The CHO Cell Line – From Reliable Workhorse to State-of-the-art Protein Powerhouse

In this podcast, we talked with Alan Dickson, Ph.D., Professor of Biology at the Manchester Institute of Biotechnology, University of Manchester about the evolution of the CHO Cell line from isolation to workhorse of the biomanufacturing industry, to gene edited knockout variants. It is an interesting look at why CHO cells have been so successful and how this success continues to be improved upon for manufacture of emerging therapeutics.

Show Notes

I began the interview by talking with Professor Dickson about his group’s long trajectory in bioprocessing research, specifically the Chinese Hamster Ovary (CHO) cell line. I mentioned that today CHO cells are the work horse for the development and manufacturing of biopharmaceutical products, but back in 1957 when Puck managed to isolate and keep in culture the first CHO-K1 cells, nobody could have anticipated this success.

The success of CHO cells

I then asked him what is so special about CHO cells and why have they been so successful. He started by saying that CHO cells have survived 40-50 years of use and were originally isolated to study cancer, where researchers found that they divided rapidly and were well suited for cancer research. At the same time, researchers developed mutants that enabled CHO cells to be used in selection systems to express proteins. By using knockout technology for specific genes, they were able to then use those same genes in a vector cassette as a marker for uptake of the recombinant gene. He went on to say that because CHO was a robust cell line, many groups worked on it and thus much was known about how the cells grew.

Once the cell line was used to successfully produce proteins and products produced in these systems were approved by the FDA and other regulatory bodies, then it made sense that others would follow and also produce products in CHO cells. In addition, the fact that they are mammalian cells and have the right sort of processing for human products was also important to their success.

Evolution of CHO cell derivatives

We then discussed how from the original isolation of the CHO-K1 cells, many derivatives have emerged over the years; CHO-S, CHO-DG44, CHO-K1 variants, and more recently knockouts to improve clonal selection or eliminate undesirable enzymatic activities. Although there has been a dramatic evolution in genetic manipulation and gene editing technologies over the last couple of decades, one would have expected an acceleration in the generation of new hosts.

I asked Alan if he thought that the original CHO variants had addressed specific industry needs at the time and that new improvements have been more difficult to realize than originally thought. Derivatives emerged because CHO cells were subject to mutation through various screening processes with variants emerging in response. These variants became more accessible and gave rise to different processes. This became valuable in that one company could use one CHO cell lineage and another company could use something different. Companies could develop their own platform that was selectable and might give them a commercial advantage. Over the years, in a world of IP related activities, those that developed CHO DG44 would have also developed special media and processes. This caused cell lines to become honed in to process derivatization or directed evolution. So every time someone used a CHO cell line to make a specific protein they were inherently creating a slightly different variant.

He went on to say that much of the early production of basic antibodies was relatively easy. Over time, enhances increased productivity with the variant becoming better adapted to media and making that protein. The continuous evolution of using a specific CHO cell line then adapting it to a specific media and creating an environmental platform for cell growth has enabled the move from .1-.2 g/L in the 1990’s to 5-10 g/L currently.  This optimization of process allowed companies to make medicines used for new therapeutics. Today, non-traditional antibodies and different products are being made, but it is difficult to reach the same yield/quality as traditional antibodies, so cell lines need to be adapted to handle these more difficult formats.

Cell line platform for biotherapeutic production

Next I asked Alan if it is better to have a ‘one size fits all’ or ‘one outfit for every occasion’ in the world of biotherapeutic production, particularly in the case of CHO. He explained that in industrial manufacturing it is best to have a platform that works very much in the same way every time. Predictability is important and thus a one size fits all approach is great and works well for fairly standard antibodies. When you have more exotic products with extra binding sites, very difficult structures, etc. it is very difficult to achieve the kind of production needed with a one size fits all approach. You need to analyze what about the exotic product makes it difficult to make, and ask if you can match it with a CHO variant engineered to accept the format of that molecule or can it be engineered? The ideal scenario in these cases would be to have a standard process with a library of different cell lines that can be tested to see which one fits best with the more exotic molecules.

