Objective:
Gene Therapy is one of the upcoming targeted treatment options. An attempt to understand the methodology for this therapy, look at the progress made/success stories, road blocks and future potential of this therapy option for patients.
Background:
In 1990, the first human gene therapy experiment was conducted on four year-old Ashanti Desilva who suffered from adenosine deaminase (ADA) deficiency. Though a complete cure was not obtained it did correct the deficiency with reduction in expensive treatment costs. In 1999, 18 year-old Jesse Gelsinger suffering from OTC disease (ornithine transcarboxylase deficiency), was the first reported death to be directly caused by gene therapy treatment. 1
Gene therapy has come a long way with
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In Somatic gene therapy inserted genetic material to the target cells, does not pass on the change to the next generation. In comparison the opposite is true for Germ line gene therapy. Due to this evident difference, current regulations allows gene therapy only on somatic cells.1 There are two lines of treatment applications for gene therapy, one for the treatment of genetic diseases and the other for non-genetic and polygenic disorders.3
Two different approaches to administer gene therapy to patients exist. “In vivo” which involves a therapeutic gene being administered directly via a vector into the tissue of the patient. This vector interacts with the target protein to produce the required therapeutic protein. The second approach is the “ex vivo” gene therapy, specific cells are isolated and purified from a patient, the vector is introduced following which these genetically modified cells are re-infused.
Vectors in Gene Therapy
The Vector, hence is a key delivery medium for gene therapy. A vector can be described as a system fulfilling several functions,
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Viruses are therefore employed as a medium to deliver the required gene with high efficiency into the target cells. Viral vectors are engineered using sophisticated methods such that the unwanted genes responsible for replication, assembling, or infection are replaced by the therapeutic gene. Current Viral vectors can further be categorized into, Non-lytic viruses, retroviruses and lentiviruses, produce virions from the cellular membrane of an infected cell, leaving the host cell relatively intact and Lytic viruses, human adenovirus and herpes simplex virus families, destroy the infected cell after replication and virion