After 5-month hiatus, bluebird bio's Zynteglo bounces back in Europe with all-clear from safety group

With a positive safety ruling in hand, bluebird bio has surmounted another hurdle and will once again forge ahead with the European rollout of its beta-thalassemia gene therapy Zynteglo.

After nearly five months off the market, the Massachusetts-based company said on Friday that it would lift its marketing hold for the blood disease treatment in Europe after the EU's Pharmacovigilance Risk Assessment Committee (PRAC) determined the drug's benefits outweigh its risks. The move will be effective immediately. 

Bluebird’s pause dates back to February when the drugmaker voluntarily stopped selling Zynteglo after a phase 1/2 trial of its gene therapy candidate LentiGlobin flagged two blood cancer cases—one of acute myeloid leukemia (AML) and one of myelodysplastic syndrome (MDS).

RELATED: Bluebird Bio hits pause on rollout for ill-fated gene therapy Zynteglo as trial flags 2 cancer cases

That investigational medicine uses the same BB305 viral vector as Zynteglo to deliver a gene into cells. While no leukemia cases were tied to Zynteglo itself, blood cancer was thought to be a potential risk when the gene therapy scored approval.

But earlier this week, the European Medicines Agency’s (EMA) safety committee ruled that there’s no evidence the viral vector used in Zynteglo spurred the AML case. The MDS diagnosis was earlier revised to transfusion-dependent anemia. 

The safety review has followed a series of setbacks since Zynteglo won conditional approval to treat transfusion-dependent beta-thalassemia (TDT) back in mid-2019. 

RELATED: Bluebird's Zynteglo trials set to resume, putting gene therapy back on flight path to FDA filing

Bluebird pushed its launch into 2020 after regulators said it needed to "tighten up" manufacturing on the gene therapy. Then came COVID-19, forcing the company to further put off dosing to the end of the year. The first patient eventually got their infusion in February, according to a financial filing

There are a few more steps before the PRAC’s review becomes legally binding across the bloc’s 27 member states, but bluebird isn’t waiting to resume sales. 

In the U.S., Zynteglo hasn’t been approved yet, but the company has estimated a filing could come any day. Just slightly over a month ago, the FDA lifted its clinical holds on two phase 3 studies of Zynteglo in TDT. The regulator also gave the biotech the all-clear to restart earlier phase studies of LentiGlobin.