Choosing eukaryotic host cell culture is crucial step in any technology development. The culture should provide proper environment for production of your gene of interest, while remaining economically feasible and industrially acceptable. The today's cell culture of choice is CHO, however, it is known to provide low yield and being unable to grow in suspension. As we developed the principally new platform of expression, we decided to fit it not to CHO cells, but to BHK-21 cell culture, that is known for its robustness, high yields of production, and ability to grow in suspension.
Using FMDV replication in trans in BHK-21 cells creates unique context for VLP folding and formation of lipoprotein coating that most likely render ISVAC with unique useful properties. To produce HCV-VLP one have to express in eukaryotic culture the structural proteins of HCV that then self-assemble into the HCV-VLP. The only reported successful application of this approach used insect cell culture. However, insect cell culture is physiological remote from the human cell culture. Hence we decided to produce HCV-VLP in BHK-21 cell culture that is more similar to the human one. Numerous previous attempts of production of HCV-VLPs in BHK-21 cells using standard DNA plasmid-based techniques, failed, so we had to devise a novel robust technology to assure efficient production of ISVAC. We built on earlier Dr. Sivov work where he demonstrated that HCV replication (non-structural) enzymes may replicate virus RNA in trans. We decided to employ this feature of virus replication to enhance mRNA coding for HCV structural proteins. FMDV was chosen as virus well know for its robust repllication in BHK-21 cells. Succesful application of this approach opens avenues for creating novel platform technology for expression of complex polypeptides in economically robust BHK-21 cell culture.
The dominant method pf VLP purification used around the world is gradient centrifugation that is cost-inefficient and non-scalable. We were able to purify ISVAC by simple and inexpensive step of PEG precipitation that allows obtaining highly concentrated VLP samples.