Altimmune (ALT) 10-Q 11 May 23 2023 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2023	May 05, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Trading Symbol	ALT
Entity Registrant Name	ALTIMMUNE, INC.
Entity Central Index Key	0001326190
Current Fiscal Year End Date	--12-31
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 Common Stock, Shares Outstanding		49,292,189
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity File Number	001-32587
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-2726770
Entity Address, Address Line One	910 Clopper Road
Entity Address, Address Line Two	Suite 201S
Entity Address, City or Town	Gaithersburg
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20878
City Area Code	240
Local Phone Number	654-1450
Document Transition Report	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 104,690	$ 111,097
Restricted cash	34	34
Total cash, cash equivalents and restricted cash	104,724	111,131
Short-term investments	61,039	73,783
Accounts receivable	252	173
Income tax and R&D incentive receivables	3,118	2,368
Prepaid expenses and other current assets	3,978	5,358
Total current assets	173,111	192,813
Property and equipment, net	1,007	1,081
Indefinite-lived intangible asset	12,419	12,419
Other assets	546	615
Total assets	187,083	206,928
Current liabilities:
Accounts payable	5,238	4,804
Accrued expenses and other current liabilities	9,713	12,250
Total current liabilities	14,951	17,054
Other long-term liabilities	4,400	4,581
Total liabilities	19,351	21,635
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 49,286,710 and 49,199,845 shares issued and outstanding as of March 31, 2023 and December 31, 2022, respectively	5	5
Additional paid-in capital	570,786	568,399
Accumulated deficit	(397,958)	(377,884)
Accumulated other comprehensive loss, net	(5,101)	(5,227)
Total stockholders' equity	167,732	185,293
Total liabilities and stockholders' equity	$ 187,083	$ 206,928

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
CONSOLIDATED BALANCE SHEETS
Common stock, par or stated value per share	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	49,286,710	49,199,845
Common stock, shares outstanding	49,286,710	49,199,845

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Revenues	$ 21	$ 32
Operating expenses:
Research and development	17,249	15,104
General and administrative	4,531	4,427
Total operating expenses	21,780	19,531
Loss from operations	(21,759)	(19,499)
Other income (expense):
Interest expense	(2)	(62)
Interest income	1,668	21
Other income (expense), net	19	110
Total other income (expense), net	1,685	69
Net loss	(20,074)	(19,430)
Other comprehensive income - unrealized gain on short-term investments	126
Comprehensive loss	$ (19,948)	$ (19,430)
Net loss per share, basic	$ (0.40)	$ (0.44)
Net loss per share, diluted	$ (0.39)	$ (0.44)
Weighted-average common shares outstanding, basic	50,125,685	43,969,481
Weighted-average common shares outstanding, diluted	50,125,685	43,969,481

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Beginning Balance at Dec. 31, 2021	$ 4	$ 497,342	$ (293,171)	$ (5,040)	$ 199,135
Beginning Balance (in shares) at Dec. 31, 2021	40,993,768
Stock-based compensation		2,033			2,033
Exercise of stock options		197			197
Exercise of stock options (in shares)	95,771
Vesting of restricted stock awards including withholding, net		(170)			(170)
Vesting of restricted stock awards including withholding, net (in shares)	17,568
Issuance of common stock from Employee Stock Purchase Plan		113			113
Issuance of common stock from Employee Stock Purchase Plan (in shares)	16,450
Issuance of common stock in at the market offerings, net		2,990			2,990
Issuance of common stock in at the market offerings, net (in shares)	335,485
Issuance of common stock upon exercise of warrants (in shares)	1,760,854
Net loss			(19,430)		(19,430)
Ending Balance at Mar. 31, 2022	$ 4	502,505	(312,601)	(5,040)	184,868
Ending Balance (in shares) at Mar. 31, 2022	43,219,896
Beginning Balance at Dec. 31, 2021	$ 4	497,342	(293,171)	(5,040)	199,135
Beginning Balance (in shares) at Dec. 31, 2021	40,993,768
Ending Balance at Dec. 31, 2022	$ 5	568,399	(377,884)	(5,227)	185,293
Ending Balance (in shares) at Dec. 31, 2022	49,199,845
Stock-based compensation		2,675			2,675
Exercise of stock options		61			61
Exercise of stock options (in shares)	19,303
Vesting of restricted stock awards including withholding, net		(484)			(484)
Vesting of restricted stock awards including withholding, net (in shares)	54,347
Issuance of common stock from Employee Stock Purchase Plan		135			135
Issuance of common stock from Employee Stock Purchase Plan (in shares)	13,215
Unrealized loss on short-term investments				126	126
Net loss			(20,074)		(20,074)
Ending Balance at Mar. 31, 2023	$ 5	$ 570,786	$ (397,958)	$ (5,101)	$ 167,732
Ending Balance (in shares) at Mar. 31, 2023	49,286,710

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (20,074)	$ (19,430)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration liability		(1,780)
Stock-based compensation expense	2,675	2,033
Depreciation and amortization	(356)	119
Loss on foreign currency exchange	(18)	(110)
Changes in operating assets and liabilities:
Accounts receivable	(80)	236
Prepaid expenses and other assets	1,589	3,046
Accounts payable	434	171
Accrued expenses and other liabilities	(2,827)	2,659
Income tax and R&D incentive receivables	(750)	(470)
Net cash used in operating activities	(19,407)	(13,526)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sales and maturities of short-term investments	34,565
Purchases of short-term investments	(21,212)
Purchases of property and equipment, net	(51)	(9)
Net cash provided by (used in) investing activities	13,302	(9)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of deferred offering costs	(13)	(119)
Proceeds from issuance of common stock in at-the-market offerings, net		2,990
Proceeds from issuance of common stock from Employee Stock Purchase Plan	135	113
(Payments for) proceeds from share-based compensation, net	(424)	197
Net cash (used in) provided by financing activities	(302)	3,181
Net decrease in cash and cash equivalents and restricted cash	(6,407)	(10,354)
Cash, cash equivalents and restricted cash at beginning of period	111,131	190,335
Cash, cash equivalents and restricted cash at end of period	104,724	$ 179,981
SUPPLEMENTAL NON-CASH ACTIVITIES:
Deferred offering costs in accrued expenses and other current liabilities	$ 182

