Soluble Antigen Arrays for Selective Desensitization of Insulin-Reactive B Cells

Abstract

Autoimmune diseases are believed to be highly dependent on loss of immune tolerance to self-antigens. Currently, no treatments have been successful clinically in inducing autoantigen-specific tolerance, including efforts to utilize antigen-specific immunotherapy (ASIT) to selectively correct the aberrant autoimmunity. Soluble antigen arrays (SAgAs) represent a novel autoantigen delivery system composed of a linear polymer, hyaluronic acid (HA), displaying multiple copies of conjugated autoantigen. We have previously reported that Soluble Antigen Arrays proteolipid protein (SAgAPLP) induced tolerance to a specific multiple sclerosis (MS) autoantigen, proteolipid peptide (PLP). Utilizing SAgA technology, we have developed a new ASIT as a possible type 1 diabetes (T1D) therapeutic by conjugating human insulin to HA, known as Soluble Antigen Array Insulin (SAgAIns). Three types were synthesized: low valency lvSAgAIns (2 insulins per HA), medium valency mvSAgAIns (4 insulins per HA) and, high valency hvSAgAIns (9 insulins per HA) to determine if valency differentially modulates the ex vivo activity of insulin-binding B cells (IBCs). Extensive biophysical characterization was performed for the SAgA molecules. SAgAIns molecules were successfully used to affect the biologic activity of IBCs by inducing desensitization of the B cell antigen receptors (BCR). SAgAIns bound specifically to insulin-reactive B cells without blocking epitopes recognized by antibodies against the Fc regions of membrane immunoglobulin or CD79 transducer components of the BCR. Pre-incubation of IBCs (125Tg) with SAgAIns, but not HA alone, rendered the IBCs refractory to re-stimulation. SAgAIns induced a decrease in BCR expression and IP3R-mediated intracellular calcium release. Surprisingly, SAgAIns binding to BCR on the surface of IBCs induced the observed effects at both high and low SAgAIns valency. Future studies aim to test the effects of SAgAIns on disease progression in the VH125.NOD mouse model of T1D.