Development of antigen-specific B cell elimination by recombinant toxins in autoimmune diseases

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Pemphigus vulgaris (PV) is an autoimmune blistering disease characterized by circulating pathogenic IgG antibodies against desmoglein 3 (Dsg3). The purpose of this study was to develop chimeric molecules for specific recognition and elimination of autoimmune B cells in PV.Mouse hybridoma cell lines producing anti-Dsg3 antibody (5H10, 12A2) were developed as an in vitro model system for B cell targeting. Dsg3-GFg a baculoprotein containing the entire extracellular domain of Dsg3 fused with green fluorescence protein, recognized and targeted the hybridoma cells through their surface immunoglobulin receptors in an antigen-specific way. The epitopes of these monoclonal antibodies were mapped on the amino-terminal EC1 and part of EC2, a region considered functionally important in cadherins. Chimeric toxin molecules containing the mapped region (Dsg3_N1) and modified Pseudomonas exotoxin (PE) were produced in bacteria (Dsg3_N1-PF4O-KDEL, PE37-Dsg3_N1-KDEL) and tested in vitro on hybridoma cell lines. The chimeric toxins, but not Dsg3_N1 alone, showed dose-dependent toxic activity with a reduction in hybridoma cell number to 40-60% of toxin-negative control cultures, compared with little or no effect on anti-Dsg3-negative hybridoma cells. Furthermore, these toxins showed toxic effects on anti-Dsg3 IgG-producing B cells from Dsg3_N1-immunized mice, with a 60% reduction in cell number compared with Dsg3_N1 alone. Thus specific recognition and targeting of antigen-specific B cells in PV was demonstrated and this strategy may hold promise as a future therapeutic option for PV and other autoimmune diseases.