The number of CD34 + CD133 + hematopoietic stem cells residing in umbilical cord blood (UCB) units is not correlated with the numbers of total nucleated cells and CD34 + cells: a possible new indicator for quality evaluation of UCB units.

Umbilical cord blood transplantation (UCBT) is often associated with delayed neutrophil and platelet recovery. Engraftment failure is another major obstacle. Several factors influence these serious complications, including the numbers of total nucleated cells (TNCs) and CD34+ cells which have been used as reliable factors for selecting UCB units for transplantation. However, whether both factors are reliable indices of the hematopoietic stem cell (HSC) activity of UCB units remains unknown. To evaluate the quality of UCB units, we quantified the actual number of transplantable CD34+ CD133+ HSCs (tHSCs) residing in UCB units. The number of tHSCs was not correlated with the numbers of TNCs or CD34+ cells. These results strongly suggest that neither factor reflects the numbers of tHSCs residing in UCB units. To validate the significance of the number of tHSCs, further analysis is required to determine whether the number of tHSCs residing in UCB units is useful as a new indicator for the quality assessment of UCB units.