Just when it seemed that a new gene therapy for sickle cell disease was heading towards success, the company that developed the treatment found that two patients now had cancer and stopped testing.
A patient who was treated five and a half years ago has developed myeloidoplastic syndrome, a form of cancer that is often a precursor to leukemia, Bluebird Bio reported, while another has developed acute myeloid leukemia.
It is not clear whether cancers are associated with experimental gene therapy. But the sudden setback is a disappointment for many sickle cell patients, mostly African-Americans, who hoped that a cure was on the horizon.
“It seems that the sickle cell disease community just might never get a break,” Dr. Melissa J. Frey-Jones is a researcher at the University of Texas School of Medicine in San Antonio.
“My second concern is that the black community will again lose faith or confidence in research studies because the medical community has been able to gain some degree of trust for so long,” he said.
It is not yet clear what caused the cancer. One possibility is that inefficient viruses used to deliver gene therapy treatments damaged critical DNA in blood-forming cells in patients’ bone marrow. This would be the worst case, with the head of the cellular and molecular therapeutic branch at the National Heart, Lung and Blood Institute, Drs. John F. Tisdale said.
But there is also the possibility that both cancers were caused by a powerful drug, Bussaflan, which is used to clean the bone marrow to make room for new cells modified by gene therapy. Dr. Tisdale said that bassulfan is known to be at risk of blood cancer. If it turned out to be the culprit in Bluebird Bio’s trial, “We know what we know.”
The passive lentivirus that Bluebird uses to deliver its gene therapy was designed with safety features. It is thought to be less risky than the virus used in gene therapy years ago, leading to cancer deficiency in children. A lentavirus is being used in gene therapy testing for sickle cell disease at Boston Children’s Hospital.
Dr. Tisdale stated that the first patient in Bluebird’s trial developed myeloidoplastic syndrome about three years after receiving gene therapy. An examination found that it was caused by busulfan.
The new case is “very similar to what we saw in the first patient” Dr. Tisdale said. At this point, however, more testing simply needs to establish that the new patient actually has the syndrome, he said.
Bluebird is completing an analysis to determine if the gene inserted into the patients’ DNA landed near the new cancer-associated gene. If not, Busulfan is the likely culprit.
Complicating the question is the fact that people with sickle cell disease are at increased risk of leukemia even without treatment. Nevertheless, no one expects two patients to be screened for the disease.
If gene therapy turns out to be at fault, it is unclear what the Food and Drug Administration will do.
Dr., a hematologist at Boston Children’s Hospital. David A. Williams stated that sickle cell disease itself is degenerative and debilitating, which over time causes intense pain and damage to harmful tissues and organs.
The risk of gene therapy can be offset by the benefits of a treatment that can reduce this terrible burden, he and other experts said.
Researchers should be careful in predicting what cancer will mean for Bluebird’s gene therapy, Drs. Michael said R. DeBaun, director of the Vikanderbilt-Mehri-Matthew Walker Center of Excellence in Sickle Cell Disease. He said he tells the diagnosis of cancer “a strange story between cutting-edge science, clinical trials with few participants and hope for a population that has largely been overlooked in the medical community.”
He However, there is optimism that there will be sufficient evidence for patients to eventually make informed choices about curious treatments, including gene therapy and bone marrow transplantation.
“At the end of the day, families want the disease option to be cured,” Dr. Debun said. “They cannot join the discussion for a cure, but they want to know that they have a choice.”