CD8-positive CD19-CAR T cells preferentially expand in vivo and have an effector memory phenotype. The phenotype of CAR-positive and CAR-negative T cells was determined by flow cytometry in the infused cell product and at peak expansion (week [wk] 1 or 2 after infusion); n = 9 (patients 2 to 6, and 8 to 11). (A-D) Comparison of CAR-positive T-cell phenotype in cell product and at peak expansion (paired t test for CD4⁺/CAR⁺ GMP vs Peak and CD8⁺/CAR⁻ GMP vs Peak. ns: not significant. ∗P < .05, ∗∗P < .01, and ∗∗∗P < .01). (A) Percent CD4-positive and CD8-positive CAR T cells. (B) Percent naïve (TN), central memory (TCM), effector memory (TEM), and effector memory T cells reexpressing CD45RA (TEMRA) T cells. (C) Percent of transitional memory (Ttm) T cells. (D) Percent of PD1⁺ and TIM3⁺ CAR-positive T cells. (E-G) Comparison of CAR-positive and CAR-negative T-cell phenotype at peak expansion (paired t test for CD4⁺/CAR⁺ vs CD4⁺/CAR⁻ and CD8⁺/CAR⁺ vs CD8⁺/CAR⁻. ∗P < .05 and ∗∗P < .01): (E) TN, TCM, TEM, and effector memory T cells reexpressing CD45RA (TEMRA) T cells. (F) Percent of Ttm T cells. (G) Percent PD1- and/or TIM3-positive T cells.