218. Enhanced Antitumor Immunity Induced By HPV16 and 18 E6/E7 DNA Vaccine in Combination with IL-12 as an Immuno-Adjuvant

Human papillomavirus (HPV) infection is associated with 99% of cervical cancers and approximately 20% of head and neck squamous cell carcinomas. HPV E6- and E7-specific T cell immunity has been considered a critical characteristic of an effective therapeutic vaccine designed to control and eliminate established pre-existing HPV infections and associated cancers. The use of molecular adjuvants is considered an important tool to increase the potency of DNA vaccines further. IL-12 has shown to drive cellular immune responses by aiding the priming and expansion of CD8 T cells. We have previously demonstrated that a highly optimized engineered DNA vaccine targeting HPV 16 and 18 E6/E7 (pGX3001 and pGX3002) elicited potent TH1 and cytotoxic cellular immune responses in a Phase I clinical trial. Here, we sought to determine whether the HPV vaccine-induced antitumor immunity could be further enhanced by the addition of IL12 as an adjuvant.We first demonstrated that IL-12 could enhance HPV16 E6 and E7-specific cellular responses measured by ELISpot in mice (average of 1037 vs 504 SFU/106 splenocytes). Then we performed an in vivo tumor therapy study to determine whether IL-12 could enhance the therapeutic efficacy of pGX3001 in TC-1 tumor bearing C57BL/6 mice. The results induced that mice immunized with pGX3001+IL-12 exhibited smaller tumors compared to those in the no adjuvant group. Thirty days post tumor transplantation, 9 out of 10 mice in the pGX3100+IL-12 group showed complete tumor regression, while there were only 4 out of 10 mice in the pGX3001 group that showed complete tumor regression, indicating that the addition of plasmid-based mouse IL-12 enhanced the vaccine-induced antitumor immunity in a murine model. Furthermore, an additional study in a more relevant, non-human primate model was performed to ensure that the vaccine-induced cellular immune responses could also be augmented by using a rhesus macaque IL-12 plasmid. The data indicated that the addition of IL-12 increased the magnitude of vaccine-induced cellular immune responses about two fold post third immunization (average of 2711 SFU vs 1400 SFU/106 PBMCs as measured by ELISpot). The HPV antigen-specific memory responses in the HPV+IL-12 group were increased more than four-fold compared to the responses in the unadjuvanted group (average of 2570 vs 577 SFU/106 PBMCs). Flow cytometric analysis revealed the induction of both HPV-specific CD4 and CD8 T cells that efficiently increased IFN-γ responses. Both adjuvant and unadjuvanted groups showed an increase in effector and central memory CD8 T cells after immunization, while the IL-12 group exhibited stronger effector memory CD8 T cell responses. Taken together, these data support the further development of this HPV DNA vaccine in combination with IL12 as a cancer immunotherapy candidate.