Analytical characterisation of cytokines and growth factors.

Cytokines (including growth factors) are playing an ever-increasing role in the therapy of human disease. The rapidity by which new cytokines are discovered, cloned and enter the clinics has placed a burden on control authorities and manufacturers to ensure their safety, quality and efficacy. The appropriate characterisation of these proteins plays a vital role in ensuring the development of cytokines as useful therapeutic agents. Highly sophisticated physicochemical techniques exist that can produce specific information about the structure and composition of cytokines including methods such as nuclear magnetic resonance (NMR) and mass spectrometry. However, even a bank of such techniques cannot yet predict the biological activity of cytokines. Biological assays are essential to assess the potency of cytokines and can take several forms, from in vivo assays to in vitro cell-line bioassays and more recently biochemically-based assays. Bioassays require a biological reference standard to define an appropriate unit that can be used to assess the potency of a biological therapeutic. However, bioassay-derived potency is a quality issue and should not have an impact on the perceived efficacy of a biological therapeutic.