Alternative methodologies for recombinant protein production

We then discussed how in recent years we have witnessed with more or less success the onset of different waves of alternative methodologies to produce biotherapeutics, from recombinant plants, to engineered microbes, to cell-free platforms. Although some of these platforms seem to cater well for specific product niches i.e., vaccines, ADCs, etc., they do not seem to replace the use of mammalian culture technologies. I asked Alan if he thought  it would ever be possible to have the perfect vehicle for biotherapeutic protein production, be it CHO or any other mammalian system. He said that CHO is not a professional protein secretory cell. We use CHO cells because because of their history and selection systems, but in terms of productivity each CHO cell is only about 10% as effective as a professional protein secretory cell. He explained that a professional protein secretory cell would be something like a plasma cell making antibodies in the human body in response to infection. A plasma cell can produce 200 picograms per cell per day. Most CHO cells only produce about 20 picograms per cell per day. One reason for this is that the CHO cell keeps dividing and uses valuable energy to make more of itself, not more of what it views as a useless protein.

However, if you understand the basics of the professional protein secretory cell, then you can select for the type of cell that is the perfect vehicle or determine how you could engineer CHO toward a more perfect vehicle. A perfect vehicle would make lots of protein per cell, per unit type and grow well at high density. Alan pointed out that these are probably incompatible goals. An ideal situation is if you could get a cell to grow well to high density, then switch onto a productivity phenotype to make the recombinant protein. Another addition would be to ensure that the cell makes protein of the right quality. For example, that it adds the right carbohydrate group or that it will modify the protein in the correct way for function. CHO as a future perfect vehicle is possible, they grow well, they can be adapted and modified, and they have the potential to grow well and then switch for productivity. Some have looked at continuous processes for CHO cells as a way to grow to high density then have them slow down the growth and keep them in productivity mode.

Another mammalian cell line could work as a perfect vehicle, provided that you have the right growth and productivity properties. Microbes could also work if they could handle and modify proteins correctly for use in therapeutics. Alan believes that we are about ten years away from having a perfect vehicle system that might be used. Cell free systems, recombinant plants and other systems are possible. However, there has been so much investment in the CHO platform that to move to another system, you would have to evaluate whether in five years you would have a good return on investment for a new system.

Future of expression technologies in bioprocessing

I then asked how he sees bioprocessing evolving in the future and whether at some point we will witness a ‘replacement’ of expression technologies. He said that he thinks that expression systems will be staying with us for years to come. He gave insulin as an example of an expressed protein, not in mammalian cells, that is a critically important therapeutic and it will remain so. There are many other therapeutics that will also remain critically important and will be produced using cell culture.

Cell and gene therapies are emerging as important therapeutics and this will increase over the next ten years. But cell and gene therapies are incredibly costly and require specialized knowledge of bioprocessing. This knowledge of how to grow cells in culture and make them stay the same is going to be important for these modalities as well. For example, much of what we learned about CHO cells and associated technologies are being applied to HEK293 cells that make viral vectors. Viral vectors can be used to create vaccines and gene therapies. Thus, the lessons learned and the processes developed with CHO cells are applicable to new therapeutics being developed. It is also important to look at a workforce that can apply CHO knowledge to new areas. Applying the right knowledge and learning to these new applications could accelerate a whole range of new therapeutics.

Biggest challenge in bioproduction today

Then we talked about the largest challenge that’s still to be addressed today in bioproduction of biotherapeutics as a whole. He said that cost is critically important. He explained that the world came together to develop therapeutics and vaccines for Covid-19 in record pace, this can be done during a pandemic. He is not sure how easy it will be to accelerate the process and decrease cost of more standard biologic medicines. He pointed out that it is important that we provide these medicines not just to the rich, western world, but instead ensure everyone has access.

In closing

Lastly, I asked if there was anything else he would like to add for listeners.  He said how important it is that we all understand the potential of these biological medicines. It is important to make people understand the importance of what we are doing. The fact that the newspapers in the UK are covering the use of mRNA to make vaccines is exciting. He feels it is our duty to explain science, show people what is possible, and to help educate people about how we treat diseases that otherwise are not treatable. He closed by saying “isn’t biology facinating, and it tells us so much of what’s possible and the diseases being treated today, 20-30 years ago would have been absolute killers. It is a pleasure to work in this area and pass on information where I can.”

Alan, I couldn’t agree more! What a delightful interview.

Learn about how CHO cells are being adapted to meet evolving industry needs:

Discover the CHOSOURCE™ CHO-K1 GS knockout expression platform

Want to know how Horizon can help you more?

Learn more about Horizon’s Gene editing CHO cell services

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