Humanigen March 2021 Cautionary Note Regarding Forward-Looking Statements

All statements other than statements of historical facts contained in this presentation, including information concerning our possible or assumed future results of operations and expenses, business strategies and plans, competitive position, business and industry environment and potential growth opportunities, 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 expectations for timing and achievement of the key corporate and COVID-19 milestones described in the presentation, including;  The target date for announcement of topline data from our Phase 3 trial of lenzilumab in COVID-19 patients;  The anticipated use of lenzilumab in the ACTIV-5 Trial sponsored by NIAID, and the anticipated scope of that trial and timeline for same;  Our potential request for and receipt of an Emergency Use Authorization from FDA for lenzilumab in COVID-19 and our expectations for filing a BLA; and  Our plans to launch and commercialize lenzilumab following receipt of the requisite regulatory authorizations or approvals; and  Our expectations for timing and achievement of milestones for our pipeline outside of COVID-19, including in respect of our ZUMA-19 Phase Ib trial of lenzilumab that is being conducted with Kite, a Gilead company; our ongoing Phase I trial of ifabotuzumab in GBM patients; our plans for a study of lenzilumab in GvHD expected to be conducted with the IMPACT Group in the United Kingdom and a study in the US, and our plans for a study of lenzilumab in CMML in Australia; 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 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, to reflect new information or the occurrence of unanticipated events, 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.

2 Company Highlights

1 Leading expertise in Hyper-inflammation and Cytokine Storm across multiple therapeutic applications

520 patient Phase 3 registration study in COVID-19 fully enrolled, top-line in March 2021; 2 ACTIV-5 200 patient, fully-sponsored COVID-19 BET study enrolling

Strong mid-to-late stage clinical pipeline including potential registration studies in CAR-T (US) 3 and GvHD (UK); collaboration with Kite/Gilead in CAR-T

Potential Emergency Use Authorization, commercial readiness and manufacturing scale-up 4 underway

Backed by blue-chip institutional shareholders, including Valiant, Citadel and Blackrock as well as 5 management

6 Experienced and execution-oriented management with prior launch experience

3 Lenzilumab Overview

Lenzilumab is a first-in-class mAb in a Phase 3 study to prevent the cytokine release syndrome in COVID-19 hospitalized patients.

Reduce risk of progression to IMV and/or death Lenzilumab, a dual action monoclonal antibody, which safely replenishes T-Cells and dampens the harmful inflammatory response, can be administered intravenously over a single day, to newly hospitalized and hypoxic COVID-19 patients, who may or may not have received other COVID-19 therapies.

First-in-Class, Novel MOA Potential Outcomes Convenient Care (Mayo Case Cohort Study) ✓ Neutralizes GM-CSF to prevent ✓ For all hospitalized patients with cytokine storm ✓ 80% relative risk reduction of SARS-CoV-2 pneumonia pre-IMV ventilation (IMV) and/or death ✓ ✓ Reduces immunogenicity ✓ Reduced time to clinical Administered IV in a single day improvement by 6 days1 ✓ Higher binding affinity ✓ Can be combined with current ✓ No serious adverse events observed standard of care across multiple studies

1Mayo Clinic Study, GM-CSF Neutralization With Lenzilumab in Severe COVID-19 4 Clinical-Stage Pipeline

Indication Phase Status Centers Partners Potential Registration Enabling Enrollment Prevention / treatment of 24 US 3 complete Hyper-inflammation / 520 11 Brazil Cytokine Storm Company sponsored ACTIV-5/BET Prevention / treatment of Enrolling 2 Up to 40 sites Hyper-inflammation / 200 patients Cytokine Storm ZUMA-19: Lenzilumab Break CAR-T Efficacy/Toxicity Linkage 10 sites 1b/21 Recruiting Prophylaxis as sequenced therapy with Including MD Anderson and Yescarta in r/r DLBCL other ZUMA-1 sites

Prevention/Treatment of Acute GvHD Advanced 2/3 Up to 23 sites2 Allogeneic HSCT planning

CMML Advanced Undisclosed Lenz + azacitidine in NRAS, KRAS or CBL 2 planning mutant-positive newly-diagnosed patients

3 Solid Tumors Active, fully Ifabotuzumab 1 (Glioblastoma Multiforme) recruited

1 Phase 3 may not be necessary for approval in ZUMA-19; precedent is CAR-Ts to date have been approved on Phase II data 2 UK 3 Australia 5 Accomplishments and Objectives

