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Cover - shares	6 Months Ended
Cover - shares	Jun. 30, 2020	Aug. 03, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
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	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		23,784,850
Entity Central Index Key	0001626199
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 88,220	$ 16,123
Short-term investments	1,998	24,397
Restricted cash, current	0	132
Prepaid expenses and other current assets	1,018	1,650
Total current assets	91,236	42,302
Restricted cash, noncurrent	254	254
Property and equipment, net	1,531	1,552
Operating lease, right-of-use asset	9,674	9,985
Total assets	102,695	54,093
Current liabilities:
Accounts payable	548	1,543
Accrued liabilities	3,824	5,285
Deferred revenue, current	23,688	1,435
Current portion of long-term debt	119	418
Total current liabilities	28,179	8,681
Deferred revenue, noncurrent	36,468	0
Operating lease liability, noncurrent	11,947	11,429
Long-term debt	9,873	4,509
Total liabilities	86,467	24,619
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.001 par value per share; 200,000,000 shares authorized at June 30, 2020 and December 31, 2019; 18,641,698 shares issued and 18,591,231 shares outstanding at June 30, 2020; 18,638,359 shares issued and 18,587,892 shares outstanding at December 31, 2019	19	19
Treasury stock, at cost; 50,467 shares at June 30, 2020 and December 31, 2019	0	0
Additional paid-in capital	119,651	117,371
Accumulated other comprehensive gain (loss)	(55)	10
Accumulated deficit	(103,387)	(87,926)
Total stockholders’ equity	16,228	29,474
Total liabilities and stockholders’ equity	$ 102,695	$ 54,093

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
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)	18,641,698	18,638,359
Common stock, shares outstanding (in shares)	18,591,231	18,587,892
Treasury stock, shares (in shares)	50,467	50,467

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Collaboration revenue	$ 688	$ 567	$ 1,779	$ 567
Operating expenses:
Research and development	7,096	10,166	11,974	20,516
General and administrative	3,344	2,553	5,122	4,898
Total operating expenses	10,440	12,719	17,096	25,414
Loss from operations	(9,752)	(12,152)	(15,317)	(24,847)
Other income (expense):
Interest expense	(226)	(61)	(346)	(131)
Interest income	44	357	196	741
Loss before taxes	(9,934)	(11,856)	(15,467)	(24,237)
Income tax benefit	6	0	6	0
Net loss	(9,928)	(11,856)	(15,461)	(24,237)
Comprehensive income (loss):
Unrealized (loss) gain on investments	(1)	17	(16)	32
Unrealized gain (loss) on foreign currency translation	64	4	(49)	(10)
Comprehensive loss	$ (9,865)	$ (11,835)	$ (15,526)	$ (24,215)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	18,588,993	18,576,199	18,588,442	18,126,556
Basic and diluted net loss per share (in dollars per share)	$ (0.53)	$ (0.64)	$ (0.83)	$ (1.34)

