REGN-EB3 was invented by Regeneron Pharmaceuticals, while mAb114 was developed by the US National Institutes of Health (NIH) and was licensed by Ridgeback Biotherapeutics last year.

REGN-EB3 is a combination of three fully-human monoclonal antibodies and mAb114 is a single monoclonal antibody.

The randomised, multi-centre, controlled PALM trial was designed to assess the safety and efficacy of REGN-EB3 and mAb114, along with Mapp Biopharmaceutical’s ZMapp and Gilead Sciences’ remdesivir.

It was commenced in November last year and is being carried out in the Democratic Republic of Congo (DRC), where an Ebola outbreak is ongoing.

A total of 681 patients have been recruited as of 9 August, with the trial aiming to enrol 725.

The study compared mortality data from the REGN-EB3, mAb114, and remdesivir arms with the ZMapp group, which was considered as the control.

An independent data and safety monitoring board (DSMB) reviewed initial results from 499 subjects and recommended that the study can be terminated early as REGN-EB3 met the required criterion.

Regeneron noted that REGN-EB3 demonstrated superiority over ZMapp in preventing death.

Reuters noted that around 29% of subjects treated with REGN-EB3 and 34% in the mAb-114 arm died, compared to 49% of those on ZMapp and 53% who received remdesivir.

Based on the findings, the DSMB recommended that all future participants in the extension phase of the study should receive either REGN-EB3 or mAb114, and that ZMapp and remdesivir should be dropped.

Regeneron Pharmaceuticals Research and Development executive vice-president Neil Stahl said: “We look forward to reviewing the trial data and are working with governments and other collaborators, including BARDA, to make REGN-EB3 available for the current outbreak and future use.”