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Encyclopedia of Physical Science and Technology EN009G-399 July 6, 2001 20:4

46 Mammalian Cell Culture

2. Gene Therapy of transgenic animals. Mouse embryos have been found
to provide a type of cell known as embryonic stem cells.
Gene therapy has the potential for treating a very wide
These cells can be cultivated, genetically modified in cul-
range of human diseases but since the first somatic gene
ture, and subsequently inserted into a developing embryo.
therapy product [T-lymphocyte-directed gene therapy of
These modified cells can contribute to all of the cells of
adenosine deaminase deficiency (ADA-SCID)] went into
the mouse embryo, including germ cells, providing the
trial in 1990 progress has been disappointingly slow, al-
opportunity to transfer a genetic character into a strain of
though there are over 300 clinical products at some stage
laboratory mice. Recently, based on the breakthrough dis-
of clinical trial. One problem is the development of safe
covery of Wilmut and Campbell when cloning the sheep
and efficient gene-delivery systems, which require careful
“Dolly” from an adult mammary tissue cell, gene con-
regulation for safety. This effort has largely concentrated
structs of interest have been inserted into cultured fetal
on engineering viruses as vectors of therapeutic genes
fibroblasts of sheep that were subsequently inserted into
Three modes of gene delivery are possible:
enucleated eggs. Using a targeting vector and selection
with a neomycin selection marker, the gene of interest
1. Ex vivo: Removal of the cells from the body, incu-
for human alpha-1-antitrypsin (AAT) has been inserted
bation with a vector, and return of the engineered cells to
into the chromosomal locus of a pro-collagen gene. Of
the body (mainly applicable to blood cells),
16 transgenic fetuses and lambs analyzed, 15 were con-
2. In situ: Vector is placed directly into the affected
firmed to contain the transgene. One individual produced
tissues (e.g., infusion of adenoviral vectors into trachea
650 mg/L of AAT in the milk from a single inserted copy
and bronchi for cystic fibrosis patients).
of the AAT gene. It is to be expected that these techniques
3. In vivo: Vector is injected directly into the blood
for gene transfer into mammalian cells will be expanded
stream (this method is a goal but has not yet been used
for the commercial use of transgenic animals for the pro-
clinically).
duction of desirable proteins, as well as for the generation
of more useful human disease models in mammals larger
The target diseases currently undergoing clinical trial than mice.
are
1. Cancer (melanoma, colon, renal cell, neuroblastoma, VI. APPLICATIONS OF CELL CULTURE
ovarian, breast, lung)
2. Genetic diseases (cystic fibrosis, Gaucher’s disease, In addition to being used as a substrate for the manufac-
SCID) ture of pharmaceutical products, cells are used in a wide
3. Viral (acquired immune deficiency syndrome, AIDS) range of other applications including diagnostic virology,
aging, cell physiology and metabolism, immunology, cell
genetics, and cancer. Testing in the fields of toxicology and
F. Other Products
pharmacology is also important to lead to more controlled
A product area of increasing interest and potential is the experiments and reduce significantly the need for using
cell-adhesion molecules (CAMs). These are molecules animals. Cell cytotoxicity assays are used to (1) identify
that mediate cell–cell and cell–matrix interactions and potentially active therapeutic compounds, (2) to identify
are being developed as drugs against inflammatory dis- the mechanism by which the compound exerts its toxic
eases. They also have the potential to treat metatas- effect, (3) to predict anticancer activity, (4) to identify
tic diseases, atherosclerosis, and microbial infection. possible target cell populations, (5) to identify the toxic
Chemokines present at sites of inflammation and dis- concentration range, and (6) to investigate the relationship
ease bind leukocyte receptors and activate a family of of concentration to exposure time.
CAMs known as integrins. Sequential activation and inter-
action of multiple CAMs in the inflammatory process offer
manytargetsfordrugintercession.Targetproductsinclude VII. CONCLUSION
antisense and antagonists. Examples of such drugs un-
dergoing trial are Cylexin (reperfusion injury), Integretin Mammalian cell culture is used widely, from small-scale
(arterial thrombosis, angina), and Celadin (inflammatory applicationsinthelaboratorythatenableresearchintocan-
diseases). There are over 30 companies developing CAMs cer and many other medical conditions, through screening
which are in various stages of preclinical and clinical trial. and assay procedures for identifying new drugs and testing
An important and topical new application is gene tar- the safety of existing products, as a basis for tissue replace-
geting into primary mammalian cells for the generation ment and gene deficiency correction, to a production of up