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Common Stock - Schedule of Shares Reserved For Future Issuance (Details) - shares	Mar. 31, 2024	Dec. 31, 2023	Oct. 17, 2023
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	5,199,828	4,028,567
2023 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,919,302	971,444	2,033,677
2023 ESPP
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	406,742	203,367
Employee Stock Option \| 2022 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,403,409	1,403,409
Employee Stock Option \| 2023 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,111,311	1,042,291
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	17,866	19,113
Early Exercisable Stock Options
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	341,198	388,943

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Pfizer License Agreement (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended			12 Months Ended
	May 02, 2023	May 03, 2022	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense			$ 11,376		$ 6,137
Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment		$ 5,000
Consideration transferred						$ 12,100
Royalty rate payment		15.00%
Expected timing satisfaction, period		12 years
Maximum payment on the timing of transaction		$ 20,000
Pfizer License Agreement \| Development and Regulatory Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent consideration, liability		128,000
Pfizer License Agreement \| Sales Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent consideration, liability		$ 525,000
Series A Convertible Preferred Stock \| Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares issued under license agreement (in shares)		7,125,000
Shares issued, price per share (usd per share)		$ 1.00
Equity interest issued and issuable		$ 7,100
Series A Convertible Preferred Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense				$ 8,800
Series A Convertible Preferred Stock \| Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares issued under license agreement (in shares)		7,125,000
Issuance of Series A convertible preferred stock pursuant to anti-dilution provision of license agreement with Pfizer Inc. (in shares)	8,823,529
Research and development expense	$ 8,800
Series A Convertible Preferred Stock \| Pfizer Inc. \| Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest percent		15.00%

Reverse Merger - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended
	Oct. 19, 2023	Mar. 31, 2024	Mar. 31, 2023
Schedule Of Reverse Recapitalization [Line Items]
Goodwill	$ 0
Intangible assets	0
Stock-based compensation expenses	2,900	$ 1,388	$ 393
Payment of reverse merger costs	6,100
Research and development
Schedule Of Reverse Recapitalization [Line Items]
Stock-based compensation expenses	1,400	556	44
General and administrative
Schedule Of Reverse Recapitalization [Line Items]
Stock-based compensation expenses	$ 1,500	$ 832	$ 349

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements as of March 31, 2024 and December 31, 2023, and for the three months ended March 31, 2024 and 2023, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and generally accepted accounting principles in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”) for condensed consolidated financial information. In the opinion of management, these condensed consolidated financial statements reflect all normal recurring adjustments which are necessary for a fair presentation of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC on March 19, 2024 (the “2023 Form 10-K”). The information presented in the condensed consolidated financial statements and related notes as of March 31, 2024, and for the three months ended March 31, 2024 and 2023, is unaudited. The condensed consolidated balance sheet as of December 31, 2023 included herein was derived from the audited financial statements included in the 2023 Form 10-K. Interim results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2024, or any future period. The condensed consolidated financial statements include the accounts of Tourmaline Bio, Inc. and its wholly-owned subsidiary, Tourmaline Sub, Inc. All intercompany transactions and balances have been eliminated in consolidation. Summary of Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2023 and the notes thereto, which are included in the related Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the three months ended March 31, 2024. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, accrued expenses and stock-based compensation expense. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Recent Accounting Pronouncements - Yet to be Adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This guidance is intended to improve reportable segment disclosure requirements through enhanced disclosures as well as clarify that entities with a single reportable segment are subject to new and existing segment reporting requirements. This guidance is effective for annual periods in fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. Entities must apply this guidance on a retrospective basis. The Company is currently evaluating this guidance to determine the impact it may have on its condensed consolidated financial statements. In March 2024, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The amendments in ASU 2023-09 address investor requests for enhanced income tax information primarily through changes to disclosure regarding rate reconciliation and income taxes paid both in the United States and in foreign jurisdictions. This guidance is effective for fiscal years beginning after December 15, 2024 on a prospective basis, with the option to apply the standard retrospectively, and early adoption is permitted. The Company is currently evaluating this guidance to determine the impact it may have on its condensed consolidated financial statements.

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands		3 Months Ended
	Oct. 19, 2023	Mar. 31, 2024	Mar. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,900	$ 1,388	$ 393
Research and development
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	1,400	556	44
General and administrative
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,500	$ 832	$ 349

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Reverse Merger

3 Months Ended

Mar. 31, 2024

Reverse Recapitalization [Abstract]

Reverse Merger

As described in Note 1, “Nature of Business”, Merger Sub merged with and into Legacy Tourmaline, with Legacy Tourmaline surviving as a wholly owned subsidiary of the Company on October 19, 2023. The Reverse Merger was accounted for as a reverse recapitalization in accordance with U.S. GAAP with Legacy Tourmaline as the accounting acquirer of Talaris. Under reverse recapitalization accounting, the assets and liabilities of Talaris were recorded at their fair value in the Company’s financial statements at the effective time of the Reverse Merger. No goodwill or intangible assets were recognized. Consequently, the consolidated financial statements of the Company reflect the operations of Legacy Tourmaline for accounting purposes together with a deemed issuance of shares, equivalent to the shares held by the former stockholders of Talaris, the legal acquirer, and a recapitalization of the equity of Legacy Tourmaline, the accounting acquirer.

The Company acquired the following assets and liabilities as part of the Reverse Merger (in thousands):


	Amount
Cash and cash equivalents	$	392
Short-term investments	65,515
Prepaid expenses and other current assets	4,254
Accounts payable	(726)
Accrued expenses	(543)
Net assets acquired	$	68,892

The Company incurred $2.9 million in stock-based compensation expense as a result of the acceleration of vesting and settlement of Talaris share-based awards at the time of the Reverse Merger. In the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023, $1.4 million and $1.5 million were recorded as research and development expense and general and administrative expense, respectively. Additionally, the Company incurred transaction costs of $6.1 million, which were recorded as a reduction to additional paid-in capital.

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Share-Based Payment Arrangement, Expensed and Capitalized, Amount

Total stock-based compensation expense recognized in the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2024 and 2023 was as follows (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	556	$	44
General and administrative	832		349
Total stock-based compensation expense	$	1,388	$	393

Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions

The fair value of stock options granted during the three months ended March 31, 2024 and 2023 was calculated on the date of grant using the following assumptions:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate	3.9% – 4.3%	3.4% – 3.7%
Dividend yield	—%	—%
Volatility	83.5% – 85.7%	83.4% – 84.3%
Expected term (in years)	6.1	5.5 – 6.1

Share-Based Payment Arrangement, Option, Activity

The following table summarizes changes in stock option activity during the three months ended March 31, 2024:


	Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2023	2,445,700	$	9.29	9.6	$	41,320
Granted	80,650	$	30.48
Exercised	—	$	—
Cancelled	(11,630)	$	10.88
Outstanding as of March 31, 2024	2,514,720	$	9.96	9.4	$	33,158
Exercisable as of March 31, 2024	42,316	$	9.94	9.4	$	549

Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity

The following table summarizes changes in restricted stock unit activity during the three months ended March 31, 2024:


	Shares	Weighted- Average Grant Date Fair Value per Share
Unvested as of December 31, 2023	19,113	$	11.89
Granted	—	$	—
Vested	(1,247)	$	11.89
Cancelled	—	$	—
Unvested as of March 31, 2024	17,866	$	11.89

