Treos Bio Presents New Translational Data Showing PolyPEPI1018 Plus Anti-PD-L1 Immunotherapy Remodels the Tumor Immune Microenvironment in MSS Colorectal Cancer

ESMO GI poster highlights increased intratumoral CD8+ T-cell infiltration, PD-L1 expression, expansion of tumor-reactive TCR clonotypes and association with clinical outcome

LONDON and BOSTON and BUDAPEST, Hungary, July 02, 2026 (GLOBE NEWSWIRE) -- Treos Bio, a clinical-stage biotechnology company developing off-the-shelf and personalized active cancer immunotherapies based on its proprietary PEPI Technology, today announced new translational data from the Phase Ib/II OBERTO-301 study (NCT05243862), presented at the ESMO Gastrointestinal Cancers Congress 2026.

Conducted in collaboration with Mayo Clinic, the retrospective translational analysis demonstrates that PolyPEPI1018 treatment in combination with anti-PD-L1 immunotherapy induced measurable immune remodeling in patients with microsatellite-stable metastatic colorectal cancer (MSS mCRC), a tumor type generally considered resistant to checkpoint inhibition.

The retrospective analysis evaluated paired baseline and on-treatment tumor biopsies and peripheral blood samples from OBERTO-301 patients treated with PolyPEPI1018 plus atezolizumab. Post-treatment tumor samples showed increased CD8+ T-cell density and PD-L1 expression, indicating conversion toward a more inflamed tumor microenvironment.
T-cell receptor (TCR) sequencing demonstrated selective expansion of tumor-reactive T-cell clonotypes, including TCRs directed against PolyPEPI1018 antigens, additional tumor-associated antigens and neoantigens. The analysis also suggested treatment-induced antigen spreading beyond the PolyPEPI1018-targeted epitopes.

Importantly, higher numbers of tumor-reactive TCR clonotypes and higher post-treatment CD8+ TIL density were associated with improved clinical outcomes, including longer overall survival and progression-free survival. Together, these findings provide mechanistic evidence that therapeutic vaccination targeting shared tumor-associated antigens can remodel the immune microenvironment of MSS colorectal cancer converting immunologically "cold" tumors into a more immunologically active, potentially checkpoint-responsive tumor microenvironment.

“MSS colorectal cancer has long been one of the most difficult settings for immunotherapy because these tumors typically lack the immune activity needed for checkpoint inhibitors to work,” said Dr. Eniko Toke, Co-founder and Chief Scientific Officer of Treos Bio. “What is encouraging in this analysis is not only that we observed immune activation in the tumor microenvironment, but that the depth of that response was associated with patient outcomes. Together with our recent clinical and platform data, these findings strengthen the rationale for advancing PolyPEPI1018 combinations in MSS colorectal cancer and applying PEPI Technology across other difficult-to-treat tumors.”

Poster number: 115P
Presentation: 02 July 2026
Congress: ESMO Gastrointestinal Cancers Congress 2026

About Treos Bio
Treos Bio is a clinical-stage biotechnology company developing off-the-shelf and personalized active cancer immunotherapies built on its proprietary PEPI Technology. The platform is designed to identify promiscuous epitopes that bind multiple HLA molecules in individual patients and support broad, multi-antigen T-cell responses. The Company’s lead program, PolyPEPI1018, is an off-the-shelf multi-peptide immunotherapy in development for MSS colorectal cancer. Treos Bio is also advancing additional programs in solid tumors, combining platform-based target selection and therapy design with diagnostic strategies intended to identify patients most likely to benefit.

For more information, visit www.treosbio.com.

For further information, please contact: IR@treosbio.com

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