 0.1	$ 0.4	$ 0.3

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2023 (remaining)	$ 132
2024	533
Total future minimum lease payments	665
Less: imputed interest	(21)
Current and non-current operating lease liabilities	$ 644

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Equity [Abstract]
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares outstanding (in shares)	0	0
Common stock, shares authorized (in shares)	350,000,000	350,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Sep. 30, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants outstanding (in shares)	12,221	5,141
Stock options outstanding (in shares)	1,643	1,040
Total common stock reserved for future issuance (in shares)	18,385
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)	3,905
2021 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)	183
Restricted stock units ("RSUs")
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs outstanding (in shares)	433	255

Warrants to Acquire Shares of_3

Warrants to Acquire Shares of Common Stock - Schedule of Warrant Activity (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	5,141
Granted (in shares)	7,220
Expired (in shares)	(140)
Outstanding, end of period (in shares)	12,221
Common stock warrants
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	5,128
Granted (in shares)	7,220
Expired (in shares)	(133)
Outstanding, end of period (in shares)	12,215
February 2023 Offering | Common stock warrants
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	0
Granted (in shares)	7,220
Expired (in shares)	0
Outstanding, end of period (in shares)	7,220
Exercise price (in dollars per share) | $ / shares	$ 2.77
April 2022 Offering | Common stock warrants
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	4,630
Granted (in shares)	0
Expired (in shares)	0
Outstanding, end of period (in shares)	4,630
Exercise price (in dollars per share) | $ / shares	$ 4.08
January 2020 Offering | Common stock warrants
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	309
Granted (in shares)	0
Expired (in shares)	0
Outstanding, end of period (in shares)	309
Exercise price (in dollars per share) | $ / shares	$ 3.93
July 2020 PIPE Offering | Common stock warrants
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	25
Granted (in shares)	0
Expired (in shares)	0
Outstanding, end of period (in shares)	25
Exercise price (in dollars per share) | $ / shares	$ 3.30
Other | Common stock warrants
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	164
Granted (in shares)	0
Expired (in shares)	(133)
Outstanding, end of period (in shares)	31
Exercise price (in dollars per share) | $ / shares	$ 7.50
Warrants classified as liability
Class of Warrant or Right, Outstanding [Roll Forward]
Outstanding, beginning of period (in shares)	13
Granted (in shares)	0
Expired (in shares)	(7)
Outstanding, end of period (in shares)	6
Exercise price (in dollars per share) | $ / shares	$ 7.50

Warrants to Acquire Shares of_4

Warrants to Acquire Shares of Common Stock - Narrative (Details) $ / shares in Units, $ in Millions	Nov. 09, 2023 $ / shares shares	Oct. 31, 2023 $ / shares	Sep. 30, 2023	Feb. 28, 2023 USD ($) $ / shares shares	Feb. 27, 2023 $ / shares	Dec. 31, 2022
Coupon rate
Class of Warrant or Right [Line Items]
Expected dividend yield			0
Expected dividend yield
Class of Warrant or Right [Line Items]
Expected dividend yield			0			0
Underwriting Agreement
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)				$ 2.77
Common stock to be called by warrants (in shares) | shares				7,220,217
Underwriting Agreement | Subsequent Event
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)	$ 0.9702	$ 1.35
February 2023 Offering | Subsequent Event
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)	0.9702	$ 1.35
October 2023 Offering | Subsequent Event
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)	0.9702
October 2023 Offering | Underwriting Agreement | Subsequent Event
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)	$ 0.9702
Common stock to be called by warrants (in shares) | shares	887,000
April 2022 Offering | Underwriting Agreement
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share)				$ 3.62	$ 5.40
Common stock to be called by warrants (in shares) | shares				3,438,851
Warrants not settleable in cash, fair value disclosure | $				$ 0.3

Warrants to Acquire Shares of_5

Warrants to Acquire Shares of Common Stock - Schedule of Fair Value of Warrants is Estimated Using Black-Scholes Option Pricing Model (Details)	Sep. 30, 2023 $ / shares yr	Dec. 31, 2022 yr
Risk free interest rate
Class of Warrant or Right [Line Items]
Warrants, measurement input	0.0555	0.0475
Volatility
Class of Warrant or Right [Line Items]
Warrants, measurement input	0.7715	1.2060
Expected term (years)
Class of Warrant or Right [Line Items]
Warrants, measurement input	0.09	0.75
Expected dividend yield
Class of Warrant or Right [Line Items]
Warrants, measurement input	0	0
Strike price
Class of Warrant or Right [Line Items]
Warrants, measurement input	7.50	7.50

