GVHD incidence and survival in tumor-bearing mice after allogeneic SCT given a single infusion of either Ly49 ligand-matched, ligand-mismatched, or no donor NK cells. Model of transplantation and adoptive NK cell infusion (A). NK cells expressing Ly49G2 (binds to H-2D^d) and Ly49C (binds to H-2K^b) represent ligand-matched “nonalloreactive” and ligand-mismatched “alloreactive” NK cells, respectively. Balb/C mice were irradiated (950 cGy) and underwent transplantation with 10 × 10⁶ to 15 × 10⁶ splenocytes and 8 × 10⁶ bone marrow cells from B10.d2 donor mice. NK cells isolated from B10.d2 mice were expanded in 500 U/mL IL-2 for 5 days and injected 5 days after transplantation (0.4 × 10⁶-1.0 × 10⁶ NK cells/mouse) with Ly49G2⁺ NK cells (•), Ly49C⁺ NK cells (○), or no NK cells (▪). Recipients were monitored for development of symptoms of GVHD. Weight loss (top panel), freedom from skin GVHD (middle panel), and the mean cumulative GVHD score (bottom panel) were evaluated (B). Alopecia, hunched posture, loss of activity, and weight loss were noted before day 40 in the majority of mice that developed GVHD. Recipients injected with 10⁵ RENCA tumor cells and 0.4 × 10⁶ to 1.0 × 10⁶ purified NK cell subpopulations on day 10 before transplantation and on day 5 after transplantation, respectively, were assessed for GVHD-free survival, overall survival, and tumor status by postmortem examination (C). Four pooled experiments with a total of 16 to 22 mice in each group are shown for panel B. Two pooled experiments with a total of 7 to 9 mice in each group are shown for panel C. *P < .05 compared with recipients of Ly49G2 NK cells and recipients of no NK cells; unpaired t test and Fisher exact test. **Recipients surviving longer than 50 days after transplantation were evaluated after death for the presence of lung metastases; 43% of mice receiving Ly49 ligand-mismatched NK cells, 17% of mice that received Ly49 ligand-matched NK cells, and 0% of mice that did not receive NK cells had no evidence of tumor.