• The RATinG (Risk Adapted Therapy in Acute GvHD) is the first trial to explore granulocyte-macrophage colony-stimulating factor (GM-CSF) neutralization for the early treatment of participants with high-risk acute Graft versus Host Disease

• Planned interim assessment expected in 2024 following treatment of first 20 participants

Short Hills, New Jersey--(Newsfile Corp. - August 7, 2023) - Humanigen, Inc. (OTC Pink: HGEN), a clinical-stage biopharmaceutical company, today announced successful dosing of the first participant in the RATinG trial of lenzilumab for the early treatment of acute Graft versus Host Disease (aGvHD), conducted by IMPACT, a world-class accelerated clinical trial network delivering innovative research for stem cell transplant patients in major centers in the UK.

"I am delighted that we have treated our first patient and am grateful to the IMPACT Partnership, Humanigen and to the US MAGIC Consortium for supporting this important study," said Professor Adrian Bloor MA, MB BChir, PhD, FRCP, FRCPath, director of Stem Cell Transplantation, The Christie NHS Foundation Trust. "We anticipate that RATinG will be enrolling patients across 18 IMPACT treatment centers in the UK."

The RATinG trial, a Phase 2/3 study, aims to evaluate the efficacy of lenzilumab as an early treatment to improve non-relapse mortality in patients with high risk aGvHD following allogeneic stem cell transplant (HSCT). aGvHD is a serious condition with significant morbidity and mortality that affects 40%-70% of all patients who undergo HSCT.^1,2 Mortality from aGvHD is as high as 70%-75% and patients with Grade III aGvHD may not survive more than two years,³ making it one of the leading causes of non-relapse mortality in this situation.² Lenzilumab is intended to neutralize the immune signalling of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF), which may initiate the inflammatory cascade that drives aGvHD.⁴Lenzilumab is administered to RATinG participants identified with markers of high-risk aGvHD using the MAGIC criteria. This population has a four-fold higher mortality rate than those identified as low-risk using the same biomarkers.⁵ The RATinG trial is being conducted in collaboration with IMPACT, the British Society of Blood and Marrow Transplantation, and the University of Birmingham's Cancer Research UK Clinical Trials Unit.

"We are excited to support of the use of lenzilumab in a clinical trial that addresses the unmet need of aGvHD and help improve patient outcomes," said Dr. Cameron Durrant, chairman and chief executive officer, Humanigen.

About the Risk Adapted Therapy in Acute Graft versus Host Disease (RATinG) Trial

The RATinG trial will evaluate lenzilumab in participants who have undergone allogeneic HSCT and been diagnosed with high-risk aGvHD. The trial is proposed to be conducted at up to 18 sites across the UK transplant network in two stages. The first stage of the trial is expected to treat 20 participants with lenzilumab before conducting an interim assessment of safety, efficacy, and feasibility. If an independent data monitoring committee deems the second stage to be feasible, then the trial would progress to its double-blind, randomized (1:1), second stage, which contemplates enrolment of approximately 220 patients. A second interim analysis is planned to assess futility based upon the 28-day response rate to the first infusion in the first 150 evaluable patients.

Investigators will assess for aGvHD diagnosis and risk stratification as measured by the Mount Sinai Acute GvHD International Consortium ("MAGIC") biomarkers. Intermediate and high-risk groups will be treated with lenzilumab and steroids in stage 1. In stage 2 they would be randomized to receive lenzilumab and steroids or placebo and steroids. The stage 2 primary endpoint, non-relapse mortality, would be assessed once all participants complete at least 6 months follow up.

About Humanigen

Humanigen, Inc. (OTC Pink: HGEN) ("Humanigen"), is a clinical-stage biopharmaceutical company focused on developing lenzilumab, a first-in-class antibody that binds to and neutralizes granulocyte-macrophage colony-stimulating factor. Humanigen is developing lenzilumab as a treatment for chronic myelomonocytic leukemia and acute graft versus host disease. Humanigen is also exploring use of lenzilumab to prevent toxicities associated with CAR-T therapy through investigator-initiated trials. Humanigen is also developing an antibody drug conjugate (ADC) utilizing its EphA-3 targeted monoclonal antibody ifabotuzumab ("ifab") for solid tumors. For more information, visit and follow Humanigen on Twitter.

About IMPACT

IMPACT is a partnership of organizations committed to improving the outcomes of stem cell transplant patients through the delivery of clinical trials across the UK. It is jointly funded by Anthony Nolan, Leukaemia UK and NHS Blood and Transplant. IMPACT aims to ensure patients benefit from scientific advances sooner by making it easier for transplant centers to work together to set up clinical trials, recruit patients and share data. The partnership allows transplant centers across the UK to work together to deliver clinical trials focused on stem cell transplantation. IMPACT provides funding for research nurses in eleven centers and works with a further eleven affiliated centers, which also participate in IMPACT trials. IMPACT trials are coordinated by the central hub, located at the University of Birmingham's Cancer Research UK Clinical Trials Unit (CRCTU).

About the University of Birmingham

The University of Birmingham is ranked amongst the world's top 100 institutions, and its work brings people from across the world to Birmingham, including researchers and teachers and more than 6,500 international students from nearly 150 countries.

Forward-Looking Statements about Humanigen

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.

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 continue as a going concern; our exploration of restructuring options, which may include a bankruptcy or other insolvency proceeding, and other strategic alternatives; 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 or arbitration; 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 press release to reflect events or circumstances after the date hereof, to reflect new information or the occurrence of unanticipated events, or to update the reasons why actual results could differ materially from those anticipated in the forward-looking statements, in each case, except as required by law.

Humanigen Investor Relations Contact
Ed Jordan
Chief Commercial Officer
IR@humanigen.com
650-243-3181

Humanigen Media Relations Contact
Charlotte Wray
cwray@rxmedyn.com
646-247-3405

IMPACT Media
Rebecca Collings
Cancer Research UK Clinical Trials Unit
Institute of Cancer and Genomic Sciences
University of Birmingham
RATinG@trials.bham.ac.uk

University of Birmingham Press Office
Emma McKinney, Media Relations Manager
University of Birmingham
e.j.mckinney@bham.ac.uk
+44 (0)7789 921 165

References

1. Zeiser, R., and Blazar, B. (2017). Acute graft-versus-host disease — biologic process, prevention, and therapy. New England Journal of Medicine, 377(22), 2167-2179.

2. Harris, A.C., et al. (2016) International, Multicenter Standardization of Acute Graft-versus-Host Disease Clinical Data Collection: A Report from the Mount Sinai Acute GvHD International Consortium. Biol. Blood Marrow Transplant. 22:4-10.

3. Malard, F. et al. (2020). Treatment and unmet needs in steroid-refractory acute graft-versus-host disease. Leukemia. 34:1229-1240

4. Gartlan, K. et al. (2019). Donor T-cell-derived GM-CSF drives alloantigen presentation by dendritic cells in the gastrointestinal tract. Blood Advances, 3(19), 2859-2865.

5. Hartwell, M.J. et al. (2017). An early-biomarker algorithm predicts lethal graft-versus-host disease and survival. JCI Insights. 2(3):e89798. doi: 10.1172/jci.insight.89798.

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