Alpine Immune Sciences (ALPN) 10-Q 10 Nov 21 2021 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2021	Oct. 28, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-37449
Entity Registrant Name	ALPINE IMMUNE SCIENCES, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8969493
Entity Address, Address Line One	188 East Blaine Street, Suite 200
Entity Address, City or Town	Seattle
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98102
City Area Code	206
Local Phone Number	788-4545
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	ALPN
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		29,220,176
Entity Central Index Key	0001626199
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 76,099	$ 34,959
Short-term investments	104,529	70,622
Prepaid expenses and other current assets	3,121	1,520
Total current assets	183,749	107,101
Restricted cash, noncurrent	254	254
Property and equipment, net	1,372	1,785
Operating lease, right-of-use asset	8,980	9,401
Long-term investments	39,064	25,549
Deferred tax asset	61	0
Total assets	233,480	144,090
Current liabilities:
Accounts payable	1,839	582
Accrued liabilities	8,653	5,777
Deferred revenue, current	48,100	31,627
Operating lease liability, current	747	655
Current portion of long-term debt	4,594	2,526
Total current liabilities	63,933	41,167
Deferred revenue, noncurrent	30,961	21,348
Operating lease liability, noncurrent	11,214	11,815
Long-term debt	4,547	7,602
Total liabilities	110,655	81,932
Commitments and contingencies
Convertible preferred stock, $0.001 par value per share; 10,000,000 shares authorized at September 30, 2021 and December 31, 2020; zero shares issued and outstanding at September 30, 2021 and December 31, 2020	0	0
Stockholders’ equity:
Common stock, $0.001 par value per share; 200,000,000 shares authorized at September 30, 2021 and December 31, 2020; 30,468,159 shares issued and 29,217,692 shares outstanding at September 30, 2021; 23,853,650 shares issued and 23,803,183 shares outstanding at December 31, 2020	29	24
Treasury stock, at cost; 1,250,467 shares at September 30, 2021 and 50,467 at December 31, 2020	0	0
Additional paid-in capital	273,813	177,947
Accumulated other comprehensive gain	15	53
Accumulated deficit	(151,032)	(115,866)
Total stockholders’ equity	122,825	62,158
Total liabilities and stockholders’ equity	$ 233,480	$ 144,090

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	30,468,159	23,853,650
Common stock, shares outstanding (in shares)	29,217,692	23,803,183
Treasury stock, shares (in shares)	1,250,467	50,467
Convertible preferred stock
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Convertible preferred stock, shares issued (in shares)	0	0
Convertible preferred stock, shares outstanding (in shares)	0	0

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Collaboration revenue	$ 8,516	$ 1,913	$ 18,913	$ 3,692
Operating expenses:
Research and development	18,309	6,156	43,380	18,130
General and administrative	3,470	2,728	10,016	7,850
Total operating expenses	21,779	8,884	53,396	25,980
Loss from operations	(13,263)	(6,971)	(34,483)	(22,288)
Other income (expense):
Interest expense	(203)	(214)	(638)	(560)
Interest income	52	11	166	202
Other income	0	1,037	0	1,042
Loss before taxes	(13,414)	(6,137)	(34,955)	(21,604)
Income tax (expense) benefit	(80)	0	(211)	6
Net loss	(13,494)	(6,137)	(35,166)	(21,598)
Comprehensive income (loss):
Unrealized loss on investments	(17)	0	(1)	(16)
Unrealized (loss) gain on foreign currency translation	(13)	14	(37)	(35)
Comprehensive loss	$ (13,524)	$ (6,123)	$ (35,204)	$ (21,649)
Weighted-average shares used to compute basic net loss per share (in shares)	24,724,442	22,277,146	24,169,993	19,826,985
Weighted-average shares used to compute diluted net loss per share (in shares)	24,724,442	22,277,146	24,169,993	19,826,985
Basic net loss per share (in dollars per share)	$ (0.55)	$ (0.28)	$ (1.45)	$ (1.09)
Diluted net loss per share (in dollars per share)	$ (0.55)	$ (0.28)	$ (1.45)	$ (1.09)
Revenue from Contract with Customer, Product and Service [Extensible Enumeration]	Collaboration [Member]	Collaboration [Member]	Collaboration [Member]	Collaboration [Member]

