• Gene Therapy FAQs

    Frequently Asked Questions

    What is gene therapy?

    Some diseases are caused by errors (mutations) in specific genes. Gene therapy delivers DNA into cells to replace mutated (“bad”) or missing genes or to add new, “good” genes.

    Scientists are investigating a number of different ways to do this. Right now, gene therapy is only done through research studies called clinical trials. Unlike medicine, gene therapy directly addresses the underlying genetic problem, not just the symptoms.

    What is a gene?

    Genes are in the nucleus of every living cell. A gene is an instruction manual for the body. It gives the direction to make the proteins that make the body work.

    How does gene therapy deliver “good” genes into cells?

    A gene cannot be inserted directly into a cell. Instead, a carrier called a vector is genetically engineered to deliver the gene. Viruses are usually used as the vectors because they are very good at “infecting” cells and inserting the gene(s) into the cells’ DNA. Types of viral vectors are retrovirus, adenovirus, adeno-associated virus and herpes simplex virus.

    Will the virus make my child sick?

    No. The virus is specially engineered to remove the infectious piece. We only keep the part of the virus that is good at burrowing into a cell’s nucleus. Once the virus delivers the gene into the cell, the virus slips away.

    What are some diseases gene therapy might treat?

    It is not for all genetic diseases. It is only for some diseases caused by a single gene mutation. Some diseases that might be treated with gene therapy are:

    What is the goal of gene therapy?

    The goal is to cure a disease or make changes so the body can better fight off disease. It does not correct 100% of your child’s cells. Instead, every time a cell with the “good” gene reproduces, it carries a copy of the new healthy gene.

    What are the types of gene therapy?

    The vector can be injected or given by IV directly into a specific tissue. Or a sample of cells can be removed and exposed to the vector in a laboratory. The cells with the vector are then returned to the patient.

    • In vivo gene therapy – the gene is transferred to a patient’s cells while still in the patient.
    • Ex vivo gene therapy – the gene is transferred into the cells in a lab and then injected back into the patient.
    in vivo and ex vivo gene therapy

    How does ex vivo gene therapy work?

    1) Stem cells are collected in one of two ways: by bone marrow aspiration, or by purifying blood drawn through a central line in a process called apheresis.

    bone marrow aspiration for gene therapycentral line apheresis for gene therapy

    2) Before the infusion, most children have chemotherapy. This makes room for the new cells by getting rid of the existing cells in the bone marrow.

    chemotherapy for gene therapy

    3) In the laboratory, the stem cells from the blood or bone marrow are exposed to a virus or other type of vector containing the desired genes.

    gen therapy vector

    4) Once the stem cells take up the vector and merge the genes into cells’ DNA, the cells are given back to the patient in an IV infusion.

    intravenous infusion for gene therapy

    What is the difference between gene therapy and a bone marrow transplant?

    Bone marrow transplants use stem cells from another person (a donor). Gene therapy uses your child’s own cells. Using your child’s own cells is a benefit because there is no risk of rejection, or graft vs. host disease, like there is with donor cells. Gene therapy is still only offered through clinical trials and at only a few research hospitals and centers.

    Can my child have gene therapy?

    Gene therapy is still very new, and is mostly used to treat children who cannot be cured by standard treatments. Gene therapy is not for every disease or a good fit for every patient. Your child needs to meet certain criteria for safety reasons. Your child’s doctor will talk to you about whether your child is a good fit for a gene therapy clinical trial.

    What happens before the gene therapy infusion?

    Your child will have 4–10 days of chemotherapy before the infusion. This is called chemotherapy conditioning. It clears out bone marrow to make room for the new stem cells. This has typical side effects from chemotherapy, like nausea/vomiting, mouth sores and pain.

    What happens during the gene therapy infusion?

    Your child has the transfusion on the Bone Marrow Transplant floor (6 West) at the Jimmy Fund Clinic. It is given one time intravenously (through an IV), just like a blood transfusion. It takes 15–30 minutes. The amount of time your child will stay in the hospital depends on many factors. Most children stay 4–6 weeks.

    What happens after the infusion?

    Your child will have blood tests to check for the vector in the cells, and to see how the cells are responding. Your child will come in for follow-ups frequently. Your child’s care team will talk to you about when you should call your child’s doctor. Always call with questions or concerns or if you notice signs of an infection.

    Is gene therapy safe?

    Many research studies are underway to test gene therapy as a safe treatment for a growing number of diseases. Improvements have already been made in safety. Early gene therapy trials showed a high risk of “turning on” oncogenes that cause cancer. Now, experts have retooled the vector to lower the likelihood of turning on oncogenes.


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