World's First CRISPR Gene Therapy Approved — A Historic Milestone for Sickle Cell Disease

The United States Food and Drug Administration approved the world's first medicine based on CRISPR-Cas9 gene-editing technology in December 2023, marking what researchers and clinicians described as one of the most significant milestones in the history of genetic medicine and offering a potential one-time cure for patients with sickle cell disease. The approved therapy, named Casgevy and developed jointly by Vertex Pharmaceuticals and CRISPR Therapeutics, was cleared for use in patients aged 12 years and older with sickle cell disease who experience recurrent episodes of severe pain known as vaso-occlusive crises. On the same day, the FDA also approved a second gene therapy for the condition — Lyfgenia, developed by bluebird bio — using a different gene-modification approach. Casgevy uses CRISPR-Cas9 — the gene-editing system for which Jennifer Doudna of the University of California Berkeley and Emmanuelle Charpentier of the Max Planck Unit for the Science of Pathogens were awarded the Nobel Prize in Chemistry in 2020. The treatment works by extracting stem cells from a patient's bone marrow, editing them in a laboratory to reactivate the production of a foetal form of haemoglobin called haemoglobin F, and then reinfusing the edited cells into the patient. Foetal haemoglobin does not carry the mutation responsible for sickle cell disease and can function in place of the defective adult haemoglobin that causes red blood cells to collapse into the rigid, sickle-shaped form that obstructs blood flow, damages organs, and causes the disease's hallmark episodes of excruciating pain. Clinical trial data submitted to the FDA demonstrated that 29 of 29 evaluable patients who received Casgevy experienced complete resolution of vaso-occlusive crises for at least 12 consecutive months following treatment — a result that researchers described as extraordinary given the chronic and debilitating nature of the disease. "For people with sickle cell disease, this is a transformative moment," said Dr. Nicole Verdun, director of the FDA's Office of Therapeutic Products. "These are serious, life-threatening conditions, and the ability to address their underlying genetic cause represents a major step forward." Sickle cell disease is caused by a single inherited mutation in the gene encoding haemoglobin and affects an estimated 100,000 people in the United States and approximately eight million worldwide. The disease disproportionately affects people of African, Middle Eastern, and South Asian descent, and carries a significantly reduced life expectancy without treatment. Existing treatments — including hydroxyurea and regular blood transfusions — manage symptoms but do not address the underlying cause. The approval nevertheless comes with profound challenges related to access. Vertex Pharmaceuticals priced Casgevy at approximately USD 2.2 million per patient for the United States market, making it among the most expensive medicines ever approved. The treatment also requires patients to undergo chemotherapy conditioning to clear existing bone marrow prior to infusion of the edited cells, a medically intensive process requiring specialised hospital facilities not available in most of the countries where sickle cell disease is most prevalent. Despite these barriers, the approval is viewed by the scientific community as confirmation that CRISPR-based editing can be deployed safely and effectively to treat serious genetic diseases in humans — establishing a platform that researchers expect will underpin future therapies for a broad range of inherited conditions, certain cancers, and infectious diseases including HIV.