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

A new monoclonal antibody recognizing a linear determinant on the HLA-DRalpha chain N-terminus

We report the generation of a monoclonal antibody (MAb) that reacts to the N-terminus of the denatured HLA-DRalpha chain. The 1C4.6 MAb was raised against a peptide corresponding to amino acid residues 10 to 32 of a highly conserved region within the alpha1 domain of HLA-DR. This region partially overlaps with the epitope recognized by the conformationally dependent L243 MAb. In Western blot analysis, MAb 1C4.6 reacted with denatured HLA-DRalpha chains, but failed to bind the HLA-DRbeta chain expressed individually by transfectant cells, confirming that it recognizes an epitope on the alpha-chain of HLA-DR. In addition, this antibody was found to be isotype specific to HLA-DRalpha, as it did not cross-react to HLA class II proteins HLA-DP and-HLA-DQ. The 1C4.6 MAb is a valuable addition to existing reagents used to probe the structure and function of MHC class II molecules. This anti-HLA-DRalpha1 domain MAb may prove valuable for studies of HLA class II heterodimer assembly, structure, and function, as well as for studies into the release of soluble MHC class II.

Development of nondonor-specific HLA-DR antibodies in allograft recipients is associated with shared epitopes with mismatched donor DR antigens

Our previous studies showed that not only donor-specific antibodies (DSA) but also nondonor-specific antibodies (NDSA) were detected in the peripheral blood of allograft recipients. The molecular mechanism involved in the development of NDSA is examined here. HLA class II single antigen (SA) beads were used to determine the presence of HLA DR-specific antibodies in renal transplant recipients with failed allografts. Sequence-based antibody-epitope mapping was determined by the comparison of the reaction profiles of different SA recombinant cell lines containing unique epitope pattern. We found that 22 out of 65 recipients with failed grafts developed antibodies against donor HLA DR that is a mismatch with the recipient. Three of them had only DSA while 19 patients had not only DSA but also NDSA. An average of 77.3% of NDSA reacted with targets that share amino acid sequence with mismatched donor DR antigens. Either surface or nonsurface amino acid residues may constitute an antibody epitope. In conclusion, development of NDSA in allograft recipients may be associated with shared amino acids with mismatched donor antigens. SA beads technique not only helps to determine antibody specificities but also provides an ideal approach for the identification of potential HLA antibody epitopes.

A novel approach to human anti-HLA mABs production: use of phage display libraries

The production of human monoclonal antibodies was previously limited to very laborious and time-consuming processes involving EBV-transformation and/or hybridoma generation. Due to the development of molecular cloning techniques, it is now possible to produce human monoclonal antibody fragments quickly by panning phage display libraries against predefined antigenic specificities. Therefore, we tested this technology for producing human single chain Fv fragments (scFvs) against HLA-DR1 purified molecules immobilized on solid phase. Enrichment of DR1-specific phages was measured through five selection rounds of a synthetic library and revealed a 100-fold amplification. Soluble antibody fragments were then expressed and 7 out of 48 clones were found to secrete scFvs which specifically bind to DR1 molecules in ELISA. Further analysis revealed binding of the scFvs also to DR3 but not to DR5 or DR7 molecules correlating with the presence of particular polymorphic aminoacid residues in the DR beta chain. Western blot analysis indicated that the 7 scFvs react with the DR1 alpha/beta-dimer but not with free alpha- or beta- chains. This study shows that the innovative approach of phage display libraries can efficiently provide scFv fragments as useful reagents for the identification and dissection of HLA polymorphic epitopes.

A murine monoclonal antibody (928) recognizing a new epitope formed with a combination of HLA-DPA1*0201 and DPB1*0301 gene products

A murine monoclonal antibody (mAb), 928, that recognizes a cell surface antigen (928 Ag) on a human Epstein-Barr virus-transformed fetal liver-derived lymphoid progenitor cell line (FL4.4) was generated. The 928 mAb reacted with only FL4.4; it did not react with any other 57 cell lines tested. Two color flowcytometry analysis of peripheral blood mononuclear cells (PBMC) revealed that the 928 mAb reacted with B cell and monocyte fractions from only two individuals out of 63 unrelated donors. Biochemical analyses showed that the 928 Ag composes of two molecules (33 and 34 Kd) and forms a SDS-resistant, noncovalently linked dimer conformation, the feature being similar to that of peptide-bound MHC class II molecules. Treatment of FL4.4 cells with the 928 mAb significantly facilitated homotypic cell aggregation. In addition, treatment of PBMC of the 928 Ag+ donor with recombinant IL-4 augmented the expression of the 928 Ag on CD64+ monocytes. Typing of HLA-DRB1, DPA1 and DPB1 alleles of the 928 Ag expressing and nonexpressing cells revealed that the 928 Ag is expressed only on PBMC of HLA-DPA1*0201 and DPB1*0301 positive donors. Finally, anti-DP antibody precleared 928 Ag from the cell lysate. These results demonstrate that the 928 mAb recognizes a polymorphic determinant of HLA-DPA1*0201-DPB1*0301 gene products. The possibility that amino acids in the groove of the peptide-binding site of HLA-DP molecules are critical for the 928 epitope is discussed.