2020 2021

Q1 ✓ Mayo case-controlled publication ❑ Fully enrolled Phase 3, topline data expected ✓ ACTIV-5/BET NIH fully-sponsored 200 patient H1 study (lenzilumab + rem vs. rem alone) ❑ ACTIV-5 topline data ✓ Outlicense Korea + Philippines rights to ❑ Application for Emergency Use Authorization KPM/Telcon ❑ Commercial distribution under EUA if granted ✓ CRADA* with DoD/BARDA in support of Operation Warp Speed ❑ ZUMA-19 Phase 1b CAR-T data ✓ Ifab GBM study enrollment completed H2 ✓ First Lenz CAR-T patent issued ❑ BLA submission ❑ Initiate GvHD study with IMPACT Group

*Cooperative Research and Development Agreement 6 1 Therapeutic for COVID-19 Patients

2 Improving efficacy / safety of CAR-T

3 Prevention / Treatment of Acute GvHD

4 Market Potential/Financial overview

7 Neutralization of GM-CSF to Prevent COVID-19 Cytokine Storm

 GM-CSF neutralization prevents CD14+CD16+ inflammatory myeloid cell activation and reduces all downstream monokine production

 IL-6 blockade reduces only IL-6 and does not block inflammatory myeloid cells activation and all downstream monokine production

 IL-6 blockade alone has not shown clinical utility as a preventative measure in CAR-T induced Cytokine Storm – IL-6 and IL-1 inhibitors have failed in almost all studies in COVID-19

 Four recent independent publications support role of GM- CSF as signature cytokine for hyperinflammation in COVID-19

Diagram: Temesgen, Zelalem et al. “GM-CSF Neutralization With Lenzilumab in Severe COVID-19 Pneumonia: A Case-Control Study.” 03 Sep. 2020 8 GM-CSF Continues to be Recognized as Essential Target for COVID-19

• UK researchers identify inflammatory protein linked to severe COVID-19

• Plasma samples from 471 patients reviewed

• GM-CSF direct contributor to inflammation

• GM-CSF levels detected in first 4 days correlated with disease severity

• GM-CSF levels 10X higher in patients that died from COVID-19

BY RYAN S THWAITES, ASHLEY SANCHEZ SEVILLA URUCHURTU, MATTHEW K SIGGINS, FELICITY LIEW, CLARK D RUSSELL, SHONA C MOORE, CAMERON FAIRFIELD, EDWIN CARTER, SIMON ABRAMS, CHARLOTTE-EVE SHORT, THILIPAN THAVENTHIRAN, EMMA BERGSTROM, ZOE GARDENER, STEPHANIE ASCOUGH, CHRISTOPHER CHIU, ANNEMARIE B DOCHERTY, DAVID HUNT, YANICK J CROW, TOM SOLOMON, GRAHAM P TAYLOR, LANCE TURTLE, EWEN M HARRISON, JAKE DUNNING, MALCOLM G SEMPLE, J KENNETH 9 BAILLIE, PETER JM OPENSHAW, ON BEHALF OF THE ISARIC4C INVESTIGATORS SCIENCE IMMUNOLOGY10 MAR 2021 Lenzilumab Phase 3 in COVID-19

Multicenter, randomized, double-blind, placebo-controlled pivotal trial NCT 04351152

Adults ≥ 18 yrs Daily assessment through Day 28 for Lenzilumab 600mg IV Q8h x 3 on Day 1 1 and 2 endpoints while hospitalized; Hospitalized, confirmed SARS-CoV-2 ° ° COVID-19 pneumonia If discharged, follow-up assessments SpO2 ≤ 94% and pre IMV Placebo IV Q8h x 3 on Day 1 (N = 520, 1:1) on Days 28 and Day 60

▪ Primary Endpoint: ▪ Ventilator Free Survival

All subjects receive institutional standard of care which may include remdesivir or corticosteroids

10 Recovery Trial Endpoints and Analysis

Two therapeutics with a mortality benefit in the randomized open label Recovery Trials • Large trials required to observe this mortality benefit given the modest clinical effect size (n >4,000 pts to observe a 12-14% relative risk reduction in mortality)

IMV and/or Death as a surrogate endpoint for mortality • Hazard ratio (HR) for IMV and/or Death approximates the HR for mortality • IMV and/or Death can provide a signal of mortality benefit with fewer patients

Death IMV and/or Death

Hazard Ratio Relative Risk Reduction Hazard Ratio Relative Risk Reduction Dexamethasone .86 14% .87 13%

Tocilizumab .88 12% .85 15%

11 ACTIV-5/BET Big Effect Trial (BET-B) for the Treatment of COVID-19 Double-blind, placebo-controlled study of 200 patients, NIH-sponsored, up to 40 US sites NCT 04583969

