The quiescent-cell (Q-Cell) E. coli expression system is a radical alternative to conventional fermentation for the production of recombinant proteins. The controlled over expression of a small RNA called Rcd in hns mutant strains generates non growing quiescent cells that are not nutrient limited. Unlike other E. coli systems, Q-Cells no longer produce biomass with their metabolic resources directed towards the expression of plasmid-borne genes. Q-Cells offer the potential for increased therapeutic protein yield in manufacturing, lower down-stream processing costs and may also be of interest to groups attempting to express toxic as well as benign proteins.

Escherichia coli (E.coli) is one of the leading hosts for large-scale plasmid-based expression of heterogonous proteins. Dr. David Summer''s group in the Department of Genetics at Cambridge University has been investigating factors affecting the stability of bacterial plasmids for more than ten years. The group has shown that the maintenance of natural plasmids in E.coli is dependent upon several factors, one of which is the expression of a small RNA called Rcd (regulator of cell division). Transient expression of the Rcd transcript delays cell division, allowing time for necessary plasmid repair and the prevention of the production of plasmide-free offspring. Cell in which Rcd is over-expressed for an extended period have a district cell cycle arrest phenotype. The majority of cells are of uniform size (two or four cell lengths) but they remain undivided since no cell septum is formed.

The Q-Cell invention arose from the further characterisation and development of Rcd expression linked to foreign plasmid-borne gene expression in metabolically active but non-growing (i.e. quiescent) cell culture. The resultant Q-cells are not nutrient limited, no longer produce biomass and have their metabolic resources channelled towards expression of plasmid-based genes.

The biosynthetic capacity of the system has been demonstrated by its ability to express a specific polypeptide (chloramphenicol acetyl transferase; CAT) at 40% of total cell protein. Furthermore, productivity of Q-cells is largely independent of the culture medium and density. Scale up studies in 15 litre fermenters shows similar productivity to shake culture flasks.

Market
In 1990, sales of the 30 leading recombinant proteins exceeded $ 13b, an increase of over 50% from 1998. Production data for 18 leading proteins showed that nine were manufactured using mammalian cell culture (chiefly CHO cells) and nine were manufactured using E.coli based systems. The E. coli-derived drugs had combined sales of $ 5.6b in 1999, a 59% increased over sales in 1998.

The continuing growth in the recombinant protein market and concerns about manufacturing under-capacity (Bioventure View, October 2000 7-13), indicate the need for new expression systems capable of delivering increased yield. Q-Cells offers to provide the solution by delivering increased protein production efficiency through reducing biomass and downstream processing costs.

It is expected that pharmaceutical companies manufacturing recombinant proteins in-house, contract manufacturing houses, R & D kit manufacturers and producers of ''industrial proteins'' will all wish to examine the potential of Q-Cells to deliver increased protein yields.

Technology
The Cambridge team have demonstrated that the Q-Cell expression system is able to uncouple protein synthesis from biomass production, retaining the cells in a nutrient rich, non-stressful environment favourable for extended protein synthesis of plasmid-borne genes. Q-cells were generated by over-expression of Rcd in hns-205 mutant cells, grown in broth culture. The Q-cells remained competent for protein synthesis from plasmid-borne genes in an environment where chromosomal gene expression was decreased. It is anticipated that the low level of chromosomal expression will be advantageous for the purification of proteins in downstream processes. The Summers'' data suggest that Q-cells are extremely productive and that a relatively small biomass may have a high level of protein production. Q-cells are extremely productive and that a relatively small biomass may have high level of protein production. Q-Cells may provide a useful expression system for ''difficult'' proteins (e.g. ploytopic membrane proteins) which disrupt cell growth and division in conventional cell culture (Rowe & Summers: Applied and Environmental Microbiology 1999, 65 2710-2715).

Patent Position
The Q-Cell invention is covered by patent applications derived from International Patent Application WO 97/34996. Claim 1 claims "A bacterial cell containing an extra-chromosomal vector including an inducible Rcd gene, which cell when in broth culture enters quiescence on expression of the Rcd gene". The US and Australian application have proceeded to allowance and a European application is pending.

The Opportunity
As a prelude to licensing , BTG is seeking collaborative partners to evaluate and use the Q-Cells E. coli expression system for the production of recombinant heterologous proteins. BTG is particularly interested in working with biopharmaceutical R&D teams who are developing processes for novel protein targets. BTG would also be interested to explore the application of this technology in the R&D kits/reagents market as well as enzyme/industrial protein manufacture and genomic/proteomic applications.

About GBTG
BTG is a global leader in commercialising technologies that shape the future. BTG acquires, develops and licensees intellectual property rights (IPR) covering innovative products and processes in the diverse fields of life sciences and high technology.

With its headquarters in London and offices in suburban Philadelphia and Tokyo, BTG capitalises on a global network of contacts in companies, universities and research institutions to identify and commercialise the promising technologies and create the most advantageous licensing relationships. Since its founding in 1949, BTG has commercialised such major innovations as magnetic resonance imaging (MRI), Interferon, and wide-spectrum cephalosporin antibiotics.