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How does gene therapy work?
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Therapy

How Does Gene Therapy Work?

Gene therapy functions by altering the genetic code to restore the function of critical proteins, using methods such as gene transfer and genome editing to correct disease-causing mutations.

Overview

Gene therapy works by altering the genetic code to recover the functions of critical proteins. Proteins are the workhorses of the cell and the structural basis of the body’s tissues. The instructions for making proteins are carried in a person’s genetic code, and variants (or mutations) in this code can impact the production or function of proteins that may be critical to how the body works. Fixing or compensating for disease-causing genetic changes may recover the role of these important proteins and allow the body to function as expected.

Mechanisms of Action

Gene therapy can compensate for genetic alterations in a couple of different ways:

  • Gene transfer therapy introduces new genetic material into cells. If an altered gene causes a necessary protein to be faulty or missing, gene transfer therapy can introduce a normal copy of the gene to recover the function of the protein. Alternatively, the therapy can introduce a different gene that provides instructions for a protein that helps the cell function normally, despite the genetic alteration.
  • Genome editing is a newer technique that may potentially be used for gene therapy. Instead of adding new genetic material, genome editing introduces gene-editing tools that can change the existing DNA in the cell. Genome editing technologies allow genetic material to be added, removed, or altered at precise locations in the genome. CRISPR-Cas9 is a well-known type of genome editing.

Delivery Vectors

Genetic material or gene-editing tools that are inserted directly into a cell usually do not function. Instead, a carrier called a vector is genetically engineered to carry and deliver the material. Certain viruses are used as vectors because they can deliver the material by infecting the cell. The viruses are modified so they can't cause disease when used in people.

  • Retroviruses: These viruses integrate their genetic material (including the new gene) into a chromosome in the human cell.
  • Adenoviruses: These viruses introduce their DNA into the nucleus of the cell, but the DNA is not integrated into a chromosome.

Viruses can also deliver the gene-editing tools to the nucleus of the cell.

Administration Methods

The vector can be injected or given intravenously (by IV) directly into a specific tissue in the body, where it is taken up by individual cells. Alternately, a sample of the patient's cells can be removed and exposed to the vector in a laboratory setting. The cells containing the vector are then returned to the patient. If the treatment is successful, the new gene delivered by the vector will make a functioning protein or the editing molecules will correct a DNA error and restore protein function.

Risks and Emerging Technologies

Gene therapy with viral vectors has been successful, but it does carry some risk. Sometimes the virus triggers a dangerous immune response. In addition, vectors that integrate the genetic material into a chromosome can cause errors that lead to cancer.

Researchers are developing newer technologies that can deliver genetic material or gene-editing tools without using viruses. One such technique uses special structures called nanoparticles as vectors to deliver the genetic material or gene-editing components into cells. Nanoparticles are incredibly small structures that have been developed for many uses. For gene therapy, these tiny particles are designed with specific characteristics to target them to particular cell types. Nanoparticles are less likely to cause immune reactions than viral vectors, and they are easier to design and modify for specific purposes.

Future Directions

Researchers continue to work to overcome the many technical challenges of gene therapy. For example, scientists are finding better ways to deliver genes or gene-editing tools and target them to particular cells. They are also working to more precisely control when the treatment is functional in the body.

Frequently Asked Questions

The timeline varies significantly depending on the specific condition and delivery method. Some therapies, like those for certain blood disorders, may show effects within weeks to months as new cells are produced. For others, such as muscular dystrophy treatments, improvements might be gradual over several months. Regarding duration, many current gene therapies are designed to be a one-time treatment because the introduced genetic material remains in the cells. However, if the therapy targets cells that turn over quickly or if the effect is temporary, follow-up treatments or monitoring may be required. Your clinical team will provide a specific schedule based on the approved protocol for your condition. What are the most common side effects I should expect after receiving gene therapy?::Common side effects often resemble those of a severe viral infection or flu, including fever, fatigue, muscle aches, and nausea, which typically occur in the first few days after infusion. More serious but less common risks include immune reactions to the viral vector used for delivery, liver toxicity, or clotting disorders. In some cases, the body may produce antibodies against the therapy, which can reduce its effectiveness or cause inflammation. Patients are closely monitored in a hospital setting for the first 24 to 48 hours to manage acute reactions, and long-term follow-up is essential to detect any delayed adverse events. Is gene therapy a cure, or does it only manage symptoms?::For many rare genetic disorders, gene therapy aims to be a functional cure by correcting the underlying genetic defect, rather than just managing symptoms. If the therapy successfully restores the production of a critical protein, the disease progression can halt or reverse. However, it is not always a complete cure in the sense that all symptoms may disappear immediately or that the genetic mutation is removed from every cell in the body. In some conditions, the therapy stabilizes the disease and prevents further deterioration, which is a significant clinical benefit. The extent of improvement depends on how early the therapy is administered and the severity of the existing damage. Who is eligible for gene therapy, and how is the decision to proceed made?::Eligibility is strictly determined by clinical trial criteria or approved labeling, which usually includes specific genetic test results confirming the mutation, age ranges, and the current stage of the disease. Patients must generally be in a stable health condition to withstand the procedure and any pre-treatment medications, such as chemotherapy to clear space for new cells. The decision involves a multidisciplinary team including geneticists, specialists in the affected organ system, and ethicists. Patients and families undergo extensive counseling to understand the risks, benefits, and the experimental nature of the treatment if it is part of a clinical trial.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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