EphA3

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--(News - 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.4 Lenzilumab 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 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. 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. Malard, F. et al. (2020). Treatment and unmet needs in steroid-refractory acute graft-versus-host disease. Leukemia. 34:1229-1240 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. 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. To view the source version of this press release, please visit

- Of the 14 participants enrolled and treated with lenzilumab plus azacitidine, ten are evaluable with three to eighteen months of follow-up and all ten have had a rapid clinical response - Building upon previously reported positive clinical responses, these additional data demonstrate statistically significant and clinically relevant improvements in hematologic outcomes, along with improvements in inflammatory markers, that occur in the early months after treatment initiation and appear durable - CMML is a rare, aggressive cancer; approximately 20% of patients survive three years from diagnosis - No new CMML medications with novel mechanisms of action have been approved in over 30 years and hypomethylating agents, such as azacitidine alone, are currently considered “standard of care” Short Hills, New Jersey – (June 9, 2023) - Humanigen, Inc. (Nasdaq: HGEN) today extended previously reported results by presenting additional, statistically significant hematologic improvements and reductions in inflammatory markers from lenzilumab, its investigational drug, in a Phase 2/3 trial of treatment-naïve participants with chronic myelomonocytic leukemia and RAS-pathway mutations. The additional data demonstrate that in all 10 participants with at least three months of treatment with both lenzilumab and azacitidine, blood monocyte count decreased fivefold (P=0.03), the percentage of blast cells and pro-monocytes decreased more than twofold (P=0.04), and C-reactive protein decreased more than threefold (P=NS) with improvements noted after both 3 months and 6 months of this combination treatment. These results suggest lenzilumab may normalize hematologic and inflammatory aberrations in CMML and improve the condition of participants. All ten evaluable participants had a rapid clinical response. CMML is a rare, aggressive cancer in which levels of monocytes, blast cells, and pro-monocytes are significantly elevated from normal levels. These pathologic changes are accompanied by significantly elevated proinflammatory markers, including C-reactive protein. Current treatment options for CMML patients are limited to blood transfusions, hydroxyurea, and supportive care alongside the current standard of care, which includes hypomethylating agents such as azacitidine and decitabine, which have limited response rates of 7% to 18%1, 2, 3 with no proven increase in overall survival. In the last 30 years, no new medicines with a novel mechanism of action have been approved for CMML patients who are at high risk of death or disease progression.4 Only about 20% of patients diagnosed with CMML survive for three years.5 “The PREACH-M trial findings to date, indicate that lenzilumab may improve treatment response in CMML,” said Humanigen Chairman and CEO Cameron Durrant, MD, MBA. “These results may create the possibility for lenzilumab development in myelodysplastic leukemias. I look forward to sharing the data at the poster presentation at the 2023 European Hematology Association congress in Frankfurt, Germany.” The presentation, entitled “Lenzilumab and Azacitidine Improve Hematologic Alterations of Chronic Myelomonocytic Leukemia in the PREACH-M Trial,” highlighted new data in poster format (P737) at 6:00 pm CEST on June 9, 2023, during the 2023 European Hematology Association congress. “Patients with CMML are normally treated with hypomethylating agents such as azacitidine, with reported response rates of just 7% to 18%, usually of limited duration,” said principal investigator Daniel Thomas, MD, PhD, program leader for blood cancer research at SAHMRI and an associate professor of medicine at the University of Adelaide. “Treating patients with lenzilumab appears to be improving clinical parameters, quality of life and systemic inflammation in the patients studied so far, and patients appear to be tolerating lenzilumab