Nature of Business and Organiza

Nature of Business and Organization	3 Months Ended
	Mar. 31, 2023
Nature of Business and Organization
Nature of Business and Organization	1. Nature of Business and Basis of Presentation Nature of Business Altimmune, Inc., headquartered in Gaithersburg, Maryland, United States, together with its subsidiaries (collectively, the “Company” or “Altimmune”) is a clinical stage biopharmaceutical company incorporated under the laws of the State of Delaware. The Company is focused on developing treatments for obesity and liver diseases. The Company’s pipeline includes next generation peptide therapeutics for obesity and non-alcoholic steatohepatitis (“NASH”) (for both, pemvidutide, formerly known as ALT-801), and for chronic hepatitis B (“HepTcell TM Basis of Presentation The accompanying unaudited consolidated financial statements are prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Accordingly, they do not include all of the information and disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete consolidated financial statements and should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2022 included in the Annual Report on Form 10-K which was filed with the SEC on February 28, 2023. In the opinion of management, the Company has prepared the accompanying unaudited consolidated financial statements on the same basis as the audited consolidated financial statements, and these consolidated financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the results of the interim periods presented. The operating results for the interim periods presented are not necessarily indicative of the results expected for the full year 2023 or any future years or periods. The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. The accompanying unaudited consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets, and the satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded assets and liabilities that might be necessary should the Company be unable to continue as a going concern.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2023
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies During the three months ended March 31, 2023, there have been no significant changes to the Company’s summary of significant accounting policies contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 as filed with the SEC, except for the recently adopted accounting standard for ASU No. 2016-13 as disclosed below. Use of Estimates The preparation of these financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not limited to, the valuation of share-based awards, income taxes, and accruals for research and development activities. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. However, actual results could differ from those estimates and there may be changes to the Company’s estimates in future periods. Short-term Investments The Company’s short-term investments are comprised of U.S. Treasuries, corporate debt securities and certificates of deposit that have original maturities less than or equal to one year and are classified as available-for-sale (“AFS”) securities. Such securities are carried at estimated fair value, net of allowance for credit loss determined based on the Current Expected Credit Loss. Any unrealized holding gains or losses are reported as accumulated other comprehensive income or loss, which is a separate component of stockholders’ equity. In the event that the AFS security's fair value is below the amortized cost and (i) the Company intends to sell the AFS security and (ii) the AFS security is required to be sold before recovery of the loss, the AFS security's amortized cost base will be written down to its fair value and the loss will be recognized in the income statement. If the Company intends not to sell the AFS security and the AFS security is not required to be sold before recovery of the loss, the Company evaluates whether a portion of the unrealized loss is a result of credit loss. The portion of unrealized loss related to credit loss will be recorded as allowance for credit loss in the balance sheet with the corresponding credit loss in the income statement and the portion of unrealized loss not related to credit loss will be recognized in other comprehensive income (“OCI”). Dividend and interest income are recognized in other income when earned. The cost of securities sold is calculated using the specific identification method. The Company places all investments with government agencies, or corporate institutions whose debt is rated as investment grade. As of March 31, 2023, none of the unrealized losses on our short-term investments are a result of credit loss, and therefore, the unrealized losses were recognized in OCI. Income Taxes Due to a full valuation allowance, the Company did not record an income tax expense (benefit) for either of the three months ended March 31, 2023 or 2022. The Company calculates its quarterly income tax provision based on an estimated, annual effective tax rates applied to ordinary income (or loss) and other known items computed and recognized as they occur. The Company’s total provision is based on the United States statutory rate, increased by state and foreign taxes and reduced by a full valuation allowance on the Company’s deferred tax assets. Recently adopted accounting pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU No. 2016-13”)

