Sensei Biotherapeutics Reports Full Year 2024 Financial Results and Update on Clinical Progress - Preliminary efficacy data from Phase 1/2 dose expansion cohort show durable responses and tumor shrinkage in a PD-(L)1 res

Sensei Biotherapeutics Reports Full Year 2024 Financial Results and Update on Clinical Progress

- Preliminary efficacy data from Phase 1/2 dose expansion cohort show durable responses and tumor shrinkage in a PD-(L)1 resistant hot tumor patient population -

- Solnerstotug continues to

demonstrate a well-tolerated safety and tolerability profile -

- Achieved target enrollment in dose expansion cohort; full data

expected by year-end 2025 -

- Cash runway into the second quarter of 2026 -

BOSTON, MA March 28, 2025 Sensei Biotherapeutics, Inc. (Nasdaq: SNSE), a clinical stage biotechnology company

focused on the discovery and development of next-generation therapeutics for cancer patients, today reported financial results for the full year 2024, and provided corporate updates.

2024 was a pivotal year for Sensei, as we advanced solnerstotug through dose expansion and began to demonstrate its clinical potential in patients who

have progressed on and are resistant to PD-(L)1 therapy said John Celebi, President and CEO of Sensei Bio. The responses we ve observed in PD-(L)1

resistant tumors are highly encouraging and we believe support solnerstotug s differentiated approach to targeting VISTA. In the context of available data across checkpoint inhibitor regimens, solnerstotug stands out for its encouraging

response rates and favorable tolerability profile in PD-(L)1 resistant tumors, a setting with limited treatment options and no approved therapies targeting VISTA. We are now focused on completing dose

expansion for patients on study and finalizing a robust Phase 2 strategy.

Highlights and Milestones

Solnerstotug (formerly SNS-101) is a conditionally active antibody designed to selectively target the immune checkpoint

VISTA (V-domain Ig suppressor of T cell activation) within the tumor microenvironment. VISTA is implicated in numerous cancer indications and its expression correlates with low survival rates.

Sensei is conducting a multi-center Phase 1/2 clinical trial to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy of

solnerstotug as both a monotherapy and in combination with Regeneron s PD-1 inhibitor Libtayo (cemiplimab) in patients with advanced solid tumors.

Recent updates include:

In March 2025, Sensei presented preliminary dose expansion data showing, as of the data cutoff of March 17, 2025:

Yesterday, Sensei hosted an investor webcast to discuss the dose expansion data, featuring Company leadership and

Dr. Shiraj Sen, M.D., Medical Oncologist and Director of Clinical Research at NEXT-Oncology, Dallas, an investigator on the Phase 1/2 study. The replay of the webcast is available here.

Sensei presented new data and mechanistic insights across multiple forums in 2024:

Year End 2024 Financial Results

Cash, cash equivalents and marketable securities were $41.3 million as of December 31, 2024, as compared to $65.8 million as of December 31, 2023. Sensei expects its current cash balance to fund operations into the second quarter

Research and Development (R&D) Expenses: R&D expenses were $18.6 million for the year ended December 31, 2024, compared

to $18.3 million for the year ended December 31, 2023. The increase in R&D expenses was primarily attributable to higher expense associated with clinical trials and one-time employee termination

benefits primarily offset by lower preclinical research expense and consulting fees.

General and Administrative (G&A) Expenses: G&A

expenses were $13.0 million for the year ended December 31, 2024, compared to $18.8 million for the year ended December 31, 2023. The decrease in G&A expense was primarily attributable to lower costs for external professional

services, lower personnel costs, and lower insurance costs.

Net Loss: Net loss was $30.2 million for the year ended December 31, 2024, compared to

$34.1 million for the year ended December 31, 2023.

About Sensei Biotherapeutics

Sensei Biotherapeutics (Nasdaq: SNSE) is a clinical stage biotechnology company focused on the discovery and development of next-generation therapeutics for

cancer patients. Through its TMAb (Tumor Microenvironment Activated biologics) platform, Sensei develops conditionally active therapeutics designed to disable immunosuppressive signals or

activate immunostimulatory signals selectively in the tumor microenvironment to unleash T cells against tumors. Sensei s lead product candidate is solnerstotug, a conditionally active antibody designed to block the V-domain Ig suppressor of T cell activation (VISTA) checkpoint selectively within the low pH tumor microenvironment, where VISTA acts as a suppressor of T cells by binding the receptor

PSGL-1. For more information, please visit www.senseibio.com, and follow the company on X @SenseiBio and LinkedIn.

Condensed Statements of Operations

(Unaudited, in thousands except share and per share data)

Selected Condensed Balance Sheet Data

(Unaudited, in thousands)

Cautionary Note Regarding Forward-Looking Statements

Any statements contained in this press release that do not describe historical facts may constitute forward-looking statements as that term is defined in the

Private Securities Litigation Reform Act of 1995. These statements may be identified by words and phrases such as believe , designed to, expect , may , plan , potential ,

will , and similar expressions, and are based on Sensei s current beliefs and expectations. These forward-looking statements include expectations regarding the development and potential therapeutic benefits of Sensei s product

candidates, the timing of Sensei s Phase 1/2 clinical trial of solnerstotug, including reporting of data therefrom, and its belief that its existing cash and cash equivalents will be sufficient to fund its operations into the second quarter of

2026. These statements involve risks and uncertainties that could cause actual results to differ materially from those reflected in such statements. Risks and uncertainties that may cause actual results to differ materially include uncertainties

inherent in the development of therapeutic product candidates, such as the risk that any one or more of Sensei s product candidates will not be successfully developed or commercialized; the risk of delay or cessation of any planned clinical

trials of Sensei s product candidates; the risk that prior results, such as signals of safety, activity or durability of effect, observed from preclinical studies and clinical trials, will not be replicated or will not continue in ongoing or

future studies or clinical trials involving Sensei s product candidates; the risk that Sensei s product candidates or procedures in connection with the administration thereof will not have the safety or efficacy profile that Sensei

anticipates; risks associated with Sensei s dependence on third-party suppliers and manufacturers, including sole source suppliers, over which Sensei may not always have full control; risks regarding the accuracy of Sensei s estimates of

expenses, capital requirements and needs for additional financing; and other risks and uncertainties that are described in Sensei s Annual Report on Form 10-K filed with the U.S. Securities and Exchange

Commission (SEC) on March 28, 2025 and Sensei s other Periodic Reports filed with the SEC. Any forward-looking statements speak only as of the date of this press release and are based on information available to Sensei as of the date of

this release, and Sensei assumes no obligation to, and does not intend to, update any forward-looking statements, whether as a result of new information, future events or otherwise.

Senior Director, Investor Relations

Sensei Biotherapeutics