<img src="https://ml-eu.globenewswire.com/Resource/Download/d47c1200-a3a8-42b0-b0b9-ffb74568b42c?size=2" nborder="0" align="left" hspace="5" vspace="5" title="Mestag-tx logo.png" alt="Mestag Therapeutics"/>-- STARLYS trial to evaluate the potential of MST-0312, a targeted lymphotoxin-beta (LTBR) agonist bispecific antibody, as a novel therapeutic strategy for the treatment of solid tumors. -- Study to evaluate tertiary lymphoid structure (TLS) and high endothelial venule (HEV) formation in the tumor as well as clinical responses, as monotherapy and in combination with PD-1 inhibitor Keytruda® (pembrolizumab). CAMBRIDGE, United Kingdom, May 19, 2026 (GLOBE NEWSWIRE) -- Mestag Therapeutics, a clinical-stage biotech company harnessing fibroblast immunology for the benefit of patients with inflammatory disease and cancer, today announced the dosing of the first patient in a Phase 1 clinical trial evaluating MST-0312 in patients with selected advanced solid tumors. The first in human trial, named the STARLYS trial, is an adaptive, modular multi-part, multi-arm open-label study designed to evaluate the safety, tolerability, pharmacodynamics, pharmacokinetics and anti-tumor activity of MST-0312 alone and in combination with pembrolizumab. MST-0312 is a bispecific antibody designed to activate lymphotoxin-beta receptor (LTBR) in the tumor microenvironment to induce the formation of tertiary lymphoid structures (TLS) and associated high endothelial venules (HEV) in tumor tissue. TLS are a hallmark of effective anti-tumor immunity consisting of aggregates of T, B and dendritic cells, associated with the recruitment, education, and activation of immune cells to drive anti-tumor immune responsesi,ii. Patients with TLS and HEV in their tumors show significantly improved response to treatment and extended survival outcomes compared to patients whose tumors lack these structuresiii,iv,v,vi. The STARLYS trial will initially evaluate MST-0312 in tumors formed in barrier organs (lung, gut, bladder, breast and skin), which are believed to be particularly sensitive to TLS formation. “Dosing the first patient with MST-0312 is a significant milestone in developing this potential new therapeutic class,” said Dr. Lindsey Rolfe, MBChB, Chief Medical Officer of Mestag. “Our carefully designed study evaluates monotherapy and combination therapy in immunologically ‘cold’ and ‘warm’ tumors, generating multiple mechanistic and clinical insights to inform future development. This important step reflects the scientific rigor and dedication of the Mestag team, as we advance novel therapies for patients." Dr. Emiliano Calvo MD PhD, a Principal Investigator of the study and Director of Clinical Research at START Madrid-CIOCC (Centro Integral Oncológico Clara Campal) Hospital in Madrid, Spain where the first patient was dosed, said “MST-0312 is an exciting new investigative approach for the treatment of solid tumors and we are thrilled to have dosed the first patient in the STARLYS trial.” Dr. Elena Garralda MD PhD, Co-Director of the Clinical Research Program and Head of Early Drug Development at Vall d’Hebron Institute of Oncology in Barcelona, Spain, and coordinating Principal Investigator of the STARLYS trial, added, “Published data show that the presence of TLS is associated with significantly improved outcomes for patients. Despite recent therapeutic advances, many patients with solid tumors derive limited benefit from current therapies. MST-0312 is designed to address this unmet need by inducing TLS and reshaping anti-tumor immunity. I look forward to working with the STARLYS investigators to evaluate MST-0312 in the clinic.”  