my project on GENE THERAPY

GENE THERAPY_________________________________________
GENE THERAPY

Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease.
Gene therapy is an experimental technique that uses genes to treat or prevent disease. In the future, this technique may allow doctors to treat a disorder by inserting a gene into a patient’s cells instead of using drugs or surgery.
It is a technique for correcting defective genes that are responsible for disease development. The most common form of gene therapy involves the insertion of functional genes into an unspecified genomic location in order to replace a mutatedgene, but other forms involve directly correcting the mutation or modifying normal gene that enables a viral infection. Although the technology is still in its infancy, it has been used with some success.

APPROACHES OF GENE THERAPY

• Replacing a mutated gene that causes disease with a healthy copy of the gene.
• Inactivating, or “knocking out,” a mutated gene that is functioning improperly.
• Introducing a new gene into the body to help fight a disease.

TYPES OF GENE THERAPY_______________________________
Gene therapy may be classified into the two following types:
Germ line gene therapy
In the case of germ line gene therapy, germ cells, i.e., sperm or eggs are modified by the introduction of functional genes, which are integrated into their genomes. Therefore, the change due to therapy would be heritable and would be passed on to later generations. This new approach, theoretically, should be highly effective in counteracting genetic disorders and hereditary diseases. However, many jurisdictions prohibit this for application in human beings, at least for the present, for a variety of technical and ethical reasons.
Somatic gene therapy
In the case of somatic gene therapy, the therapeutic genes are transferred into the somatic cells of a patient. Any modifications and effects will be restricted to the individual patient only, and will not be inherited by the patient's offspring or later generations.
Somatic cells are non-reproductive. Somatic cell therapy is viewed as a more conservative, safer approach because it affects only the targeted cells in the patient, and is not passed on to future generations. In other words, the therapeutic effect ends with the individual who receives the therapy. This type of therapy presents unique problems of its own. Often the effects of somatic cell therapy are short-lived. Because the cells of most tissues ultimately die and are replaced by new cells, repeated treatments over the course of the individual's life span are required to maintain the therapeutic effect. Transporting the gene to the target cells or tissue is also problematic.
Regardless of these difficulties, however, somatic cell gene therapy is appropriate and acceptable for many disorders, including cystic fibrosis, muscular dystrophy, cancer, and certain infectious diseases. Clinicians can even perform this therapy in utero, potentially correcting or treating a life-threatening disorder that may significantly impair a baby's health or development if not treated before birth.


CATEGORIES OF SOMATIC GENE THERAPY________________________
Somatic gene therapy can be broadly split into two categories:

EX VIVO TECHNIQUE
Ex vivo, which means exterior (where cells are modified outside the body and then transplanted back in again). In some gene therapy clinical trials, cells from the patient’s blood or bone marrow are removed and grown in the laboratory. The cells are exposed to the virus that is carrying the desired gene. The virus enters the cells and inserts the desired gene into the cells’ DNA. The cells grow in the laboratory and are then returned to the patient by injection into a vein. This type of gene therapy is called ex vivo because the cells are treated outside the body.
IN VIVO TECHNIQUE
In vivo, which means interior (where genes are changed in cells still in the body). This form of gene therapy is called in vivo, because the gene is transferred to cells inside the patient’s body.


