Humanigen Announces Oral Presentation of Lenzilumab LIVE-AIR Phase 3 Study Results at IDWeek 2021

• Lenzilumab significantly improved the likelihood of survival without ventilation (SWOV) by 54% versus standard treatment in hospitalized patients with COVID-19 pneumonia
• IDWeek is the premier global scientific meeting that brings together infectious disease specialists from the Infectious Disease Society of America (IDSA) and other medical societies

Humanigen, Inc. (Nasdaq: HGEN), a clinical-stage biopharmaceutical company focused on preventing and treating an immune hyper-response called ‘cytokine storm’ with its lead drug candidate, lenzilumab, today announced a presentation of the results from the Company’s randomized, double-blind, placebo-controlled LIVE-AIR Phase 3 study at IDWeek 2021, which is the joint annual meeting of the IDSA, the Society for Healthcare Epidemiology of America (SHEA), the HIV Medical Association (HIVMA), the Pediatric Infectious Diseases Society (PIDS), and the Society of Infectious Diseases Pharmacists (SIDP) taking place virtually from September 29^th to October 3^rd.

Zelalem Temesgen, MD, Professor of Medicine at Mayo Clinic and Principal Investigator of the LIVE-AIR Phase 3 trial, will deliver a presentation regarding the efficacy and safety of lenzilumab in hospitalized COVID-19 patients at the meeting. The abstract (Number 1071804) entitled: “Lenzilumab Efficacy and Safety in Hospitalized COVID-19 Subjects: Results from a Phase 3 Randomized Double-Blind Placebo-Controlled Trial” has been accepted for oral presentation. The presentation will be available to participants throughout IDWeek 2021.

“As the principal investigator of the LIVE-AIR Phase 3 study, I am excited to share these data with the scientific community at IDWeek,” said Zelalem Temesgen, MD, Professor of Medicine at Mayo Clinic. “These results support the proposition that lenzilumab may be a foundational therapy to prevent the hyperinflammatory immune response which can lead to mechanical ventilation and ultimately death in hospitalized COVID-19 patients.”

The LIVE-AIR study achieved its primary endpoint of survival without ventilation measured through day 28 following treatment (HR: 1.54; 95%CI: 1.02-2.32, p=0.0403). Survival without ventilation is an important clinical endpoint that measures not only mortality, but the morbidity associated with mechanical ventilation. The Kaplan-Meier estimate for IMV and/or death was 15.6% (95%CI: 11.5-20.9) in the lenzilumab arm versus 22.1% (95%CI: 17.4-27.9) in the placebo arm. Approximately 94% of patients received dexamethasone (or other steroids), 72% received remdesivir, and 69% received both. In the subgroup of patients treated with both remdesivir and corticosteroids, lenzilumab improved survival without ventilation relative to placebo (HR: 1.92; 95%CI: 1.20-3.07, p=0.0067). In this study, lenzilumab appeared to be safe and well-tolerated, there were no serious adverse events (SAEs) attributed to lenzilumab and no suspected unexpected serious adverse reactions (SUSARS) reported for lenzilumab.

“We are pleased the phase 3 LIVE-AIR data have been selected for oral presentation at the most prestigious infectious disease meeting of the year,” said Cameron Durrant, CEO of Humanigen. “At Humanigen, we are committed to helping patients survive COVID-19 and believe that the clinical results seen with lenzilumab show its potential. There are 73,000 patients currently hospitalized in the U.S who have limited treatment options available to them.”¹

Humanigen once again thanks the investigators and patients in the LIVE-AIR study who helped to advance the development of lenzilumab and enable the achievement of this important milestone for the company.

About the LIVE-AIR, Phase 3 Study of Lenzilumab

This study was a randomized, double-blind, placebo-controlled, multi-center Phase 3 trial for the treatment and prevention of serious and potentially fatal outcomes in patients hospitalized with COVID-19 pneumonia. The primary objective was to assess whether lenzilumab, in addition to other treatments, which included dexamethasone (or other steroids) and/or remdesivir, could alleviate the immune-mediated ‘cytokine storm’ and improve survival without ventilation, or ‘SWOV’ (sometimes referred to as ‘ventilator-free survival’). SWOV is a composite endpoint of time to death and time to invasive mechanical ventilation (IMV), which is a robust measure that is less prone to favor a treatment with discordant effects on survival or days free of ventilation.

The LIVE-AIR study enrolled 520 patients in 29 sites in the US and Brazil who were at least 18 years of age; experienced blood oxygen saturation (SpO2) of less than or equal to 94%; or required low-flow supplemental oxygen, or high-flow oxygen support, or non-invasive positive pressure ventilation; and were hospitalized but did not require IMV. Following enrollment, subjects were randomized to receive three infusions of either lenzilumab or placebo, with each infusion separated by eight hours over a 24-hour period. The primary endpoint was the difference between lenzilumab treatment and placebo treatment in SWOV through day 28 following treatment. Results of the trial have been submitted for publication in a peer-reviewed journal.

