CD19/BAFF-R dual targeted CAR T cells for treatment of mixed antigen-negative variants of acute lymphoblastic leukemia

Chimeric antigen receptor (CAR) T cells targeting CD19 mediate potent anti-tumor effects in B cell malignancies including acute lymphoblastic leukemia (ALL), but antigen loss remains the major cause of treatment failure. To mitigate antigen escape and potentially improve durability of remission, we developed a dual-targeting approach using an optimized, bispecific CAR construct that targets both CD19 and BAFF-R. CD19-BAFF-R dual CAR T cells exhibited antigen-specific cytokine release, degranulation and cytotoxicity against both CD19−/− and BAFF-R−/− variant human ALL cells in vitro. Immunodeficient mice engrafted with mixed CD19−/− and BAFF-R−/− variant ALL cells and treated with a single dose of CD19-BAFF-R dual CAR T cells experienced complete eradication of both CD19−/− and BAFF-R−/− ALL variants, while mice treated with monospecific CD19 or BAFF-R CAR T cells succumbed to outgrowths of CD19-/BAFF-R+ or CD19+/BAFF-R- tumors, respectively. Further, CD19-BAFF-R dual CAR T cells showed prolonged in vivo persistence, raising the possibility that these cells may have potential to promote durable remissions. Together, our data support clinical translation of BAFF-R/CD19 dual CAR T cells to treat ALL.