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2023
Fair Value Measurements
Fair Value Measurements	3. Fair Value Measurements The Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2023 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at March 31, 2023 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents - money market funds ​ $ 100,611 ​ $ 100,611 ​ $ — ​ $ — Short-term investments ​ 61,039 ​ — ​ 61,039 ​ — Total ​ $ 161,650 ​ $ 100,611 ​ $ 61,039 ​ $ — ​ The Company’s assets and liabilities measured at fair value on a recurring basis as of December 31, 2022 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at December 31, 2022 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents - money market funds ​ $ 105,794 $ 105,794 ​ $ — ​ $ — Short-term investments ​ 73,783 ​ — ​ 73,783 ​ — Total ​ $ 179,577 ​ $ 105,794 ​ $ 73,783 ​ $ — ​ ​ Short-term investments have been initially valued at the transaction price and subsequently valued at the end of each reporting period utilizing third party pricing services or other market observable data (Level 2). The pricing services utilize industry standard valuation models, including both income and market-based approaches and observable market inputs to determine value. Short-term investments with quoted prices as of March 31, 2023 as shown below (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ ​ Amortized Cost ​ Unrealized (Loss) Gain ​ Credit loss ​ Market Value United States treasury securities $ 15,718 $ (15) $ — $ 15,703 Commercial paper and corporate debt securities ​ ​ 37,982 ​ ​ (27) ​ ​ — ​ ​ 37,955 Asset backed securities ​ 5,448 ​ (20) ​ — ​ 5,428 Agency debt securities ​ ​ 1,952 ​ ​ 1 ​ ​ — ​ ​ 1,953 Total ​ $ 61,100 ​ $ (61) ​ $ — ​ $ 61,039 ​ Short-term investments with quoted prices as of December 31, 2022 as shown below (in thousand): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 ​ ​ Amortized Cost ​ Unrealized (Loss) Gain ​ Credit Loss ​ Market Value United States treasury securities $ 15,868 $ (86) $ — $ 15,782 Commercial paper and corporate debt securities ​ ​ 50,747 ​ ​ (71) ​ ​ — ​ ​ 50,676 Asset backed securities ​ 5,427 ​ (35) ​ — ​ 5,392 Agency debt securities ​ ​ 1,928 ​ ​ 5 ​ ​ — ​ ​ 1,933 Total ​ $ 73,970 ​ $ (187) ​ $ — ​ $ 73,783 ​ Separate disclosure is required for assets and liabilities measured at fair value on a recurring basis from those measured at fair value on a non-recurring basis. Assets recorded at fair value on a non-recurring basis, such as property and equipment and intangible assets are recognized at fair value when they are impaired. During the three months ended March 31, 2023 and year ended December 31, 2022, the Company had no significant assets or liabilities that were measured at fair value on a non-recurring basis.

Operating Leases

Operating Leases	3 Months Ended
	Mar. 31, 2023
Leases
Leases	4. Operating Leases The Company’s operating leases consist of leases for office and laboratory space in the United States, which expire in April 2025. Rent expense during the three months ended March 31, 2023 and 2022 under all of the Company’s operating leases was $0.2 million and $0.1 million, respectively. Rent expense includes short-term leases and variable lease costs that are not included in the lease obligation. Short-term leases are leases having a term of twelve months or less. The Company recognizes short-term leases on a straight-line basis and does not record a related lease asset or liability for such leases. The office space lease provides for increases in future minimum annual rental payments as defined in the lease agreements. The office space lease also includes an option to renew the lease as of the end of the term. The Company has determined that the lease renewal option is not reasonably certain of being exercised. The cash paid for operating lease liabilities for each of the three months ended March 31, 2023 and 2022 was $0.1 million. Supplemental other information related to the operating leases balance sheet information is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ December 31, 2022 ​ Operating lease obligations (see Note 5 and 7) $ 1,015 $ 1,124 ​ Operating lease right-of-use assets (included in "Other assets" in Balance Sheet) ​ $ 541 ​ $ 596 ​ ​ Weighted-average remaining lease term (years) ​ 2.1 ​ 2.3 ​ ​ Weighted-average discount rate ​ 7.2 % 7.2 % ​ ​

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2023
Accrued Expenses and Other Current Liabilities.
Accrued Expenses	5. Accrued Expenses Accrued expenses and other current liabilities consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ December 31, 2022 ​ Accrued professional services $ 299 $ 276 Accrued payroll and employee benefits ​ 1,000 ​ 2,955 ​ Accrued research and development ​ 6,715 ​ 7,295 ​ Lease obligation, current portion (see Note 4) ​ 463 ​ 452 ​ Excess tax refund payable ​ ​ 1,169 ​ ​ 1,169 ​ Accrued interest and other ​ 67 ​ 103 ​ Total accrued expenses and other current liabilities ​ $ 9,713 ​ $ 12,250 ​ ​

Contingent Consideration

Contingent Consideration	3 Months Ended
	Mar. 31, 2023
Contingent Consideration
Contingent consideration	6. Contingent Consideration The Company entered into an Agreement and Plan of Merger and Reorganization, dated July 8, 2019, by and among the Company, Springfield Merger Sub, Inc., Springfield Merger Sub, LLC, Spitfire Pharma, Inc. and David Collier, as the Stockholder Representative (the “Spitfire Merger Agreement”) to acquire all of the equity interests of Spitfire Pharma, Inc. (“Spitfire”). Spitfire was a privately held, preclinical pharmaceutical company developing a novel GLP-1/glucagon receptor dual agonist for the treatment of NASH. The transaction closed on July 12, 2019. The Company issued 1,887,250 unregistered shares of its common stock as upfront consideration to certain former securityholders of Spitfire, representing an amount equal to $5.0 million less working capital and transaction expense adjustment amounts as defined in the agreement. The acquisition of Spitfire was accounted for as an asset acquisition instead of a business combination because substantially all of the fair value of the gross assets acquired was concentrated in a single identifiable asset or group of similar identifiable assets, and therefore, the asset was not considered a business. The Company expensed the acquired intellectual property as of the acquisition date as in-process research and development with no alternative future uses. The Spitfire Merger Agreement also includes future contingent payments up to $88.0 million payable in either cash or shares of the Company’s common stock as follows: ● a one-time payment of $5.0 million (the “IND Milestone Consideration Amount”) within sixty days of the submission of an Investigational New Drug Application (“IND”) to the United States Food and Drug Administration (the “FDA”) or other applicable governmental authority in a foreign jurisdiction, which IND has not been rejected or placed on clinical hold by the FDA or such applicable foreign governmental authority within time specified in the Spitfire Merger Agreement. In November 2020, the Company issued 1,694,906 shares of its common stock to fully satisfy the obligations under the IND Milestone. ● a one-time payment of $3.0 million (the “Phase 2 Milestone Consideration Amount” and together with the IND Milestone Consideration Amount, the “Regulatory Milestones”) within sixty days of the initiation (first patient, first dosing) of the first Phase 2 clinical trial of a product candidate anywhere in the world. In June 2022 the Company issued 847,444 shares of its common stock to fully satisfy the obligations under the Phase 2 Milestone. ● payments of up to $80.0 million upon the achievement of specified worldwide net sales (the “Sales Milestones”) of all products developed using the technology acquired in the License Agreement within ten years following the approval of a new drug application filed with the FDA. The contingent payments related to the Sales Milestones are predominately cash-based payments accounted for under FASB Accounting Standards Codification Topic 450, Contingencies During the three months ended March 31, 2022, the Company recognized $1.8 million gain from change in fair value of contingent consideration liability. Any changes in fair value have been recorded within research and development expense during the respective periods presented. As described above, the Company fully satisfied the contingent consideration liability in June 2022. As of March 31, 2023 and December 31, 2022, the Company had no contingent consideration liability. ​