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, 2018		13,854,205	50,467
Beginning balance at Dec. 31, 2018	$ 44,591	$ 14	$ 0	$ 90,664	$ (13)	$ (46,074)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued during period (in shares)		4,706,700
Issuance of Units in Private Placement, net of offering costs	23,618	$ 5		23,613
Exercise of stock options (in shares)		124
Exercise of stock options	0
Stock-based compensation	754			754
Unrealized gain (loss) on investments	15				15
Unrealized (loss) gain on foreign currency translation	(14)				(14)
Net loss	(12,381)					(12,381)
Ending balance (in shares) at Mar. 31, 2019		18,561,029	50,467
Ending balance at Mar. 31, 2019	56,583	$ 19	$ 0	115,031	(12)	(58,455)
Beginning balance (in shares) at Dec. 31, 2018		13,854,205	50,467
Beginning balance at Dec. 31, 2018	44,591	$ 14	$ 0	90,664	(13)	(46,074)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on investments	32
Unrealized (loss) gain on foreign currency translation	(10)
Net loss	(24,237)
Ending balance (in shares) at Jun. 30, 2019		18,584,730	50,467
Ending balance at Jun. 30, 2019	45,421	$ 19	$ 0	115,704	9	(70,311)
Beginning balance (in shares) at Mar. 31, 2019		18,561,029	50,467
Beginning balance at Mar. 31, 2019	56,583	$ 19	$ 0	115,031	(12)	(58,455)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Units in Private Placement, net of offering costs	(20)			(20)
Exercise of stock options (in shares)		23,701
Exercise of stock options	11			11
Stock-based compensation	682			682
Unrealized gain (loss) on investments	17				17
Unrealized (loss) gain on foreign currency translation	4				4
Net loss	(11,856)					(11,856)
Ending balance (in shares) at Jun. 30, 2019		18,584,730	50,467
Ending balance at Jun. 30, 2019	45,421	$ 19	$ 0	115,704	9	(70,311)
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]
Issuance of warrants	60			60
Stock-based compensation	986			986
Unrealized gain (loss) on investments	(15)				(15)
Unrealized (loss) gain 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 (loss) gain on foreign currency translation	(49)
Net loss	(15,461)
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)
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]
Exercise of stock options (in shares)		3,339
Exercise of stock options	2			2
Stock-based compensation	1,232			1,232
Unrealized gain (loss) on investments	(1)				(1)
Unrealized (loss) gain 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)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (15,461)	$ (24,237)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	279	229
Amortization of premium/discount on investments	(58)	(185)
Non-cash interest expense	125	67
Stock-based compensation expense	2,218	1,436
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	632	(415)
Right-of-use asset	318	454
Accounts payable and accrued liabilities	(2,467)	1,829
Deferred revenue	58,721	2,108
Lease liabilities	518	(386)
Net cash provided by (used in) operating activities	44,825	(19,100)
Investing activities
Purchases of property and equipment	(254)	(200)
Purchase of short-term investments	(4,871)	(39,804)
Maturities of short-term investments	27,312	40,125
Proceeds from the sale of short-term investments	0	1,391
Net cash provided by investing activities	22,187	1,512
Financing activities
Proceeds from borrowings, net of issuance costs	5,000	0
Proceeds from sale of common stock, net of offering costs	0	23,598
Repayment of debt	0	(1,000)
Proceeds from exercise of stock options	2	11
Net cash provided by financing activities	5,002	22,609
Effect of exchange rate on cash, cash equivalents and restricted cash	(49)	(10)
Net increase in cash and cash equivalents and restricted cash	71,965	5,011
Cash and cash equivalents and restricted cash, beginning of period	16,509	10,843
Cash and cash equivalents and restricted cash, end of period	88,474	15,854
Supplemental Information
Discount in connection with issuance of debt	335	0
Cash paid for interest	198	67
Recognition of right-of-use asset	$ 0	$ 11,757

Description of Business	6 Months Ended
Description of Business	Jun. 30, 2020
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 immunotherapy company committed to leading a new wave of immune therapeutics, creating potentially powerful multifunctional immunotherapies to improve patients’ lives via unique protein engineering technologies. Our approach includes a proprietary scientific platform that uses a process known as directed evolution to convert native immune system proteins into multi-targeted therapeutics potentially capable of modulating the human immune system. 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 June 30, 2020. The full extent of the future impacts of the COVID-19 outbreak on our operations is uncertain. A prolonged outbreak may adversely impact our business, including our clinical trials.

