Sensei Biotherapeutics Reports Full Year 2023 Financial Results and Recent Business Highlights - Updated dose escalation data from SNS-101 clinical study supports favorable and potentially best-in-class safety and PK pro

Sensei Biotherapeutics Reports Full Year 2023 Financial Results and Recent Business Highlights

- Updated dose escalation data from SNS-101 clinical study supports favorable and potentially best-in-class safety and PK profile both as monotherapy and in combination with PD-1 blockade -

- Topline efficacy and biomarker data for both monotherapy and combination arms of dose escalation study now expected in Q2 2024, ahead of

- Strong balance sheet with cash runway into fourth quarter of 2025 -

BOSTON, MA February 28, 2024 Sensei Biotherapeutics, Inc. (Nasdaq: SNSE), a clinical stage immuno-oncology

company focused on the discovery and development of next-generation therapeutics for cancer patients, today reported financial results for the full year 2023, and provided corporate updates.

2023 saw the entry of our differentiated anti-VISTA antibody, SNS-101, into clinical development, said

John Celebi, President and Chief Executive Officer. Initial data revealed in November, and updated today, support a favorable and potentially best-in-class

clinical safety and PK profile, consistent with preclinical studies, thus overcoming major hurdles associated with prior efforts to drug VISTA. We believe SNS-101 is now the first anti-VISTA therapy to reach

pharmacologically relevant dose levels in a clinical study, and we are looking forward to an exciting year for Sensei. Based on the rapid pace of enrollment, we now plan to share topline efficacy and biomarker data for both monotherapy and

combination arms in the second quarter of 2024, which is ahead of previous guidance. Looking ahead, part of management s attention in 2024 will be directed toward preparations for an end-of-Phase 1 meeting with FDA in the fourth quarter of 2024 and defining the paths we intend to follow over the next several years to maximize the value of SNS-101

and our additional novel product candidates.

Highlights and Milestones

SNS-101 is a conditionally active antibody harnessing the acidic tumor microenvironment to target the immune checkpoint VISTA (V-domain Ig suppressor of T cell activation).

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 SNS-101 as both a monotherapy and in combination with Regeneron s PD-1 inhibitor Libtayo

(cemiplimab) in patients with advanced solid tumors. Recent updates include:

Year End 2023 Financial Results

Cash Position: Cash, cash equivalents and marketable securities were $65.8 million as of December 31, 2023, as compared to $107.1 million

as of December 31, 2022. The decrease is due to cash used to fund operations and $9.8 million relating to shares repurchased during the year ended December 31, 2023. Sensei expects its current cash balance to fund operations into the

fourth quarter of 2025.

Research and Development (R&D) Expenses: R&D expenses were $18.3 million for the year

ended December 31, 2023, compared to $30.4 million for the year ended December 31, 2022. The decrease in R&D expenses was primarily attributable to lower manufacturing-related expenses, lower personnel costs due to the

Company s December 2022 restructuring and lower expense relating to lab supply purchases, partially offset by higher expense associated with clinical trials.

General and Administrative (G&A) Expenses: G&A expenses were $18.8 million for the year ended December 31, 2023, compared to

$19.8 million for the year ended December 31, 2022. The decrease in G&A expense was primarily attributable to lower expense related to director and officer insurance and decreased personnel costs due to the Company s December 2022

Net Loss: Net loss was $34.1 million for the year ended December 31, 2023, compared to $48.6 million for the year

ended December 31, 2022.

About Sensei Biotherapeutics

Sensei Biotherapeutics (Nasdaq: SNSE) is a clinical stage immuno-oncology 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 investigational candidate is SNS-101, 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. The company is also developing SNS-102, a conditionally active monoclonal antibody targeting V-Set and Immunoglobulin Domain

Containing 4 (VSIG-4); SNS-103, a conditionally active monoclonal antibody targeting ecto-nucleoside triphosphate

diphosphohydrolase-1 (ENTPDase1), also known as CD39; and SNS-201, a conditionally active VISTAxCD28 bispecific antibody consisting of a CD28 agonist arm and a pH-sensitive anti-VISTA arm. 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 SNS-101, including reporting of data therefrom, the timing of preclinical R&D activities, and its belief that its existing cash and cash

equivalents will be sufficient to fund its operations at least into the fourth quarter of 2025. 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 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 or about February 29, 2024 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