Recombinant Proteins from CHO cells â€" Key to Infectious Diseases in Therapeutics
Author: By Dr Madhusudan P Dabhole - Group Manager at Richcore Life Sciences Ltd. Bangalore

Biosimilars have brought in the new dimension for recombinant protein production, characterization and purification towards the treatment of infectious diseases. Biosimilars and therapeutics biobetter can be defined as the large organic molecules, primarily proteins. Amino acids are building blocks of Proteins arranged in a linear chain and folded into a globular form. The sequence of amino acids forming a protein is concomitant by the sequence of a gene, which is encoded in the genetic code.

Different types of cells are used for recombinant protein production, viz, Bacterial, fungal, yeast, insect and CHO (Chinese Hamster Ovary) cells. CHO cells have been extensively used for recombinant protein expression and for toxicity screening and gene expression. Today, CHO cells are the most commonly used mammalian hosts for industrial production of recombinant protein therapeutics.

Chinese hamsters (Cricetulus griseus) were first introduced in 1960 which belong to a family of rodents and are native of the deserts of northern China and Mongolia. CHO cells were first introduced into the laboratory for typing pneumococci (1919).

The recombinant proteins require precise folding and post translational modifications including glycosylation to obtain active forms. Glycosylation is a modification where certain carbohydrate moieties are added to specific amino acids residues of the proteins. The mammalian glycosylation patterns are the characteristics of CHO cells producing glycoproteins.

Common features of in vitro mammalian cell growth include:

1] Slow growth rates of cells

2] Complex metabolism and possibly complex media requirements

3] Requirement for surface attachment

4] Relative fragility of some cells

5] Genetic and phenotypic instability of some cell types ⁽²⁾

CHO cells are epithelial cells which grow as an adherent monolayer in culture. They require the amino acid proline in their culture medium. Single Chinese hamster ovary (CHO) cells plated on agar form macroscopic colonies with high efficiency. Colonies produced by cells from the uncloned cell line increase in diameter continuously for 10-12 days after plating to form mounds of cells about 1 mm in diameter. On plastic substrate, all these CHO cells form colonies which increase continuously in diameter for as long as 21 days, and little clonal difference in the morphology of colonies or of single cells is observed. These observations reveal a previously unsuspected heterogeneity in an established line of cultured mammalian cells and provide a method for studying new classes of In vitro growth control phenomena. These control phenomena may help in the building an in vitro model for tumor growth. ⁽¹⁾

More than 60 % of the recombinant proteins are manufactured by mammalian cells. CHO cells have gained importance due to high expression, protein yields and high stability. Mammalian cells have been used widely for complex biomolecules like monoclonal antibody production. It is very important at the initial stages to characterize the CHO cells to obtain genetically stable cell line for regulatory approvals and consistent production. Development of animal origin free media for CHO cells is a challenge for antibody production which may give rise to undesired metabolites during production

Many strategies have been elucidated to reduce lactate and ammonium ions during the production of recombinant proteins by CHO cells for yield improvement. This will all depend on the scale of dynamics adapted by the CHO cell during transport of nutrients for glycolysis and oxidative phosphorylation based on the metabolic shift.

Most of the mammalian cells are grown as suspension culture which provides better growth rate and cell culture mass. Currently, Fed batch and continous perfusion culture are the two types of suspension culture used for mammalian cell culture products. Fed batch manufacturing of recombinant proteins and monoclonal antibodies is preferred due to high titers and yield.

Single use Disposable mobile platforms are being evaluated for manufacturing both proteins and antibodies by mammalian cells to reduce manufacturing cost and obtain high yields. Significant progress is being made in this area of upstream and downstream purification for different products. CHO cells for production of bio therapeutics products are the promising candidate for treatment of existing and imminent infectious diseases.

References:
1. Michael W Konrad et al, Clonal variation in colony morphology and growth of CHO cells cultured on agar, Cell, Vol 10, issue 2, 305-312,1977

2. C P Marquis, Mammalian Cell Culture, Biotechnology - Vol. I - ELOSS.

About Author / Additional Info:
I hold a Ph.D in Microbiology and am currently working with Richcore Life Sciences Ltd as Group Manager with 15 years of experience in fermentation.