Inhibiting HLA–B27 homodimer–driven immune cell inflammation in spondylarthritis

Abstract Objective Spondylarthritides (SpA), including ankylosing spondylitis (AS), are common inflammatory rheumatic diseases that are strongly associated with positivity for the HLA class I allotype B27. HLA–B27 normally forms complexes with β 2 ‐microglobulin (β 2 m) and peptide to form heterotrimers. However, an unusual characteristic of HLA–B27 is its ability to form β 2 m‐free heavy chain homodimers (HLA–B27 2 ), which, unlike classic HLA–B27, bind to killer cell immunoglobulin‐like receptor 3DL2 (KIR‐3DL2). Binding of HLA–B27 2 to KIR‐3DL2–positive CD4+ T and natural killer (NK) cells stimulates cell survival and modulates cytokine production. This study was undertaken to produce an antibody to HLA–B27 2 in order to confirm its expression in SpA and to inhibit its proinflammatory properties. Methods We generated monoclonal antibodies by screening a human phage display library positively against B27 2 and negatively against B27 heterotrimers. Specificity was tested by enzyme‐linked immunosorbent assay (ELISA), surface plasmon resonance (SPR) assay, and fluorescence‐activated cell sorting (FACS) analysis of B27 2 ‐expressing cell lines and peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) from patients with SpA. Functional inhibition of KIR‐3DL2–B27 2 interactions was tested using cell lines and PBMCs from patients with SpA. Results Monoclonal antibody HD6 specifically recognized recombinant HLA–B27 2 by ELISA and by SPR assay. HD6 bound to cell lines expressing B27 2 . FACS revealed binding of HD6 to PBMCs and SFMCs from patients with AS but not from controls. HD6 inhibited both the binding of HLA–B27 2 to KIR‐3DL2 and the survival and proliferation of KIR‐3DL2–positive NK cells. Finally, HD6 inhibited production of the proinflammatory disease–associated cytokine interleukin‐17 by PBMCs from patients with AS. Conclusion These results demonstrate that antibody HD6 has potential for use in both the investigation and the treatment of AS and other B27‐associated spondylarthritides.