Fabry disease is a lysosomal storage disorder caused by a deficiency of the lysosomal enzyme ␣-galactosidase A (␣-gal A). This enzymatic defect results in the accumulation of the glycosphingolipid globotriaosylceramide (Gb 3; also referred to as ceramidetrihexoside) throughout the body. To investigate the effects of purified ␣-gal A, 10 patients with Fabry disease received a single i.v. infusion of one of five escalating dose levels of the enzyme. The objectives of this study were: (i) to evaluate the safety of administered ␣-gal A, (ii) to assess the pharmacokinetics of i.v.-administered ␣-gal A in plasma and liver, and (iii) to determine the effect of this replacement enzyme on hepatic, urine sediment and plasma concentrations of Gb3. ␣-Gal A infusions were well tolerated in all patients. Immunohistochemical staining of liver tissue approximately 2 days after enzyme infusion identified ␣-gal A in several cell types, including sinusoidal endothelial cells, Kupffer cells, and hepatocytes, suggesting diffuse uptake via the mannose 6-phosphate receptor. The tissue half-life in the liver was greater than 24 hr. After the single dose of ␣-gal A, nine of the 10 patients had significantly reduced Gb3 levels both in the liver and shed renal tubular epithelial cells in the urine sediment. These data demonstrate that single infusions of ␣-gal A prepared from transfected human fibroblasts are both safe and biochemically active in patients with Fabry disease. The degree of substrate reduction seen in the study is potentially clinically significant in view of the fact that Gb 3 burden in Fabry patients increases gradually over decades. Taken together, these results suggest that enzyme replacement is likely to be an effective therapy for patients with this metabolic disorder.
We have genetically replaced the diphtheria toxin receptor binding domain with a synthetic gene encoding interleukin-2 (IL-2) and a translational stop signal. The diphtheria toxin-related T-cell growth factor fusion gene encodes a 70 586-d polypeptide, pro-IL-2-toxin. The mature form of IL-2-toxin has a deduced mol. wt of 68,086 and is shown to be exported to the periplasmic compartment of Escherichia coli (pABI508), and contain immunologic determinants intrinsic to both its diphtheria toxin and IL-2 components. IL-2-toxin has been purified from periplasmic extracts of recombinant strains of E. coli (pABI508) by immunoaffinity chromatography using immobilized anti-IL-2. The purified chimeric toxin is shown to selectively inhibit protein synthesis in IL-2 receptor bearing targeted cells, whereas cell lines which do not express the IL-2 receptor are resistant to IL-2-toxin action.
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