Abstract 3652: Combinational activity of LAG3 and PD-1 targeted therapies is significantly enhanced by the addition of phosphatidylserine targeting antibodies and establishes an anti-tumor memory response in murine triple negative breast cancer
Authors: Gray Michael J. , Gong Jian , Hutchins Jeff T. , Freimark Bruce D. 
Published: July 2017

Abstract
Previous studies utilizing NanoString immune profile analysis demonstrated that intratumoral levels of LAG3 (lymphocyte activation gene 3) mRNA increased in response to phosphatidylserine (PS) and PD-1 targeting antibodies in murine triple negative breast cancers (TNBC). This suggests LAG3 acts to attenuate immune system activation during I/O therapies - and that PD-1 and LAG3 function cooperatively in suppressing immune system activation. Here we show that adding PS targeting antibodies can further enhance the effectiveness of antibodies targeting LAG3 and/or LAG3+PD-1. We first examined expression of LAG3 and PD-1 in the murine TNBC model E0771 and found that tumor associated T-cells (CD4+ and CD8+) have expression of both markers. Mice implanted with TNBC tumors were next treated with antibodies targeting PS, PD-1, and LAG3 alone and in combination with each other. Interestingly, the addition of PS targeting antibodies not only increased the effectiveness anti-PD-1 effectiveness as previously observed, but also enhanced anti-LAG3 treatment, showing that PS targeting antibodies are capable of augmenting additional I/O therapeutic regimens. Comparison of anti-PD-1+LAG3 combination vs. single anti-PD-1 or anti-LAG3 treatments showed moderately more anti-tumor activity than single treatments, however the addition of PS targeting antibodies to either checkpoint inhibitor was as equally effective in inhibiting tumor growth as observed in the anti-LAG3+PD-1 treatment. Further comparison of antibody treatments targeting PD-1+LAG3 vs. PS+PD-1+LAG3 demonstrated that the addition of PS targeting antibodies resulted in a significant decrease in tumor growth with complete tumor regression in 80% of the animals (along with the ability to completely reject secondary TNBC challenge) compared to 0% in the anti-PD-1+LAG3 treatment group. Immunoprofiling showed that the addition of PS targeting antibodies to these checkpoint therapies, including the combination of anti-PD-1+LAG3, resulted in a phenotype associated with enhanced immune system activation and immune-surveillance including increased tumor infiltrating lymphocytes (TILs) with upregulation of T-cell associated activation pathways, increased Th1 to Th2 profile, and enhanced antigen presentation processing /presentation mechanisms along with cytokines associated with immune system activation. Overall our data demonstrate that adding PS targeting antibodies to clinically relevant therapies, including PD-1 and LAG3, may significantly enhance their ability to activate and redirect the host immune system into recognition and elimination of tumor cells compared to single and combinational treatments that lack PS targeting antibodies.
Citation Format: Michael J. Gray, Jian Gong, Jeff T. Hutchins, Bruce D. Freimark. Combinational activity of LAG3 and PD-1 targeted therapies is significantly enhanced by the addition of phosphatidylserine targeting antibodies and establishes an anti-tumor memory response in murine triple negative breast cancer [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 3652. doi:10.1158/1538-7445.AM2017-3652