Toward reducing immunogenicity of enzyme replacement therapy: altering the specificity of human β-glucuronidase to compensate for α-iduronidase deficiency

Enzyme replacement therapy (ERT) is an effective treatment for many patients with lysosomal storage disorders caused by deficiency in enzymes involved in cell metabolism. However, immune responses that develop against the administered enzyme in some patients can hinder therapeutic efficacy and cause serious side effects. Here we investigated the feasibility of a general approach to decrease ERT immunogenicity by altering the specificity of a normal endogenous enzyme to compensate for a defective enzyme. We sought to identify human beta-glucuronidase variants that display alpha-iduronidase activity, which is defective in mucopolysaccharidosis (MPS) type I patients. A human beta-glucuronidase library was screened by the Enzyme Cleavable Surface-Tethered All-purpose Screen sYstem to isolate variants that exhibited 100-290-fold greater activity against the alpha-iduronidase substrate 4-methylumbelliferyl alpha-L-iduronide and 7900-24 500-fold enzymatic specificity shift when compared with wild-type beta-glucuronidase. In vitro treatment of MPS I cells with the beta-glucuronidase variants significantly restored lysosome appearance similar to treatment with alpha-iduronidase. Our study suggests that beta-glucuronidase variants can be isolated to display alpha-iduronidase activity and produce significant phenotype improvement of MPS I cells. This strategy may represent a possible approach to produce enzymes that display therapeutic benefits with potentially less immunogenicity.