State of the Art Review: HLA Matching and Outcome of Unrelated Donor Umbilical Cord Blood Transplants
Cord Blood Stem Cell Transplantation
UCB graft cell dose is a critical determinant of hematopoietic recovery and survival after UCBT. However, there is increasing evidence that HLA match is also a key factor in UCBT outcome with mismatch adversely impacting on both engraftment and survival. Because of the relatively low numbers of patients transplanted with UCB to date it is not currently known how cell dose and HLA match interact as determinants of UCBT outcome. Also, it is not clear whether the same criteria will apply to both pediatric and adult recipients. Current data suggest that HLA match is critically important in the setting of a low cell dose. The elucidation of the impact of cell dose and match on UCBT outcome will be a major research priority for the future, and may impact determinations of the size of the cord blood inventory. Specifically, the available data does not allow us to fully discern the impact of a 1 versus 2 antigen mismatch, or how to "trade-off" the HLA-match and cell dose in unit selection. In addition, the importance of allele level matching at HLA-A and B, the match vector, and whether HLA-C or DQB1 should be considered in the selection of UCB units for transplantation is yet to be determined, and will rely on the collection of the appropriate allele level data to permit future analyses. The interaction between cell dose and HLA matching is especially critical in adults undergoing UCBT, and underlines the need for drastic increases in the unrelated cord blood inventory. Table 4 summarizes the NMDP's current recommendations for typing and matching of UCB units for transplantation based on the current literature. All recommendations are based on selection of a unit with an appropriate cell dose. Currently available data would consider this to be a unit that has >2.5-3 × 107 total precryopreserved nucleated cells per kg recipient body weight. It is hoped, however, that an increased UCB inventory will allow patients to receive units that are both of better match and sufficient cell dose, and that this will result in improved hematopoietic engraftment and survival after UCBT. © 2008 American Society for Blood and Marrow Transplantation.
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