Effective immunotherapeutic treatment of various cancers may require combinational approaches to induce specific immunity to the tumor as well as inhibition of immune check-points. We have developed a viral gene delivery platform to immunize against numerous tumor associated antigens (TAA) such as carcinoembryonic antigen (CEA), HER2/neu and HPV 16. We investigated the therapeutic benefit of the immunotherapeutics alone and in combination with check-point inhibitors such as programmed death-ligand 1 (PD-1) blockade and LAG3 blockade in murine tumor models. As single agents, immunization with the viral delivery platform encoding the TAA induced target-specific cell-mediated immunity and anti-tumor responses in the respective model. When the immunotherapies were combined with immune checkpoint blockade, an increased level of anti-tumor activity against was observed in addition to an improvement in survival. Tumor microenvironment analysis immunized mice revealed an increase in CD8+ tumor-infiltrating lymphocytes (TILs). In addition, we observed induction of suppressive mechanisms such as programmed death-ligand 1 (PD-L1) expression on tumor cells and an increase in PD-1+ TILs. When immunotherapy was combined with anti-PD-1 antibody, we observed CD8+ TILs at the same increased level but found that a smaller fraction of these were PD-1+. Furthermore, we observed a reduction in PD-L1 expression on tumor cells, providing a mechanism by which combination therapy favors tumor clearance and a rationale for pairing antigen-specific vaccines with checkpoint inhibitors in future clinical trials.

Citation Format: Elizabeth Gabitzsch, Adrian Rice, Yvette Latchman, Joseph P. Balint, Frank Jones. Combinational therapy with specific immunization plus checkpoint inhibition results in enhanced tumor regression and survival benefit. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2363.