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Gene Therapy for Sickle Cell Disease

illustration showing normal red blood cells and sickle cells in a blood vessel

Sickle-shaped red blood cells can clump together and block the flow of blood.

Sickle cell disease is a group of blood disorders that affects hemoglobin in red blood cells. People with sickle cell disease have red blood cells that are hard, sticky, and shaped like a banana (sickle-shaped).

Sickle cells clump together and block tiny blood vessels and slow the delivery of blood and oxygen to the body’s organs. Sickle cell disease can cause many health problems such as pain, fatigue, breathing problems, infections, stroke, and organ damage. 

Treatments for sickle cell disease include medicines and blood transfusions to help manage pain episodes and other health problems. The only potential cures currently available for sickle cell disease are stem cell (bone marrow) transplant and gene therapy.

What is gene therapy?

Gene therapies work by adding, changing, or repairing genes in a patient’s stem cells. Stem cells are cells that can develop into other types of cells, such as blood cells.

Genes carry instructions that tell the body how to work. When there is a mistake in a gene, it can cause a disease like sickle cell disease. Gene therapy is a treatment that helps correct these mistakes.

Gene therapies for sickle cell disease work to decrease the number of sickle cells in the blood and increase the number of healthy red blood cells. Different gene therapy approaches are being studied. These therapies are very new and only done in certain specialty hospitals or as part of a clinical trial.  

Benefits of gene therapy

Gene therapies alter a patient’s hemoglobin genes so that red blood cells are less likely to be sickle shaped. This can prevent or treat many of the problems associated with sickle cell disease.

Gene therapy may be an alternative option for patients with sickle cell disease who are not eligible for a bone marrow transplant using donor stem cells from a matched donor (usually a brother or sister). Gene therapy uses the patient’s own cells, so a donor is not needed.  

Potential benefits of gene therapy for sickle cell disease include: 

  • Less pain
  • Fewer hospital visits
  • Increased energy and better overall health
  • Improved hemoglobin levels

With improved hemoglobin levels after gene therapy, your child may have fewer complications and less risk of additional organ damage. Gene therapy may also decrease the need for ongoing treatments, such as blood transfusions. 

Gene therapy only treats or corrects a patient’s blood cells. Your child can still pass the gene for sickle cell disease onto their children. 

Your care team will discuss your child’s treatment options with you. Treatment options will be based on factors such as child’s age, type of sickle cell disease, response to other treatments, and health status. 

Your child’s options will also depend on whether your child has a fully matched donor for a bone marrow transplant. If a suitable donor is not available for a transplant, gene therapy may be a treatment option. Talk with your care team to see what treatment options are best for your child. 

What to expect during gene therapy

Gene therapy is a long process and involves several steps. Your family should plan for 1–2 years for the entire process. Your care team will explain each of the steps and let you know what to expect.  

  1. Screening and planning

    Your child will need several tests before the gene therapy process begins. Tests may include imaging tests, lab tests, bone marrow aspiration, and tests to measure heart, lung, and kidney function. You will meet with your care team to go over the results. 

    Some of the treatments used in the gene therapy process can affect your child’s fertility, or their ability to get pregnant or father a child in the future. Your care team will discuss options to preserve your child’s fertility. 

    A care team member will go over the gene therapy timeline with you. This includes: 

    • 6–12 months of preparation, mostly done as outpatient visits
    • 5–6 weeks to receive the gene therapy, which is done during an inpatient hospital stay
    • Frequent follow-up visits after gene therapy

    Planning for this entire process is important. Be sure to ask any questions that you have. You will sign a consent form that allows your child to begin the gene therapy process. 

    Screening and planning

    Your child will have several tests before the gene therapy process begins. Your care team will help you plan and know what to expect.

  2. Exchange transfusions

    For about 3 months before gene therapy, your child will stop hydroxyurea (if taken) and begin regular, monthly exchange blood transfusions. This procedure removes your child’s red blood cells and replaces them with healthy red blood cells from a donor. These exchange transfusions occur about every 3–4 weeks. 

