French biotech company Transgene (Euronext Paris:TNG) and the University of Copenhagen have dosed the first patient in the Phase 1 OV-PRIME-R trial evaluating BT-001 in patients with localised rectal cancer, Transgene announced on Thursday.

The investigator-sponsored study is assessing the combination of the armed oncolytic virus BT-001, administered through intratumoural injection, followed by intravenous pembrolizumab.

The trial targets patients with proficient mismatch repair (pMMR) rectal cancer, representing approximately 95% of rectal cancer cases, a population that has historically shown limited responses to immunotherapy alone. The study will evaluate the safety, tolerability and efficacy of the neoadjuvant combination ahead of standard surgery.

BT-001 is being co-developed by Transgene and Swedish biotech company BioInvent International AB (STO:BINV) using Transgene's Invir.IO platform. The oncolytic virus is engineered to express GM-CSF and BioInvent's full-length anti-CTLA-4 monoclonal antibody, aiming to stimulate local and systemic anti-tumour immune responses while limiting systemic exposure.

The development addresses an unmet medical need, as fewer than 30% of patients achieve a complete response following neoadjuvant (chemo)-radiotherapy, while existing treatment options remain limited in preventing recurrence.