Non-Inherited Maternal Antigens Identify Acceptable HLA Mismatches: A New Policy for the Hellenic Cord Blood Bank

Background: During pregnancy, the maternal-fetal contact may lead to the development of tolerance against the maternal human leukocyte antigen (HLA) that is not inherited by the fetus. These non-inherited maternal antigens (NIMAs) define acceptable HLA mismatches; therefore, the number of HLA phenotypes that are suitable matches for patients who need a hematopoietic stem cell transplant could be increased. Cord blood unit (CBU) transplantations to patients mismatched for a HLA loci, but similar to the ΝΙΜAs of the CBU, have a prognosis similar to 6/6-matched ones. Methods: The Hellenic Cord Blood Bank (HCBB) identified the maternal HLA of 380 cord blood donors, specifying the NIMA haplotypes of the related cryostored CBUs. Results: The HCBB extended the pool of HLA phenotypes through the generation of unique virtual phenotypes (VPs). A “VP database” was set up, using Microsoft Office—Access™, in order to provide NIMA-matched CBUs for potential recipients. The effectiveness of VPs’ matching was tested in 80 Greek patients. Conclusion: This methodology may contribute to the increase of the number of available CBUs for patients, in the case where there is no available CBU, or in case an additional one is needed. Through this method, the CBUs could be used faster and more effectively, rather than being cryostored for long periods of time.