Update on HLAMatchmaker: A Molecularly Based Algorithm for Histocompatibility Determination at the Epitope Level

A previous issue of the ASHI Quarterly introduced HLAMatchmaker as a matching program that considers the structural basis of epitopes on class I HLA antigens. Each HLA antigen can be viewed as a string of short sequences (triplets) involving polymorphic amino acid residues in antibodyaccessible positions; the triplets are considered key elements of epitopes that can induce the formation of specific antibodies. The patient’s own HLA antigens represent the repertoire of self-triplets to which no antibodies can be made and HLAMatchmaker determines, for each mismatched donor HLA antigen, which triplets in corresponding sequence positions are different. The HLA phenotype of the recipient determines the degree of structural compatibility of a mismatched HLA antigen. For certain HLA phenotypes, a given mismatch has no or few mismatched triplets, while for other phenotypes, the same HLA antigen has many mismatched triplets and is, therefore, structurally highly incompatible.