Combinatorial treatment with lithium chloride enhances recombinant antibody production in transiently transfected CHO and HEK293E cells

Investigation and development of transient production process for porcine circovirus Type-2 (PCV2) capsid protein in HEK293F cells

Porcine circovirus type-2 capsid protein contains a major immunodominant epitope used as a subunit vaccine. Transient expression in mammalian cells is an efficient process for producing recombinant proteins. However, there is still a lack of research on the efficient production of virus capsid proteins in mammalian cells. Here we present a comprehensive study to investigate and optimize the production process of a model "difficult-to-express" virus capsid protein, PCV2 capsid protein in HEK293F transient expression system. The study evaluated the transient expression of PCV2 capsid protein in the mammalian cell line HEK293F and investigated the subcellular distribution by confocal microscopy. In addition, the RNA sequencing (RNA-seq) was used to detect the differential expression of genes after cells transfected with pEGFP-N1-Capsid or empty vectors. The analysis revealed that the PCV2 capsid gene affected a panel of differential genes of HEK293F cells involved in protein folding, stress response, and translation process, such as SHP90β, GRP78, HSP47, and eIF4A. An integrated strategy of protein engineering combined with VPA addition was applied to promote the expression of PCV2 capsid protein in HEK293F. Moreover, this study significantly increased the production of the engineered PCV2 capsid protein in HEK293F cells, reaching a yield of 8.7 mg/L. Conclusively, this study may provide deep insight for other "difficult-to-express" virus capsid proteins in the mammalian cell system.

The secretory pathway - the key for unlocking the potential of Chinese hamster ovary cell factories for manufacturing therapeutic proteins

Mammalian cell factories (in particular the CHO cell system) have been crucial in the rise of biopharmaceuticals. Mammalian cells have compartmentalized organelles where intricate networks of proteins manufacture highly sophisticated biopharmaceuticals in a specialized production pipeline - the secretory pathway. In the bioproduction context, the secretory pathway functioning is key for the effectiveness of cell factories to manufacture these life-changing medicines. This review describes the molecular components and events involved in the secretory pathway, and provides a comprehensive summary of the intracellular steps limiting the production of therapeutic proteins as well as the achievements in engineering CHO cell secretory machinery. We also consider antibody-producing plasma cells (so called "professional" secretory cells) to explore the mechanisms underpinning their unique secretory function/features. Such understandings offer the potential to further enhancement of the current CHO cell production platforms for manufacturing next generation of biopharmaceuticals.

Effects of autophagy inducers on recombinant antibody production in insect cells

Insect cells have recently proven to be an excellent platform for the high-level production of functional recombinant proteins. Autophagy is an important mechanism that promotes cell survival by eliminating damaged organelles and protein aggregates, and it also may influence recombinant protein production. In the present study, we compared the effects that autophagy inducers rapamycin, everolimus, and lithium chloride exert on recombinant lepidopteran insect cells that secrete an engineered antibody molecule. Compared with nontreatment, treatment with either rapamycin or everolimus prolonged cell growth to allow high cell density, improved viability in the declining phase, and then increased the yield of secreted antibodies. These positive effects appeared to be induced via autophagy since autophagosomes were clearly detected, particularly in cells treated with rapamycin or everolimus. Unlike rapamycin, another autophagy inducer, FK506, was ineffective in insect cells. The addition of an appropriate autophagy inducer may be effective in increasing the productivity of recombinant proteins in insect cells.

Coexpression of CMP-sialic acid transporter reduces N-glycolylneuraminic acid levels of recombinant glycoproteins in Chinese hamster ovary cells

Recombinant glycoproteins expressed in Chinese hamster ovary (CHO) cells contain two forms of sialic acids; N-acetylneuraminic acid (Neu5Ac) as a major type and N-glycolylneuraminic acid (Neu5Gc) as a minor type. The Neu5Gc glycan moieties in therapeutic glycoproteins can elicit immune responses because they do not exist in human. In the present work, to reduce Neu5Gc levels of recombinant glycoproteins from CHO cell cultures, we coexpressed cytidine-5'-monophosphate-sialic acid transporter (CMP-SAT) that is an antiporter and transports cytosolic CMP-sialic acids (both forms) into Golgi lumen. When human erythropoietin was used as a target human glycoprotein, coexpression of CMP-SAT resulted in a significant decrease of Neu5Gc level by 41.4% and a notable increase of Neu5Ac level by 21.2%. This result could be reasonably explained by our hypothesis that the turnover rate of Neu5Ac to Neu5Gc catalyzed by CMP-Neu5Ac hydroxylase would be reduced through facilitated transportation of Neu5Ac into Golgi apparatus by coexpression of CMP-SAT. We confirmed the effects of CMP-SAT coexpression on the decrease of Neu5Gc level and the increase of Neu5Ac level using another glycoprotein human DNase I. Therefore, CMP-SAT coexpression might be an effective strategy to reduce the levels of undesired Neu5Gc in recombinant therapeutic glycoproteins from CHO cell cultures.