Gene Therapy Novel Therapeutic Branch of Modern Medicine

by Sudeep Joseph for Future Makers    August 29, 2008

Gene therapy is a novel therapeutic branch of modern medicine. It is a technique for correcting defective genes responsible for disease development. Genes are the basic physical and functional units of heredity. Although genes get a lot of attention, it’s the proteins that perform most life functions and even make up the majority of cellular structures. When genes are altered, the encoded proteins are unable to carry out their normal functions and genetic disorders can result.

In most gene therapy studies, a normal gene is inserted into the genome to replace an abnormal, disease-causing gene either by direct transfer of genes into the patient or by using living cells as vehicles to transport the genes of interest. Direct gene transfer is particularly attractive because of its relative simplicity. In this scenario, genes are delivered directly into a patient’s tissue by packaging them into liposomes or other biological microparticles. The alternative method is packaging the genes into a carrier molecule called a vector to deliver the therapeutic gene to the patient's target cells. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state. The generally used viruses are retroviruses and adenoviruses. Embryonic stem cells that have been explanted, in vitro are manipulated and retransplanted into the same patient or a different patient and they have the ability to contribute to all mature cell types of the recipient for an extended period of time.             Despite promising scientific results with genetically modified stem cells, some major problems remain to be overcome. Although human embryonic stem cells in the culture dish remain remarkably stable, the cells may accumulate genetic and epigenetic changes that might harm the patient. Another issue is patient’s immune system response. Transgenic genes, as well as vectors introducing these genes potentially trigger immune system responses. Current gene therapy is experimental and has not proven very successful in clinical trials. Little progress has been made since the first gene therapy clinical trial began in 1990. In 1999, gene therapy suffered a major setback with the death of 18-year-old Jesse Gelsinger. Jesse was participating in a gene therapy trial for ornithine transcarboxylase deficiency (OTCD). He died from multiple organ failures 4 days after starting the treatment. His death is believed to have been triggered by a severe immune response to the adenovirus carrier.             Another major blow came in January 2003, when the FDA placed a temporary halt on all gene therapy trials using retroviral vectors in blood stem cells. FDA took this action after it learned that a second child treated in a French gene therapy trial had developed a leukemia-like condition. Both this child and another who had developed a similar condition in August 2002 had been successfully treated by gene therapy for X-linked severe combined immunodeficiency disease (X-SCID), also known as "bubble baby syndrome." FDA's Biological Response Modifiers Advisory Committee (BRMAC) met at the end of February 2003 to discuss possible measures that could allow a number of retroviral gene therapy trials for treatment of life-threatening diseases to proceed with appropriate safeguards. In April 2003 the FDA eased the ban on gene therapy trials using retroviral vectors in blood stem cells.             If we are able to overcome all these difficulties, gene therapy will become the most powerful tool to fight against diseases.

This work is licensed under a Creative Commons Attribution 3.0 License.

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