Summary of Significant Accounting Policies	6 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 2020
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 June 30, 2020 and for the three and six months ended June 30, 2020 and 2019 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 December 31, 2019 and 2018 included in our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 30, 2020 (“Annual Report”). The results of our operations for the three and six months ended June 30, 2020 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 lines of credit used to establish collateral to support the security deposit on our operating leases 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. Short-Term Investments Our short-term 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 one year. These investments are classified as available-for-sale debt securities, which are recorded at fair value based on quoted prices in active markets. 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 8. 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 Issued Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes. The objective of the standard is to improve areas of GAAP by removing certain exceptions permitted by ASC Topic 740, Income Taxes, and clarifying existing guidance to facilitate consistent application. The standard will become effective for us beginning on January 1, 2021. We are currently evaluating the new standard to determine the potential impact on our financial condition, results of operations, cash flows, and financial statement disclosures. Recently Adopted Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements: Clarifying the Interaction between Topic 808 and Topic 606. This ASU clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. We adopted this ASU effective January 1, 2020 and it did not have a material impact on our financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement. ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. We adopted this ASU effective January 1, 2020 and it did not have a material impact on our financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments: Credit Losses, as clarified in ASU 2019-04 and ASU 2019-05. The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than-temporary impairments on investment securities are recorded. We adopted this ASU effective January 1, 2020 and it did not have a material impact on our financial statements and related disclosures. We will continue to monitor the impact of the COVID-19 outbreak on expected credit losses.

Net Loss Per Share

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

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.



	June 30,
	2020	2019
	(unaudited)
Warrants to purchase common stock	1,894,455	1,859,733
Stock options and restricted stock units outstanding	4,040,935	3,266,572
Total	5,935,390	5,126,305

Cash Equivalents and Short-Term Investments

6 Months Ended

Jun. 30, 2020

Cash, Cash Equivalents, and Short-term Investments [Abstract]

Cash Equivalents and Short-term Investments

Cash Equivalents and Short-Term Investments

The amortized cost and fair value of our cash equivalents and short-term investments are as follows (in thousands):



	June 30, 2020
Assets:	(unaudited)
	Amortized Cost		Gross unrealized gains		Gross unrealized losses		Fair market value
Money market funds	$	27,053	$	—	$	—	$	27,053
Corporate debt securities and commercial paper	1,998		—		—		1,998
Total	$	29,051	$	—	$	—	$	29,051



	December 31, 2019
Assets:	Amortized Cost		Gross unrealized gains		Gross unrealized losses		Fair market value
Money market funds	$	9,995	$	—	$	—	$	9,995
U.S. treasury bills	5,019		2		—		5,021
Corporate debt securities and commercial paper	21,862		14		—		21,876
Total	$	36,876	$	16	$	—	$	36,892

All short-term investments held as of June 30, 2020 and December 31, 2019 were classified as available-for-sale securities and had contractual maturities of less than one year. There were no realized gains and losses on these securities for the periods presented.

Fair Value Measurements

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

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 June 30, 2020, and December 31, 2019, cash of $61.2 million and $3.6 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):



	June 30, 2020
	(unaudited)
Assets:	Level 1		Level 2		Level 3		Total
Money market funds	$	27,053	$	—	$	—	$	27,053
Corporate debt securities and commercial paper	—		1,998		—		1,998
Total	$	27,053	$	1,998	$	—	$	29,051



	December 31, 2019
Assets:	Level 1		Level 2		Level 3		Total
Money market funds	$	9,995	$	—	$	—	$	9,995
U.S. treasury bills	5,021		—		—		5,021
Corporate debt securities and commercial paper	—		21,876		—		21,876
Total	$	15,016	$	21,876	$	—	$	36,892

Our Level 2 assets consist of commercial paper and corporate debt securities. We review trading activity and pricing for our available-for-sale securities as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data.

