Tumor-infiltrating naive CB T cells rapidly differentiate into memory/effector cells. (A) Comparison of median percentages of naive, central memory, and effector memory subsets in TILs and CLs on day +15 after T-cell injection. Naive CB T cells rapidly switched to the memory/effector phenotype in the tumor; however, circulating CB lymphocytes remained naive. A similar percentage of CD8⁺ TILs had central memory and effector memory phenotypes in both groups (P = not significant). Interestingly, in the PB group, a significantly higher percentage of CLs had an effector memory phenotype compared with TILs (P < .0001). (B) Representative flow cytometry plots of CD8⁺ T cells infused on day 0, CD8⁺ tumor-infiltrating lymphocytes, and CD8⁺ circulating lymphocytes.