HLA-B27-Homodimer-Specific Antibody Modulates the Expansion of Pro-Inflammatory T-Cells in HLA-B27 Transgenic Rats

OBJECTIVES: HLA-B27 is a common genetic risk factor for the development of Spondyloarthritides (SpA). HLA-B27 can misfold to form cell-surface heavy chain homodimers (B27(2)) and induce pro-inflammatory responses that may lead to SpA pathogenesis. The presence of B27(2) can be detected on leukocytes of HLA-B27+ Ankylosing spondylitis (AS) patients and HLA-B27 transgenic rats. We characterized a novel B27(2)–specific monoclonal antibody to study its therapeutic use in HLA-B27 associated disorders. METHODS: The monoclonal HD5 antibody was selected from a phage library to target cell-surface B27(2) homodimers and characterized for affinity, specificity and ligand binding. The immune modulating effect of HD5 was tested in HLA-B27 transgenic rats. Onset and progression of disease profiles were monitored during therapy. Cell-surface B27(2) and expansion of pro-inflammatory cells from blood, spleen and draining lymph nodes were assessed by flow cytometry. RESULTS: HD5 bound B27(2) with high specificity and affinity (K(d) = 0.32 nM). HD5 blocked cell-surface interaction of B27(2) with immune regulatory receptors KIR3DL2, LILRB2 and Pirb. In addition, HD5 modulated the production of TNF from CD4+ T-cells by limiting B27(2) interactions in vitro. In an HLA-B27 transgenic rat model repetitive dosing of HD5 reduced the expansion of pro-inflammatory CD4+ T-cells, and decreased the levels of soluble TNF and number of cell-surface B27(2) molecules. CONCLUSION: HD5 predominantly inhibits early TNF production and expansion of pro-inflammatory CD4+ T-cells in HLA-B27 transgenic rats. Monoclonal antibodies targeting cell-surface B27(2) propose a new concept for the modulation of inflammatory responses in HLA-B27 related disorders.