• A confirmed complete response was observed in the first patient in the lowest-dose cohort of the Phase 1 SQZ-AAC-HPV-101 clinical trial
• Following review and recommendation by the Study Safety Committee, the Company is advancing SQZ-AAC-HPV-101 trial to the highest-dose cohort
• Strong enrollment rates; Anticipate initial clinical data from the highest-dose cohort in the fourth quarter of 2023

SQZ Biotechnologies Company (NYSE: SQZ), focused on unlocking the full potential of cell therapies, today announced that, according to RECIST 1.1 criteria, a confirmed complete response was observed in the first patient in the lowest-dose cohort of the Phase 1 SQZ-AAC-HPV-101 clinical trial. The company has decided to continue to enroll patients in the SQZ-AAC-HPV-101 clinical trial. The second and third patients have also been enrolled in the trial. The company has completed the dose-limiting toxicity period for the lowest-dose cohort. The Study Safety Committee has completed their review and recommends that the company enroll patients in the highest-dose cohort. The company anticipates initial clinical data from the highest-dose cohort by the fourth quarter of 2023.

“Although early in this trial, we have observed good tolerability among the patients. The confirmed complete response observed in this patient demonstrates the potential of the investigational therapy’s intended immunotherapy mechanism,” said Richard T. Maziarz, M.D., Professor of Medicine and Investigator, Oregon Health & Science University.

“We are motivated by the clinical response in our first patient in the AAC trial,” said Marshelle Smith Warren, M.D., Chief Medical Officer at SQZ Biotechnologies. “We find it encouraging that the confirmed complete response occurred in our lowest-dose cohort. It is still early days, but we are optimistic as we look to enroll additional patients and anticipate initial data from the highest-dose cohort in the fourth quarter of this year.”

Patient Characteristics & Treatment Journey

The patient is a 61-year-old male with a history of metastatic HPV16+ rectal squamous cell carcinoma. The patient had two prior lines of treatment but had not been treated with immune checkpoint inhibitors. The patient remains on study and the treatment has been well tolerated to date.

In December 2022, after two cycles of SQZ-AAC-HPV, a CT scan showed reduction of the target lesion to meet RECIST 1.1 criteria for a partial response. In February 2023, after four cycles of SQZ-AAC-HPV, a CT scan showed further reduction of the target lesion which was consistent with a confirmed partial response by RECIST 1.1 criteria. In March 2023, after seven cycles of SQZ-AAC-HPV, a CT scan confirmed the complete response by RECIST 1.1 criteria.

An investor presentation is available on the Events & Presentations page within the investor relations section of the company’s corporate website, investors.sqzbiotech.com. Based on guidance from the SEC, investors should note that the company may utilize its corporate website to post updated corporate and scientific presentations. It is possible that the information posted there could be deemed to be material information.

About SQZ-AAC-HPV

SQZ® Activating Antigen Carriers (AAC) are derived from red blood cells (RBCs) engineered with the Cell Squeeze® technology to contain tumor-specific antigens and adjuvant. Cell Squeeze® is designed to increase the phosphatidylserine (PS) on the surface of the AACs resulting in the AACs resembling aged RBCs. AACs are designed to take advantage of the natural physiological process of aged RBC clearance by resident, professional APCs in lymphoid organs. These professional APCs can subsequently prime endogenous T cells to potentially drive antitumor activity. The company has an ongoing Phase 1 clinical trial for the SQZ-AAC-HPV investigational therapy in HPV16+ advanced or metastatic tumors.

ENVOY-001 Trial Design

SQZ-AAC-HPV is being evaluated in a Phase 1 clinical trial (ENVOY-001. SQZ-AAC-HPV-101) for the treatment of HPV16+ advanced or metastatic solid tumors. The investigational candidate, which targets E6 and E7 oncoproteins, is being studied as a monotherapy and in combination with immune checkpoint inhibitors. The study consists of two parts. The first part is designed to assess the safety and tolerability of multiple doses of SQZ-AAC-HPV monotherapy in treatment-experienced patients. The second part of the study will assess safety and tolerability of SQZ-AAC-HPV in combination with nivolumab and/or ipilimumab.

About Human Papillomavirus Positive Cancers

Human papillomavirus (HPV) is one of the most common viruses worldwide and certain strains persist for many years, often leading to cancer. According to the Centers for Disease Control (CDC), in the United States HPV+ tumors represent 3% of all cancers in women and 2% of all cancers in men, resulting in over 39,000 new cases of HPV+ tumors every year. HPV infection is larger outside of the U.S., and according to the International Journal of Cancer, HPV+ tumors account for 4.5% of all cancers worldwide resulting in approximately 630,000 new cases every year. According to the CDC, HPV infection plays a significant role in the formation of more than 90% of anal and cervical cancers, and most cases of vaginal (75%), oropharyngeal (70%), vulval (70%) and penile (60%) cancers.

About SQZ Biotechnologies

SQZ Biotechnologies is a clinical-stage biotechnology company focused on unlocking the full potential of cell therapies. The company’s proprietary Cell Squeeze® technology offers the unique ability to deliver multiple biological materials into many patient cell types to engineer what the company believes can be a broad range of potential therapeutics. The company’s goal is to create well-tolerated cell therapies that can provide therapeutic benefit for patients and improve the patient experience over existing cell therapy approaches. With production timelines under 24 hours and the opportunity to eliminate preconditioning and lengthy hospital stays, the company believes its approach could change the way people think about cell therapies. For more information, please visit www.sqzbiotech.com.

Forward Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation statements relating to the timing and outcome of the company’s clinical trials, clinical safety and efficacy of its therapeutic candidates and the potential addressable market for the company’s therapeutic candidates. These forward-looking statements are based on management's current expectations. Actual results could differ from those projected in any forward-looking statements due to several risk factors. Such factors include, among others, risks and uncertainties related to the company’s significant losses incurred since inception and expectation to incur significant additional losses for the foreseeable future; the company’s need for additional funding; the development of the company’s initial product candidates, upon which its business is highly dependent; the impact of the COVID-19 pandemic on the company’s operations and clinical activities; the lengthy, expensive, and uncertain process of clinical drug development, including uncertain outcomes of clinical trials and potential delays in regulatory approval; and protection of the company’s proprietary technology, intellectual property portfolio and the confidentiality of its trade secrets. These and other important factors discussed under the caption "Risk Factors" in the company’s Quarterly Report on Form 10-Q, the company’s Annual Report on Form 10-K, and other filings with the U.S. Securities and Exchange Commission could cause actual results to differ materially from those indicated by the forward-looking statements. Any forward-looking statements represent management's estimates as of this date and the company undertakes no duty to update these forward-looking statements, whether as a result of new information, the occurrence of current events, or otherwise, unless required by law.

Certain information contained in this press release 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 press release, the company has not independently verified, and the company makes no representation as to the adequacy, fairness, accuracy, or completeness of any information obtained from third-party sources.

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