The tissue culture is “the culture of whole organs, tissue fragments as well as dispersed cell on a suitable nutrient medium”. An important aspect of any biotechnological processes is the culture of animal cells in artificial media. These animal cells in culture are used in recombinant DNA technology, genetic manipulations and in a variety of industrial processes. Now-a -days it has become possible to use the cell and tissue culture in the areas of research which have a potential for economic value and commercialization. The animal cell cultures are being extensively used in production of vaccines, monoclonal antibodies, pharmaceutical drugs, cancer research, genetic manipulations etc.
Animal cells e.g. egg cells are used for multiplication of superior livestock using a variety of techniques like cloning of superior embryonic cells, transformation of cultured cells leading to the production of transgenic animals. The animal cells are also used in vitro fertilization and transfer of embryos to surrogate mothers. Hence the establishment and maintenance of a proper animal culture is the first step towards using them as tools for biotechnology, it’s a method for studying the behavior of animal cells free of systemic variations that might arise in vivo both during normal homeostasis and under the stress of an experiment. As culture of cells from such primary explants of tissue dominated the field for more than 50 years [Fischer, 1925; Parker, 1961], it is not surprising that the name ‘‘tissue culture’’ has remained in use as a generic term despite the fact that most of the explosive expansion in this area in the second half of the twentieth century was made possible by the use of dispersed cell cultures
CONCLAVE'S OF ANIMAL CELL CULTURE
DATE
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SCIENTIFIC EVENT’S
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SCIENTIST’S
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1855
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Medullary plate of chik embryo on warm saline.
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Roux
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1903
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In vitro cell survival & cell division in salamander leucocytes.
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Jolly
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1907
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Frog embryo nerve fiber outgrowth in vitro.
Cultured connective tissue cells for extended periods
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Ross Harrison
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1912
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Explants of chick connective tissue; heart muscle contractile for 2–3 months. Aseptic technique to tissue culture, used trypsin/embryo extract/ animal serum
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Alexis Carrel
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1913
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Used Antibiotics Penicillin/ Streptomycin
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Rous & Jones
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1940
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Used trypsinization to produce homogenous cell strain for tissue culture media
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“
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1943
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Establishment of the L-cell mouse fibroblast; first continuous cell line
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Earle et al.,
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1940-50
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1st cloned from L-cells.
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Katherine Sanford et al.
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1948
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Observed contact inhibition between fibroblasts
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Margaret Gey & George Gey
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1952
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Polio Virus in Human E-cells. Production of polio vaccine
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Abercrombie & Heaysmam
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1954
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Human cell line for production of vaccines human & veterinary
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Ender et al.
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1962
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Developed defined media
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Harry Eagle
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1970
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Described attachment factors & feeder layers.
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“
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1955
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Describe finite lifespan of normal human diploid cells
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Hayflick & Moorhead
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1961
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Published method for maintaining differentiated cells
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“
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1962
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Studied the differentiation of normal myoblasts in vitro.
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Buonassisi et al.
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1968
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Retention of differentiation in cultured normal myoblasts, Anchorage-independent cell proliferation [Human foetal lung foetal lung fibroblasts]
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David Yaffe
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1969
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Colony formation in hematopoietic cells
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Metcalf
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1970
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Development of laminar-flow cabinets
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Kruse et al
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1973
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DNA transfer, calcium phosphate
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Graham & Van der Eb
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1975
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Fibroblast growth factor ,
Hybridomas—monoclonal antibodies
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Gospodarowicz et al.
Kohler & Milstein
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1976
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Totipotency of embryonal stem cells
Growth factor-supplemented serum- free media
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Illmensee & Mintz
Hayashi & Sato
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1977
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Confirmation of HeLa cell cross-contamination of many cell lines.
3T3 feeder layer and skin culture
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Nelson-Rees & Flandermeyer
Rheinwald & Green, 1975
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1978
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MCDB-selective, serum-free media
Cell shape and growth control
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Ham & McKeehan
Folkman & Moscona, 1978
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1979
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Matrix interactions
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Gospodarowicz et al., 1978b;
Reid & Rojkind, 1979
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1982
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Regulation of gene expression
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Darnell, 1982
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1980
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Oncogenes, malignancy, and transformation
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Weinberg
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1980-87
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Development of many specialized cell lines
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Peehl & Ham, 1980;
Hammond et al., 1984;
Knedler & Ham, 1987
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1983
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Reconstituted skin cultures
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Bell et al.,
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1984
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Production of recombinant tissue-type plasminogen activator in mammalian cells
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Collen et al.,
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1990s
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Industrial-scale culture of transfected cells for production of
Biopharmaceuticals
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Butler
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1991
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Culture of human adult mesenchymal stem cells
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Caplan,
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1998
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Tissue-engineered cartilage
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Aigner et al.,
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1998
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Culture of human embryonic stem cells
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Thomson et a
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2002
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Exploitation of tissue engineering
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Atala & Lanza, 2002;
Vunjak-Novakovic &Freshney, 2004
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Tissue culture was first devised at the beginning of the twentieth century [Harrison, 1907; Carrel, 1912] It was Jolly, who (1903) showed for the first time that the cells can survive and divide in vitro. Ross Harrison, (1907) was able to show the development of nerve fibres from frog embryo tissue, cultured in a blood clot. Later, Alexis Carriel (1912) used tissue and embryo extracts as cultural media to keep the fragments of chick embryo heart alive. In the late 1940s, Enders, Weller and Robbins grew poliomyelitis virus in culture which paved way for testing many chemicals and antibiotics that affect multiplication of virus in living host cells. The significance of animal cell culture was increased when viruses were used to produce vaccines on animal cell cultures in late 1940s. For about 50 years, mainly tissue explants rather than cells were used for culture techniques, although later after 1950s, mainly dispersed cells in culture were utilized. In 1966, Alec Issacs discovered Interferon by infecting cells in tissue culture with viruses. He took filtrates from virus infected cells and grew fresh cells in the filtered medium. When the virus was reintroduced in the medium, the cells did not get infected. He proposed that cells infected with the virus secreted a molecule which coated onto uninfected cells and interfered with the viral entry. This molecule was called “Interferon”. Chinese Hamster Ovary (CHO) cell lines were developed during 1980s. Recombinant erythropoietin was produced on CHO cell lines by AMGEN (U.S.A.). It is used to prevent anaemia in patients with kidney failure who require dialysis. After this discovery, the Food and Drug Administration (U.S.A) granted the approval for manufacturing erythropoietin on CHO cell lines. In 1982, Thilly and co-workers used the conventional conditions of medium, serum, and O2 with suitable beads as carriers and grew certain mammalian cell lines to densities as high as 5x106 cells/ml. A lot of progress has been also made in the area of stem cell technology which will have their use in the possible replacement of damaged and dead cells. In 1996, Wilmut and co-workers successfully produced a transgenic sheep named Dolly through nuclear transfer technique. Thereafter, many such animals (like sheep, goat, pigs, fishes, birds etc.) were produced. Recently in 2002, Clonaid, a human genome society of France claimed to produce a cloned human baby named EVE. For animals, if the explants maintains its structure and function in culture it is called as an ‘organotypic culture’. If the cells in culture reassociate to create a three dimensional structure irrespective of the tissue from which it was derived, it is described as a ‘histotypic culture’
ANIMAL CELL CULTURE
Salient Features of Animal cell culture
1) Animal cells can grow in simple glass or plastic containers in nutritive media but they grow only to limited generations.
