Umbilical cord blood (UCB) transplantation is limited by the low number of hematopoietic stem cells in UCB units, which results in a low engraftment rate in transplant recipients. Here, we measured the total nucleated cell count and CD34+, CD3+, CD4+, CD8+, CD14+, and CD16+/56+ cell doses in each UCB unit and evaluated their influence on engraftment and other outcomes in 146 recipients. Multivariate analysis showed a significant association between a higher incidence of successful engraftment and a dose of CD34+ and CD8+ cells above the median (1.4 × 105 and 15.7 × 105 cells/kg, respectively). Engraftment occurred 4 days earlier in patients who received UCB with more than the median dose of CD34+ cells than those receiving UCB at or below the median. Stratification of the group according to CD34+ cell dose revealed a significant influence of the CD8+ cell dose on the time to achieve neutrophil engraftment in patients receiving a lower CD34+ cell dose, whereas there was no significant influence in the patients receiving a higher CD34+ cell dose. These results suggest that consideration of CD34+ and CD8+ cell doses in UCB units may improve the engraftment in recipients of UCB transplantation.
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