About Lenzilumab

Lenzilumab is a proprietary Humaneered® first-in-class monoclonal antibody that has been proven to neutralize GM-CSF, a cytokine of critical importance in the hyperinflammatory cascade, sometimes referred to as cytokine release syndrome (“CRS”) or cytokine storm (CS), associated with COVID-19 and other indications. Lenzilumab binds to and neutralizes GM-CSF, consequently improving outcomes for hypoxic patients hospitalized with COVID-19. Humanigen believes that its GM-CSF neutralization has the potential to reduce the hyper-inflammatory cascade known as cytokine release syndrome common to chimeric antigen receptor T-cell (CAR-T) therapy and acute Graft versus Host Disease (aGvHD).

In CAR-T, lenzilumab successfully achieved pre-specified primary endpoint at the recommended dose in a Phase 1b study with Yescarta® in which the overall response rate was 100% and no patient experienced severe cytokine release syndrome or severe neurotoxicity. Based on these results, Humanigen plans to test lenzilumab in a randomized, multicenter, potentially registrational, Phase 2 study to evaluate its efficacy and safety when combined with other commercially available CD19 CAR-T therapies in DLBCL. Lenzilumab will also be tested to assess its ability prevent and/or treat aGvHD in patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT).

A study of lenzilumab is also being prepared for patients with chronic myelomonocytic leukemia (CMML) exhibiting RAS pathway mutations. This study will build on evidence from a Phase 1 study, conducted by Humanigen, that showed RAS mutations are associated with hyper-proliferative features, which may be sensitive to GM-CSF neutralization.

Lenzilumab has not been authorized or approved for use in any indication by any regulatory agency.

About Humanigen

Humanigen, Inc. (Nasdaq: HGEN) (“Humanigen”), is a clinical-stage biopharmaceutical company focused on preventing and treating an immune hyper-response called ‘cytokine storm’. Lenzilumab is a first-in class antibody that binds to and neutralizes granulocyte-macrophage colony-stimulating factor (GM-CSF). Results from preclinical models indicate GM-CSF is an upstream regulator of many inflammatory cytokines and chemokines involved in the cytokine storm. Early in the COVID-19 pandemic, investigation showed high levels of GM-CSF secreting T cells were associated with disease severity and intensive care unit admission. Humanigen’s Phase 3 LIVE-AIR study suggests early intervention with lenzilumab may prevent consequences of a full-blown cytokine storm in hospitalized patients with COVID-19. Humanigen has submitted lenzilumab to Medicines and Health Regulatory Agency in the United Kingdom for a rolling review towards potential Marketing Authorization. Humanigen is developing lenzilumab as a treatment for cytokine storm associated with COVID-19 and CD19-targeted CAR-T cell therapies and is also exploring the effectiveness of lenzilumab in other inflammatory conditions such as acute Graft versus Host Disease in patients undergoing allogeneic hematopoietic stem cell transplantation, eosinophilic asthma, and rheumatoid arthritis. For more information, visit www.humanigen.com and follow Humanigen on LinkedIn, Twitter, and Facebook.

Forward-Looking Statements

All statements other than statements of historical facts contained in this press release are forward-looking statements. Forward-looking statements reflect management's current knowledge, assumptions, judgment, and expectations regarding future performance or events. Although management believes that the expectations reflected in such statements are reasonable, they give no assurance that such expectations will prove to be correct, and you should be aware that actual events or results may differ materially from those contained in the forward-looking statements. Words such as "will," "expect," "intend," "plan," "potential," "possible," "goals," "accelerate," "continue," and similar expressions identify forward-looking statements, including, without limitation, statements regarding the potential use of lenzilumab as a therapy for the treatment of patients hospitalized with COVID-19 pneumonia; our plans to develop lenzilumab for CAR-T and other indications; and our other plans relating to lenzilumab.

Forward-looking statements are subject to a number of risks and uncertainties including, but not limited to, the risks inherent in our lack of profitability and need for additional capital to grow our business; our dependence on partners to further the development of our product candidates; the uncertainties inherent in the development, attainment of the requisite regulatory authorizations and approvals and launch of any new pharmaceutical product; the outcome of pending or future litigation; and the various risks and uncertainties described in the "Risk Factors" sections of our latest annual and quarterly reports and other filings with the SEC.

All forward-looking statements are expressly qualified in their entirety by this cautionary notice. You should not rely upon any forward-looking statements as predictions of future events. We undertake no obligation to revise or update any forward-looking statements made in this presentation to reflect events or circumstances after the date hereof or to reflect new information or the occurrence of unanticipated events, except as required by law.

Reference

1. Hannah Ritchie, Edouard Mathieu, et. Al. (2020) - "Coronavirus Pandemic (COVID-19)". Published online at OurWorldInData.org. Current hospitalizations for September 27, 2021. Retrieved from: https://ourworldindata.org/coronavirus on Sep. 28, 2021.

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