Other Long-Term Liabilities

Other Long-Term Liabilities	3 Months Ended
	Mar. 31, 2023
Other Long-Term Liabilities
Other Long-Term Liabilities	7. Other Long-Term Liabilities The Company’s other long-term liabilities are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ December 31, 2022 ​ Research and development incentive credit ​ $ 3,542 ​ $ 3,599 ​ Lease obligation, long-term portion (see Note 4) ​ 552 ​ 672 Conditional economic incentive grants ​ 250 ​ 250 ​ Other ​ 56 ​ 60 ​ Total other long-term liabilities ​ $ 4,400 ​ $ 4,581 ​ ​

Common Stock

Common Stock	3 Months Ended
	Mar. 31, 2023
Common Stock
Common Stock	8. Common Stock The Amended and Restated Certificate of Incorporation, as amended (“Charter”), authorizes the Company to issue 200,000,000 shares of common stock, par value $0.0001 per share. As of March 31, 2023, the Company had 49,286,710 shares of common stock issued and outstanding Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors. The Charter also authorizes the Company to issue 1,000,000 shares of preferred stock, par value $0.0001 per share. As of March 31, 2023, the Company had no shares of preferred stock issued and outstanding At-the-Market Offerings On February 28, 2023, the Company entered into an Equity Distribution Agreement (the “2023 Agreement”) with Evercore Group L.L.C., JMP Securities LLC and B. Riley Securities, Inc., serving as sales agents (the “Sales Agents”) with respect to an at-the-market offerings program under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock, having an aggregate offering price of up to $150.0 million (the “Shares”) through the Sales Agents (the “2023 Offering”). All Shares offered and sold in the 2023 Offering will be issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on February 28, 2023, which was declared effective immediately, the prospectus supplement relating to the 2023 Offering filed with the SEC on February 28, 2023 and any applicable additional prospectus supplements related to the 2023 Offering that form a part of the Registration Statement. The Company capitalized approximately $0.2 million of other offering costs which will offset the proceeds received from the shares sold under the 2023 Agreement. No shares were sold under the 2023 Agreement during the three months ended March 31, 2023, and as of March 31, 2023, $150.0 million remained available to be sold under the 2023 Agreement. As of March 31, 2023, there was $0.2 million deferred offering costs included in prepaid expenses and other current assets on the accompanying consolidated balance sheets. On February 25, 2021, the Company entered into an Equity Distribution Agreement (the “2021 Agreement”) with Piper Sandler & Co., Evercore Group L.L.C. and B. Riley Securities, Inc., serving as sales agents (the “2021 Sales Agents”) with respect to an at-the-market offerings program under which the Company offered and sold shares of its common stock, having an aggregate offering price of up to $125.0 million (the “2021 Shares”) through the 2021 Sales Agents (the “2021 Offering”). All 2021 Shares offered and sold in the 2021 Offering were issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on December 31, 2020, which was declared effective on January 11, 2021, the prospectus supplement relating to the 2021 Offering filed with the SEC on February 25, 2021 and any applicable additional prospectus supplements related to the 2021 Offering that form a part of the Registration Statement. Under the 2021 Agreement, the Company sold 10,004,869 shares of common stock resulting in approximately $121.0 million in proceeds, net of $4.0 million commission and other offering costs. As of March 31, 2023, there were no remaining shares available under the 2021 Agreement. Exchange Agreement On February 25, 2021, the Company entered into an exchange agreement (the “Exchange Agreement”) with an Investor and its affiliates (the “Exchanging Stockholders”), pursuant to which the Company exchanged an aggregate of 1,000,000 shares of common stock, owned by the Exchanging Stockholders for pre-funded warrants (the “Exchange Warrants”) to purchase an aggregate of 1,000,000 shares of common stock (subject to adjustment in the event of any stock dividends and splits, reverse stock split, recapitalization, reorganization or similar transaction, as described in the Exchange Warrants), with an exercise price of $0.0001 per share. On January 24, 2022, the Exchange Warrants to purchase 1,000,000 shares were net exercised, resulting in the issuance of 999,984 shares of common stock, and no Exchange Warrants remain outstanding. Public Offering On July 16, 2020, the Company offered and sold (i) 3,369,564 shares of common stock, at a price to the public of $23.00 per share, and (ii) pre-funded warrants of the Company to purchase 1,630,436 shares of common stock at an exercise price equal to $0.0001 per share (the “Pre-Funded Warrants”), at a price to the public of $22.9999 per share of common stock underlying the Pre-Funded Warrants (equal to the public offering price per share of common stock, minus the exercise price of each Pre-Funded Warrant). The Pre-Funded Warrants are exercisable at any time, provided that each Pre-Funded Warrant holder will be prohibited from exercising such Pre-Funded Warrants into shares of the Company’s common stock if, as a result of such exercise, the holder, together with its affiliates, would own more than 4.99% of the total number of shares of the Company’s common stock then issued and outstanding, which percentage may change at the holders’ election to any other number less than or equal to 19.99% upon 61 days’ notice to the Company. The Company has assessed the Pre-Funded Warrants for appropriate equity or liability classification and determined that the Pre-Funded Warrants are freestanding instruments that do not meet the definition of a liability pursuant to ASC 480 and do not meet the definition of a derivative pursuant to FASB Accounting Standards Codification Topic 815, Derivatives and Hedging As of March 31, 2023, including the remaining 869,566 Pre-Funded Warrants, there were 1,015,166 outstanding warrants with a weighted-average exercise price of $0.66 and weighted-average contractual term of 0.7 years.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2023
Stock-Based Compensation
Stock-Based Compensation	9. Stock-Based Compensation Stock Options The Company’s stock option awards generally vest over four years and typically have a contractual life of ten years. As of March 31, 2023, there was $20.5 million of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted-average period of 3.1 years. During the three months ended March 31, 2023, the Company granted 1,159,725 stock options with a weighted average exercise price of $12.81 and per share weighted average grant date fair value of $10.42. Information related to stock options outstanding as of March 31, 2023 is as follows (in thousands, except share, exercise price and contractual term): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ Weighted- ​ Remaining ​ ​ ​ ​ ​ Number of ​ Average ​ Contractual Term ​ Aggregate Intrinsic ​ ​ Stock Options ​ Exercise Price ​ (Years) ​ Value Outstanding 4,479,330 ​ $ 10.06 6.0 ​ $ 29,683 Exercisable 1,836,727 ​ $ 8.66 5.8 ​ $ 15,131 Unvested 2,642,603 ​ $ 11.03 6.0 ​ $ 14,552 ​ Restricted Stock Units (RSUs) During the three months ended March 31, 2023, the Company granted 319,700 shares of RSUs with a weighted average grant date fair value of $13.20 which vest over four years. As of March 31, 2023, the Company had unvested RSUs of 629,793 shares with total unrecognized compensation expense of $6.1 million, which the Company expects to recognize over a weighted average period of approximately 3.2 years. During the three months ended March 31, 2023, the Company issued 54,347 shares of unrestricted common stock as a result of the vesting of 89,392 RSUs net of 35,045 shares of common stock withheld to satisfy tax withholding obligations. 2019 Employee Stock Purchase Plan Under the Employee Stock Purchase Plan, employees purchased 13,215 shares for $0.1 million during the three months ended March 31, 2023. During the three months ended March 31, 2023, the Company recognized compensation expense of $0.1 million. Stock-based Compensation Expense Stock-based compensation expense is classified in the unaudited consolidated statements of operations and comprehensive loss for the three months ended March 31, 2023 and 2022 as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months Ended ​ ​ March 31, ​ ​ 2023 2022 Research and development ​ $ 1,187 ​ $ 618 General and administrative ​ 1,488 ​ 1,415 Total ​ $ 2,675 ​ $ 2,033 ​