2) Animal cells exhibit contact inhibition. In culture the cancer cells apparently differ from the normal cells. Due to uncontrolled growth and more rounded shape, they lose contact inhibition and pile over each other.
3) There is a difference in the in vitro and in vivo growth pattern of cells.
For example
(i) there is an absence of cell-cell interaction and cell matrix interaction,
(ii) there is a lack of three-dimensional architectural appearance, and
(iii) changed hormonal and nutritional environment.
They way of adherence to glass or plastic container in which they grow, cell proliferation and shape of cell results in alterations.
4) The maintenance of growth of cells under laboratory conditions in suitable culture medium is known as Primary Cell Culture.
5) Cells are dissociated form tissues by mechanical means and by enzymatic digestion using proteolytic enzymes.
6) Cells can grow as adherent cells (anchorage dependent) or as suspension cultures (anchorage independent).
7) The primary culture is subcultured in fresh media to establish Secondary Cultures.
8) The various types of cell lines are categorized into two types as Finite cell line and Continuous cell line. Finite cell lines are those cell lines which have a limited life span and grow through a limited number of cell generations. The cells normally divide 20 to 100 times (i.e. is 20-100 population doublings) before extinction. Cell lines transformed under in vitro conditions give rise to continuous cell lines. The continuous cell lines are transformed, immortal and tumorigenic.
9) The physical environment includes the optimum pH, temperature, osmolality and gaseous environment, supporting surface and protecting the cells from chemical, physical, and mechanical stresses.
10) Nutrient media is the mixture of inorganic salts and other nutrients capable of sustaining cell survival in vitro
11) Serum is essential for animal cell culture and contains growth factors which promote cell proliferation. It is obtained as exuded liquid from blood undergoing coagulation and filtered using Millipore filters.
12) Cryo preservation is storing of cells at very low temperature (-1800C to -196 0C) using liquid nitrogen. DMSO is a cryopreservative molecule which prevents damage to cells.
13) In order to maintain the aseptic conditions in a cell culture, a LAF hood is used. Based on the nature of cells and organism the tissue culture hoods are grouped into three types: Class I, Class II, and Class III.
14) CO2 incubators are used and designed to mimic the environmental conditions of the living cells.
15) An inverted microscope is used for visualizing cell cultures in situ
16) For most animal cell cultures low speed centrifuges are needed.
17) Neuronal cells constitute the nervous system. In culture the neuronal cells cannot divide and grow.
18) The cells that form connective tissue (skin) is called fibroblast. The fibroblast can divide and grow in culture to some generations after which they die. All normal animal cells are mortal.
19) Organ culture- The culture of native tissue that retains most of the in vivo histological features is regarded as organ culture.
20) Histotypic culture- The culturing of the cells for their reaggregation to form a tissue-like structure represents histotypic culture.
21) Organotypic culture- This culture technique involves the recombination of different cell types to form a more defined tissue or an organ.
There are certain terms that are associated with the cell lines.
These are as follows:
(i) Split ratio- The divisor of the dilution ratio of a cell culture at subculture.
(ii) Passage number- It is the number of times that the culture has been cultured,
(iii) Generation number- It refers to the number of doublings that a cell population has undergone.
In fact these parameters help us to distinguish the cancer cells in culture from the normal cells because the cancer cells in culture, change shape (more rounded), loose contact inhibition, pile on each other due to overgrowth and uncontrolled growth.
REQUIREMENTS FOR ANIMAL CELL CULTURE
Among the essential requirements for animal cell culture are special incubators to maintain the levels of oxygen, carbon dioxide, temperature, humidity as present in the animal’s body. The synthetic media with vitamins, amino acids and fetal calf serum.
Following parameters are essential for successful animal cell culture:
a) Temperature- In most of the mammalian cell cultures, the temperature is maintained at 37ºC in the incubators as the body temperature of Homo sapiens is 37ºC.
b) Culture media- The culture media is prepared in such a way that it provides-
1) The optimum conditions of factors like pH, osmotic pressure, etc.
2) It should contain chemical constituents which the cells or tissues are incapable of synthesizing.
Generally the media is the mixture of inorganic salts and other nutrients capable of sustaining cells in culture such as amino acids, fatty acids, sugars, ions, trace elements, vitamins, cofactors, and ions. Glucose is added as energy source-it’s concentration varying depending on the requirement. Phenol Red is added as a pH indicator of the medium.
There are two types of media used for culture of animal cells and tissues- the natural media and the synthesized media.
A) Natural Media - The natural sources of nutrient sufficient for growth and proliferation of animal cells and tissues. The Natural Media used to promote cell growth fall in three categories.
i) Coagulant, such as plasma clots. It is now commercially available in the form of liquid plasma kept in silicon ampoules or lyophilized plasma. Plasma can also be prepared in the laboratory taking out blood from male fowl and adding heparin to prevent blood coagulation.
ii) Biological fluids such as serum. Serum is one of the very important components of animal cell culture which is the source of various amino acids, hormones, lipids, vitamins, polyamines, and salts containing ions such as calcium, ferrous, ferric, potassium etc. It also contains the growth factors which promotes cell proliferation, cell attachment and adhesion factors. Serum is obtained from human adult blood, placental, cord blood, horse blood, calf blood. The other forms of biological fluids used are coconut water, amniotic fluid, pleural fluid, insect haemolymph serum, culture filtrate, aqueous humour, from eyes etc.
iii) Tissue extracts for example Embryo extracts- Extracts from tissues such as embryo, liver, spleen, leukocytes, tumour, bone marrow etc are also used for culture of animal cells.
B) Synthetic media- prepared artificially by adding several organic and inorganic nutrients, vitamins, salts, serum proteins, carbohydrates, cofactors etc. Different types of synthetic media can be prepared for a variety of cells and tissues to be cultured. Synthetic media are of two types- Serum containing media (media containing serum) and serum- free media (media without serum). Examples of some media are: minimal essential medium (MEM), RPMI 1640 medium, CMRL 1066, F12 etc.
