The US Food and Drug Administration (FDA) has rejected Humanigen’s request for emergency use authorization (EUA) of its antibody lenzilumab for treating recently hospitalised Covid-19 patients.

A first-in-class antibody, lenzilumab attaches to and kills granulocyte-macrophage colony-stimulating factor (GM-CSF).

GM-CSF is a key cytokine that causes a hyperinflammatory cascade or cytokine storm linked to Covid-19 and other indications.

In a letter to the company, FDA noted that it was not able to conclude that the known and possible benefits of lenzilumab outweigh the known and potential risks of its usage as a Covid-19 therapy.

The FDA also invited Humanigen to present further data when it becomes available.

In the Phase III LIVE-AIR clinical trial, early intervention with lenzilumab was demonstrated to prevent the consequences of a full-blown cytokine storm in hospitalised Covid-19 patients.

Furthermore, lenzilumab showed improvement in the relative likelihood of survival in hospitalised patients in a Phase III trial.

A 54% greater chance of survival without requiring invasive mechanical ventilation was observed in patients receiving lenzilumab plus other treatments versus those on placebo plus other treatments. Humanigen noted that the results were statistically significant.

Last month, the company reported that the National Institutes of Health (NIH) progressed the ACTIV-5/BET-B study of its lenzilumab for Covid-19 from a Phase II exploratory trial to a Phase II/III trial.

Humanigen CEO Cameron Durrant said: “We remain committed to bringing lenzilumab to patients hospitalised with Covid-19.

“We believe the ongoing ACTIV-5/BET-B trial, which has been advanced to enrol up to 500 patients, may provide additional safety and efficacy data sufficient to support our efforts to obtain a EUA to treat hospitalised Covid-19 patients.”

The company commenced a rolling review submission to the UK Medicines and Healthcare Products Regulatory Agency, seeking marketing approval for lenzilumab.

Humanigen is developing lenzilumab for the treatment of cytokine storm linked to Covid-19, CD19-targeted CAR-T cell therapies and is assessing the efficacy of the treatment for various other inflammatory ailments.