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2024

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities as of March 31, 2024 and December 31, 2023 were comprised as follows (in thousands):


	March 31,		December 31,
	2024		2023
Accrued bonus	$	828	$	1,994
Accrued clinical and manufacturing costs	609		438
Accrued consulting fees	658		692
Accrued legal fees	264		237
Other accrued expenses and other current liabilities	309		349
Total accrued expenses and other current liabilities	$	2,668	$	3,710

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Options
Beginning balance, outstanding (in shares)	2,445,700
Granted (in shares)	80,650
Exercised (in shares)	0	0
Cancelled (in shares)	(11,630)
Ending balance, outstanding (in shares)	2,514,720		2,445,700
Exercisable (in shares)	42,316
Weighted- Average Exercise Price
Beginning balance, outstanding (usd per share)	$ 9.29
Granted (usd per share)	30.48
Exercised (usd per share)	0
Cancelled (usd per share)	10.88
Ending balance, outstanding (usd per share)	9.96		$ 9.29
Exercisable (usd per share)	$ 9.94
Stock Options Additional Disclosures
Weighted average remaining contractual term, outstanding	9 years 4 months 24 days		9 years 7 months 6 days
Weighted average remaining contractual term, exercisable	9 years 4 months 24 days
Aggregate intrinsic value, outstanding	$ 33,158		$ 41,320
Aggregate intrinsic value, exercisable	$ 549

Commitments and Contingencies - Narrative (Details) $ in Millions		2 Months Ended
	Feb. 13, 2024 USD ($)	Oct. 03, 2023 letter lawsuit
Commitments and Contingencies Disclosure [Abstract]
Demand letters \| letter		11
Number of lawsuits \| lawsuit		3
Litigation settlement \| $	$ 0.2

Fair Value Measurements - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 194,773	$ 62,225
Total cash equivalents and short-term investments	215,053	66,830
Corporate debt securities	57,237	0
Total long-term investments	57,237
Total cash equivalents and investments	272,290	66,830
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	74,850	32,555
Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	79,854	26,724
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	52,988	2,947
Corporate debt securities	57,237
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	74,749	12,511
Total long-term investments	0
Total cash equivalents and investments	74,749	12,511
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	67,388	7,907
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Corporate debt securities	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	140,304	54,319
Total long-term investments	57,237
Total cash equivalents and investments	197,541	54,319
Significant Other Observable Inputs (Level 2) \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	74,850	32,555
Significant Other Observable Inputs (Level 2) \| Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	12,466	18,817
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	52,988	2,947
Corporate debt securities	57,237
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and short-term investments	0	0
Total long-term investments	0
Total cash equivalents and investments	0	0
Significant Unobservable Inputs (Level 3) \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Corporate debt securities	0
Money market funds, included in cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	7,361	4,604
Money market funds, included in cash equivalents \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	7,361	4,604
Money market funds, included in cash equivalents \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	0	0
Money market funds, included in cash equivalents \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	$ 0	$ 0

Convertible Preferred Stock	3 Months Ended
Convertible Preferred Stock	Mar. 31, 2024
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	Convertible Preferred Stock On April 18, 2022, the Company entered into a Securities Purchase Agreement (the “Initial Series A Securities Purchase Agreement”) with various entities and individuals for the purchase of Series A convertible preferred units. As part of the Initial Series A Securities Purchase Agreement, the Company authorized the issuance and sale of up to 20,000,000 shares of its Series A convertible preferred units at a price of $1.00 per unit for total proceeds of $20.0 million. The Series A convertible preferred units were convertible into the Company’s Common Units at a 1:1 ratio. The obligations of the parties to purchase and sell the Series A convertible preferred units were subject to the Company entering into the Pfizer License Agreement. As outlined further within Note 4, “Pfizer License Agreement”, the Company also issued to Pfizer 7,125,000 Series A convertible preferred units in May 2022 conjunction with the Pfizer License Agreement. On September 2, 2022, Legacy Tourmaline converted from Tourmaline Bio, LLC, a Delaware limited liability company, to Tourmaline Bio, Inc., a Delaware corporation (the “Conversion”). As part of the Conversion, Series A convertible preferred units were converted at a 1:1 ratio to shares of Series A convertible preferred stock. Upon the Conversion, the Company was authorized to issue up to 27,125,000 shares of Series A convertible preferred stock with a par value of $0.0001. The Company subsequently entered into a Series A Preferred Stock Purchase Agreement on May 2, 2023 (the “Closing Date”) with various entities and individuals for the purchase of additional shares of Series A convertible preferred stock (the “Series A Extension”). On the Closing Date, the Company authorized the issuance and sale of 92,200,000 shares of Series A convertible preferred stock at a price of $1.00 per share for total gross proceeds of $92.2 million. In addition, pursuant to the anti-dilution provision of the Pfizer License Agreement, the Company issued 8,823,529 additional shares of Series A convertible preferred stock to Pfizer in connection with the Series A Extension and recognized corresponding research and development expense of $8.8 million during the second quarter of 2023. The additional shares of Series A convertible preferred stock had the same terms, conditions, rights and preferences as the Series A convertible preferred stock issued during the year ended December 31, 2022. Upon consummation of the Series A Extension, the anti-dilution provision of the Pfizer License Agreement was no longer in force and effect. Prior to the completion of the Reverse Merger, the Company classified its Series A convertible preferred stock outside of permanent equity as the shares had redemption features that were not entirely within the control of the Company. Upon the consummation of the Reverse Merger, all outstanding shares of Series A convertible preferred stock were converted into 10,222,414 shares of common stock. Subsequent to consummation of the Reverse Merger, the Company is authorized to issue 10,000,000 shares of undesignated preferred stock, however no such shares were issued or outstanding as of March 31, 2024.

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating activities:
Net loss	$ (13,311)	$ (7,502)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,388	393
Non-cash lease expense	35	32
Depreciation on property and equipment	10	6
Accretion of discount on investments	(1,181)	0
Realized gain on investments	(54)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,118)	(676)
Other non-current assets	(457)	0
Accounts payable	866	3,018
Accrued expenses and other current liabilities	(1,061)	938
Operating lease liabilities	(40)	0
Net cash used in operating activities	(14,923)	(3,791)
Investing activities:
Purchases of property and equipment	0	(24)
Purchases of investments	(215,869)	0
Maturities of investments	27,000	0
Net cash used in investing activities	(188,869)	(24)
Financing activities:
Proceeds from public offering of common stock, net of issuance costs	161,352	0
Net cash provided by financing activities	161,352	0
Net decrease in cash, cash equivalents and restricted cash	(42,440)	(3,815)
Cash, cash equivalents and restricted cash—Beginning of period	140,953	8,474
Cash, cash equivalents and restricted cash—End of period	98,513	4,659
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	98,286	4,443
Restricted cash	227	216
Total cash, cash equivalents and restricted cash	98,513	4,659
Non-cash investing and financing activities:
Unpaid public offering costs included in accrued expenses	20	0
Purchases of property and equipment included in accounts payable and accrued expenses	0	9
Unpaid deferred offering costs included in accrued expenses	$ 0	$ 63

Common Stock

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Common Stock

On January 25, 2024, the Company entered into an underwriting agreement with Jefferies LLC, Piper Sandler & Co., Guggenheim Securities, LLC and Truist Securities, Inc. (collectively, the “Underwriters”) in connection with the offering, issuance and sale by the Company of 4,615,384 shares of the Company’s common stock at a public offering price of $32.50 per share, less underwriting discounts and commissions, pursuant to an effective shelf registration statement on Form S-3 (the “January 2024 Offering”). Under the January 2024 Offering, the Company also granted the Underwriters a 30-day option to purchase up to 692,307 shares of common stock at the public offering price, less the underwriting discounts and commissions, which was exercised by the Underwriters in full on January 25, 2024. The January 2024 Offering closed on January 29, 2024.

