Oncolytic virotherapy in cancer: cellular mechanisms, engineering strategies, and clinical translation

Abstract Oncolytic viruses (OVs) combine tumour-selective infection and replication with direct tumour-cell destruction and the capacity to induce antitumour immune responses. This review critically synthesises the cellular mechanisms, engineering strategies, preclinical development, clinical translation, major limitations, and future directions of oncolytic virotherapy. A narrative synthesis was conducted using the mechanistic, preclinical, clinical, regulatory, and translational literature assembled in the source review. The evidence encompasses naturally occurring and genetically engineered viral platforms, experimental models, delivery and combination strategies, biomarkers, and selected clinical studies across different stages of development. OV activity depends on interactions among viral characteristics, tumour-cell permissiveness, cell-death pathways, innate immune sensing, adaptive immunity, and the tumour microenvironment. Engineering approaches include tumour-selective replication control, immunomodulatory transgenes, tumour-associated antigens, small-RNA-based regulation, and programmable genome-editing strategies. Preclinical development increasingly incorporates three-dimensional and patient-derived models alongside xenograft, syngeneic, and humanised systems, while combination strategies with chemotherapy, radiotherapy, and immune checkpoint blockade remain strongly context and sequence dependent. Clinical development spans melanoma, glioblastoma, pancreatic, ovarian, pleural, and haematological malignancies, with selected regulatory milestones but mixed late-stage outcomes. However, much of the evidence remains derived from preclinical or early-phase studies, and translation is constrained by antiviral immunity, tumour heterogeneity, stromal and immunosuppressive barriers, systemic delivery, manufacturing complexity, and biosafety requirements. OVs are increasingly being developed as multifunctional immunotherapeutic platforms rather than solely as lytic agents. Their broader clinical integration will require rational treatment combinations, validated biomarkers and patient-selection strategies, improved delivery, and reproducible manufacturing, regulatory, and biosafety frameworks.