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Jan 4, 2024 · 2023 was a strong year for innovative new drugs, with new medications for Alzheimer’s disease, weight loss, and the first treatment based on the gene-editing technology CRISPR.
Dec 8, 2023 · The Food and Drug Administration approved two genetic treatments for sickle cell disease, including one that uses gene-editing. The approvals offer hope for patients and signal a new...
- Rob Stein
- kathy.katella-cofrancesco@yale.edu
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- Overview
- How Casgevy works
- Long-term questions
The Food and Drug Administration on Friday approved a powerful treatment for sickle cell disease, a devastating illness that affects more than 100,000 Americans, the majority of whom are Black.
The therapy, called Casgevy, from Vertex Pharmaceuticals and CRISPR Therapeutics, is the first medicine to be approved in the United States that uses the gene-editing tool CRISPR, which won its inventors the Nobel Prize in chemistry in 2020.
“I think this is a pivotal moment in the field,” said Dr. Alexis Thompson, chief of the division of hematology at Children’s Hospital of Philadelphia, who has previously consulted for Vertex. “It’s been really remarkable how quickly we went from the actual discovery of CRISPR, the awarding of a Nobel Prize, and now actually seeing it being an approved product.”
The approval marks the first of two potential breakthroughs for the inherited blood disorder. The FDA on Friday also approved a second treatment for sickle cell disease, called Lyfgenia, a gene therapy from drugmaker Bluebird Bio. Both treatments work by genetically modifying a patient’s own stem cells.
Until now, the only known cure for sickle cell disease was a bone marrow transplant from a donor, which carries the risk of rejection by the immune system, in addition to the difficult process of finding a matching donor.
Casgevy, which was approved for people ages 12 and older, removes the need for a donor. Using CRISPR, it edits the DNA found in a patient’s stem cells to remove the gene that causes the disease.
In patients with sickle cell disease, red blood cells, which are usually disk-shaped, take on a crescent or sickle shape. This change can cause cells to clump together, leading to clots and blockages in the blood vessels, starving tissues of oxygen. Patients can experience excruciating pain, breathing problems and stroke.
Casgevy works by editing the DNA in a patient’s stem cells — which are responsible for making the body’s blood cells — so that they no longer produce sickle-shaped cells.
While technically a one-time treatment, a number of steps that span months are required before the patient actually gets the modified stem cells. It begins with a series of blood transfusions over three to four months, after which the stem cells are extracted from the patient’s bone marrow and sent off to a lab where they are edited, Hanna said.
Before they can be reinfused into the patient, however, doctors need to make sure no flawed stem cells remain in the body. To do so, chemotherapy is used to destroy the patient’s bone marrow.
Only then can the edited stem cells be reinfused into the patient, followed by another month or two in the hospital to allow the cells to grow and the patient to recover.
Hanna said he’s always “cautious” when telling families and patients about the one-time treatment because they may have unrealistic expectations.
Although Casgevy has been shown to be effective, experts still don’t know about potential long-term effects, since the trial is only set to run for two years.
During a meeting in October, an FDA advisory committee discussed the risk of “off-target” effects, which refers to when the gene-editing tool makes cuts to other stretches of DNA other than the intended target and how the FDA should consider those risks moving forward.
It’s unclear what effects an off-target edit would have on a patient, but the fear is that it could result in unintended health consequences down the road, Thompson said. “To date, there do not appear to be measurable consequences.”
The FDA did, however, add a boxed warning — the strongest safety warning label— to Bluebird Bio’s Lyfgenia, noting that in rare cases the treatment can cause certain blood cancers.
Dr. Nicole Verdun, director of the Office of Therapeutic Products in the FDA's Center for Biologics Evaluation and Research, said Lyfgenia was given the warning after two patients who got the therapy in a clinical trial died from a form of leukemia.
It's unclear whether the gene therapy itself or another part of the treatment process, such as the chemotherapy, caused the cancer, but Verdun said the agency thought the deaths "rose to the level of a black-box warning." No cases were seen in the Vertex clinical trial, she said.
Dec 14, 2023 · Here are some of the biggest medical advances in 2023. New treatments include the first CRISPR gene-editing therapy, an Alzheimer’s drug and RSV vaccines. In March, the U.S. Food and Drug...
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