Advantages of serum in culture medium are:
i) serum binds and neutralizes toxins,
(ii) serum contains a complete set of essential growth factors, hormones, attachment and spreading factors, binding and transport proteins,
(iii) it contains the protease inhibitors,
(iv) it increases the buffering capacity,
(v) it provides trace elements.
Disadvantages of serum in culture medium are:
(i) it is not chemically defined and therefore it’s composition varies a lot,
(ii) it is sometimes source of contamination by viruses, mycoplasma, prions etc,
(iii) it increases the difficulties and cost of downstream processing,
(iv) it is the most expensive component of the culture medium.
4) pH- Most media maintain the pH between 7 and 7.4. A pH below 6.8 inhibits cell growth. The optimum pH is essential to maintain the proper ion balance, optimal functioning of cellular enzymes and binding of hormones and growth factors to cell surface receptors in the cell cultures. The regulation of pH is done using a variety of buffering systems. Most media use a bicarbonate-CO2 system as its major component.
5) Osmolality- A change in osmolality can affect cell growth and function. Salt, Glucose and Amino acids in the growth media determine the osmolality of the medium. All commercial media are formulated in such a way that their final osmolality is around 300 mOsm.
CELL BASED THERAPY
"The animal cell culture techniques are used in replacing the damaged and dead cells with normal and healthy cells using the stem cell technology". This therapy is called Cell-Based therapy which involves the use of "Stem cell technology" involving the replacement of damaged and dead cells with normal and healthy cells. This is used to treat blood cancer, and other neuro-degenerative diseases etc.
APPLICATIONS OF ANIMAL CELL CULTURE
The animal cell cultures are used for a diverse range of research and development. These areas are:
a) production of antiviral vaccines, which requires the standardization of cell lines for the multiplication and assay of viruses.
b) Cancer research, which requires the study of uncontrolled cell division in cultures.
c) Cell fusion techniques.
d) Genetic manipulation, which is easy to carry out in cells or organ cultures.
e) Production of monoclonal antibodies requires cell lines in culture.
f) Production of pharmaceutical drugs using cell lines.
g) Chromosome analysis of cells derived from womb.
h) Study of the effects of toxins and pollutants using cell lines.
i) Use of artificial skin.
j) Study the function of the nerve cells.
Somatic Cell Fusion
One of the applications of animal cell culture is the production of hybrid cells by the fusion of different cell types.
These hybrid cells are used for a the following purposes:
(i) study of the control of gene expression and differentiation,
(ii) study of the problem of ‘ malignancy’,
(iii) viral application,
(iv) gene mapping,
(v) production of hybridomas for antibody production.
In 1960s, in France for the first time, the hybrid cells were successfully produced from mixed cultures of two different cell lines of mouse. Cells growing in culture are induced by some of the viruses such as ‘Sendai virus’ to fuse and form hybrids. This virus induces two different cells first to form heterokaryons. During mitosis, chromosomes of heterokaryon move towards the two poles and later on fuse to form hybrids. It is important to remove the surface carbohydrates to bring about cell fusion. Some other chemicals like polyethylene glycol also induce somatic cell fusion. Many commercial proteins have been produced by animal cell culture and there medical application is being evaluated.
Tissue Plasminogen activator (t-PA) was the first drug that was produced by the mammalian cell culture by using rDNA technology. The recombinant t-PA is safe and effective for dissolving blood clots in patients with heart diseases and thrombotic disorders.
Blood Factor VIII
Haemophilia A is a blood disorder which is a sex-linked genetic disease in humans. The patients suffering from Haemophilia A lack factor VIII, which plays an important role in the clotting of blood. This factor VIII is secreted by a gene present on X-chromosome but this gene undergoes mutations in people suffering from Haemophilia. Current therapy for this disease is the transfusion of blood factor VIII into patients. Using rDNA technology, Factor VIII has been produced from mammalian cell culture e.g. Hamster kidney cell.
Erythropoietin (EPO)
The EPO is a glycoprotein consisting of 165 amino acids and is formed in the foetal liver and kidneys of the adults. It causes proliferation and differentiation of progenitor cells into the erythrocytes (erythroblasts) in the bone marrow. Erythropoietin is hormone-like in nature and is released by the kidney under hypoxic or anoxic conditions caused by anaemia. Amgen Inc. holds US patent for preparation of, eErythropoietin, by recombinant method using Chinese Hamster Ovary cell lines. Erythropoietin (EPO) is a "hormone-like substance released by the kidney under hypoxic or anoxic conditions caused by anaemia. r-HUEPO- recombinant human erythro- protein has been effectively used to treat anemia associated with AIDS, renal failure etc".
The production of Monoclonal Antibodies using hybridoma technology
Antibodies are proteins synthesized in blood against antigens and are collected from the blood serum. The antibodies, which are heterogenous and non specific in action are called Polyclonal antibodies. If a specific lymphocyte, after isolation and culture in vitro becomes capable of producing a single type of antibody bearing specificity against specific antigen, it is known as Monoclonal antibody. The monoclonal antibodies are used in the diagnosis of diseases because of the presence of desired immunity.
However, these antibody secreting cells cannot be maintained in culture. It was observed that the myeloma cells (bone marrow tumour cells due to cancer) grow indefinitely and also produce immunoglobulins which are infact monoclonal antibodies .
In 1974, George Kohler and Milstein isolated clones of cells from the fusion of two parental cell lines – lymphocytes from spleen of mice immunized with red blood cells from sheep and myeloma cells. These cells were maintained in vitro and produced antibodies. The hybrid cells maintained the character of lymphocytes to secrete the antibodies, and of myeloma cells to multiply in culture. These hybrid cell lines are called “Hybridoma” and are capable of producing unlimited supply of antibodies. Hybridoma are obtained by using an antibody producing lymphocytes cell and a single myeloma cell. Monoclonal antibodies bind very specifically to an epitope (specific domains) on an antigen and by using them it is possible to detect the presence of specific antigens.
The Monoclonal antibodies are used for the treatment of patients with malignant leukaemia cells, B cell lymphomas and allograft rejection after transplantation. CD3 is an antigen present on the surface of mature T- cells lymphocytes. If T- cell population is depleted or controlled, the transplanted organ will not be rejected. An antibody that acts against CD3 surface antigen of T-cells is called OKT3 i.e. anti-CD3 Moab. OKT3 is a monoclonal antibody which has been licensed for clinical use for the treatment of acute renal allograft rejection. OKT3 removes antigen bearing cells from circulation thereby helps in accepting the graft.