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Treasury	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		18,587,892	50,467
Beginning balance at Dec. 31, 2019	$ 29,474	$ 19	$ 0	$ 117,371	$ 10	$ (87,926)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	986			986
Issuance of warrants	60			60
Unrealized gain (loss) on investments	(15)				(15)
Unrealized gain (loss) on foreign currency translation	(113)				(113)
Net loss	(5,533)					(5,533)
Ending balance (in shares) at Mar. 31, 2020		18,587,892	50,467
Ending balance at Mar. 31, 2020	24,859	$ 19	$ 0	118,417	(118)	(93,459)
Beginning balance (in shares) at Dec. 31, 2019		18,587,892	50,467
Beginning balance at Dec. 31, 2019	29,474	$ 19	$ 0	117,371	10	(87,926)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on investments	(16)
Unrealized gain (loss) on foreign currency translation	(35)
Net loss	(21,598)
Ending balance (in shares) at Sep. 30, 2020		23,803,183	50,467
Ending balance at Sep. 30, 2020	67,468	$ 24	$ 0	177,009	(41)	(109,524)
Beginning balance (in shares) at Mar. 31, 2020		18,587,892	50,467
Beginning balance at Mar. 31, 2020	24,859	$ 19	$ 0	118,417	(118)	(93,459)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,232			1,232
Exercise of stock options (in shares)		3,339
Exercise of stock options	2			2
Unrealized gain (loss) on investments	(1)				(1)
Unrealized gain (loss) on foreign currency translation	64				64
Net loss	(9,928)					(9,928)
Ending balance (in shares) at Jun. 30, 2020		18,591,231	50,467
Ending balance at Jun. 30, 2020	16,228	$ 19	$ 0	119,651	(55)	(103,387)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	973			973
Issuance of Units/common stock, net of offering costs (in shares)		5,139,610
Issuance of Units/common stock, net of offering costs	56,271	$ 5		56,266
Issuance of common stock under equity incentive plans (in shares)		72,342
Issuance of common stock under equity incentive plans	119			119
Unrealized gain (loss) on investments	0
Unrealized gain (loss) on foreign currency translation	14				14
Net loss	(6,137)					(6,137)
Ending balance (in shares) at Sep. 30, 2020		23,803,183	50,467
Ending balance at Sep. 30, 2020	67,468	$ 24	$ 0	177,009	(41)	(109,524)
Beginning balance (in shares) at Dec. 31, 2020		23,803,183	50,467
Beginning balance at Dec. 31, 2020	62,158	$ 24	$ 0	177,947	53	(115,866)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,597			1,597
Issuance of common stock under equity incentive plans (in shares)		78,955
Issuance of common stock under equity incentive plans	202			202
Unrealized gain (loss) on investments	(5)				(5)
Unrealized gain (loss) on foreign currency translation	(15)				(15)
Net loss	(10,643)					(10,643)
Ending balance (in shares) at Mar. 31, 2021		23,882,138	50,467
Ending balance at Mar. 31, 2021	53,294	$ 24	$ 0	179,746	33	(126,509)
Beginning balance (in shares) at Dec. 31, 2020		23,803,183	50,467
Beginning balance at Dec. 31, 2020	62,158	$ 24	$ 0	177,947	53	(115,866)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on investments	(1)
Unrealized gain (loss) on foreign currency translation	(37)
Net loss	(35,166)
Ending balance (in shares) at Sep. 30, 2021		29,217,692	1,250,467
Ending balance at Sep. 30, 2021	122,825	$ 29	$ 0	273,813	15	(151,032)
Beginning balance (in shares) at Mar. 31, 2021		23,882,138	50,467
Beginning balance at Mar. 31, 2021	53,294	$ 24	$ 0	179,746	33	(126,509)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,545			1,545
Exercise of stock options (in shares)		32,741
Exercise of stock options	9			9
Unrealized gain (loss) on investments	21				21
Unrealized gain (loss) on foreign currency translation	(9)				(9)
Net loss	(11,029)					(11,029)
Ending balance (in shares) at Jun. 30, 2021		23,914,879	50,467
Ending balance at Jun. 30, 2021	43,831	$ 24	$ 0	181,300	45	(137,538)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,638			1,638
Exercise of stock options (in shares)		13,456
Exercise of stock options	69			69
Issuance of Units/common stock, net of offering costs (in shares)		6,489,357
Issuance of Units/common stock, net of offering costs	90,811	$ 6		90,805
Exchange of common stock for prefunded warrants (in shares)		(1,200,000)	1,200,000
Exchange of common stock for prefunded warrants	0	$ (1)		1
Unrealized gain (loss) on investments	(17)				(17)
Unrealized gain (loss) on foreign currency translation	(13)				(13)
Net loss	(13,494)					(13,494)
Ending balance (in shares) at Sep. 30, 2021		29,217,692	1,250,467
Ending balance at Sep. 30, 2021	$ 122,825	$ 29	$ 0	$ 273,813	$ 15	$ (151,032)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net loss	$ (35,166)	$ (21,598)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	482	419
Amortization of premium/discount on investments	602	(60)
Non-cash interest expense	213	192
Deferred income tax	(61)	0
Stock-based compensation expense	4,780	3,191
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,500)	272
Right-of-use asset	421	458
Accounts payable and accrued liabilities	4,133	(1,276)
Deferred revenue	26,086	57,058
Lease liabilities	(509)	777
Net cash (used in) provided by operating activities	(519)	39,433
Investing activities
Purchases of property and equipment	(69)	(314)
Purchase of investments	(99,957)	(4,967)
Maturities of investments	51,831	29,311
Net cash (used in) provided by investing activities	(48,195)	24,030
Financing activities
Proceeds from borrowings, net of issuance costs	0	5,000
Proceeds from sale of common stock and warrants, net of offering costs	90,812	56,271
Repayment of debt	(1,200)	0
Proceeds from exercise of stock options	279	121
Net cash provided by financing activities	89,891	61,392
Effect of exchange rate on cash, cash equivalents and restricted cash	(37)	(35)
Net increase in cash and cash equivalents and restricted cash	41,140	124,820
Cash and cash equivalents and restricted cash, beginning of period	35,213	16,509
Cash and cash equivalents and restricted cash, end of period	76,353	141,329
Supplemental Information
Discount in connection with issuance of debt	0	335
Cash paid for interest	$ 432	$ 345

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Alpine Immune Sciences, Inc. (the “Company”, “Alpine”, “we”, “us”, or “our”), together with its consolidated subsidiaries, is a clinical-stage biopharmaceutical company dedicated to discovering and developing innovative, protein-based immunotherapies to treat cancer and autoimmune and inflammatory diseases. Our approach includes a proprietary scientific platform that converts native immune system proteins into differentiated, multi-targeted therapeutics. We believe our strategies are capable of meaningfully modulating the human immune system and significantly improving outcomes in patients with serious diseases. We were incorporated under the laws of the State of Delaware and are headquartered in Seattle, Washington. A novel strain of coronavirus, SARS-CoV-2 (“COVID-19”), was first reported in December 2019, and subsequently declared a global pandemic by the World Health Organization in March 2020. As a result of the COVID-19 outbreak, many companies have experienced disruptions in their operations and in markets served. We have implemented some and may take additional temporary precautionary measures intended to help ensure the well-being of our employees and minimize business disruption. We considered the impact of COVID-19 on the assumptions and estimates used and determined that there were no material adverse impacts to our results of operations and financial position at September 30, 2021. The full extent of the future impacts of the continuing COVID-19 outbreak on our operations is uncertain and may adversely impact our business, including our clinical trials.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation and Use of Estimates The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (“SEC”) and generally accepted accounting principles in the United States of America (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the amounts reported in the unaudited condensed consolidated financial statements and accompanying notes. Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include those used for revenue recognition, accruals for clinical trial activities and other accruals, and the estimated fair value of equity-based awards. We base our estimates and assumptions on historical experience when available and on various factors we believe to be reasonable under the circumstances. Actual results could differ materially from those estimates. The accompanying unaudited condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 and the related interim information contained within the notes to the condensed consolidated financial statements are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited financial statements and in the opinion of management, reflect all normal recurring adjustments necessary for a fair statement of our financial position for the interim periods presented. The accompanying unaudited condensed consolidated financial statements should be read in conjunction with our audited consolidated financial statements and accompanying notes for the years ended December 31, 2020 and December 31, 2019 included in our Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 18, 2021 (“Annual Report”). The results of our operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the full year. Principles of Consolidation Our unaudited condensed consolidated financial statements include the financial position and results of operations of Alpine Immune Sciences, Inc. and our wholly owned operating company and subsidiary, AIS Operating Co., Inc., and our wholly-owned subsidiary, Alpine Immune Sciences Australia PTY LTD. All inter-company balances and transactions have been eliminated in consolidation. Cash and Cash Equivalents and Restricted Cash We consider all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking and interest-bearing accounts, and highly liquid money market funds. Restricted cash represents cash drawn on our line of credit used to establish collateral to support the security deposit on our operating lease to rent office and laboratory space in Seattle, Washington. Periodically, we maintain deposits in financial institutions in excess of government insured limits. We believe we are not exposed to significant credit risk as our deposits, which are held at financial institutions, are high credit quality securities such as money market funds, U.S. Treasury securities, and commercial paper. To date, we have not realized any losses on these deposits. Investments Our investments include funds invested in highly liquid money market funds, U.S. Treasury securities, commercial paper, and corporate debt securities with a final maturity of each security of less than two years. These investments are classified as available-for-sale debt securities, which are recorded at fair value based on quoted prices in active markets. We classify our investments maturing within one year of the reporting date as short-term investments. If the estimated fair value of a debt security is below its amortized cost basis, we evaluate whether it is more likely than not that we will sell the security before its anticipated recovery in market value. If an impairment exists, the security is written down to its estimated fair value and we consider whether credit losses exist for the related securities. A credit loss exists if the present value of expected cash flows is less than the amortized cost basis of the security. Credit-related losses are recognized as an allowance for credit losses on the balance sheet with a corresponding adjustment to earnings. Unrealized gains and losses that are unrelated to credit deterioration are reported in other comprehensive income (loss). Purchase premiums and discounts are recognized as interest income using the interest method over the terms of the securities. Realized gains and losses and declines in fair value deemed to be other than temporary are reflected in the Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) using the specific-identification method. Revenue Recognition Revenue is recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Our steps for recognizing revenue consist of; (1) identifying the contract, (2) identifying the performance obligations as either distinct or bundled goods and services, (3) determining the transaction price associated with each performance obligation for which we expect to be entitled in exchange for transferring such goods and services, (4) allocating the transaction price to the performance obligations in the contract and (5) recognizing revenue upon satisfaction of performance obligations. Our collaboration agreements principally contain multiple performance obligations, which may include (1) grants of, or options to obtain, intellectual property licenses; (2) research and development services; and/or (3) manufacturing or supply services. Payments typically received under these arrangements include one or more of the following: non-refundable upfront license fees, option exercise fees, payment for research and/or development efforts, amounts due upon the achievement of specified objectives, and/or royalties on future product sales. Our revenue is primarily derived from our collaboration agreements with Adaptimmune Therapeutics plc (“Adaptimmune”) and AbbVie Ireland Unlimited Company (“AbbVie”). See further discussion of our collaboration agreements in Note 9 . We allocate revenue to each performance obligation based on its relative stand-alone selling price. We generally determine stand-alone selling prices at the inception of the contract based on our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying Condensed Consolidated Balance Sheets and recognized as revenue when the related revenue recognition criteria are met. We recognize revenue under our collaboration agreements based on employee hours contributed to each performance obligation, or by using a cost-based input method to measure progress toward completion of the performance obligation and to calculate the corresponding revenue to recognize each period. Our collaboration agreements provide for non-refundable milestone payments. We recognize revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to us for such milestone (1) is consistent with our performance necessary to achieve the milestone or the increase in value to the collaboration resulting from our performance; (2) relates solely to our past performance; and (3) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, we consider all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial, and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. We review the contributed employee hours and progress towards completion for each performance obligation under our collaboration agreements, and adjust the revenue recognized to reflect changes in assumptions relating to the estimated satisfaction of the performance obligation. We could accelerate revenue recognition in the event of early termination of programs or if our expectations change. Alternatively, we could decelerate revenue recognition if programs are extended or delayed. While such changes to our estimates have no impact on our reported cash flows, the timing of revenue recorded in future periods could be materially impacted. Recently Adopted Accounting Pronouncements