- Definition

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

+ References + Details

Additional Balance Sheet Information

6 Months Ended

Jun. 30, 2020

Disclosure Text Block Supplement [Abstract]

Additional Balance Sheet Information

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



	June 30, 2020		December 31, 2019
	(unaudited)
Prepaid research and development	$	580	$	574
Tenant improvement allowance receivable	42		586
Prepaid insurance	90		301
Prepaid other	285		89
Other receivables	21		100
Prepaid expenses and other current assets	$	1,018	$	1,650

Accrued liabilities consist of the following (in thousands):



	June 30, 2020		December 31, 2019
	(unaudited)
Research and development services	$	1,970	$	2,543
Employee compensation	1,073		1,761
Legal and professional fees	687		515
Accrued other	94		466
Accrued Liabilities	$	3,824	$	5,285

Long-term Debt

6 Months Ended

Jun. 30, 2020

Debt Disclosure [Abstract]

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 consist 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 are interest only until September 30, 2020, however, under the Loan Agreement our interest only period automatically extends to June 30, 2021 if we receive 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 AbbVie agreement, discussed in detail in Note 8. 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 June 30, 2020. As such, as of June 30, 2020, 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 $81,000 and $31,000 for the three months ended June 30, 2020 and 2019, respectively, and $125,000 and $67,000 for the six months ended June 30, 2020 and 2019, respectively. The unamortized discount was $632,000 as of June 30, 2020.

Scheduled principal payments on our outstanding debt as of June 30, 2020 under our Loan Agreement, excluding final fee amounts, are as follows (in thousands):



Year ending December 31,	Total
2020 (remainder of year)	$	—
2021	2,400
2022	4,800
2023	2,800
Total future principal payments	$	10,000

License and Collaboration Agreements	6 Months Ended
License and Collaboration Agreements	Jun. 30, 2020
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. The AbbVie Agreement grants AbbVie the exclusive option to purchase an exclusive worldwide license to ALPN-101 (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 ALPN-101 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. 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 are fully constrained and were not included in the transaction price. We will 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 $86,000 for the three and six months ended June 30, 2020. As of June 30, 2020 the remaining balance of the transaction price is $59.9 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. Adaptimmune In May 2019, we entered into a collaboration and licensing agreement with Adaptimmune (the “Adaptimmune Collaboration”) to develop next-generation SPEAR T-cell products. Under the Adaptimmune Collaboration, 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 Collaboration, we received an upfront license payment of $2.0 million, and through June 30, 2020 we have received an additional $1.3 million in research support payments to fund ongoing programs. These payments are recorded as deferred revenue upon receipt and are recognized to revenue based on employee hours contributed to each performance obligation. Under the Adaptimmune Collaboration we have recognized revenue of $602,000 and $142,000 for the three months ended June 30, 2020, and 2019, respectively and $1.7 million and $142,000 for the for the six months ended June 30, 2020 and 2019, respectively. In addition, we are eligible for additional research support payments, one-time payments and downstream development and commercialization milestones of up to $288.0 million, if all pre-specified milestones for each program are achieved. We are also eligible to receive low-single digit percentage royalties on worldwide net sales of the applicable products. As of June 30, 2020, we have $242,000 remaining in current deferred revenue on our Condensed Consolidated Balance Sheets.

Stockholders’ Equity

6 Months Ended

Jun. 30, 2020

Stockholders' Equity Note [Abstract]

Stockholders’ Equity

Securities Offerings

In July 2020, 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 5,139,610 units (the “Common Units”) and 790,710 units (the “Prefunded Warrant Units”), for an aggregate purchase price of $60.0 million. Each Common Unit consists of one share of our common stock plus a warrant to purchase 0.3 shares of common stock (the “Common Stock Warrants”), and each Prefunded Warrant Unit consists of one prefunded warrant to purchase one share of common stock (the “Prefunded Warrants”) plus 0.3 Common Stock Warrants. The Prefunded Warrant Units and the Common Units are collectively referred to

as the “Units” and each Unit has a purchase price of $10.1175. The Common Stock Warrants have an exercise price of $12.74 and a term of 3.5 years. The Prefunded Warrants became fully exercisable upon the closing date and have an exercise price of $0.001 per share.

