Human gene therapy is one of the methods to manipulate the inside genetic material in humans for therapeutic use. It is a technique for repairing defective genes responsible for disease development.
The primary effort to change human DNA was done by Martin Cline in 1980, however, the first successful nuclear gene transfer in humans approved by the National Institutes of health was acted in May 1989.
1960: The idea of gene therapy was popularised.
1970: The author Friedman and Roblin penned down a paper in science termed “Gene Therapy for human genetic disease”.
1984: A retrovirus vector system was originated that could efficiently place foreign genes into mammalian chromosomes.
- The first therapy approved in the US took place on 14 September 1990 at the National Institutes of Health (NIH) under the guidance of William French Anderson.
- A four-year-old girl, Ashanti Desilva. She was the first girl to receive the treatment for a genetic defect that left her with ADA-SCID, a severe immune system deficiency.
- This new method has the power to treat the blood disorders like Thalassemia, Cystic Fibrosis, and some cancers.
- Through this technique, sickle cell disease is successfully treated in mice
1992: The first method of gene therapy using hematopoietic stem cells as vectors to deliver genes intended to correct hereditary diseases was done by Dr Claudio Bordignon.
1999: The death of Jesse Gelsinger has taken place in a gene therapy experiment.
2006: Metastatic Melanoma was successfully treated in two patients by the scientists at the National Institutes of Health(Bethesda, Maryland) which concludes that gene therapy can be used for the treatment of cancer patients.
2007-2011: The no of diseases for successful treatment by gene therapy is increasing i.e. Retinal disease, colour blindness, Adrenoleukodystrophy.
2011: A man suffering from HIV is cured by using gene therapy.
Types of Gene Therapy
Germline therapy includes the therapeutic genes transferred into the germ cells. This involves modification into egg cells or sperms and that is why it is passed onto the next generations. Some of the countries like Australia, Canada, Germany, Israel, Switzerland and the Netherlands doesn’t allow the use of germline therapy due to fear of the unknown dangers of this treatment and whether it brings out any drawn-out impacts in people in the future. This treatment is also additionally incredibly costly which also restricts its practical use.
Somatic Gene Therapy
In this type of therapy, therapeutical cells are transferred into somatic cells i.e. blood cells, bone marrow cells, liver cells, skin cells etc. As somatic cells are not transferred onto the next generation that’s why the effects of therapy are not passed to the next generation. This is one of the best and most secure methods of gene therapy.
Somatic gene cell therapy is divided into two classifications:
Ex vivo– It means cells are operated on outside the body and then they are transplanted back. Cells from the patient’s blood or bone marrow are taken out and treated in the laboratory. The cells are presented to the virus that is conveying the desired gene. The virus enters the cell and supplements the ideal quality into the cells DNA. The cells develop in the laboratory and are then get back to the patient by infusion into a vein.
In vivo – In this type genes are treated inside the person’s body. Genes are changed in cells when the cells are still in the body.
VIRUSES – Genetic material is introduced in the host as a part of replication by the viruses. It removes the viral DNA and uses the virus as a vehicle to deliver the therapeutic DNA. The viruses used are altered to make them safe although there is some risk still exist with the gene therapy.
The types of viral vectors involved which are used for human gene therapy are:
- Adeno- associated virus
- Herpes simplex virus
NON VIRAL VECTOR SYSTEM
- PURE DNA CONSTRUCT –
- Direct introduction of pure DNA constructs into target issue.
- The efficiency of DNA uptake by cells and expression rather low.
- Consequently, large quantities of DNA has to be injected periodically.
- LIPOPLEXES –
- Lipid DNA complexes
- DNA construct encompassed by false lipid layer.
- Most of it gets degraded by lysosomes.
- DNA MOLECULAR CONJUGATES –
- The commonly used synthetic conjugate is poly – L- lysine bound to a specific target receptor cell.
- Therapeutic DNA is then made to consolidate with the form to shape a complex.
- It avoids the lysosomal breakdown of DNA.
- HUMAN ARTIFICIAL CHROMOSOME –
- Can carry a large DNA i.e. with one or more therapeutic genes with regulatory elements.
Applications of Gene Therapy
- It is utilized in the substitution of qualities that cause clinical infirmity.
- This technique usually destroys the problem causing genes.
- It assists the body with battling against infections by adding genes to the human body.
- This technique is utilized to treat infections like cancer, ADA lack, cystic fibrosis, and so forth.