Tu132 - Engineering Soluble Fcγ Receptors to Antagonize Autoantibodies & Treat Autoimmunity

Abstract Text:

Introduction: Autoantibodies drive autoimmune diseases by providing a link between the immune system and innocuous target cells. Tissues expressing self-antigens are opsonised by autoantibodies which in turn, facilitate the activation of Fc receptor-expressing innate immune cells and trigger the complement cascade. In this project, we aim to limit the inflammatory function of autoantibodies by engineering therapeutic proteins that occlude their Fc region.

Hypothesis: Soluble proteins comprising the extracellular domain of Fcγ receptors will reduce antibody-mediated activation of innate immune cells by creating a competitive environment for engaging antibody Fc regions.

Results: Using HER2 as a model target antigen, we have developed an in vitro culture system that mimics autoantibody-driven inflammatory responses. In this system, HER2-expressing SKBR3 cells are opsonised with a clinically-relevant anti-HER2 antibody (Herceptin) and subsequently co-cultured with Fc receptor-expressing monocytes/macrophages. Upon co-culture, monocytes/macrophages upregulate co-stimulatory molecules and secrete significant quantities of pro-inflammatory cytokines including IL-1β, IL-6 and TNFα. We have also demonstrated that soluble Fcγ receptors are capable of binding Herceptin-opsonised SKBR3 cells in a dose-dependent manner. In these assays, His-tagged proteins comprising the high affinity CD64 (FcγRI) ectodomain bound opsonised SKBR3 cells significantly better than proteins comprising CD32a (FcγRIIa), CD32b/c (FcγRIIb/c) or CD16 (FcγRIII) ectodomains.

Future directions: We will assess whether soluble Fcγ receptors inhibit the antibody-mediated activation of monocytes/macrophages, as well as NK cell-mediated lysis, upon co-culture with Herceptin-opsonised SKBR3 cells. We will also probe whether Fc occlusion using soluble Fcγ receptors affects triggering of the complement cascade.