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2023
Net Loss Per Share
Net Loss Per Share	10. Net Loss Per Share Because the Company has reported a net loss attributable to common stockholders for the three months ended March 31, 2023 and 2022, basic and diluted net loss per share attributable to common stockholders in each period are the same. Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average numbers of shares of common stock outstanding for the period. Basic shares outstanding includes the weighted average effect of the Company’s outstanding pre-funded warrants, the exercise of which requires little or no consideration for the delivery of shares of common stock. Diluted net loss per share is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period. As such, all unvested restricted stock, RSUs, common stock warrants, and stock options have been excluded from the computation of diluted weighted average shares outstanding because such securities would have an anti-dilutive impact for all periods presented. Potential common shares issuable upon conversion, vesting or exercise of unvested restricted stock, RSUs, common stock warrants, and stock options that are excluded from the computation of diluted weighted-average shares outstanding, as they are anti-dilutive, are as follows: ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ 2023 ​ 2022 Common stock warrants 145,600 145,755 Common stock options 4,494,994 3,479,992 Restricted stock units 629,793 ​ 446,837 Restricted stock — 53,818 ​

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2023
Commitments And Contingencies.
Commitments and Contingencies	11. Commitments and Contingencies Spitfire Acquisition As disclosed in Note 6, the Company is obligated to make payments of up to $80.0 million upon the achievement of specified worldwide net sales of all products developed using the technology acquired from Spitfire Pharma Inc. within ten years following the approval of a new drug application filed with the FDA. Litigation In December 2019, a complaint was filed by Dr. De-chu Christopher Tang (“Plaintiff”) against the Company, which the Company removed to the United States District Court for the Eastern District of Texas. The Plaintiff amended the complaint in February 2020 to include Vipin K. Garg and David J. Drutz as defendants, in addition to the Company (Dr. Garg, Dr. Drutz, and the Company are collectively referred to as “Defendants”). In March 2020 the Defendants filed a motion to dismiss the complaint. On March 25, 2021, the court granted the motion and dismissed the action for lack of personal jurisdiction. In December 2021, the Plaintiff refiled the case in the United States District Court for the District of Maryland, captioned Tang v. Altimmune, Inc., et al The Company is a party in various contracts and subject to disputes, litigation, and potential claims arising in the ordinary course of business none of which are currently reasonably possible or probable of material loss.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2023
Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of these financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not limited to, the valuation of share-based awards, income taxes, and accruals for research and development activities. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. However, actual results could differ from those estimates and there may be changes to the Company’s estimates in future periods.
Short-term Investments	Short-term Investments The Company’s short-term investments are comprised of U.S. Treasuries, corporate debt securities and certificates of deposit that have original maturities less than or equal to one year and are classified as available-for-sale (“AFS”) securities. Such securities are carried at estimated fair value, net of allowance for credit loss determined based on the Current Expected Credit Loss. Any unrealized holding gains or losses are reported as accumulated other comprehensive income or loss, which is a separate component of stockholders’ equity. In the event that the AFS security's fair value is below the amortized cost and (i) the Company intends to sell the AFS security and (ii) the AFS security is required to be sold before recovery of the loss, the AFS security's amortized cost base will be written down to its fair value and the loss will be recognized in the income statement. If the Company intends not to sell the AFS security and the AFS security is not required to be sold before recovery of the loss, the Company evaluates whether a portion of the unrealized loss is a result of credit loss. The portion of unrealized loss related to credit loss will be recorded as allowance for credit loss in the balance sheet with the corresponding credit loss in the income statement and the portion of unrealized loss not related to credit loss will be recognized in other comprehensive income (“OCI”). Dividend and interest income are recognized in other income when earned. The cost of securities sold is calculated using the specific identification method. The Company places all investments with government agencies, or corporate institutions whose debt is rated as investment grade. As of March 31, 2023, none of the unrealized losses on our short-term investments are a result of credit loss, and therefore, the unrealized losses were recognized in OCI.
