Anti-HLA Antibodies Other than Against HLA-A, -B, -DRB1 Adversely Affect Engraftment and Nonrelapse Mortality in HLA-Mismatched Single Cord Blood Transplantation: Possible Implications of Unrecognized Donor-specific Antibodies

The impact of anti-HLA antibodies, except for donor-specific anti-HLA-A, -B, -DRB1 antibodies, on engraftment was retrospectively evaluated in 175 single cord blood transplantations (CBT). Patients and donors had been typed at HLA-A, -B, and -DRB1 antigens, and anti-HLA antibodies had been screened before transplantation to avoid the use of cord blood (CB) units with corresponding antigens. The median age was 59 (range, 17 to 74) years. Overall, 61% were male, 89% had high-risk disease status, 77% received myeloablative conditioning regimens, and over 80% were heavily transfused patients. Sixty-nine of the 175 (39.4%) were positive for anti-HLA antibodies. Thirty-nine patients had antibodies only against HLA-A, -B, or -DRB1, 13 had antibodies only against HLA-C, -DP, -DQ, or -DRB3/4/5, and 17 had antibodies both against HLA-C, -DP, -DQ, or -DRB3/4/5 and against HLA-A, -B, or -DRB1. Because CB units had not been typed at HLA-C, -DP, -DQ, or -DRB3/4/5, it was possible that antibodies against them were unrecognized donor-specific antibodies. Patients with antibodies only against HLA-A, -B, or -DRB1 showed comparable neutrophil engraftment rates to those without antibodies (89.7% versus 83%, P = .65), whereas patients having antibodies against C, DP, DQ, or -DRB3/4/5 showed lower engraftment rate (66.7%, P = .12), which became statistically significant in a subgroup of HLA-mismatched donor-recipient pairs (50%, P = .01). Our results demonstrated that the presence of donor nonspecific anti-HLA-A, -B, -DRB1 antibodies had no significant influence on engraftment, whereas anti-HLA-C, -DP, -DQ, or -DRB3/4/5 antibodies adversely affect engraftment, possibly because of unrecognized donor-specific anti-HLA antibodies against them, especially in HLA-mismatched CBT.