Sensei Biotherapeutics Reports Full Year 2021 Financial Results and Business Highlights - Reported preclinical proof of concept data from TMAb platform demonstrating potent and selective pH-dependent binding to active VI

Sensei Biotherapeutics Reports Full Year 2021 Financial Results and Business Highlights

- Reported preclinical proof of concept data from TMAb platform demonstrating potent and selective

pH-dependent binding to active VISTA -

- Initiated 2 new therapeutic programs

and IND-enabling studies with SNS-101, a tumor-selective anti-VISTA antibody product candidate from TMAb platform -

- Strengthened management team and Board of Directors with key appointments -

- Ended fourth quarter 2021 with strong cash, cash equivalents and marketable securities position of $147.6 million; company reiterated

cash runway at least into first half of 2024

BOSTON, MA March 10, 2022 Sensei Biotherapeutics, Inc. (NASDAQ: SNSE), an

immunotherapy company focused on the discovery and development of next generation therapeutics for cancer, today reported financial results for 2021 and provided recent corporate updates.

In 2021, we established important proof points for our SNS-101 program, which is designed to block the VISTA

immune checkpoint, said John Celebi, president and chief executive officer of Sensei Biotherapeutics. VISTA is widely expressed on myeloid cells, presenting a challenge for drug development, yet plays a decisive role in suppressing the

immune system in a broad set of tumor types. SNS-101 is a potent and pH-selective fully human anti-VISTA antibody that is designed to be highly selective for tumors and

therefore has potential to overcome historical challenges associated with targeting VISTA.

Mr. Celebi continued, More broadly, our TMAb

platform represents a fundamental advance for a number of important immune targets that are expressed in both normal tissues and tumors, avoiding potential pharmacokinetic sinks and on-target, off-tumor toxicities. Importantly, we are well funded with more than $147 million as of December 31, 2021 to advance our programs.

2021 Highlights and Milestones:

SNS-101 is a monoclonal antibody targeting the immune checkpoint VISTA and is currently in IND-enabling studies. VISTA (V-domain Ig suppressor of T cell activation) is an immune checkpoint that is implicated in resistance to PD-1/PD-L1 and correlates with poor survival across numerous cancers. In 2021, Sensei achieved the following milestones for this program:

SNS-102 is a monoclonal antibody targeting VSIG4 (V-Set and

Immunoglobulin Domain Containing 4), a B7-family related protein that is frequently overexpressed on tumor-associated macrophages. VSIG4 is a potent inhibitor of

T-cell activity and potential driver of immunosuppressive macrophage polarization. Expression of VSIG4 is also found within normal tissues, presenting potential safety challenges, making VSIG4 an ideal

candidate for Sensei s TMAb platform.

SNS-103 is a monoclonal antibody targeting ENTPDase1

(ecto-nucleoside triphosphate diphosphohydrolase-1), also known as CD39. ENTPDase1 is the upstream, rate-limiting enzyme, leading to the breakdown of extracellular ATP. Extracellular ATP represents a

potent immunologic danger signal , which drives immune activation. The ultimate downstream product of this pathway, adenosine, has potent immunosuppressive activity through binding to adenosine receptors. Upregulation of ENTPDase1 by

tumors is common and leads to a diminished anti-tumor immune response.

SNS-401-NG is a potential first-in-class, multi-antigenic personalized ImmunoPhage candidate being developed in collaboration with the University of Washington designed to treat a broad range of cancers. The first proof-of concept clinical application is directed to the treatment of Merkel cell carcinoma (MCC), an aggressive form of skin cancer commonly driven by the Merkel Cell Polyoma Virus. Sensei plans to conduct a

broader study in patients with multiple tumor types, potentially including head and neck cancer, lung cancer, melanoma, and triple negative breast cancer based on the prevalence of Phortress antigens.

Year End 2021 Financial Results

Cash Position Cash, cash equivalents and marketable securities were $147.6 million as of December 31, 2021, as

compared to $16.6 as of December 31, 2020. Sensei expects the current cash balance to fund operations at least into the first half of 2024.

Research and Development (R&D) Expenses R&D expenses were

$21.7 million for the year ended December 31, 2021, compared to $11.9 million for the year ended December 31, 2020, including Alvaxa IPR+D. The increase in R&D expenses was primarily attributable to increased headcount to

support Sensei s research, development, and manufacturing activities.

General and Administrative (G&A)

Expenses G&A expenses were $15.8 million for the year ended December 31, 2021, compared to $7.5 million for the year ended December 31, 2020. The increase in G&A expenses was primarily

attributable to higher personnel costs, including stock-based compensation expense, and costs associated with operating as a public company.

Loss Net loss was $36.8 million, for the year ended December 31, 2021, compared to $20.1 million for the year ended December 31, 2020.

Condensed Statements of Operations

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

About Sensei Biotherapeutics

Sensei Biotherapeutics is a biopharmaceutical company engaged in discovery, development, and delivery of next generation immunotherapies with an initial focus

on treatments for cancer. Sensei has developed two unique approaches its TMAb (Tumor Microenvironment Activated biologics) platform, comprising unique human monoclonal antibodies and

alpaca derived nanobodies that are selectively active in the tumor microenvironment, and its ImmunoPhage platform that leverages bacteriophage to drive the generation of tumor

antigen-specific immune responses. Using its TMAb platform, the company is developing SNS-101, an antibody-based therapeutic targeting an immune checkpoint gene that inhibits anti-tumor immune responses called V-domain Ig suppressor of T cell

activation (VISTA). Using the ImmunoPhage platform, Sensei is developing a library of ImmunoPhage, called Phortress , with multiple tumor-associated antigens to create a personalized, yet

off-the-shelf cocktail approach for treating cancer patients. The platform is designed to enable efficient, scalable and cost-effective manufacturing to support all of Sensei s clinical programs. SNS-401-NG is an ImmunoPhage cocktail in

preclinical development for the treatment of Merkel cell carcinoma. For more information, please visit www.senseibio.com, and follow the company on Twitter @SenseiBio and LinkedIn.

Cautionary Note Regarding Forward-Looking Statements

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 such as believe , 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 of Sensei s product candidates and platforms, the availability of data from Sensei s preclinical studies, the timing of selection of product candidates, the timing of IND

submissions to the FDA, and its belief that its existing cash and cash equivalents will be sufficient to fund its operations at least into the first half of 2024. 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 preclinical discovery

and development, conduct of clinical trials and related regulatory requirements, Sensei s reliance on third parties over which it may not always have full control, 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 30, 2021 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.

Chief Financial Officer

Sensei Biotherapeutics

Ten Bridge Communications