Evaluation of Potential Antigenicity of Active-Site-Inhibited Recombinant Human FVIIa (FFR-rFVIIa) in an Immune-Tolerant Rat Model

Summary Recombinant human FVIIa (rFVIIa) was inactivated by coupling Phe-Phe-Arg-CO- (FFR) covalently to the active site of the enzyme. To test the chemically-modified human protein for potential antigenicity prior to clinical trial an immune-tolerant rat model was established. Intraperitoneal injection of the parent compound, human rFVIIa, within 30 h after birth, followed by repeated subcutaneous challenge with rFVIIa in Freunds incomplete adjuvant resulted in 79% non-responding rats at day 32. Monthly subcutaneous challenge showed that the induced tolerance was stable over the 3 months study period in 80% of the rats. The clinically relevant route, intravenous administration, was used for evaluating the potential antigenicity of FFR-rFVIIa. Repeated intravenous administration of different dosages of FFR-rFVIIa did not break tolerance, indicating that FFR-rFVIIa might not be antigenic, for a limited number of intravenous administrations in a clinical setting.

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