Developing Leading-Edge Immunotherapy, Oncology Treatments  OTCQB: HGENwww.humanigen.com  1  With Goal of Potential Significant Near-Term Value Inflection  | Corporate Overview - January 29, 2018  

 Forward-Looking Statements  2  This presentation contains forward-looking statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. 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 actual results could differ materially from the forward-looking statements.Words such as “will,” “expect,” “intend,” “plan,” “predict,” “potential,” “possible,” and similar expressions identify forward-looking statements, including, without limitation, statements related to the scope, progress, expansion, and costs of developing and commercializing the Company’s product candidates; opportunity to benefit from anticipated regulatory incentives for product candidates; and anticipated expenses related to development activities, clinical trials and the development and potential commercialization of product candidates.Forward-looking statements are subject to risks and uncertainties including, but not limited to, the Company’s ability to complete the restructuring transactions announced on December 21, 2017 on the terms described, the Company’s lack of revenues, history of operating losses, limited cash reserves and ability to obtain additional capital to develop and commercialize its product candidates, including the additional capital which will be necessary to complete the clinical trials that the Company has initiated or plans to initiate, and continue as a going concern; the Company’s ability to execute its strategy and business plan; the potential timing and outcomes of clinical studies of lenzilumab, ifabotuzumab or any other product candidates and the uncertainties inherent in clinical testing; the ability of the Company to timely source adequate supply of its development products from third-party manufacturers on which the Company depends; the potential, if any, for future development of any of its present or future products; the Company's ability to successfully progress, partner or complete further development of its programs; the ability of the Company to identify and develop additional products; the Company's ability to attain market exclusivity or to protect its intellectual property; competition; changes in the regulatory landscape that may prevent the Company from pursuing or realizing any of the expected benefits from the various regulatory incentives at the center of its strategy, or the imposition of regulations that affect the Company's products; and the various risks described in the "Risk Factors" and elsewhere in the Company's periodic and other filings with the Securities and Exchange Commission.You are cautioned not to place undue reliance on any forward-looking statements, which speak only as of the date of this presentation. The company has no obligation, and expressly disclaims any obligation to update, revise or correct any of the forward-looking statements, whether as a result of new information, future events or otherwise.  

       Investor Overview  Cutting-edge science monoclonal antibody biotechnology company – with improving financial profileDeveloping key asset (lenzilumab) for prevention of side effects associated with CAR-T – one of the hottest areas in biotechWorking with leading KOLs to start phase 1/2 trials Lenzilumab has the potential to make CAR-T: Safer, more effective, and a more routine out-patient procedureMore shots on goal in portfolio: Lenzilumab phase 1 trial in chronic myelomonocytic leukemia (CMML) underway to inform potential work in JMMLIfabotuzumab phase 1 radio-imaging trial in glioblastoma multiforme (GBM) underwayIfabotuzumab is a potential CAR constructModest capital requirements anticipated to reach value inflection point in early 2019 – and significant upside potential    3 

 CAR-T’s ‘Achilles Heel’: Neurotoxicity (NT) and Cytokine Release Syndrome (CRS) – Key Impediments to Safe Use  4    64% had NT and 93% had CRS*~1/3 of patients had grade ≥3 NT, leading to ICU admissionMedian time to resolution of NT – 17 daysSeveral deaths    Management of NT, CRS Is Limited  Tocilizumab (IL-6 receptor antagonist) for severe CRSCorticosteroids for tocilizumab-refractory CRSBeds need to be booked in ICU in case patient develops life-threatening side-effects   Chalice L. Bonifant, published online20 April 2016, doi:10.1038/mto.2016.11  *Neelapu, Locke et al. ICML 2017, Abstract 8; Locke, Neelapu et al. ASH 2017, Abstract 1547  

 Time Course of NT and CRS Following CAR-T Infusion  Lee, et al. Blood. 2014 July 10;124(2)188-195  5 

 Z.J Roberts, et al. Leukemia & Lymphoma 2017. https://doi.org/10.1080/10428194.2017.1387905   Recent Leading Research Shows GM-CSF Correlation to NT, CRS   6    GM-CSF levels precede and modulate other cytokinesCorrelate with NT, CRS    GM-CSF is a key biomarker associated with > grade 3 NT     Locke, Neelapu et al, AACR 2017   

 Scientific Basis for GM-CSF as Initiator in CAR-T Toxicity  7  GM-CSF may be a trigger – potentially switching CAR-T from cancer killing to off-target inflammation  Inflammatory cascade potentially initiated by GM-CSFTrafficking and recruitment of myeloid cells to the tumor site through key chemokines such as CCL2 and CCL3/4Myeloid cells perpetuate a self-reinforcing inflammatory reaction  

