Ans. 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.
Fig showing the production of t-PA
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 197, 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. CD 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 CD surface antigen of T-cells is called OKT i.e. anti-CD Moab. OKT is a monoclonal antibody which has been licensed for clinical use for the treatment of acute renal allograft rejection. OKT 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.