Development of Conformer-Specific Anti-HLA Class II mAbs

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Summary: Murine MHC class II molecules exist in two distinct conformational states formed by differential pairing of class II transmembrane (TM) domain GxxxG dimerization motifs (i.e., M1 and M2 paired class II), and these two conformers are linked to different immunological functions. Moreover, we have recently reported that: 1) HLA class II HLA-DR, DP and DQ molecules mirror mouse class II in possessing three TM domain GxxxG motifs, 2) in silico molecular modeling reveals that HLA-DR and DQ TM domains can adopt energetically favorable M1 and M2 paired states, and 3) hybrid class II molecules with an HLA-DR or DQ TM domain can adopt both an M1 and M2 conformation. In this proposal, we show that a commercially-available anti-HLA class II mAb (H0002) exhibits differential reactivity to wild type vs. an HLA-DR M1 GxxxG>VxxxV mutant molecule (which would have an altered conformer state). These findings strongly suggesting that like mouse class II, human class II molecules also exist in two distinct conformational states (M1 and M2 paired class II). In addition to published work on the differential signaling of M1 vs. M2 paired class II in normal B murine cells, our preliminary studies show that M1 and M2 class II are linked to distinct signaling pathways in neoplastic B cells. Herein, we show that while selective engagement of M1 class II inhibits B cell lymphoma proliferation, co-ligation of M1 and M2 class II blocks this effect. This is important because three anti-HLA-DR mAbs (IMMU-114, 1D09C3 and Hu1D10) have undergone clinical trials as treatment for B cell leukemia/lymphoma with mixed results. Since the conformer specificity of these three anti-DR mAbs is unclear, it raises the possibility that anti-DR mAb therapeutic efficacy is linked to mAb conformer reactivity. These findings lead to the hypothesis that like mouse class II, human HLA class II molecules exist in two distinct conformational states based on alternative pairing of transmembrane domain GxxxG dimerization motifs and that these two distinct HLA class II conformers are linked to different clinically-relevant B cell signaling pathways. To test this core hypothesis, we will; 1) Define the HLA-DR conformer specificity of a large panel of available anti-HLA class II mAbs, including those that have undergone clinical trials as therapeutics for B cell leukemia/lymphoma, and 2) Develop a panel of new monoclonal antibodies that recognize the conformational differences between M1 and M2 paired human HLA-DR and HLA-DQ class II molecules. Completion of these aims will help bring the M1/M2 class II conformer paradigm to the HLA field, provide insight into whether there is a correlation between the conformer-specificity of clinically-relevant anti-DR mAbs and demonstrated therapeutic effect, and provide the field with a new set of tools (i.e., conformer-specific anti- HLA-DR and anti-HLA-DQ mAbs) to further investigate the role of M1 and M2 HLA class II in human health and disease.