Gene Delivery

Whether given as pills or injections, most conventional drugs simply need to reach a minimal level in the bloodstream in order to be effective. In gene therapy, the drug (DNA) must be delivered to the nucleus of a cell in order to function, and a huge number of individual cells must each receive the DNA in order for the treatment to be effective. The situation is further complicated by the fact that a given gene may normally function in only a ectopic ^ expression small portion of the cells in the body, and ectopic expression may be toxic.

Thus, successful gene therapy often requires highly efficient delivery of expression of a gene in the wrong cells or tissues DNA to a very restricted population of cells within the body.

In 1999 doctors at the Ohio State University Medical Center prepare a gene therapy injection for 36-year-old Donovan Decker. He is the first patient to ever receive gene therapy for muscular dystrophy.

To achieve these goals, many researchers have turned to viruses. Viruses are parasites that normally reproduce by infecting individual cells in the human body, delivering their DNA to the nucleus of those cells. Once there, the viral DNA takes over the cell, converting it to a factory to make more viruses. The cell eventually dies, releasing more viruses to continue the cycle. Scientists can remove or disable some of the genetic material of the virus, making it unable to reproduce outside of the laboratory. This genetic material can then be replaced by the gene needed to treat a patient. The modified (or recombinant) virus can then be administered to the patient, where it will carry the therapeutic gene into the target cells. In this way, scientists can take advantage of the virus's ability, gained over millions of years of evolution, to deliver DNA to cells with tremendous efficiency. One of the most commonly used is a cold virus called adenovirus. Recombinant adenoviruses have been used in experimental gene therapy for muscle diseases, and can deliver genes to almost all of the cells in a small region surrounding the site of injection. Unfortunately, while adenoviruses excel at gene delivery, evolution is a double-edged sword, and the many mechanisms our own bodies have evolved to combat harmful viral infections are also used against therapeutic viruses, as will be discussed in more detail below.

Recombinant adenoviruses cannot be used to transfer DNA to all cell types, because they cannot reproduce themselves outside of the laboratory.

In 1999 doctors at the Ohio State University Medical Center prepare a gene therapy injection for 36-year-old Donovan Decker. He is the first patient to ever receive gene therapy for muscular dystrophy.

In April 2002 researchers announced that ex vivo gene therapy for severe combined immunodeficiency had been successful in five boys for up to 2.5 years.

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