Gene Therapy Glossary

Cancer is responsible for the death of millions of people on a worldwide basis. Gene therapy, the deliberate manipulation of genes, (replace bad disease causing genes with good ones) may some day be able to treat and cure cancer, as well as other diseases such as Alzheimer's and Parkinson's. To fully understand gene therapy it is necessary to master the basic terminology associated with it. Let's review the main concepts of gene therapy.

Vectors

The idea behind gene therapy is, in many cases, to introduce working genes into malfunctioning cells to repair the damage being caused by a faulty gene. To do this the new gene should be inserted into target cells to do its job. Any agent that carries a modified gene is called a vector. Viruses and small pieces of DNA can function as vectors if they carry therapeutic genes into host cells.

Naked DNA

This is, perhaps, the simplest vector that can be used therapeutically. Naked DNA is called naked because it is free of proteins (histones) that normally are associated with the genetic molecule. Thus, naked DNA has the advantage of provoking smaller immune reactions by the individual when the DNA fragment is introduced into the patient's body.

Oligonucleotides

These are synthetic portions of DNA created to aid gene therapy applications. A synthetic oligonucleotide can be used to inactivate the expression of mutated genes involved in a disease. For example, by using two antisense small nucleotides (22 and 18 bases) scientists were able to inhibit the replication of the hepatitis C virus. The same approach can successfully be used to inhibit an oncogene, that is a cancer-promoting gene.

Lipoplexes

The use of naked DNA, although simple in design, has a huge drawback. It is very difficult to deliver the molecule to the target cell because the DNA has to go through different body fluids and structures where it could be destroyed (since it is seen as foreign material, an invader). To partially solve this problem, a lipoplex structure could be assembled to protect DNA molecules. A lipoplex is, basically a bio-capsule made of lipids.

Somatic Gene Therapy

In somatic gene therapy, a new therapeutic gene is introduced, using a vector, into somatic diseased cells of a patient. Somatic cells are those cells NOT involved in the reproduction of an individual. Any cell of the body is a somatic cell except eggs in women and sperm in men. The results of a somatic cell gene therapy is restricted only to the individual being treated and not to his or her offspring.

Germline Gene Therapy

Contrary to somatic gene therapy, sperm or egg cells could be targeted for the introduction of new functional (working) genes. Thus, using germline therapy it would be possible, at least theoretically, to pass on genetic modifications to the next generation, to ensure that they would not succumb to a particular genetic disease that may have blighted a family. The use of germline genetic therapies is hugely controversial, and at this time research in humans in this area is prohibited and illegal in most countries.