Serial stimulation of individual CTLs through native αβTCR and CAR.CD19. (A) Secretion of IFNγ by CAR.CD19⁺ MV-CTLs in response to stimulation with YSE peptide (y-axis) and CD19⁺ K562 cells (x-axis). (i) CTLs stimulated with both YSE and CD19. (ii) CTLs stimulated with YSE alone. (iii) CTLs stimulated with CD19 alone. (iv) CTLs stimulated with neither YSE nor CD19. (B) Secretion of IFNγ by nontransduced MV-CTLs in response to stimulation with YSE peptide (y-axis) and CD19⁺ K562 cells (x-axis). (i) CTLs stimulated with both YSE and CD19. (ii) CTLs stimulated with YSE alone. (iii) CTLs stimulated with CD19 alone. (iv) CTLs stimulated with neither YSE nor CD19. TD CTLs indicates transduced cytotoxic T lymphocytes; and NT CTLs, nontransduced cytotoxic T lymphocytes.