What is gene therapy?

Gene therapy introduces a normal gene into an individual’s genome to repair a mutation that causes a genetic disease. Prerequisites include a delivery system (often a virus), demonstration that the transferred gene can express itself in the host cell, and proof that the procedure is safe. There are two approaches to gene therapy: * Somatic cell gene therapy, which reverses disease symptoms in the treated individual, but the modification is not passed on to the next generation. * Germline gene therapy, which places corrected cells inside the germ line so that those cells will undergo meiosis and provide a normal gametic contribution to the next generation. Germline gene therapy has been achieved experimentally in animals but not in humans.

How does gene therapy work in the human body?

Gene therapy introduces normal genes into the body to repair mutations that cause genetic diseases. This process often involves a viral vector to deliver the therapeutic gene to the host cell. If the normal gene replaces the mutant allele, the transformed cells may proliferate and produce enough normal gene product to restore the body to an undiseased state. Gene therapy has been explored for diseases like cystic fibrosis, cancer, and severe combined immunodeficiency syndrome (SCID). There are two types of gene therapy: somatic and germline. Somatic cell gene therapy reverses disease symptoms in the treated individual, but the changes aren't passed to future generations. Germline gene therapy, which aims to correct cells in the germ line, has been achieved experimentally in animals but not humans.

What kinds of diseases can gene therapy help treat?

Gene therapy has been explored as a treatment option for several diseases, including cystic fibrosis , severe combined immunodeficiency (SCID) , and cancer . Gene therapy introduces a normal gene into an individual’s genome to repair a mutation that causes a genetic disease. For example, a normal beta-globin gene may be introduced into the DNA of bone marrow-derived hematopoietic stem cells from a patient with sickle cell anemia; introduction of these GM cells into the patient could cure the disease without the need for a matched donor.

How are genes delivered into a patient's cells during gene therapy?

During gene therapy , genes are often delivered into a patient's cells using a viral vector , which is a virus that has been modified to transport and deliver specific genetic material of interest. Different types of viruses, such as adenoviruses and adeno-associated viruses, can be used as vectors. These vectors either integrate into the host cell's DNA or temporarily express the genes they carry within the cells. The selection of a vector depends on factors such as gene expression efficiency, ease of generation, stability, and potential toxicity. A major focus of gene therapy is developing an effective gene delivery system to overcome obstacles to cellular uptake of the viral vector.

What are some challenges or risks of gene therapy?

Gene therapy faces several challenges and risks, including ethical and safety concerns regarding genetic manipulation, embryonic tissue research, and human experimentation. A significant risk involves the delivery system, often a viral vector, which may not effectively reach cells or express genes. Clinical trials have revealed potential dangers, such as immune responses and the development of leukemia-like illnesses. There are also concerns that gene therapy could lead to eugenics, aiming to improve future generations through the selection of desired traits. The advent of targeted therapy marked a shift toward more advanced therapeutic strategies for cancer that offer enhanced precision, leading to greater effectiveness and fewer harmful side effects relative to conventional chemotherapy.

How might gene therapy change medicine in the future?

Gene therapy holds promise for revolutionizing medicine by treating diseases at their genetic roots. It involves introducing normal genes into a patient's genome to repair mutations that cause genetic diseases such as cystic fibrosis and SCID . Gene therapy may reverse disease symptoms in treated individuals, but these modifications are not passed to future generations. While gene therapy presents potential benefits, there are also safety and ethical concerns, including the possibility of immune responses andinsertional mutagenesis. However, nanotechnology is helping to develop improved gene therapy systems, such as nanoparticles that target and kill cancer cells without harming healthy cells.

gene therapy

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gene therapy summary

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Also called:: gene transfer therapy

Key People:: Fred H. Gage

Related Topics:: therapeutics; human genetic disease; gene doping; genetic disease

On the Web:: National Center for Biotechnology Information - PubMed Central - Gene therapy: advances, challenges and perspectives (Oct. 28, 2026)

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gene therapy

medicine

Also known as: gene transfer therapy, genetic modification

Written by

Anthony J.F. GriffithsAll

Fact-checked by

Britannica Editors

Last updated

Oct. 28, 2026 •History

Top Questions

What is gene therapy?
Gene therapy introduces a normal gene into an individual’s genome to repair a mutation that causes a genetic disease. Prerequisites include a delivery system (often a virus), demonstration that the transferred gene can express itself in the host cell, and proof that the procedure is safe.