Total gross proceeds from the January 2024 Offering were approximately $172.5 million, including the full exercise by the Underwriters of their option to purchase additional shares. Net proceeds were approximately $161.3 million after deducting underwriting discounts and commissions and offering expenses payable by the Company.

As of March 31, 2024, the Company is authorized to issue 140,000,000 shares of voting common stock and 10,000,000 shares of non-voting common stock. Holders of voting common stock are entitled to one vote per share. In addition, holders of voting common stock are entitled to receive dividends, if and when declared by the Company’s Board of Directors. As of March 31, 2024, no dividends had been declared.

As of March 31, 2024 and December 31, 2023, the Company had reserved for future issuance the following number of shares of common stock:


	March 31,	December 31,
	2024	2023
Exercises of outstanding stock options under 2022 Equity Incentive Plan	1,403,409	1,403,409
Exercises of outstanding stock options under 2023 Equity Incentive Plan	1,111,311	1,042,291
Vesting of restricted stock units under 2023 Equity Incentive Plan	17,866	19,113
Common stock subject to repurchase related to early exercised stock options	341,198	388,943
Future issuances under 2023 Equity Incentive Plan	1,919,302	971,444
Future issuances under 2023 Employee Stock Purchase Plan	406,742	203,367
Total shares reserved for future issuance	5,199,828	4,028,567

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Paragraph 14
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
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-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
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-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

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

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

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

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

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

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

+ Details

Investments - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Unrealized loss position, less than 12 months	$ 229.6	$ 49.3

Pfizer License Agreement	3 Months Ended
Pfizer License Agreement	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Pfizer License Agreement	Pfizer License Agreement On May 3, 2022 (the “Effective Date”), the Company entered into a License Agreement (the “Pfizer License Agreement”) with Pfizer Inc. (“Pfizer”), pursuant to which the Company obtained an exclusive, sublicensable, royalty-bearing, worldwide right to use and license under certain know-how for the development, commercialization and manufacture of PF-04236921 (the “Compound”, now known as TOUR006) and any pharmaceutical or biopharmaceutical product incorporating the Compound (the “Product”), for the treatment, diagnosis, or prevention of any and all diseases, disorders, illnesses and conditions in humans and animals. In consideration for the license and other rights the Company received under the Pfizer License Agreement, the Company paid Pfizer an upfront payment of $5.0 million and issued to Pfizer 7,125,000 Series A preferred units of Tourmaline Bio, LLC (the predecessor of Legacy Tourmaline), which subsequently converted to 7,125,000 shares of Series A convertible preferred stock of Legacy Tourmaline, representing a 15% interest in the Company on a fully-diluted basis at the time of issuance. The units were issued for $1.00 per unit, representing a total value of $7.1 million. In accordance with ASC Topic 805, Business Combinations, the Pfizer License Agreement was accounted for as an asset acquisition as the licensed compound represented substantially all of the fair value of the gross assets acquired. On the Effective Date, the licensed compound had not yet received regulatory approval and did not have an alternative use. Accordingly, the total consideration transferred of $12.1 million was recorded as research and development expense in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2022. As additional consideration for the license, the Company is obligated to pay Pfizer up to $128.0 million upon the achievement of specific development and regulatory milestones. The Company is also obligated to pay Pfizer up to $525.0 million upon the first achievement of specific sales milestones. The Company is also obligated to pay Pfizer a marginal royalty rate in the low double digits (less than 15%), subject to specified royalty reductions. The royalty term, on a Product-by-Product and country-by-country basis, begins on the first commercial sale of such Product and expires upon the later of twelve years following the date of the first commercial sale or the expiration of regulatory exclusivity protecting such Product. In the event the Company completes a Significant Transaction (as defined in the Pfizer License Agreement), the Company will be obligated to pay Pfizer a one-time payment in the low-eight digits (up to $20.0 million); the amount of such payment is based on the timing of the transaction. As of March 31, 2024, the Company does not owe any milestone or royalties under the Pfizer License Agreement and no such milestones or royalties have been paid to date. The Pfizer License Agreement originally contained an anti-dilution provision allowing Pfizer to maintain a 15% interest in the Company on a fully-diluted basis unless and until certain thresholds are met, whereupon the anti-dilution provision would no longer apply. As outlined further within Note 9, “Convertible Preferred Stock”, on May 2, 2023, the Company issued 8,823,529 additional shares of Series A convertible preferred stock to Pfizer pursuant this anti-dilution provision. The Company recognized research and development expense of $8.8 million related to this issuance of Series A convertible preferred stock. Subsequent to the issuance of these additional shares of Series A convertible preferred stock, the anti-dilution provision is no longer in force and effect.

Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Millions			3 Months Ended
	Jan. 01, 2024 shares	Oct. 17, 2023 shares	Mar. 31, 2024 USD ($) $ / shares shares	Mar. 31, 2023 $ / shares shares	Dec. 31, 2023 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)			5,199,828		4,028,567
Share-based compensation arrangement by share-based payment award, options, grants in period, weighted average grant date fair value (usd per share) \| $ / shares			$ 22.57	$ 4.01
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)			0	0
Share-based payment arrangement, nonvested award, option, cost not yet recognized, amount \| $			$ 17.2
Proceeds from stock options exercised \| $			0.1
Deferred compensation share-based arrangements, liability, current \| $			$ 0.1
Employee Stock Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, fair value assumptions, weighted average fair value of common stock (usd per share) \| $ / shares			$ 30.48	$ 0.25
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition			3 years 2 months 12 days
Early Exercisable Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)			341,198		388,943
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)			647,386
Share-based compensation arrangement by share-based payment award, repurchase of options, period			6 months
Share-based compensation arrangement by share-based payment award, options, nonvested, number of shares (in shares)			341,198
Restricted Stock Units (RSUs)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)			17,866		19,113
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition			3 years 6 months
Share-based compensation arrangement by share-based payment award, equity instruments other than options, vested in period, fair value \| $			$ 0.1
Share-based payment arrangement, nonvested award, excluding option, cost not yet recognized, amount \| $			$ 0.2
2023 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)		2,033,677	1,919,302		971,444
Share-based compensation arrangement by share-based payment award, number of annual increase of shares authorized, period		10 years
Share-based compensation arrangement by share-based payment award, percentage of outstanding stock maximum		5.00%
Share-based compensation arrangement by share-based payment award, maximum number of shares authorized, multiple of share reserve		3
Common stock, capital shares added for future issuance (in shares)	1,016,878
2023 Equity Incentive Plan \| Employee Stock Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, expiration period		10 years
Shares reserved for future issuance (in shares)			1,111,311		1,042,291
2023 ESPP
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)			406,742		203,367
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)			406,742
Share-based compensation arrangement by share-based payment award, number of additional shares authorized (in shares)	203,375
2023 ESPP \| Employee Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of annual increase of shares authorized, period		10 years
Share-based compensation arrangement by share-based payment award, percentage of outstanding stock maximum		1.00%
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)		203,367
Share-based compensation arrangement by share-based payment award, maximum number of shares authorized, multiple of share reserve		3