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding during the period. The common stock issuable upon the conversion or exercise of the following dilutive securities has been excluded from the diluted net loss per share calculation because their effect would have been anti-dilutive. Diluted net loss per share, therefore, does not differ from basic net loss per share for the periods presented. September 30, 2021 2020 (unaudited) Warrants to purchase common stock 8,851,116 4,464,261 Stock options and restricted stock units outstanding 5,692,264 4,136,352 Total 14,543,380 8,600,613

Cash Equivalents and Investment

Cash Equivalents and Investments	9 Months Ended
	Sep. 30, 2021
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash Equivalents and Investments	Cash Equivalents and Investments The amortized cost and fair value of our cash equivalents and investments are as follows (in thousands): September 30, 2021 (unaudited) Assets: Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 74,116 $ — $ — $ 74,116 U.S. treasury bills 30,004 7 (9) 30,002 Corporate debt securities and commercial paper 113,589 12 (10) 113,591 Total $ 217,709 $ 19 $ (19) $ 217,709 Classified as: Cash equivalents $ 74,116 Short-term investments 104,529 Long-term investments 39,064 Total $ 217,709 December 31, 2020 Assets: Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 28,424 $ — $ — $ 28,424 U.S. treasury bills 18,122 8 — 18,130 Corporate debt securities and commercial paper 82,047 2 (9) 82,040 Total $ 128,593 $ 10 $ (9) $ 128,594 Classified as: Cash equivalents $ 32,423 Short-term investments 70,622 Long-term investments 25,549 Total $ 128,594

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Cash and cash equivalents, restricted cash, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. Fair value is defined as the exchange price received for an asset or paid to transfer a liability, or an exit price, in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs supported by little or no market activity and significant to the fair value of the assets or liabilities. As of September 30, 2021 and December 31, 2020, cash of $2.0 million and $2.5 million, respectively, is excluded from the fair value table below. The following tables summarize our financial assets and liabilities measured at fair value on a recurring basis (in thousands): September 30, 2021 (unaudited) Assets: Level 1 Level 2 Level 3 Total Money market funds $ 74,116 $ — $ — $ 74,116 U.S. treasury bills 30,002 — — $ 30,002 Corporate debt securities and commercial paper — 113,591 — 113,591 Total $ 104,118 $ 113,591 $ — $ 217,709 December 31, 2020 Assets: Level 1 Level 2 Level 3 Total Money market funds $ 28,424 $ — $ — $ 28,424 U.S. treasury bills 18,130 — — 18,130 Corporate debt securities and commercial paper — 82,040 — 82,040 Total $ 46,554 $ 82,040 $ — $ 128,594

Additional Balance Sheet Inform

Additional Balance Sheet Information	9 Months Ended
	Sep. 30, 2021
Disclosure Text Block Supplement [Abstract]
Additional Balance Sheet Information	Additional Balance Sheet Information Prepaid expenses and other current assets consist of the following (in thousands): September 30, 2021 December 31, 2020 (unaudited) Prepaid research and development $ 1,536 $ 517 Prepaid insurance 435 447 Deferred financing 291 — Tenant improvement allowance receivable — 84 Prepaid other 305 168 Other receivables 554 304 Prepaid expenses and other current assets $ 3,121 $ 1,520 Accrued liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 (unaudited) Research and development services $ 5,599 $ 2,571 Employee compensation 1,635 2,619 Legal and professional fees 629 482 Accrued taxes 451 1 Accrued other 339 104 Accrued Liabilities $ 8,653 $ 5,777

