Systemically Administered Sindbis Virus in Combination with Immune Checkpoint Blockade Induces Curative Anti-tumor Immunity.

Oncolytic viruses represent a promising form of cancer immunotherapy. We investigated the potential of Sindbis virus (SV) for the treatment of solid tumors expressing the human cancer testis antigen NYESO-1. NYESO-1 is an immunogenic antigen frequently expressed in numerous cancers, such as ovarian cancer. We show that SV expressing the tumor-associated antigen NYESO-1 (SV-NYESO1) acts as an immunostimulatory agent, inducing systemic and rapid lymphocyte activation, leading to a pro-inflammatory environment. SV-NYESO1 treatment combined with anti-programmed death 1 (anti-PD-1) markedly augmented the anti-tumor immunity in mice over the course of treatment, resulting in an avid systemic and intratumoral immune response. This response involved reduced presence of granulocytic myeloid-derived suppressor cells in tumors and an increase in the activation of splenic and tumor-infiltrating T cells. Combined therapy also induced enhanced cytotoxic activity of T cells against NYESO-1-expressing tumors. These results were in line with an observed inverse correlation between T cell activation and tumor growth. Finally, we show that combined therapy resulted in complete clearance of NYESO-1-expressing tumors in vivo and led to long-term protection against recurrences. These findings provide a rationale for clinical studies of SV-NYESO1 combined with immune checkpoint blockade anti-PD-1 to be used in the treatment of NYESO-1-expressing tumors.