Mammalian Cell Expression - General Info - Protein Expression Facility

The dominant host system for producing therapeutic recombinant proteins over the last few decades has been the mammalian expression system.

The benefit of this system includes:

Highest capacity for generating complex post-translational modifications (PTMs) compared to other expression systems
High success rate of soluble protein recovery
Suitable for antibody production

One of the main drawbacks of the system is the increased expense when compared to other systems such as bacteria.

Transient vs stable cell culture

There are two main methods for recombinant protein production in mammalian cells i.e. stably transfected and transiently transfected cell lines.

Stably transfected cell lines enable continuous expression of the recombinant protein at high yields. The creation of a stable cell line can take up to several months to complete.

A transient transfection can be used for small- to large-scale expression cultures. Recent improvements to the method have been able to increase yields from milligram to gram quantities. The advantages of a transient transfection method lie in the shorter timeframe from DNA delivery to protein harvest.

How do I optimise my protein expression in the mammalian system?

Several parameters can impact the success of protein production in the mammalian system, as described below:

Cell lines

Commonly used mammalian cell lines for protein production, in particular biotherapuetics, are the Chinese hamster ovary (CHO), Human embryonic kidney (HEK-293) and Mouse myeloma (NS0) cell lines. PEF recommends screening multiple cell lines when determining the optimal condition for producing your target protein. Cell lines are available from the UQ resource centre.

Growth temperature

Although mammalian cells are typically cultured at 37°C, using a temperature shift during protein expression (e.g. decreasing the culture temperature from 37˚C to 32˚C following transfection) can improve target protein production.

Expression duration

The timeframe of protein expression can also play a role in target protein production. For example, protein harvested 4 days post transfection may have a different expression profile to protein harvested at 5 days post transfection. Screening protein expression at multiple time points may determine the optimal condition for your target protein.