When Monoclonal antibodies are used as enzymes using the technique of enzyme engineering, then they are called Abzymes.
Using animal cell cultures, it is also possible to produce Polyclonal Antibodies. Polyclonal antisera are derived from many cells therefore contains heterogeneous antibodies that are specific for several epitopes or an antigen.
SCALE-UP OF ANIMAL CELL CULTURE
Modifying a laboratory procedure, so that it can be used on an industrial scale is called scaling up. Laboratory procedures are normally scaled up via intermediate models of increasing size. The larger the plant, the greater the running costs, as skilled people are required to monitor and maintain the machinery. The first pre-requisite for any large scale cell culture system and its scaling up is the establishment of a cell bank. Master cell banks (MCB) are first established and they are used to develop Master Working Cell Banks (MWCB). The MWCB should be sufficient to feed the production system at a particular scale for the predicted life of the product. The cell stability is an important criteria so MWCB needs to be repeatedly subcultured and each generation should be checked for changes. A close attention should be paid to the volume of cultured cells as the volume should be large enough to produce a product in amounts which is economically viable. The volume is maintained by a) increasing the culture volume, (b) by increasing the concentration of cells in a reactor by continuous perfusion of fresh medium, so that the cells keep on increasing in number without the dilution of the medium.
A fully automated bioreactor maintains the physicochemical and biological factors to optimum level and maintains the cells in suspension medium. The most suitable bioreactor used is a compact-loop bioreactor consisting of marine impellers. The animal cells unlike bacterial cells, grow very slowly. The main carbon and energy sources are glucose and glutamine. Lactate and ammonia are their metabolic products that affect growth and productivity of cells. So, the on-line monitoring of glucose, glutamate, and ammonia is carried out by on line flow injection analysis (FIA) using gas chromatography (GC), high performance liquid chromatography (HPLC) etc.
In batch cultures, mainly Roller Bottles with Micro Carrier Beads (for adherent cells) and spinner flasks (for suspension cultures) are used in Scale-up of animal cell culture process.
Roller Bottles
The Roller bottles provide total curved surface area of the micro carrier beads for growth. The continuous rotation of the bottles in the CO2 incubators helps to provide medium to the entire cell monolayer in culture.The roller bottles are well attached inside a specialized CO2 incubators. The attachments rotate the bottles along the long axis which helps to expose the entire cell monolayer to the medium during the one full rotation. This system has the advantage over the static monolayer culture: (a) it provides increase in the surface area, (b) provides constant gentle agitation of the medium, (c) provides increased ratio of surface area of medium to its volume, which allows gas exchange at an increased rate through the thin film of the medium over the cells. Typically, a surface area of 750-1500 cm2 with 200-500 ml medium will yield 1-2x108cells.
Micro Carrier Beads
Micro carrier beads are small spherical particles with diameter 90-300 micrometers, made up of dextran or glass. Micro Carrier beads, increase the number of adherent cells per flask. These dextran or glass-based beads come in a range of densities and sizes. The cells grow at a very high density which rapidly exhausts the medium and therefore the medium has to be replaced for the optimum cell growth. At the recommended concentration when the microcarriers are suspended they provide 0.24 m2 area for every 100 ml of culture flask.
Spinner cultures
The spinner flask, was originally developed to provide the gentle stirring of microcarriers but are now used for scaling up the production of suspension cells. The flat surface glass flask is fitted with a Teflon paddle that continuously turns and agitates the medium. This stirring of the medium improves gas exchange in the cells in culture. The spinner flask used at commercial scale consists of one or more side arms for taking out samples and decantation as well.
Equipments Required for Animal Cell Culture
Laminar Flow Cabinets
LAF hoods are the aseptic working table for inoculation of animal cells. The basic purpose of using a LAF hood is to provide protection from contamination from any organism like fungi or bacterial cells under aseptic conditions, and to protect the operator from potential infection risk of infection from the cultured cells.
The working area of LAF hood is first made sterile by using 70% ethanol. When the LAF is kept in “ON” position, the sterile air flows inside the cabinet which maintains the sterile conditions required for the transfer of cultured cells.
Depending on the nature of the cells and organisms being handled, tissue culture hoods can be grouped as follows :
a) Class I hoods are found with in specially designed sterile work areas and give good protection to the operator and, to a lesser degree, the cell culture. There is an open front from which the air is drawn over the cell culture and goes out through the top of the hood.
b) Class II hoods offer protection to both operator and the cell culture and is the most common type found in a tissue culture laboratory. The cell culture is protected in a stream of sterile air and the operator is protected from contamination by the inflow of air into the base of the work area. The inflow of stream of sterile air into the base of work area protects the culture and operator from contamination.
c) Class III hoods contains a full physical barrier which screens the worker, and is mainly used for working with highly pathogenic organisms. In this, a physical barrier separates the operator from the inoculation work. The open front is replaced with glass or Perspex with a pair of heavy duty gloves attached to it. All the work is assessed from this glass.
The Incubators
The CO2 incubators provide the suitable environmental conditions to the growing animal cells. Generally CO2 incubators are used in animal cell cultures But also
a) to maintain the sterility of the chamber for which filtered High Efficiency Particulate Air (HEPA) is used.
b) to maintain constant temperature the incubators is made airtight using a silicon gasket on the inner door.
c) to keep an atmosphere with a fixed level of CO2 and high relative humidity which prevents the dessication of the medium and maintains the osmolality?
Inverted Microscope
This type of microscope is used for visualizing cell cultures in situ.The cells in culture vessel remain at the bottom of the vessel and the medium floats above the growing cells. It is impossible to observe these cells under the ordinary microscope, therefore, the inverted microscope is used for such purposes. The inverted microscope has the optical system at the bottom and the light source at the top, this arrangement helps to observe the cultured cells in the plates.
Centrifuges
Only low speed centrifuges are used generally at 20oC to avoid disruption of the separated bands of cells. The motor releases the heat which leads to the increase in temperature. Therefore, use of low temperature for centrifugation is recommended so that cells are not exposed to high temperature.
Besides these conditions, the culture rooms should have light (diffused light and darkness each for a period of 12 hours) and temperature maintained at 25+/- 20C, with relative humidity at 98% and uniform air ventilation. The cultures should be monitored at regular intervals under aseptic conditions.
Sterilized Glassware, culture media and other equipments
The glassware are thoroughly washed and all the equipment sterilized by heat, steam, or Millipore filter paper. The glassware like glass coverslips, instruments, Pasteur pipettes, test tubes etc are sterilized by dry heat. Apparatus containing glass and silicon tubing, disposable tips for micropipettes, screw caps, Millipore filters etc are sterilized by autoclaving.