    Your child may have a procedure to place a central line, such as a PICC line or tunneled central line. The central line will allow your child to receive blood transfusions, chemotherapy, and other medicines during the gene therapy process with fewer needle sticks.  

    exchange transfusions

    About 3 months before stem cell collection, your child will stop hydroxyurea (if taken) and begin having regular exchange transfusions.

  3. Stem cell mobilization and collection

    Before stem cells are collected, your child will get medicine to help release stem cells from the bone marrow and increase the number of stem cells that circulate in the blood. 

    Stem cells are collected from the blood through a process called apheresis. A machine takes blood from a vein and separates the blood to remove the stem cells. The rest of the blood is returned to the body through a vein. Only a small amount of blood is out of the body at any time. Apheresis typically takes 6–8 hours. Your child may have another temporary central line placed, which is used only for the apheresis.

    The process of mobilization and stem cell collection may take several cycles before enough stem cells are collected. Your child will stay in the hospital for about a week for each collection cycle. The entire process can take 1–3 months to get the amount of stem cells needed. 

    Stem cell mobilization and collection

    Your child will get medicine to increase stem cells that circulate in the blood. Then the stem cells will be collected through apheresis.

  4. Gene modification and cell processing

    After stem cells are collected, they are taken to a special laboratory for editing and processing. Scientists add a new gene or correct the faulty hemoglobin gene to help the body make healthy red blood cells. The process can take 2–4 months depending on the type of gene therapy approach.

    Gene modification and stem cell processing

    The collected stem cells are sent to a lab where scientists will add or correct the hemoglobin gene.

  5. Pre-infusion testing

    Your child will have additional tests before they are admitted to the hospital. These tests are similar to the initial screening tests and will occur about 2 weeks before gene therapy begins.

    A long time can pass between the initial screening and gene therapy. Repeat testing helps to make sure it is safe for your child to continue with the procedure.

    Pre-infusion testing may include blood tests, MRI, CT, x-rays, tests of heart, lung, and kidney function, and consultations with different members of your child’s care team. You can expect these appointments to last several hours each day.

    pre-infusion testing

    Your child will need additional tests before they can begin the process to receive the modified stem cells. These tests are similar to the initial screening tests.

  6. Conditioning treatment (chemotherapy)

    To prepare for the gene-modified stem cells, your child will get chemotherapy medicines. This is called conditioning, the preparative regimen, or “prep.”

    Conditioning helps your child’s body get rid of the old stem cells to make room for the new stem cells that will grow and make healthy blood cells. Conditioning will take about 1–2 weeks.

    Your care team will give you information about the chemotherapy, so you and your child know what to expect. Your child must complete their chemotherapy before they can receive the modified stem cells. 

    Your child will be admitted to the hospital for the conditioning treatment. They will remain in the hospital for 4–6 weeks until after the infusion and engraftment when the body starts making healthy red blood cells.

    conditioning treatment (chemotherapy)

    Your child will get chemotherapy medicines to help prepare their body for the gene-modified stem cells. This is called conditioning, the preparative regimen, or “prep.”

  7. Infusion of gene edited stem cells

    Your child will get the modified stem cells after chemotherapy is complete. The cells are given to your child through their central line. This is called an infusion. The infusion takes about 1 hour. 

    Several nurses and other staff will be in the room to monitor your child for signs of a reaction to the infused cells. A parent or family caregiver may stay with your child during the infusion.  

    stem cell infusion

    After conditioning is complete, your child will get the gene-modified stem cells through an injection or infusion.

  8. Engraftment

    The next step is waiting for the modified stem cells to grow and multiply in your child’s body. This is called engraftment. Engraftment takes several weeks. Your child’s body will start making healthy red blood cells. 

    Your child will have regular blood tests to see if the new cells are working correctly. 

    Your child will remain in the hospital until engraftment occurs. Then, your child will be discharged to home or housing. 

    Engraftment

    If gene therapy is successful, the modified stem cells will grow and multiply. Then, your child’s body will start making healthy red blood cells.

