Humanigen Announces Abstracts Accepted for the British Thoracic Society Winter Meeting 2021

• Abstract #S48 describes top-line results from the Humanigen Phase 3 LIVE-AIR study in hospitalized COVID-19 patients, which reveal a 54% relative improvement in the likelihood of survival without invasive mechanical ventilation (“SWOV”) in lenzilumab-treated patients compared to those treated with standard of care plus placebo
• Abstract #S49 describes an exploratory analysis from LIVE-AIR demonstrating a 3-fold improvement in SWOV in hospitalized COVID-19 patients less than 85 years with baseline CRP<150 mg/L treated with lenzilumab compared to those treated with standard of care plus placebo
• Abstract #S51 describes an analysis from the literature related to several in-hospital COVID-19 treatments, which shows the number of patients needed to be treated to prevent a single death in the subsequent 28-day period was 22.7 for lenzilumab, 26.3 for remdesivir, and 37.0 for baricitinib

Humanigen, Inc. (Nasdaq: HGEN) (“Humanigen”), 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 three abstracts pertaining to the potential use of lenzilumab in hospitalized COVID-19 patients will be presented at the British Thoracic Society Winter 2021 Meeting taking place Nov. 24-26, 2021. The society counts more than 4,000 members comprised of doctors, nurses, respiratory physiotherapists, scientists, and other professionals with a respiratory interest.

“We are pleased to have the opportunity to share the results of our Phase 3 study of lenzilumab in hospitalized COVID-19 patients with our medical and scientific colleagues in the United Kingdom,” said Cameron Durrant, MD, Chairman & CEO, Humanigen. “We believe the analysis of our LIVE-AIR data using baseline C-reactive protein (CRP) levels is important because it identifies a subset of patients, approximately 75% of the study population, for which lenzilumab treatment appears to show the greatest benefit. This is particularly relevant in the United Kingdom, where the government funded the formation of the International Severe Acute Respiratory Infection Consortium (ISARIC), a UK-wide consortium of doctors and scientists, that developed the 4C Mortality Score, which utilizes CRP levels as the only biomarker marker used to calculate the score. By focusing on patients most likely to benefit from treatment with lenzilumab, analysis shows the number needed to be treated to potentially prevent a death over a subsequent 28-day period may be reduced from 22.7 to 13.9.”

Lenzilumab is not authorized, or approved, in any country.

Abstract #S48

Lenzilumab Efficacy and Safety in Newly Hospitalized Covid-19 Subjects: Results from the LIVE-AIR Phase 3 Randomized Double-Blind Placebo-Controlled Trial

Summary: The abstract describes top-line results from Humanigen’s LIVE-AIR Phase 3 study, which reveal a 54% improvement (HR: 1.54; p=0.0403) in SWOV in lenzilumab-treated patients hospitalized with COVID-19 compared to those treated with standard of care plus placebo. The study also demonstrated significant improvement in SWOV for the predefined subgroup of subjects who received both corticosteroids and remdesivir (HR: 1.92; nominal p=0.0067). The incidence of treatment-emergent serious adverse events was similar across treatment groups. Treatment with lenzilumab resulted in no serious infusion-related reactions, no increase in the incidence of secondary infections and no attributable serious adverse events, including, hematologic or liver enzyme abnormalities. In addition, no cases of pulmonary alveolar proteinosis were reported.

Abstract #S49

C-Reactive Protein as a Biomarker for Improved Efficacy of Lenzilumab in Covid-19 Patients: Results from the LIVE-AIR Trial

Summary: The abstract describes an exploratory analysis of LIVE-AIR data, from the Phase 3 study of lenzilumab in patients hospitalized with COVID-19, based upon an assessment of baseline CRP measurements, a biomarker that is commonly used to assess the body’s inflammatory response. The analysis shows those patients in the LIVE-AIR clinical trial with baseline CRP<150 mg/L and age <85 who were treated with lenzilumab benefited from a 3-fold improvement in SWOV (HR: 3.04; nominal p=0.0003) compared to those treated with standard of care plus placebo. The analysis led to the conclusion that inhibition of GM-CSF, an orchestrator of cytokine storm, by lenzilumab early in the hyperinflammatory response improves outcomes in COVID-19.

