Sensei Biotherapeutics : Company Presentation April 2024

Conditionally Active Antibodies for

Immuno-oncology

Corporate Deck | April 2024

Disclaimer

This presentation has been prepared by Sensei Biotherapeutics, Inc. (the "Company," "we," "us") and is made for informational purposes only.

The information set forth herein does not purport to be complete or to contain all of the information you may desire. Statements contained herein are made as of the date of this presentation unless stated otherwise, and neither the delivery of this presentation at any time, nor any

sale of securities, shall under any circumstances create an implication that the information contained herein is correct as of any time after such date or that information will be updated or revised to reflect information that subsequently becomes available or changes occ urring after the date hereof.

This presentation contains estimates and other statistical data made by independent parties and by us relating to market shares and other data about our industry. This presentation also contains "forward-looking" statements as that term is defined in the Private Securities Litigation Reform Act of 1995 that are based on our management's beliefs and assumptions and on information currently available to management. These forward-looking statements include, without limitation, expectations regarding the development and potential therapeutic benefits of our

product candidates; the expected safety, pharmacokinetic and efficacy profile of our product candidates, including SNS-101; the expected timing of clinical data from our Phase 1/2 clinical trial of SNS-101; the expansion of the Phase 1 clinical trial to include additional patients with

specific tumor types; and our belief that our existing cash and cash equivalents will be sufficient to fund our operations at least into the fourth quarter of 2025 and reach midway into Phase 2 clinical studies of SNS-101.

When used in this presentation, the words and phrases "designed to," "may," "believes," "intends," "seeks," "anticipates," "plans," "estimates," "expects," "should," "assumes," "continues," "could," "will," "future" and the negative of these or similar terms and phrases are intended to identify forward-looking statements. Forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking 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; c onduct of clinical trials and related regulatory requirements, including the risk of delay or cessation of any 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 and early results from the clinical trial of

SNS-101, will not be replicated or will not continue in ongoing or future studies or clinical trials involving Sensei's product candidates, including

SNS-101; our reliance on third parties over which we may not always have full control; risks regarding the accuracy of our estimates of

expenses, capital requirements and needs for additional financing; and other risk and uncertainties that are described in our Annual Report on Form 10-K filed with the SEC on or about February 29, 2024 and our other Periodic Reports filed with the SEC. Forward-looking statements represent our management's beliefs and assumptions only as of the date of this presentation and include all matters that are not historical facts.

Our actual future results may be materially different from what we expect. Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in t he forward-looking

statements, even if new information becomes available in the future.

Certain information contained in this presentation relates to, or is based on, studies, publications, surveys and other data obtained from third-

party sources and the Company's own internal estimates and research. While the Company believes these third-party sources to be reliable as of the date of this presentation, it has not independently verified, and makes no representation as to the adequacy, fairness , accuracy or

completeness of, any information obtained from third-party sources. In addition, all of the market data included in this presentation involves a number of assumptions andlimitations, and there can be no guarantee as to the accuracy or reliability of such assumptions. F inally, while we believe our own internal research is reliable, such research has not been verified by any independent source.

Company Highlights

Sensei Bio's proprietary platform is designed to harness the unique acidic tumor microenvironment to widen the therapeutic window and enable druggability of promising oncology targets

SNS-101, the company's lead asset, targets VISTA, a critical negative regulator of T-cell function and promising immune checkpoint target

SNS-101 is currently in Phase 1 clinical testing with initial data displaying an attractive safety profile and potentially best-in-class pharmacokinetics

Anticipated near-term milestones include topline Phase 1 monotherapy & combination dose escalation data in Q2 2024

Three additional early-stage drug candidates

Cash runway into the fourth quarter of 2025, which is expected to fund operations midway into Phase 2 studies of SNS-101

Seasoned Leadership Team

John Celebi, MBA	Christopher Gerry, J.D.	Edward van der Horst, Ph.D.	Stephanie Krebs, M.S., MBA	Ron Weitzman, M.D.
President and CEO	SVP, General Counsel	Chief Scientific Officer	Chief Business Officer	Chief Medical Officer (part-time)

Large Commercial Opportunity still exists in Immuno-Oncology (IO)

Newly Diagnosed Patients Annually in 20262

Head and Neck Cancer (H+N)

• 1. Market opportunity estimates for PD-1, PDL-1 & anti-CTLA-4 Inhibitors - TD Cowen's Guide to Immuno-oncology

• 2. GlobalData; Incident cases diagnosed in 8MM 2026 (US, UK, Japan, China, France, Germany, Italy, Spain)

VISTA's Potential Commercial Impact

• ❖ The checkpoint market is large and growing fast1

• ❖ Despite the widespread use of checkpoint inhibitors, only 20% of patients experience an objective response

• ❖ Indications such as CRC see little to no benefit from current treatment options

• ❖ VISTA is implicated in numerous solid tumor types with large patient populations

Lack of Tumor Targeting is a Major Obstacle in IO Innovation

Industry Problem

Sensei's Solution

Conventional antibodies target immune checkpoints that are highly expressed in normal tissues, resulting in:Conditionally active antibodies are selectively targeted to the tumor microenvironment, potentially providing:

• • Dose-limiting toxicities due to on-target/off-tumor action

  • • Little or no toxicity due to selective on-target/on-tumor action

• • Pharmacological sink effect requires higher & more frequent dosing

• • Suboptimal activity due to poor PK & dose-limiting toxicities

• • Lower & less frequent doses with tumor-specific binding

• • Powerful activity selectively focused on the tumor microenvironment

2011

2014

One new IO checkpoint inhibitor approved after the CTLA-4 and PD-1/PD-L1 group

2022

The TMAb Platform: pH-sensitive Antibodies Selectively Bind to Targets in the Low-pH Tumor Microenvironment

• • Exploits the tumor microenvironment using pH-selective properties

• • Intended to alleviate undesirable PK/PD properties:

  • • Dose-limiting toxicities due to on-target/off-tumor binding

  • • Higher and more frequent dosing due to poor pharmacokinetics

• • Bolsters specific activities

• • Unlocks previously undruggable immune targets

Innovative Pipeline of IO Drugs with Broad Commercial Potential

*Sensei has entered into a clinical supply agreement with Regeneron supporting the planned evaluation of SNS-101 in combination with Regeneron's anti-PD-1 therapy Libtayo® (cemiplimab) in a Phase 1/2 clinical trial in solid tumors.

*Sensei has entered into a Cooperative Research and Development Agreement (CRADA) with the National Cancer Institute. The goal of this collaborative effort is to further elucidate the role of VISTA in immune checkpoint resistance and expand the potential of SNS-101 as a combination therapy beyond anti-PD-1.

STNESX-1T01 (VISTA)

VISTA is a Potent T cell Checkpoint Extensively Expressed on Myeloid Cells

VISTA is a B7 family member that inhibits T cell activation1

Immunosuppressive function believed to be mediated by PSGL-1 receptorExtensive VISTA expression on off-tumor myeloid-lineage cells demands a conditionally active antibody approach

Upregulated on immune suppressive myeloid-derived suppressor cells (MDSCs) via hypoxia2

Increased expression on tissue infiltrating immune cells upon checkpoint therapy failure3

IS ACTIVATED IN A pH SENSITIVE MANNER

Myeloid lineage cell or tumor cell (less common)

T-cell proliferation & activation

• 1 Wang et al, JEM, 2011

• 2 Deng et al, Cancer Immunonol Res 2019

• 3 Gao et al., Nat Med. 2017

• 4 Johnston et al., Nature 2019

VISTA has inherent pH sensitivity: its extracellular domain is uniquely rich in histidines4

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