Humanigen announces preparation of Phase 1b study of ifabotuzumab in solid tumors following presentation of Phase 1 study results at EANM?21

Humanigen, Inc. (Nasdaq: HGEN), a clinical-stage biopharmaceutical company, today announced its research partners will present Phase 1 results from a study of ifabotuzumab in glioblastoma multiforme (GBM) at the Annual Congress of the European Association of Nuclear Medicine (EANM'21) and plan to initiate a follow-on Phase 1b study in non-CNS solid tumors in early 2022. EANM is the largest organization dedicated to nuclear medicine in Europe and represents more than 9,000 specialists from 41 different countries.

The abstract will be presented virtually by Principal Investigator Prof. Andrew Scott, Head, Tumor Targeting Laboratory, Olivia Newton-John Cancer Research Institute; Director of the Department of Molecular Imaging and Therapy, Austin Health; and Professor, School of Cancer Medicine, La Trobe University. The abstract (OP-0854) entitled: "Phase I safety and bioimaging trial of ifabotuzumab in patients with glioblastoma" has been published in the EANM?21 abstract book and was chosen to be included in a TOP 3 trials session at EANM'21 that will take place from 3:05-4:35pm Central European Standard Time on October 22, 2021.¹

"The biodistribution characteristics demonstrated in the Phase 1 GBM study indicate ifabotuzumab has ideal characteristics for a range of therapeutic options including the creation of an antibody-drug conjugate," said Prof. Scott. "Our preclinical studies with antibody-drug conjugate forms of ifabotuzumab have shown promising results. We hope to take this payload delivery approach into the clinic in the next 1-2 years."

The Olivia Newton-John Cancer Research Institute plans to conduct a Phase 1b dose-escalation and imaging study in non-CNS solid tumors that is scheduled to begin in early 2022. This will be led by Prof. Andrew Scott and Prof. Hui Gan, Clinical Research Lead, Olivia Newton-John Cancer Research Institute and Director, Cancer Clinical Trials Center, Austin Health.

"We are excited by the potential ifabotuzumab holds to create a novel cancer therapeutic that delivers cytotoxic agents to tumor cells while minimizing toxicity to normal tissue," said Cameron Durrant, Chairman and CEO of Humanigen. "We look forward to supporting our valued partners in Australia as they advance research of ifabotuzumab into solid tumors."

About Ifabotuzumab
Ifabotuzumab is a proprietary Humaneered® monoclonal antibody that binds the EphA3 receptor, which plays an important role during fetal development but is not thought to be expressed nor play a significant role in healthy adults. EphA3 is a tyrosine kinase receptor, aberrantly expressed on the tumor vasculature and tumor stroma in many solid tumors including melanoma, breast cancer, lung cancer, colorectal cancer, GBM and prostate cancer, making it an attractive target for a range of cancers.

Humanigen has completed a Phase 1 study in multiple hematologic malignancies that suggest it is well tolerated with mild-to-moderate infusion reactions that can be managed by stopping infusion, or using medications to treat reactions (chills, fever, nausea, hypertension, and rapid heart rate).

In 2021, a Phase 1 safety and bioimaging study of ifabotuzumab, supported by Cure Brain Cancer Foundation, and Humanigen, showed specific and reproducible targeting of the tumor and its microenvironment, with no normal tissue uptake, in all patients. Future development plans, in conjunction with our research partners in Australia, are intended to confirm highly specific tumor uptake in non-CNS solid tumors with the intention of creating an antibody-drug conjugate by linking ifabotuzumab to a cytotoxic (cell-killing) agent.

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' with lenzilumab, 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 of ifabotuzumab to be used as part of an antibody-drug conjugate to treat cancer, statements regarding plans for future plans for further studies of ifabotuzumab; statements regarding use of lenzilumab as a therapy for the treatment of patients hospitalized with COVID-19; and statements regarding 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. Scott, A., et al. (2021). Phase I safety and bioimaging trial of ifabotuzumab in patients with glioblastoma (OP-0854). European Journal of Nuclear Medicine and Molecular Imaging September 24, 2021;48, s299 https://doi.org/10.1007/s00259-021-05547-1