The combined effects of HLA-allele matching at six-loci (HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1) and CD34+ cell dose on clinical outcomes were analyzed in 1,226 adult cases with single-unit unrelated cord blood transplantation. In the six-loci analysis, low HLA-allele matches did not significantly increase the overall mortality compared to higher matches, whereas in the five-loci analysis excluding HLA-DPB1, they caused a higher overall mortality (HR 1.42, p =.002), possibly due to the graft-versus-leukemia effect of HLA-DPB1 mismatches. A lower CD34+ cell dose (<.50 × 105/kg) resulted in higher mortality and lower engraftment; these inferior outcomes were offset by high HLA-allele matches (7-10/10 match), while the inferior outcomes of low HLA-allele matches were improved by increasing the CD34+ cell dose. Consideration of the combined effects of the CD34+ cell dose and HLA matching may expand the options for transplantable units when HLA matching or the CD34+ cell dose is inadequate.
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