For more information, please contact: Optimum Strategic Communications Zoe Bolt, Josh Evans, Henry Williams +44 (0) 203 882 9621 <a href="https://www.globenewswire.com/Tracker?data=TjN8owkX8c3BdMUtDnHU6t9n2JnsxLFHalnnStJ6K3nmqTplUs572HfEP8hLaY6sqmnXj_uIbpB5rrKXiRFPf7_HImKGIei0DiigM1riAy5YXtSfh5s65JNnWvLTiXBM" rel="nofollow" target="_blank" title="Mestag@optimumcomms.com">Mestag@optimumcomms.com</a> About MST-0312 MST-0312 is a novel FAP-targeted bispecific agonist antibody directed to lymphotoxin-β receptor (LTBR), designed to induce the formation of tertiary lymphoid structures (TLS) and high endothelial venules (HEV) in solid tumors. TLS are a hallmark of effective anti-tumor immunity consisting of aggregates of T, B and dendritic cells, associated with the recruitment, education, and activation of immune cells to drive anti-tumor immune responses. HEVs are specialized venules that facilitate lymphocyte entry into tissues and tumors, forming reversibly in the tumor microenvironment. An extensive body of clinical data correlates the presence of TLS and HEV in solid tumors with improved patient survival and enhanced response to therapyvii. MST-0312 is an investigational program pioneering a new therapeutic approach for the treatment of cancer, including tumors that are typically resistant to immunotherapy. MST-0312 is an unlicensed medical product. About Mestag Therapeutics Mestag is a clinical-stage biotech company harnessing new insights into fibroblast immunology to develop impactful antibody therapeutics for patients with cancer and inflammatory diseases. Our pipeline includes MST-0312, a FAP-targeted LTBR agonist bispecific antibody that leverages a new understanding of tertiary lymphoid structures (TLS) and high endothelial venules (HEV) in solid tumors; the M402 program, designed to inhibit the activation of specific immune cell subsets in inflammatory disease; and earlier programs in discovery stage. Separately, we are also identifying novel targets for future therapies utilizing our specialist fibroblast-immune RAFT Platform including in collaboration with MSD (tradename of Merck &amp; Co., Inc., Rahway, N.J., USA). We previously licensed a novel target to Johnson &amp; Johnson under a 2021 target discovery, option and license agreement with Janssen Biotech, Inc. Our founding investigators comprise global experts in inflammatory disease, cancer, computational biology and fibroblast biology from the University of Oxford, Brigham &amp; Women’s Hospital, Harvard Medical School and Cold Spring Harbor Laboratory. Mestag was founded by SV Health Investors and is supported by leading life science investors Johnson &amp; Johnson, through its corporate venture capital organization, Johnson &amp; Johnson Innovation – JJDC, Inc., Forbion, GV (Google Ventures) and Northpond Ventures. For further information, please visit our website <a href="https://www.globenewswire.com/Tracker?data=gI5DlC3kyjaPW59EN0SKoG-9kE_P1Lw7gwmDiNTHbHlZKuSSime448z71fZuXlnEmZiGKFneZRjGIGPCom2B-cwT-3SeYH9x0c0Vn8qXFRE8wCX5X7pD5Rb0pdkO_PW9" rel="nofollow" target="_blank" title="www.mestagtherapeutics.com">www.mestagtherapeutics.com</a>. ________________________________ i Teillaud et al Nature Reviews Cancer 2024 ii Schumacher et al Science 2022 iii Hua et al Cancer Cell 2022 iv Hou et al, Cancer 2024 v Zhang et al J Gastroint. Oncol 2025 vi Ma et al BMC Cancer. 2024 vii Hayashi et al. Br J Cancer. 2023 FAP: fibroblast activated protein <img alt="" src='https://ml-eu.globenewswire.com/media/OTJmY2RmYzYtYThlYi00YzM2LTgxZGEtOGE1YjFmOGMxMjQ2LTcwMDAyNzM3MC0yMDI2LTA1LTE5LWVu/tiny/Mestag-Therapeutics.png' referrerpolicy='no-referrer-when-downgrade' />

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Mestag Therapeutics Announces the First Patient Dosed with MST-0312 in the Phase I STARLYS Trial

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