Abstract 2296 Modeling the hydrophobic interactions of the CD19 and scFv binder FMC63 interface

Approximately 6,000 patients are diagnosed with B-cell acute lymphoblastic leukemia in the U.S. yearly. With the FDA approval of Tisagenlecleucel gene therapy, which targets relapsed refractory pediatric B-cell acute lymphoblastic leukemia patients using the B-cell antigenic surface protein CD19, there is hope for increasing the survival rate of leukemia. Tisagenlecleucel, an FDA approved chimeric antigen receptor (CAR) T cell therapy, works to target patients' unique cancer cells by genetically modifying the CD19-specific single chain variable fragment (scFv), FMC63, that facilitates the binding between B-cell CD19 and the cancer lysing CAR T-cell. The challenge is designing a scFv with an optimal affinity for CD19. High-affinity for CD19 allows for binding to cancer cells, in which CD19 is overexpressed, but also allows for binding to healthy cells with lower levels of CD19. However, low-affinity for CD19 may not provide the necessary level of antigen interaction to activate the CAR T cells. The specificity needed for affective scFv and CD19 affinity makes structural knowledge of how the CD19 antigen interacts with the scFv binder vital; the information may be used to optimize binder residue to improve CAR T-cells' ability to target unique CD19 densities. The Summit Country Day School SMART Team modeled the residue interactions between CD19 and CAR's scFv FMC63 in Jmol. We selected the FMC63 residues Tyr70, Tyr261, and Tyr260 and CD19 residues Arg163, Lys220, and Pro222 positioned within loop 1 (residues 154-166) and loop 2 (residues 214-224) for their role in hydrophobic interactions at the interface between FMC63 and CD19. Our custom 3D model, printed by 3D Molecular Designs, provides insight into the structural interaction between the residues in FMC63 and its CD19 epitope and for customization of new binders for CAR T cell therapies. Customized binder affinity tuning can enhance treatment for acute lymphoblastic leukemia patients to optimize for existing variations in tumor cell CD19 densities.