            Very high unmet medical need No effective treatment; high-dose steroids may impact efficacy; not FDA approved or useful in preventionNo effective prophylaxis – which could minimize need for and time in ICU Fatal in ~5% patients; cytokine storm in cerebral spinal fluid   CAR-T-related Neurotoxicity (NT)  8  New understanding and need to manage neurotoxicity in CAR-T therapy  Occurs in almost 2/3 of CAR-T patients and no FDA approved treatment or prophylaxis  Side effect limiting higher CAR-T dose, usage  Symptoms can include delirium, confusion, headache, seizures, cerebral edema                                    a/k/a CAR-T-cell-related encephalopathy syndrome (CRES)                                                                                   KEY TAKEAWAYS                  64%     

         GM-CSF implicated as upstream of other cytokinesExpect more CAR-T use (earlier lines of therapy, solid tumors, out-patient administration) and investment by big pharmaProphylaxis may allow for higher doses of CAR-T with greater efficacy In-patient readmission/ICU impacts payers  CRS   9  CAR-T label requires trained staff in CRS, anti-CRS treatment stocked + ICU reserved bed as precaution  Multiple cytokines implicated: IL-6, other IL family, IFNg, TNFa, GM-CSF    ~3000                                                              KEY TAKEAWAYS                New US cases per year with ped ALL  Half have severe CRS (tocilizumab effective for some – but no effect on NT)   Cytokine Release Syndrome   80-90% 

 Kymriah® and Yescarta® Have Black-Box Warnings for NT, CRS    10      Kymriah® label  Yescarta® label 

 Lenzilumab: Novel, First-in-Class Monoclonal Antibody  11                                        Lenzilumab  First-in-class; binds to and neutralizes circulating GM-CSF    Potent inhibitor of GM-CSF Safety, tolerability shown in multiple Phase 2 trialsEfficacy signals in eosinophilic asthma and RA Phase 2 trialsKey patent through 2029, extensions possible    Associated with NT and CRSInhibition could improve utility of CAR-T:Prevent or minimize dangerous side-effectsImprove CAR-T cell expansion, allowing delivery of a higher CAR-T dose, potentially improving efficacyDecrease re-hospitalization ratesMove CAR-T to earlier lines of therapy hematologic cancers; expand into solid tumorsGM-CSF also a demonstrated target in many other autoimmune indications with significant unmet need  GM-CSF 

 Sentman, et al. www.jimmunol.org/content/197/12/4674.long; Coxford, et al. Immunity 2015 (43)510-514; Ishii, et al. Blood 2016 128:3358 Teachey, et al. Cancer Discov. 2016 June ; 6(6): 664–679. doi:10.1158/2159-8290.CD-16-0040; Lee, et al. Blood 2016 124:2:188; David M. Barrett et al. Blood 2016;128:654  GM-CSF May Be the Essential Bad Actor Driving CAR-T Toxicity  Direct action on CCR2+ myeloid cells through recruitment and trafficking via CCL17, CCL6, CCL24, CXCL3, CCL9, and CCL22GM-CSF-activated CCR2+ myeloid cells traffic to the site of T cell activation and secrete inflammatory cytokines (IL-1b, IL-6, IL-8, GM-CSF)Recruit other myeloid cells through CCL2 production, amplifying inflammatory cascade in a self-perpetuating mannerIL-6-related CRS produced by APCs, not T cells IL-15 and GM-CSF significantly elevated one day after CAR-T infusion with grade >3 NT  GM-CSF k/o mice  no sign of CRS illness, adverse events or change in body weight following CAR-TGM-CSF k/o mice  serum cytokine levels of INFg, IL-10, IL-6, MCP-1, MIP-1 at levels comparable to controlsIL-6 k/o mice  CRS develops as long as CAR-T is capable of producing GM-CSF and the myeloid compartment intactGM-CSF receptor k/o from CCR2+ myeloid cells  seems to abrogate the inflammatory cascade in neuro-inflammation models  12    Mechanism Becoming Clearer    Animal Models Show Building Evidence  GM-CSF plays a role initiating the inflammatory storm 

