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Assay developed using Abyssinia proprietary antibodies shows promise as sensitive and specific companion diagnostic Further pre-clinical data hints at potential therapeutic applications of antibodies DURHAM, N.H. and BOSTON, Nov. 16, 2021 (GLOBE NEWSWIRE) -- Abyssinia Biologics, LLC, a biotechnology company focused on developing Alzheimer’s disease (AD) diagnostic and therapeutic monoclonal antibodies, today announced the publication of a study entitled, “An Ultra-sensitive Immunoassay Detects and Quantifies Soluble Aβ Oligomers in Human Plasma,” in the Journal Alzheimer’s and Dementia. The publication is the result of a two-year collaboration designed to characterize and investigate the preclinical diagnostic and therapeutic utility of Abyssinia Biologics’ two monoclonal antibody candidates, ABY-71A1 and ABY-1G5, having novel anti-oligomeric Aβ binding properties. Over the last two decades, independent research institutes worldwide have provided data supporting the role of soluble oligomers of the amyloid β-protein (oAβ) as an important and early trigger in the pathogenic cascade of Alzheimer’s disease. For example, soluble oligomers cause synaptic dysfunction, neuritic injury, microgliosis, and increased tau phosphorylation. To date, there are few antibodies in clinical development that selectively target soluble synaptotoxic Aβ oligomers, and there have been no rigorously validated immunoassays specific for capturing and quantifying this low-abundance biomarker of AD in human blood. “We are encouraged by the excellent data coming from the Selkoe Lab that validates our candidates’ potential. Our focus is on the science and bringing this immunoassay and the potential immunotherapies to the clinic and on a path to help patients with AD,” said Dr. Robert Lawton, founding scientist of Abyssinia Biologics. Experiments just published in the journal Alzheimer’s & Dementia led by the Selkoe Lab at the Ann Romney Center for Neurologic Diseases, Brigham and Women’s Hospital and Harvard Medical School, further characterized the unique oligomer-preferring properties of monoclonal antibodies ABY-71A1 and ABY-1G5 and detailed their use as sensitive and specific reagents for capture of soluble Aβ oligomers in human brain tissue, CSF and plasma. The immunoassay developed by Brigham Drs. Lei Liu and Dennis Selkoe and colleagues showed excellent dilution linearity in CSF and plasma with little to no matrix effects, good spike-recovery, and specific immunodepletion. The paper also presents early CSF correlative data suggesting that the oAβ levels detected by ABY-71A1 in CSF may correlate with tau and phospho-tau protein levels that can be diagnostic of AD. Additional pre-clinical experiments at the Selkoe Lab elucidated the therapeutic potential of the antibodies. Selkoe et al. showed ABY-71A1 can potently neutralize the synaptotoxicity of AD brain-derived soluble oAβ, as demonstrated by experiments measuring long-term potentiation (LTP) in mouse hippocampus. Furthermore, oAβ purified from AD brain by ABY-71A1 potently inhibits hippocampal LTP, suggesting that the antibody is binding to synaptotoxic species of Aβ. The study publication can be found in the journal Alzheimer’s & Dementia at the following link: Liu L, Kwak H, Lawton TL, Jin SX, Meunier AL, Dang Y, Ostaszewski B, Pietras AC, Stern AM, Selkoe DJ. An ultra-sensitive immunoassay detects and quantifies soluble Aβ oligomers in human plasma. Alzheimers Dement. 2021 Sep 22. doi: 10.1002/alz.12457. Media coverage: About ABY-71A1 and ABY-1G5 ABY-71A1 and ABY-1G5 are monoclonal antibodies designed to bind oligomers of Aβ, and they are currently in preclinical development as plasma-based diagnostic tools and as potential immunotherapeutics. About Abyssinia Biologics, LLC: Abyssinia Biologics is a preclinical-stage biotechnology company focused on developing Alzheimer's disease (AD) diagnostic and therapeutic candidates with world-leading academic collaborators. The Company’s portfolio includes a sensitive immunoassay in preclinical development as a diagnostic tool, two monoclonal antibody potential immunotherapy candidates in preclinical development, and a novel oligomeric amyloid beta (Aβ) immunogen. Antibodies ABY-71A1 and ABY-1G5 specifically target toxic, soluble, oligomeric species of Aβ. Abyssinia Biologics is actively looking for partnership opportunities with companies in the CNS space that are dedicated to diagnosing, treating, and preventing Alzheimer’s disease. The Company is headquartered in Durham, New Hampshire. Additional information on the Company can be found at: Please follow us on LinkedIn Media and/or Investor inquiries for Abyssinia Biologics, LLC: Noah Ullman Noah@aby-bio.com 1+(617) 682-9360‬