Income Taxes	Income Taxes Due to a full valuation allowance, the Company did not record an income tax expense (benefit) for either of the three months ended March 31, 2023 or 2022. The Company calculates its quarterly income tax provision based on an estimated, annual effective tax rates applied to ordinary income (or loss) and other known items computed and recognized as they occur. The Company’s total provision is based on the United States statutory rate, increased by state and foreign taxes and reduced by a full valuation allowance on the Company’s deferred tax assets.
Recently Adopted Accounting Pronouncements	Recently adopted accounting pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU No. 2016-13”)

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2023
Fair Value Measurements
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	The Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2023 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at March 31, 2023 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents - money market funds ​ $ 100,611 ​ $ 100,611 ​ $ — ​ $ — Short-term investments ​ 61,039 ​ — ​ 61,039 ​ — Total ​ $ 161,650 ​ $ 100,611 ​ $ 61,039 ​ $ — ​ The Company’s assets and liabilities measured at fair value on a recurring basis as of December 31, 2022 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at December 31, 2022 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents - money market funds ​ $ 105,794 $ 105,794 ​ $ — ​ $ — Short-term investments ​ 73,783 ​ — ​ 73,783 ​ — Total ​ $ 179,577 ​ $ 105,794 ​ $ 73,783 ​ $ —
Schedule of Short Term Investments	Short-term investments have been initially valued at the transaction price and subsequently valued at the end of each reporting period utilizing third party pricing services or other market observable data (Level 2). The pricing services utilize industry standard valuation models, including both income and market-based approaches and observable market inputs to determine value. Short-term investments with quoted prices as of March 31, 2023 as shown below (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ ​ Amortized Cost ​ Unrealized (Loss) Gain ​ Credit loss ​ Market Value United States treasury securities $ 15,718 $ (15) $ — $ 15,703 Commercial paper and corporate debt securities ​ ​ 37,982 ​ ​ (27) ​ ​ — ​ ​ 37,955 Asset backed securities ​ 5,448 ​ (20) ​ — ​ 5,428 Agency debt securities ​ ​ 1,952 ​ ​ 1 ​ ​ — ​ ​ 1,953 Total ​ $ 61,100 ​ $ (61) ​ $ — ​ $ 61,039 ​ Short-term investments with quoted prices as of December 31, 2022 as shown below (in thousand): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 ​ ​ Amortized Cost ​ Unrealized (Loss) Gain ​ Credit Loss ​ Market Value United States treasury securities $ 15,868 $ (86) $ — $ 15,782 Commercial paper and corporate debt securities ​ ​ 50,747 ​ ​ (71) ​ ​ — ​ ​ 50,676 Asset backed securities ​ 5,427 ​ (35) ​ — ​ 5,392 Agency debt securities ​ ​ 1,928 ​ ​ 5 ​ ​ — ​ ​ 1,933 Total ​ $ 73,970 ​ $ (187) ​ $ — ​ $ 73,783 ​

Operating Leases (Tables)

Operating Leases (Tables)	3 Months Ended
	Mar. 31, 2023
Leases
Summary of Supplemental other Information Related to Operating Leases Balance Sheet	Supplemental other information related to the operating leases balance sheet information is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ December 31, 2022 ​ Operating lease obligations (see Note 5 and 7) $ 1,015 $ 1,124 ​ Operating lease right-of-use assets (included in "Other assets" in Balance Sheet) ​ $ 541 ​ $ 596 ​ ​ Weighted-average remaining lease term (years) ​ 2.1 ​ 2.3 ​ ​ Weighted-average discount rate ​ 7.2 % 7.2 % ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2023
Accrued Expenses and Other Current Liabilities.
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ December 31, 2022 ​ Accrued professional services $ 299 $ 276 Accrued payroll and employee benefits ​ 1,000 ​ 2,955 ​ Accrued research and development ​ 6,715 ​ 7,295 ​ Lease obligation, current portion (see Note 4) ​ 463 ​ 452 ​ Excess tax refund payable ​ ​ 1,169 ​ ​ 1,169 ​ Accrued interest and other ​ 67 ​ 103 ​ Total accrued expenses and other current liabilities ​ $ 9,713 ​ $ 12,250 ​

