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"He feels perfectly normal."ĬRISPR appears to have done at least as well. They include a teenager who can now go swimming without pain, and a young man who once needed transfusions but has gone without them for nearly 2.5 years, says Erica Esrick of Boston Children's. In one NEJM paper today, the Boston Children's team reports on the success of its virus gene therapy in six sickle cell patients treated for at least 6 months. Patients treated in both trials have begun to make sufficiently high levels of fetal hemoglobin and no longer have sickle cell crises or, except in one case a need for transfusions. They used a harmless virus to paste into the blood stem cells' genome a stretch of DNA coding for a strand of RNA that silences the fetal hemoglobin off switch.
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In a more traditional gene therapy effort, a team led by gene therapy researcher David Williams of Boston Children's Hospital achieved the same goal. They engineered CRISPR's DNA-cutting enzyme and "guide RNA" to home in on and break the BCL11A gene. "It's enough to dilute the effect," says Samarth Kulkarni, CEO of CRISPR Therapeutics, which partnered with Vertex Pharmaceuticals on using the genome editor. In sickle cell disease it replaces some of the flawed adult hemoglobin, and also blocks any remaining from forming sticky polymers. With the fetal gene now active, the fetal protein restores missing hemoglobin in thalassemia. The patient then receives chemotherapy to wipe out their diseased cells, and the altered stem cells are infused. They remove a patient's blood stem cells and, in the lab, disable a genetic switch called BCL11A that, early in life, shuts off the gene for a fetal form of hemoglobin. In the two new treatments, investigators have tinkered with genes to counter the malfunctioning hemoglobin. Blood transfusions are standard treatment for both diseases, relieving the severe anemia they can cause, and drugs can somewhat reduce the debilitating "crises" that often send sickle cell patients to the hospital. About 60,000 babies are born each year globally with symptoms of the disease, largely of Mediterranean, Middle Eastern, and South Asian ancestry. People with beta-thalassemia make little or no functioning hemoglobin, because of mutations that affect the same subunit of the protein. (The sickling mutations became widespread in African people, as one copy protects blood cells from malaria parasites.) Sickle cell disease is among the most common inherited diseases, affecting 100,000 Black people in the United States alone. The cells can clog blood vessels, triggering severe pain and raising the risk of organ damage and strokes. The altered proteins stiffen normally flexible red blood cells into a sicklelike shape. People born with sickle cell disease have mutations in their two copies of a gene for hemoglobin, the oxygen-carrying protein in red blood cells. "This is an amazing time, and it's exciting because it's happening all at once," says hematologist Alexis Thompson of Northwestern University, who with a company called Bluebird Bio continues to test yet another genetic strategy that first demonstrated a sickle cell fix several years ago. The novel genetic treatments have the same safety issues as bone marrow transplants for now, and may also be extraordinarily expensive, but there is hope those risks can be eliminated and the costs pared down.
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The only current cure, a bone marrow transplant, is risky, and appropriately matched donors are often scarce. And both treatments are among a wave of genetic strategies poised to widely expand who can be freed of the two conditions. One relies on CRISPR, marking the first inherited disease treated with the powerful tool created just 8 years ago. Today in The New England Journal of Medicine ( NEJM) and tomorrow at the American Society of Hematology (ASH) meeting, teams report that two strategies for directly fixing malfunctioning blood cells have dramatically improved the health of a handful of people with these genetic diseases. It is a double milestone: new evidence that cures are possible for many people born with sickle cell disease and another serious blood disorder, beta-thalassemia, and a first for the genome editor CRISPR.