“My other concern is that the Black community will lose faith or trust in research studies again after it has taken the medical community so long to even regain some degree of trust,” she added.
It is not yet clear what caused the cancers. One possibility is that the disabled virus used to deliver the gene therapy treatment damaged crucial DNA in blood-forming cells in the patients’ bone marrows. That would be the worst-case scenario, said Dr. John F. Tisdale, head of the cellular and molecular therapeutics branch at the National Heart, Lung and Blood Institute.
But there is also the likelihood that both cancers were caused by a powerful drug, busulfan, which is used to clear bone marrow in order to make space for new cells modified by gene therapy. Busulfan is known to confer a blood cancer risk, Dr. Tisdale noted. If it turns out to be the culprit in Bluebird Bio’s trials, “We are back to what we know,” he said.
The disabled lentivirus that Bluebird uses to deliver its gene therapy was designed with safety features. It is thought to be far less risky than the viruses used in gene therapy years ago, which caused cancer in children with an immune deficiency. A lentivirus is also being used in a gene therapy trial for sickle cell disease at Boston Children’s Hospital.
The first patient in Bluebird’s trial also developed myelodysplastic syndrome about three years after receiving gene therapy, Dr. Tisdale said. An examination found it was caused by busulfan.