Micelle-associated protein in epoetin formulations: A risk factor for immunogenicity?

Purpose. An upsurge of pure red cell aplasia (PRCA) cases associated with subcutaneous treatment with epoetin alpha has been reported. A formulation change introduced in 1998 is suspected to be the reason for the induction of antibodies that also neutralize the native protein. The aim of this study was to detect the mechanism by which the new formulation may induce these antibodies. Methods. Formulations of epoetin were subjected to gel permeation chromatography with UV detection, and the fractions were analyzed by an immunoassay for the presence of epoetin. Results. The chromatograms showed that Eprex(R)/Erypo(R) contained micelles of Tween 80. A minute amount of epoetin (0.008 - 0.033% of the total epoetin content) coeluted with the micelles, as evidenced by ELISA. When 0.03% (w/v) Tween 80, corresponding to the concentration in the formulation, was added to the elution medium, the percentage of epoetin eluting before the main peak was 0.68%. Conclusions. Eprex(R)/Erypo(R) contains micelle-associated epoetin, which may be a risk factor for the development of antibodies against epoetin.