well. Critically, clinical responses appear to occur early, prior to the fourth monthly treatment cycle. No patients have relapsed, and we currently have two patients remaining on treatment for more than 18 months.” Lenzilumab, a granulocyte-macrophage colony-stimulating factor (GM-CSF) neutralizing antibody, prevents GMCSF from binding to receptors on hematologic progenitor cells. When GM-CSF binds to those receptors, it triggers normal myelocyte proliferation and maturation. In the presence of RAS-pathway mutations, GM-CSF contributes to the hyperproliferation of myelocytes in myelodysplastic leukemias such as CMML, juvenile myelomonocytic leukemia (JMML), and acute myeloid leukemia (AML).6,7,8 Therefore, lenzilumab’s ability to prevent GM-CSF binding to its receptor may inhibit the hyperproliferation in these conditions. PREACH-M (PREcision Approach to CHronic Myelomonocytic Leukemia), a non-randomized, open-label trial, is being conducted at multiple sites in Australia. It is sponsored by the South Australian Health and Medical Research Institute (SAHMRI), with grant funding from the Australian government and the study drug supplied by Humanigen. As of May 9, 2023, 14 CMML patients at intermediate or high risk of death or disease progression have received at least one dose of lenzilumab, along with azacitidine. Ten of those participants were evaluable based on at least three months of follow-up, and each experienced a rapid clinical benefit. Twenty-one grade 3 or 4 serious adverse events were observed, of which investigators assessed five as possibly related to lenzilumab. +++ About CMML CMML is an orphan disease with an approximate annual incidence of 1-4 cases per million1 in western countries and has limited therapeutic options. CMML is an aggressive and poorly understood cancer with only about 20% of patients surviving up to the three-year mark.9 The incidence of CMML in the US, UK, and Australia is about 1,700 patients annually.9 As an orphan disease, lenzilumab may qualify for certain regulatory and commercial advantages that could expedite development and potential approval. Humanigen and the Principal Investigator are assessing regulatory pathways that may enable early results to support a regulatory submission and potential approval by the Therapeutic Goods Administration in Australia, which could be expanded through Project Orbis10 to the United States and the United Kingdom ( ). About the PREACH-M Trial PREACH-M (PREcision Approach to CHronic Myelomonocytic Leukemia) is a Phase 2/3, non-randomized, openlabel clinical trial investigating precision medicine for adults with CMML.11 This trial investigates treatment response rates determined by the Savona Criteria for patients with CMML after administration of lenzilumab alongside azacitidine in patients with RAS pathway mutations. The study also measures the patients’ quality of life, using the MPN Symptoms Assessment Form: Total Symptom Score. Fourteen study participants were enrolled and treated with lenzilumab and azacitidine as of May 9, 2023, of which ten were evaluable for hematologic and inflammatory parameters based on at least three months of follow-up. The initial data demonstrate that blood monocyte count decreased by fivefold (p=0.03), percentage of blast cells and pro-monocytes decreased by more than twofold (p=0.04), platelet count and hemoglobin concentration both increased and remained elevated at 12 months (p=0.07 and p=0.02, respectively), and craniocaudal spleen size decreased by nearly 50% by 6 months (p=0.03). The inflammatory marker, C-reactive protein decreased by more than threefold (p=NS). All ten evaluable participants had a rapid clinical response. During the active treatment phase of the study, participants are required to attend clinic visits on Days 1 & 15 of the first cycle, and then on Day 1 of each subsequent 28-day cycle to assess how the participant is tolerating the therapy and ensure ongoing safety.12 In addition to regular safety blood tests throughout each cycle, participants’ disease response assessments are scheduled after 3, 6, 12 and 24 cycles of therapy to measure their disease response.12 Such assessments include blood tests, bone marrow aspirate and trephine, ultrasound of the spleen, physical exam and assessment of transfusion requirements and clinical symptoms.12 Participants who complete 24 cycles of active treatment enter the follow-up phase of the study where they are followed