An anti-cytokine bioactivity assay for interferons-alpha, -beta and -omega

Interferons-alpha and -beta (IFN-alpha and -beta) are cytokines that are widely known to induce potent anti-viral activity. However, it has become increasingly apparent that IFN-alpha and -beta exert a variety of other biological effects, including anti-tumour and immunomodulatory activities and are increasingly used clinically to treat a range of malignancies, myelodysplasias and autoimmune diseases, e.g., IFN-beta for multiple sclerosis. The most widely used bioassays for the IFNs are based on their anti-viral activity, but these do not predict the biological activity of the IFNs in anti-tumour and immunomodulatory therapies. Thus, we have developed anti-cytokine-based bioassays that may be more reflective of such activity and which have several advantages over existing anti-viral bioassays. The anti-cytokine bioassay is based on the ability of IFN-alpha, -beta and -omega to inhibit granulocyte-macrophage-colony-stimulating factor (GM-CSF) induced proliferation of the erythroleukaemic cell line TF-1. This assay can take only 24 h, is sensitive to 200 fg (0.04 IU) IFN-alpha or -beta and 100 fg (0.02 IU) IFN-omega and is able to detect down to these levels in serum or plasma samples. The usefulness of anti-cytokine bioassays for IFN-alpha, -beta and -omega is not restricted to the GM-CSF/TF-1 cell format and other alternatives are available, such as erythropoietin (EPO)/TF-1 cells and EPO/UT-7-EPO cells. These assays can be made specific for each of the IFNs by including neutralising antibodies in the bioassay.