An engineered oncolytic parapoxvirus induces immunogenic tumor cell death and displays antitumor efficacy by enhancing T cell responses.

Oncolytic viruses (OVs) is a class of promising cancer biotherapeutics by selectively lysing tumor cells and stimulating antitumor immunity. However, most OV-based clinical efficacy were often restricted by rapid viral clearance mediated by pre-existing neutralizing antibodies and immunosuppressive tumor microenvironment (TME). These barriers particularly limit the efficient activation of T cell-mediated immune responses, thereby compromising durable systemic antitumor effects. Leveraging the distinctive advantage that oncolytic parapoxvirus ovis (ORFV) does not induce neutralizing antibodies in vivo, we developed an engineered ORFV recombinant through simultaneous deleting multiple virulence-associated genes together with inserting Il15 gene, named ORFVΔ-IL15. This newly generated ORFV recombinant retains full replication competence and significantly potentiating anti-tumor efficacy, which was demonstrated by greater capacity in suppressing tumor growth and metastasis especially in immunologically 'cold' tumors. Mechanistically, ORFVΔ-IL15 reprograms TME by modulating inflammatory cytokines, affecting intratumoral T cell recruitment and redirecting T cell subpopulation distribution. Functionally, ORFVΔ-IL15 could induce T cell involved co-stimulation, tumor antigen presenting and tumor killing, which was illustrated by the finding that antigen-specific, cytotoxic and activated CD8+ T cells were highly enriched in tumor lesions. Notably, systemic antitumor immunity was induced, as abscopal effects against distant untreated tumors have been discovered, indicating that long-term immunological memory has been established. Our findings establish ORFVΔ-IL15 as a novel therapeutic agent that integrates oncolytic and immunoregulatory functions, demonstrating robust tumor-suppressive efficacy and offering a promising strategy for next-generation oncolytic virus engineering.