The issuance of the securities sold under the Securities Purchase Agreement have not been registered under the Securities Act of 1933, as amended, or state securities laws and may not be offered or sold in the United States absent registration with the SEC or an applicable exemption from such registration requirements. We have agreed to file a registration statement with the SEC covering the resale of the shares of common stock issuable in connection with the Securities Purchase Agreement and upon exercise of the warrants.

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. Under the Equity Distribution Agreement, we will set the parameters for the sale of shares, including the number of shares to be issued, the time period during which sales are requested to be made, limitation on the number of shares that may be sold in any one trading day and any minimum price below which sales may not be made. We will be unable to sell shares under the Equity Distribution Agreement until a prospectus supplement relating to any sales under the Equity Distribution Agreement is filed with the SEC. As of June 30, 2020, no sales under our Equity Distribution Agreement have occurred.

Equity Incentive Plans

On January 1, 2020, in connection with our 2018 Equity Incentive Plan (the “2018 Plan”) annual increase provision, a total of 929,394 additional shares were automatically added to the shares authorized under the 2018 Plan. In June 2020, in conjunction with our annual meeting of stockholders, our stockholders approved an additional increase of 743,515 shares authorized under our 2018 Plan.

In January 2020, annual stock option grants totaling 1,026,950 shares with a weighted average exercise price of $3.25 per share were issued to eligible employees and board members.

Also in January 2020, we issued 156,328 shares of RSUs at a grant date fair value of $3.23 per share to certain employees in lieu of cash incentive compensation. Half of the shares underlying each RSU vested on June 30, 2020, with the remaining half scheduled to vest on December 31, 2020, subject to each grantee’s continued employment or service to the Company on the applicable vesting dates. In addition, upon a change in control as defined in the 2018 Plan, any unvested shares underlying the RSU will immediately vest.

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. The fair value of RSUs is equal to the closing stock price on the date of grant. 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 June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(unaudited)
Employee:
Research and development	$	716	$	422	$	1,225	$	762
General and administrative	507		248		972		631
Non-Employee:
Research and development	7		11		18		40
General and administrative	2		1		3		3
Total stock-based compensation expense	$	1,232	$	682	$	2,218	$	1,436

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2020
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 for the six months ended June 30, 2020 and 2019 was (0.04)% and 0.00%, respectively. The difference between the effective tax rate of (0.04)% for the six months ended June 30, 2020, the effective tax rate of 0.00% for the six months ended June 30, 2019, and the U.S. federal statutory rate of 21% was primarily due to recognizing a full valuation allowance on deferred tax assets. As of June 30, 2020, 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 deferred tax assets would be realized and therefore we continued to record a full valuation allowance. No current tax liability or expense has been recorded in the financial statements, with the exception of a minimal amount of state income tax refunded during the three-month period ended June 30, 2020.

- Definition

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

+ References + Details

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	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 June 30, 2020 and for the three and six months ended June 30, 2020 and 2019 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 December 31, 2019 and 2018 included in our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 30, 2020 (“Annual Report”). The results of our operations for the three and six months ended June 30, 2020 are not necessarily indicative of the results to be expected for the full year.
Principles of Consolidation	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	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 lines of credit used to establish collateral to support the security deposit on our operating leases 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.
Short-Term Investments	Short-Term Investments Our short-term 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 one year. These investments are classified as available-for-sale debt securities, which are recorded at fair value based on quoted prices in active markets. 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 8. 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 Issued and Adopted Accounting Pronouncements	Recently Issued Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes. The objective of the standard is to improve areas of GAAP by removing certain exceptions permitted by ASC Topic 740, Income Taxes, and clarifying existing guidance to facilitate consistent application. The standard will become effective for us beginning on January 1, 2021. We are currently evaluating the new standard to determine the potential impact on our financial condition, results of operations, cash flows, and financial statement disclosures. Recently Adopted Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements: Clarifying the Interaction between Topic 808 and Topic 606. This ASU clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. We adopted this ASU effective January 1, 2020 and it did not have a material impact on our financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement. ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. We adopted this ASU effective January 1, 2020 and it did not have a material impact on our financial statements and related disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments: Credit Losses, as clarified in ASU 2019-04 and ASU 2019-05. The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than-temporary impairments on investment securities are recorded. We adopted this ASU effective January 1, 2020 and it did not have a material impact on our financial statements and related disclosures. We will continue to monitor the impact of the COVID-19 outbreak on expected credit losses.
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.
Share-Based Compensation Expense	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. The fair value of RSUs is equal to the closing stock price on the date of grant. We recognize the fair value of stock-based compensation as compensation expense over the requisite service period, which is the vesting period.

