Abstract A174: The anti-LAG-3 antibody REGN3767 promotes immune activation in the tumor microenvironment and enhances antitumor activity of anti-PD-1 antibody REGN2810 in PD-1/LAG-3 humanized mice
Authors: Burova Elena , Halls Gabor , Allbritton Omaira , Zhang Wen , Olson William , Mohrs Markus , Thurston Gavin , Ioffe Ella 
Published: February 2019

Abstract
The immune checkpoint receptor lymphocyte activation gene 3 (LAG-3) inhibits proliferation and cytokine production by activated CD4 and CD8 T-cells upon binding to major histocompatibility complex class II (MHC II). Another inhibitory receptor, programmed death 1 (PD-1), and its ligands PD-L1 and PD-L2, are critical for the establishment and maintenance of peripheral T-cell tolerance. Because PD-1 and LAG-3 signaling in the tumor microenvironment enables tumors to escape immune surveillance, combined targeting of PD-1 and LAG-3 has emerged as a promising therapeutic strategy. REGN3767 is a human monoclonal antibody that binds LAG-3 with high affinity and rescues T-cell function by blocking its interaction with MHC II. Similarly, the human monoclonal antibody REGN2810 blocks PD-1 interaction with PD-L1 and PD-L2. To test the in vivo activity of REGN3767 alone or in combination with REGN2810, we generated humanized PD-1/LAG-3 knock-in mice, in which the extracellular domains of mouse Pdcd1 and Lag3 genes were replaced with the corresponding regions of human PD-1 and human LAG-3, respectively. In these mice, combined REGN2810 and REGN3767 therapy reduced MC38.Ova tumor growth and prolonged survival, compared to REGN2810 and REGN3767 monotherapies. To explore the underlying molecular mechanisms, we conducted RNA sequencing and RT PCR analyses of MC38.Ova tumors in PD-1/LAG-3 humanized mice following administration of one or two doses of REGN2810, REGN3767, or the combination. Both REGN3767 and REGN2810 promoted robust transcriptional changes in tumors, and combined PD-1 and LAG-3 blockade resulted in enhanced immune activation signatures. Analysis of differentially expressed genes revealed T-cell expansion and activation induced by either antibody monotherapy. While tumor immune responses to REGN3767 were delayed compared to REGN2810, both agents induced similar gene changes via shared pathways. In addition to T-cell activation, REGN2810 or REGN3767 treatments engaged other tumor-infiltrating leukocytes, including neutrophils, myeloid and NK cells. Stronger tumor growth inhibition in response to REGN2810 or REGN3767 therapy was associated with more robust immune activation signatures. Combination of REGN2810 and REGN3767 enhanced antitumor efficacy, resulting in gene expression changes not seen with either monotherapy. The combination therapy also enhanced immune responses promoted by either antibody alone, including genes associated with T-cell activation and effector function. REGN2810 and REGN3767 combination also increased the expression of other checkpoint and costimulatory molecules, including CTLA-4, CD40 and VISTA. The robust intratumoral immune activation associated with antitumor efficacy in preclinical setting supports the clinical development of REGN2810 and REGN3767 as a combination cancer immunotherapy.
Citation Format: Elena Burova, Gabor Halls, Omaira Allbritton, Wen Zhang, William Olson, Markus Mohrs, Gavin Thurston, Ella Ioffe. The anti-LAG-3 antibody REGN3767 promotes immune activation in the tumor microenvironment and enhances antitumor activity of anti-PD-1 antibody REGN2810 in PD-1/LAG-3 humanized mice [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A174.