Long-term Debt

Long-term Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Long-term Debt	Long-term Debt In December 2016, we entered into a Loan and Security Agreement (the “Original Agreement”), with Silicon Valley Bank (“SVB”), under which we borrowed $5.0 million. The Original Agreement accrued interest at a floating per annum rate equal to the lender’s prime rate minus 1.75%. The Original Agreement had an interest-only period through July 2018. In August 2019 (the “Effective Date”), we entered into an Amended and Restated Loan and Security Agreement (the “Loan Agreement”) with SVB, pursuant to which SVB agreed to extend term loans to us with an aggregate principal amount of up to $15.0 million (the “Term Loans”). Borrowings under the Loan Agreement consisted of up to three separate tranches. The initial tranche of $5.0 million was funded in August 2019, $3.0 million of which was used to repay amounts owing under our Original Agreement. In March 2020, the second tranche of $5.0 million was funded to us. We did not draw down the final tranche of $5.0 million, which expired on July 31, 2020. We intend to use the debt proceeds for working capital and other general corporate purposes, including the advancement of our development programs. The Term Loans accrue interest at a floating per annum rate of 0.25% above the prime rate, subject to a floor of 5.75%, which interest is payable monthly commencing in September 2019. Upon the occurrence and during the continuance of an event of default, a default interest rate will apply that is 4.0% above the otherwise applicable interest rate. The Term Loans were interest only until September 30, 2020, however, under the Loan Agreement our interest only period automatically extended to June 30, 2021 if we received aggregate new capital of at least $40.0 million no later than June 30, 2020. We met this milestone in June 2020 in conjunction with the execution of the AbbVie agreement, discussed in detail in Note 9 . As a result of the interest only extension, the Term Loans will be payable in 25 equal monthly installments of principal plus interest, with the final installment due and payable on July 1, 2023. We may prepay all of the Term Loans subject to a prepayment fee equal to $75,000, which represents the deferred portion of the final payment due under the Original Agreement, plus the outstanding principal balance under the Term Loans at the time of such prepayment multiplied by a prepayment fee of 2.0% in the first year, 1.0% in the second year, and 0% in the third year and thereafter. Additionally, a final payment in the amount of 5.5% of the funded Term Loans is payable to SVB on the date on which the Term Loans are prepaid, paid or become due and payable in full. The final payment fees are recorded in long-term debt with an offsetting reduction to debt discount on our accompanying Condensed Consolidated Balance Sheets . The Loan Agreement contains customary representations and warranties, events of default and affirmative and negative covenants, including, among others, covenants that limit or restrict our ability to, among other things, incur additional indebtedness, grant liens, merge or consolidate, make acquisitions, pay dividends or other distributions or repurchase equity, make investments, dispose of assets, engage in any new lines of business, and enter into certain transactions with affiliates, in each case subject to certain exceptions. We assessed the likelihood of the lender accelerating payment of the loan due to a material adverse change in our business, operations, financial, or other condition as remote. We were in compliance with our covenants as of September 30, 2021. As such, as of September 30, 2021, the classification of the loan is split between current and noncurrent based on the timing of payment obligations. As security for its obligations under the Loan Agreement, we granted SVB a first priority security interest on substantially all of our assets, except intellectual property, and subject to certain other exceptions. In connection with the Loan Agreement, we issued a warrant to SVB to purchase up to 52,083 shares of our common stock at a price of $4.32 per share, 17,361 shares of which became exercisable in August 2019 after we drew down the initial tranche. In March 2020, after we drew down the second tranche of our Term Loan, an additional 17,361 shares became exercisable. The remaining warrants did not vest and expired on July 31, 2020, upon the expiration of the third tranche of our Term Loan. The fair value of the warrants on the date of issuance for the initial tranche and second tranche was $60,000 and $60,000, respectively, determined using the Black-Scholes option-pricing model, and was recorded as a component of equity and as a debt discount on our accompanying Condensed Consolidated Balance Sheets . In connection with Original Agreement, SVB also holds 7,069 fully vested common stock warrants at an exercise price of $12.38 per share. The Term Loan was accounted for as a debt modification in a non-troubled debt restructuring, rather than a debt extinguishment, based on a comparison of the present value of the cash flows under the terms of the debt immediately before and after the Effective Date of the Term Loan, which resulted in a change of less than 10%. As a result, the remaining unamortized debt discount recorded in connection with the Original Agreement will be amortized to interest expense over the repayment term of Loan Agreement. In connection with the initial and second tranches of the Loan Agreement, we recorded a total debt discount of $812,000, which is being amortized to interest expense using the effective interest method over the repayment term of the loan. Non-cash interest expense associated with the amortization of the discount was $67,000 and $67,000 for the three months ended September 30, 2021 and 2020, respectively, and $213,000 and $192,000 for the nine months ended September 30, 2021 and 2020, respectively. The unamortized discount was $284,000 as of September 30, 2021. Scheduled principal payments on our outstanding debt as of September 30, 2021 under our Loan Agreement, excluding final fee amounts, are as follows (in thousands): Year ending December 31, Total 2021 (remainder of year, unaudited) $ 1,200 2022 4,800 2023 2,800 Total future principal payments $ 8,800

