Genetics and Gene therapy

A brief history of gene therapy

This is probably one of the wonders of science and genetics precisely. Although a genetic disorder cannot be completely cured but gene therapy can modify 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 thalassemia ( 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.

Table of Contents

1. A brief history of gene therapy

2. What is gene therapy?

3. Gene therapy by using vectors

4. Method of injection

5. Associated risks of gene therapy

 

What is gene therapy?

Conventionally, gene therapy was all about fixing the genetic problem at its source. In gene therapy, polymers are either translated into proteins that will interfere with target gene expression so that they can be made error-free or possibly that corrects genetic mutations. On a simplistic mode, the gene therapy is nothing but replacing a mutant gene with a normal gene instead of fixing the one with issues. Such genes are cultured outside by using recombinant technology. The cultured gene is a polymer molecule that is packaged safely within a "vector", which will transfer the molecule inside the target cells. Since 2006, there has been an array of successful therapies that have gained popularity and India being one of the leading treatment centres for genetic illnesses. Some of the examples of genetic therapies being conducted in the past are 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 of 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, instead, a vector or mediator can be used certain viruses are often used as vectors because they can deliver the new gene by infecting the cell. .The viral vectors can be Retrovirus, Lentivirus, Herpes virus, Adenovirus plasmid etc.  In addition to the viruses, stem cells and liposomes also. At first, these viruses are modified in such a way that they can't affect the host body but they can just deliver the genome to the target cells. DNA of the vector cell is being used to integrate the artificially made genome, 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 contamination.

 

Method of injection

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.

Gene therapy by adenovirus-image from US National library

 

Associated 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.





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