Shares of Bluebird Bio Inc. BLUE,
dropped 34% in premarket trading Tuesday, after the biotech said it was temporarily halting its Phase 1/2 and Phase 3 trials of its LentiGlobin gene therapy for sickle cell disease following a report of a suspected unexpected serious side effect of acute myeloid leukemia. The affected patient was treated more than five years ago and no diagnosis of AML has been made, the company said in a statement. “The company is investigating the cause of this patient’s AML to determine whether there is a link with the use of the lentiviral vector BB305 in the manufacture of LentiGlobin gene therapy for SCD,” said Bluebird. “In addition, a second SUSAR of myelodysplastic syndrome (MDS) in a group C patient of HGB-206 was reported to the company last week and is currently under investigation.” The company said it will work with regulators to complete the investigation. Shares are down 49% in the last 12 months, while the SPDR S&P Biotech ETF XBI,
has won 69% and the S&P 500 SPX,
is up 16%.