Related Party Transactions (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	3 Months Ended
	Jun. 01, 2023	May 31, 2023	May 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Related Party Transaction [Line Items]
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)				0	0
Exercised (usd per share)				$ 0
Shares acquired, average cost per share (usd per share)		$ 2.76
Treasury stock, value, acquired, cost method	$ 0.2
Affiliated Entity
Related Party Transaction [Line Items]
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)			75,782
Exercised (usd per share)		$ 0.13

Common Stock (Tables)

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Schedule of Stock by Class

As of March 31, 2024 and December 31, 2023, the Company had reserved for future issuance the following number of shares of common stock:


	March 31,	December 31,
	2024	2023
Exercises of outstanding stock options under 2022 Equity Incentive Plan	1,403,409	1,403,409
Exercises of outstanding stock options under 2023 Equity Incentive Plan	1,111,311	1,042,291
Vesting of restricted stock units under 2023 Equity Incentive Plan	17,866	19,113
Common stock subject to repurchase related to early exercised stock options	341,198	388,943
Future issuances under 2023 Equity Incentive Plan	1,919,302	971,444
Future issuances under 2023 Employee Stock Purchase Plan	406,742	203,367
Total shares reserved for future issuance	5,199,828	4,028,567

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27))
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-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section S99
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-Subparagraph (SX 210.5-02(29))
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 13: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

Assets measured at fair value on a recurring basis as of March 31, 2024 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	7,361	$	7,361	$	—	$	—
Commercial paper	74,850		—		74,850		—
Government securities	79,854		67,388		12,466		—
Corporate debt securities	52,988		—		52,988		—
Total cash equivalents and short-term investments	215,053		74,749		140,304		—
Long-term investments:
Corporate debt securities	57,237		—		57,237		—
Total long-term investments	57,237		—		57,237		—
Total cash equivalents and investments	$	272,290	$	74,749	$	197,541	$	—

Assets measured at fair value on a recurring basis as of December 31, 2023 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	4,604	$	4,604	$	—	$	—
Commercial paper	32,555		—		32,555		—
Government securities	26,724		7,907		18,817		—
Corporate debt securities	2,947		—		2,947		—
Total cash equivalents and short-term investments	66,830		12,511		54,319		—
Total cash equivalents and investments	$	66,830	$	12,511	$	54,319	$	—

Investments - Debt Securities, Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	$ 272,610	$ 66,763
Unrealized Gains	0	75
Unrealized Losses	(320)	(8)
Fair Value	272,290	66,830
Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	215,242
Unrealized Gains	0
Unrealized Losses	(189)
Fair Value	215,053
Long Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	57,368
Unrealized Gains	0
Unrealized Losses	(131)
Fair Value	57,237
Money market funds, included in cash equivalents \| Cash and Cash Equivalents
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	7,361	4,604
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	7,361	4,604
Commercial paper \| Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	74,954	32,515
Unrealized Gains	0	44
Unrealized Losses	(104)	(4)
Fair Value	74,850	32,555
Government securities \| Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	79,878	26,703
Unrealized Gains	0	25
Unrealized Losses	(24)	(4)
Fair Value	79,854	26,724
Corporate debt securities \| Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	53,049	2,941
Unrealized Gains	0	6
Unrealized Losses	(61)	0
Fair Value	52,988	$ 2,947
Corporate debt securities \| Long Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	57,368
Unrealized Gains	0
Unrealized Losses	(131)
Fair Value	$ 57,237

Investments

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Investments

Cash equivalents, short-term and long-term investments as of March 31, 2024 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	7,361	$	—	$	—	$	7,361
Commercial paper	74,954		—		(104)		74,850
Government securities	79,878		—		(24)		79,854
Corporate debt securities	53,049		—		(61)		52,988
Total cash equivalents and short-term investments	215,242		—		(189)		215,053
Long-term investments:
Corporate debt securities	57,368		—		(131)		57,237
Total long-term investments	57,368		—		(131)		57,237
Total cash equivalents and investments	$	272,610	$	—	$	(320)	$	272,290

Cash equivalents and short-term investments as of December 31, 2023 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	4,604	$	—	$	—	$	4,604
Commercial paper	32,515		44		(4)		32,555
Government securities	26,703		25		(4)		26,724
Corporate debt securities	2,941		6		—		2,947
Total cash equivalents and short-term investments	66,763		75		(8)		66,830
Total cash equivalents and investments	$	66,763	$	75	$	(8)	$	66,830

As of March 31, 2024, the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $229.6 million. As of December 31, 2023, the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $49.3 million. As of March 31, 2024 and December 31, 2023, the Company did not hold any securities that were in an unrealized loss position for greater than twelve months. Based upon its assessment of securities in an unrealized loss position, the Company did not record any allowances for credit losses during the three months ended March 31, 2024 or during the year ended December 31, 2023.

Stock-Based Compensation - Schedule of Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs)	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Shares
Beginning balance, unvested, outstanding (in shares) \| shares	19,113
Granted (in shares) \| shares	0
Vested (in shares) \| shares	(1,247)
Forfeited (in shares) \| shares	0
Ending balance, unvested, outstanding (in shares) \| shares	17,866
Weighted- Average Grant Date Fair Value per Share
Beginning balance, unvested (usd per share) \| $ / shares	$ 11.89
Granted (usd per share) \| $ / shares	0
Vested (usd per share) \| $ / shares	11.89
Cancelled (usd per share) \| $ / shares	0
Ending balance, unvested (usd per share) \| $ / shares	$ 11.89

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development	$ 11,376	$ 6,137
General and administrative	6,141	1,365
Total operating expenses	17,517	7,502
Loss from operations	(17,517)	(7,502)
Other income, net	4,206	0
Net loss	$ (13,311)	$ (7,502)
Net loss per share, basic (usd per share)	$ (0.55)	$ (8.28)
Net loss per share, diluted (usd per share)	$ (0.55)	$ (8.28)
Weighted-average, common shares outstanding, basic (in shares)	24,082	906
Weighted-average, common shares outstanding, diluted (in shares)	24,082	906
Other comprehensive loss:
Unrealized loss on investments	$ (320)	$ 0
Comprehensive loss	$ (13,631)	$ (7,502)

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2024

Payables and Accruals [Abstract]

Schedule of Accrued Liabilities

Accrued expenses and other current liabilities as of March 31, 2024 and December 31, 2023 were comprised as follows (in thousands):


	March 31,		December 31,
	2024		2023
Accrued bonus	$	828	$	1,994
Accrued clinical and manufacturing costs	609		438
Accrued consulting fees	658		692
Accrued legal fees	264		237
Other accrued expenses and other current liabilities	309		349
Total accrued expenses and other current liabilities	$	2,668	$	3,710

Reverse Merger (Tables)

3 Months Ended

Mar. 31, 2024

Reverse Recapitalization [Abstract]

Schedule Of Reverse Capitalization

The Company acquired the following assets and liabilities as part of the Reverse Merger (in thousands):


	Amount
Cash and cash equivalents	$	392
Short-term investments	65,515
Prepaid expenses and other current assets	4,254
Accounts payable	(726)
Accrued expenses	(543)
Net assets acquired	$	68,892

