Abstract 6819: Exploring the impact of IDH1-mutations on antitumor immunity in intrahepatic cholangiocarcinoma

Abstract Intrahepatic cholangiocarcinoma (CCA) is an aggressive biliary tract cancer that carries unfavorable prognosis. 10-20% of intrahepatic CCAs harbor a mutation in IDH1 that can be targeted with mutant IDH1-specific inhibitors. However, objective and durable responses to treatment with mutant IDH1 inhibitors are rare in CCA. Mutant IDH1 has neomorphic enzymatic activity that produces the oncometabolite D-2-hydroxyglutarate (D-2-HG). D-2-HG promotes biliary tumor formation through cancer cell-intrinsic mechanisms but is also a paracrine factor in the tumor microenvironment (TME). Our group and others have identified that IDH1-mutant CCAs are not responsive to immunotherapy treatment approaches in part due to decreased CD8+ T cell infiltration and an increase in immunosuppressive macrophage cells in the TME. To better understand the immunosuppressive features of the IDH1-mutant CCA TME, we generated an isogenic cell line panel of IDH1-mutant (MUT) and IDH1-wild type (WT) mouse cholangiocarcinoma cells in the SB1 cell line background through a CRISPR homology directed repair approach. Compared to IDH1-WT cells, IDH1-MUT cells produce high levels of D-2-HG and both cell line panels readily form tumors in immunocompetent C57BL/6 mice. Tumors formed from IDH1-mut cells have reduced CD8+ T cell infiltration compared to IDH1-WT tumors, a finding that correlates with analysis of human CCA samples. Using cytometry by time of flight (CyTOF), we identified that CD8+ T cells in IDH1-MUT tumors have decreased expression of key regulators of the antitumor immune response including EOMES, TBET, and GZMB compared to those isolated from IDH1-WT tumors. Analysis of secreted factors from these IDH1-MUT and IDH1-WT cells identified that IDH1-MUT cells release increased levels of CCL2, a chemokine shown to diminish the antitumor immune response across multiple cancer types, compared to IDH1-WT cells. Further, IDH1-MUT tumors grown in syngeneic, immunocompetent mice have increased CCL2 staining by IHC compared to IDH1-WT tumors. CCL2 expression is also increased in a preliminary analysis of IDH1-mutant human CCA primary tumors. Treatment of mice harboring orthotopic liver tumors formed from IDH1-MUT cells with a CCL2 neutralizing antibody resulted in decreased tumor size compared to isotype control. Together, our data suggest that CCL2 is a mediator of immunosuppression in the IDH1-mutant CCA TME and that modulation of CCL2 activity may improve outcomes in this rare disease subtype. Further work to understand the mechanisms through which IDH1 mutations regulate CCL2 levels in these tumors is underway. Citation Format: Emma Kartalia, James M. Leatherman, Jae W. Lee, Kiyoko Yoshima, Daniel J. Zabransky, Mark Yarchoan. Exploring the impact of IDH1-mutations on antitumor immunity in intrahepatic cholangiocarcinoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6819.