 Prophylactic Use of Lenzilumab May Prevent CAR-T-related NT, CRS  13  1Grupp, et al. Blood 2012; 120:2604. 2Analysis of ZUMA-1, 30pt safety cohort, ASH 2017. 3Brudno, et al. Blood 2016; 127:26  Without concomitant IL-6 rise, may not respond to tocilizumab; early intervention with lenzilumab may be beneficial    Tocilizumab may impair depth/duration of anti-malignancy responses if given prior to initiation of significant CAR-T proliferation1Prophylactic administration of tocilizumab reduces severe CRS – but not NTUnderlying pathophysiology of NT may differ from CRS2Prophylactic use of tocilizumab following CAR-T infusion often ineffective35% patients receiving tocilizumab prophylactically had >3 NT (one cerebral edema death)2Saturation of IL-6 receptors following systemic tocilizumab may increase serum IL-6 levels3    Limited to severe CRS refractory to tocilizumab and severe, refractory NT3         

 Lenzilumab Has an Established Safety Profile in >94 Patients*  14  Study♦  Population  Objectives  Enrollment/Dose   Safety Results            Phase 1          Single-dose, dose-escalation  Healthy adult volunteers  Safety/tolerabilityPKImmunogenicity  (n=12)3 / 1 mg/kg3 / 3 mg/kg3 / 10 mg/kg3 / placebo  Clean safety profileNo drug related SAEsNon-immunogenic            Phase 2          Dose at weeks 0, 2, 4, 8, 12  Rheumatoid arthritis  EfficacySafety/tolerabilityPKImmunogenicity  (n=9)7 / 600 mg2 / placebo  Clean safety profileNo drug related SAEsNon-immunogenic  Dose at weeks 0, 2, 4, 8, 12, 16, 20  Severe asthma  EfficacySafety/tolerabilityPKImmunogenicity  (n=160)78 / 400 mg82 / placebo  Clean safety profileNo drug related SAEsNon-immunogenic            * Does not include 9 patients in ongoing CMML Phase 1 trial, where drug has been well-tolerated; an additional 76 patients received a chimeric version of lenzilumab (KB002) and showed a similar safety profile♦ All studies are randomized double-blind placebo-controlled, intravenous administration 

   Current Summary of In Vitro and In Vivo Preclinical Data     15    Lenzilumab does not impede CAR-T cell function in vivoCAR-T cells’ ability to kill cancer remain robust CAR-T control and CAR-T + lenzilumab survival is the same in xenograft model    Lenzilumab does not alter in vitro CAR-T-specific cancer killingCAR-T antigen-specific proliferation not affected – with or without PBMCs – by lenzilumabLenzilumab does not inhibit CAR-T degranulation, intracellular GM-CSF production, or IL-2 production  

 Lenzilumab Prophylaxis in CAR-T NT Development Plan  16  1    Thought Leader Validation   GM-CSF target, preclinical and clinical development plan developed in collaboration with world’s leading CAR-T experts  Scientific Advisory Board meeting convened at ASH 2017Significant input and feedback before, during and after SAB Continue to seek cutting-edge KOL insights; SAB report produced 

 Lenzilumab Prophylaxis in CAR-T NT Development Plan  17    Preclinical Development  Completed by Dr. Saad Kenderian (Mayo Clinic) using validated animal model Initial data positive Final preclinical data expected Jan/Feb 2018  2 

 Lenzilumab Prophylaxis in CAR-T NT Development Plan  18    Clinical Development  Phase 1/2 study design developed by Dr. Sattva Neelapu at MD Anderson – lead investigator for Gilead/Kite’s Yescarta CAR-T Lenzilumab to be studied as prophylactic therapy prior to CAR-T infusion to prevent NTStudy initiation expected Q2 2018 Target primary completion date Q4 2018  3 

 Lenzilumab Prophylaxis in CAR-T NT Development Plan  19    Regulatory Submission  Potential adaptive study design to allow roll-over of Phase 1/2 study into potential pivotal registration/approval studyPrecedents for flexibility in approach: tocilizumab was approved with 29 patients, case reports, no control arm and no formal study, due to high unmet needTargeting FDA Orphan, Breakthrough and Fast Track designations  4 

 Lenzilumab Prophylaxis in CAR-T NT Development Plan  20    Value Proposition for Strategic Partner, Deal  Differentiate a CAR-T offering from competitorsPotentially improve safety, allow for higher CAR-T dosesAssist hospitals/payers with fewer ICU days, readmissionsMove to true out-patient CAR-T treatment and follow-upPotentially increase market share penetration and sales of companion CAR-TDeliver possible standalone lenzilumab salesAid in the evolution of CAR-T therapyEnable possible CAR-T use in solid tumorsCombo therapy with 4-1BB agonists, CPIs, other mAbs    5 

