Preclinical Optimization of a Fully Human CD19 Chimeric Antigen Receptor T (CART) Cell to Enhance Efficacy Against CD19-Antigen Low B-Acute Lymphoblastic Leukemia (B-ALL)

Résumé fourni par la source

Background Enhancing CD19 CART efficacy against low antigen density leukemias and improving the safety profile remain key goals for the next generation of CAR constructs. Recent studies indicate that the hinge domain in CAR design can play a crucial role in functionality and efficacy against low antigen density leukemia (Majzner Can Discov 2020, Mirazee J Immunol 2023) . Additionally, fully human binders may be associated with lower rates of inflammatory toxicities than murine FMC63-based constructs (Brudno Nat Med 2020). Accordingly, we evaluated a fully human CD19 CAR harboring a 55 amino acid (aa) CD8α hinge and a CD28 costimulatory domain (Hu19-CD828Z) –abbreviated to Hu19-CD8H 55 -28Z– with established efficacy and limited toxicity against B cell lymphoma ( Brudno Nat Med 2020 ). Our objective is to use an iterative approach modifying the hinge length of Hu19-CD8H 55 -28Z CAR to optimize efficacy against B-ALL. Methods Hu19-CD8H 55 -28Z was compared with murine FMC63-based CAR constructs incorporating CD28 hinge/CD28 (28Z) costimulatory and CD8α hinge/4-1BB (BBZ) costimulatory domains against CD19-high (100k CD19 molecules/cell) and CD19-low (1k CD19 molecules/cell) NALM6 leukemia. CART function was evaluated using a high throughput in-vitro Immunotron cytokine assay, cytotoxicity assay and an in-vivo NSG mouse model. Novel Hu19-CD8H28Z constructs incorporating distinct CD8α hinges of 45, 25, and 13 aa were generated for further evaluation. Results Novel Hu19 CAR constructs, modified as a function of CD8α hinge length, were compared to the parental Hu19-CD8H 55 -28Z CAR and commercially available FMC63 CAR constructs. All CAR constructs exhibited high cytokine secretion and cytotoxicity against CD19-high leukemia. However, a Hu19 CAR construct with a shorter hinge of 25 amino acids (Hu19-CD8H 25 -28Z) outperformed the parental Hu19-CD8H 55 -28Z CAR as well as the FMC63-BBZ CAR following repeat exposure to CD19-low leukemia, at both high and low effector-to-target ratios ( Figure 1 ). Moreover, cytokine profiles of Hu19-CD8H 25 -28Z were equivalent to commercially available FMC63-based CARTs against CD19-high leukemia and decreased against CD19-low leukemia, highlighting the potential to maintain the safety profile of the human CAR construct. Finally, in vivo studies revealed a sustained cytotoxic response to Hu19-CD8H 25 -28Z CART against CD19-high leukemia, superior to either the parental Hu19-CD8H 55 -28Z or the FMC63-based-CARTs ( Figure 2 ). Conclusion An altered CD8α hinge domain improves efficacy of the Hu19-CD828Z CAR in low antigen density leukemia and may harbor an improved safety profile. Additional preclinical studies including the evaluation of in vivo cytotoxicity of Hu19-CD8H 25 -28Z CART against CD19-low leukemia are underway to facilitate its clinical translation.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.