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Certain credits received related to our research and development expenditures and recorded within other income in our accompanying Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) are subject to review by foreign taxing authorities. It is reasonably possible we may incur losses upon the completion of these reviews ranging from $0 to $1.8 million, which we could be required to repay to certain tax authorities.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements AbbVie In June 2020, we entered into an option and license agreement with AbbVie (the “AbbVie Agreement”) for the development of ALPN-101, (“acazicolcept”). The AbbVie Agreement grants AbbVie the exclusive option to purchase an exclusive worldwide license to acazicolcept (the “License Option”). The License Option is exercisable by AbbVie at any time and will expire 90 days from the achievement of certain development milestones. If AbbVie exercises the License Option, AbbVie will take over the future development and commercialization. Prior to the exercise of the License Option, we will perform research and development services, including conducting a Phase 2 study in systemic lupus erythematosus, based on an agreed-upon development plan (the “Development Plan”). We will be fully responsible for all costs incurred to conduct the activities under the Development Plan, provided that, AbbVie may be responsible for increased costs under the Development Plan in connection with certain material amendments proposed by AbbVie. We will also be solely responsible, at our sole cost and expense, for manufacturing and regulatory filings for acazicolcept necessary to complete activities under the Development Plan. In June 2020, in connection with the execution of the AbbVie Agreement, AbbVie paid us a nonrefundable upfront payment of $60.0 million. Prior to the exercise of the License Option, AbbVie has agreed to make cash payments upon our achievement of certain predefined pre-option development milestones (the “Alpine Development Milestones”) up to an aggregate amount of $75.0 million. In the third quarter of 2021, we received $45.0 million of the Alpine Development Milestones, which was achieved in June 2021. If AbbVie exercises the License Option, they will pay a one-time cash payment of $75.0 million. Following the exercise of the License Option, AbbVie has also agreed to make aggregate cash payments of up to $205.0 million upon AbbVie’s achievement of certain development and commercial milestones and additional aggregate cash payments of up to $450.0 million upon AbbVie’s achievement of certain sales-based cash milestones, collectively referred to as (the “AbbVie Milestones”). Subsequent to commercialization, we are also eligible to receive high single-digit to low double-digit percentage royalties on worldwide net sales of licensed products. For revenue recognition purposes, we determined that our contractual promises in the AbbVie Agreement are not distinct and are interdependent with our performance obligation to provide research and development services under the Development Plan. Thus, all contractual promises related to the upfront payment and Alpine’s Development Milestones were combined into a single performance obligation. We determined the Alpine Development Milestone payments are probable of significant revenue reversal as the achievement is highly dependent on factors outside our control. Therefore, these milestone payments were fully constrained and were not initially included in the transaction price. In June 2021, we re-evaluated and updated the transaction price to include the achieved portion of the Alpine Development Milestones. We will continue to re-evaluate the transaction price each reporting period and update as uncertain events are resolved or other changes in circumstances occur. The License Option and the AbbVie Milestones were not determined to be performance obligations at the inception of the contract as they did not represent material rights. If exercised, the License Option and AbbVie Milestones will be accounted for as a separate contract and will be recognized as revenue if and when triggered. Any consideration related to sales-based royalties and profit-sharing payments will be recognized when the related sales occur. We use a cost-based input method to measure progress toward completion of the performance obligation and to calculate the corresponding revenue to recognize each period. In applying the cost-based input, we use actual costs incurred relative to budgeted costs for the combined performance obligation. These costs consist primarily of internal personnel efforts and third-party contract costs relative to the level of patient enrollment in the study. Revenue will be recognized based on the level of costs incurred relative to the total budgeted costs for the performance obligation. A cost-based input method of revenue recognition requires management to make estimates of costs to complete our performance obligation. In making such estimates, significant judgment is required to evaluate assumptions related to cost estimates. The cumulative effect of revisions to estimated costs to complete our performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. A significant change in these assumptions and estimates could have a material impact on the timing and amount of revenue recognized in future periods. We recognized revenue from the AbbVie Agreement of $8.5 million and $1.6 million for the t hree months ended September 30, 2021 and 2020, respectively, and $18.9 million and $1.6 million for the nine months ended September 30, 2021, and 2020, respectively. As of September 30, 2021 the remaining balance of the transaction price is $79.1 million and is recorded as current and noncurrent deferred revenue on our accompanying Condensed Consolidated Balance Sheets . We expect to recognize the remaining deferred revenue over the remainder of our Development Plan, which began in June 2020 and ends upon the later of the exercise or expiration of the option. In May 2019, we entered into a collaboration and licensing agreement with Adaptimmune (the “Adaptimmune Agreement”) to develop next-generation SPEAR T cell products. Under the Adaptimmune Agreement, we are to perform certain research services and grant Adaptimmune an exclusive license to programs from our secreted immunomodulatory protein (“SIP”) and transmembrane immunomodulatory protein (“TIP”) technologies. In June 2019, under the terms of the Adaptimmune Agreement, we received an upfront license payment of $2.0 million, and through September 30, 2021 we have received an additional $1.6 million in research support payments to fund ongoing programs. These payments were recorded as deferred revenue upon receipt and were recognized to revenue based on employee hours contributed to each performance obligation. In the fourth quarter of 2020, based on the completion of our initial research and development efforts in connection with our performance obligations, we recognized the remaining balance in deferred revenue associated with Adaptimmune on our accompanying Condensed Consolidated Balance Sheets . Under the Adaptimmune Agreement we recognized revenue of $356,000 and $2.0 million for the three and nine months ended September 30, 2020, respectively .

Stockholders_ Equity

Stockholders’ Equity	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Stockholders’ Equity	Stockholders’ Equity Securities Offering In September 2021, we entered into a securities purchase agreement (the “Securities Purchase Agreement”) for a private placement with a select group of institutional investors, pursuant to which we sold 6,489,357 shares of our common stock (the “Shares”) and prefunded warrants to purchase 3,191,487 Shares (the “Prefunded Warrants”). The purchase price for each Share and for each Prefunded Warrant was $9.40 per share, for an aggregate purchase price of approximately $91.0 million. The Prefunded Warrants became fully exercisable upon the closing date and have an exercise price of $0.001 per share. We incurred $188,000 in financing costs associated with the Securities Purchase Agreement, which was netted against the proceeds within additional-paid-in-capital on our accompanying Condensed Consolidated Balance Sheets . In September 2021, we entered into an exchange agreement (the “Exchange Agreement”) with Frazier Life Sciences VIII, L.P. (the “Exchanging Stockholder”), which Exchanging Stockholder is affiliated with a member of our board of directors, pursuant to which we exchanged an aggregate of 1,200,000 shares of common stock held by the Exchanging Stockholder for Prefunded Warrants (the “Exchange Warrants”) to purchase an aggregate of 1,200,000 shares of common stock. Upon the closing of the exchange, we reclassified 1,200,000 shares of common stock into treasury stock on our accompanying Condensed Consolidated Balance Sheets . Financing Agreements In July 2021, we entered into a sales agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”) pursuant to which we may sell shares of our common stock from time to time through an “at the market” equity offering for up to $75.0 million in gross cash proceeds. Cowen will act as the sales agent and will be entitled to compensation for services of up to 3.0% of the gross sales price per share of all shares sold through Cowen under the Sales Agreement. The shares would be issued pursuant to our effective shelf registration statement on Form S-3 (File No. 333-256107), declared effective by the SEC on May 20, 2021. We filed a prospectus supplement, dated July 2, 2021, with the SEC in connection with the offer and sale of the shares pursuant to the Sales Agreement. As of September 30, 2021, no sales have been made under the Sales Agreement. In June 2018, we entered into an equity distribution agreement, (“Equity Distribution Agreement”), with Piper Jaffray & Co., (“Piper Jaffray”), pursuant to which we may sell shares of our common stock through an “at the market” equity offering program for up to $50.0 million in gross cash proceeds. The Equity Distribution Agreement was terminated by us upon written notice to Piper Jaffray in March 2021. No sales were made under the Equity Distribution Agreement. Equity Incentive Plans On January 1, 2021, in connection with our 2018 Equity Incentive Plan (the “2018 Plan”) annual increase provision, a total of 1,190,159 additional shares were automatically added to the shares authorized under the 2018 Plan. During the nine months ended September 30, 2021, we issued stock option grants totaling 1,711,518 shares with a weighted average exercise price of $12.41 per share to eligible employees and board members. Stock-Based Compensation Expense We use the Black-Scholes option pricing model to estimate the fair value of stock options granted at the grant date. We recognize the fair value of stock-based compensation as compensation expense over the requisite service period, which is the vesting period. Stock-based compensation is classified in the Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) as follows (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 (unaudited) Employee: Research and development $ 929 $ 462 $ 2,575 $ 1,687 General and administrative 702 501 2,182 1,473 Non-Employee: Research and development 7 8 21 26 General and administrative — 2 2 5 Total stock-based compensation expense $ 1,638 $ 973 $ 4,780 $ 3,191

