Recombinant cells

The ground rules for cellular characterization were set with human diploid cells and these particular substrates for vaccines are subject to guidelines developed by the WHO (1997). In turn, WHO guidelines have provided the parameters for characterization of heteroploid cells (WHO, 1987). It is therefore a natural progression that this level of characterization should also provide the basis for the characterization of master and working cell banks (see Chapter 1, section 1.3), even though this does present problems. 

In particular, the relevance of some of the procedures is questionable (e.g. karyology) because a lot of the cells are inherently unstable and a certain amount of controversy surrounds in vivo tests involving animals that are now considered redundant . For example, if it is accepted that every hybridoma is capable of producing tumours in model systems, what is the point of repeating the exercise with newly derived hybridomas Unfortunately, what has tended to happen is that each new test that is added as technology advances is additional rather than a replacement. This leads to an ever-increasing number of quality control tests to be performed and thus adds to the expense of validation studies and is a growth industry in itself. 

In practice, most animal cell-derived biotherapeutic products are evaluated by a series of meetings with experts from the regulatory bodies to discuss results and thus build up an overall picture of the cell line and its product. In particular, virus testing procedures are important to exclude contamination of therapeutic products, and therefore have to be exhaustive. Regulatory authorities may request an extended range of tests, including retrovirus testing. 

If adventitious agents are found, how does this affect the final acceptability of the product The answer to this question rests on the product itself and the efficiency of the purification procedures in removing contaminants. In such cases the amount of residual DNA in the product is an important factor. Recent guidehnes state that each dose must contain less than 100 pg DNA (WHO, 1987). VaUdation of purification procedures must also include the establishment of spiking experiments to provide that viruses representative of pathogens (i.e. in terms of their characteristics relevant to the purification process) are removed (Tao et at, 1994). 

Centres for Biologies Evaluation and Research (CBER) (1993) Points to Consider in the Characterisation of Cell Lines Used to Produce Biologicals. CBER, US Food and Drug Administration, Bethesda, MD. 

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Garrison, P.M., Tullis, K., and Aarts J.M.M.J.G. et al. (1996). Species specific recombinant cell lines as bioassay systems for the detection of dioxin-like chemicals. Fundamental and Applied Toxicology 30, 194-203. 

Cell-free translation system, used for the identification of cloned genes and gene expression, has been investigated extensively as a preparative production system of commercially interesting proteins after the development of continuous-flow cell-free translation system. Many efforts have been devoted to improve the productivity of cell-free system [1], but the relatively low productivity of cell-free translation system still limits its potential as an alternative to the protein production using recombinant cells. One approach to enhance the translational efficiency is to use a condensed cell-free translation extract. However, simple addition of a condensed extract to a continuous-flow cell-free system equipped with an ultrafiltration membrane can cause fouling. Therefore, it needs to be developed a selective condensation of cell-free extract for the improvement of translational efficiency without fouling problem. 

On the other hand, 3-phenylpropionitrile was synthesized from Z-3-phenyl-propionaldoxime (0.75 M) in a quantitative yield (98gP ) by the use of cells of E. coli JM 109/pOxD-9OF, a transformant harboring a gene for a new enzyme, phenylacetaldoxime dehydratase, from Bacillus sp. strain OxB-1. Other arylalkyl- and alkyl-nitriles were also synthesized in high yields from the corresponding aldoximes. Moreover, 3-phenylpropionitrile was successfully synthesized by the recombinant cells in 70 and 100% yields from 0.1 M unpurified P/Z-3-phenylpropionaldoxime, which is spontaneously formed from 3-phenylpropionaldehyde and hydroxylamine in a butyl acetate/water biphasic system and aqueous phase, respectively. 

Abremski, K., Hoess, R., and Sternberg, N. (1983). Studies on the properties of PI site-specific recombination evidence for topologically unlinked products following recombination. Cell 32, 1301-1311. 

Racher, A. J., and Griffiths, J. B., Investigation of Parameters Affecting a Fixed Bed Bioreactor Process for Recombinant Cell Lines, Cytotechnol., 13 125... 

