An Engineered Complement Factor H Construct for Treatment of C3 Glomerulopathy

Abstract

Background C3 glomerulopathy (C3G) is associated with dysregulation of the alternative pathway of complement activation, and treatment options for C3G remain limited. Complement factor H (FH) is a potent regulator of the alternative pathway and might offer a solution, but the mass and complexity of FH makes generation of full-length FH far from trivial. We previously generated a mini-FH construct, with FH short consensus repeats 1-5 linked to repeats 18-20 (FH^{1-5^18-20}), that was effective in experimental C3G. However, the serum t_1/2 of FH^{1-5^18-20} was significantly shorter than that of serum-purified FH.Methods We introduced the oligomerization domain of human FH-related protein 1 (denoted by R1-2) at the carboxy or amino terminus of human FH^{1-5^18-20} to generate two homodimeric mini-FH constructs (FH^{R1-2^1-5^18-20} and FH^{1-5^18-20^R1-2}, respectively) in Chinese hamster ovary cells and tested these constructs using binding, fluid-phase, and erythrocyte lysis assays, followed by experiments in FH-deficient Cfh-/- mice.Results FH^{R1-2^1-5^18-20} and FH^{1-5^18-20^R1-2} homodimerized in solution and displayed avid binding profiles on clustered C3b surfaces, particularly FH^{R1-2^1-5^18-20} Each construct was >10-fold more effective than FH at inhibiting cell surface complement activity in vitro and restricted glomerular basement membrane C3 deposition in vivo significantly better than FH or FH^{1-5^18-20} FH^{1-5^18-20^R1-2} had a C3 breakdown fragment binding profile similar to that of FH, a >5-fold increase in serum t_1/2 compared with that of FH^{1-5^18-20}_, and significantly better retention in the kidney than FH or FH^{1-5^18-20}Conclusions FH^{1-5^18-20^R1-2} may have utility as a treatment option for C3G or other complement-mediated diseases.

Keywords: Immunology and pathology; complement; glomerulopathy; membranoproliferative glomerulonephritis (MPGN).