French biotech company Transgene (Euronext Paris:TNG) and Swedish biotech company BioInvent International AB (STO:BINV) on Monday presented new clinical data at the 2025 European Society for Medical Oncology (ESMO) Annual Meeting showing that their co-developed oncolytic virus BT-001, in combination with Keytruda (pembrolizumab), demonstrated favourable safety and strong anti-tumour activity in patients with advanced refractory tumours.

Keytruda is owned by US pharmaceutical company Merck & Co Inc (NYSE:MRK), known as MSD outside the US and Canada.

BT-001, administered via intra-tumoural injection alongside intravenous pembrolizumab, was well tolerated and produced local, abscopal, and sustained responses in both injected and non-injected lesions. Translational analyses revealed increased T cell chemoattractants and infiltration of activated CD8+ T cells and macrophages following treatment.

Tumour shrinkage of at least 30% was recorded in five of 16 injected lesions, while four patients experienced reductions in non-injected tumours. Long-lasting partial responses were observed in melanoma and leiomyosarcoma patients resistant to prior checkpoint inhibitor therapy.

These results support the mechanistic premise that BT-001 can convert immunologically "cold" tumours into active ones, potentially improving outcomes for patients unresponsive to existing cancer immunotherapies.

BT-001 was developed using Transgene's Invir.IO platform and BioInvent's anti-CTLA-4 antibody technology.