Stock-Based Compensation - Stock Option Valuation Assumptions (Details) - Employee Stock Option	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk-free interest rate (minimum)	3.90%	3.40%
Risk-free interest rate (maximum)	4.30%	3.70%
Dividend yield	0.00%	0.00%
Volatility (minimum)	83.50%	83.40%
Volatility (maximum)	85.70%	84.30%
Expected term (in years)	6 years 1 month 6 days
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)		5 years 6 months
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)		6 years 1 month 6 days

Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands			3 Months Ended
	May 02, 2023 USD ($) $ / shares shares	Apr. 18, 2022 USD ($) $ / shares shares	Mar. 31, 2024 USD ($) shares	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 02, 2022 $ / shares shares	May 03, 2022 shares
Class of Stock [Line Items]
Research and development expense \| $			$ 11,376		$ 6,137
Conversion of convertible securities (in shares)			10,222,414
Undesignated preferred stock, shares authorized (in shares)			10,000,000
Shares outstanding (in shares)			0
Stock issued (in shares)			0
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Conversion ratio		1
Series A Convertible Preferred Stock \| Pfizer License Agreement
Class of Stock [Line Items]
Shares issued under license agreement (in shares)							7,125,000
Series A Convertible Preferred Stock \| Initial Series A Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		20,000,000
Price per share (usd per share) \| $ / shares		$ 1.00
Consideration received on transaction \| $		$ 20,000
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Conversion ratio						1
Convertible preferred stock, shares authorized (in shares)						27,125,000
Convertible preferred stock, par value ( usd per share) \| $ / shares						$ 0.0001
Research and development expense \| $				$ 8,800
Series A Convertible Preferred Stock \| Pfizer License Agreement
Class of Stock [Line Items]
Shares issued under license agreement (in shares)							7,125,000
Issuance of Series A convertible preferred stock pursuant to anti-dilution provision of license agreement with Pfizer Inc. (in shares)	8,823,529
Research and development expense \| $	$ 8,800
Series A Convertible Preferred Stock \| Series A Extension
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	92,200,000
Price per share (usd per share) \| $ / shares	$ 1.00
Consideration received on transaction \| $	$ 92,200

Fair Value Measurements

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company measures the fair value of money market funds based on quoted prices in active markets for identical securities. Investments also include commercial paper,government securities, and corporate debt securities which are valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The carrying amounts reflected in the condensed consolidated balance sheets for cash, prepaid expenses and other current assets, accounts payable, and accrued expenses and other current liabilities approximate their fair values, due to their short-term nature.

Assets measured at fair value on a recurring basis as of March 31, 2024 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	7,361	$	7,361	$	—	$	—
Commercial paper	74,850		—		74,850		—
Government securities	79,854		67,388		12,466		—
Corporate debt securities	52,988		—		52,988		—
Total cash equivalents and short-term investments	215,053		74,749		140,304		—
Long-term investments:
Corporate debt securities	57,237		—		57,237		—
Total long-term investments	57,237		—		57,237		—
Total cash equivalents and investments	$	272,290	$	74,749	$	197,541	$	—

Assets measured at fair value on a recurring basis as of December 31, 2023 were as follows (in thousands):


	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	4,604	$	4,604	$	—	$	—
Commercial paper	32,555		—		32,555		—
Government securities	26,724		7,907		18,817		—
Corporate debt securities	2,947		—		2,947		—
Total cash equivalents and short-term investments	66,830		12,511		54,319		—
Total cash equivalents and investments	$	66,830	$	12,511	$	54,319	$	—

There were no liabilities measured at fair value on a recurring basis as of March 31, 2024 or December 31, 2023. There were no changes in valuation techniques, nor were there any transfers among the fair value hierarchy levels during the three months ended March 31, 2024 or during the year ended December 31, 2023.

- 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

Reverse Merger - Schedule Of Net Assets Acquired (Details) $ in Thousands	Oct. 19, 2023 USD ($)
Reverse Recapitalization [Abstract]
Cash and cash equivalents	$ 392
Short-term investments	65,515
Prepaid expenses and other current assets	4,254
Accounts payable	(726)
Accrued expenses	(543)
Net assets acquired	$ 68,892

Net Loss per Share

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Net Loss per Share

The following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive:


	Three Months Ended March 31,
	2024	2023
Series A convertible preferred stock	—	2,163,764
Outstanding stock options under 2022 Equity Inventive Plan	1,403,409	681,310
Outstanding stock options under 2023 Equity Inventive Plan	1,111,311	—
Unvested restricted stock units under 2023 Equity Incentive Plan	17,451	—
Common stock subject to repurchase related to early exercised stock options	341,198	—
Total	2,873,369	2,845,074

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets
Cash and cash equivalents	$ 98,286	$ 140,726
Short-term investments	194,773	62,225
Prepaid expenses and other current assets	7,040	5,923
Total current assets	300,099	208,874
Property and equipment, net	75	85
Total long-term investments	57,237	0
Restricted cash	227	227
Operating lease right-of-use asset	327	362
Other non-current assets	1,204	747
Total assets	359,169	210,295
Current liabilities
Accounts payable	1,936	1,071
Accrued expenses and other current liabilities	2,668	3,710
Operating lease liability, current portion	223	221
Total current liabilities	4,827	5,002
Operating lease liability, net of current portion	153	194
Other liabilities	50	57
Total liabilities	5,030	5,253
Commitments and Contingencies (Note 11)
Stockholders’ equity
Undesignated preferred stock, $0.0001 par value – 10,000,000 shares authorized as of March 31, 2024 and December 31, 2023, no shares issued or outstanding as of March 31, 2024 or December 31, 2023	0	0
Common stock, $0.0001 par value – 140,000,000 voting shares authorized as of March 31, 2024 and December 31, 2023, 25,646,509 and $20,337,571 voting shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively; 10,000,000 non-voting shares authorized as of March 31, 2024 and December 31, 2023, no non-voting shares issued or outstanding as of March 31, 2024 or December 31, 2023	3	2
Additional paid-in capital	429,751	267,024
Accumulated other comprehensive (loss) income	(253)	67
Accumulated deficit	(75,362)	(62,051)
Total stockholders’ equity	354,139	205,042
Total liabilities and stockholders’ equity	$ 359,169	$ 210,295

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements as of March 31, 2024 and December 31, 2023, and for the three months ended March 31, 2024 and 2023, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and generally accepted accounting principles in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”) for condensed consolidated financial information. In the opinion of management, these condensed consolidated financial statements reflect all normal recurring adjustments which are necessary for a fair presentation of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC on March 19, 2024 (the “2023 Form 10-K”). The information presented in the condensed consolidated financial statements and related notes as of March 31, 2024, and for the three months ended March 31, 2024 and 2023, is unaudited. The condensed consolidated balance sheet as of December 31, 2023 included herein was derived from the audited financial statements included in the 2023 Form 10-K. Interim results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2024, or any future period.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, accrued expenses and stock-based compensation expense. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances.
Recent Accounting Pronouncements - Yet to be Adopted	Recent Accounting Pronouncements - Yet to be Adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This guidance is intended to improve reportable segment disclosure requirements through enhanced disclosures as well as clarify that entities with a single reportable segment are subject to new and existing segment reporting requirements. This guidance is effective for annual periods in fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. Entities must apply this guidance on a retrospective basis. The Company is currently evaluating this guidance to determine the impact it may have on its condensed consolidated financial statements. In March 2024, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The amendments in ASU 2023-09 address investor requests for enhanced income tax information primarily through changes to disclosure regarding rate reconciliation and income taxes paid both in the United States and in foreign jurisdictions. This guidance is effective for fiscal years beginning after December 15, 2024 on a prospective basis, with the option to apply the standard retrospectively, and early adoption is permitted. The Company is currently evaluating this guidance to determine the impact it may have on its condensed consolidated financial statements.

