How the Chinese Hamster might save your life
The recently released genomic sequence information of CHO cells will reduce the cost of production of biotherapeutic proteins by increasing our understanding of the most important mammalian cell factory
Although little recognised, 2012 is the 25th anniversary of the market introduction of the first recombinant therapeutic protein produced in mammalian cells. When Genentech introduced human tissue plasminogen activator for therapy of heart attacks in 1987, this was equivalent to a revolution in the Life Sciences. A strong controversy was going on at the time on the potential dangers of using immortalized mammalian cells for production of therapeutics: fear of transfer of oncogenic properties of the cell line into patients was as prevalent as the fear of viral infections. What only few expected was that now, 25 years later, human antibodies would be produced annually in kg-amounts, with more than 100 such products on the market, and with 4 times more in the pipelines of pharmaceutical companies. Annual revenues currently exceed 100 billion US$ and the largest danger for the future of biopharmaceutics is the fact that many public health services, while trying to provide these superior therapies to patients, struggle with their still high costs.
Throughout those 25 years one cell line has been the major player in this industry: Chinese Hamster Ovary cells, also known as CHO, developed in the late 1950´s as a model cell line for biological research, turned out to be ideally suited for the task they were given more or less by chance. The cell line is able to produce post-translation modifications closely resembling those produced in humans. These changes in protein structure, most importantly the addition of specific sugar residues, are critical for the biological function as well as for the length of time the therapeutic protein can remain active: proteins with incorrect modifications are recognised by our body as dysfunctional and quickly removed, or, even worse, they can cause severe immunological reactions. On several occasions therapeutics produced in mouse cell lines had to be withdrawn due to severe immune reactions caused by such non-human sugar structures. Why precisely the Chinese Hamster should have a glycosylation pattern similar to humans is one of the mysteries of natures, but fortunately, such a cell line was at hand when we started producing complex recombinant proteins. Thus, over the past 25 years, such proteins from CHO cells have saved and prolonged many lives.
Since then, the optimisation of bioprocesses and media has led to a dramatic increase in yield and efficiency of production runs with mammalian cell lines, nevertheless, due to the relatively long time required to establish a production cell line and bioprocess (typically between 6 and 12 months) the cost are still painfully high. With more and more efficient therapies pushing onto the market and with Public Health Systems notoriously under pressure, there is a strong drive to further improve these bioprocesses, both in terms of speeding up development and reducing running cost. One of the most hopeful approaches here is systems biotechnology which aims at a better and more detailed understanding of the underlying molecular mechanisms that enable cells to produce high quality proteins in a reliable and predictable manner. In fact, 2011 was the year that heralded the start of the systems biotechnology era for Chinese Hamster Ovary cells with the publication of the first genome sequence for this cell line.
This sequence information has long been waited for, as in other areas of research genomic studies have in the meantime become state of the art. It was not surprising therefore that immediately both the industry and the academic community came together to create a resource to provide easy access to the genomic information and other bioinformatics resources on CHO cells at www.CHOgenome.org .
With these resources at hand, extremely interesting opportunities open up that should enable the transit from high price specialty therapies to commodity medicines for mammalian cell derived products. Three topics stand out that, over the next 5 to 10 years, will benefit the most from a systems biotechnology approach:
Cell line heterogeneity and unpredictability: Due to their long time in culture and the large number of chromosomal rearrangements that are characteristic for this cell line, no two CHO cells are the same. Recent sequencing results have shown that even the two earliest CHO cell lines deposited at the American Type Culture Collection ATCC and the European Collection of Cell Cultures ECACC differ in their genomic sequence. The establishment of production cell lines per se is enhancing genomic rearrangements, so that each production cell line will have a different genome. The next step obviously is to analyse a large number of existing production cell lines to understand the range and relevance of genomic differences relative to product quality and safety. On the long term this will enable us to generate such cell lines by targeted gene integration rather than the random approach that is now used, so that cells with known and characterised properties will be created in a defined and predictable manner. This will reduce the amount of time and work needed, thus reducing cost and speeding up market introduction.
Understanding gene function under culture conditions: Similar to established approaches in biological research, where by an international collaborative effort a collection of gene knockout mice was established that allows detailed research into the function of each individual gene and its connection to diverse disease states, a similar approach should be taken for CHO cells as a model for cell factories that produce recombinant proteins under controlled culture conditions. Many of the genes present in a higher eukaryotic cell have functions important for the organism to cope with a variety of environmental and developmental states. Such genes may not be required for a cell factory in a bioreactor, and in fact, may interfere with proper performance of the cell due to unexpected or inappropriate activation of regulatory pathways. Understanding how these genes function and interact will allow engineers to optimise culture control so that high quality, functional and safe proteins can be reliably produced. This knowledge will reduce the cost of bioprocess runs, and thus the Cost of Goods of biotherapeutic proteins.
Minimal cell line: With a detailed knowledge of the function of individual genes, a strategy of gene reduction becomes feasible that eliminates genes from CHO cells that are not required for the task of recombinant protein production, thus reducing the burden of gene transcription that the cell has to bear and eliminating all potentially interfering genes that might lead to inferior product quality.
With these studies underway the production of biotherapeutic proteins in mammalian cells will achieve a better predictability and reproducibility. The task however is huge, so that a collaborative effort of both academia and the industry will be required which should happen in a coordinated fashion throughout Europe and the world. And, last but not least, this will require substantial financial input which should be shared by the industry and public funding agencies. The benefit to the public is clear: the ability to produce high quality therapeutics efficiently on a high-knowledge base will maintain the relevant jobs within Europe while the provision of cheaper medication will relieve financial stress on the public health sector.
(Published in European Science and Technology, Issue 15, page 218)
