Subsequent Events	6 Months Ended
Jun. 30, 2026
Subsequent Events [Abstract]
Subsequent Events	14. SUBSEQUENT EVENTS Next-Generation In Vivo CAR-T Platform and TPST-4003 Clinical Plan On July 15, 2026, the Company announced details of its next-generation in vivo CAR-T platform, CD7-tLNP, and its plans to advance TPST-4003, its lead in vivo CAR-T product candidate, into a first investigator-initiated clinical trial (the “IIT”) in patients with nervous system autoimmune diseases, initially focusing on myasthenia gravis and multiple sclerosis. TPST-4003 combines the Company’s CD7-targeted mRNA lipid nanoparticle delivery platform with the same dual-targeting CD19/BCMA CAR architecture used in TPST-2003, the Company’s clinical-stage CAR-T program. Collaboration Agreement with Senlang Biotechnology On July 17, 2026, the Company entered into a product development and collaboration agreement (the “Collaboration Agreement”) with Hebei Senlang Biotechnology Co., Ltd. (“Senlang”), a clinical-stage cell therapy company with expertise in CD7-targeted CAR-T development. Pursuant to the Collaboration Agreement, the Company and Senlang agreed to collaborate on product development and investigator-initiated trial activities in China for certain of the Company’s in vivo CAR-T product candidates. Collaboration activities for each product candidate under the Collaboration Agreement will be governed by a separate statement of work specifying the applicable product development plan, budget, and timeline. The Collaboration Agreement also grants Senlang an exclusive option to negotiate and enter into a definitive license agreement for TPST-4003 in China. Lincoln Park Capital Purchase Agreement In August 2026, the Company entered into a purchase agreement and a registration rights agreement with Lincoln Park Capital Fund, LLC (“Lincoln Park”), pursuant to which the Company has the right, but not the obligation, to sell to Lincoln Park from time to time, at the Company’s sole discretion and subject to the satisfaction of certain conditions, up to $25.0 million of shares of the Company’s common stock. Upon the purchase by Lincoln Park of the full initial $25.0 million commitment, the available commitment will automatically increase by an additional $25.0 million, for an aggregate commitment of up to $50.0 million. The Company’s ability to commence sales under the purchase agreement is subject to certain conditions, including the effectiveness of a registration statement covering the resale of shares issuable under the agreements. Pursuant to the registration rights agreement, the Company is required to file such registration statement with the SEC within ten days following execution of the agreements. Upon the execution of the Purchase Agreement, the Company issued 560,356 shares of the Company’s common stock issued to Lincoln Park as consideration for its commitment to purchase shares of the Company’s common stock under the purchase agreement. Lincoln Park has agreed not to cause or engage in any manner whatsoever, any direct or indirect short selling or hedging of the Company’s common stock.

Subsequent Events

6 Months Ended

Jun. 30, 2026

14. SUBSEQUENT EVENTS

Next-Generation In Vivo CAR-T Platform and TPST-4003 Clinical Plan

On July 15, 2026, the Company announced details of its next-generation in vivo CAR-T platform, CD7-tLNP, and its plans to advance TPST-4003, its lead in vivo CAR-T product candidate, into a first investigator-initiated clinical trial (the “IIT”) in patients with nervous system autoimmune diseases, initially focusing on myasthenia gravis and multiple sclerosis. TPST-4003 combines the Company’s CD7-targeted mRNA lipid nanoparticle delivery platform with the same dual-targeting CD19/BCMA CAR architecture used in TPST-2003, the Company’s clinical-stage CAR-T program.

Collaboration Agreement with Senlang Biotechnology

On July 17, 2026, the Company entered into a product development and collaboration agreement (the “Collaboration Agreement”) with Hebei Senlang Biotechnology Co., Ltd. (“Senlang”), a clinical-stage cell therapy company with expertise in CD7-targeted CAR-T development. Pursuant to the Collaboration Agreement, the Company and Senlang agreed to collaborate on product development and investigator-initiated trial activities in China for certain of the Company’s in vivo CAR-T product candidates.

Collaboration activities for each product candidate under the Collaboration Agreement will be governed by a separate statement of work specifying the applicable product development plan, budget, and timeline. The Collaboration Agreement also grants Senlang an exclusive option to negotiate and enter into a definitive license agreement for TPST-4003 in China.

Lincoln Park Capital Purchase Agreement

In August 2026, the Company entered into a purchase agreement and a registration rights agreement with Lincoln Park Capital Fund, LLC (“Lincoln Park”), pursuant to which the Company has the right, but not the obligation, to sell to Lincoln Park from time to time, at the Company’s sole discretion and subject to the satisfaction of certain conditions, up to $25.0 million of shares of the Company’s common stock. Upon the purchase by Lincoln Park of the full initial $25.0 million commitment, the available commitment will automatically increase by an additional $25.0 million, for an aggregate commitment of up to $50.0 million.

The Company’s ability to commence sales under the purchase agreement is subject to certain conditions, including the effectiveness of a registration statement covering the resale of shares issuable under the agreements. Pursuant to the registration rights agreement, the Company is required to file such registration statement with the SEC within ten days following execution of the agreements. Upon the execution of the Purchase Agreement, the Company issued 560,356 shares of the Company’s common stock issued to Lincoln Park as consideration for its commitment to purchase shares of the Company’s common stock under the purchase agreement. Lincoln Park has agreed not to cause or engage in any manner whatsoever, any direct or indirect short selling or hedging of the Company’s common stock.