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We are subject to income taxes in the United States and Australia and our effective tax rate is calculated quarterly based upon current assumptions relating to the full year’s estimated operating results and various tax-related items. Each quarter an estimate of the annual effective tax rate is updated should we revise our forecast of earnings based upon our operating results. If there is a change in the estimated effective annual tax rate, a cumulative adjustment is made. Our effective tax rate was 0.61% and (0.03)% for the nine months ended September 30, 2021 and 2020, respectively. The difference between the effective tax rate of 0.61% and (0.03)% for the nine months ended September 30, 2021 and 2020, respectively, and the U.S. federal statutory rate of 21% for the nine months ended September 30, 2021 and 2020, was primarily due to recognizing a full valuation allowance on deferred tax assets. As of September 30, 2021, we determined that, based on an evaluation of the four sources of income and all available evidence, both positive and negative, including our latest forecasts and cumulative losses in recent years, it was more likely than not that none of our domestic deferred tax assets would be realized and therefore we continued to record a full valuation allowance. As of September 30, 2021, we determined that it was more likely than not that our foreign deferred tax assets would be realized. As such, we removed the valuation allowance previously in place against our foreign deferred tax assets as we have generated sufficient foreign taxable income to utilize all historical operating losses and are expecting future foreign taxable income. We recorded current tax liabilities and expense of $274,000 and $0 in the financial statements for the nine months ended September 30, 2021 and 2020, respectively. We recorded deferred tax benefits of $63,000 and $0 in the financial statements for the nine months ended September 30, 2021 and 2020, respectively. Our $63,000 deferred tax benefit was recorded in June 2021 due to the removal of the valuation allowance previously in place against our foreign deferred tax assets.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (“SEC”) and generally accepted accounting principles in the United States of America (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the amounts reported in the unaudited condensed consolidated financial statements and accompanying notes. Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include those used for revenue recognition, accruals for clinical trial activities and other accruals, and the estimated fair value of equity-based awards. We base our estimates and assumptions on historical experience when available and on various factors we believe to be reasonable under the circumstances. Actual results could differ materially from those estimates. The accompanying unaudited condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 and the related interim information contained within the notes to the condensed consolidated financial statements are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited financial statements and in the opinion of management, reflect all normal recurring adjustments necessary for a fair statement of our financial position for the interim periods presented. The accompanying unaudited condensed consolidated financial statements should be read in conjunction with our audited consolidated financial statements and accompanying notes for the years ended December 31, 2020 and December 31, 2019 included in our Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 18, 2021 (“Annual Report”). The results of our operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the full year.
Principles of Consolidation	Principles of ConsolidationOur unaudited condensed consolidated financial statements include the financial position and results of operations of Alpine Immune Sciences, Inc. and our wholly owned operating company and subsidiary, AIS Operating Co., Inc., and our wholly-owned subsidiary, Alpine Immune Sciences Australia PTY LTD. All inter-company balances and transactions have been eliminated in consolidation.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash We consider all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking and interest-bearing accounts, and highly liquid money market funds. Restricted cash represents cash drawn on our line of credit used to establish collateral to support the security deposit on our operating lease to rent office and laboratory space in Seattle, Washington. Periodically, we maintain deposits in financial institutions in excess of government insured limits. We believe we are not exposed to significant credit risk as our deposits, which are held at financial institutions, are high credit quality securities such as money market funds, U.S. Treasury securities, and commercial paper. To date, we have not realized any losses on these deposits.
Investments	Investments Our investments include funds invested in highly liquid money market funds, U.S. Treasury securities, commercial paper, and corporate debt securities with a final maturity of each security of less than two years. These investments are classified as available-for-sale debt securities, which are recorded at fair value based on quoted prices in active markets. We classify our investments maturing within one year of the reporting date as short-term investments. If the estimated fair value of a debt security is below its amortized cost basis, we evaluate whether it is more likely than not that we will sell the security before its anticipated recovery in market value. If an impairment exists, the security is written down to its estimated fair value and we consider whether credit losses exist for the related securities. A credit loss exists if the present value of expected cash flows is less than the amortized cost basis of the security. Credit-related losses are recognized as an allowance for credit losses on the balance sheet with a corresponding adjustment to earnings. Unrealized gains and losses that are unrelated to credit deterioration are reported in other comprehensive income (loss). Purchase premiums and discounts are recognized as interest income using the interest method over the terms of the securities. Realized gains and losses and declines in fair value deemed to be other than temporary are reflected in the Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) using the specific-identification method.
Revenue Recognition	Revenue Recognition Revenue is recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Our steps for recognizing revenue consist of; (1) identifying the contract, (2) identifying the performance obligations as either distinct or bundled goods and services, (3) determining the transaction price associated with each performance obligation for which we expect to be entitled in exchange for transferring such goods and services, (4) allocating the transaction price to the performance obligations in the contract and (5) recognizing revenue upon satisfaction of performance obligations. Our collaboration agreements principally contain multiple performance obligations, which may include (1) grants of, or options to obtain, intellectual property licenses; (2) research and development services; and/or (3) manufacturing or supply services. Payments typically received under these arrangements include one or more of the following: non-refundable upfront license fees, option exercise fees, payment for research and/or development efforts, amounts due upon the achievement of specified objectives, and/or royalties on future product sales. Our revenue is primarily derived from our collaboration agreements with Adaptimmune Therapeutics plc (“Adaptimmune”) and AbbVie Ireland Unlimited Company (“AbbVie”). See further discussion of our collaboration agreements in Note 9 . We allocate revenue to each performance obligation based on its relative stand-alone selling price. We generally determine stand-alone selling prices at the inception of the contract based on our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying Condensed Consolidated Balance Sheets and recognized as revenue when the related revenue recognition criteria are met. We recognize revenue under our collaboration agreements based on employee hours contributed to each performance obligation, or by using a cost-based input method to measure progress toward completion of the performance obligation and to calculate the corresponding revenue to recognize each period. Our collaboration agreements provide for non-refundable milestone payments. We recognize revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to us for such milestone (1) is consistent with our performance necessary to achieve the milestone or the increase in value to the collaboration resulting from our performance; (2) relates solely to our past performance; and (3) is reasonable relative to all of the other deliverables and payments within the
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting PronouncementsIn December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2019-12, Income Taxes (“Topic 740”): Simplifying the Accounting for Income Taxes. This ASU simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and also improves consistent application by clarifying and amending existing guidance. The standard is effective for fiscal years and interim periods within those fiscal years, beginning after December 15, 2020. We adopted this standard on January 1, 2021, and concluded that the adoption of the standard did not have a material impact on our consolidated financial statements and related disclosures.
Net Loss Per Share	Net Loss Per ShareBasic net loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding during the period.
Fair Value Measurements	Fair Value Measurements Cash and cash equivalents, restricted cash, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. Fair value is defined as the exchange price received for an asset or paid to transfer a liability, or an exit price, in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs supported by little or no market activity and significant to the fair value of the assets or liabilities.
Stock-Based Compensation Expense	Stock-Based Compensation Expense

