Relationship between radiosensitivity of human neonatal hematopoietic stem/progenitor cells and individual maternal/neonatal obstetric factors.

Hematopoietic stem/progenitor cells (HSPCs) in placental/umbilical cord blood (CB), which is neonatal peripheral blood, have increasingly been used for hematopoietic stem cell transplantations. It is likely HSPCs are sensitive to extracellular oxidative stresses, such as ionizing radiation and redox-directed chemotherapeutic agents. However, the radiosensitivity of HSPCs and neonatal hematopoietic system remains unclear. This study investigated the potential relationship between the radiosensitivity of HSPCs in CB, which was obtained from singleton and full-term deliveries, and maternal/neonatal obstetric factors. Freshly prepared CB CD34(+) cells exposed to 2 Gy X-irradiation were assayed for hematopoietic progenitor cells such as colony-forming unit-granulocyte-macrophage (CFU-GM), burst-forming unit-erythroid (BFU-E), colony-forming unit-granulocyte-erythroid-macrophage-megakaryocyte (CFU-Mix), and colony-forming unit-megakaryocyte (CFU-Meg). As a result, the neonatal weight, placental weight, CB volume, total low-density (LD) cells, and CD34(+) cells showed mutually significant positive correlations. The CB volume and total LD cells showed a significant reverse correlation with the surviving fraction of CFU-Meg. The surviving fraction of CFU-GM in spring (March-May) was significantly higher than that in autumn (September-November). The surviving fraction of CFU-Meg in the spring was significantly lower than that in the autumn. Male neonates showed a significantly higher surviving fraction of CFU-GM than female neonates. Contrarily, females showed a significantly higher surviving fraction of CFU-Meg than males. The present results suggest that the obstetric factors, such as the season of birth and neonatal gender, influence the radiosensitivity of neonatal hematopoiesis.