The development and manufacture of recombinant therapeutics requires the production of stable, high-yielding cell lines. The success of this process depends to a large degree on both the method chosen for transfection and clone selection, and also the cell line selected for culture.
The identification of high-yielding cells has traditionally been a lengthy process that involves sorting through thousands of clones in search of the few that, to some extent by chance, express the recombinant protein at suitably high levels. While optimizing media, feed strategy, and bioreactor parameters play an important role in ensuring maximum protein production, the optimization process starts at the very beginning, at the level of DNA.
The site of gene integration during transformation can determine the levels of protein produced—if a gene integrates into an area of the host genome that is transcriptionally silenced (heterochromatin), expression levels will be low. Genes that are constantly or regularly active are found within euchromatin and have high levels of histone acetylation. In contrast, heterochromatin is generally characterized by extensive histone deacetylation and high levels of histone methylation.
A number of strategies have been developed to change the structure of chromatin surrounding the integrated gene in order to circumvent the issue of integration site-specific repression.
In collaboration with King’s College London, Cobra Biomanufacturing has identified short polynucleotide sequences encompassing genetic regions surrounding housekeeping genes that maintain an open chromatin structure, thus allowing high levels of transcription of the subsequent genetic sequence. The DNA elements have been termed ubiquitous chromatin opening elements (UCOEs) and now are proving to be of great value in bioprocessing.