Abstract #S51

Evaluation of Treatment Approaches for Hospitalized COVID-19 Patients

Summary: The abstract describes an analysis from literature of several in-hospital COVID-19 treatments, which showed the number patients needed to be treated (NNT) to prevent a single death in a subsequent 28-day period were 22.7 for lenzilumab, 26.3 for remdesivir, and 37.0 for baricitinib. The NNT for lenzilumab improved with refinement of concomitant medications and patient phenotype. The NNT to prevent a single death in a subsequent 28-day period is reduced to 13.9 in patients age less than 85 years with a CRP<150 mg/L.

About ISARIC Coronavirus Clinical Characterisation Consortium (4C) Mortality Score

The UK government funded the formation of ISARIC 4C (Coronavirus Clinical Characterisation Consortium), a consortium of doctors and scientists across the UK that gathered and analyzed samples from COVID-19 patients.¹ Using data from 57,824 patients, ISARIC developed the 4-C Mortality Score.² This risk-stratification tool outperformed existing risk-stratification tools and has been extensively validated in independent studies in other countries across the world, including France, The Netherlands, Italy, Pakistan, Turkey, and Canada.³ Use of the assessment tool results in a 4C Mortality Score that can range from 0-21 with direct correlation between a higher score and higher mortality rate. For example, a score of 1 equates to a mortality rate of 0.3%, while a score of 10 equates to 22.9% mortality rate, and a score of 21 is associated with an 87.5% mortality rate.⁴ CRP levels are one of the eight variables and the only biomarker utilized in this scoring system to arrive at the 4C Mortality Score and increasing CRP levels lead to higher scores (e.g., CRP<50 mg/L = +0, CRP 50-99 mg/L = +1, CRP≥ 100 mg/L = +2)⁴.

About Humanigen, Inc.

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 Conditional 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.

Humanigen 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: Humanigen’s beliefs as to the potential benefits of lenzilumab as a treatment for hospitalized COVID-19 patients; its efforts to request and receive Conditional Marketing Authorization for lenzilumab in COVID-19 in the UK and other territories; and its other plans to initiate or participate in planned clinical trials and otherwise explore the effectiveness of lenzilumab and other candidates in its development portfolio as therapies for other inflammation and immune-oncology indications.

Forward-looking statements are subject to a number of risks and uncertainties including, but not limited to, the risks inherent in the company’s lack of profitability and need for additional capital to conduct its business; its dependence on partners to further the development of its product candidates; the uncertainties inherent in the development, attainment of the requisite regulatory authorizations and approvals and launch of any new pharmaceutical product; challenges associated with manufacturing and commercializing a biologic such as lenzilumab; the outcome of pending or future litigation; and the various risks and uncertainties described in the "Risk Factors" sections and elsewhere in Humanigen's periodic and other filings with the Securities and Exchange Commission.

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. The Company undertakes no obligation to revise or update any forward-looking statements made in this press release 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.

References

1. ISARIC4C (Coronavirus Clinical Characterisation Consortium). Retrieved Nov. 19, 2021, from https://isaric4c.net/
2. Knight S, et al. Risk stratification of patients admitted to hospital with covid-19 using the ISARIC WHO Clinical Characterisation Protocol: development and validation of the 4C Mortality Score. BMJ 2020;370:m3339 doi:10.1136/bmj.m3339
3. Risk prediction: the 4C Mortality Score. Retrieved Nov. 19, 2021, from https://isaric4c.net/outputs/4c_score/
4. 4C Mortality Score [online assessment tool]. Retrieved Nov. 19, 2021, from https://isaric4c.net/risk/v2/

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