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Diluted Net Loss Per Share Attributable to Common Stockholders	The common stock issuable upon the conversion or exercise of the following dilutive securities has been excluded from the diluted net loss per share calculation because their effect would have been anti-dilutive. Diluted net loss per share, therefore, does not differ from basic net loss per share for the periods presented. September 30, 2021 2020 (unaudited) Warrants to purchase common stock 8,851,116 4,464,261 Stock options and restricted stock units outstanding 5,692,264 4,136,352 Total 14,543,380 8,600,613

Cash Equivalents and Investme_2

Cash Equivalents and Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Summary of Amortized Cost and Fair Value of Cash Equivalents and Short Term Investments	The amortized cost and fair value of our cash equivalents and investments are as follows (in thousands): September 30, 2021 (unaudited) Assets: Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 74,116 $ — $ — $ 74,116 U.S. treasury bills 30,004 7 (9) 30,002 Corporate debt securities and commercial paper 113,589 12 (10) 113,591 Total $ 217,709 $ 19 $ (19) $ 217,709 Classified as: Cash equivalents $ 74,116 Short-term investments 104,529 Long-term investments 39,064 Total $ 217,709 December 31, 2020 Assets: Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 28,424 $ — $ — $ 28,424 U.S. treasury bills 18,122 8 — 18,130 Corporate debt securities and commercial paper 82,047 2 (9) 82,040 Total $ 128,593 $ 10 $ (9) $ 128,594 Classified as: Cash equivalents $ 32,423 Short-term investments 70,622 Long-term investments 25,549 Total $ 128,594

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following tables summarize our financial assets and liabilities measured at fair value on a recurring basis (in thousands): September 30, 2021 (unaudited) Assets: Level 1 Level 2 Level 3 Total Money market funds $ 74,116 $ — $ — $ 74,116 U.S. treasury bills 30,002 — — $ 30,002 Corporate debt securities and commercial paper — 113,591 — 113,591 Total $ 104,118 $ 113,591 $ — $ 217,709 December 31, 2020 Assets: Level 1 Level 2 Level 3 Total Money market funds $ 28,424 $ — $ — $ 28,424 U.S. treasury bills 18,130 — — 18,130 Corporate debt securities and commercial paper — 82,040 — 82,040 Total $ 46,554 $ 82,040 $ — $ 128,594

Additional Balance Sheet Info_2

Additional Balance Sheet Information (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Text Block Supplement [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): September 30, 2021 December 31, 2020 (unaudited) Prepaid research and development $ 1,536 $ 517 Prepaid insurance 435 447 Deferred financing 291 — Tenant improvement allowance receivable — 84 Prepaid other 305 168 Other receivables 554 304 Prepaid expenses and other current assets $ 3,121 $ 1,520
Summary of Accrued Liabilities	Accrued liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 (unaudited) Research and development services $ 5,599 $ 2,571 Employee compensation 1,635 2,619 Legal and professional fees 629 482 Accrued taxes 451 1 Accrued other 339 104 Accrued Liabilities $ 8,653 $ 5,777

Long-term Debt (Tables)

Long-term Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	Scheduled principal payments on our outstanding debt as of September 30, 2021 under our Loan Agreement, excluding final fee amounts, are as follows (in thousands): Year ending December 31, Total 2021 (remainder of year, unaudited) $ 1,200 2022 4,800 2023 2,800 Total future principal payments $ 8,800

Stockholders_ Equity (Tables)

Stockholders’ Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Schedule of Stock-based Compensation Expense	Stock-based compensation is classified in the Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) as follows (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 (unaudited) Employee: Research and development $ 929 $ 462 $ 2,575 $ 1,687 General and administrative 702 501 2,182 1,473 Non-Employee: Research and development 7 8 21 26 General and administrative — 2 2 5 Total stock-based compensation expense $ 1,638 $ 973 $ 4,780 $ 3,191

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details)	Sep. 30, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Debt securities, available-for-sale, term (less than)	2 years	2 years

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Anti-dilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	14,543,380	8,600,613
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	8,851,116	4,464,261
Stock options and restricted stock units outstanding
Antidilutive Securities Excluded from Computation of Earnings per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,692,264	4,136,352

Cash Equivalents and Investme_3

Cash Equivalents and Investments - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 217,709	$ 128,593
Gross unrealized gains	19	10
Gross unrealized losses	(19)	(9)
Fair market value	217,709	128,594
Cash equivalents
Debt Securities, Available-for-sale [Line Items]
Fair market value	74,116	32,423
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	104,529	70,622
Long-term investments
Debt Securities, Available-for-sale [Line Items]
Fair market value	39,064	25,549
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	74,116	28,424
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair market value	74,116	28,424
U.S. treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	30,004	18,122
Gross unrealized gains	7	8
Gross unrealized losses	(9)	0
Fair market value	30,002	18,130
Corporate debt securities and commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	113,589	82,047
Gross unrealized gains	12	2
Gross unrealized losses	(10)	(9)
Fair market value	$ 113,591	$ 82,040

Cash Equivalents and Investme_4

Cash Equivalents and Investments - Narrative (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Debt securities, available-for-sale, term (less than)	2 years	2 years
Realized gains (losses) on securities	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Cash	$ 2	$ 2.5

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 217,709	$ 128,594
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	104,118	46,554
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	113,591	82,040
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	74,116	28,424
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	74,116	28,424
Money market funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Money market funds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
U.S. treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	30,002	18,130
U.S. treasury bills | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	30,002	18,130
U.S. treasury bills | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
U.S. treasury bills | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Corporate debt securities and commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	113,591	82,040
Corporate debt securities and commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Corporate debt securities and commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	113,591	82,040
Corporate debt securities and commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 0	$ 0

Additional Balance Sheet Info_3

Additional Balance Sheet Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Disclosure Text Block Supplement [Abstract]
Prepaid research and development	$ 1,536	$ 517
Prepaid insurance	435	447
Deferred financing	291	0
Tenant improvement allowance receivable	0	84
Prepaid other	305	168
Other receivables	554	304
Prepaid expenses and other current assets	$ 3,121	$ 1,520

Additional Balance Sheet Info_4

Additional Balance Sheet Information - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Disclosure Text Block Supplement [Abstract]
Research and development services	$ 5,599	$ 2,571
Employee compensation	1,635	2,619
Legal and professional fees	629	482
Accrued taxes	451	1
Accrued other	339	104
Accrued liabilities	$ 8,653	$ 5,777

