Long-term in vivo persistence of human T cells in surviving mice treated with ΔLNGFR–, IL-7–, IL-15–, or IL-21–overexpressing T cells. (A) Identification of human T cells in the spleen of tumor-free mice on days 106 to 110 after tumor challenge. Dot plots represent the indicated mice. Graphs indicate the percentage and absolute number of human CD3⁺ cells in the spleen of individual mice. Each circle represents an individual mouse (no T cells, n = 2; 19z1-ΔLNGFR, n = 4; 19z1-IL7, n = 7; 19z1-IL15, n = 4; 19z1-IL21, n = 10). Horizontal bar indicates average. (B) Expression of CD45RA, CCR7, and CD62L by persisting human CD8⁺ T cells in long-term surviving mice. Histograms are from representative mice and have been gated on the CD3⁺CD8⁺ subset (inferred from the CD3⁺CD4⁻ gate). Dot plots for the 19z1-ΔLNGFR and 19z1-IL21 groups have been gated on the CD3⁺CD4⁻CD45RA⁻ cells and dot plots for the 19z1-IL15 group have been gated on the CD3⁺CD4⁻CD45RA⁺ cells.