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2020

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.



	June 30,
	2020	2019
	(unaudited)
Warrants to purchase common stock	1,894,455	1,859,733
Stock options and restricted stock units outstanding	4,040,935	3,266,572
Total	5,935,390	5,126,305

Cash Equivalents and Short-Term Investments (Tables)

6 Months Ended

Jun. 30, 2020

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 short-term investments are as follows (in thousands):



	June 30, 2020
Assets:	(unaudited)
	Amortized Cost		Gross unrealized gains		Gross unrealized losses		Fair market value
Money market funds	$	27,053	$	—	$	—	$	27,053
Corporate debt securities and commercial paper	1,998		—		—		1,998
Total	$	29,051	$	—	$	—	$	29,051



	December 31, 2019
Assets:	Amortized Cost		Gross unrealized gains		Gross unrealized losses		Fair market value
Money market funds	$	9,995	$	—	$	—	$	9,995
U.S. treasury bills	5,019		2		—		5,021
Corporate debt securities and commercial paper	21,862		14		—		21,876
Total	$	36,876	$	16	$	—	$	36,892

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

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):



	June 30, 2020
	(unaudited)
Assets:	Level 1		Level 2		Level 3		Total
Money market funds	$	27,053	$	—	$	—	$	27,053
Corporate debt securities and commercial paper	—		1,998		—		1,998
Total	$	27,053	$	1,998	$	—	$	29,051



	December 31, 2019
Assets:	Level 1		Level 2		Level 3		Total
Money market funds	$	9,995	$	—	$	—	$	9,995
U.S. treasury bills	5,021		—		—		5,021
Corporate debt securities and commercial paper	—		21,876		—		21,876
Total	$	15,016	$	21,876	$	—	$	36,892

Additional Balance Sheet Information (Tables)

6 Months Ended

Jun. 30, 2020

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):



	June 30, 2020		December 31, 2019
	(unaudited)
Prepaid research and development	$	580	$	574
Tenant improvement allowance receivable	42		586
Prepaid insurance	90		301
Prepaid other	285		89
Other receivables	21		100
Prepaid expenses and other current assets	$	1,018	$	1,650

Summary of Accrued Liabilities

Accrued liabilities consist of the following (in thousands):



	June 30, 2020		December 31, 2019
	(unaudited)
Research and development services	$	1,970	$	2,543
Employee compensation	1,073		1,761
Legal and professional fees	687		515
Accrued other	94		466
Accrued Liabilities	$	3,824	$	5,285

Long-term Debt (Tables)

6 Months Ended

Jun. 30, 2020

Debt Disclosure [Abstract]

Schedule of Maturities of Long-term Debt

Scheduled principal payments on our outstanding debt as of June 30, 2020 under our Loan Agreement, excluding final fee amounts, are as follows (in thousands):



Year ending December 31,	Total
2020 (remainder of year)	$	—
2021	2,400
2022	4,800
2023	2,800
Total future principal payments	$	10,000

Stockholders’ Equity (Tables)

6 Months Ended

Jun. 30, 2020

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 June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(unaudited)
Employee:
Research and development	$	716	$	422	$	1,225	$	762
General and administrative	507		248		972		631
Non-Employee:
Research and development	7		11		18		40
General and administrative	2		1		3		3
Total stock-based compensation expense	$	1,232	$	682	$	2,218	$	1,436