• Lenzilumab is the third of six agents selected by NIH, the only GM-CSF molecule selected

• Over 400 compounds reviewed by NIH for inclusion in ACTIV protocols

• Humanigen is the only small company in NIH-sponsored studies

• 17 sites currently recruiting, more planned

• Planned interim analysis for efficacy at 50% enrollment

• Study expands number of patients for BLA submission and potential label to include use with remdesivir

March 4, 2021

12 1 Therapeutic for COVID-19 Patients

2 Improving efficacy / safety of CAR-T

3 Prevention / Treatment of Acute GvHD

4 Market Potential/Financial overview

13 ZUMA-19 Potential Registration Study ZUMA-19

Phase 1b Phase 2 • 3+3 Design to find recommended phase II dose ▪ At Recommended Dose • Cohort 1 with Starting Dose • Cohort 2 with Escalating Dose Endpoints Efficacy Safety • Complete Response (CR) • Minimizing Toxicities • Partial Response (PR) • NT • Objective Response Rate (ORR) • CRS • Duration of Response (DOR) • Days in ICU (Exploratory)

Clinical Trial Design Trial Clinical • Progression Free Survival (PFS) • Days on Vasopressors (Exploratory) • Overall Survival (OS) • % Patients with observed T-cell expansion • Kinetics of T-cell expansion

Day -5,-4,-3 Day 0 Day 28 Primary endpoint for Leukapheresis CAR-T ~ 6 Months NT / other key measures

Top Line Data for Lenzilumab Infusion Durable Response Evaluation of T-cell kinetics

Dosing Schedule Dosing Lymphodepleting Chemotherapy (Cyclophosphamide/Fludarabine) Ongoing follow-up for safety and efficacy

ClinicalTrials.gov Identifier: NCT04314843

14 1 Therapeutic for COVID-19 Patients

2 Improving efficacy / safety of CAR-T

3 Prevention / Treatment of Acute GvHD

4 Market Potential/Financial overview

15 IMPACT Partnership/HGEN GvHD Trial Design

N= 240 Patients Phase 2 (case-cohort) • Screened 40 patients • 20 treated with lenzilumab • Go/no-go decision Phase 3

• Screened 215/yr • Randomized 110/yr • Total sample size 220 randomized 1:1 Clinical Trial Design Trial Clinical

Day 0 Day 28 6 Months Intermediate + High Allo Lenzilumab + SOC GvHD Dx Risk (AA2+AA3) Transplant Randomized vs. Response rate NRM assessment Placebo + SOC assessment

MAGIC biomarker (<48 hours Low Risk SOC post Dx)

Ongoing follow-up for safety and efficacy Dosing Schedule (every 2 weeks) 2 (every Schedule Dosing

16 1 Therapeutic for COVID-19 Patients

2 Improving efficacy / safety of CAR-T

3 Prevention / Treatment of Acute GvHD

4 Market Potential / Financial overview

17 Lenz Commercial Preparation Underway Humanigen is positioned for commercial success in 2021 and beyond.

1 Anticipated lenzilumab EUA in 1H2021 and BLA filing in 2H2021

2 Unique MOA addressing an unmet need in the quest for effective COVID-19 treatments

3 >$1B peak opportunity estimated for lenzilumab in hospitalized and hypoxic COVID-19 patients

4 Anticipate favorable access and reimbursement to support rapid lenzilumab uptake

5 Commercial organization is swiftly scaling and resourced for a successful launch, if EUA granted

6 Experienced leadership team with deep expertise and a proven commercial track record

18 Impact of COVID-19 in the US

US Patient Population Estimated Cost of Care

$9.6 - $16.9B is the estimated Over 28.5M patients diagnosed cost to US healthcare system for with COVID-19 in the US¹ Positive COVID-19 Cases in US inpatient COVID-19 related care⁶

of patients (~1.9M) are hospitalized is the estimated charge per day of ~7% due to COVID-19 complications ² ³ care for a hospitalized patient ⁷ Hospitalized Patients ~$13K Per Day of hospitalized patients are hypoxic is the estimated charge per day of care for a hypoxic hospitalized 89% with SpO2 Levels <94%⁴ Hypoxic Patients patient ⁷

is estimated charge per day of of hospitalized patients (1-in-5) are admitted ~$16K care for a COVID-19 patient in 20% to the ICU and likely ventilated (IMV)⁵ ICU Patients Per Day the ICU ⁷

patient deaths due to complications Patient Significant emotional and >515K with COVID-19 in the US to date² Mortality --- financial toll on patient’s family