After gene therapy

Patients are closely monitored for the first 100 days after gene therapy. Your child will stay in local or long-term housing for several months after hospital discharge. They may need to stay longer if there are problems. 

During this time, your child will have regular outpatient clinic visits and lab tests several times a week to check their progress. If the gene therapy works, your child will have fewer sickle cells and more healthy red blood cells in their blood.

Your child will have routine appointments as part of long-term follow-up care. Your child will have fewer checkups as they get older if they are doing well. Follow-up care continues for up to 15 years.

Possible risks of gene therapy 

Side effects of chemotherapy (conditioning treatment) 

Most patients who receive chemotherapy have some degree of side effects. These may include:

Your care team will take steps to help manage side effects including giving medicines to help control nausea, vomiting, and pain. Red light therapy may be used to prevent and treat mouth sores (oral mucositis). Your child may also need a nasogastric (NG) tube for nutrition support.  

Because of the increased risk of infection, your child will stay in their room on the transplant unit for their inpatient stay. All caregivers and visitors must follow strict guidelines for infection prevention.

Infertility

Some people who have gene therapy may not be able to have children on their own. Chemotherapy can impact the ability to have children later in life. If your child is old enough, it might be possible to collect their sperm or eggs before treatment so they can be frozen and stored to use later if they choose.

Talk to your care team about your child’s risk of infertility and fertility preservation options that may be available.

Veno-occlusive disease (VOD) 

Veno-occlusive disease (VOD) occurs when blood clots form in blood vessels of the liver. Stem cell transplant, certain chemotherapy medicines, and frequent blood transfusions can increase the risk of VOD. VOD can cause increased bilirubin levels, an enlarged liver, and fluid retention or weight gain. If not treated, VOD can lead to organ failure and even death. 

VOD is a serious condition. If your child develops VOD, they may need to be treated in the intensive care unit (ICU). VOD treatment often includes limiting fluids and treatment with the medication defibrotide. 

To help prevent VOD, your child may get the medicine ursodiol before hospital admission. Your care team will also monitor your child’s weight and fluid balance while they are in the hospital. 

Cancer

Gene therapy may increase your child’s risk of cancer. The risk is thought to be small, but the exact risk is not known. A few patients have developed a type of leukemia. But there has been no definite evidence to show that these cancers are directly related to the gene therapy.

Ongoing effects of sickle cell disease

Gene therapy aims to replace sickled red blood cells with healthy red blood cells to prevent future complications of sickle cell disease. However, gene therapy is new. The long-term outcomes and effects on organ function and overall health are unknown at this early time.

Gene therapy offers the potential for a long-term treatment or even cure for sickle cell disease. However, it only treats the patient. Your child can still pass the gene for sickle cell disease on to their children. 

Gene therapy is still being studied and is not available at every treatment center. Talk with your care team to know if gene therapy might be an option for your child. 

Questions to ask your care team

  • Is my child a good candidate for gene therapy?
  • Does gene therapy cure sickle cell disease?
  • What other treatments could help manage my child’s sickle cell disease?
  • What are the potential benefits of gene therapy compared to other treatments?
  • What are the short-term and long-term risks or side effects?
  • How long does the whole procedure take, including recovery time?
  • What kind of follow-up care and monitoring will my child need?

Key points about gene therapy for sickle cell disease

  • Gene therapy works by modifying or repairing the hemoglobin gene that causes red blood cells to become sickle shaped.
  • Gene therapy can help your child’s body make healthy red blood cells. This can reduce symptoms and complications of sickle cell disease and may even be a cure for some patients.  
  • The process involves collecting stem cells from the patient, modifying them in a lab, and then infusing the modified stem cells back into the patient after a conditioning treatment (chemotherapy).
  • Gene therapy has risks, including potential short-term and long-term side effects.  
  • Your care team can help determine if gene therapy is a good treatment option for your child and let you know what to expect.

Find more information

Related Factsheets

Gene Therapy for Sickle Cell Disease Factsheet

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Reviewed: July 2025

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