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' (Deficit) Equity (unaudited) - USD ($)
$ in Thousands

Total

Common Stock

Additional Paid-In Capital

Accumulated Other Comprehensive Income

Accumulated Deficit

Series A Convertible Preferred Stock

Beginning balance (in shares) at Dec. 31, 2022

27,125,000

Beginning balance at Dec. 31, 2022

$ 27,125

Ending balance at Mar. 31, 2023

$ 27,125

Ending balance (in shares) at Mar. 31, 2023

27,125,000

Beginning balance (in shares) at Dec. 31, 2022

^[1]

867,499

Beginning balance at Dec. 31, 2022

$ (19,732)

$ 0

$ 195

$ 0

$ (19,927)

Increase (Decrease) in Stockholders' Equity [Roll Forward]

Stock-based compensation expense

393

Unrealized loss on investments

Net loss

(7,502)

Ending balance at Mar. 31, 2023

$ (26,841)

$ 0

588

(27,429)

Ending balance (in shares) at Mar. 31, 2023

^[1]

867,499

Beginning balance (in shares) at Dec. 31, 2023

Beginning balance at Dec. 31, 2023

$ 0

Ending balance at Mar. 31, 2024

$ 0

Ending balance (in shares) at Mar. 31, 2024

Beginning balance (in shares) at Dec. 31, 2023

20,337,571

Beginning balance at Dec. 31, 2023

$ 205,042

$ 2

267,024

(62,051)

Increase (Decrease) in Stockholders' Equity [Roll Forward]

Issuance of common stock from public offering, net of issuance costs (in shares)

5,307,691

Issuance of common stock from public offering, net of issuance costs

161,333

$ 1

161,332

Stock-based compensation expense

1,388

Vesting of early exercised stock options

Issuance of common stock upon vesting of restricted stock units (in shares)

1,247

Unrealized loss on investments

(320)

Net loss

(13,311)

Ending balance at Mar. 31, 2024

$ 354,139

$ 3

$ 429,751

$ (253)

$ (75,362)

Ending balance (in shares) at Mar. 31, 2024

25,646,509

[1]	* Amounts have been restated for the impact of the reverse merger outlined further within Notes 1 and 3.

Cover - shares	3 Months Ended
Cover - shares	Mar. 31, 2024	May 10, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-40384
Entity Registrant Name	TOURMALINE BIO, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-2377352
Entity Address, Address Line One	27 West 24th Street
Entity Address, Address Line Two	Suite 702
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10010
City Area Code	646
Local Phone Number	481-9832
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	TRML
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	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		25,646,509
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001827506
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false

Nature of Business (Details) $ in Millions	Oct. 19, 2023 USD ($) shares	Mar. 31, 2024 USD ($) shares	Dec. 31, 2023 shares
Class of Stock [Line Items]
Stock split ratio, common stock	0.1
Exchange ratio	0.07977
Common stock, shares, issued (in shares)	20,336,741	25,646,509	20,337,571
Investments and cash \| $		$ 350.3
Private Placement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	4,092,035
Consideration received on transaction \| $	$ 75.0
Common Stock
Class of Stock [Line Items]
Stock issued during period, shares, new issues (in shares)	15,877,090

Net Loss per Share (Details) - shares	3 Months Ended
Net Loss per Share (Details) - shares	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	2,873,369	2,845,074
Series A convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	0	2,163,764
Employee Stock Option \| 2022 Equity Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	1,403,409	681,310
Employee Stock Option \| 2023 Equity Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	1,111,311	0
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	17,451	0
Early Exercisable Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	341,198	0

Related Party Transactions	3 Months Ended
Related Party Transactions	Mar. 31, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In May 2023, an advisor affiliated with Fourth Avenue FF Opportunities LP – Series Z, previously a beneficial owner the Company’s outstanding capital stock, exercised stock options to purchase 75,782 shares of the Company’s common stock for $0.13 per share. The Company subsequently repurchased the shares from the advisor at $2.76 per share, equivalent to fair value as of the repurchase date, for an aggregate purchase price of $0.2 million. Fourth Avenue FF Opportunities LP – Series Z then purchased the shares from the Company at the same amount $2.76 per share for an aggregate purchase price of $0.2 million. There were no amounts due to or from any related party as of either March 31, 2024 or December 31, 2023.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Investments (Tables)

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Debt Securities, Available-for-Sale

Cash equivalents, short-term and long-term investments as of March 31, 2024 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	7,361	$	—	$	—	$	7,361
Commercial paper	74,954		—		(104)		74,850
Government securities	79,878		—		(24)		79,854
Corporate debt securities	53,049		—		(61)		52,988
Total cash equivalents and short-term investments	215,242		—		(189)		215,053
Long-term investments:
Corporate debt securities	57,368		—		(131)		57,237
Total long-term investments	57,368		—		(131)		57,237
Total cash equivalents and investments	$	272,610	$	—	$	(320)	$	272,290

Cash equivalents and short-term investments as of December 31, 2023 were comprised as follows (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Cash equivalents and short-term investments:
Money market funds, included in cash equivalents	$	4,604	$	—	$	—	$	4,604
Commercial paper	32,515		44		(4)		32,555
Government securities	26,703		25		(4)		26,724
Corporate debt securities	2,941		6		—		2,947
Total cash equivalents and short-term investments	66,763		75		(8)		66,830
Total cash equivalents and investments	$	66,763	$	75	$	(8)	$	66,830

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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+ Details

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Liabilities, fair value disclosure	$ 0.0	$ 0.0

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive:


	Three Months Ended March 31,
	2024	2023
Series A convertible preferred stock	—	2,163,764
Outstanding stock options under 2022 Equity Inventive Plan	1,403,409	681,310
Outstanding stock options under 2023 Equity Inventive Plan	1,111,311	—
Unvested restricted stock units under 2023 Equity Incentive Plan	17,451	—
Common stock subject to repurchase related to early exercised stock options	341,198	—
Total	2,873,369	2,845,074

