Immune Response in Subjects With Fabry Disease Who Are Switching From Agalsidase Alfa to Agalsidase Beta

• Monitoring antibody formation against agalsidase alfa and beta [ Time Frame: 12 months ] [ Designated as safety issue: Yes ]
  Blood samples will be collected prior to infusion (screening & month 12). At baseline, antibodies against agalsidase alfa and beta measured, and at 12 months, antibodies against agalsidase beta will be measured by ELISA technique and will be isotyped immunoglobulins (IgG, IgA, IgM, or IgE). Positive samples will subsequently tested for enzyme neutralizing activity using an in vitro assay. Antibody measurements will be done by Shire Human Genetics Therapies, INC.
  
  

• Measurement of plasma/urine Gb3 and plasma lyso-Gb3 [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  Plasma samples collected after at least 8 hours of fasting prior to the blood draw. Plasma and urine samples (Gb3 only) analyzed using mass spectrometry. Gb3 measurements will be performed by Shire HGT.
  
  

Clinically, the development of an immune response is anticipated in a number of patients treated with any recombinant human proteins and suggested to be more common especially when the native protein is deficient or absent as many male patients with Fabry disease.

The immune response that results in the development of antibodies against the infused proteins may affect the clinical outcome of enzyme replacement therapy by the development of hypersensitivity, anaphylactoid, or febrile reactions, or may lead to the development of cytokine release and a generalized inflammatory response or immune complex formation. Furthermore, the mounted immune response may lead to inactivation or degradation of the recombinant enzyme or may change the pharmacokinetic and pharmacodynamic properties of the therapeutic protein.

The different rates of antibody formation with agalsidase alfa and agalsidases beta are often attributed to differences in techniques used to measure antibody formation. However, other factors such as host, structural similarity of the infused protein and tertiary structural difference such as glycosylation may lead to differences in the immune response. Among the factors that may affect host response are also the dose and the infusion frequency. Although agalsidase alfa and beta are derived from the same complementary DNA sequence there are minor differences in glycosylation patterns, and different dosing is used, 0.2 mg per kg every other week for agalsidase alfa, 1.0 mg per kg for agalsidase beta.

The investigator hypothesize that although the observation that the antibodies exhibit in vitro neutralizing capacity may suggest the presence of a single immunogenic epitope for both human recombinant alpha-galactosidases, the immunogenicity may not be similar for both agalsidase alfa and beta, and thus the differences in immune response will be determined by the host factors and the escalating dose of infused protein.