To treat with gene therapy, doctors have to know about the genetics of that disease. That is which gene is mutated or altered or missing, in order to induce a disease or disorder in an individual. At present we know very little about the gene mutations involved in many diseases like cancer, neurological disorders or autoimmune disease. But researches in this area are at a very rapid speed; hence knowledge of genetics of these diseases is also improving at a rapid pace.
Techniques for getting genes into the cell:
Getting the functional genes into the target cell is main obstacle faced in the gene therapy technique. Two main types of techniques are used known as in vivo technique and ex vivo technique.
In vivo Technique:
In this method functional copy of gene is introduced into the target cell using some vectors. One of the main disadvantages of this technique is that the genes may have to be taken up by the target cell, for example cancer cells, to be effective against the disease. This may be a problem to reach interior body cells, which have been affected by mutated forms of gene.
Ex vivo Technique:
In ex vivo approach effected body cells are extracted from the patient's body and mutated forms of genes which are present in these cells are replaced by the functional gene in the laboratory and then they are put back into patient's body.
This technique can be used to activate the immune system of the body. For example, immune cells can be removed from the bone marrow or blood, and genes are added in the lab. These genes help immune system to find and kill diseased cells. Same technique can be used to treat cancer in humans.
Vectors Used to Transfer Genes into Target Cell:
Genes or small strands of DNA are very difficult to get inserted into the target cell. Injecting many copies of the genes directly into the body will get destroyed before it reaches the cytoplasm not even the nucleus of the cell. For this reasons vectors or carriers of genes are used to get genes into the target cells of the body.
Viruses have the capacity to introduce their gene into the genome of the host. Therefore viruses are used as vectors to carry and insert the functional gene into the target cell. Many kinds of viruses are host specific and also cell type specific, hence by using the genetic engineering technique viruses can be modified and directed into the particular type of cells in the body.
Viruses which are fairly stable inside the host body and also non-virulent form of virus are used for this purpose. Using genetic engineering technique virulent genes are removed from the viral genome and functional gene is added to the viral genome. These modified forms of virus are injected into the patient body, and viruses infect the target cells and insert the gene into the target cell nucleus.
Viral vector has got some disadvantages, such as viruses may trigger some allergy or some reactions as immune system recognise them as foreign body. Another main problem is that we cannot control the position of gene insertion in the host genome. That is insertion of gene is random, this may lead to some kind of mutation if gene is inserted in between a gene.
Liposomes are hollow cells made up of fat molecules. These hollow cells are formed in the lab around plasmids; plasmids are double stranded circular DNA which also contains gene of interest or functional form of gene. Liposomes are injected into the body, are taken up by the cell membrane, emptying the DNA into the cell.
Liposomes most of the times do not induce immune response in the patient. When compared with other vectors liposomes can be used to transfer larger genes into the host.Liposomes can be constructed to target particular type of cells.
But major limitation of this technique is liposomes cannot insert the DNA directly into the genome of the target cell.
By improving the gene delivery system techniques, gene therapy can be used to treat many types of genetic diseases.
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