The Food and Drug Administration on Friday approved a powerful gene-editing treatment for sickle cell disease, a devastating illness that affects more than 100,000 Americans, the majority of whom are Black.
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.
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.
“The patient is their own donor,” Thompson said.
“It’s a game-changer,” said Dr. Asmaa Ferdjallah, a pediatric hematologist and bone marrow transplant physician at the Mayo Clinic in Rochester, Minnesota. “To really reimagine and re-discuss sickle cell disease as a curable disease and not as this painful and debilitating chronic disease is hope enough with this news.”
Still, the new therapy is extremely expensive — $2.2 million per patient, Vertex said. The pricing strategy, experts argue, may place it out of reach for many families. What’s more, that price doesn’t include the cost of care associated with the treatment, like a stay in the hospital or chemotherapy.
“We really have to make sure that it is accessible,” said Dr. Rabi Hanna, a pediatric hematologist-oncologist at the Cleveland Clinic who has previously served on the advisory board for Vertex. “This could be an equalizer for people with sickle cell because many patients cannot pursue career options” because of the illness.
How Casgevy works
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.