A cytotoxic human hybridoma monoclonal antibody (TrJ6) defining an epitope expressed by HLA-DQ4 and -DQ5

A Comprehensive Evaluation of the Antibody-Verified Status of Eplets Listed in the HLA Epitope Registry

Matching strategies based on HLA eplets instead of HLA antigens in solid organ transplantation may not only increase the donor pool for highly sensitized patients, but also decrease the incidence of de novo donor-specific antibody formation. However, since not all eplets are equally capable of inducing an immune response, antibody verification is needed to confirm their ability to be bound by antibodies, such that only clinically relevant eplets are considered. The HLA Epitope Registry has documented all theoretically defined HLA eplets along with their antibody verification status and has been the foundation for many clinical studies investigating eplet mismatch in transplantation. The verification methods for eplets in the Registry range from polyclonal sera from multi- and uni-parous women to murine and human monoclonal antibodies (mAbs), and antibodies purified by adsorption and elution from sera of HLA immunized individuals. The classification of antibody verification based on different methods for validation is problematic, since not all approaches represent the same level of evidence. In this study, we introduce a classification system to evaluate the level of evidence for the antibody-verified status of all eplets in the HLA Epitope Registry. We demonstrate that for a considerable number of eplets, the antibody-verified status is solely based on polyclonal serum reactivity of multiparous women or on reactivity of murine mAbs. Furthermore, we noted that a substantial proportion of patient sera analyses and human mAb data presented in the HLA Epitope Registry Database has never been published in a peer-reviewed journal. Therefore, we tested several unpublished human HLA-specific mAbs by luminex single antigen beads assay to analyze their HLA reactivity for eplet antibody verification. Although the majority of analyzed mAbs indeed verified their assigned eplets, this was not the case for a number of eplets. This comprehensive overview of evidence for antibody verification of eplets in the HLA Epitope Registry is instrumental for future investigations towards eplet immunogenicity and clinical studies considering antibody-verified eplet mismatch in transplantation and warrants further standardization of antibody verification using high quality data.

A human hybridoma monoclonal antibody (TrJ11) recognizing a new HLA-DR epitope shared by DR4, DR8, DR11, and DRB1*1303

The cytotoxic IgM lambda human hybridoma mAb TrJ11 reacts with lymphoblastoid B-cell lines expressing DR4, DR8, DR11, and DRB1*1303. However, TrJ11 was monospecific when normal B cells freshly isolated from blood served as targets in that it only killed HLA-DR4-positive cells. Thus, of 235 HLA-typed persons TrJ11 was strongly cytotoxic for normal B cells of all 90 DR4-positive individuals, but it did not react with B cells from any of the 145 DR4-negative donors. Hence, mAb TrJ11 proved to be suitable for routine DR4 typing. The specific binding of TrJ11 to a DR4-positive cell line was profoundly blocked by the mouse HLA-DR beta chain-specific monomorphic mAb TAL 14.1, indicating that the epitope recognized by TrJ11 is located in the DR beta chain. The possibility that amino acids located in the floor of the peptide-binding site are critical for the TrJ11 epitope is discussed.

A novel HLA-A determinant recognized by a cytotoxic human hybridoma IgG1 monoclonal antibody (TrJ14)

TrJ14 is a cytotoxic human IgG1 lambda hybridoma mAb that recognized a novel HLA-A epitope expressed by lymphoblastoid B cells that are homo- or heterozygous for A2, A3, A11, A30, A31, A33, A68 and A69. Based on these results, the HLA type of cell line TEM (10w9057) was retyped as A66. When peripheral blood T cells isolated freshly from 265 HLA-typed normal individuals served as targets, TrJ14 killed cells expressing two TrJ14-positive HLA-A alleles, as well as the majority of cells having one TrJ14-positive and one TrJ14-negative HLA-A antigen. However, TrJ14 failed to recognize or reacted weakly with most HLA-A2 and -A3 heterozygous normal T cells when A2 or A3 was coexpressed together with a TrJ14-negative antigen. The serological reactivity of TrJ14 correlated with the amino acid valine and aspartic acid at positions 76 and 77 of the alpha 1-domain helix. These amino acids were shared exclusively by all the identified TrJ14+ alleles.