Reexposure of cord blood to noninherited maternal HLA antigens improves transplant outcome in hematological malignancies.

Cord blood (CB) hematopoietic stem cell transplantation can be successful even if donor and recipient are not fully matched for human leukocyte antigens (HLA). This may result from tolerance-inducing events during pregnancy but to date this concept has not been tested in CB transplantation. Hence we analyzed the impact of fetal exposure to noninherited maternal antigens (NIMA) of the HLA-A, -B antigens, or -DRB1 alleles on the outcome of CB transplants. The 1,121 patients studied were transplanted for hematological malignancy with a single CB unit: 1,059 received grafts mismatched for one or two HLA antigens. Of these patients, 79 patients had a mismatched antigen that was identical to a donor NIMA, 25 with one HLA mismatch (MM), and 54 with two. If there was a NIMA match, transplant-related mortality (TRM) was improved, especially in patients >or=10 years (P = 0.012) as were overall mortality and treatment failure (P = 0.022 and 0.020, respectively, in the older subset), perhaps related to improved neutrophil recovery, especially in patients who received a low total nucleated cell (TNC) dose (P = 0.031). Posttransplant relapse rate also tended to be reduced, especially in patients with myelogenous malignancies given units with a single HLA mismatch (P = 0.074). These findings represent unique evidence that donor exposure to NIMA can improve survival in unrelated CB transplantation and might reduce relapse, indicating that cord blood cells can mount an antileukemic effect. By matching for donor NIMAs in search algorithms of CB inventories, the probability of selecting a graft with an optimal outcome will increase significantly.