In February, bluebird bio (NASDAQ:BLUE) announced a temporary suspension of two clinical trials evaluating LentiGlobin, an experimental gene therapy, after a trial patient was diagnosed with acute myeloid leukemia (AML), a blood and bone marrow cancer. The possibility that a lentiviral vector used in Bluebird's drugs caused the cancer called into question the viability of its genetic program, causing a sharp sell-off in its shares.

Today, Bluebird unveiled updated results from its internal investigation, suggesting it's unlikely the AML case reported in its phase 1/2 (HGB-206) study of LentiGlobin for sickle cell disease (SCD) was caused by its lentiviral vector. 

A woman scientist looking through a microscope.

Image source: Getty Images.

Specifically, Philip Gregory, its chief scientific officer, said:

Analyses identified the integration site for the vector within a gene called VAMP4. VAMP4 has no known association with the development of AML nor with processes such as cellular proliferation or genome stability. Moreover, we see no significant gene misregulation attributable to the insertion event.

Gregory went on to say it's "very unlikely" Bluebird's lentiviral vector played a role in this case.

Bluebird is providing this research to the Food and Drug Administration, and the clinical holds that are currently hamstringing its beta-thalassemia and sickle cell disease programs could be lifted if the FDA agrees with Bluebird's assessment.

A positive opinion could also allow Bluebird to restart commercialization efforts in the European Union for Zynteglo, a gene therapy for transfusion-dependent beta-thalassemia patients. Previously, it had voluntarily stopped marketing Zynteglo because it relies on the same viral vector used in its sickle cell disease study.

Separately, the company continues to investigate a second Suspected Unexpected Serious Adverse Reaction (SUSAR), involving a patient diagnosed with myelodysplastic syndrome in February. 

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