- Company announced first set of pH-sensitive anti-VISTA antibodies showing significant in vivo anti-tumor activity in combination with PD-1 blockade in a human VISTA knock-in mouse model – - Company plans to select a lead SNS-VISTA candidate and initiate IND-enabling studies by year-end 2021 - SNS-401-NG on track to start IND-enabling studies in second half of 2022 – -Strong cash position of $162.5 million to support platform innovation and next generation program development - BOSTON, Aug. 04, 2021 (GLOBE NEWSWIRE) -- 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 the second quarter ended June 30, 2021 and provided recent corporate updates, including new in vivo data from the company’s SNS-VISTA program. “The second quarter of 2021 was an important one for Sensei as we advanced our next-generation ImmunoPhage platform technology based on critical learnings from our first generation ImmunoPhage and expanded our R&D footprint and capabilities. We also continue to make important strides toward the clinic with our SNS-VISTA program,” said John Celebi, president and chief executive officer of Sensei Biotherapeutics. “As we enter the third quarter of 2021, we are in a strong cash position to progress our development programs. By leveraging the synergies of these programs, our goal is to generate tumor-specific T-cells through our ImmunoPhage platform and to unleash the full potential of tumor-specific T-cells through our TMAb platform. We are looking forward to sharing additional data and to announcing new programs.” Sensei also announced today early in vivo data from its SNS-VISTA program. VISTA is recognized as an important immune checkpoint regulator. Disrupting the interaction of VISTA and its receptor on T-cells, known as PSGL1, has been shown to enhance T-cell activation and tumor cell killing. The VISTA-PSGL1 T-cell checkpoint is activated under low pH conditions such as the tumor microenvironment. Sensei’s research team has identified a set of fully-human, highly selective, pH-dependent anti-VISTA antibodies. In a human VISTA knock-in mouse model, these parental antibodies significantly enhanced anti-tumor responses in combination with PD-1 blockade compared to treatment with PD-1 blockade alone. Based on these nonclinical data, the company plans to initiate IND-enabling studies with a lead candidate and present data at a scientific conference by the end of 2021. “Since the inception of our SNS-VISTA program, we have believed the key to unlocking the power of this immune checkpoint is to design an antibody that selectively binds and blocks VISTA at low pH levels in the tumor microenvironment,” said Robert Pierce, MD, chief scientific officer of Sensei Biotherapeutics. “This pH-driven, tumor-selective approach is an important feature of our VISTA platform due to high levels of expression on blood cells at physiologic pH. Thus, blood represents a significant pharmacokinetic sink, which can hinder distribution into the tumor microenvironment. Additionally, we believe that by engineering pH-sensitivity into our VISTA antibody, the safety profile may be improved by limiting on-target and off-tumor binding and activity. We believe these nonclinical data are an important proof point for our platform. We look forward to selecting a lead candidate and moving into IND-enabling studies.” Recent Updates and Second Quarter Highlights: Strengthened Board of Directors and Immuno-Oncology Advisory Board – In August, Sensei announced that it appointed Kristian Humer as an independent director to its Board. Additionally, in the second quarter, Sensei announced the addition of Jessie English, Ph.D. to its Board of Directors and Maura Gillison, M.D. and Richard Ulevitch, Ph.D. to its Immuno-Oncology Advisory Board. Prioritized pipeline toward next-generation platform programs – In June, Sensei announced its decision to reprioritize its resources toward its pipeline of next generation product candidates, including: its multi-antigenic next generation ImmunoPhage candidate SNS-401-NG, which uses an optimized antigen linkage technology developed at Sensei; its monoclonal antibody SNS-VISTA (V-set Immunoglobulin Domain Suppressor of T