up every 6 months for 24 months for survival, disease status and further CMML-related treatment.11 For patients with confirmed progressive disease or relapse during the active treatment phase of the study, further study treatment will cease. Patients remain on study and are followed up for disease status, survival, and further CMML-related treatment every 6 months until 48 months from Cycle 1, Day 1.11 During the follow-up period, participants no longer receive any investigational drugs but are permitted to receive any CMML treatment at the discretion of the treating clinician. As part of the screening process, participants are required to have a bone marrow aspirate and trephine to test for certain acquired mutations that can be present in CMML.11 The study is seeking participants with TET2 and/or RAS pathway mutations. Participants with RAS pathway mutations or both TET2 and RAS mutations, receive azacitidine (administered subcutaneously at a dose of 75mg/m2 on Days 1-5, 8-9 or Days 1-7 for a total of 7 doses per 28-day cycle) in combination with lenzilumab (administered intravenously at a dose of 552mg on Days 1 & 15 of Cycle 1. Day 1 only for all subsequent cycles).11 The trial is sponsored by the South Australian Health and Medical Research Institute (“SAHMRI”) and funded by a Medical Research Future Fund grant from the National Health and Medical Research Council of the Australian government to the University of Adelaide. Humanigen provides lenzilumab for use in the study through its Australian subsidiary, Humanigen Australia Pty Ltd. Enrollment is open to newly diagnosed CMML patients who haven’t received any treatment. Anyone who is interested in learning more about the study, or obtaining additional information can visit the Australian New Zealand Clinical Trials Registry ( ). About Humanigen Humanigen, Inc. (Nasdaq: HGEN) ("Humanigen"), is a clinical-stage biopharmaceutical company focused on developing lenzilumab, a first-in-class antibody that binds to and neutralizes granulocyte-macrophage colonystimulating factor. Humanigen is developing lenzilumab as a treatment for chronic myelomonocytic leukemia. Humanigen is also exploring the 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 About the European Hematology Association The European Hematology Association serves medical professionals, researchers, and scientists with an active interest in hematology. They are the largest European-based organization connecting hematologists worldwide to support career development and research, harmonize hematology education, and advocate for hematologists and hematology. About the EHA Hybrid Congress The EHA2023 Hybrid Congress, being held in Frankfurt, Germany, from June 8-11, 2023, offers an interactive, comprehensive program dedicated to clinical research and practice, basic and translational research, as well as important opportunities for collaboration with stakeholders in the field of hematology. The educational and scientific program highlights state-of-the-art clinical practice, the latest findings in hematology research, and recent approaches on the diagnosis and treatment of hematologic diseases. 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 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 References 1. Costa, R., et. al. (2010). Activity of azacitidine in chronic myelomonocytic leukemia. Cancer, 117(12), 2690– 2696. 2. South Australian Registry data, South Australian Health and Medical Research Institute, April 14, 2021 3. Pleyer, L., et. al. (2014). Azacitidine in CMML: Matched-pair analyses of daily-life patients reveal modest effects on clinical course and survival. Leukemia Research, 38(4), 475–483. 4. Aim of first-ever CMML study – to improve survival. Leukaemia Foundation. (2023, January 3). Retrieved January 3, 2023, from survival/ 5. Ma, L., Jiang, L., Yang, W., Luo, Y., Mei, C., Zhou, X., Xu, G., Xu, W., Ye, L., Ren, Y., Lu, C., Lin, P., Jin, J., & Tong, H. (2021). Real-world data of chronic myelomonocytic leukemia: A chinese single-center retrospective study. Cancer medicine, 10(5), 1715–1725. 6. Gupta, A. et al. (2021). Juvenile myelomonocytic leukemia-A comprehensive review and recent advances in management. American Journal of Blood Research, 11(1), 1–21. Retrieved July 21, 2022, from 7. Padron, E., et al. (2013). GM-CSF–dependent PSTAT5 sensitivity is a feature with therapeutic potential in chronic myelomonocytic leukemia. Blood, 121(25), 5068–5077. 