Low CD34 dose is associated with poor survival after reduced-intensity conditioning allogeneic transplantation for acute myeloid leukemia and myelodysplastic syndrome.

Reduced-intensity conditioning/nonmyeloablative conditioning regimens are increasingly used in allogeneic hematopoietic cell transplantation (HCT). Reports have shown CD34(+) dose to be important for transplantation outcome using myeloablative conditioning. The role of CD34(+) dose of peripheral blood progenitor cells (PBPC) has not been previously analyzed in a large population undergoing reduced-intensity conditioning/nonmyeloablative HCT. We studied 1054 patients, ages 45 to 75 years, with acute myeloid leukemia or myelodysplastic syndrome who underwent transplantation between 2002 and 2011. Results of multivariate analysis showed that PBPC from HLA-matched siblings containing <4 × 10(6) CD34(+)/kg was associated with higher nonrelapse mortality (hazard ratio [HR], 2.03; P = .001), overall mortality (HR, 1.48; P = .008), and lower neutrophil (odds ratio [OR], .76; P = .03) and platelet (OR, .76; P = .03) recovery. PBPC from unrelated donors with CD34(+) dose < 6 × 10(6) CD34(+)/kg was also associated with higher nonrelapse (HR, 1.38; P = .02) and overall mortality (HR, 1.20; P = .05). In contrast to reports after myeloablative HCT, CD34(+) dose did not affect relapse or graft-versus-host disease with either donor type. An upper cell dose limit was not associated with adverse outcomes. These data suggest that PBPC CD34(+) doses >4 × 10(6) CD34(+)/kg and >6 × 10(6) CD34(+)/kg are optimal for HLA-matched sibling and unrelated donor HCT, respectively.