Warrants to Acquire Shares of_6

Warrants to Acquire Shares of Common Stock - Schedule of Changes in Fair Value of Warrant Liability (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Class of Warrant or Right, Fair Value [Roll Forward]
Warrant liability, December 31, 2022	$ 4
Change in fair value of warrants	(4)
Warrant liability, September 30, 2023	$ 0

Licensing Revenue (Details)

Licensing Revenue (Details) - USD ($)		1 Months Ended	3 Months Ended			9 Months Ended
	Sep. 30, 2023	Dec. 31, 2020	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue from Contract with Customer [Abstract]
Upfront cash payment received		$ 7,500,000
Future milestone payments received		194,500,000
Performance obligation, amount		9,500,000
Milestones probable of being achieved		$ 2,000,000
Deferred revenue recognized license					$ 1,000,000
Potential milestone payments to be received	$ 191,500,000
Licensing revenue			$ 0	$ 0		$ 0	$ 1,000,000
Cost of licensing revenue			$ 0	$ 0		$ 0	$ 100,000

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		9 Months Ended
	Jun. 20, 2023	Apr. 22, 2021	Sep. 10, 2019	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 29, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance (in shares)				18,385,000		18,385,000
Closing price of the Company's common stock (in dollars per share)				$ 1.64		$ 1.64
Granted (in shares)				0		682,000
Weighted average exercise price, granted (in dollars per share)					$ 2.78	$ 2.88	$ 4.52
Averages contractual term						10 years
Expected dividend yield (as a percent)					0%	0%	0%
Unrecognized compensation cost, options				$ 3,400		$ 3,400
Proceeds from employee stock purchases						$ 107	$ 85
Restricted stock units ("RSUs")
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average exercise price, granted (in dollars per share)						$ 3.34
Weighted average recognition period						2 years 4 months 9 days
Unrecognized compensation cost				$ 1,100		$ 1,100
RSUs vested (in shares)						0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average recognition period						2 years 6 months 10 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average vesting term						4 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average vesting term						6 years
2017 Equity Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized for issuance (in shares)								22,000
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized for issuance (in shares)			6,036,000
Option term			4 years
Increase in number of shares available for future issuance under stock based awards (as a percent)			5%
Increase in number of shares authorized (in shares)	3,000,000
Shares of common stock reserved for issuance (in shares)				3,905,000		3,905,000
2021 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized for issuance (in shares)		300,000
2021 ESPP | Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance (in shares)				183,457		183,457
Cash earnings contributed per year		20%
Purchase price of common stock		85%
Offering period		6 months
Shares purchased for award				46,038		91,454
Proceeds from employee stock purchases				$ 54		$ 107

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Allocated Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share based compensation expense	$ 543	$ 455	$ 1,597	$ 1,280
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share based compensation expense	93	72	281	197
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share based compensation expense	$ 450	$ 383	$ 1,316	$ 1,083

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning balance (in shares)		1,040,000
Granted (in shares)	0	682,000
Canceled (in shares)		(79,000)
Options outstanding, ending balance (in shares)	1,643,000	1,643,000
Options exercisable (in shares)	586,000	586,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price, beginning balance (in dollars per share)		$ 7.57
Weighted average exercise price, granted (in dollars per share)		3.20
Weighted average exercise price, granted canceled (in dollars per share)		5.28
Weighted average exercise price, ending balance (in dollars per share)	$ 5.87	5.87
Weighted average exercise price, options exercisable (in dollars per share)	$ 9.08	$ 9.08
Weighted average remaining contractual term, outstanding (in years)		8 years 4 months 24 days
Weighted average remaining contractual term, options exercisable (in years)		7 years 5 months 26 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Aggregate Intrinsic Value [Roll Forward]
Aggregate intrinsic value, outstanding	$ 3	$ 3	$ 91
Aggregate intrinsic value, options exercisable	$ 0	$ 0

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Assumptions for Option Grants Issued (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-Based Payment Arrangement [Abstract]
Risk free interest rate	3%	3.78%	1.95%
Volatility	138.57%	127.77%	131.54%
Expected lives (years)	6 years 10 days	6 years 2 months 12 days	6 years 2 months 4 days
Expected dividend yield	0%	0%	0%

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of RSU Activity (Details) - $ / shares shares in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 2.78	$ 2.88	$ 4.52
Restricted stock units ("RSUs")
Shares
Beginning balance (in shares)		255
Granted (in shares)		195
Canceled (in shares)		(17)
Ending balance (in shares)		433
Weighted Average Grant Date Fair Value
Beginning balance (in dollars per share)		$ 3.25
Granted (in dollars per share)		3.34
Canceled (in dollars per share)		3.76
Ending balance (in dollars per share)		$ 3.27