What is the aim of gene therapy

Overview

Gene therapy involves altering the genes inside your body’s cells in an effort to treat or stop disease.

Genes contain your DNA — the code that controls much of your body’s form and function, from making you grow taller to regulating your body systems. Genes that don’t work properly can cause disease.

Gene therapy replaces a faulty gene or adds a new gene in an attempt to cure disease or improve your body’s ability to fight disease. Gene therapy holds promise for treating a wide range of diseases, such as cancer, cystic fibrosis, heart disease, diabetes, hemophilia and AIDS.

Researchers are still studying how and when to use gene therapy. Currently, in the United States, gene therapy is available only as part of a clinical trial.

Why it’s done

Gene therapy is used to correct defective genes in order to cure a disease or help your body better fight disease.

Researchers are investigating several ways to do this, including:

• Replacing mutated genes. Some cells become diseased because certain genes work incorrectly or no longer work at all. Replacing the defective genes may help treat certain diseases. For instance, a gene called p53 normally prevents tumor growth. Several types of cancer have been linked to problems with the p53 gene. If doctors could replace the defective p53 gene, that might trigger the cancer cells to die.
• Fixing mutated genes. Mutated genes that cause disease could be turned off so that they no longer promote disease, or healthy genes that help prevent disease could be turned on so that they could inhibit the disease.
• Making diseased cells more evident to the immune system. In some cases, your immune system doesn’t attack diseased cells because it doesn’t recognize them as intruders. Doctors could use gene therapy to train your immune system to recognize the cells that are a threat.

Risks

Gene therapy has some potential risks. A gene can’t easily be inserted directly into your cells. Rather, it usually has to be delivered using a carrier, called a vector.

The most common gene therapy vectors are viruses because they can recognize certain cells and carry genetic material into the cells’ genes. Researchers remove the original disease-causing genes from the viruses, replacing them with the genes needed to stop disease.

This technique presents the following risks:

• Unwanted immune system reaction. Your body’s immune system may see the newly introduced viruses as intruders and attack them. This may cause inflammation and, in severe cases, organ failure.
• Targeting the wrong cells. Because viruses can affect more than one type of cells, it’s possible that the altered viruses may infect additional cells — not just the targeted cells containing mutated genes. If this happens, healthy cells may be damaged, causing other illness or diseases, such as cancer.
• Infection caused by the virus. It’s possible that once introduced into the body, the viruses may recover their original ability to cause disease.
• Possibility of causing a tumor. If the new genes get inserted in the wrong spot in your DNA, there is a chance that the insertion might lead to tumor formation.

The gene therapy clinical trials underway in the U.S. are closely monitored by the Food and Drug Administration and the National Institutes of Health to ensure that patient safety issues are a top priority during research.

What you can expect

Currently, the only way for you to receive gene therapy is to participate in a clinical trial. Clinical trials are research studies that help doctors determine whether a gene therapy approach is safe for people. They also help doctors understand the effects of gene therapy on the body.

Your specific procedure will depend on the disease you have and the type of gene therapy being used.

For example, in one type of gene therapy:

• You may have blood drawn or you may need bone marrow removed from your hipbone with a large needle.
• Then, in a lab, cells from the blood or bone marrow are exposed to a virus or another type of vector that contains the desired genetic material.
• Once the vector has entered the cells in the lab, those cells are injected back into your body into a vein or into tissue, where your cells take up the vector along with the altered genes.

Viruses aren’t the only vectors that can be used to carry altered genes into your body’s cells. Other vectors being studied in clinical trials include:

• Stem cells. Stem cells are the cells from which all other cells in your body are created. For gene therapy, stem cells can be trained in a lab to become cells that can help fight disease.
• Liposomes. These fatty particles have the ability to carry the new, therapeutic genes to the target cells and pass the genes into your cells’ DNA.

Results

The possibilities of gene therapy hold much promise. Clinical trials of gene therapy in people have shown some success in treating certain diseases, such as:

• Severe combined immune deficiency
• Hemophilia
• Blindness caused by retinitis pigmentosa
• Leukemia

But several significant barriers stand in the way of gene therapy becoming a reliable form of treatment, including:

• Finding a reliable way to get genetic material into cells
• Targeting the correct cells
• Reducing the risk of side effects

Gene therapy continues to be a very important and active area of research aimed at developing new, effective treatments for a variety of diseases.

Clinical trials

Explore Mayo Clinic studies of tests and procedures to help prevent, detect, treat or manage conditions.

Human gene therapy seeks to modify or manipulate the expression of a gene or to alter the biological properties of living cells for therapeutic use 1.

Gene therapy is a technique that modifies a person’s genes to treat or cure disease. Gene therapies can work by several mechanisms:

• Replacing a disease-causing gene with a healthy copy of the gene
• Inactivating a disease-causing gene that is not functioning properly
• Introducing a new or modified gene into the body to help treat a disease

Gene therapy products are being studied to treat diseases including cancer, genetic diseases, and infectious diseases.

There are a variety of types of gene therapy products, including:

• Plasmid DNA: Circular DNA molecules can be genetically engineered to carry therapeutic genes into human cells.
• Viral vectors: Viruses have a natural ability to deliver genetic material into cells, and therefore some gene therapy products are derived from viruses. Once viruses have been modified to remove their ability to cause infectious disease, these modified viruses can be used as vectors (vehicles) to carry therapeutic genes into human cells.
• Bacterial vectors: Bacteria can be modified to prevent them from causing infectious disease and then used as vectors (vehicles) to carry therapeutic genes into human tissues.
• Human gene editing technology: The goals of gene editing are to disrupt harmful genes or to repair mutated genes.
• Patient-derived cellular gene therapy products: Cells are removed from the patient, genetically modified (often using a viral vector) and then returned to the patient.

Gene therapy products are biological products regulated by the FDA’s Center for Biologics Evaluation and Research (CBER). Clinical studies in humans require the submission of an investigational new drug application (IND) prior to initiating clinical studies in the United States. Marketing a gene therapy product requires submission and approval of a biologics license application (BLA).

Long Term Follow-Up After Administration of Human Gene Therapy Products; Guidance for Industry, January 2020