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies From time to time, the Company may become subject to legal proceedings, claims and litigation arising in the ordinary course of business. From time to time, the Company may be involved in legal proceedings arising in the ordinary course of its business. Between July 25 and October 3, 2023, Talaris received eleven demand letters (the “Demands”) regarding the Proxy Statement (as defined below). In addition, three lawsuits were filed (captioned Wieder v. Talaris Therapeutics, Inc., et al., No. 1:23-cv-08355 (S.D.N.Y. filed Sept. 21, 2023), Carlisle v. Talaris Therapeutics, Inc., et al., No. 1:23-cv-08520 (S.D.N.Y. filed Sept. 27, 2023), and Roberts v. Talaris Therapeutics, Inc., et al., No. 1:23-cv-01063 (D. Del. filed Sept. 27, 2023)) (the “Lawsuits,” and together with the Demands, the “Actions”), in each case, by purported stockholders of Talaris challenging the proposed Reverse Merger and the disclosures in the definitive proxy statement filed by Talaris with the SEC on July 20, 2023, and as amended on August 25, 2023 and September 11, 2023 (the “Proxy Statement”). The Actions generally alleged that certain disclosures in the Proxy Statement were false or misleading and asserted claims against Talaris and its Board of Directors for violations of Sections 14(a) and 20(a) of the Exchange Act of 1934. The purported stockholders sought unspecified monetary damages and an award of costs and expenses, including reasonable attorney’s fees. On October 10, 2023, Talaris filed a Current Report on Form 8-K to update and supplement the Proxy Statement, which contained certain additional disclosures relating to the Reverse Merger (the “Supplemental Disclosures”). Thereafter, plaintiffs in the Lawsuits voluntarily dismissed their complaints, and opposing counsel (for the stockholders in the Actions) requested a mootness fee in connection with the Supplemental Disclosures. The Reverse Merger subsequently closed on October 19, 2023. Thereafter, the parties engaged in a negotiation over payment of a potential mootness fee(s) to resolve all the fee demands. On February 13, 2024, the parties entered into an agreement, under which the Company agreed to pay a total of approximately $0.2 million to resolve all the fee demands and the stockholders released all claims in connection with the Reverse Merger. This amount was recognized as general and administrative expense by the Company during the year ended December 31, 2023.

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued bonus	$ 828	$ 1,994
Accrued clinical and manufacturing costs	609	438
Accrued consulting fees	658	692
Accrued legal fees	264	237
Other accrued expenses and other current liabilities	309	349
Total accrued expenses and other current liabilities	$ 2,668	$ 3,710

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Undesignated preferred stock, par value (usd per share)	$ 0.0001	$ 0.0001
Undesignated preferred stock, shares authorized (in shares)	10,000,000
Undesignated preferred stock, shares outstanding (in shares)	0
Undesignated preferred stock, shares issued (in shares)	0
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	140,000,000	140,000,000
Common stock, shares, issued (in shares)	25,646,509	20,337,571
Common stock, shares, outstanding (in shares)	25,646,509	20,337,571
Nonvoting Common Stock
Common stock, shares authorized (in shares)	10,000,000	10,000,000
Common stock, shares, issued (in shares)	0	0
Common stock, shares, outstanding (in shares)	0	0

Nature of Business	3 Months Ended
Nature of Business	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business Overview Tourmaline Bio, Inc. (the “Company”) is a late-stage clinical biotechnology company focused on developing transformative medicines that dramatically improve the lives of patients with life-altering immune and inflammatory diseases. The Company is developing TOUR006, a fully human monoclonal antibody that selectively binds to interleukin-6, a key proinflammatory cytokine involved in the pathogenesis of many autoimmune and inflammatory disorders. The Company’s corporate headquarters are in New York, New York. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive clinical testing and regulatory approval, prior to commercialization. These efforts will require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales. Reverse Merger and Pre-Merger Financing Transaction On October 19, 2023, the Company completed its reverse merger with Tourmaline Sub, Inc. (formerly Tourmaline Bio, Inc.) (“Legacy Tourmaline”) in accordance with the terms of the Agreement and Plan of Merger, dated as of June 22, 2023 (the “Merger Agreement”), by and among the Company, Terrain Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Company (“Merger Sub”), and Legacy Tourmaline, pursuant to which, among other matters, Merger Sub merged with and into Legacy Tourmaline, with Legacy Tourmaline surviving as a wholly owned subsidiary of the Company (the “Reverse Merger”). In connection with the completion of the Reverse Merger, the Company changed its name from “Talaris Therapeutics, Inc.” to “Tourmaline Bio, Inc.,” and the business conducted by the Company became primarily the business conducted by Legacy Tourmaline. References to “the Company” refer to Legacy Tourmaline for periods prior to the closing of the Reverse Merger, and to Tourmaline Bio, Inc. (formerly Talaris Therapeutics, Inc., or “Talaris”) for all other periods, as the context requires. Immediately prior to the effective time of the Reverse Merger, Talaris effected a 1-for-10 reverse stock split of its common stock. At the effective time of the Reverse Merger, the Company issued an aggregate of 15,877,090 shares of Company common stock to the Legacy Tourmaline stockholders, based on the exchange ratio of approximately 0.07977 shares of Company common stock for each share of Legacy Tourmaline common stock, including those shares of Legacy Tourmaline common stock issued upon the conversion of Legacy Tourmaline Series A convertible preferred stock and those shares of the Legacy Tourmaline common stock issued in the Pre-Merger Financing Transaction (as defined below), resulting in 20,336,741 shares of Company common stock being issued and outstanding following the effective time of the Reverse Merger. At the effective time of the Reverse Merger, Legacy Tourmaline’s 2022 Equity Incentive Plan was assumed by the Company, and each outstanding and unexercised option to purchase shares of Legacy Tourmaline common stock immediately prior to the effective time of the Reverse Merger was assumed by the Company and converted into an option to purchase shares of Company common stock, with necessary adjustments to the number of shares and exercise price to reflect the exchange ratio. The Reverse Merger was accounted for as a reverse recapitalization in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). Under this method of accounting, Legacy Tourmaline was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the expectation that, immediately following the Reverse Merger: (i) Legacy Tourmaline’s stockholders own a substantial majority of the voting rights in the combined company; (ii) Legacy Tourmaline’s largest stockholders retain the largest interest in the combined company; (iii) Legacy Tourmaline designated a majority (five of seven) of the initial members of the board of directors of the combined company; and (iv) Legacy Tourmaline’s executive management team became the management team of the combined company. Accordingly, for accounting purposes: (i) the Reverse Merger was treated as the equivalent of Legacy Tourmaline issuing stock to acquire the net assets of Talaris; (ii) the net assets of Talaris are recorded at their acquisition-date fair value in the consolidated financial statements of Legacy Tourmaline and (iii) the reported historical operating results of the combined company prior to the Reverse Merger are those of Legacy Tourmaline. Historical common share figures of Legacy Tourmaline have been retroactively restated based on the exchange ratio of 0.07977. Additional information regarding the accounting for the Reverse Merger is included in Note 3, “Reverse Merger”. Concurrently with the execution and delivery of the Merger Agreement, and in order to provide Legacy Tourmaline with additional capital for its development programs, Legacy Tourmaline entered into a Securities Purchase Agreement (the “Private Placement Agreement”), with certain investors named therein (the “Private Placement Investors”), pursuant to which, subject to the terms and conditions of the Private Placement Agreement, immediately prior to the effective time of the Reverse Merger, Legacy Tourmaline issued and sold, and the Private Placement Investors purchased 4,092,035 shares (as effected by the exchange ratio described above) of Legacy Tourmaline common stock for gross proceeds of approximately $75.0 million (the “Pre-Merger Financing Transaction”). Liquidity As of March 31, 2024, the Company had cash, cash equivalents, and investments of $350.3 million. The Company expects that its existing cash, cash equivalents and investments will enable it to fund its expected operating expenses and capital expenditure requirements for at least 12 months from May 13, 2024, the filing date of this Quarterly Report on Form 10-Q. The Company expects to finance its future cash needs through a combination of equity or debt financings, collaborations, licensing arrangements and strategic alliances.

Stock-Based Compensation

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

2022 Equity Incentive Plan

On September 2, 2022, the Board of Directors and the stockholders of the Company adopted the 2022 Equity Incentive Plan (the “2022 Plan”), which provided for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards and other stock awards to employees, consultants, and non-employee directors of the Company.