Isolation of animal material (Tissue)
The culture animal material is washed in balanced salt solution to avoid contamination. The tissue to be cultured should be properly sterilized with 70% ethanol and removed surgically under aseptic conditions.
Disaggregation of tissue – To obtain the cell suspension for primary cell culture, the tissue is disintegrated either mechanically or by using enzymes.
(i) Physical or mechanical disaggregation- After removing the tissue under aseptic conditions, it is pressed through a sieve of 100 micrometer. It is then kept in a sterile Petri dish containing buffered medium with balanced salt solution. The cells are then alternately passed through the sieve of decreasing pore size (50 micrometer and 20 micrometer mesh). The debris which remains on the sieve is discarded and the medium containing cells is collected and cells are counted by using Haemocytometer. This method is cheap and quick but it damages a lot of cells.
(ii) Enzymatic disaggregation- In this method, enzymes are used for dislodging the cells of tissues. The two important enzymes used in tissue disaggregation are-collagenase and trypsin. –
a) Collagenase- The intracellular matrix contains collagen therefore collagenase is used for disaggregation of embryonic, normal as well as malignant tissues. The tissues are kept in medium containing antibiotics and then dissected into pieces in basal salt solution. After washing the chopped tissue with distilled water, it is transferred to complete medium containing collagenase. After a few days (around 5 days), the mixture is pipetted so that the medium gets dispersed. The whole treatment is left for sometimes during which the epithelial cells settle on bottom of test tubes. The enzyme collagenase is removed by centrifugation. Suspension consists of cells which are then plated out on the medium.
(b) Trypsin- Use of trypsin for disaggregation is called trypsinization. On the basis of role of temperature on trypsin, the activity of trypsin is of two types- Cold trypsinization and warm trypsinization.
Cold trypsinization- The sample tissue to be disaggregated is chopped into 2-3 small pieces and kept in sterile glass vial. The tissues are subsequently washed with sterile water and dissected and then kept in BSS. The whole content is then placed on ice and soaked in cold trypsin for 4-6 hours to allow the penetration of enzymes in tissue. After this the trypsin is removed and the tissue is incubated at 36.50C for 20-30 minutes. About 10 ml of medium containing serum is added to the vials containing the cells and the cells are dispersed by repeated pipetting. The cells are counted by haemocytometer and are plated and incubated for 48-72 hours for cell growth.
Warm trypsinization- The initial steps are the same as in cold trypsinization however, in this case the tissue pieces are treated with warm trypsin (36.50C). The tissues are stirred for 4 hours and then pieces are allowed to settle down. The disassociated cells are collected at every 30 minutes. The process is repeated by adding fresh trypsin back to pieces and incubating the contents. The trypsin is removed by centrifugation after 3-4 hours during which the complete disaggregation of tissues takes place. The glass vials containing dispersed cells are then placed on ice. The cells are counted using haemocytometer and cell density is maintained at an appropriate number. The cells are then plated on medium and incubated for 48-72 hours for cell growth.
(iii) Treatment with chelating agents- The tissues like epithelium (which needs Ca2+ and Mg2+ ions for it’s integrity are treated with chelating agents such as citrate and ethylene-diamine-tetra-acetic acid (EDTA). Chelating agents are mainly used for production of cell suspensions from established cultures of epithelial type.
TYPES OF CELL CULTURES
Primary cell culture
The maintenance of growth of cells dissociated from the parental tissue (such as kidney, liver) using the mechanical or enzymatic methods, in culture medium using suitable glass or plastic containers is called Primary Cell Culture.
The primary cell culture could be of two types depending upon the kind of cells in culture.
a) Anchorage Dependent /Adherent cells- Cells shown to require attachment for growth are set to be Anchorage Dependent cells. The Adherent cells are usually derived from tissues of organs such as kidney where they are immobile and embedded in connective tissue. They grow adhering to the cell culture.
b) Suspension Culture/Anchorage Independent cells - Cells which do not require attachment for growth or do not attach to the surface of the culture vessels are anchorage independent cells/suspension cells. All suspension cultures are derived from cells of the blood system because these cells are also suspended in plasma in vitro e.g. lymphocytes.
Secondary cell cultures
When a primary culture is sub-cultured, it becomes known as secondary culture or cell line. Subculture (or passage) refers to the transfer of cells from one culture vessel to another culture vessel.
Subculturing- Subculturing or splitting cells is required to periodically provide fresh nutrients and growing space for continuously growing cell lines. The process involves removing the growth media, washing the plate, disassociating the adhered cells, usually enzymatically. Such cultures may be called secondary cultures.
Cell Line
A Cell Line or Cell Strain may be finite or continuous depending upon whether it has limited culture life span or it is immortal in culture.
On the basis of the life span of culture, the cell lines are categorized into two types:
a) Finite cell Lines - The cell lines which have a limited life span and go through a limited number of cell generations (usually 20-80 population doublings) are known as Finite cell lines. These cell lines exhibit the property of contact inhibition, density limitation and anchorage dependence. The growth rate is slow and doubling time is around 24-96 hours.
b) Continuous Cell Lines - Cell lines transformed under laboratory conditions or in vitro culture conditions give rise to continuous cell lines. The cell lines show the property of ploidy (aneupliody or heteroploidy), absence of contact inhibition and anchorage dependence. They grow in monolayer or suspension form. The growth rate is rapid and doubling time is 12-24 hours.
c) Monolayer cultures - When the bottom of the culture vessel is covered with a continuous layer of cells, usually one cell in thickness, they are referred to as monolayer cultures.
d) Suspension cultures - Majority of continuous cell lines grow as monolayers. Some of the cells which are non-adhesive e.g. cells of leukemia or certain cells which can be mechanically kept in suspension, can be propagated in suspension.
There are certain advantages in propagation of cells by suspension culture method:
(a) The process of propagation is much faster.,
(b) The frequent replacement of the medium is not required.,
(c) Suspension cultures have a short lag period,
(d) treatment with trypsin is not required,
(e) a homogenous suspension of cells is obtained,
(f) the maintenance of suspension cultures is easy and bulk production of the cells is easily achieved.,
(g) scale-up is also very convenient.
The cell lines are known by:
a) A code e.g. NHB for Normal Human Brain.
b) A cell line number- This is applicable when several cell lines are derived from the same cell culture source e.g. NHB1, NHB2.
c) Number of population doublings, the cell line has already undergone e.g. NHB2/2 means two doublings.
