ABSTRACT
Chimeric antigen receptor (CAR) T-cell therapy has emerged as a promising immunotherapeutic strategy for eradicating human cancers. Their therapeutic success and durability of clinical responses hinges, in large part, on their functional capacity, including the ability of these engineered cells to simultaneously expand and persist after infusion into patients. CD19 CAR T-cell polyfunctionality, assessing the simultaneous functions of cytokine production, proliferation, and cytotoxicity has been reported to correlate with clinical outcomes. Assay optimization is potentially limited by the heterogeneous nature of CAR T-cell infusion products and target specificity. We optimized a single-cell platform for polyfunctionality using CAR T cell products manufactured from healthy donors, engineered against a novel target, BAFF-R, and validated the protocol using CD19 CAR T cells. We observed distinct qualitative differences between BAFF-R and CD19 CAR T cells relative to the proportions of stimulatory vs. effector cytokines, based on target antigen density, and generally, CD19 CAR T cells exhibited lower indices of polyfunctionality. Finally, we applied our assay to the autologous BAFF-R CAR T-cell product generated from the first NHL patient treated on an ongoing clinical trial who had progressed after prior CD19 CAR T-cell therapy. We observed robust indicators of polyfunctionality, which correlated with successful CAR T cell expansion after infusion and achievement of durable complete remission ongoing after 18 months. The precise identification of factors determining the role of BAFF-R CAR T-cell fitness on toxicity and clinical outcome will require the application of this robust assay in the analysis of additional treated patients.
ABSTRACT
Chimeric antigen receptor (CAR) T cells targeting CD19 mediate potent antitumor effects in B-cell malignancies including acute lymphoblastic leukemia (ALL), but antigen loss remains the major cause of treatment failure. To mitigate antigen escape and potentially improve the durability of remission, we developed a dual-targeting approach using an optimized, bispecific CAR construct that targets both CD19 and BAFF-R. CD19/BAFF-R dual CAR T cells exhibited antigen-specific cytokine release, degranulation, and cytotoxicity against both CD19-/- and BAFF-R-/- variant human ALL cells in vitro. Immunodeficient mice engrafted with mixed CD19-/- and BAFF-R-/- variant ALL cells and treated with a single dose of CD19/BAFF-R dual CAR T cells experienced complete eradication of both CD19-/- and BAFF-R-/- ALL variants, whereas mice treated with monospecific CD19 or BAFF-R CAR T cells succumbed to outgrowths of CD19-/BAFF-R+ or CD19+/BAFF-R- tumors, respectively. Further, CD19/BAFF-R dual CAR T cells showed prolonged in vivo persistence, raising the possibility that these cells may have the potential to promote durable remissions. Together, our data support clinical translation of BAFF-R/CD19 dual CAR T cells to treat ALL.
