Treatment of solid tumors with oncolytic adenoviruses is a promising approach to induce anti-tumor immune responses. However, the strong humoral immune responses against these viruses limit viral spread and readministrations.

We investigated whether anti-adenoviral antibodies can be exploited by means of tumor-specific molecular retargeting. We established bispecific adapter molecules consisting of a tumor-specific scFv (against polysialic acid as target) and a protein fragment (DE1) derived from the adenoviral capsid protein hexon, which binds substantial amounts of anti-adenoviral IgGs. In adenovirus pre-challenged mice, systemic application of this adapter molecule inhibited tumor growth and prolonged survival in immunocompetent murine tumor models of CMT64 lung carcinoma, MC38 colon carcinoma, and B16F10 melanoma. Antibody retargeting also inhibited disseminated disease in a model with CMT64 lung colonies. Analysis of TILs and depletion experiments revealed NK-cells and CD8 T-cells as essential mediators of tumor growth inhibition by antibody retargeting. Furthermore, adapter treatment leads to a systemic induction of tumor antigen-specific CD8 T-cells in a NK cell-dependent manner. Antibody retargeting following an intratumoral treatment of MC38 tumors with an oncolytic adenovirus resulted in enhanced therapeutic efficacy compared to virotherapy alone, including complete tumor remissions and long-term tumor free survival which was further improved by blocking PD-1/PD-L1. Finally, we demonstrated that antibody retargeting resulted in improved survival in a transgenic model of orthotopic liver cancer.

Our data demonstrate that retargeting of antiviral antibodies using bispecific adapter molecules is a promising approach for cancer immunotherapy and improves the therapeutic potential of oncolytic virotherapy.