In vivo expansion of EpoRm-CAR-T cells in immunodeficient mice. (A) Representative flow cytometric contour plots illustrate the presence of human CD45⁺ GFP⁺ T cells in mouse peripheral blood. (B) Percentage of human CD45⁺ GFP⁺ cells in peripheral blood of mice injected IV with T cells transduced with CAR, EpoRm-CAR, or GFP only; some mice received 100 IU Epo IP 3 times a week for 2 weeks, as indicated. Blood was obtained via cheek bleed 13 days after T-cell infusion. **P < .01; ***P < .001. (C) Experiments performed as in panel B with T cells from a different donor transduced with EpoRm or GFP only; no exogenous Epo was administered. ***P < .001. (D) pSTAT5 MFI in T cells transduced with CAR, EpoRm-CAR, EpoRm, or GFP only following 15-minute stimulation with 80 ng/mL of either mouse or human Epo.