CHARACTERIZATION OF CELL LINES
The cell lines are characterized by their a) growth rate and b) karyotyping.
a) Growth Rate - A growth curve of a particular cell line is established taking into consideration the population doubling time, a lag time, and a saturation density of a particular cell line. A growth curve consist of:
1) Lag Phase: The time the cell population takes to recover from such sub culture, attach to the culture vessel and spread.
2) Log Phase: In this phase the cell number begins to increase exponentially.
3) Plateau Phase: During this phase, the growth rate slows or stops due to exhaustion of growth medium or confluency.
b) Karyotyping - Karyotyping is important as it determines the species of origin and determine the extent of gross chromosomal changes in the line. The cell lines with abnormal karyotype are also used if they continue to perform normal function. Karyotype is affected by the growth conditions used, the way in which the cells are subcultured and whether or not the cells are frozen.
c) There are certain terms that are associated with the cell lines.
These are as follows:
(i) Split ratio- The divisor of the dilution ratio of a cell culture at subculture.
(ii) Passage number- It is the number of times that the culture has been cultured.,
(iii) Generation number- It refers to the number of doublings that a cell population has undergone.
TABLE-SOME ANIMAL CELL LINES AND THE PRODUCTS OBTAINED FROM THEM
Cell line
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Product
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Human tumour
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Angiogenic factor
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Human leucocytes
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Interferon
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Mouse fibroblasts
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Interferon
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Human Kidney
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Urokinase
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Transformed human kidney cell line, TCL-598
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Single chain urokinase-type plasminogen activator (scu-PA)
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Human kidney cell (293)
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Human protein (HPC)
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Dog kidney
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Canine distemper vaccine
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Cow kidney
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Foot and Mouth disease (FMD) vaccine
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Chick embryo fluid
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Vaccines for influenza, measles and mumps
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Duck embryo fluid
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Vaccines for rabies and rubella
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Chinese hamster ovary (CHO) cells
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- Tissue-type plasminogen activator (t-PA)
- B-and gamma interferons
- Factor VIII
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Stem cells retain the capacity to self renew as well as to produce progeny with a restricted mitotic potential and restricted range of distinct types of differentiated cell they give rise to. The formation of blood cells also called haematopoiesis is the classical example of concept of stem cells. Indirect assay methods were developed to identify the haematopoietic stem cells. The process ofhaematopoeis is occurs in the spleen and bone marrow in mouse. In human beings about 100,000 haematopoietic stem cells produce one billion RBC, one billion platelets, one million T-cells, one million B cells per kg body weight per day.
Several methods have been developed to study haematopoiesis and stem cells:
a) Repopulation assay- Edmens Snell’s group created mice which were genetically identical by mating of sibling mice after 21 generations. Two groups of mice were lethally X- irradiated to destroy their blood cell forming capacity. One of this group was injected with marrow cells from the femur bone of a normal and healthy albino mice. It was observed that this group survived whereas the mice in the other group died. The spleen of mice which survived had the colonies of the bone marrow cells just like bacterial colonies on a Petri plate. This came to be known as colony forming units of spleen (CFU-S) and the technique is known as repopulation assay.
b) The in vitro clonal assay- In this assay, the stem cells proliferate to form colonies of differentiated cells on semi-solid media. This assay helps in identifying growth factors required for the formation of blood cells from the primitive stem cells. One of the first commercialized biotechnology product – erythropoietin was assayed by this procedure.
c) Long term marrow culture- In this method, the marrow cells from femur bone were grown under in vitro conditions on plastic surfaces. These techniques were helpful in bone marrow transplantation and treatment of blood cancer by releasing immature blood cells into the blood stream.
d) Embryonic stem cell culture- Embryonic stem cells are cell lines derived from the inner cell mass of fertilized mouse embryo without the use of immortalizing or transforming agents. The Inner cell mass (ICM) are the cells that are maintained in tissue culture in the presence of irradiated fibroblast cells. These cells are often used in creating chimeric mice. In 1998, J.A. Thomson developed the method to multiply the human embryonic stem cells. Human ICM can also be now derived either by IVF or from germ cell precursors and cultured on a Petri plate. The differentiation of these cells into lineage restricted (neuronal and glial) cells can be accomplished by altering the media in which the cells grow.
e) The ICM cells could be used to create chimeric mice. In chimeric mice it was possible to take ES cells from a black mouse and implant it into the embryo of an albino mouse (white). The progeny so developed had skin colour of black and white ( a chimera).
Genetic Engineering of animal cells and their applications
The mammalian cells are genetically modified by introducing the genes needed for specific purposes such as production of specific proteins or to improve the characteristics of a cell line. The methods used to introduce the foreign genes/DNA into mammalian cells are: Electroporation, Lipofection, Microinjection and/or fusion of mammalian cells with bacteria or viruses. After the integration of the foreign DNA into the mammalian cells, the transfected/transformed cells are selected by using suitable markers. Some of such markers in use are: Viral thymidine kinase, Bacterial dihydrofolate reductase, Bacterial neomycin phosphotransferase. It has been possible to overproduce several proteins in mammalian cells through genetic manipulations e.g. tissue plasminogen activator, erythropoietin, interleukin-2, interferon- beta, clotting factors VIII and IX, tumor necrosis factors. The recombinant mammalian cells are also conveniently used for the production of monoclonal antibodies.
Manipulation of Gene Expression in Eukaryotes
The eukaryotic organisms have the capability to bring about the post-translational modifications such as glycosylation, phosphorylation, proteolytic cleavage etc which ultimately helps in the production of stable and biologically active proteins. Due to these reasons the use of eukaryotic expression system is preferred however it is difficult to conduct experiments with eukaryotic cells. The introduction of a foreign DNA into animal cells is called transfection. The insert DNA in the eukaryotic cells may be associated with vector or integrated into the host chromosomal DNA. Among the various hosts used for the expression of cloned genes, the common yeast Saccharomyces cerevisiae is the most extensively used. Besides this, the cultured insect cells are in use for expressing cloned DNAs. Baculoviruses exclusively infect insect cells. The DNA of these viruses encode for several products and their productivity in cells is very high to the extent of more than 10,000 times compared to mammalian cells. The baculoviruses not only carry a large number of foreign genes but can also express and process the products formed. By using baculovirus as an expression vector system, a good number of mammalian and viral proteins have been synthesized. The most commonly used baculovirus is Autographa californica multiple nuclear polyhedrosis virus (AcMNPV). It grows on the insect cell lines and produce high levels of polyhedrin or a recombinant protein. The mammalian cell expression vectors are used for the production of specific recombinant proteins and to study the function and regulation of mammalian genes. However, large-scale production of recombinant proteins with engineered mammalian cells is costly. The mammalian vector contains a eukaryotic origin of replication from an animal virus such as Simian virus 40 (SV 40) and a prokaryotic origin of replication. It has a multiple cloning site and a selectable marker gene, both of which remain under the control of eukaryotic promoter and polyadenylation sequences. These sequences are obtained from either animal viruses (SV40, herpes simplex virus) or mammalian genes (growth hormone, metallothionein). The promoter sequences facilitate the transcription of cloned genes (at the multiple cloning site) and the selectable marker genes. On the other hand, the polyadenylation sequences terminate the transcription.
