Gene Therapy,Gene Augmentation Model,Gene Correction,Embryo Therapy,Patient Therapy

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Home >> Biotechnology in Medicine >> Gene Therapy

	Gene Therapy - Gene therapy. If a child or an embryo (fetus) is diagnosed to carry a defective gene leading to disability, one may like to correct this defect by any of the following three methods: (i) by replacement of defective gene with a normal gene; (ii) by correcting the defective gene through gene targeting or (iii) by gene augmentation either through increasing the number of copies of the gene or through a higher level of expression of the introduced gene.
Such a correction of a genetic defect is described as gene therapy. There is no knowledge at present, how a defective gene can be replaced by a functional gene, but techniques are available either for targeted gene modification leading to gene correction or for gene augmentation by ,introducing normal foreign gene sequences. Several reports are now available where targeted gene modification has been demonstrated in mammalian systems. In most of these cases, genes have been introduced by any of the traditional gene transfer methods including calcium phosphate mediated transfection, electroporation, or microinjection
This will be followed by site specific mutations as demonstrated for the IJGPRT ( hypoxanthine-guanine phosphoribosyl transferase) locus and int-2 loci in mouse embryonal stem cells. Therefore, there is a hope that in due course of time, gene correction will be possible by site specific mutagenesis. More important than the above gene correction method is the gene augmentation method, where normal foreign gene sequences for the defective gene are introduced. A number of efficient methods for this purpose are already available, where a number of copies of the desired gene are introduced in the .cell and are made to express at high level.
Expression and transfer vectors, in the form of a number of viruses are. now available to achieve this goal. In view of this, maximum progress in the area of gene therapy has been achieved through the above gene augmentation model involving vector mediated DNA delivery system. Once the gene correction or gene augmentation has been achieved at the cellular level (in the cells obtained from the affected organ depending upon the disease), the modified cells can be implanted into a suitable region either in an organ of the patient or in the embryo.
	Direct delivery of the DNA (carried by the vector) into the living cells of the body has also been suggested in several cases, so that both in vitro and in vivo introduction of corrected gene has been suggested. Therefore, gene therapy can be used at two different levels: (i) embryo therapy, in which the genetic constitution of embryo at the post zygotic level is altered, so that the inheritance will also be altered, and (ii) patient therapy, in which cells with healthy gene may be introduced in the affected tissue, so that the healthy gene overcomes the defect without affecting the inheritance of the patient. It is believed that in future, gene therapy of both types will be possible.

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