302 Characterization of TIGIT and PVR expression in colorectal liver metastases

Background Metastatic colorectal cancer (CRC) is common and lethal generally not responsive to current immunotherapies. We hypothesize that efficacious T cell-based immunotherapy can be developed for this malignancy, provided immune checkpoints relevant liver metastasis, the first site of disease progression, are targeted. Here, we characterized CRC metastases by RNAseq, FACS in vitro functional assays identify candidate checkpoints. Methods performed deep RNAseq clustering differential gene expression analysis on bulk RNA extracted from 52 mismatch repair proficient metastases. By multiparameter FACS, analyzed cell suspensions derived 18 metastases, matched non-tumoral livers, pre-operative PBMCs. evaluated IFN-γ (ELISA) secretion tumor lysis (Incucyte) tumor-infiltrating lymphocytes (TILs) expanded stimulated autologous cells with or without monoclonal antibodies blocking Results Out 21 (40.3%) clustered as reactive (IR) defined concurrent high transcripts related antigen processing, lineage, checkpoints, interferon-gamma response, cytokines, chemokines, whereas 25 (48.1%) were classified non-IR. Of all inhibitory ligands assessed, PVR PVRL2 had highest expression, both IR non-IR higher than PD-L1 PD-L2 expression. The corresponding receptors TIGIT CD226 was significantly compared at absolute levels PD-1. analysis, myeloid High also found hepatocytes, macrophages circulating monocytes same patients. In TILs, overexpressed activated CD4+CD25+ (74.8 ±3.0%) CD8+CD25+ (68.7 ± 8.4%) resting CD25neg cells, an pattern seen PD-1 infiltrating blood. majority lines expressed PVR, but low PD-L1. TIL clones various inducible TCR stimulation. Upon co-culture lines, more lytic secreted presence anti-TIGIT antibody. Conclusions data, TIGIT/PVR suppressive axis appears a biologically promising target development patients metastatic liver. Acknowledgements This work supported Bristol Myers Squibb Quebec Cancer Consortium. A.B. holds postdoctoral scholarship award Institut du de Montréal. S.T. Junior 2 clinical-scientist salary Fond recherche Santé-Québec. University Montreal Roger des Groseillers Research Chair hepatopancreatobiliary surgical oncology supports biobanking clinicopathological database associated project. Ethics Approval Institutional review board approvals obtain conduct project (16.262) informed consent contribute biospecimens data (09.237).