Summary of Significant Accounting Policies (Details)	6 Months Ended
Summary of Significant Accounting Policies (Details)	Jun. 30, 2020
Maximum
Significant Accounting Policies
Available for sale securities, contractual maturity period (less than)	1 year

Net Loss Per Share - Schedule of Anti-dilutive Securities (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,935,390	5,126,305
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)	1,894,455	1,859,733
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)	4,040,935	3,266,572

Cash Equivalents and Short-Term Investments - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 29,051	$ 36,876
Gross unrealized gains	0	16
Gross unrealized losses	0	0
Fair market value	29,051	36,892
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	27,053	9,995
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair market value	27,053	9,995
U.S. treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		5,019
Gross unrealized gains		2
Gross unrealized losses		0
Fair market value		5,021
Corporate debt securities and commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,998	21,862
Gross unrealized gains	0	14
Gross unrealized losses	0	0
Fair market value	$ 1,998	$ 21,876

Cash Equivalents and Short-Term Investments - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Realized gains (losses) on securities	$ 0	$ 0

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Cash	$ 61.2	$ 3.6

Fair Value Measurements - Summary of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 29,051	$ 36,892
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	27,053	15,016
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	1,998	21,876
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	27,053	9,995
Money market funds \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	27,053	9,995
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		5,021
U.S. treasury bills \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure		5,021
U.S. treasury bills \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure		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
Corporate debt securities and commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	1,998	21,876
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	1,998	21,876
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 Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Disclosure Text Block Supplement [Abstract]
Prepaid research and development	$ 580	$ 574
Tenant improvement allowance receivable	42	586
Prepaid insurance	90	301
Prepaid other	285	89
Other receivables	21	100
Prepaid expenses and other current assets	$ 1,018	$ 1,650

Additional Balance Sheet Information - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Disclosure Text Block Supplement [Abstract]
Research and development services	$ 1,970	$ 2,543
Employee compensation	1,073	1,761
Legal and professional fees	687	515
Accrued other	94	466
Accrued Liabilities	$ 3,824	$ 5,285

Long-term Debt - Narrative (Details)	1 Months Ended			3 Months Ended		6 Months Ended
Long-term Debt - Narrative (Details)	Mar. 31, 2020 USD ($) shares	Aug. 31, 2019 USD ($) installment tranche $ / shares shares	Dec. 31, 2016 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jul. 24, 2017 shares
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs						$ 5,000,000	$ 0
Amortization of debt discount				$ 81,000	$ 31,000	125,000	$ 67,000
Unamortized debt discount				632,000		632,000
Silicon Valley Bank \| Original Agreement
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs			$ 5,000,000.0
Repayments of debt		$ 3,000,000.0
Prepayment fee (equal to)		75,000
Silicon Valley Bank \| Original Agreement \| Common Stock Warrant
Debt Instrument [Line Items]
Warrants issued for shares of common stock (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			1.75%
Term Loans
Debt Instrument [Line Items]
Debt instrument, total discount recorded				$ 812,000		$ 812,000
Term Loans \| Term Loans, Tranche One \| Common Stock Warrant
Debt Instrument [Line Items]
Fair value of warrant		$ 60,000
Term Loans \| Term Loans, Tranche Two \| Common Stock Warrant
Debt Instrument [Line Items]
Fair value of warrant	$ 60,000
Term Loans \| Silicon Valley Bank
Debt Instrument [Line Items]
Debt instrument variable interest rate		0.25%
Maximum borrowing capacity, amount		$ 15,000,000.0
Number of tranches (up to) \| tranche		3
Percentage of default interest rate		4.00%
New capital milestone for continuation of interest only payment period		$ 40,000,000.0
Number of equal monthly installments payable \| installment		25
Final payment percentage		5.50%
Term Loans \| Silicon Valley Bank \| Common Stock Warrant
Debt Instrument [Line Items]
Warrants issued for shares of common stock (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
Term Loans \| Silicon Valley Bank \| Base Rate
Debt Instrument [Line Items]
Debt instrument, interest rate floor		5.75%
Term Loans \| Silicon Valley Bank \| Term Loans, Tranche One
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs		$ 5,000,000.0
Term Loans \| Silicon Valley Bank \| Term Loans, Tranche Two
Debt Instrument [Line Items]
Proceeds from borrowings, net of issuance costs	$ 5,000,000.0
Term Loans \| Silicon Valley Bank \| Term Loans, Tranche Three
Debt Instrument [Line Items]
Unused borrowing capacity, expired amount		$ 5,000,000.0
Debt Instrument, Redemption, Period One \| Term Loans \| Silicon Valley Bank
Debt Instrument [Line Items]
Redemption price, percentage		2.00%
Debt Instrument, Redemption, Period Two \| Term Loans \| Silicon Valley Bank
Debt Instrument [Line Items]
Redemption price, percentage		1.00%
Debt Instrument, Redemption, Period Three \| Term Loans \| Silicon Valley Bank
Debt Instrument [Line Items]
Redemption price, percentage		0.00%
Maximum
Debt Instrument [Line Items]
Percentage change in loan in a non-troubled debt restructuring (less than)		0.10

