A novel two chain structure utilizing KIRS2/DAP12 domain improves the safety and efficacy and of CAR-T cells in adult patients with acute relapsed/refractory B lymphoblastic leukemia

Abstract Engineered T cells that express chimeric antigen receptors (CAR) have been a promising therapy for hematologic malignancies. The optimization of CAR structure using different signaling domains can alter a wide range of CAR-T cells properties, including anti-tumor activity, long-term persistence and safety. In this study, we developed a novel CAR structure based on the KIRS2/Dap12 for the B-cell acute lymphoblastic leukemia (B-ALL) antigen CD19, and compared the anti-tumor efficacy and safety of this construct transduced T cells with standard second-generation CAR-T cells targeting CD19 for B-ALL in vitro and in vivo, and in adult r/r BALL patients. We discovered that KIRS2/Dap12 receptor infused with 4-1BB co-stimulation domain could enhance anti-tumor efficacy via remarkably increasing the production of pro-inflammatory IL-2, especially when co-cultured with antigen positive tumor cells. In addition, CD19-KIRS2/Dap12-BB CAR-T cells showed an inspiring outcome that complete responses were seen in 4 of 4 (100%) patients without neurotoxicity and high rate of severe cytokine release syndrome (CRS) after CAR-T infusion in a phase I clinical trial. Given these encouraging findings, CD19-KIRS2/Dap12-BB CAR-T cells are safe and can lead to clinical responses in adult patients with r/r B-ALL, indicating that further assessment of this therapy is warranted.