Expression of Intracellular Reactive Oxygen Species in Hematopoietic Stem Cells Correlates with Time to Neutrophil and Platelet Engraftment in Patients Undergoing Autologous Bone Marrow Transplantation

Reactive oxygen species (ROS) play important roles in hematopoiesis and regulate the self-renewal, migration, and myeloid differentiation of hematopoietic stem cells (HSCs). This study was conducted to determine whether ROS levels in donor HSCs correlate with neutrophil and platelet engraftment in patients after bone marrow transplantation. Cryopreserved HSC samples from 51 patients who underwent autologous transplantation were studied. Levels of intracellular ROS were assessed by flow cytometry using 2′,7′-dichlorodihydrofluorescein diacetate (H ₂DCFDA) in the CD45 ⁺/CD34 ⁺ HSC population. Colony forming unit assays were performed on HSCs isolated from the ROS ^high and ROS ^low populations to assess the differentiation potential of these 2 cell subsets. Distinct populations of ROS ^high and ROS ^low cells were evident in all patient samples. The median percentage of ROS ^high expressing HSCs in the study cohort was 75.8% (range, 2% to 95.2%). A significant correlation was identified between the percentage of ROS ^high stem cells present in the hematopoietic progenitor cells collected by apheresis product infused and the time to neutrophil engraftment (P <.001, r = –.54), as well as time to plt20, plt50, and plt100 (P < 0.001; r = –.55, –.59, and –.56 respectively). The dose of CD34 ⁺/ROS ^high/kg infused also inversely correlated with a shorter time to neutrophil engraftment; time to engraftment for patients receiving > or ≤3 × 10 ⁶ cells/kg was 11.5 days (range, 9 to 23) versus 14 days (range, 10 to 28), respectively (P =.02). The dose of ROS ^high HSCs delivered did not correlate with platelet engraftment. Collectively, these data suggest that the dose of ROS ^high stem cells delivered to patients may predict time to neutrophil engraftment after autologous transplantation.