Production and characterization of chimeric anti-HLA monoclonal antibodies targeting public epitopes as tools for standardizations of the anti-HLA antibody detection.

Two chimeric monoclonal antibodies (MoAbs) were designed with variable parts of the mouse antibodies W6/32 and F3.3, and the human constant parts C-gamma1 and C-kappa. These chimeric MoAbs are specific for HLA-class I and HLA-class II public epitopes, respectively. The anti-class I MoAb recognizes all HLA-class I tested so far, and the anti-class II MoAb recognize all HLA-DR, DP, and only DQ antigens of the DQ2 subgroup. These Moabs were used as positive controls in routine tests for the detection of IgG anti-HLA antibodies in the sera of patients (Luminex, flow cytometry, and complement-dependent lymphocytotoxicity assay: CD-LCT). In tests with the LABScreen MIX assay, serial dilutions of the two MoAbs have allowed to determine the thresholds of detection by the Boltzmann sigmoidal regression. The thresholds of detection in mean of fluorescence intensity (MFI) were 926 and 866 for the anti-class I MoAb and the anti-class II MoAb, respectively. The thresholds defined as mean+3SD of MFI values obtained with 30 negative control sera were 411 and 251 for the anti-class I beads and the anti-class II beads, respectively. For the daily validation of the anti-HLA IgG antibodies screening by LABScreen MIX we decided to use the positive control MoAbs at three concentrations (5, 50, and 500ng/ml) and we measured the repeatability (<10%) and reproducibility (<16%) of the method. Used as positive controls in tests with the LABScreen Single Antigen kit, the two MoAbs allowed to estimate daily the quality of beads coated with HLA antigens. The two anti HLA MoAbs were also used as positive control in the cross-match assay by flow cytometry or CD-LCT. In total these two chimeric anti-HLA-MoAbs, which have no equivalent so far, are valuable positive controls for the daily validations of most techniques used for the detection of anti-HLA antibodies according to the good practice guidelines for laboratories.