Maximizing Protein Expression in CHO Suspension Cells Through Transient Transfection

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xU-Maximizing-Prote_230382aTransient transfection in mammalian cell lines provides an avenue for researchers to bridge the development bottleneck and shorten the time to usable protein. The method also maintains post translational modifications crucial for biotherapeutic function. Chinese Hamster Ovary (CHO) suspension cells are especially suited for high yield production of recombinant proteins, despite being refractory to commonly used transfection methods (e.g. 25kDa linear PEI). Mirus Bio has developed a more effective alternative, the TransIT-PRO® Transfection Kit.

Transfection efficiencies are affected by many parameters including cell density at the time of transfection, DNA concentration and reagent dosing. Based on extensive testing performed during product development and the data presented herein our starting recom-mendations include an initial cell density of 0.5 – 1.0 x 106 cells/ml, 1 μg of DNA per milliliter of culture volume and TransIT-PRO:PRO Boost Reagent:DNA ratio of 1:0.5:1. Optimization of transfection parameters will maximize transfection efficiency and reduce the impact of variables such as differences in cell lineage, handling and media formulation.


Cell culture growth medium has a considerable influence on transfection efficiency. To further examine these effects, suspension CHO cells were adapted to five representative growth media, transfected using multiple methods and analyzed for efficiency by luciferase reporter assay or IgG titer. The media formulation impacted transfection efficiencies by greater than 10-fold within a given trans-fection methodology. In addition, not all commercially available transfection reagents had broad spectrum media compatibility. A 10-fold increase in IgG yield was obtained when the TransIT-PRO Transfection Kit was used in conjunction with suspension CHO cells adapted to BD-SelectTM CD1000 medium. Notably, in many media formulations (BD SelectTM CHO, ProCHOTM5 and PowerCHO®2 CD) the TransIT-PRO Transfection kit provided detectable levels of antibody production, significantly outperformed 25kDa linear PEI and FreeStyleTM Max Transfection Reagent.


The TransIT-PRO Transfection Kit uses animal origin free components designed for high and reproducible protein yield in suspen-sion CHO cells. Transfections using the TransIT-PRO Transfection Kit are linear in culture volumes ranging from 4-400 milliliters in shake or spinner vessels. Competitor benchmarking experiments were performed utilizing the FreeStyle Max expression system and multiple transfection methods. Western blot and ELISA detecting human IgG levels demonstrate that the TransIT-PRO Transfection Kit and FreeStyle Max Transfection Reagent perform similarly, outperforming 25 kDa linear PEI by 5-fold. The results demonstrate that maximum levels of transient expression are achieved when an effective delivery reagent is combined with optimized transfection parameters and growth conditions.