Long-term Debt - Narrative (Det

Long-term Debt - Narrative (Details)	1 Months Ended			3 Months Ended		6 Months Ended	9 Months Ended
	Mar. 31, 2020USD ($)shares	Aug. 31, 2019USD ($)tranche$ / sharesshares	Dec. 31, 2016USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)installment	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Jul. 31, 2020USD ($)	Jul. 24, 2017$ / sharesshares
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs							$ 0	$ 5,000,000
Amortization of debt discount				$ 67,000	$ 67,000		213,000	$ 192,000
Unamortized debt discount				$ 284,000			$ 284,000
Maximum
Debt Instrument [Line Items]
Percentage change in loan in a non-troubled debt restructuring (less than) (as a percent)		0.10
Term Loans
Debt Instrument [Line Items]
Debt instrument, total discount recorded		$ 812,000
Term Loans, Tranche One | Term Loans | Common Stock Warrant
Debt Instrument [Line Items]
Fair value of warrant		$ 60,000
Term Loans, Tranche Two | Term Loans | Common Stock Warrant
Debt Instrument [Line Items]
Fair value of warrant	$ 60,000
Silicon Valley Bank | Term Loans
Debt Instrument [Line Items]
Debt instrument variable interest rate (as a percent)		0.25%
Maximum borrowing capacity, amount		$ 15,000,000
Number of tranches (up to) | tranche		3
Percentage of default interest rate (as a percent)		4.00%
New capital milestone for continuation of interest only payment period						$ 40,000,000
Number of equal monthly installments payable | installment						25
Final payment percentage (as a percent)		5.50%
Silicon Valley Bank | Term Loans | Common Stock Warrant
Debt Instrument [Line Items]
Warrants issued (in shares) | shares		52,083
Warrants issued, exercise price (in dollars per share) | $ / shares		$ 4.32
Number of shares exercisable (in shares) | shares	17,361	17,361
Silicon Valley Bank | Term Loans | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Redemption price, percentage (as a percent)		2.00%
Silicon Valley Bank | Term Loans | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Redemption price, percentage (as a percent)		1.00%
Silicon Valley Bank | Term Loans | Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Redemption price, percentage (as a percent)		0.00%
Silicon Valley Bank | Base Rate | Term Loans
Debt Instrument [Line Items]
Debt instrument, interest rate floor (as a percent)		5.75%
Silicon Valley Bank | Original Agreement
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs			$ 5,000,000
Repayments of debt		$ 3,000,000
Prepayment fee (equal to)		75,000
Silicon Valley Bank | Original Agreement | Common Stock Warrant
Debt Instrument [Line Items]
Warrants issued (in shares) | shares										7,069
Warrants issued, exercise price (in dollars per share) | $ / shares										$ 12.38
Silicon Valley Bank | Original Agreement | Prime Rate
Debt Instrument [Line Items]
Debt instrument variable interest rate (as a percent)			1.75%
Silicon Valley Bank | Term Loans, Tranche One | Term Loans
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs		$ 5,000,000
Silicon Valley Bank | Term Loans, Tranche Two | Term Loans
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs	$ 5,000,000
Silicon Valley Bank | Term Loans, Tranche Three | Term Loans
Debt Instrument [Line Items]
Unused borrowing capacity, expired amount									$ 5,000,000

Long-term Debt - Schedule of Ma

Long-term Debt - Schedule of Maturities of Long-term Debt (Details) $ in Thousands	Sep. 30, 2021USD ($)
Debt Disclosure [Abstract]
2021 (remainder of year, unaudited)	$ 1,200
2022	4,800
2023	2,800
Total future principal payments	$ 8,800

Contingencies (Details)

Contingencies (Details) - Foreign Tax Authority	9 Months Ended
	Sep. 30, 2021USD ($)
Minimum
Loss Contingencies [Line Items]
Income tax examination, estimate of possible loss	$ 0
Maximum
Loss Contingencies [Line Items]
Income tax examination, estimate of possible loss	$ 1,800,000

License and Collaboration Agr_2

License and Collaboration Agreements (Details) $ in Thousands	3 Months Ended		9 Months Ended		18 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jun. 30, 2020USD ($)payment	Jun. 30, 2019USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 8,516	$ 1,913	$ 18,913	$ 3,692
AbbVie | Product
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability	79,100		79,100
Potential future revenue recognition, milestone method, number of payments | payment						1
Potential cash payment upon exercising license option						$ 75,000
Potential cash payment upon achievement of certain development and commercial milestones						205,000
Potential cash payment upon achievement of certain sales-based cash milestones						450,000
Revenue	8,500	1,600	18,900	1,600
AbbVie | Product | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)						75,000
AbbVie | Product | Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability						$ 60,000
AbbVie | Product | Achieved Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability	45,000		45,000
Adaptimmune | Product
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue		$ 356		$ 2,000
Adaptimmune | Product | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)	$ 288,000		$ 288,000
Adaptimmune | Product | Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability							$ 2,000
Revenue recognized from contract with customer					$ 2,000
Adaptimmune | Product | Research Support Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract with customer, liability							$ 1,600
Revenue recognized from contract with customer					$ 1,600

Stockholders_ Equity - Narrativ

Stockholders’ Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2021	Sep. 30, 2021	Jul. 31, 2021	Jun. 30, 2018	Sep. 30, 2021
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Gross proceeds from issuance of private placement		$ 91,000
Stock issuance costs incurred		$ 188
Treasury stock, common shares (in shares)		1,200,000			1,200,000
Options, grants in period (in shares)					1,711,518
Grants in period, weighted average exercise price (in dollars per share)					$ 12.41
Financing Agreements | Cowen
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Number of shares issued in transaction (in shares)					0
Maximum amount of common stock eligible to be sold (up to)			$ 75,000
Percentage of compensation for services			3.00%
Equity Distribution Agreement | Piper Jaffray
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Number of shares issued in transaction (in shares)					0
Maximum amount of common stock eligible to be sold (up to)				$ 50,000
2018 Plan
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Number of additional shares authorized (in shares)	1,190,159
Prefunded Warrant Units
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Warrants issued (in shares)		3,191,487			3,191,487
Purchase price per share (in dollars per share)		$ 9.40			$ 9.40
Warrants issued, exercise price (in dollars per share)		$ 0.001			$ 0.001
Exchange Warrants
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Warrants issued (in shares)		1,200,000			1,200,000
Common Stock
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Number of shares issued in transaction (in shares)		6,489,357
Purchase price per share (in dollars per share)		$ 9.40			$ 9.40

Stockholders_ Equity - Stock-Ba

Stockholders’ Equity - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock [Line Items]
Total stock-based compensation expense	$ 1,638	$ 973	$ 4,780	$ 3,191
Employee: | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	929	462	2,575	1,687
Employee: | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	702	501	2,182	1,473
Non-Employee: | Research and development
Class of Stock [Line Items]
Total stock-based compensation expense	7	8	21	26
Non-Employee: | General and administrative
Class of Stock [Line Items]
Total stock-based compensation expense	$ 0	$ 2	$ 2	$ 5

Income Taxes (Details)

Income Taxes (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)income_source	Sep. 30, 2020USD ($)
Income Tax Contingency [Line Items]
Effective tax rate (as a percent)	0.61%	(0.03%)
Difference between effective tax rate from valuation allowance on deferred tax assets (as a percent)	0.61%	(0.03%)
Number of sources of income | income_source	4
Current foreign tax liabilities	$ 274	$ 0
Deferred tax benefit	61	$ 0
Previously Reported
Income Tax Contingency [Line Items]
Deferred tax benefit	$ 63