A new universal chimeric-antigen receptor (CAR)- fragment antibody binder (FAB) split system for cancer immunotherapy

Chimeric antigen receptor T (CAR-T) cell therapy has shown extraordinary results in treating hematological cancer. However, many patients relapse because of heterogeneous antigen expression and outgrowth of antigen lost variants. Other problems include on-target-off-tumor toxicity and the requirement for manufacturing of complex cellular products. Universal and modular CAR constructs offer significantly improved flexibility, safety and cost-effectiveness over conventional CAR constructs. Here we present a new chimeric-antigen receptor (CAR)-fragment antibody binder (Fab) platform based on an engineered protein G variant (GA1) and Fab scaffolds that present exquisite specificity and selectivity on antibody capture. The expression of GA1CAR on human CD8 ⁺ T cells leads to antigen recognition and T cell effector function that can be modulated according to the affinity of the CAR for the Fab scaffold and of the Fab for the target. GA1CAR-T cells can recognize multiple Fab-antigen pairs on breast and ovarian cancer cell lines. Adoptive transfer of GA1CAR-T cells/Fabs in breast cancer xenograft models leads to effective tumor control. Rapid re-direction of the CAR-T cells to a new target can be achieved by using different Fabs. GA1CAR expression confers favorable phenotypic properties to T cells including a higher effector function upon exposure to antigen as compared to conventional scFv CAR-T cells. This highly versatile “plug and play” CAR-T platform has potential for application in personalized therapy, preventing antigen loss variant escape, decreasing toxicity and increasing access.