An Innovative in Vitro Potency Assay Designed to Predict the Fate of Chimeric Antigen Receptors Modified T Cell Therapy Post Infusion in ALL

Background: Chimeric antigen receptors modified T cells (CARTs) are T cells engineered to express tumor CARs that consist of T cell activation domains coupled to anti-tumor antigen single-chain variable fragments. Upon binding of tumor antigen to anti-tumor antigen antibody fragments on CART cells, the intracellular T-cell receptor CD3-zeta chain signaling domain induces T cell activation. The activated T cells undergo proliferation, cytokines release and tumor cells killing in an antigen-dependent manner. A number of CART-cell immunotherapies are now advancing to pivotal trials, however, little is known about how to characterize these cellular products before administration; one such gap relates to cell therapy product potency. Methods: Within this context, we developed a novel potency assay that quantifies the in vitro proliferative capacity of CART cell therapy products. We tested this assay using CART cell therapy products from patients with pediatric acute lymphoblastic leukemia (pedALL) and diffuse large B cell lymphoma (DLBCL). Results: In 40 CART products from pedALL patients evaluated for proliferation, and 37 products demonstrated significant (20% higher than background) proliferation. Overall, in vitro proliferation was correlated the expansion of the cell product in the patient after infusion. 23 CART products from DLBCL patients were analyzed, and 20 demonstrated significant specific in vitro proliferation. A strong correlation between in vitro proliferation and cell growth has been observed for the DLBCL patient samples. Conclusions: These data suggest that in vitro proliferation is a highly informative potency assay that may help predict product efficacy and safety of CAR T cell therapies.