cell Activation) candidate; and complete discovery work for its VSIG4 (V-Set And Immunoglobulin Domain Containing 4) TMAb program. As part of the company’s prioritization, it discontinued development of SNS-301, a first-generation, single-antigen ImmunoPhage that expressed a fragment of the tumor-associated antigen, human aspartate β-hydroxylase (ASPH). Strengthened TMAb (Tumor Microenvironment Antibody Biologics) platform – In July, Sensei expanded the scope of its collaboration with AdiMab, LLC to include additional antibody campaigns focused on the generation of human monoclonal antibodies for its next generation pH sensitive antibody programs. Selected Contract manufacturer (CDMO) for SNS-VISTA – In July, Sensei selected a CDMO for the manufacture of GMP-grade material to advance its SNS-VISTA program toward clinical studies. Expanded Operational Footprint – In June, Sensei expanded its research footprint by adding an additional 5,000 square feet of laboratory space at its 451D Street Boston headquarters. The additional lab space will support the advancement of Sensei technologies used for the discovery of nanobodies used in its ImmunoPhage platform or as standalone therapeutics. Upcoming Program Milestones: Sensei is focused on progressing novel product candidates generated from both its ImmunoPhage platform and Phortress Library™, and TMAb platform. Sensei’s Phortress Library of Immunophages, derived from antigens found across multiple patient populations and tumor types, enables a personalized, yet off-the-shelf therapeutic option to patients. TMAb (Tumor Microenvironment Antibody Biologics) Platform VISTA (V-domain Ig suppressor of T cell activation) is an immune checkpoint that inhibits anti-tumor immune responses. VISTA may play a role in both intrinsic and acquired PD-1/PD-L1 resistance. VSIG4 (V-Set and Immunoglobulin Domain Containing 4) is a B7-family related protein and a potent inhibitor of T-cell activity, often overexpressed on macrophages within the tumor microenvironment. VSIG4 may play a role in enforcing the immunosuppressive program in macrophage-rich tumors. Inhibition of VSIG4 activity could also enhance T-cell-mediated anti-tumor immune responses. ImmunoPhage™ Platform SNS-401-NG is a potential first-in-class, multi-antigenic personalized ImmunoPhage candidate being developed in collaboration with the University of Washington. The first 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. Once clinical proof of concept is achieved, Sensei plans to evaluate a broader basket study in patients with head and neck cancer, lung cancer, melanoma, and triple negative breast cancer based on the prevalence of Phortress antigens. Second Quarter 2021 Financial Results Cash Position – Cash, cash equivalents and marketable securities were $162.5 million as of June 30, 2021, as compared to $16.6 million 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 $5.9 million for the quarter ended June 30, 2021, compared to $2.9 million for the quarter ended June 30, 2020. 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 $3.9 million for the quarter ended June 30, 2021, compared to $1.3 million for the quarter ended June 30, 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. Net Loss – Net loss was $9.8 million, for the quarter ended June 30, 2021, compared to $4.9 million for the quarter ended June 30, 2020. About Sensei BiotherapeuticsSensei 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 ImmunoPhage platform that leverages bacteriophage to fully engage the immune system, and its TMAb (Tumor Microenvironment Antibody Biologics) platform, comprising unique human monoclonal antibodies and alpaca derived nanobodies that are selectively active in the tumor microenvironment. Using the ImmunoPhage platform, Sensei is developing a library of ImmunoPhage, called Phortress™, to target 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. Using its TMAb platform, the company has developed SNS-VISTA, an antibody-based therapeutic in lead generation targeting an immune checkpoint gene that inhibits anti-tumor immune responses called V-domain Ig suppressor of T cell activation (VISTA). For more information, please visit , and follow the company on Twitter @SenseiBio and LinkedIn. 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 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, 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. Investor Contact:Lora PikeVP, Investor Relations and CommunicationsSensei Biotherapeuticslpike@senseibio.com Media Contact:Mike BeyerSam Brown Inc. Healthcare Communications312-961-2502mikebeyer@sambrown.com