There are two approaches to gene therapy:
* Somatic cell gene therapy, which reverses disease symptoms in the treated individual, but the modification is not passed on to the next generation.
* Germline gene therapy, which places corrected cells inside the germ line so that those cells will undergo meiosis and provide a normal gametic contribution to the next generation. Germline gene therapy has been achieved experimentally in animals but not in humans.
2 Britannica Sources
1. gene therapy: Ethical and safety concerns
2. recombinant DNA: Gene therapy
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does gene therapy work in the human body?
Gene therapy introduces normal genes into the body to repair mutations that cause genetic diseases. This process often involves a viral vector to deliver the therapeutic gene to the host cell. If the normal gene replaces the mutant allele, the transformed cells may proliferate and produce enough normal gene product to restore the body to an undiseased state. Gene therapy has been explored for diseases like cystic fibrosis, cancer, and severe combined immunodeficiency syndrome (SCID).

There are two types of gene therapy: somatic and germline. Somatic cell gene therapy reverses disease symptoms in the treated individual, but the changes aren't passed to future generations. Germline gene therapy, which aims to correct cells in the germ line, has been achieved experimentally in animals but not humans.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What kinds of diseases can gene therapy help treat?
Gene therapy has been explored as a treatment option for several diseases, including cystic fibrosis, severe combined immunodeficiency (SCID), and cancer. Gene therapy introduces a normal gene into an individual’s genome to repair a mutation that causes a genetic disease. For example, a normal beta-globin gene may be introduced into the DNA of bone marrow-derived hematopoietic stem cells from a patient with sickle cell anemia; introduction of these GM cells into the patient could cure the disease without the need for a matched donor.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are genes delivered into a patient's cells during gene therapy?
During gene therapy, genes are often delivered into a patient's cells using a viral vector, which is a virus that has been modified to transport and deliver specific genetic material of interest. Different types of viruses, such as adenoviruses and adeno-associated viruses, can be used as vectors. These vectors either integrate into the host cell's DNA or temporarily express the genes they carry within the cells.

The selection of a vector depends on factors such as gene expression efficiency, ease of generation, stability, and potential toxicity. A major focus of gene therapy is developing an effective gene delivery system to overcome obstacles to cellular uptake of the viral vector.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some challenges or risks of gene therapy?
Gene therapy faces several challenges and risks, including ethical and safety concerns regarding genetic manipulation, embryonic tissue research, and human experimentation. A significant risk involves the delivery system, often a viral vector, which may not effectively reach cells or express genes.

Clinical trials have revealed potential dangers, such as immune responses and the development of leukemia-like illnesses. There are also concerns that gene therapy could lead to eugenics, aiming to improve future generations through the selection of desired traits. The advent of targeted therapy marked a shift toward more advanced therapeutic strategies for cancer that offer enhanced precision, leading to greater effectiveness and fewer harmful side effects relative to conventional chemotherapy.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How might gene therapy change medicine in the future?
Gene therapy holds promise for revolutionizing medicine by treating diseases at their genetic roots. It involves introducing normal genes into a patient's genome to repair mutations that cause genetic diseases such as cystic fibrosis and SCID. Gene therapy may reverse disease symptoms in treated individuals, but these modifications are not passed to future generations.