            Orphan conditionHigh unmet needUp to 90% of patients have hypersensitivity to GM-CSFPatients typically unsuitable for stem cell transplantFocus on salvage patients with no other treatment options  CMML  21  Rare hematologic cancer; recently classified as separate disease with distinct natural history*  Median overall survival rate in months  Newly diagnosed US patients per year  Age at diagnosis  ~1,100                                * Formerly classified as subtype of the myelodysplastic syndromes (MDS)       60-70  Chronic Myelomonocytic Leukemia                                                                                          20  KEY TAKEAWAYS           

 Ifabotuzumab: Dosing Begun in Patients with GBM (a Brain Cancer); Potential Use as a CAR-T Construct  22                                        Ifabotuzumab  First-in-class Humaneered mAb for Ephrin type-A receptor 3 (EphA3)    Phase 1 bio-imaging study in GBM to enable CAR-T constructCAR design potential using ifabotuzumab backbonePrior clinical experience in hematologic malignanciesKey patent through 2030                                                                                                                                                                                                                                        EphA3 Receptor  Ifabotuzumab  INTRACELLULAR  Inhibition of cell positioning, survival and tumor growth                                                  Not expressed in normal tissue - overexpressed in certain blood cancers, solid tumors and tumor vasculature; ifabotuzumab targets tumor vasculature 

  Monoclonal Antibody Pipeline    Indication  Phase  Anticipated Readout  Expected Next Study  Value Point  Lenzilumab(anti-GM-CSF mAb)          Clinical proof of concept                        *Potential pivot to JMML on interim data  Ifabotuzumab(anti-EphA3 mAb)          Study to enable CAR construct development                  Q1 2018            Q2 2018*      Q3 2018    Q1 2019    CMML  GBM   I  I  PC(Mayo)  Q2 2018 (MD Anderson)    Phase1/2  Q4 2018*    Phase2  Roll CAR-T phase 2 into pivotal registration study  CAR-T-relatedNeurotoxicity  23  PC = pre-clinical  PC  CAR construct   Certain leukemias, lymphomas, solid tumors    CAR collaboration in 2018 

 Anticipated Near-Term Catalysts            Q12018  Q22018  Q32018  Q42018      Ifabotuzumab  Lenzilumab  GBM Phase 1 first patient dosed (Melbourne/Brisbane, Australia)  GBM imaging results  GBM Phase 1 interim imaging data  CAR-T animal POC data (Mayo)  CAR-T NT Phase 1/2 first patient(MD Anderson)  CMML Phase 1 interim readout geared for possible JMML pivot  CAR-T NT Phase 1/2 data   $10-12MM ($3MM already committed by existing investor)  24 

 Differentiated, Valuable Niche in the Hottest Area of Biotech – Mitigating Side Effects, Improving Efficacy of CAR-T    Obsidian Therapeutics  Cell Design Labs  HGEN  Valuation   $49.5MM post-money  $567MM acquisition by Gilead($175MM up-front) 12/7/17   ~$50MM*  Development stage  Pre-clinical  Pre-clinical  Completed pre-clinicalPreparing Phase 1/2 Q2 2018   Safety data  None  None  ~180 patients   Key technology  Destabilizing domains encoded in a “synthetic biologic cassette,” packaged in a vector for the disposal of dysfunctional proteins  SynNotch - synthetic gene expression system Throttle - “on switch” using small molecules   Monoclonal antibody against key validated target   Scientific publication support  Minimal   Minimal  Significant  Likely costs to POC clinical data  Unknown  Unknown  ~$10MM through Phase 2  Investors  Google Ventures, Atlas, ShangPharma, Takeda/Vertex/Amgen ventures  Kleiner Perkins, Kite, Osage, Mission Bay  Public  25  * implied value assuming HGEN share price as of 1/23/18 and new shares outstanding total at close of pending transactions announced 12/21/17  

       HGEN Summary  CAR-T is one of the hottest fields in biotech; Neurotoxicity the “Achilles Heel’ of CAR-TPositioned to deliver significant value with strong scientific rationale for lenzilumab as prophylaxis to CAR-T NT Working with leading KOLs/CAR-T treatment centers to start lenzilumab phase 1/2 trials for NT in Q2 2018Lenzilumab has the potential to: Make CAR-T safer, more effective, and a more routine out-patient procedureOffer significant strategic value, sales acceleration for CAR-T treatment, plus generate standalone revenue stream More shots on goal in attractive CAR-T/oncology pipeline with highly efficient R+D spend: Lenzilumab phase 1 trial in CMML almost fully recruited – study structured to enable possible JMML pivotIfabotuzumab phase 1 radio-imaging trial in glioblastoma multiforme (GBM) underwayIfabotuzumab is a potential backbone for novel CAR constructComparable valuations are highly attractive and potential for significant transactions near term    26