Other Long-Term Liabilities (Ta

Other Long-Term Liabilities (Tables)	3 Months Ended
	Mar. 31, 2023
Other Long-Term Liabilities
Summary of Other Long-Term Liabilities	The Company’s other long-term liabilities are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2023 ​ December 31, 2022 ​ Research and development incentive credit ​ $ 3,542 ​ $ 3,599 ​ Lease obligation, long-term portion (see Note 4) ​ 552 ​ 672 Conditional economic incentive grants ​ 250 ​ 250 ​ Other ​ 56 ​ 60 ​ Total other long-term liabilities ​ $ 4,400 ​ $ 4,581 ​

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2023
Stock-Based Compensation
Schedule of Information Related to Stock Options Outstanding	Information related to stock options outstanding as of March 31, 2023 is as follows (in thousands, except share, exercise price and contractual term): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ Weighted- ​ Remaining ​ ​ ​ ​ ​ Number of ​ Average ​ Contractual Term ​ Aggregate Intrinsic ​ ​ Stock Options ​ Exercise Price ​ (Years) ​ Value Outstanding 4,479,330 ​ $ 10.06 6.0 ​ $ 29,683 Exercisable 1,836,727 ​ $ 8.66 5.8 ​ $ 15,131 Unvested 2,642,603 ​ $ 11.03 6.0 ​ $ 14,552 ​
Schedule of Stock-based Compensation Expense	Stock-based compensation expense is classified in the unaudited consolidated statements of operations and comprehensive loss for the three months ended March 31, 2023 and 2022 as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ For the Three Months Ended ​ ​ March 31, ​ ​ 2023 2022 Research and development ​ $ 1,187 ​ $ 618 General and administrative ​ 1,488 ​ 1,415 Total ​ $ 2,675 ​ $ 2,033

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2023
Net Loss Per Share
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Potential common shares issuable upon conversion, vesting or exercise of unvested restricted stock, RSUs, common stock warrants, and stock options that are excluded from the computation of diluted weighted-average shares outstanding, as they are anti-dilutive, are as follows: ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ ​ March 31, ​ ​ 2023 ​ 2022 Common stock warrants 145,600 145,755 Common stock options 4,494,994 3,479,992 Restricted stock units 629,793 ​ 446,837 Restricted stock — 53,818

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Summary of Significant Accounting Policies
Income tax expense (benefit)	$ 0	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 61,039	$ 73,783
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	61,039	73,783
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	161,650	179,577
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	100,611	105,794
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	61,039	73,783
Money Market Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	100,611	105,794
Money Market Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 100,611	$ 105,794

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Short Term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 61,100	$ 73,970
Unrealized (Loss) Gain	(61)	(187)
Market Value	61,039	73,783
United States Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,718	15,868
Unrealized (Loss) Gain	(15)	(86)
Market Value	15,703	15,782
Commercial Paper and Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	37,982	50,747
Unrealized (Loss) Gain	(27)	(71)
Market Value	37,955	50,676
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	5,448	5,427
Unrealized (Loss) Gain	(20)	(35)
Market Value	5,428	5,392
Agency Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,952	1,928
Unrealized (Loss) Gain	1	5
Market Value	$ 1,953	$ 1,933

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Fair Value Measurements
Assets or liabilities measured at fair value on a non-recurring basis.	$ 0	$ 0

Operating Leases - Additional I

Operating Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Leases
Cash paid for operating lease liabilities	$ 0.1	$ 0.1
Operating lease rent expense	$ 0.2	$ 0.1

Operating Leases - Summary of S

Operating Leases - Summary of Supplemental other Information Related to Operating Leases Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Leases
Operating lease obligations (see Note 5 and 7)	$ 1,015	$ 1,124
Operating lease right-of-use assets (included in "Other assets" in Balance Sheet)	$ 541	$ 596
Weighted-average remaining lease term (years)	2 years 1 month 6 days	2 years 3 months 18 days
Weighted-average discount rate	7.20%	7.20%

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Accrued Liabilities And Other Liabilities [Abstract]
Accrued professional services	$ 299	$ 276
Accrued payroll and employee benefits	1,000	2,955
Accrued research and development	6,715	7,295
Lease obligation, current portion (see Note 4)	463	452
Excess tax refund payable	1,169	1,169
Accrued interest and other	67	103
Total accrued expenses and other current liabilities	$ 9,713	$ 12,250

Contingent Consideration - Addi

Contingent Consideration - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended
	Jul. 12, 2019	Jun. 30, 2022	Nov. 30, 2020	Mar. 31, 2022	Mar. 31, 2023	Dec. 31, 2022
Business Acquisition [Line Items]
Estimated future contingent consideration					$ 0	$ 0
Change in value of contingent consideration for acquired in-process research and development				$ (1,780)
Spitfire Pharma, Inc. [Member]
Business Acquisition [Line Items]
Agreement date	Jul. 08, 2019
Unregistered shares of common stock	1,887,250
Up-front consideration	$ 5,000
Spitfire Pharma, Inc. [Member] | Investigational New Drug Application Milestone [Member]
Business Acquisition [Line Items]
Estimated future contingent consideration	$ 5,000
Estimated future contingent consideration term	60 days
Shares issued for contingent milestone payment			1,694,906
Spitfire Pharma, Inc. [Member] | Investigational New Drug Application and Regulatory Milestones [Member]
Business Acquisition [Line Items]
Estimated future contingent consideration	$ 3,000
Estimated future contingent consideration term	60 days
Shares issued for contingent milestone payment		847,444
Spitfire Pharma, Inc. [Member] | Sales Milestones [Member]
Business Acquisition [Line Items]
Estimated future contingent consideration	$ 80,000
License agreement term	10 years
Spitfire Pharma, Inc. [Member] | Common Stock [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated future contingent consideration	$ 88,000