460170 8. Emanuel, P. D., et al. (1991). Selective hypersensitivity to granulocyte-macrophage colony-stimulating factor by juvenile chronic myeloid leukemia hematopoietic progenitors. Blood, 77(5), 925–929. 9. Incidence extrapolated by applying NIH SEER incidence rate of five per one million people found at to the population of U.S., UK, and Australia, Prevalence data also from NIH SEER. 10. U.S. Food and Drug Administration. A framework for concurrent submission and review of Oncology Products. Retrieved March 20, 2023, from excellence/project-orbis 11. Australian New Zealand Clinical Trials Registry. Retrieved March 20, 2023, from 12. Preach-M: Precision medicine for chronic myelomonocytic leukaemia in adults: A phase II trial studying the efficacy of lenzilumab and high dose ascorbate with azacitidine based on molecular profiling. PREACH-M - Victorian Cancer Trials Link. (n.d.). Retrieved January 3, 2023, from

CMML is an aggressive, poorly understood cancer; approximately 20% of patients survive three years from diagnosis Eleven subjects dosed with lenzilumab and with current standard of care, azacitidine Six evaluable subjects, including those with high risk CMML, demonstrated clinical benefit at three months follow-up Lenzilumab appears to be well-tolerated Short Hills, New Jersey and Adelaide, South Australia--(News - April 14, 2023) - Humanigen, Inc. (Nasdaq: HGEN), Humanigen Australia Pty Ltd, (Humanigen) and the South Australian Health and Medical Research Institute (SAHMRI) today presented (poster CT085/13); the design and baseline results of the Precision Approach to Chronic Myelomonocytic Leukemia (PREACH-M) study of lenzilumab in chronic myelomonocytic leukemia (CMML), at the 2023 annual meeting of the American Association of Cancer Research being held in Orlando, FL April 14-19. PREACH-M is currently treating 11 intermediate and high risk CMML subjects (five male, six female; mean age 68 years) with lenzilumab, a granulocyte-macrophage colony-stimulating factor (GM-CSF) neutralizing antibody, and azacitidine, the current standard of care for CMML. As of December 31, 2022, six subjects were evaluable based on at least three months of follow-up and all demonstrated clinical benefit. Ten grade 3/4 Serious Adverse Events were observed, of which two were assessed by the investigator as possibly related to lenzilumab. CMML remains a disease with high unmet medical need and there have been no new therapeutic agents with a novel mechanism of action for patients with high-risk CMML in the last 30 years.1 Treatment options for these patients are limited to blood transfusions, hydroxyurea and supportive care alongside the current standard of care, which includes hypomethylating agents such as azacytidine and decitabine with limited response rates of 7-18%2,3,4 and no proven increase in overall survival. "GM-CSF is a cytokine that helps make white blood cells in the body and promotes myeloid cell development and maturation, playing a major role in the development of CMML.5 The clinical benefits of GM-CSF neutralization in life-threatening conditions such as CMML may be highlighted by these early results," said Cameron Durrant, MD, MBA, Chairman and CEO, Humanigen. "PREACH-M has brought together experts from around the world and enabled Humanigen and its clinical partners to quickly obtain important data that may help us address a critical unmet need in oncology. We believe that the results observed to date have the potential to qualify lenzilumab for expedited regulatory pathways." "PREACH-M is enrolling intermediate and high risk CMML patients with TET2 and RAS pathway mutations who would ordinarily be treated only with azacitidine or another hypomethylating agent, the standard of care for the past thirty years. These patients have significant hematologic indices and constitutional symptoms of CMML," said Associate Professor Daniel Thomas, principal investigator of the PREACH-M study and Program Leader for Blood Cancers at SAHMRI and Associate Professor of Medicine at the University of Adelaide. "The current early data from PREACH-M suggests promise in improving treatment response rates in CMML through GM-CSF neutralization with lenzilumab. Patients undergoing treatment in PREACH-M also appear to tolerate lenzilumab well." Treatment with lenzilumab and azacitidine led to rapid clinical response in all evaluable patients. Three high-risk patients, as defined by CMML-specific prognostic