Previous pre-clinical modeling demonstrated that phosphatidylserine (PS) targeting antibodies are capable of significantly enhancing the effectiveness of anti- programmed cell death ligand 1 (PD-1) therapy in murine breast cancers (BC). These results prompted our hypothesis that PS blocking antibodies should also be capable of enhancing the activity of additional immunotherapies in BC, including triple negative breast cancer (TNBC). PS normally resides in the inner leaflet of the plasma membrane in most cell types. Conditions that promote cellular stress in the tumor microenvironment, such as reactive oxygen species (ROS), hypoxia, and irradiation, cause PS externalization and exposure on tumor associated endothelial cells and tumor cells, where it is recognized by specific receptors, including members of the TIM and TAM family. This PS recognition promotes an innate system driven immunosuppressive condition by promoting an influx of myeloid derived suppressor cells (MDSCs), an M2-macrophage shift, and suppression of dendritic cell maturation, while inducing anti-inflammatory cytokines. To identify additional immuno-therapeutic targets that may be potential targets for combinational treatment with PS-targeting antibodies, we employed gene expression analysis on tumors from murine TNBC treated with single and combinations of PS and PD-1 targeting antibodies. Of the genes assayed, expression of the lymphocyte activation gene 3 (LAG3) increased in each treatment arm, suggesting it may be a potential target for combinational therapy in breast cancers. To test our hypothesis, C57BL/6 mice hosting the murine TNBC line E0771 were treated with a PS targeting antibody or a LAG3 targeting antibody alone or in combination. Our data demonstrate that while PS-blocking and anti-LAG3 therapies each have moderate efficacy as single agents, combinational treatment significantly impeded the growth of TNBC, and was capable of increasing tumor infiltrating lymphocytes (TILs), including CD8 + and CD3 + T-cells, and reducing the percentage of MDSCs over that observed by single treatments. Combined, our data demonstrate that LAG3 targeting also represents a viable option for the treatment of TNBC, and that the addition of PS targeting antibodies to LAG3 therapy can effectively increase the anti-tumor and immune-activating effects mediated by multiple checkpoint therapies.
Citation Format: Michael J. Gray, Jian Gong, Jeff Hutchins, Bruce Freimark. LAG3 is an immunotherapeutic target in murine triple negative breast cancers whose activity is significantly enhanced in combination with phosphatidylserine targeting antibodies [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B019.
- ©2016 American Association for Cancer Research.