An HPV-E6/E7 immunotherapy plus PD-1 checkpoint inhibition results in tumor regression and reduction in PD-L1 expression

We have investigated if immunotherapy against human papilloma virus (HPV) using a viral gene delivery platform to immunize against HPV 16 genes E6 and E7 (Ad5 [E1-, E2b-]-E6/E7) combined with programmed death-ligand 1 (PD-1) blockade could increase therapeutic effect as compared to the vaccine alone. Ad5 [E1-, E2b-]-E6/E7 as a single agent induced HPV-E6/E7 cell-mediated immunity. Immunotherapy using Ad5 [E1-, E2b-]-E6/E7 resulted in clearance of small tumors and an overall survival benefit in mice with larger established tumors. When immunotherapy was combined with immune checkpoint blockade, an increased level of antitumor activity against large tumors was observed. Analysis of the tumor microenvironment in Ad5 [E1-, E2b-]-E6/E7 treated mice revealed elevated CD8(+) tumor infiltrating lymphocytes (TILs); however, 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 Ad5 [E1(-), E2b-]-E6/E7 immunotherapy was combined with anti-PD-1 antibody, we observed CD8+ TILs at the same level but a reduction in tumor PD-L1 expression on tumor cells and reduced PD-1+ TILs providing a mechanism by which combination therapy favors a tumor clearance state and a rationale for pairing antigen-specific vaccines with checkpoint inhibitors in future clinical trials.