RARA and neoplasm: To test this idea, we transduced WT, RARα‐KO, and RARα‐TG CTLs with a retroviral vector expressing a CAR against hCD19 and co‐cultured the cells with hCD19‐expressing B16 or MC38 tumor cells at various effector‐to‐target ratios (Figure7A,B; Figure S14A–C and Movies S1–S8, Supporting Information).