Collection and purification process of Recombinant proteins
As the recombinant proteins start accumulating in the host cells, it becomes important to collect and purify them. This is a tricky process since many times the recombinant protein is a foreign body for the host cells and the enzyme machinery of the host cell becomes activated to degrade the outside protein. One of the strategies adopted is the use of bacterial strains deficient in proteases or alternatively, the recombinant proteins are fused with the native host proteins. The fusion proteins are resistant to protease activity. Sometimes, the foreign proteins accumulate as aggregates in the host organism which minimizes the protease degradation. The best way out is to quickly export and secrete out the recombinant proteins in to the surrounding medium. The recovery and the purification of foreign proteins is easier from the exported proteins. The efforts have been made to develop methods to increase the export of recombinant proteins. Some of the species of the bacterium, Bacillus subtilis normally secrete large quantities of extracellular proteins. A short DNA sequence called signal sequence from such species is introduced into other B. subtilis. These bacteria produce recombinant DNA tagged with signal peptide, which promotes export and secretion. This signal peptide is removed after the purification of foreign protein. The techniques used for the purification of recombinant proteins from the mixture of secreted proteins are affinity tagging, immunoaffinity purification etc.
Organ culture and Histotypic cultures
The cell-cell interaction leads to a multistep events in in vivo situations. For example, hormone stimulation of fibroblasts is responsible for the release of surfactant by the lung alveolar cells. Androgen binding to stomal cells stimulates the prostrate epithelium. In other words, hormones, nutritional factors and xenobiotics exert stimulating effects on the cells to function in a coordinated manner. Xenobiotics broadly refers to the unnatural, foreign, and synthetic chemicals such as pesticides, herbicides, refrigents, solvents and other organic compounds. It is impossible to study these cellular interactions that occur in the in vivo system with isolated cells or cells in culture. This has lead to the attempts to develop organ and histotypic culture with the aim of creating in vitro models comparable to the in vivo system.
The three types of such cultures are:
a) Organ culture- In this type of culture, the whole organs or small fragments of the organs with their special and intrinsic properties intact are used in culture.
b) Histotypic culture- The cell lines grown in three dimensional matrix to high density represent histotypic cultures.
c) Organotypic cultures- A component of an organ is created by using cells from different lineages in proper ratio and spatial relationship under laboratory conditions.
Organ culture
In the organ culture, the cells are integrated as a single unit which helps to retain the cell to cell interactions found in the native tissues or organs. Due to the preservation of structural integrity of the original tissue, the associated cells continue to exchange signals through cell adhesion or communications. Due to the lack of a vascular system in the organ culture, the nutrient supply and gas exchange of the cells become limited. In order to overcome this problem, the organ cultures are placed at the interface between the liquid and gaseous phases. Sometimes, the cells are exposed to high O2 concentration which may also lead to oxygen induced toxicity. Due to the inadequate supply of the nutrients and oxygen, some degree of necrosis at the central part of the organ may occur. In general, the organ cultures donot grow except some amount of proliferation that may occur on the outer cell layers.
Techniques and Procedure for organ culture
In order to optimize the nutrient and gas exchanges, the tissues are kept at gas limited interface using the support material which ranges from semisolid gel of agar, clotted plasma, micropore filter, lens paper, or strips of Perspex or plexiglass. The organ cultures can also be grown on top of a stainless steel grid. Another popular choice for growing organ cultures is the filter-well inserts. Filter-well inserts with different materials like ceramic, collagen, nitrocellulose are now commercially available. Filter well inserts have been successfully used to develop functionally integrated thyroid epithelium, stratified epidermis, intestinal epithelium, and renal epithelium.
The procedure for organ cultures has the following steps:
a) The organ tissue is collected after the dissection.
b) The size of the tissue is reduced to less than 1mm in thickness.
c) The tissue is placed on a gas medium interface support.
d) Incubation in a CO2 incubator.
e) M199 or CMRL 1066 medium is used and changed frequently.
f) The techniques of histology, autoradiography, and immunochemistry are used to study the organ cultures.
The advantages of organ culture
The organ cultures can be used to study the behavior of an integrated tissue in the laboratory. It provides an opportunity to understand the biochemical and molecular functions of an organ/tissue.
Limitations of organ culture
It is a difficult and expensive technique. The variations are high with low reproducibility. For each experiment, a new or fresh organ is needed as organ cultures are not propagated.
Histotypic cultures
Using histotypic culture, it is possible to use dispersed monolayers to regenerate tissue like structures. It the growth and propagation of cell lines in three-dimensional matrix to high cell density that contributes to this. The techniques used in histotypic cultures are:
a) Gel and sponge technique- In this method, the gel (collagen) or sponges (gelatin) are used which provides the matrix for the morphogenesis and cell growth. The cells penetrate these gels and sponges while growing.
b) Hollow fibers technique- In this method, hollow fibers are used which helps in more efficient nutrient and gas exchange. In recent years, perfusion chambers with a bed of plastic capillary fibers have been developed to be used for histotypic type of cultures. The cells get attached to capillary fibers and increase in cell density to form tissue like structures.
c) Spheroids – The re-association of dissociated cultured cells leads to the formation of cluster of cells called spheroids. It is similar to the reassembling of embryonic cells into specialized structures. The principle followed in spheroid cultures is that the cells in heterotypic or homotypic aggregates have the ability to sort themselves out and form groups which form tissue like architecture. However, there is a limitation of diffusion of nutrients and gases in these cultures.
d) Multicellular tumour spheroids- These are used as an in vitro proliferating models for studies on tumour cells. The multicellular tumour spheroids have a three dimensional structure which helps in performing experimental studies related to drug therapy, penetration of drugs besides using them for studying regulation of cell proliferation, immune response, cell death, and invasion and gene therapy. A size bigger than 500 mm leads to the development of necrosis at the centre of the MCTS. The monolayer of cells or aggregated tumour is treated with trypsin to obtain a single cell suspension. The cell suspension is inoculated into the medium in magnetic stirrer flasks or roller tubes. After 3-5 days, aggregates of cells representing spheroids are formed. Spheroid growth is quantified by measuring their diameters regularly. The spheroids are used for many purposes. They are used as models for a vascular tumour growth. They are used to study gene expression in a three-dimensional configuration of cells. They are also used to study the effect of cytotoxic drugs, antibodies, radionucleotides, and the spread of certain diseases like rheumatoid arthritis.
