Background: IgA nephropathy is a common primary glomerulonephritis caused by mesangial deposition of poly-IgA complexes. The disease follows a variable course of clinical progression, with a high risk of kidney failure. Although no specific therapy is available, enzymatic strategies to clear IgA deposits are being considered for the treatment of rapidly progressive IgA nephropathy.
Methods: We chose an IgA protease of commensal bacterium Clostridium ramosum, termed AK183, as the template for constructing a recombinant biologic. To extend the t1/2 in blood, we fused AK183 to the Fc segment of human IgG1. Activities of this Fc-AK183 fusion protein toward the cleavage and subsequent clearance of IgA were tested in mouse models.
Results: First, we discovered an autocleavage activity of AK183 that separates the N-terminal protease from its C-terminal autotransporter β domain. Therefore, we grafted Fc to the N terminus of AK183 and demonstrated its week-long enzymatic activity in mice. In addition, the proteolytic fragments of IgA generated in the reaction with Fc-AK183 were effectively removed from circulation via kidney filtration. The combined actions of Fc-AK183-mediated cleavage and subsequent renal clearance of IgA resulted in a lasting obliteration of blood IgA, as demonstrated in a human IgA-injection model and in a humanized α1KI transgenic model. Fc-AK183 was also able to remove chronic IgA and associated complement C3 deposits in the glomerulus.
Conclusion: We constructed a chimeric fusion of IgA protease with Fc and demonstrated its long-lasting efficacy as a promising targeted therapy for IgA nephropathy in mouse models.
Keywords: AK183; Clostridium ramosum; Fc-fusion protein; IgA nephropathy; IgA protease; neonatal Fc receptor/FcRn; recombinant biologics.
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