HLAMatchmaker: A molecularly based algorithm for histocompatibility determination. II. Verification of the algorithm and determination of the relative immunogenicity triplet-defined of amino acid epitopes

HLAMatchmaker is a computer algorithm that assesses human leukocyte antigen (HLA) compatibility at the structural level by intralocus and interlocus comparisons of polymorphic amino acid triplets in antibody-accessible sequences of HLA class I molecules. This program permits the identification of mismatched HLA antigens that share all of their polymorphic triplets with the patient's HLA antigens and, therefore, could be considered fully compatible. The validity of this algorithm has been verified by analyzing the antibody specificity patterns of 127 well-characterized sera (panel reactive antibody [PRA] > 80%) that had been screened by direct complement-dependent and/or anti-human globulin augmented lymphocytotoxicity testing with large HLA-typed cell panels. A 2X2 table-based Chi-square analysis program was applied to determine positive and negative correlations between serum reactivity and the presence HLA triplets assigned from the HLA types in the cell panel. The results indicate that high PRA patients do not produce antibodies to shared triplets on mismatched FILA antigens. Moreover, this serum analysis has permitted the identification of triplets with different degrees of immunogenicity as indicated by the frequencies of positive and negative correlations of serum reactivity with the HLA-typed cell panel. Mismatching for triplets with low immunogenicity provides further opportunities for identifying donors with acceptable HLA mismatches for highly sensitized patients.