While gene therapy presents potential benefits, there are also safety and ethical concerns, including the possibility of immune responses andinsertional mutagenesis. However, nanotechnology is helping to develop improved gene therapy systems, such as nanoparticles that target and kill cancer cells without harming healthy cells.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

gene therapy, introduction of a normal gene into an individual’s genome in order to repair a mutation that causes a genetic disease. When a normal gene is inserted into the nucleus of a mutant cell, the gene most likely will integrate into a chromosomal site different from the defective allele; although that may repair the mutation, a new mutation may result if the normal gene integrates into another functional gene. If the normal gene replaces the mutant allele, there is a chance that the transformed cells will proliferate and produce enough normal gene product for the entire body to be restored to the undiseased phenotype.

Approaches to gene therapy

Human gene therapy has been attempted on somatic (body) cells for diseases such as cystic fibrosis, adenosine deaminase deficiency, familial hypercholesterolemia, cancer, and severe combined immunodeficiency (SCID) syndrome. Somatic cells cured by gene therapy may reverse the symptoms of disease in the treated individual, but the modification is not passed on to the next generation. Germline gene therapy aims to place corrected cells inside the germ line (e.g., cells of the ovary or testis). If that is achieved, those cells will undergo meiosis and provide a normal gametic contribution to the next generation. Germline gene therapy has been achieved experimentally in animals but not in humans.

Scientists have also explored the possibility of combining gene therapy with stem cell therapy. In a preliminary test of that approach, scientists collected skin cells from a patient with alpha-1 antitrypsin deficiency (an inherited disorder associated with certain types of lung and liver disease), reprogrammed the cells into stem cells, corrected the causative gene mutation, and then stimulated the cells to mature into liver cells. The reprogrammed, genetically corrected cells functioned normally.

Prerequisites for gene therapy

Prerequisites for gene therapy include finding the best delivery system (often a virus, typically referred to as a viral vector) for the gene, demonstrating that the transferred gene can express itself in the host cell, and establishing that the procedure is safe. Few clinical trials of gene therapy in humans have satisfied all those conditions, often because the delivery system fails to reach cells or the genes are not expressed by cells. Improved gene therapy systems are being developed by using nanotechnology. A promising application of that research involves packaging genes into nanoparticles that are targeted to cancer cells, thereby killing cancer cells specifically and leaving healthy cells unharmed.

The Editors of Encyclopaedia Britannica

Ethical and safety concerns

Some aspects of gene therapy, including genetic manipulation and selection, research on embryonic tissue, and experimentation on human subjects, have aroused ethical controversy and safety concerns. Some objections to gene therapy are based on the view that humans should not “play God” and interfere in the natural order. On the other hand, others have argued that genetic engineering may be justified where it is consistent with the purposes of God as creator. Some critics are particularly concerned about the safety of germline gene therapy, because any harm caused by such treatment could be passed to successive generations. Benefits, however, would also be passed on indefinitely. There also has been concern that the use of somatic gene therapy may affect germ cells.

Although the successful use of somatic gene therapy has been reported, clinical trials have revealed risks. In 1999 American teenager Jesse Gelsinger died after having taken part in a gene therapy trial. In 2000 researchers in France announced that they had successfully used gene therapy to treat infants who suffered from X-linked SCID (XSCID; an inherited disorder that affects males). The researchers treated 11 patients, two of whom later developed a leukemia-like illness. Those outcomes highlight the difficulties foreseen in the use of viral vectors in somatic gene therapy. Although the viruses that are used as vectors are disabled so that they cannot replicate, patients may suffer an immune response.

Another concern associated with gene therapy is that it represents a form of eugenics, which aims to improve future generations through the selection of desired traits. While some have argued that gene therapy is eugenic, others claim that it is a treatment that can be adopted to avoid disability. To others, such a view of gene therapy legitimates the so-called medical model of disability (in which disability is seen as an individual problem to be fixed with medicine) and raises peoples’ hopes for new treatments that may never materialize.

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