scoring system-Molecular (CPSS-Mol)6 achieved clinical benefits, as defined by the Savona criteria7 for myelodysplastic/myeloproliferative neoplasms (MDS/MPN). Quality of life is also being measured. +++ About CMML CMML is an orphan disease with an approximate annual incidence of 1-4 cases per million9 in western countries and has limited therapeutic options. CMML is an aggressive and poorly understood cancer with only about 20% of patients surviving up to the three-year mark.10 The median overall survival for patients with CMML after diagnosis ranges from 12-29 months.9 The incidence of CMML in the US, UK, and Australia is about 1,700 patients annually.11 As an orphan disease, lenzilumab may qualify for certain regulatory and commercial advantages that could expedite development and potential approval. Humanigen and the Principal Investigator are assessing regulatory pathways that may enable early results to support a regulatory submission and potential approval by the Therapeutic Goods Administration in Australia, which could be expanded through Project Orbis12 to the United States and the United Kingdom ( ). About the PREACH-M Trial PREACH-M (PREcision Approach to CHronic Myelomonocytic Leukemia) is a Phase 2/3, non-randomized, open-label clinical trial investigating precision medicine for adults with CMML.13 This trial investigates treatment response rates determined by the Savona Criteria for patients with CMML after administration of lenzilumab alongside azacitidine in patients with RAS pathway mutations. The study also measures the patients' quality of life, using the MPN Symptoms Assessment Form: Total Symptom Score. Eleven of twenty-nine subjects were enrolled in the study as of December 31, 2022, of which eight were treated (five females, mean age of 67 years; three males, mean age of 69 years), and six were evaluable based on at least three months of follow-up. During the active treatment phase of the study, participants are required to attend clinic visits on Days 1 & 15 of the first cycle, and then on Day 1 of each subsequent 28-day cycle to assess how the participant is tolerating the therapy and ensure ongoing safety.14 In addition to regular safety blood tests throughout each cycle, participants' disease response assessments are scheduled after 3, 6, 12 and 24 cycles of therapy to measure their disease response.14 Such assessments include blood tests, bone marrow aspirate and trephine, ultrasound of the spleen, physical exam and assessment of transfusion requirements and clinical symptoms.14 Participants who complete 24 cycles of active treatment enter the follow-up phase of the study where they are followed up every 6 months for 24 months for survival, disease status and further CMML-related treatment.13 For patients with confirmed progressive disease or relapse during the active treatment phase of the study, further study treatment will cease. Patients remain on study and are followed up for disease status, survival and further CMML-related treatment every 6 months until 48 months from Cycle 1, Day 1.13 During the follow-up period, participants no longer receive any investigational drugs but are permitted to receive any CMML treatment at the discretion of the treating clinician. As part of the screening process, participants are required to have a bone marrow aspirate and trephine to test for certain acquired mutations that can be present in CMML.13 The study is seeking participants with TET2 and/or RAS pathway mutations. Participants with RAS pathway mutations or both TET2 and RAS mutations, receive azacitidine (administered subcutaneously at a dose of 75mg/m2 on Days 1-5, 8-9 or Days 1-7 for a total of 7 doses per 28-day cycle) in combination with lenzilumab (administered intravenously at a dose of 552mg on Days 1 & 15 of Cycle 1. Day 1 only for all subsequent cycles).13 The trial is sponsored by the South Australian Health and Medical Research Institute ("SAHMRI") and funded by a Medical Research Future Fund grant from the National Health and Medical Research Council of the Australian government to the University of Adelaide. Humanigen provides lenzilumab for use in the study through its Australian subsidiary, Humanigen Australia Pty Ltd. Enrollment is open to newly diagnosed CMML patients who haven't received any treatment. Anyone who is interested in learning more about the study, or additional information can visit the Australian New Zealand Clinical Trials Registry ( ). About Humanigen Humanigen, Inc. (Nasdaq: HGEN) ("Humanigen") Source: 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. 