On July 2, 2026 Treos Bio, a clinical-stage biotechnology company developing off-the-shelf and personalized active cancer immunotherapies based on its proprietary PEPI Technology, reported new translational data from the Phase Ib/II OBERTO-301 study (NCT05243862), presented at the ESMO (Free ESMO Whitepaper) Gastrointestinal Cancers Congress 2026.
Schedule your 30 min Free 1stOncology Demo!
Discover why more than 1,500 members use 1stOncology™ to excel in:
Early/Late Stage Pipeline Development - Target Scouting - Clinical Biomarkers - Indication Selection & Expansion - BD&L Contacts - Conference Reports - Combinatorial Drug Settings - Companion Diagnostics - Drug Repositioning - First-in-class Analysis - Competitive Analysis - Deals & Licensing
Schedule Your 30 min Free Demo!
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 (Free ESMO Whitepaper) Gastrointestinal Cancers Congress 2026
(Press release, Treos Bio, JUL 2, 2026, View Source [SID1234669059])