Bluebird's One-Time Gene Therapy for Sickle Cell on Partial Hold

The U.S. Food and Drug Administration (FDA) placed bluebird bio's clinical trial for its candidate sickle cell disease (SCD) treatment on partial hold for participants under 18 years old. 

The partial suspension is temporary due to the firm's ongoing investigation into one of its adolescent patients diagnosed with persistent, non-transfusion-dependent anemia after receiving lovotibeglogene autotemcel (lovo-cel), who has been receiving the drug for 18 months now. The patient is reportedly clinically well and does not demonstrate any clonal predominance or malignancy. 

Lovo-cel is a one-time investigational treatment being assessed for SCD and works by adding functional copies of a modified type of β-globin gene into a patient's own blood stem cells. Once patients have this gene, red blood cells are able to produce anti-sickling hemoglobin, which then reduces the amount of HbS and then later reduces sickled RBCs, hemolysis, and related complications. 

So far, lovo-cel's safety profile has been consistent with the known risks of autologous stem cell transplantation and myeloablative single-agent busulfan conditioning and underlying SCD. Adverse reactions include decreased blood pressure, anemia, hot flush, and acute myeloid leukemia (AML).

In a statement, bluebird bio said that the FDA's guidance does not affect the rest of its trial for ages 18 years and older and that it will continue enrolling new participants into the HGB-205, HGB-201, and LTF-307 studies, as planned. A total 49 patients have been treated with lovo-cel as of February 17, 2021, with up to six years of follow-up in all three studies. The company also said it is preparing to answer any written queries that the regulator might have in early 2022 regarding the partial hold. 

"The safety of patients treated with our gene therapies is always our top priority. Consistent with the FDA’s direction, we have paused enrollment and treatment of patients younger than 18 in our SCD clinical program, and we will continue to work collaboratively with the FDA to understand and address their concerns," commented Dr. Richard Colvin, the chief medical officer for bluebird bio. 

The company is currently evaluating the impact of the hold order on its biologics license application (BLA) for lovo-cel, which has been planned for the first quarter of 2023. The approval for this application will be based on efficacy outcomes from patients in the HGB-206 Group C group. Bluebird bio will perform analytical comparisons and validate its commercial manufacturing process before submitting its BLA to the FDA. 

Lovo-cel has already received an orphan drug designation, fast track designation, rare pediatric disease designation, and regenerative medicine advanced therapy (RMAT) designation from the FDA. As of this writing, the drug is still being evaluated and has not been approved for use in any location.