CHO cells: a staple of recombinant antibody production

CHO cells have become one of the most popular cell types for recombinant antibody production — for good reason. They meet several key requirements for industrial-scale monoclonal antibody manufacture in ways that alternative cell lines do not attain. The biopharma sector is growing rapidly, and CHO cells are a staple workhorse for companies that are trying to fulfil the rising market demands.

Recombinant antibody expert Desmond Schofield, Head of Business Development, EMEA at evitria, here reveals the astonishing abilities of CHO cells and some of their most interesting characteristics. evitria is a Switzerland-based recombinant antibody service provider with a substantial product and service portfolio.

CHO cells are mainly used for antibody production. How do CHO cells produce antibodies?

DS: CHO cells do not naturally produce any antibodies because they lack the genetic blueprints. However, they do contain the biochemical machinery required to do so. So what we do is, we create the genetic blueprints for antibodies according to our customers’ needs and introduce them into CHO cells in a process termed transfection. We essentially reprogram the cells to produce the antibodies of interest in large amounts. The CHO cells are kept in an environment containing all the nutrients they need and they in turn release antibodies into the growth medium, from which we isolate the product in a procedure termed downstream processing.

Why are Chinese hamster ovary cells the go-to cell line when it comes to antibody production for human uses?

DS: Even though the cell line is derived from Chinese hamster, their biochemical machinery is close enough to human to produce proteins with an acceptable ‘fingerprint’ in the form of post-translational modifications like glycosylation patterns. Human antibodies are glycoproteins, consisting of a protein-part and a glyco-(carbohydrate)-part. Using state-of-the-art recombinant technologies, we are now able to engineer antibodies with essentially human protein sequences, thus minimising immunogenic side effects compared with older antibody generations. On the other hand, the glycosylation patterns depend mostly on the host cells, and CHO cells do a much better job than, eg, E. coli or yeast cultures.

What makes CHO cells so popular in biologics manufacturing?

DS: The high popularity of CHO cells in biologics manufacture and especially in the production of recombinant antibodies is the result of them having so many advantageous properties. On an industrial scale, the financial side of things is very important, and CHO cells are able to be at the centre of very cost-efficient processes with high product yields. Biologics manufacturing using CHO cells is comparably easy to scale up; therefore, many producers decided to develop their production processes with CHO cells. This has led to many regulatory approvals and general acceptance with regulatory bodies in the past, which in turn increases the likelihood of gaining approval of novel processes relying on CHO cells.

Have CHO cells changed the biopharma industry?

DS: Yes. CHO cells not only brought the efficiency and yields of biopharma processes to another level, the use of them has led to the development of innovative technologies which in turn spawned novel classes of therapeutics like ADCC enhanced antibodies, that have improved desired functionality. The ability to control and reduce the fucose content of antibodies produced in CHO cells allows the adjustment of biological activity of therapeutic antibodies. The aggressiveness of antibodies that are used to fight cancer can be maximised by a lack of fucose. These afucosylated antibodies are highly promising drug candidates in oncology.

Their size decreases rather than increases over time. Why? Does this have negative effects on antibody production?

DS: Interestingly, CHO cells shrink as they age and do their work. CHO cells feed on nutrients in the culture medium and release antibodies and side products, thus shifting the composition of their environment. They regulate their water content accordingly and their volume changes. This is a striking, though completely normal, process and does not affect antibody production in a negative way.

evitria uses transient transfection to express proteins. What are the advantages of transient transfection over stable transfection?

DS: The difference between stable and transient transfection is in the timescale of expression of the protein of interest. The key advantage of transient transfection lies in the relative speed and ease of the process. Stable transfection involves permanent insertion of the foreign genes into the host cells. Unsuccessfully transfected cells must be weeded out from the hits. This complicates the protein expression, making it laborious and time-consuming. Transient transfection avoids these additional steps — therefore, it is a much faster process — but this method does indeed have some difficulties one has to overcome.

How do you overcome the difficulties of transient transfection?

DS: There are two key possibilities to enhance transient transfection: first, using the best expression vector to promote maximal expression levels. This involves the stimulation of the host cell’s expression machinery to produce the protein of interest over other tasks. Second, maximising the transfection efficiency. Getting enough copies of the genes into the host cells, while keeping them healthy and growing, is crucial. We use an optimised workflow to ensure high yields and success rates.

Do you think that HEK cells will be obsolete in the future (because of CHO cells)?

DS: CHO cells are definitely superior on the industrial scale. They allow the development of very efficient, high-yielding processes. For very small scales, eg, research purposes, HEK cells provide an alternative that is easier in handling and transient transfection. This is their righteous place, where they can provide value. That is why I don’t think HEK cells will ever be completely obsolete.

What do you think the future holds for CHO cells?

DS: CHO cells already became the workhorse of antibody production. Their use is very efficient on an industrial scale and widely accepted by regulatory bodies. CHO cells are poised for a bright future in the biopharma sector. We will see further increases in process yields and ecologic footprint reduction, making use of CHO cells even more. On top of that, we expect to witness genuine innovation and breakthroughs in methodologies leading to novel product families, just like ADCC enhanced antibodies. I think it’s safe to say that CHO cells are here to stay.

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