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 . About Lenzilumab Lenzilumab is a proprietary Humaneered® first-in-class monoclonal antibody that has been proven to neutralize GM-CSF with high specificity and affinity to prevent signaling through its receptor. GM-CSF along with RAS pathway mutations play key roles in CMML and other cancers, including juvenile myelomonocytic leukemia (JMML), myelodysplastic syndromes, myeloproliferative neoplasms, and acute myeloid leukemia.15,16,17 GM-CSF is also of critical importance in the hyperinflammatory cascade, sometimes referred to as cytokine release syndrome, or cytokine storm, associated with COVID-19 and common to chimeric antigen receptor T-cell (CAR-T) therapy, acute Graft versus Host Disease (aGvHD) and other indications. About SAHMRI SAHMRI is South Australia's flagship independent not-for-profit health and medical research institute. The Precision Cancer Medicine Theme is committed to understanding the factors that determine patient-specific responses to disease or therapeutic intervention, enabling us to better predict patient outcomes, to stratify patients to the best treatment options and to develop more personalized, targeted interventions. 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. 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; 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 References Aim of first-ever CMML study - to improve survival. Leukaemia Foundation. (2023, January 3). Retrieved January 3, 2023, from Costa, R., et. al. (2010). Activity of azacitidine in chronic myelomonocytic leukemia. Cancer, 117(12), 2690-2696. . South Australian Registry data, South Australian Health and Medical Research Institute, April 14, 2021 Pleyer, L., et. al. (2014). Azacitidine in CMML: Matched-pair analyses of daily-life patients reveal modest effects on clinical course and survival. Leukemia Research, 38(4), 475-483. Egea, L., Hirata, Y., & Kagnoff, M. F. (2010). GM-CSF: a role in immune and inflammatory reactions in the intestine. Expert review of gastroenterology & hepatology, 4(6), 723-731. Elena C, Galli A, Such E, et al. (2016) Integrating clinical features and genetic lesions in the risk assessment of patients with chronic myelomonocytic leukemia. Blood.128(10):1408-1417 Savona, et al. (2015) An international consortium proposal of uniform response criteria for myelodysplastic/myeloproliferative neoplasms (MDS/MPN) in adults. BLOOD.125: 1857. 10.1182/blood-2014-10-607341. Myeloproliferative Neoplasm symptom assessment form. Retrieved January 3, 2023, from Ma, L., Jiang, L., Yang, W., Luo, Y., Mei, C., Zhou, X., Xu, G., Xu, W., Ye, L., Ren, Y., Lu, C., Lin, P., Jin, J., & Tong, H. (2021). Real-world data of chronic myelomonocytic leukemia: A chinese single-center retrospective study. Cancer medicine, 10(5), 1715-1725. Incidence extrapolated by applying NIH SEER incidence rate of five per one million people found at to the population of U.S., UK, and Australia, Prevalence data also from NIH SEER. Incidence extrapolated by applying NIH SEER incidence rate of five per one million people found at to the population of U.S., UK, and Australia, Prevalence data also from NIH SEER. U.S. Food and Drug Administration. A framework for concurrent submission and review of Oncology Products.. Retrieved March 20, 2023, from Australian New Zealand Clinical Trials Registry. Retrieved March 20, 2023, from Preach-M : Precision medicine for chronic myelomonocytic leukaemia in adults: A phase II trial studying the efficacy of lenzilumab and high dose ascorbate with azacitidine based on molecular profiling. PREACH-M - Victorian Cancer Trials Link. (n.d.). Retrieved January 3, 2023, from Gupta, A. et al. (2021). Juvenile myelomonocytic leukemia-A comprehensive review and recent advances in management. American Journal of Blood Research, 11(1), 1-21. Retrieved July 21, 2022, from Padron, E., et al. (2013). GM-CSF-dependent PSTAT5 sensitivity is a feature with therapeutic potential in chronic myelomonocytic leukemia. Blood, 121(25), 5068-5077. Emanuel, P. D., et al. (1991). Selective hypersensitivity to granulocyte-macrophage colony-stimulating factor by juvenile chronic myeloid leukemia hematopoietic progenitors. Blood, 77(5), 925-929. To view the source version of this press release, please visit