The US Food and Drug Administration (FDA) has placed a partial clinical hold on bluebird bio’s clinical programme for lovotibeglogene autotemcel (lovo-cel) gene therapy to treat sickle cell disease (SCD) in adolescents.

An experimental one-time therapy, lovo-cel can potentially provide functional copies of a modified form of the β-globin gene into the blood stem cells of the patients. This approach aids in producing anti-sickling haemoglobin (HbAT87Q) that lowers the HbS proportion.

The move comes after an adolescent trial participant contracted persistent, non-transfusion-dependent anaemia 18 months after receiving lovo-cel.

The participant is in good clinical condition, with no signs of malignancy or clonal predominance, the company said.

With the partial suspension, the company will halt the dosing and administration of the trial drug in subjects aged below 18 years.

Recruitment and dosing of the SCD patients aged 18 years and above living in the HGB-206, HGB-210 and LTF-307 trials and follow up of already treated subjects of all age groups in all trials will progress as scheduled.

In accordance with the clinical hold, bluebird expects to receive written queries from the FDA early next year. The company plans to work rapidly to provide answers that could aid in lifting the partial hold.

It is assessing the potential effect of the partial clinical hold on the filing of biologics license application (BLA) expected in the first quarter of 2023.

bluebird bio chief medical officer Richard Colvin said: “Consistent with the FDA’s direction, we have paused enrolment and treatment of patients younger than 18 in our SCD clinical programme, and we will continue to work collaboratively with the FDA to understand and address their concerns.

“While the partial hold is in place, we intend to continue planned follow-up on previously treated patients from HGB-206 and HGB-210 and plan to enrol and treat new adult patients with lovo-cel through study HGB-210 to further characterise the efficacy and safety of lovo-cel for patients with SCD and to continue to advance the field of gene therapy.”

In June this year, the FDA lifted the clinical hold placed on the company’s gene therapy trials.

Cell & Gene Therapy Coverage on Clinical Trials Arena supported by Cytiva.

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