Genetics and Gene therapy

A brief history of gene therapy

Gene therapy is probably one of the wonders of genetic science. Although, a genetic disorder cannot be completely cured but gene therapy can modify the condition by reducimg its seriousness and the consequences. The first attempt of genetic therapy was done by Martin Cline but found to be unsuccessful while he experimented with one of his patients to treat thalassaemia ( a blood disorder).  On 14th of September 1990, when Ashi De-Silva was treated for ADA dependent SCID(Adenosine deaminase deficiency dependent  Severe combined immunodeficiency).  But the first somatic treatment that led to a permanent genetic change was noticed in the year 1993 where the therapy was aimed at curing malignant brain tumours by using recombinant DNA. Gene therapy has successfully treated many conditions in the past such as severe combined immune deficiency, haemophilia,  blindness caused by retinitis pigmentosa and leukaemia.

 

What is gene therapy?

Conventionally, gene therapy was all about fixing the genetic problem at its source where the polymers are translated into proteins to interfere with target gene expression, as a result, error-free genes are produced. But the modern gene therapy is all about replacing a mutant gene by a normal gene instead of fixing a gene with the error. The required genes are cultured in the laboratory with the help of recombinant technology. The newly cultured gene is a polymer packaged safely within a "vector", which will later transfer the molecule inside the target cells. 

 

Approaches to gene therapy 

Since 2006, there have been an array of successful genetic therapies gained their popularity in India. Some of the examples of genetic therapies being conducted in the past are the treatments against chronic lymphocytic leukaemia (CLL), acute lymphocytic leukaemia (ALL), multiple myeloma, haemophilia, Parkinson’s disease, retinal diseases, X-linked SCID, ADA-SCID, and adrenoleukodystrophy. Two major approaches towards gene therapy are either replace the defective gene or correct the defect. Depending upon which types of cells are to be treated, 2 types of gene therapy are, somatic gene therapy and germ-line gene therapy. Somatic therapy is the transfer of a section of recombinant DNA to any cell of the somatic part (body part other than sexual part) whereas germ-line gene therapy is the transfer of a section of recombinant DNA to cells that produce eggs or sperm.

 

Gene therapy by using vectors

A gene cannot be inserted directly to the defective place. Some of the viruses can be used as a vector or mediator that can help in transferring the cultured, DNA from the laboratory setup to the host. The viral vectors can be Retrovirus, Lentivirus, Herpes virus, Adenovirus plasmid etc.  In addition to the viruses, stem cells and liposomes are also a popular way of gene transfer.  DNA of the vector cell is being used to integrate the artificially made genome with the host.  As a general rule whole DNA is not going to be inserted into the target cell, instead only the genome is pushed in order to prevent the contamination of host.

 

Method of injection

A sample of the patient's cells can be collected and cultured inside the viral RNA. The vector is injected by the intravenous route with the help of a probe directly into a specific tissue or the target cell. Before injecting, the virus must be packed in a vesicle that can break to form pentons while the acidity level is raised inside the target cell. Below is the image showing the example of Gene therapy using adenovirus.

 

Gene therapy by adenovirus-image from US National library

 

Risks of gene therapy

A sample of the patient's cells can be collected exposed to the vector in a laboratory setting to identify any unavoidable reactions and compatibility. The vector is injected by the intravenous route by using a probe directly into a specific tissue or the target cell. Below is the image showing the example of Gene therapy using adenovirus.Want to participate in a quiz on Genetics ? Here it is.

 

Questions

  1. What is gene therapy? Name some diseases that have been treated sucesfully by gene therapy.
  2. What are the risks of gene therapy?
  3. Explain about th egene therapy using adenovirus.



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