Abstract 4714: Blockade of LAG-3 amplifies immune activation signatures and augments curative antitumor responses to anti-PD-1 therapy in immune competent mouse models of cancer
Authors: Haines Brian B. , Javaid Sarah , Cui Long , Hirsch Heather , Cemerski Saso , McClanahan Terri , Sathe Manjiri , Zhang Shuli , Rosenzweig Michael , Long Brian , Malefyt Rene de Waal 
Published: July 2017

Abstract
MK-4280 is a humanized IgG4 monoclonal antibody (mAb) that binds to the immune checkpoint receptor Lymphocyte Activation Gene-3 (LAG-3) to block the interaction with its ligand, Major Histocompatibility Complex (MHC) Class II. LAG-3 is frequently co-expressed with other immune checkpoint receptors, most notably programmed cell death protein-1 (PD-1), on T cells with an exhausted phenotype. LAG-3 and PD-1 cooperate to regulate peripheral immune tolerance in healthy individuals, and, conversely, play critical roles in several diseases, including autoimmunity, graft rejection, viral infections, and cancer. Co-blockade of LAG-3 and PD-1 in immunocompetent mouse tumor models have demonstrated augmented anti-tumor activity over single agents. However, the molecular mechanisms behind these combination effects have not been fully investigated. Here, preclinical proof-of-biology studies are presented for co-targeting LAG-3 and PD-1 in cancer. c28G10-mG1-[D265A] (abbreviated 28G10-mG1) is a rat:mouse chimera that mimics MK-4280 by its ability to directly block the mouse LAG-3:MHC Class II interaction without initiating Fc-mediated effector functions. As a single agent, 28G10-mG1 demonstrated modest anti-tumor activity across several syngeneic mouse tumor models, despite evidence of systemic drug exposure and target engagement (as assessed by sLAG-3-mAb complex accumulation). The combination of 28G10-mG1 and the anti-mouse PD-1 blocking antibody mDX400 resulted in greater tumor growth inhibition and increased numbers of complete responses (CR) over mDX400 alone in the MBT-2 tumor model. Furthermore, animals that had achieved CR to combination therapy were subsequently protected from MBT-2 re-challenge, suggesting the establishment of immune memory. RT-qPCR analyses revealed up-regulation of immune-related genes, primarily at Day 4 in the blood and Day 8 in the tumor with mDX400, but not 28G10-mG1, treatment. However, when combined with mDX400, 28G10-mG1 further altered the expression of many immune-related genes that were perturbed by mDX400 single agent therapy. Genes unique to combination treatment were also observed. Significantly, immune pathway signatures associated with clinical efficacy to Keytruda were upregulated with combination therapy. Tumor transcriptome and network analysis by RNAseq revealed enrichment in several immune- and cytokine-related pathways with combination therapy compared to mDX400 single agent therapy. Taken together, these preclinical oncology studies support the concept of co-targeting LAG-3 to increase the therapeutic efficacy of PD-1 blockade. Clinical investigation of MK-4280 in combination with anti-PD-1 therapy (pembrolizumab/Keytruda) is ongoing.
Citation Format: Brian B. Haines, Sarah Javaid, Long Cui, Heather Hirsch, Saso Cemerski, Terri McClanahan, Manjiri Sathe, Shuli Zhang, Michael Rosenzweig, Brian Long, Rene de Waal Malefyt. Blockade of LAG-3 amplifies immune activation signatures and augments curative antitumor responses to anti-PD-1 therapy in immune competent mouse models of 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 4714. doi:10.1158/1538-7445.AM2017-4714