High sensitivity of megakaryocytic progenitor cells contained in placental/umbilical cord blood to the stresses during cryopreservation.

摘要

In placental/umbilical cord blood (PCB) banking and PCB transplantation (PCBT), long-term cryopreservation of hematopoietic stem and progenitor cells is a unique requirement as compared to that for bone marrow transplantation and cytokine-mobilized peripheral blood transplantation. A long period of severe thrombocytopenia is a problem in many patients after PCBT. The object of this study was to define whether megakaryocytic progenitor cells (CFU-Meg), which produce platelets, are more sensitive to cryopreservation than the other myeloid progenitor cells in PCB. The leukocyte concentrates (LCs) obtained from clinical PCB banks were cryopreserved, and progenitor cell recoveries were determined by differential count of colony-forming cells (CFCs). The LCs were exposed to stresses which cells face during freezing, thawing, and washing out cryoprotectants. Most of the myeloid progenitor cells contained in the LCs showed good survival when cryopreserved at slow cooling rates, although cellular injury was observed at higher cooling rates and higher osmolalities. In contrast, the recovery rate of CFU-Meg was significantly lower than other progenitor cells, indicating a higher sensitivity to the various stresses they were exposed to during cryopreservation. Thrombocytopenia observed in patients receiving PCBT may be explained, at least in part, by the disappearance of CFU-Meg during cryopreservation.