DLBCL Cells Emerge after CD19 CAR T Cells with Cross-Antigen Resistance and a Gene Signature Predictive of Clinical CAR T-cell Response.

Current understanding of lymphoma cell-intrinsic mechanisms of relapse following chimeric antigen receptor (CAR) T-cell treatment of diffuse large B-cell lymphoma (DLBCL) include antigen loss and apoptosis resistance. Herein, CD19 CAR T-cell response and resistance were modeled, and it was identified that treatment-naïve CD19 expression does not correlate with CAR T-cell sensitivity, but resistance is frequently accompanied by reversible downregulation of CD19 that once restored is not paralleled with restored sensitivity to CAR T cell-mediated killing. Profiling a suite of DLBCL cell lines to CD19 CAR T-cell sensitivity reveals that DLBCL cells become nonresponsive to CAR T cell-killing, including to alternative antigen targeting of CD20 or CD22. Leveraging these resistant models, we identified gene signatures present in the CAR T cell-resistant DLBCL cell lines that correlate with patient response to CTL019 in two independent clinical trials. Finally, we show that combination strategies to overcome this resistance, including up-front dual-antigen targeting and combined treatment with an Mcl-1 inhibitor, improve CAR T-cell responses. SIGNIFICANCE: We demonstrate that DLBCL cells surviving CD19 CAR T-cell treatment develop a resistance phenotype with a "resistance signature" predictive of clinical CAR T-cell response, mediating cross-resistance between CAR T cells targeting different antigens. Our findings suggest that up-front dual-antigen targeting and combination therapies could improve clinical outcomes.