Differences in Human Growth Factors Induced by Non-Human Cell Expression.

Expression of recombinant human proteins in cells from different species, including bacteria, yeast, insect, mouse, hamster or primates, imparts species-specific changes post-translation. The impact of these species-specific differences in post-translational modifications (PTMs) can be far-reaching, resulting in effects ranging from inaccurate quantitation of proteins in serum to in-vivo immunogenicity (Porter, J Pharm Sci 90: 1–11, 2001) or even autoimmunity to the patient’s own native protein (Ryan et al., Int Immunopharmacol 4:647–55, 2006). Currently, most human proteins are still produced from bacteria, including several of the World Health Organization international growth factor standards. For example, present-day clinical grade recombinant human growth factors such as G-CSF, IL-4 and GM-CSF are manufactured from bacteria. The expression of human proteins that naturally exhibit a high degree of glycosylation, such as GM-CSF, in bacterial cells has major implications for immunoassays and therapeutics. Since bacterial cells do not glycosylate human proteins, exposure of cryptic or masked epitopes, normally buried on the native protein, can result in generation of antibodies that bind falsely in immunoassays and can cause reduced potency or adverse reactions in patients. The expression of recombinant human proteins in non-human mammalian cells can result in non-natural epitopes due to the addition of non-human sugar structures. We have expressed several human growth factors in human cells and have demonstrated differences in their immunoreactivity patterns when compared to the same recombinant proteins expressed in non-human cells. These changes in the biological properties of the proteins are likely related to differences in glycosylation and other PTMs unique to proteins expressed in human cells. We have demonstrated that expression of human growth factors in human cells may have significant benefits for the accuracy of native human protein assays and the therapeutic efficacy of human growth factors.