Uses of gene therapy
Gene therapy is being used in many ways. For example, to:
• Replace missing or defective genes;
• Deliver genes that speed the destruction of cancer cells;
• Supply genes that cause cancer cells to revert back to normal cells;
• Deliver bacterial or viral genes as a form of vaccination;
• Provide genes that promote or impede the growth of new tissue; and;
• Deliver genes that stimulate the healing of damaged tissue.
A large variety of genes are now being tested for use in gene therapy.
Examples : a gene for the treatment of cystic fibrosis (a gene called CFTR that regulates chloride); genes for factors VIII and IX, deficiency of which is responsible for classic hemophilia (hemophilia A) and another form of hemophilia (hemophilia B), respectively; genes called E1A and P53 that cause cancer cells to undergo cell death or revert to normal; AC6 gene which increases the ability of the heart to contract and may help in heart failure; and VEGF, a gene that induces the growth of new blood vessels (angiogenesis) of use in blood vessel disease.
A short synthetic piece of DNA (called an oligonucleotide) is being used by researchers to "pre-treat" veins used as grafts for heart bypass surgery. The piece of DNA seems to switch off certain genes in the grafted veins to prevent their cells from dividing and thereby prevent atherosclerosis.
Delivery of genes into cells
Genes can be carried into cells by viruses. Viral vectors or carriers take advantage of the natural ability of a virus to enter a cell and deliver genetic material to the nucleus of the cell that contains its DNA. In developing virus carriers, the DNA coding for some or all of the normal genes of the virus to be used as a carrier are removed and replaced with a treatment gene. Most of these virus carriers are engineered so that they are able to enter cells, but they cannot reproduce themselves and so are innocuous.
Genes can also be delivered within tiny synthetic "envelopes" of fat molecules. Cell membranes contain a very high concentration of fat molecules. The fat molecule "envelope" can carry the therapeutic gene into the cell by being admitted through the cell membrane as if it were one of its own molecules.
Genes can also gain entrance into cells when an electrical charge is applied to the cell to create tiny openings in the membrane that surrounds a cell. This technique is called electroporation.
Route of administration of gene therapy
The choice of route for gene therapy depends on the tissue to be treated and the mechanism by which the therapeutic gene exerts its effect. Gene therapy for cystic fibrosis, a disease which effects cells within the lung and airway, may be inhaled. Most genes designed to treat cancer are injected directly into the tumor. Proteins such as factor VIII or IX for hemophilia are also being introduced directly into target tissue (the liver).




PROBLEMS OF GENE THERAPY____________________________
Some of the problems of gene therapy include:
• Short-lived nature of gene therapy – Before gene therapy can become a permanent cure for any condition, the therapeutic DNA introduced into target cells must remain functional and the cells containing the therapeutic DNA must be long-lived and stable. Problems with integrating therapeutic DNA into the genome and the rapidly dividing nature of many cells prevent gene therapy from achieving any long-term benefits. Patients will have to undergo multiple rounds of gene therapy.
• Immune response – Anytime a foreign object is introduced into human tissues, the immune system has evolved to attack the invader. The risk of stimulating the immune system in a way that reduces gene therapy effectiveness is always a possibility. Furthermore, the immune system's enhanced response to invaders that it has seen before makes it difficult for gene therapy to be repeated in patients.
• Problems with viral vectors – Viruses, the carrier of choice in most gene therapy studies, present a variety of potential problems to the patient —toxicity, immune and inflammatory responses, and gene control and targeting issues. In addition, there is always the fear that the viral vector, once inside the patient, may recover its ability to cause disease.
• Multigene disorders – Conditions or disorders that arise from mutations in a single gene are the best candidates for gene therapy. Unfortunately, some of the most commonly occurring disorders, such as heart disease, high blood pressure, Alzheimer's disease, arthritis, and diabetes, are caused by the combined effects of variations in many genes. Multigene or multifactorial disorders such as these would be especially difficult to treat effectively using gene therapy.
• Chance of inducing a tumor (insertional mutagenesis) - If the DNA is integrated in the wrong place in the genome, for example in a tumor suppressor gene, it could induce a tumor. This has occurred in clinical trials for X-linked severe combined immunodeficiency (X-SCID) patients, in which hematopoietic stem cells were transduced with a corrective transgene using a retrovirus, and this led to the development of T cell leukemia in 3 of 20 patients.

APPLICATIONS OF GENE THERAPY________________________
A "bionic chip"
A new "bionic chip" has been developed to help gene therapists using electroporation to slip fragments of DNA into cells. Electroporation was originally a hit-or-miss technique because there was no way to determine how much of an electrical jolt it took to open the cell membrane.
The "bionic chip" solves this problem. It contains a single living cell embedded in a tiny silicon circuit. The cell acts as a diode, or electrical gate. When it is hit with just the right charge, the cell membrane opens, allowing the electricity to pass from the top to the bottom of the bionic chip. By recording what voltage caused this phenomenon to occur, it is now posssible to determine precisely how much electricity it takes to pry open different types of cells.

GENE THERAPY IN FUTURE______________________________
The potential of gene therapy is great but, compared to its promise, the results to date are still quite limited. However, the benefits of gene therapy are believed to be on the near horizon. Gene therapy is one of the hottest areas of medical research today.
The remarkable advances in genetics, including the human genome project, have opened new doors for the exploration of gene therapy. New technologies are needed to speed the progress of gene therapy. As these new technologies such as the "bionic chip" arrive, we believe that, without a doubt, gene therapy will play an increasingly important and prominent part in medicine in the decades to come.