Transient gene expression systems in mammalian cells continue to grow in popularity due to their capacity to produce significant amounts of recombinant protein in a rapid and scalable manner, without the lengthy time periods and resources required for stable cell line development. Traditionally, production of recombinant monoclonal antibodies for pre-clinical assessment by transient expression in CHO cells has been hampered by low titers. In this report, we demonstrate transient monoclonal antibody titers of 140 mg/l with CHO cells using the episomal-based transient expression system, Epi-CHO. Such titers were achieved by implementing an optimized transfection protocol incorporating mild-hypothermia and through screening of a variety of chemically defined and serum-free media for their ability to support elevated and prolonged viable cell densities post-transfection, and in turn, improve recombinant protein yields. Further evidence supporting Epi-CHO's capacity to enhance transgene expression is provided, where we demonstrate higher transgene mRNA and protein levels of two monoclonal antibodies and a destabilized enhanced green fluorescent protein with Epi-CHO compared to cell lines deficient in plasmid DNA replication and/or retention post-transfection. The results demonstrate the Epi-CHO system's capacity for the rapid production of CHO cell-derived recombinant monoclonal antibodies in serum-free conditions.

PER.C6 cells, an industrially relevant cell line for adenovirus manufacture, were extensively passaged in serum-free suspension cell culture to better adapt them to process conditions. The changes in cell physiology that occurred during this passaging were characterized by investigating cell growth, cell size, metabolism, and cultivation of replication-deficient adenovirus. The changes in cell physiology occurred gradually as the population doubling level, the number of times the cell population had doubled, increased. Higher passage PER.C6 (HP PER.C6) proliferated at a specific growth rate of 0.043 h -1 , 2-fold faster than lower passage PER.C6, and were capable of proliferation from lower inoculation cell densities. HP PER.C6 cell volume was 16% greater, and cellular yields on glucose, lactate, oxygen, and amino acids were greater as well. In batch cultures, HP PER.C6 cells volumetrically produced 3-fold more adenovirus, confirmed with three different constructs. The increase in productivity was also seen on a cell-specific basis. Although HP PER.C6 were more sensitive to the "cell density effect", requiring lower infection cell densities for optimal specific productivity, they proliferated more after infection than lower passage PER.C6, increasing the number of cells available for virus production. The extensive passaging established HP PER.C6 cells with several desirable attributes for adenovirus manufacture.

BACKGROUND: Transient gene expression (TGE) provides a rapid way to generate recombinant protein biologics for pre-clinical assessment. Human embryonic kidney (HEK293) cells have traditionally been used for TGE; however, there is demand from industry for efficient, high-producing TGE systems that utilize Chinese hamster ovary (CHO) cells. A polyethyleneimine (PEI) -based TGE process has been developed for CHO cells using an episomal expression system to generate enhanced recombinant protein titers.

BACKGROUND: Human embryonic kidney-293 (HEK-293) cells are commonly used as a transient expression host but their application in stable therapeutic protein production is limited. This is presumably due to the absence of a suitable amplifiable expression system and hence limited protein output compared with other mammalian cells such as Chinese hamster ovary cells. This paper describes a rapid clonal selection method for isolating HEK293 cell lines with high specific productivity, for a non-amplifiable expression system, to achieve high-level, scalable expression of recombinant antibodies.

Worldwide sales of biologic drugs exceeded US$92 billion in 2009. With many biopharmaceutical patents expiring over the next decade, a wave of second-generation or 'follow-on' biologics will be vying for market share and regulatory approval. Patents cover not only the drugs, but also the molecular modalities that facilitate their high-level expression. Companies have historically relied on gene amplification to create productive cell lines, yet this lengthy and imprecise process usually leads to extensive variation and unpredictable stability of expression. Biosimilar manufacturers must therefore decide whether traditional methods of cell line development will suffice or if emerging technologies can provide greater reproducibility and speed. Volumetric yields of 1-2 g L −1 are adequate for most production processes and the focus has shifted towards reliable and predicable product quality attributes over maximum possible titres. Recent advances in this area include cell lines with targeted genetic modifications, alternative production hosts such as PER.C6 or yeast, and engineered expression vectors, including the UCOE  and Selexis platforms. Host cell engineering, single-use technologies, and rapid transient gene expression are also likely to be enablers of biosimilars. Given the well-known biologics industry mantra 'the process defines the product', it remains to be seen how novel cell line development strategies will affect product equivalence and regulatory approval in a biosimilars context. Some recent advances in the field and how they relate to biosimilars are explored.