19 * Sources Included In Notes Field Sizeable and Sustainable Market Opportunity The number of hospitalized COVID-19 patients is expected to rise beyond current levels and remain significant through 2022 and beyond2 ~677,000 COVID-19 COVID-19 Hospitalizations Hospitalizations in 20201 Despite a vaccine, hospitalizations will increase 600K+ Hospitalizations Anticipating a Greater Despite herd immunity and Number of Hospitalizations widespread vaccinations, in 2021 hospitalizations remain

Hospitalizations Will Remain Through 2022 and Beyond 2020 2021 2022 and Beyond

1. Covid Tracking Report 2. Data on file 20 Facility-Level Hospital Data

US Hospital-Level Data – Patient Mix, Hospital Capacity, and Bed Utilization Illustrative Visibility into facility-level data provides insight into key treating institutions, as well as detailed data on hospitalized patients at specific hospitals and institutions

# of Patients

% of Beds

# in ICU

% of ICU

21 Future Need For COVID-19 Therapeutics There is consensus across the industry that hospitalizations and the need for therapeutics will continue well into 2021 and beyond

• Herd immunity unlikely with new variants • Children not included in vaccine programs and 25% of US adults will not vaccinate • Vaccines 50% effective B.1.351

“While safe and efficacious vaccines are a large step forward towards ending the COVID-19 crisis…there will be a continued need for novel anti-inflammatory and immunomodulatory compounds.”

- Dr. Matthew Robinson, Austin Infectious Disease Consultants3

1. Eli Lilly Press Release: December 15, 2020 2. Regeneron Press Release: November 21, 2020 22 3. H.C. Wainwright, Joseph Pantginis, Ph.D.: December 3, 2020 Emergent Variant Cases in the United States

Variants Continue to Growth

Variant Cases States

B.1.1.7 4,686 50

B.1.351 142 25

P.1 27 12

https://www.cdc.gov/coronavirus/2019-ncov/transmission/variant-cases.html 23 Patient Journey There is a significant therapeutic need for those COVID-19 Patients Hospitalized and Hypoxic

COVID-19 Disease Progression

1 Early Infection Phase 2 Pulmonary/Inflammatory Phase 3 Hyperinflammatory Phase

Patient Outpatient In Hospital Journey COVID-19 Outpatient Symptom Present to Hospital with Hypoxia Low Flow or High Flow Invasive Mechanical Diagnosis Management (SpO2<94% on Room Air) Supplemental O2 Ventilation

Treatment OTC Treatments Remdesivir Options Patients quarantine & manage symptoms at home Optimal efficacy when viral load is highest, but often given too late. Efficacy is questionable.1,2

Neutralizing mAbs Corticosteroids Patients required to present to Most effective in IMV patients. outpatient infusion centers Concerns remain when administered too early Bamlanivimab Treatment Opportunity Casirivimab + Imdevimab Need for an effective therapy that interrupts immune hyper-response and prevents disease progression in hospitalized patients

1. “Remdesivir in adults with severe COVID-19: a randomised, double-blind, placebo-controlled, multicentre trial.” Wang et al. Lancet. 2020 May 16; 395 (10236): 1569-1578 2. WHO Solidarity Trial 24 Target Physicians

Infectious Disease Physicians, Pulmonologists, and Critical Care Physicians Oversee Treatment Decisions for Hospitalized COVID-19 Patients Concentration of COVID-Cases (3% of US Counties Represent 43% of Total Cases)

~34.5K COVID Specialists

13,500 12,000 Pulmonologists 9,000

Identify Specialists in Urban Areas with High Number of COVID Cases Pulmonologists Infectious Disease Critical Care Physicians Physicians

1. PUD Source: NCBI – HHS Author Manuscript (~12k) 2. ID Source: The Lancet: Infectious Disease (~9k) 25 3. CC Source: Society of Critical Care Medicine (~13.5k) Competitive Landscape

