After autologous or allogeneic transplants of peripheral blood stem cells (PBSC), an adequate dose of CD34+ cells is necessary to ensure early and sustained hematopoietic engraftment and favorable clinical outcome. There are no comparable data on the relationship between CD34+ cell dose and recovery after allogeneic bone marrow transplants (BMT). Twenty-eight patients with hematologic malignancies received a BMT from an HLA-identical sibling, using T-cell depletion and cyclosporin for graft-versus-host disease prophylaxis and delayed donor lymphocyte transfusions in an attempt to prevent leukemia relapse. The treatment-related mortality (TRM), primarily due to infections and cytopenias, was significantly higher for 13 patients receiving less than 1 x 10(6) CD34+ cells/kg (64.9% +/- 12.8% v 6.9% +/- 6.4%, P = .003). Survival at a median follow-up of 1 year was also lower in the group receiving less than 1 x 10(6) CD34+ cells/kg (30.8% +/- 12.8 v 74.3% +/- 13.7%, P = .005). The CD34+ cell dose was the only variable significantly associated with TRM. The dose of CD34+ cells also correlated with speed of hematopoistic recovery. Patients receiving more than 2 x 10(6) CD34+ cells/kg showed significantly earlier recovery of monocytes and a trend for earlier recovery of lymphocytes. They achieved platelet and red blood cell transfusion independence earlier, required less granulocyte colony-stimulating factor support during ganciclovir treatment, and spent fewer days in the hospital after transplantation. These results suggest that, for allogeneic T-cell-depleted BMT, the higher CD34+ cell doses may improve outcome in engrafting patients.

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