- Company to focus on development of next-generation phage product candidates from ImmunoPhage platform and monoclonal antibody and nanobody programs - - Discontinuation of first-generation, single-antigen phage SNS-301 program upon analysis of clinical activity and antigen specific T-cell data - - Cash runway extended into first half of 2024 - - Conference call scheduled for today at 4:30 p.m. ET - BOSTON, June 28, 2021 (GLOBE NEWSWIRE) -- Sensei Biotherapeutics, an immunotherapy company focused on the discovery and development of next generation therapeutics for cancer, today announced that it is reprioritizing its pipeline programs to focus on its product candidates, including its multi-antigenic next generation ImmunoPhage candidate, now referred to as SNS-401-NG, and its monoclonal antibody SNS-VISTA (V-set Immunoglobulin Domain Suppressor of T cell Activation) candidate. With this reallocation of resources, Sensei expects its cash and cash equivalents will be sufficient to fund its operations into the first half of 2024. “Sensei’s approach to drug development is deeply rooted in targeting key mechanisms of checkpoint resistance to induce a robust, focused and coordinated immune response to cancer. We believe our next generation, multi-antigenic ImmunoPhage product candidates have the potential to drive robust antigen-specific T cell responses that will translate into clinical benefit,” said John Celebi, president and chief executive officer of Sensei Biotherapeutics. “Given the totality of data generated to-date from the Phase 1/2 combination trial of first-generation SNS-301, we believe we have captured important insights into the power of our ImmunoPhage platform that will further advance development of our pipeline product candidates. Through SNS-301, we have gained important information on key product attributes that we believe contribute to the safety and immunogenicity of our ImmunoPhage platform as well as how to manufacture and scale our product candidates. Specifically, we have learned that the use of gpD fusion as an antigen display technology is suboptimal for use in an active cancer vaccine. We believe the incorporation of new antigen attachment technologies will ensure optimal immunogenicity. We are excited by our next generation programs, and we look forward to further advancing our two ongoing programs SNS-401-NG and SNS-VISTA into the clinic and completing discovery work for our VSIG4 antibody program.” “I would like to express my gratitude to all of the patients and their families, investigators and collaborators who participated in the SNS-301 study,” said, Marie-Louise Fjaellskog, M.D., Ph.D. chief medical officer of Sensei Biotherapeutics. “Our data-driven decision-making process is at the forefront of our work, and we are well positioned and capitalized to further progress our next-generation pipeline programs, SNS-401-NG and SNS-VISTA, by utilizing our two unique drug discovery approaches – our ImmunoPhage platform and our monoclonal antibody and nanobody platform. We look forward to initiating IND-enabling studies for SNS-VISTA by the end of 2021 and for SNS-401-NG in second half of 2022.” SNS-301 was developed as a first-generation, bio-engineered, inactivated bacteriophage virus expressing a fragment of the tumor-associated antigen, human aspartate β-hydroxylase (ASPH), as a fusion protein to the bacteriophage lambda capsid decoration protein, gpD, for patients with locally advanced unresectable or metastatic squamous cell head and neck cancer (SCCHN). To date, 25 patients were enrolled in the Phase 1/2 clinical study and received at least one dose of SNS-301 in combination with pembrolizumab; one patient had a deep and durable partial response (PR) and 8 patients had stable diseases. While encouraged by the safety pro the SNS-301 single antigen approach, based upon the recent analysis of antigen specific T-cell activation which did not show a significant increase in ASPH-specific T cells, including the one patient who experienced a long-standing and deep PR, and an updated analysis of clinical data, Sensei has decided to reprioritize its pipeline and refocus resources. Sensei anticipates sharing full SNS-301 clinical data and the results of specific B and T cell response data at a future scientific conference. Next-Generation Pipeline Highlights