A Novel Anti-CD19 Chimeric Antigen Receptor T Cell Product Targeting a Membrane-Proximal Domain of CD19

Introduction: CD19-directed chimeric antigen receptor T (CART19) cell therapies have shown impressive clinical outcomes in CD19+ B-cell malignancies. All the FDA-approved CART19, including tisagenlecleucel, axicabtagene ciloleucel, brexucabtagene autoleucel, and lisocabtagene maraucel use an anti-CD19 single-chain variable fragments (scFv) derived from the FMC63 antibody that binds to a CD19 epitope that is located in the membrane-distal portion of CD19. While this CART19 products are very effective in the clinic, the majority of patients still fails treatment or eventually relapses due to several mechanisms of resistance, including CAR T cell dysfunction in the immunosuppressive microenvironment. Novel strategies to enhance the activity of CART cells are critically needed. We and others recently demonstrated that modifications of the binding region of the CAR (scFv) (Singh N., Nat Med, 2021) can drastically change the interaction between the CAR T cell and the cancer cells, potentially improving the anti-tumor effect. In this study, we aimed to develop a novel anti-CD19 CAR that binds to a membrane-proximal domain of CD19 with the goal of improving CART functions. Moreover, we hypothesized that such a CART product would be active against B-cell acute lymphoblastic leukemia (B-ALL) blasts that present aberrant expression of the CAR19(FMC63) on the surface as we described in two pediatric B-ALL patients relapsed after CART19 (CTL019) at our Institution (Ruella M., Nat Med, 2018).