Cytokine and growth factor standardization: the need for research to answer modern issues

New and novel cytokines are being discovered, cloned and entered into clinical trials at such a rate that often the biological activities of these proteins are poorly understood during their development as therapeutic agents. When estimating the biological activity of different preparations with different specific activities by bioassay, mass units cannot be used. Biological activity is therefore expressed as "biological potency units". Due to the pleiotropic nature of cytokine activity, the biological unit requires definition by a standard that is assay-independent. The need to investigate the biological activity of any proposed standard material in a variety of assays, with statistically valid numbers of participants and with appropriate scientific rationale, has led to the design of international collaborative studies that have provided extremely useful data about the biological activity of cytokines. Such information has had a great impact on the choice of material to serve as a standard and has prevented the establishment of inappropriate preparations. Over the years, WHO international standards have been used to reduce the variation in estimates of cytokine preparations within and between laboratories for both immunoassays and bioassays.