Impact of a Low CD34 ⁺ Cell Dose on Allogeneic Peripheral Blood Stem Cell Transplantation

Although the CD34 ⁺ cell dose in allogeneic peripheral blood stem cell transplantation (PBSCT) is considered to be associated with transplantation outcomes, a lower acceptable threshold has not been defined. We retrospectively analyzed 2919 adult patients with hematologic malignancies who underwent related PBSCT in Japan between 2001 and 2014. According to the number of CD34 ⁺ cells in the graft, we categorized 2494 patients in the standard group (2 to 5 × 10 ⁶ cells/kg), 377 patient in the low group (1 to 2 × 10 ⁶ cells/kg), and 48 patients in the very low group (<1 × 10 ⁶ cells/kg). Compared with the standard group, the low and very low groups showed delayed neutrophil recovery (93.8%, 89.5%, and 78.3%, respectively at day +28; P <.001) and platelet recovery (69.3%, 53.0%, and 45.5%, respectively at day +28; P <.001). The 2-year overall survival (OS) in the 3 groups was 45.5%, 45.3%, and 29.8%, respectively, with inferior survival in the very low group. However, a higher percentage of high-risk patients may account for the inferior survival in the very low group, and no significant difference in OS was found in a multivariate analysis. There were no differences in relapse, nonrelapse mortality, or the development of graft-versus-host disease among the 3 groups. In conclusion, allogeneic PBSCT with low CD34 ⁺ cell doses of 1 to 2 × 10 ⁶ cells/kg gives acceptable results, whereas further investigations are needed to evaluate the effects of lower doses of <1 × 10 ⁶ cells/kg owing to the smaller number and the higher percentage of patients with adverse prognostic factors in this cohort.