DNA plasmid-based treatment ( gene therapy ) is considered an alternative to the one based on classical chemical drugs or proteins recovered from recombinant cells. Treatment of acquired and inherent genetic diseases as well as the use of DNA for the purpose of vaccination are potential applications of plasmid DNA (pDNA). The plasmid carries information that allows protein expression in the targeted human cells as well as eukaryotic regulatory elements and specific prokaryotic sequences that control replication in the host cell, see Fig. 10. Formulation is required for ex- or in-vivo administration. Selected systems for gene expression can be viral or non-viral. 

Biopharmaceutical quantities of EPO are produced with recombinant cells. This is achieved through the isolation of the human gene that codes for EPO and transfection of the gene into cell lines such as Chinese hamster ovary cells (see Section 10.5). The product is called rhEPO—recombinant human EPO. EPO is normally administered subcutaneously and is generally well tolerated by patients. 

Recombinant cells expressing a cloned ADH have also been used in a coupled enzyme method to efficiently produce the (R)-2-chloromandelate intermediate in the synthetic route to clopidogrel in 90 % yield and >99 % ee at 200 gL substrate concentration (Scheme 1.53). This procedure does not use hydrogen cyanide and, therefore, represents... 

Agrawal, A. and Schatz, D.G. (1997) RAGl and RAG2 form a stable postcleavage synaptic complex with DNA containing signal ends in V(D)J recombination. Cell 89, 43-53. 

Plasmid instability can arise when the foreign protein is toxic to the host cell. During rapid growth plasmids may be lost or the copy number reduced, allowing the non-recombinant cells to take over. As a... 

A number of other, more specialized systems are available to the reproductive toxicologist to answer specific mechanistic questions. In particular, the hormonal control of reproductive function and its perturbation by toxicants have received much attention. Such investigations can use intact cells to investigate the downstream consequences of toxicants on hormone-receptor interactions or use cells that respond to specific hormones (e.g., the MCF-7 breast cancer cell line and estrogen Soto et al., 1995). Receptor biology/ligand binding can be examined in membrane preparations of specific cell types or in recombinant cell systems (e.g., human and yeast cells Klein et al.,... 

Klein , Baron J, Colli MJ, McDonnell DP, Cutler GBJ (1994) Estrogen levels in childhood determined by an ultrasensitive recombinant cell bioassay. J Clin Invest, 94 2475-2480. 

Xanthamonas campestris strain engineered to bioluminesce (Shaw et al., 1992). The strain was applied to cabbage plants and surrounding soils in a limited field study conducted in 1990. The fate of the organisms was monitored by both CCD-microscopy and plate counts, Recombinant cells were found for up to six weeks, with the CCD and plate counts giving quantitatively similar results. Bioluminescence in this case was no more sensitive than plate counts, and required a precision instrument,... 

Schwacha, A., Kleckner, N. (1995) Identification of double Holliday junctions as intermediates in meiotic recombination. Cell 83, 783-791. 

Cell construction is mainly confined to two types, using either pocket plate electrodes (vented cells) or sintered , bonded or fibre plate electrodes (vented and sealed cells). In the former, the active materials are retained within pockets of finely perforated nickel-plated sheet steel which are interlocked to form a plate. Positive and negative plates are then interleaved with insulating spacers placed between them. In sintered plate electrodes, a porous sintered nickel mass is formed and the active materials are distributed within the pores. In sintered plate vented cells, cellulose or other membrane materials are used in combination with a woven nylon separator. In sealed or recombining cells, special nylon separators are used which permit rapid oxygen diffusion through the electrolyte layer. 

Oka, M., Yang, Y.S., Nagata, S., Esaki, N., Tanaka, M., and Soda, K. 1989. Overproduction of thermostable leucine dehydrogenase of Bacillus stearothermophilus and its one-step purification from recombinant cells of Escherichia coli. Biotechnol. Appl. Biochem. 11 307-316. Sassenfeld, H.M. 1990. Engineering proteins for purification. Trends Biotechnol. 8 88-93. 

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