Further optimization of CAR T functionality will be necessary, because despite initial clearance of the leukemia in the WSU-AML and Kasumi-1 FOLR1+ xenograft mice to below the level of detection by IVIS imaging in response to treatment with FOLR1 CAR T cells (5 × 106 cells/mouse), the treated mice eventually relapsed. Here, FOLR1 is linked to acute myeloid leukemia.