Analysis of Polyfunctionality for Enhanced CAR T-Cell Therapy for Hematologic Malignancies

• The polyfunctionality of CAR T cells is impacted by stimulation conditions, effector-target ratio, antigen density, and CAR specificity.

• Robust indicators of polyfunctionality correlate with successful CAR T cell expansion post-infusion and achievement of durable remission.

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.