To decrease the incidence of graft-versus-host disease (GVHD) observed after nonmyeloablative stem cell transplantation (NMSCT), we studied the feasibility of CD8-depleted or CD34-selected NMSCT followed by CD8-depleted preemptive donor lymphocyte infusion (DLI) given in incremental doses on days 40 and 80. Fourteen patients with high-risk malignancies and an HLA-identical sibling (n = 8) or alternative donor (n = 6) but ineligible for a conventional transplant were included. Nonmyeloablative conditioning regimen consisted in 2 Gy total body irradiation (TBI) alone, 2 Gy TBI and fludarabine (previously untreated patients) or cyclophosphamide and fludarabine (patients who had previously received > or =12 Gy TBI). Patients 1-4 (controls) received unmanipulated peripheral blood stem cells (PBSC) and DLI and patients 5-14 CD8-depleted or CD34-selected PBSC followed by CD8-depleted DLI. Post-transplant immunosuppression was carried out with cyclosporine A (CsA) and mycophenolate mofetil (MMF). Initial engraftment was seen in all patients, but 1 patient (7%) later rejected her graft. The actuarial 180-day incidence of grades II-IV acute GVHD was 75% for patients 1-4 versus 0% for patients 5-14 (p = 0.0019). Five of 14 patients were in complete remission (CR) 180 days after the transplant and 6/14 had partial responses. The 1-year survival rate was 69%, and nonrelapse and relapse mortality rates were 16 and 18%, respectively. We conclude that CD8-depleted or CD34-selected NMSCT followed by CD8-depleted DLI is feasible and considerably decreases the incidence of acute GVHD while preserving engraftment and apparently also the graft-versus-leukemia (GVL) effect. Further studies are needed to confirm this encouraging preliminary report.