Shares of Humanigen Inc. (NASDAQ:HGEN) climbed 30.2% to $5.31 on Monday after the company disclosed that, when treated with the company's anti-GM-CSF antibody, lenzilumab, 12 hospitalized patients with severe or critical pneumonia as a result of COVID-19 showed "rapid clinical improvement." Median time to recovery and discharge for the group was five days.

The research, based on compassionate use of the experimental therapy at Mayo Clinic, precedes a registration-directed phase III trial in COVID-19 pneumonia patients that the company is currently enrolling. Humanigen CEO Cameron Durrant told BioWorld the data were "very encouraging." Though recognizing the limitations of uncontrolled compassionate use studies, he said they give his team "even more confidence" in Humanigen's own study, "because the kind of patients we're recruiting are perhaps similar, if not potentially younger and perhaps less sick."

Humanigen's trial, NCT04351152, aims to enlist 238 participants and is slated to reach completion in September, according to

Mayo's data, "First Clinical Use of Lenzilumab to Neutralize GM-CSF in Patients with Severe and Critical COVID-19 Pneumonia," were published in an unrefereed preprint on the preprint server Medrxiv.

All patients in the study were hospitalized in the Mayo Clinic system and had severe or critical pneumonia as a result of COVID-19. They were also viewed as being at high risk of further disease progression, according to Humanigen. All of them required oxygen supplementation and had elevation in at least one inflammatory biomarker prior to receiving lenzilumab. They also all had at least one co-morbidity associated with poor outcomes in COVID-19 and several patients had multiple co-morbidities. The median age was 65.

Mayo's research found what they described as significant improvements in oxygenation and mean CRP and IL-6 values, as well as a reduction in inflammatory myeloid cells two days after lenzilumab treatment. Cytokine analysis showed a reduction in inflammatory myeloid cells two days after lenzilumab treatment, they said. There were no treatment-emergent adverse events attributable to the drug, and no mortality in the patients studied.

Humanigen has been working on the inflammatory cascade, sometimes referred to as cytokine release syndrome or cytokine storm, for more than three years. As part of those efforts, it established a collaboration agreement with Gilead Sciences Inc.-owned Kite Pharmaceuticals Inc. in May 2019 to evaluate lenzilumab with Kite’s Yescarta (axicabtagene ciloleucel) in patients with relapsed or refractory B-cell lymphoma. To fund its ongoing work, the company raised gross proceeds of about $71.8 million in a private placement of its shares.

In addition to Humanigen, at least two other companies are investigating anti-GM-CSF antibodies for the treatment of COVID-19 patients. Izana Bioscience Ltd., of Oxford, U.K., said namilumab (IZN-101) has been selected for testing as part of the U.K.-based CATALYST trial, which is also testing medicines in hospitalized COVID-19 patients. Namilumab is also under evaluation as part of a compassionate use study in Italy.

Meanwhile, Kiniksa Pharmaceuticals Ltd., of Hamilton, Bermuda, has also supplied its anti-GM-CSF antibody, mavrilimumab, on a compassionate-use basis.

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