Organotypic cultures
These cultures are used to develop certain tissues or tissue models for example skin equivalents have been created by culturing dermis, epidermis and intervening layer of collagen simultaneously. Similarly models have been developed for prostrate, breast etc. Organotypic culture involves the combination of cells in a specific ratio to create a component of an organ.
CELL AND TISSUE ENGINEERING
Tissue engineering refers to the application of the principles of engineering to cell culture for the construction of functional anatomical units- tissues/organs. The aim of tissue engineering is nothing but to supply the various body parts for the repair or replacement of damaged tissues or organs. It is now possible to grow skin cells, blood cells cardiac cells etc. by using the ability of stem cells to proliferate and differentiate.
During the last decade, the tissue culture work in animals demonstrated that virtually any human tissue or organ can be grown in culture. This became possible only after it became known that the ability of cultured cells to undergo differentiation can be restored. ‘Skin’ was the first organ to be cultured in artificial media and could be successfully used for transplantation following serious skin burns. For past few years some of the biotech companies like ATS (Advanced Tissue Science, USA), Biosurface Technology (BTI, Cambridge) and Organogenesis, are developing artificial skins to the stage of clinical trials.
In the field of tissue replacement, focus of attention is the Artificial cartilage. As it is not vascularized, it is not rejected due to immunogenic response. This will have lots of implications in the treatment of sport related injuries and diseases like arthritis.
Design and engineering of tissues
The design and tissue engineering should essentially cause minimal discomfort to the patient. The damaged tissues should be easily fixed with the desired functions quickly restored. Another important factor controlling the designing of tissue culture is the source of donor cells. The cells from the patient himself, is always preferred as it considerably reduces the immunological complications. However under certain situations allogeneic cells (cells taken from a person other than the patient) are also used. The other important factors are –the support material, it’s degradation products, cell adhesion characteristics etc. It was demonstrated in 1975 that human keratinocytes could be grown in the laboratory in a form suitable for grafting. A continuous sheet of epithelial cells can be grown now however there is still difficult to grow TE skin with the dermal layer with all the blood capillaries, nerves, sweat glands, and other accessory organs.
Some of the implantable skin substitutes which are tissue engineering skin constructs with a limited shelf life of about 5 days are:
a) Integra TM – A bioartificial material composed of collagen-glycosaminoglycan and is mainly used to carry the seeded cells.
b) DermagraftTM- This is composed of poly glycolic acid polymer mesh seeded with human dermal fibroblasts from neonatal foreskins.
c) ApligrafTM- It is constructed by seeding human dermal fibroblasts into collagen gel with the placement of a layer of human keratinocytes on the upper surface.
These tissue constructs integrate into the surrounding normal tissue and form a good skin cover with minimum immunological complications.
The urothelial cells and smooth muscle cells from bladder are now being cultured and attempts are on to construct TE urothelium. Some progress has also been made in the repair of injured peripheral nerves using tissue engineered peripheral nerve implants. The regeneration of the injured nerve occurs from the proximal stump to rejoin at distal stump.
The regeneration process requires substances like-
(a) Conduct material- The conduct material is composed of collagen- glycosaminoglycans, PLGA (poly lactic- co- glycolicacid), hyaluronan and fibronectin and forms the outer layer.
(b) Filling material- The filling material contains collagen, fibrin, fibronectin and agarose. This supports the neural cells for regeneration. and
(c) Additives- A large number of other factors are also added e.g. growth factors, neurotrophic factors such as fibroblast growth factor (FGF), nerve growth factor (NGF).
The other important applications of tissue engineering are in gene therapy, pseudo-organs and as model cell systems for developing new therapeutic approaches to human diseases.The attempts are on to create tissue models in the form of artificial organs using tissue engineering. The artificial liver is being created using hepatocytes cultured as spheroids and held suspended in artificial support system such as porous gelatin sponges, agarose or collagen. Some progress has been made in the area of creating the artificial pancreas using spheroids of insulin secreting cells which have been developed from mouse insulinoma beta cells.
Three dimensional brain cell cultures have been used for the study of neural myelination, neuronal regeneration, and neurotoxicity of lead. The aggregated brain cells are also being used to study Alzheimer’s disease and Parkinson’s disease. Thyroid cell spheroids are being used to study cell adhesion, motility, and thyroid follicle biogenesis. (Table 8.2 page 155, gupta)
TABLE DEPICTING THE TECHNOLOGICAL GOALS AND AREAS OF RESEARCH IN TISSUE ENGINEERING
Growth of cells in three- dimensional systems
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Delivery systems for protein therapeutics
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Cell cultivation methods for culturing ‘recalcitrant cells’
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Expression of transgenic proteins in transplantable cells
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To develop vehicles for delivering transplantable cells
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Development of markers for tracking transplanted cells
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Avoiding immunogenicity in transplantable cells
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Development of in vivo and ex vivo biosensors for monitoring cell
behaviour during tissue production
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BIOETHICS IN ANIMAL GENETIC ENGINEERING
There are some serious issues related to genetic modification of animals using animal genetic engineering techniques. One is not sure of the consequences of these genetic modifications and the further interaction with the environment. Proper clinical trials are also necessary before one can use it for commercial purposes. In the recent past people have raised objections on some of the methods used e.g. the transfer of a human genes into food animals, use of organisms containing human genes as animal feed. Some religious groups have expressed their concern about the transfer of genes from animals whose flesh is forbidden for use as food into the animals that they normally eat. Transfer of animal genes into food plants that may be objectionable to the vegetarians.
Besides this, there are several other aspects of this issue have to be sorted out.
a) What will be the consequences, if a modified animal will breed with other domestic or wild animals thereby transferring the introduced genes to these populations?
b) What are the health risks to human on consumption of genetically modified animals and their products?
c) With the production of disease resistant animals, what will be the effect on ecology?
d) There is also wide spread concern about the risks of human recipients getting infected with animal viral diseases after a xenotransplantation, which might infect the population at large.
e) There are also concerns about the risk that drug resistance gene markers used in genetic engineering procedures might inadvertently be transferred and expressed.
The need of the hour is to formulate clear guidelines which should be followed while using genetic engineering techniques in bio-medical research. e.g. products from transgenic organisms should be clearly marked to give choice to people who follow dietary restrictions due to religious beliefs. In fact all the ethical and moral issues raised by some aspects of biotechnology should be addressed by open discussion and dialogue.
