Abstract 3657: Phosphatidylserine-targeting antibodies enhance anti-tumor activity of a tumor vaccine in a HPV-induced tumor model

Antibodies targeting phosphatidylserine (PS) have been shown to induce anti-tumor responses by induction of tumor-specific T cells. Based on this observation, we evaluated the responses of PS and PD-1 targeting antibody therapy to enhance anti-tumor responses of a HPV16 peptide vaccine formulated in DepoVax™ (DPX) in mice bearing HPV-transformed C3 mouse tumors. The addition of PS-targeting antibody (mch1N11) to DPX/metronomic cyclophosphamide (mCPA) immunotherapy prolonged survival in comparison to mice receiving an isotype control in combination with DPX/mCPA. When anti-PD-1 was added to mch1N11 + mCPA, there was no increase in survival. The addition of mch1N11 to DPX/mCPA immunotherapy had no effect on tumor growth or survival in the aggressive B16-F10 model. TIL analysis revealed an increase in CD8+ T cells, antigen specific CD8+ T cells and PD-1+ T cells in the tumor with mch1N11 treatment. The expression of surface markers for macrophages (CD68high, F4/80) and dendritic cells (CD11c) were also increased in the tumors of mice treated with mch1N11. RT-qPCR analysis of the tumor confirmed higher mRNA expression of T cells markers (CD8, Granzyme B, PD-1) and antigen presenting cell markers (F4/80, CD74). In the spleen, expression of cell surface markers for monocytes (CD11b) and PD-1+ T cells (CD8) were elevated in groups treated with mch1N11 in combination with anti-PD-1. Combined, these findings indicate that in this model, PS-targeting antibodies can enhance the activity of phagocytic cells involved in antigen presentation. We have found that PD-1 expression increases as anti-tumor activity increases, therefore these results also provide an indication that antibodies targeting PS enhance the anti-tumor immune response induced by DPX/mCPA therapy. The observations suggest that PS-targeting antibodies may enhance therapeutic vaccines for the treatment of cancer. Citation Format: Genevieve Weir, Tara Quinton, Jeff T. Hutchins, Bruce D. Freimark, Marianne Stanford. Phosphatidylserine-targeting antibodies enhance anti-tumor activity of a tumor vaccine in a HPV-induced tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3657. doi:10.1158/1538-7445.AM2017-3657