Exogenous IL-15 administration restores donor NK-cell reconstitution during GVHD. (A) B6D2F1 recipients were transplanted with B6 BM and CD3⁺ T cells and treated with saline (red) or IL-15/IL-15Rα complexes (blue). On day 7 posttransplant, donor-derived NK cells in the BM, spleen, and pLNs were quantified. Mean ± SEM pooled from 2 independent experiments; n = 6 per group. (B) Mice transplanted as in panel A were treated with IL-2/anti-IL-2 S4B6 complex. Donor NK-cell numbers were quantified on day 7. Mean ± SD from 1 of 2 independent experiments; n = 4-5 per group. (C) Mice were transplanted as in panel A, but received daily doses of saline or rapamycin (600 μg/kg; Wyeth) intraperitoneally daily for 9 days. Donor NK cells in the BM and spleen were enumerated at day 10 posttransplant. Mean ± SEM pooled from 2 independent experiments; n = 9-10 per group. Mann-Whitney tests were performed in panels A-C.