CHO Cells

CHO Cells, CHO cell lines

Biological therapeutics such as monoclonal antibodies are an increasingly prominent part of many drug development pipelines.

To maintain pace with industry needs in this area, access to cutting edge CHO cells must be improved to make them available to companies of all sizes. Currently, high entry costs and restrictive licensing conditions prevent access for the majority of biomanufacturing groups.

CHO Cell Lines

To directly address this problem, we used our proprietary gene editing platform to design and manufacture our CHO K1 GS Null knockout line and have released these cell lines at a competitive price with minimal restrictions. A license to use these cells for biotherapeutic manufacture is available for a one-time fee. This means no per-product payments, no milestones and no royalties.

While we are offering cutting edge CHO cell lines, we're not content to stop there. We are using our expertise in genome engineering to undertake an unprecedented program to modify a range of pathways in parallel in order to continually improve the biomanufacturing capabilities of our cell lines and redefine the gold standard in cell line technology.

This will lead to decreased costs by increasing clone productivity, decreasing variability in product consistency and increasing bioproduction efficiency. Following release of improved versions of our CHO cells, we will continue our open license, low cost philosophy.

Details of our CHO cell lines can be found in the table below:

 Product CodeDescriptionLicensing Terms
CHO GS Null InformationHD-BIOP3cGMP CHO cells with exon 6 of GS gene removed and adapted for growth in suspension culture in chemically defined, animal component free mediaClick here for information on our Royalty Free, Multiproduct License options


CHO Source

Due to an increased body of expression and safety data, our early access scheme has closed as of 31st May.

Licensing Terms  Contact Us to Get Started

GS vs. DHFR Metabolic Selection

CHO cells have become the expression system of choice for the manufacturing of biological therapeutics. They have been shown to have the capacity to express a variety of proteins such as therapeutic enzymes or monoclonal antibodies at multi-gram per litre titres.

As expression technologies have developed, focus on increasing titre has mainly been achieved through improvements to media and feed, while the ability to identify high productivity clones has been streamlined through the use of different selection systems.

Antibiotic selection has been used for a number of years, but the requirement to maintain cells in antibiotics is costly and requires removal of the antibiotic from the production media during downstream steps, which means that metabolic selection has become the preferred industry method.

Metabolic selection can broadly be split into those that use Glutamine Synthetase (GS) or Dihydrofolate reductase (DHFR) systems.

Glutamine Synthetase (GS) Null

Glutamine Synthetase is an enzyme that catalyses the conversion of glutamate to the amino acid glutamine, and is the only mechanism for cells to generate their own glutamine. If the expression of Glutamine Synthetase is reduced through chemical or genetic means, then the cells are not viable unless they are either cultured in media containing additional glutamine or have an alternative Glutamine Synthetase exogenously expressed. This mechanism has been exploited for over ten years to generate a metabolic selection system that links the expression of an exogenous GS gene to the expression of a protein of interest (for example a monoclonal antibody). This means that when the cassette stably integrates into the genome, expression of the monoclonal antibody is proportional to the amount of Glutamine Synthetase expressed.

Cells can then be placed into media that lacks glutamine, and those expressing insufficient GS (and by extension a low level of monoclonal antibody) are unable to survive. Originally, the mouse cell line NS0 exploited this mechanism as it is naturally deficient in Glutamine Synthetase. To adapt this system for use in CHO cell expression, GS was inhibited by the chemical inhibitor Methionine Sulphoximine (MSX). However, this led to high levels of background due to the cell line increasing the expression of its endogenous GS gene, and also MSX needed to be included in production culture to maintain the selection. As a highly toxic compound, this needs to be removed from the production media during downstream processing, leading to increased costs and time. More recently, CHO K1 cells have been engineered to be null for Glutamine Synthetase. Horizon has engineered a GS null CHO cell line using its proprietary rAAV technology, while Lonza used Meganucleases and Sigma Aldrich used Zinc Fingers (ZFNs). This GS null CHO K1 selection system is now considered to be the industry standard method of selecting high expressing clones following transfection with a vector expressing the biotherapeutic.


An alternative metabolic selection system exists that utilises the DHFR gene. DHFR reduces dihydrofolic acid to tetrahydrofolic acid and in its absence, cells require supplementation of the media with glycine, hypoxanthine, and thymidine for viability. To reduce the level of DHFR in the cells, increasing levels of the chemical inhibitor Methotrexate (MTX) was used, or there are also cells lines (such as DG44 cells) that are null for the DHFR gene.

Similar to the GS system, vectors have been designed that express the protein of interest (for example a monoclonal antibody) as well as a separate expression of an exogenous DHFR gene. However, due to decreased timelines associated with the GS system, this has become the system of choice for most companies.

Furthermore, metabolic selection using MSX or MTX is often performed using a number of amplification steps to increase copy number and expression levels of clones, which has led to some concerns over long-term stability of the final producer clone. Together with the increased downstream processing burden, null cell lines are a preferable technology for utilising the metabolic selection through DHFR or GS.


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