The immunosuppressive lipid, phosphatidylserine (PS), becomes exposed on tumor blood vessels and tumor cells responding to therapy. The exposed PS contributes to the immunosuppressed tumor microenvironment. Bavituximab is a phosphatidylserine (PS)-targeting antibody that is being combined with chemotherapy in clinical trials in cancer patients. Here, we tested the hypothesis that innate immunity against cancer can be elicited by combining chemotherapy with a monoclonal antibody that indirectly binds exposed phosphatidylserine (PS). We used a murine version of bavituximab, 2aG4, plus docetaxel to treat prostate tumors in mice. Combination treatment markedly retarded tumor growth, prolonged survival times and delayed progression to androgen-independent disease. Antibody treatment reduced the presence of myeloid-derived suppressor cells (MDSCs) in the tumors and caused macrophages to repolarize from the immunosuppressive, proangiogenic M2-like state into a tumoricidal M1-like state. The reactivated macrophages destroyed antibody-coated tumor vasculature and tumor cells. Addition of 2aG4 to MDSCs in vitro caused them to differentiate into M1-like macrophages and DCs. Thus, PS-targeting antibodies appear to reactivate innate immunity in tumors resulting in tumor growth inhibition.

Citation Format: Yi Yin, Xianming Huang, Dan Ye, Philip Thorpe. Phosphatidylserine-targeting antibody reactivates tumor immunity and destroys tumor vasculature in mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1244. doi:10.1158/1538-7445.AM2013-1244