The success of engineered monoclonal antibodies as biopharmaceuticals has generated considerable interest in strategies designed to accelerate development of antibody expressing cell lines. Stable mammalian cell lines that express therapeutic antibodies at high levels typically take 6-12 months to develop. Here we describe a novel method to accelerate selection of cells expressing recombinant proteins (e.g., antibodies) using multiparameter fluorescence activated cell sorting (FACS) in association with dual intracellular autofluorescent reporter proteins. The method is co-factor-independent and does not require complex sample preparation. Chinese hamster ovary (CHO) clones expressing high levels of recombinant antibody were selected on the basis of a two-color FACS sorting strategy using heavy and light chain-specific fluorescent reporter proteins. We were able to establish within 12 weeks of transfection cell lines with greater than a 38-fold increase in antibody production when compared to the pool from which they were isolated, following a single round of FACS. The method provides a robust strategy to accelerate selection and characterization of clones and builds a foundation for a predictive model of specific productivity based upon on two-color fluorescence.

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.

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.

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.

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