Immunomodulatory Agents for Hospitalized COVID-19 Pts (except Neutralizing mAbs) Overview of Investigational Agents in Mid-Late Stage Development for Treatment of SARS-CoV-2 Associated Cytokine Storm Anti-GM-CSF mAbs Anti-IL-6 & Anti-IL-1 mAbs Tocilizumab (Actemra®) Phase 3 (Global) Roche: RECOVERY 15% RR+ (Open anti-IL-6R Phase 3 (US) label) other Ph 3’s failed Lenzilumab Phase 3 Sarilumab (Kevzara®) Phase 2/3 (US) Regeneron: FAILED anti-IL-6R Phase 3 (Ex-US) Sanofi GSK – Trend on primary and Siltuximab (Sylvant®) Otilimab Phase 2 Phase 2 (EU) EUSA: DELAYED all-comers, stat sig >70 yrs anti-IL-6 Sirukumab (unapproved) Phase 2 (US) Janssen: DELAYED Gimsilumab Phase 2 Roivant (Kinevant): FAILED anti-IL6 Canakinumab (Ilaris®) Phase 3 (Global) Novartis: FAILED Plonmarlimab Phase 2/3 I-Mab: DELAYED anti-IL-1β Anakinra (Kineret®) Phase 3 (EU) SOBI: FAILED Roivant (Kinevant) anti-IL1Ra Namilumab Compassionate Use (Italy) Izana Oral JAK & BTK Inhibitors ACTT-2: EUA (+ Remdesivir) NIAID Mavrilimumab* Phase 2/3 Kiniksa Baricitinib ACTT-4: Bari+Rem vs Dex+Rem NIAID (Olumiant®, JAK1/2) Lilly Phase 3: DELAYED Lilly SARS-CoV-2 Neutralizing mAbs Ruxolitinib Phase 3 (US): DELAYED Incyte Severe (+ Rem) NIH/Lilly: FAILED (Jakafi®, JAK1/2) Phase 3 (Global): FAILED Novartis Bamlanivimab Acalabrutinib Mild-Mod (Mono) NIH/Lilly: EUA 2 Phase 2 studies: FAILED Astrazeneca Bamlanivimab NIH/Lilly: EUA (Calquence®, BTK) Mono, Mild-Mod Combo, Mild-Mod ® + Etesevimab Lilly: EUA Ibrutinib (Imbruvica , BTK) Phase 2 (US): DELAYED Abbvie Abivertinib (Sorrento) Phase 2 (US): DELAYED Sorrento Casirivimab Mild-to-Mod Outpatient Only Regeneron: EUA + Imdevimab Other MOA Casirivimab Severe: High Flow Regeneron: FAILED Regeneron: Leronlimab (anti-CCR5 mAb) Phase 2/3 (US) FAILED CytoDyn + Imdevimab Severe: Low Flow DELAYED Ravulizumab (Ultomiris®, C5 inhibitor) Phase 3 (US): FAILED Alexion AR-701 + AR-711: IV Human IgG1 Aridis: Phase 1/2 Phase 3 (US): Positive Data Mod-Severe Hospitalized pts MK-7110 [Saccovid (CD24Fc)] EUA rejected more P3 data mAb cocktail planned 1H 2021 Acquired by Merck

Aridis: Phase 1/2 SNG001 (inhaled IFNb-1a) Phase 2 (UK) Synairgen AR-711: Inhaled Human IgG1 mAb Mild-Mod (Outpatient) planned 1H 2021 Molnupiravir (MK-4482, oral antiviral) Phase 2/3 (UK): Partial activity Merck Remestemcel-L (Mesenchymal Stromal Cells) Phase 3 (US): FAILED Mesoblast

*anti-GM-CSFR mAb 26 Established Manufacturing Agreements for Lenzilumab

Bioreactor (BDS) batches • Catalent - Madison, WI Manufacturing Partners • Catalent - Bloomington, IN • ThermoFisher - St. Louis, MO • Avid Biosciences - Tustin, CA

Drug Product (DP) vials • Emergent - Baltimore, MD • Ajinomoto - San Diego, CA Packaging • Additional CMO’s selected • Catalent - Philadelphia, PA (clinical)

Bulk Drug Drug Product Supply Supply Specialty BDS Vials Substance Fill/Finish (Vials) Packaging Distribution Distributor

Cardinal Health

Engaged multiple contract manufacturing organizations (CMOs) to scale-up and optimize the manufacturing process to meet a target of supplying ~100,000 treatment courses within 12 months

27 Financial Overview Strong Balance Sheet Supports Commercial and Manufacturing Scale-up

Current Balance (M) Hercules Loan Facility (M)

• Cash and cash equivalents 12.31.20 $68 • Total credit available $80

• Current Cash and cash equivalents* $74 • Initial draw $25

• Shares outstanding* 53 • EUA/BLA $25/$35

• Market cap* $806 • Additional $20

*March 5, 2021, 10K 28 Upcoming Catalysts and Goals

1 Topline data Phase 3 lenzilumab in COVID-19

2 Complete recruitment in ACTIV-5

3 EUA submission and subsequent approval

4 Prepare for EUA distribution and scale-up manufacturing, BLA

5 Continue CAR-T recruitment and initiate GvHD study

29 Plasma mediators at the time of study enrollment demonstrated a broad exaggerated immune response in patients hospitalized with COVID-19

Ryan S Thwaites et al. Sci. Immunol. 2021;6:eabg9873