and Upcoming Milestones Sensei is focused on progressing novel product candidates generated from both its ImmunoPhage platform and Phortress Library™, coupled with its human monoclonal antibody and nanobody platform. Sensei’s Phortress Library of immunophages, derived from antigens found across multiple patient populations and tumor types, enables a personalized, yet off-the-shelf therapeutic option to patients. SNS-401-NG is a first-in-class, multi-antigenic personalized ImmunoPhage candidate being developed in collaboration with the University of Washington. Sensei has designed SNS-401-NG as a personalized product candidate composed of premanufactured Immunophage from Sensei’s Phortress library on an improved and proprietary bacteriophage construct. Sensei intends to initiate IND-enabling studies for this product candidate in the second half of 2022. The first 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. If clinical proof of concept is achieved, Sensei plans to evaluate a broader basket study in patients with head and neck cancer, lung cancer, melanoma, and triple negative breast cancer based on the prevalence of Phortress antigens. VISTA (V-domain Ig suppressor of T cell activation) is an immune checkpoint that inhibits anti-tumor immune responses. VISTA is implicated in PD-1/PD-L1 resistance and therapeutic intervention. VISTA has the potential to be effective as a monotherapy and synergistic with PD-1/PD-L1 inhibition. Sensei has generated potent pH-dependent parental antibodies that block the interaction of VISTA with its receptor, PSGL1, expected to result in a favorable pharmacokinetic (PK) pro selective activity in the acidic tumor microenvironment – a critical feature of this product candidate, and an important differentiator to other compounds in development targeting VISTA. Sensei plans to present preclinical data from the SNS-VISTA program at a scientific conference in 2021 and to initiate IND-enabling studies by the end of 2021. VSIG4 (V-Set And Immunoglobulin Domain Containing 4) is a potent inhibitor of T cell activity, often overexpressed on macrophages within the tumor microenvironment. Sensei believes that a tumor-selective blocking monoclonal antibody will have potent anti-tumor immune effects. Sensei is extending its approach to developing antibodies with enhanced tumor selective activity to other candidate immune checkpoint targets, and anticipates selecting a product candidate from this program in 2023. Conference Call and Webcast Information Sensei will host a live conference and webcast today, June 28, 2021, at 4:30 p.m. ET, to discuss these company updates. To access the conference call, please dial 833-362-0204 (domestic) or 914-987-7673 (international) and refer to conference ID number 7464477. The live webcast can be accessed under the “Events & Presentations” section of Sensei’s website at . The webcast will be archived and made available for replay on Sensei’s website approximately two hours after the call and will be available for 30 days. 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 ImmunoPhage platform that leverages bacteriophage to fully engage the immune system, and its monoclonal antibody (mAb) and nanobody platform, comprising unique human monoclonal antibodies and alpaca derived nanobodies that are selectively active in the tumor microenvironment. Using the ImmunoPhage platform, Sensei is developing a library of ImmunoPhage, called Phortress™, to target 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. Using its mAb platform, the company has developed SNS-VISTA, an antibody-based therapeutic in lead generation targeting an immune checkpoint gene that inhibits anti-tumor immune responses called V-domain Ig suppressor of T cell activation (VISTA). For more information, please visit , and follow the company on Twitter @SenseiBio and LinkedIn. 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 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 preclinical and clinical development of Sensei’s product candidates and platforms, the availability of data from Sensei’s clinical trials, and its belief that its existing cash and cash equivalents will be sufficient to fund its operations 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. Investor Contact: Lora Pike VP, Investor Relations and Communications Sensei Biotherapeutics lpike@senseibio.com Media Contact: Mike Beyer Sam Brown Inc. Healthcare Communications 312-961-2502 mikebeyer@sambrown.com