Other Long-Term Liabilities - S

Other Long-Term Liabilities - Summary of Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Other Long-Term Liabilities
Research and development incentive credit	$ 3,542	$ 3,599
Lease obligation, long-term portion (see Note 4)	552	672
Conditional economic incentive grants	250	250
Other	56	60
Total other long-term liabilities	$ 4,400	$ 4,581

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended		12 Months Ended
	Feb. 28, 2023	Jan. 24, 2022	Feb. 25, 2021	Jul. 16, 2020	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Changes In Equity And Comprehensive Income Line Items [Line Items]
Proceeds from issuance of common stock in public offering						$ 2,990
Common stock, shares authorized					200,000,000		200,000,000
Common stock, par or stated value per share					$ 0.0001		$ 0.0001
Common stock, shares issued					49,286,710		49,199,845
Common stock, shares outstanding					49,286,710		49,199,845
Preferred stock, shares authorized					1,000,000
Preferred stock, par or stated value per share					$ 0.0001
Preferred stock, shares issued					0
Preferred stock, shares outstanding					0
Warrants outstanding					1,015,166
Exercise price of warrants or rights					$ 0.66
Weighted average remaining contractual term, warrants					8 months 12 days
Pre-Funded Warrants [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Number of securities called by warrants or rights		760,870
Shares of common stock sold		760,870
Warrants outstanding					869,566
Common Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Shares of common stock sold						335,485
Exchange Warrants [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Number of securities called by warrants or rights			1,000,000
Number Of Warrants Exercised		1,000,000
Common stock exchanged for pre-funded warrants			1,000,000
Shares of common stock sold		999,984
Warrants outstanding		0
Exercise price of warrants or rights			$ 0.0001
Public Offering [Member] | Pre-Funded Warrants [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Purchase price of warrants issued				$ 22.9999
Ownership percentage on exercise of warrants without notice, minimum				4.99%
Ownership percentage on exercise of warrants with notice, maximum				19.99%
Notice period to increase ownership percentage on exercise of warrants				61 days
Exercise price of warrants or rights				$ 0.0001
Public Offering [Member] | Common Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price, per share				$ 23
Shares of common stock sold				3,369,564
Public Offering [Member] | Common Stock [Member] | Pre-Funded Warrants [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Number of securities called by warrants or rights				1,630,436
At-The-Market Offering [Member] | Equity Distribution Agreement [Member] | Evercore Group and JMP Securities LLC and B Riley Securities [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock available to be sold					$ 150,000
Deferred Offering Costs	$ 200				$ 200
Aggregate offering price	$ 150,000
Shares of common stock sold					0
At-The-Market Offering [Member] | Equity Distribution Agreement [Member] | Piper Sandler company and Evercore group limited liability company and B Riley Securities inc [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Proceeds from issuance of common stock in public offering							$ 121,000
Aggregate offering price			$ 125,000
Shares of common stock sold							10,004,869
Issuance costs							$ 4,000
Remaining shares available for issuance							0

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employees purchased, value	$ 135	$ 113
Stock-based compensation expense	$ 2,675	$ 2,033
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Stock Options, Granted	1,159,725
Stock options granted, weighted-average exercise price	$ 12.81
Stock option expiration Period	10 years
Weighted-average grant date fair value of stock options granted	$ 10.42
Unrecognized compensation cost, stock options	$ 20,500
Unrecognized stock-based compensation expense, period for recognition	3 years 1 month 6 days
Restricted stock vesting period	4 years
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense, period for recognition	3 years 2 months 12 days
Restricted stock authorized and granted	319,700
Weighted average grant date fair value of restricted stock award	$ 13.20
Unrestricted common stock	54,347
Common stock issued as result of vesting of restricted stock	89,392
Common stock withheld to satisfy tax withholding obligations.	35,045
Unvested restricted stock, shares	629,793
Unrecognized compensation expense	$ 6,100
Restricted stock vesting period	4 years
Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrestricted common stock	54,347	17,568
Employees purchased, shares	13,215	16,450
2019 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employees purchased, shares	13,215
Employees purchased, value	$ 100
Stock-based compensation expense	$ 100

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Information Related to Stock Options Outstanding (Detail)	3 Months Ended
	Mar. 31, 2023 USD ($) $ / shares shares
Stock-Based Compensation
Number of Stock Options, Outstanding | shares	4,479,330
Number of Stock Options, Exercisable | shares	1,836,727
Number of Stock Options, Unvested | shares	2,642,603
Weighted-average Exercise Price, Outstanding | $ / shares	$ 10.06
Weighted-average Exercise Price, Exercisable | $ / shares	8.66
Weighted-average Exercise Price, Unvested | $ / shares	$ 11.03
Weighted-average Remaining Contractual Term, Outstanding	6 years
Weighted-average Remaining Contractual Term, Exercisable	5 years 9 months 18 days
Weighted-average Remaining Contractual Term, Unvested	6 years
Aggregate Intrinsic Value, Outstanding | $	$ 29,683
Aggregate Intrinsic Value, Exercisable | $	15,131
Aggregate Intrinsic Value, Unvested | $	$ 14,552

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 2,675	$ 2,033
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	1,187	618
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 1,488	$ 1,415

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	145,600	145,755
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,494,994	3,479,992
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	629,793	446,837
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		53,818

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	Jul. 12, 2019	Mar. 31, 2023	Dec. 31, 2022
Commitments And Contingencies [Line Items]
Estimated future contingent consideration		$ 0	$ 0
Spitfire Pharma, Inc. [Member] | Sales Milestones [Member]
Commitments And Contingencies [Line Items]
Estimated future contingent consideration	$ 80
License agreement term	10 years