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The biological properties, assay, and standardization of interferon-alpha: a need for a WHO collaborative study.

Interferon-alpha (IFN-alpha) exists as a range of closely related, biologically active proteins and has been the subject of extensive research and clinical investigation. Standardization of IFN-alpha and the uniform reporting of IFN-alpha activity in International Units (IU) is critical to preclinical research and the clinical development of IFN-alpha products as therapeutic agents. Currently, several different IFN-alpha-containing reference preparations, established as World Health Organization (WHO) International Standards (IS) for particular IFN-alpha proteins (mixtures or single molecular species) are available for assay calibration. Nevertheless, the heterogeneous nature of IFN-alpha has raised standardization issues relating to the activity of individual IFN-alpha proteins, hence-forth termed subtypes, in the various biologic assays used for determining IFN-alpha levels. These issues include the question of parallelism of dose-response curves among particular IFN-alpha subtypes and different, naturally produced IFN-alpha subtype mixtures, for example, leukocyte IFN-alpha, and the applicability of IU of IFN-alpha activity defined by antiviral assays to alternative biologic assays, for example, antiproliferative assays. To address such issues, a WHO Consultative Group on Cytokine Standardization requested that the National Institute for Biological Standards and Control (NIBSC) and the Centre for Biologics Evaluation and Research (CBER) organize an international collaborative study to compare the activities and relative potencies of the several available IFN-alpha preparations, including those derived from human cells containing mixtures of IFN-alpha subtypes and those derived by rDNA methods containing single IFN-alpha subtypes, in different assays. To date, 111 participants in 32 countries have been recruited to the study and have agreed to assay a total of 17 different natural and recombinant IFN-alpha preparations or a defined subset thereof in specific in-house assays. The assay results generated will be statistically analyzed and evaluated to address the stated issues and to assess whether any individual IFN-alpha preparation is suitable to serve as an IS for all IFN-alpha preparations or whether more than one IS will be needed for this purpose.