• Abstract #2777 describes preclinical models that demonstrate GM-CSF neutralization with lenzilumab improves CAR-T cell proliferation, but blocking the GM-CSFα receptor may inhibit CAR-T cell proliferation
• Abstract #1758 describes the Phase 3 SHIELD study, which is planned to confirm whether lenzilumab can break the efficacy/toxicity link thereby improving the toxicity profile of commercially available CAR-T therapies for non-Hodgkin lymphoma while maintaining or improving efficacy

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 two abstracts pertaining to the potential use of lenzilumab in CAR-T will be presented at the 63rd Annual Meeting of the American Society of Hematology (ASH) taking place December 11-14, 2021. The society counts more than 18,000 hematologists among its membership from more than 100 countries, and its annual meeting attracts over 30,000 professional attendees.

“After completing a Phase 3 trial of lenzilumab, in 2021, for the treatment of patients hospitalized with COVID-19 pneumonia, we look forward to advancing our efforts to develop lenzilumab as a complementary therapy to potentially reduce CAR-T associated toxicities and to potentially improve outcomes for non-Hodgkin lymphoma patients,” said Adrian Kilcoyne, Chief Medical Officer, Humanigen. “My experience working in the development of CAR-T therapies, which are now currently commercially available, suggests preventing toxicity and optimizing durable response rates remain challenges. Our plans include initiating the Phase 3 SHIELD study of lenzilumab in the first half of 2022 and we may be able to announce interim data at ASH 2022.”

Abstract #2777

Optimized Inhibition of GM-CSF in Preclinical Models of Anti-CD19 Chimeric Antigen Receptor T Cell Therapy

Summary: The abstract describes the evaluation of differential targeting of the GM-CSF ligand using lenzilumab compared to targeting the GM-CSFα receptor using a different antibody in pre-clinical models. The research demonstrated significant differences on CAR-T cell functions and CAR-T cell-monocyte interactions when GM-CSF is neutralized with lenzilumab compared to blocking its receptor with other agents. A key finding is that lenzilumab neutralization of GM-CSF improved CAR-T cell proliferation, but the GM-CSFRα receptor blocking antibody may significantly inhibit CAR-T cell proliferation in a dose-dependent manner. This may have efficacy implications.

Presenter: Evandro Bezerra, MD, Mayo Clinic in Rochester, MN.

Session: 703. Cellular Immunotherapies: Basic and Translational: Poster II

Date: December 12, 2021; 6:00-8:00 PM EST

Abstract #175

A Phase 3 Randomized, Placebo-Controlled, Open-Label, Multi-Center Trial of Lenzilumab to Improve the Safety and Efficacy of CAR-T Cell Therapy in Adults with Relapsed or Refractory Large B-Cell Lymphoma* (The SHIELD Study)

Summary: The abstract describes a planned Phase 3 study of prophylactic lenzilumab administration in sequenced therapy with commercially available CAR-Ts to treat non-Hodgkin lymphoma. The study aim is to determine if lenzilumab can break the efficacy/toxicity linkage associated with CAR-T therapy thereby improving the toxicity and tolerance of CAR-T while maintaining or improving efficacy by neutralizing GM-CSF.

Presenter: Saad Kenderian, MD, principal investigator in the T Cell Engineering Lab at Mayo Clinic in Rochester, MN.

Session: 704. Cellular Immunotherapies: Clinical: Poster I

Date: December 11, 2021; 5:30 PM-7:30 PM EST

* The SHIELD study protocol has been adapted since submission of the abstract to include a broader patient population

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 our plans to initiate the SHIELD study of lenzilumab with CAR-T and present interim results from the study at ASH 2022; statements pertaining to potential benefits of lenzilumab treatment in conjunction with CAR-T for non-Hodkin lymphoma; our effort to seek Conditional Marketing Authorization of lenzilumab by the MHRA for treatment of patients hospitalized with COVID-19; our beliefs regarding potential benefits of lenzilumab as a therapy for certain hospitalized patients with COVID-19; and our other plans to explore the effectiveness of lenzilumab as therapy for other indications.

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 conduct 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, except as required by law.

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