PolySia-Specific Retargeting of Oncolytic Viruses Triggers Tumor-Specific Immune Responses and Facilitates Therapy of Disseminated Lung Cancer.

Polysialic acid (polySia) is expressed on several malignant tumors of neuroendocrine origin, including small cell lung cancer. In this study, we investigated the therapeutic efficacy of tumor-directed T-cell responses, elicited by polySia-retargeted oncolytic adenovirus infection, in an orthotopic murine model of disseminated polySia-positive lung cancer. In several cell lines, we demonstrated highly polySia-selective retargeting of adenoviral infection using a bispecific adapter comprising the ectodomain of the coxsackievirus/adenovirus receptor and a polySia-recognizing single-chain antibody domain. PolySia-dependent systemic infection in vivo facilitated effective uptake of viruses in subcutaneous polySia-expressing human tumors, whereas hepatic viral load and hepatotoxicity were significantly reduced. The impact and nature of antitumoral immune responses triggered by systemic delivery of polySia-retargeted oncolytic adenoviruses were investigated in an orthotopic model of disseminated lung cancer. Interestingly, improved transduction by polySia-retargeted oncolytic adenoviruses led to CD45-positive cell infiltrates in close association with large lytic areas. Consistently, enhanced tumor regression and prolonged survival was only observed in immunocompetent mice, but not in T-cell-deficient mice. To investigate whether improved systemic infection by polySia retargeting would elicit a tumor-specific T-cell response, we screened the used lung cancer cells for mutated oncogenes by complete exon sequencing. In agreement with our other results, only retargeted oncolysis was able to induce a significant response specific for the tumor-associated neoepitope Gsta2-Y9H. In conclusion, we demonstrated that effective retargeting of oncolytic adenovirus against polySia-expressing tumors elicits an effective tumor-directed T-cell response after systemic virus delivery and facilitates therapy of disseminated lung cancer.