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Frequently Asked Questions: Mammalian Expression System


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Frequently Asked Questions: Mammalian Expression System

1. How many different mammalian cell lines were established?
2. What are the differences between mammalian, yeast, insect, and plant cell expression systems?
3. What are the advantages of mammalian cell expression?
4. What does the usage of mammalian expression system include?
5. What is the limitation of mammalian expression system?


1. How many different mammalian cell lines were established?

Creative Biogene has established a number of mammalian cell lines to use for protein expression with the most common being CHO (Chinese hamster ovary) and HEK 293 (Human embryonic kidney). HEK 293 cells exhibit the highest level of polyethyleneimine (PEI)-mediated transfection with 50–80% of cells showing green fluorescent protein (GFP) expression, and are widely used for the production of recombinant proteins both by transient transfection and by the formation of stable cell lines. Other cell lines such as COS and Vero, HeLa, and NS0 have also been used for structural studies.

2. What are the differences between mammalian, yeast, insect, and plant cell expression systems?

Expression of glycoproteins in mammalian cells will lead to mammalian-type glycosylation. For human proteins this is ideal, however, some cell lines will add the N-glycolylneuraminic acid (NGNA) and the non-human Gal α1-3 Gal epitope. Insect expression systems will add shorter N-glycans, with little sialylation. Plant cells typically have glycans that include extra fucose and xylose residues. Yeast expression systems have a quite different glycosylation pattern from mammalian cells, with only mannose-containing glycans. Determining the optimal expression system depends on the target protein and experimental needs.

3. What are the advantages of mammalian cell expression?

Mammalian cell expression exhibits the highest level of protein processing, which is crucial for complete biological activity. Thus, the mammalian expression system is suitable for expressing modified, complicated, functional proteins; secreted or membrane proteins, such as recombinant glycoproteins (vaccines and enzymes), antibodies, hormones, interleukins and lymphokines.

4. What does the usage of mammalian expression system include?

The proteins produced in the mammalian system have the best structural and functional features that are commonly most close to their cognate native form and can satisfy the following application needs:

  • Transgene expression, cell line development
  • Functional studies of the protein (in vitro and ex vivo)
  • Structural studies, including protein crystallization, protein structure and NMR
  • Immunogen for antibodies development, and prophylactic (vaccine) development
  • Drug target discovery and validation
  • Animal studies, including in vivo functional and ADME, PK/TK and safety studies
  • Diagnostic application

5. What is the limitation of mammalian expression system?

Mammalian cell expression systems have been traditionally seen as expensive because of the cost associated with transfection reagents, specialized media, consumables and the expert workforce required. Moreover, the complicated technology and potential contamination with animal viruses of mammalian cell expression have been bottlenecks for its use in large-scale industrial production.

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