The demand for therapeutic proteins is constantly growing and gives further reason for continuing the development of high-quality protein production technologies. Mammalian cell lines are the preferred choice to create recombinant proteins, in particular Chinese hamster ovary (CHO) cells and human embryonic kidney (HEK or HEK293) cells.
However, with the higher demand also comes higher confusion as to which cell line to pick for one’s own studies. Due to the many possibilities, as well as advantages and disadvantages, it can be quite troubling to decide which cells would serve specific research the best. Therefore, this article is designed to help scientists make the right choice.
HEK cells are known to be very popular due to their easy handling and use for protein production. However, CHO cells are the most-used mammalian production cell line within the biopharmaceutical industry.
HEK cells are popular protein expression hosts among researchers due to their fast transfectability and protein production. Adding to that, HEK cells are easy to reproduce and maintain and are suitable for various transfection methods. They are also known to be a reliable base for the translation and processing of proteins and can therefore be used for many experiments. As Dr. Desmond Schofield, Director of Business Development at evitria AG explains:
"HEK cells are a well-established and commonly used host for transient expression in R&D labs. They are easy to transiently transfect using a variety of different and low-cost methods and produce fully human glycosylation patterns. Their transfectability is the main reason for their widespread use and popularity."
However, HEK cells are rarely used beyond research settings, due to several limitations. One of the biggest obstacles a researcher could face when using HEK cells is that they are difficult to grow in large-scale, serum-free cultures. They form clumps that hinder nutrient transfer and growth and cause heterogeneity in the culture process. Furthermore, these clumps reduce the efficiency of downstream processing and purification.
CHO cells are the workhorse of the biopharma industry — over 70% of biopharmaceuticals, and almost all antibodies, are produced within this cell line. A review by Dumont et al. found that only five FDA-approved biotherapeutics are produced within HEK, and 50 with CHO (as of 2016).
CHO cells are robust hosts that grow well in suspension culture, can easily be adapted to serum free media, and can produce and secrete recombinant antibodies in the multi-gram scale. As they are hamster-derived cells, they are less susceptible to contamination by human viruses, but still perform human-compatible glycosylation. They do lack α-2,6-sialyltransferase α-1,3/4-fucosyltransferases, and they produce glycans that are not expressed in humans, namely α-gal and NGNA. However, the glycosylation modifications from these changes are rarely required for the function of a given product, and the additional glycans only occur at very low (<2%) levels that can be screened out from the host in later stages.
“CHO cells are difficult to transiently transfect — there are few CROs that offer this service, fewer still with their own IP-free cell line, and none with the experience of evitria,” says Dr. Desmond Schofield, Director of Business Development at evitria AG.
CHO cells are the go-to cell line for clinical and commercial production of therapeutic antibodies and proteins. Their production processes are well established and embedded at all major biopharma and CDMO companies and have been repeatedly approved by regulatory authorities. Therefore, using CHO for a therapeutic antibody or protein is more an inevitability than a choice.
However, due to the difficulties in using transient CHO, biopharma research teams often use in-house transient HEK production for screening and development purposes, then switch to CHO after lead candidates have been selected and a stable cell line is required. This introduces risk into the commercialization process, as differences in the posttranslational and glycosylation machinery (Fig 1)1 can change product activity. Developing a stable CHO cell line alone requires an investment of >1Mio EUR, and this comes on top of the time and financial investment of early discovery and development work.
The lesson is clear: using a transient CHO service provider to supply material for early-stage development work significantly de-risks the commercialization process whilst minimizing effort for any in-house scientists.
Diagnostic companies can also benefit by using transient CHO to generate recombinant antibodies for their assays. The improved scalability and robustness of CHO cells allows large scale cultures to be grown and processed, delivering >10 g quantities for commercial, population-scale diagnostics. By using a transient process, this can be accomplished without a significant upfront investment and under short timelines, as no stable cell line is required.
“At evitria, this only takes a few weeks for all scales. Our tightly controlled, transient process was built and optimized for therapeutic applications, where generating material with the same activity and quality, regardless of batch size or time between productions, is essential,” says Dr. Schofield.
This robust process is then perfect for supporting the development and commercialization of a diagnostic, where identical performance is needed at both the 1 mg and 10+ g scales.
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