2023 Equity Incentive Plan

On October 17, 2023, the Company adopted the 2023 Equity Incentive Plan (the “2023 Plan”) which became effective upon completion of the Reverse Merger. The 2023 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other forms of awards to employees, consultants, and non-employee directors of the Company. The terms of stock award agreements, including vesting requirements, are determined by the Company’s Board of Directors and are subject to the provisions of the 2023 Plan. The term of each stock option shall be no more than ten years from the date of grant. Following the effectiveness of the 2023 Plan, no further grants will be made under the 2022 Plan; however, any outstanding equity awards granted under the 2022 Plan will continue to be governed by the terms of the 2022 Plan.

The 2023 Plan initially provided for the issuance of up to 2,033,677 shares of common stock (the “Initial 2023 Plan Share Reserve”). Subject to any other adjustments as defined in the 2023 Plan, such aggregate number of shares of common stock will automatically increase on January 1st of each year for a period of ten years commencing on January 1, 2024 and ending on (and including) January 1, 2033, in an amount equal to 5% of the total number of shares of common stock issued and outstanding determined as of the day prior to such increase (such increase, the “2023 Plan Evergreen Refresh”); provided, however that the board of directors may act prior to January 1st of a given year to provide that the increase for such year will be a lesser number of shares of common stock. The aggregate maximum number of shares of common stock that may be issued pursuant to the exercise of incentive stock options is three multiplied by the Initial 2023 Plan Share Reserve.

Under the aforementioned 2023 Plan Evergreen Refresh, 1,016,878 shares were added to the Initial 2023 Plan Share Reserve effective January 1, 2024. As of March 31, 2024, there were 1,919,302 shares available for issuance under the 2023 Plan.

2023 Employee Stock Purchase Plan

On October 17, 2023, the Company adopted the 2023 Employee Stock Purchase Plan (the “2023 ESPP”), which became effective upon completion of the Reverse Merger. The maximum number of shares of common stock that may be issued under the 2023 ESPP will not exceed 203,367 shares (the “Initial ESPP Share Reserve”), plus the number of shares of common stock that are automatically added on January 1st of each year for a period of up to ten years commencing on January 1, 2024 and ending on (and including) January 1, 2033, in an amount equal to the lesser of (x) 1% of the total number of shares of common stock issued and outstanding determined as of the day prior to such increase and (y) a number of shares equal to three times the Initial ESPP Share Reserve (such increase, the “ESPP Evergreen Refresh”).

Notwithstanding the foregoing, the Board of Directors may act prior to the first day of any calendar year to provide that there will be no January 1st increase in the share reserve for such calendar year or that the increase in the share reserve for such calendar year will be a lesser number of shares of common stock than would otherwise occur pursuant to the preceding sentence.

Under the aforementioned ESPP Evergreen Refresh, 203,375 shares were added to the Initial ESPP Share Reserve effective January 1, 2024 such that 406,742 shares of common stock may be issued under the 2023 ESPP as of March 31, 2024.

No offering periods under the 2023 ESPP had been initiated as of March 31, 2024.

Stock-based Compensation Expense


	Three Months Ended March 31,
	2024		2023
Research and development	$	556	$	44
General and administrative	832		349
Total stock-based compensation expense	$	1,388	$	393

Stock Option Activity

The fair value of stock options granted during the three months ended March 31, 2024 and 2023 was calculated on the date of grant using the following assumptions:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate	3.9% – 4.3%	3.4% – 3.7%
Dividend yield	—%	—%
Volatility	83.5% – 85.7%	83.4% – 84.3%
Expected term (in years)	6.1	5.5 – 6.1

The weighted-average fair value of the Company’s common stock utilized in the valuation of stock options granted during the three months ended March 31, 2024 and 2023 was $30.48 and $0.25 per share, respectively. Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the three months ended March 31, 2024 and 2023 was $22.57 and $4.01 per share, respectively.

The following table summarizes changes in stock option activity during the three months ended March 31, 2024:


	Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2023	2,445,700	$	9.29	9.6	$	41,320
Granted	80,650	$	30.48
Exercised	—	$	—
Cancelled	(11,630)	$	10.88
Outstanding as of March 31, 2024	2,514,720	$	9.96	9.4	$	33,158
Exercisable as of March 31, 2024	42,316	$	9.94	9.4	$	549

No stock options were exercised during the three months ended March 31, 2024 and 2023.

As of March 31, 2024, the total unrecognized stock-based compensation expense related to unvested stock options was $17.2 million, which the Company expects to recognize over a weighted-average period of approximately 3.2 years.

Early Exercise of Stock Options

The 2022 Plan and certain stock options issued under the 2022 Plan were amended in February 2023 to permit the stock option holder to early exercise at any time between the grant date and the vesting date. The amendment did not result in any incremental stock-based compensation expense. During the year ended December 31, 2023, certain employees, advisors and non-employee directors early exercised 647,386 stock options. In the event of termination of an employee, advisor or non-employee director, the Company can repurchase early exercised and unvested stock options for a period of six months following the later of (i) the termination date of the employee or non-employee director or (ii) the exercise date. The Company received $0.1 million in cash proceeds related to the early exercise of stock options during the year ended December 31, 2023.

As a result of the aforementioned repurchase right, the Company initially records the proceeds received from the early exercise of stock options as a liability in the condensed consolidated balance sheets. Amounts are reclassified to additional paid-in capital when the underlying stock options vest and the Company’s right of repurchase lapses. The aggregate liability associated with the early exercise of stock options was $0.1 million as of March 31, 2024. As of March 31, 2024, 341,198 early exercised stock options remain unvested. The shares of common stock subject to repurchase related to early exercised stock options are legally outstanding, as each holder is deemed to be a common stockholder that has dividend and voting rights during the vesting term.

Restricted Stock Unit Activity

The following table summarizes changes in restricted stock unit activity during the three months ended March 31, 2024:


	Shares	Weighted- Average Grant Date Fair Value per Share
Unvested as of December 31, 2023	19,113	$	11.89
Granted	—	$	—
Vested	(1,247)	$	11.89
Cancelled	—	$	—
Unvested as of March 31, 2024	17,866	$	11.89

The total grant date fair value of restricted stock units vested during the three months ended March 31, 2024 was less than $0.1 million. No restricted stock units vested during the three months ended March 31, 2023. As of March 31, 2024, the

total unrecognized stock-based compensation expense related to unvested restricted stock units was $0.2 million, which the Company expects to recognize over a weighted-average period of approximately 3.5 years.

Common Stock - Narrative (Details)		1 Months Ended	3 Months Ended
Common Stock - Narrative (Details)	Jan. 25, 2024 $ / shares shares	Jan. 31, 2024 USD ($)	Mar. 31, 2024 USD ($) vote shares	Dec. 31, 2023 shares
Class of Stock [Line Items]
Common stock, shares authorized (in shares)			140,000,000	140,000,000
Number of votes for each share of common stock \| vote			1
Dividends, common stock \| $			$ 0
Underwriting Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	4,615,384
Price per share (usd per share) \| $ / shares	$ 32.50
Over-Allotment Option
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	692,307
Period granted to underwriters	30 days
January 2024 Offering
Class of Stock [Line Items]
Gross proceeds from issuance initial public offering \| $		$ 172,500,000
Consideration received on transaction \| $		$ 161,300,000
Nonvoting Common Stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)			10,000,000	10,000,000