IL-15 increases T-cell engraftment in hu-PBL-SCID mice. (A) Spleens were harvested from hu-PBL-SCID mice treated with either rhIL-15 or PBS for 10 days. Mice receiving IL-15 demonstrated significantly higher engraftment with respect to the absolute number of both CD4⁺ and CD8⁺ T cells. (B) CD8⁺ T cells demonstrated an activated memory phenotype. Data from one representative mouse are shown. (C) Hu-PBL-SCID mice were treated with either PBS or rhIL-15 and then each group was randomized for in vivo human T-cell depletion with OKT3 antibody or control IgG. Depletion of human T cells completely abrogated IL-15-mediated X-GVHD lethality (P = .003). Survival data were compared using the log-rank test, and all other data were compared using Student t test. Error bars indicate standard error of the mean.