RHOA Loss of Function Impairs the IFNγ Response and Promotes CD19 Antigen Escape to Drive CAR-T Resistance in Diffuse Large B-cell Lymphoma.

CD19-directed chimeric antigen receptor (CAR)-T cells are breakthrough therapies for aggressive B-cell lymphomas, but less than half of patients achieve durable responses. We previously showed through whole-genome sequencing of tumors from CAR-T-treated patients that deletions of (3p21.31) are enriched in cases progressing after treatment. 's roles in resistance and pathogenesis are poorly defined, despite loss-of-function alterations that occur in ~20% of newly diagnosed diffuse large B-cell lymphoma (DLBCL) cases. To evaluate mechanisms of CAR-T resistance, we created RHOA-deficient DLBCL systems and confirmed cell-intrinsic loss of response to CAR-19 in vitro and in vivo. RHOA loss promotes AKT activation that impairs cell-intrinsic responses to interferon gamma (IFNγ). Moreover, expression of the CAR target CD19 is consistently down-regulated accompanied by a drive toward plasmablast differentiation. RHOA deficient tumors demonstrate greatly increased sensitivity to AKT-pathway inhibitors, which reverse impaired IFNγ responses. Lymphoma microenvironments in vivo in immunocompetent mice reveal that RHOA loss promotes decreased infiltration by cytotoxic T cells and enrichment of M2-polarized macrophages, known markers of CAR-T resistance in lymphoma clinical cases. Overall, we characterize RHOA deficiency as an AKT-mediated CAR-T resistance driver and implicate avoidance of T-cell mediated killing as a likely reason for RHOA's frequent loss in DLBCL pathogenesis.