CAR cells maintain potency despite the allogeneic environment. (A) Absolute number of donor CAR T cells in 1 μL of peripheral blood, following B6 → C3h.sw allo-BMT (black solid) or B6 → B6 syngeneic BMT (gray dotted), gated on CD45.1⁺ CAR⁺ T cells. Data shown was generated from 5 mice per group and are representative of 2 separate experiments. (B) T-cell subsets in the CAR T-cell product prior to infusion and in allogeneic vs syngeneic recipients as in (A). (C-D) Mice were euthanized on day 7 post-BMT and CD45.1⁺ sorted splenocytes were incubated for 4 hours with target. Data are representative of 3 separate experiments. (C) CD107a expression on CD8⁺CD45.1⁺ cells in culture. CD45.1⁺ cells co-cultured with E2a:PBX CD19⁺ leukemia (dark gray plot); CD45.1⁺ cells co-cultured with EL4 CD19⁻ cells (dashed line); CD45.1⁺ cells co-cultured with E2a:PBX1 and stained with isotype control (gray shadow). (D) IFN-γ production by ELISA following the same co-cultures. *P < .05, **P < .01, ***P < .001. ND, not detected.