Long-term Debt - Schedule of Maturities of Long-term Debt (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Debt Disclosure [Abstract]
2020 (remainder of year)	$ 0
2021	2,400
2022	4,800
2023	2,800
Total future principal payments	$ 10,000

License and Collaboration Agreements (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, current	$ 23,688,000		$ 23,688,000		$ 1,435,000
Product \| AbbVie
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue	59,900,000		59,900,000
Potential cash payment upon excercising license option	75,000,000.0		75,000,000.0
Potential cash payment upon achievement of certain development and commercial milestones	205,000,000.0		205,000,000.0
Potential cash payment upon achievement of certain sales-based cash milestones	450,000,000.0		450,000,000.0
Revenue	86,000		86,000
Product \| AbbVie \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)	75,000,000.0		75,000,000.0
Product \| AbbVie \| Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue	60,000,000.0		60,000,000.0
Product \| Adaptimmune
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	602,000	$ 142,000	1,700,000	$ 142,000
Deferred revenue, current	242,000		242,000
Product \| Adaptimmune \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential future milestones receivable (up to)	288,000,000.0		288,000,000.0
Product \| Adaptimmune \| Upfront License Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue		$ 2,000,000.0		$ 2,000,000.0
Product \| Adaptimmune \| Research Support Payment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining balance in deferred revenue	$ 1,300,000		$ 1,300,000

Stockholders’ Equity - Narrative (Details) $ / shares in Units, $ in Thousands		1 Months Ended				6 Months Ended
	Jan. 01, 2020 shares	Jul. 31, 2020 USD ($) shares warrant $ / shares	Jun. 30, 2020 shares	Jan. 31, 2020 $ / shares shares	Jun. 30, 2018 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Proceeds from issuance of common stock and prefunded warrants, gross \| $						$ 0	$ 23,598
Options, grants in period (in shares)				1,026,950
Grants in period, weighted average exercise price (in dollars per share) \| $ / shares				$ 3.25
Piper Jaffray & Co.
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
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)	929,394		743,515
Restricted Stock Units (RSUs)
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
RSUs issued during period (in shares)				156,328
Grant date fair value (in dollars per share) \| $ / shares				$ 3.23
Subsequent Event
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Proceeds from issuance of common stock and prefunded warrants, gross \| $		$ 60,000
Purchase agreement, aggregate purchase price per unit (in dollars per share) \| $ / shares		$ 10.1175
Subsequent Event \| Common Units
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Shares issued in transaction		5,139,610
Subsequent Event \| Prefunded Warrant Units
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Warrants exercisable for shares of common stock (in shares)		790,710