Abstract 5557: PMC-309, a highly selective anti-VISTA antibody reverses immunosuppressive TME to immune-supportive TME

Abstract

Abstract Purpose: We investigated the pharmacology of PMC-309 in ex vivo or in vivo characterization for the development of the preclinical study. Experimental procedures: Target selectivity: it was measured by SPR assay. Human VISTA expressing CHO k1 cells or CHO k1 mock cells were used in cell binding assay. Target cell analysis: human peripheral blood mononuclear cells (PBMC) containing lymphocyte and myeloid lineage cells were used for target cells analysis with flow cytometry. In vitro T cell activity: human PBMC was employed for the evaluation of T cell activity (IRB #1041107-201703-BR-002-02) and was stimulated with or w/o PMC-309 in the presence of anti-CD3/28 Antibody. In vivo study: MC38 bearing human VISTA knock-in (KI) mice were employed for the assessment of anti-tumor activity of PMC-309. The tumor infiltrated immune cells: Immune cells in the TME were evaluated by immunohistochemistry (IHC) or flow cytometry (FACS) analysis. Statistics: All data were presented as the mean ± SEM and analyzed using one-way ANOVA followed by Dunnett’s multiple comparison tests in Graph pad prism®. ***p<0.001, **p<0.01 and *p<0.05 compared to Control group. Summary of data: PMC-309 binding to VISTA expressing cells is highly selective and the selectivity is maintained even in the low pH conditions that mimic TME. PMC-309 enhances the secretion of IFN-gamma, TNF-alpha, and IL-2 in Mixed Lymphocyte Reaction (MLR) settings. In addition, PMC-309 promoted monocyte differentiation into M1 macrophage that stimulates proinflammatory cytokine secretion of T cells. For the in vivo study, PMC-309 was intravenously administrated in VISTA-KI mice. The tumor growth rate was suppressed in accompanied by a synergistic effect with an anti-PD1 antibody. The anti-tumor activity was associated with enhanced T cell activation, increased secretion of pro-inflammatory cytokines, and increased penetration of cytotoxic T cells, but lowing immune-suppressive MDSC cells into TME as demonstrated with IHC analysis. Conclusions: PMC-309 is a fully human anti-VISTA antibody that targets human VISTA specifically. PMC-309 enhanced both T cell activation and monocyte activation when monocytes were cultured with or without T cells by targeting VISTA. PMC-309 increased the number of T cell infiltration while a decrease of MDSCs in the TME. PMC-309 in combination with chemotherapy or other IO drugs could address highly medical unmet needs from patients with drug resistance to currently available IO treatment options. Citation Format: Cheon Ho Park, Sang Soon Byun, Jin Yong An, Hyerim Han, Weon Sup Lee. PMC-309, a highly selective anti-VISTA antibody reverses immunosuppressive TME to immune-supportive TME [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5557.