During early stage drug development, quickly obtaining relevant candidate proteins through transient transfection can accelerate drug discovery. High titers are often obtained from Human Embryonic Kidney (HEK) 293 derived cell types; however, the use of different host cells between early stage transient and later stable protein production is a concern and can lead to the advancement of false-positive candidates. Chinese hamster ovary (CHO) cells are a desirable target cell type due to growth characteristics and a history of regulatory approval; however, their use has been hampered by low transient gene expression levels. To address this short-coming, we have created a robust and simple CHO transient protein expression system enabled by critical media attributes such as high density cell growth, quick adaptation, and minimization of cell clumping post-transfection.
The CHOgro® Expression System was developed through systematic optimization of transfection protocol parameters including: cell density, transfection reagent, media formulation and culture temperature leading to a commercially accessible high titer CHO transient transfection platform. Through this optimization, antibody titers increased 2-10 fold over existing technologies with higher amounts of antibody secreted per cell. Six different representative antibody constructs were also successfully expressed using the CHOgro® Expression System. Notably, even CHO cells maintained in other commercially available media formulations (e.g. FreeStyle™ CHO Expression Medium) can be seamlessly adapted with a full media exchange to the CHOgro® Expression Medium 24 hours prior to transfection and yield multi-fold increases in transient expression levels. With the CHOgro® Expression System, high protein titers can now be achieved in suspension CHO cells through high density transient transfection.