An update on HLA matching, including HLA "epitope" matching: a new approach.

1. HLA mismatching for -A, -B, and DR loci was updated from the UCLA Transplant Registry and showed a strong effect at 1, 2, and 3 years posttransplant. The effect of mismatching was most prominent in the zero-mismatched groups compared to 1 or more mismatched for HLA-A, -B, and -DR. 2. Patient survival was analyzed as a function of HLA matching and shown to be significantly improved in comparison to those groups of patients that were more poorly matched. The better patient survival is postulated to be a function of fewer rejection episodes and decreased amount of immunosuppression necessary for transplant function in better-matched groups of patients. 3. HLA-A, -B, and -DR epitope matching was considered on the basis of serological crossreactivity for the A and B loci and oligonucleotide homologies for the DR locus. Epitope matching showed that there was a 15% difference between the zero mismatched and the over 25 mismatched recipient groups, thus increasing range and resolution of the analysis of the zero versus very highly mismatched recipient combinations. HLA epitope matching is an important first step in determining the immunogenicity of the homologies and disparities among the HLA-A, -B, and -DR antigens.