The anti-virus T cell response dominates the anti-cancer response in oncolytic virus therapy.

Oncolytic viruses have strong potential as immunotherapies. By causing cancer cells to die and relieve antigens, these viruses can stimulate robust, systemic immune responses that may eliminate disseminated disease and prevent recurrence. Unfortunately, clinical trials using oncolytic viruses have not induced clearance of metastasis or protection from recurrence. Likewise, the combination of the only FDA-approved oncolytic virus-Talimogene laherparapvec-with immune checkpoint blockade did not improve progression-free or overall survival. Because of these disappointing clinical trials, we sought to measure the ability of oncolytic viruses to induce cancer antigen presentation and the elicitation of cancer antigen-specific immune responses. Our data revealed that despite improved antigen presentation by dendritic cells, priming of cancer antigen-specific T cells was limited. However, viral antigen-specific T cells did develop and were in a phenotypic state to induce an effective response against virally infected cells. These preclinical results were mirrored in human peripheral blood samples. Overall, these data show that oncolytic virus treatment induces a response against the virus itself, but not cancer antigen, explaining the lack of response in metastatic disease. These interesting findings identify a critical mechanism that needs to be overcome to increase the efficacy of oncolytic virus therapy.