A modified virus used in a sickle cell gene therapy is unlikely to be the cause of a patient's leukemia, Science reports.
Bluebird Bio paused its sickle cell and β-thalassemia gene therapy clinical trials last month after learning that a patient treated with one of its gene therapies developed acute myeloid leukemia and that another patient developed myelodysplastic syndrome. At the time, Stat News noted that the report could raise new worries about cancer risk for gene therapy patients.
But according to Science, an investigation by Bluebird indicates that the lentiviral vector it uses is likely not the cause of the patient's leukemia, as the patient's leukemia cells harbored alterations in known leukemia-linked genes and as the vector inserted in the VAMP4 gene, which has no known role in cancer.
"Moreover, we see no significant gene misregulation attributable to the insertion event," Philip Gregory, chief scientific officer of Bluebird, says in a statement. "In totality, the data from our assessments provide important evidence demonstrating that it is very unlikely our BB305 lentiviral vector played a role in this case."
He adds that the company has shared the data with the US Food and Drug Administration as it seeks to re-start its trials.
The New York Times notes that the company is still investigating the myelodysplastic syndrome case.