A Multicenter, Randomized, Double-Blind Phase 3 Study of HBI-8000 Combined with Nivolumab versus Placebo with Nivolumab in Patients with Unresectable or Metastatic Melanoma Not Previously Treated with PD-1 or PD-L1 Inhibitors

Patients may be entered in the study only if they meet all of the following criteria: 1. Histopathologically confirmed diagnosis of non-uveal, Stage III (unresectable), or Stage IV (metastatic) melanoma according to AJCC staging system (8th edition). 2. Known BRAF V600 mutation status or consent to BRAF V600 mutation testing before randomization. 3. Tumor tissue available for PD-L1 testing at central lab. PD-L1 expression level is required for randomization. In order to be randomized, a patient must be classified as PD-L1 positive or PD-L1 negative according to the following criteria: • PD-L1 positive (≥ 1% tumor cell membrane staining in a minimum of a hundred evaluable tumor cells) vs. • PD-L1 negative (< 1% tumor cell membrane staining in a minimum of a hundred evaluable tumor cells). Note: If an insufficient amount of tumor tissue from an unresectable or metastatic site is available prior to the start of the Screening Phase, patients must consent to allow the acquisition of additional tumor tissue for assessment of the biomarker. 4. Males or females 12 years of age or older. 5. ECOG performance status ≤ 1 for age ≥ 18 years, Lansky performance score ≥ 80% for age 12 to 17 years. 6. At least one measurable lesion defined by RECIST 1.1 criteria, (separate from the lesion to be used for tumor tissue collection for PD-L1 testing) not counting brain metastasis with: • Longest diameter ≥ 10 mm by CT (when slice thickness is ≤ 5 mm); or ≥ 2 × slice thickness (when slice thickness is > 5 mm) • Pathologically enlarged lymph node: ≥ 15 mm in short axis by CT (when slice thickness is ≤ 5 mm) • Clinical: ≥ 10 mm (that can be accurately measured with callipers). 7. Have not received anti-PD-1, anti-PD-L1 or other systemic therapy for unresectable or metastatic melanoma, except for the following, provided that the patient has recovered from all treatment-related toxicities: a. BRAF mutation targeting therapy > 4 weeks before administration of Study Treatment. b. Adjuvant or neoadjuvant therapy with PD-1 or PD-L1 inhibitors or anti-CTLA-4) is allowed if disease progression/or recurrence occurred at least 6 months after the last dose and no clinically significant immune related toxicities leading to treatment discontinuation were observed. c. Adjuvant interferon therapy must have been completed > 6 weeks before administration of Study Treatment. 8. Any prior radiotherapy or minor surgery must be completed at least 2 weeks and 1 week respectively before Day 1 dosing and recovered from all treatment related toxicities. 9. Screening laboratory results within 14 days prior to randomization: a. Haematology: WBC ≥ 3000/μL, neutrophils ≥ 1500/μL, platelets ≥ 100 × 103/μL, hemoglobin ≥ 10.0 g/dL independent of transfusion. The use of erythropoietic growth factor to achieve hemoglobin (Hgb) ≥ 10 g/dl is acceptable. b. The CrCL ≥ 30 mL/min using Cockcroft-Gault formula (Cockcroft et al. 1976). c. AST and ALT ≤ 3 × ULN, alkaline phosphatase ≤ 2.5 × ULN unless bone metastases present (patients with documented bone metastases: alkaline phosphatase < 5 x ULN), bilirubin ≤ 1.5 × ULN (unless known Gilbert’s disease where it must be ≤ 3 × ULN), serum albumin ≥ 3.0 g/dL). 10. Negative serum pregnancy test at baseline for women of childbearing potential. 11. Females of childbearing potential (non-surgically sterile or premenopausal female capable of becoming pregnant) and all males (due to potential risk of drug exposure through the ejaculate) must agree to use adequate birth control measures from study start, during the study and for 5 months after the last dose of Study Drug. Acceptable methods of birth control in this trial include two highly effective methods of birth control (as determined by the Investigator; one of the methods must be a barrier technique) or abstinence. 12. Have the ability to understand and the willingness to sign a written informed consent document, comply with study scheduled treatment, visits and assessments.

1. History of ≥ Grade 3 hypersensitivity reactions to monoclonal antibodies. 2. Previous treatment with a PD-1, PD-L1, PD-L2, CTLA-4 inhibitor, or any other agents targeting T-cell co-stimulation or immune checkpoint pathways for unresectable or metastatic melanoma. 3. History of a cardiovascular illness including: congestive heart failure (New York Heart Association Grade III or IV) unstable angina or myocardial infarction within the previous 6 months; or symptomatic cardiac arrhythmia despite medical management. QT interval corrected by heart rate using QTcF > 450 ms in males or > 470 ms in females, or congenital long QT syndrome. 4. Uncontrolled hypertension, systolic blood pressure (SBP) > 160 mmHg or diastolic blood pressure (DBP) > 100 mmHg. 5. Patients with new, active, or progressive brain metastases or eptomeningeal disease with except when considered for a separate special open-label cohort. 6. History of haemorrhagic diarrhoea, inflammatory bowel disease, active uncontrolled peptic ulcer, or bowel resection that affects absorption of orally administered drugs. 7. Active, known, or suspected autoimmune disease, except for Type I diabetes mellitus, hypothyroidism requiring only hormone replacement, or skin disorders (such as vitiligo, psoriasis, or alopecia) not requiring systemic therapy. 8. Active uncontrolled bacterial, viral, or fungal infection requiring systemic therapy. 9. Known history of testing positive for HIV, known AIDS. 10. Hepatitis B surface antigen positive or hepatitis C antibody positive. Further investigation per institutional practices may be performed to exclude active infection. 11. Patients with a condition requiring chronic systemic treatment with either corticosteroids (> 10 mg daily prednisone or equivalents) or other immunosuppressive medications within 14 days before administration of Study Treatment. Inhaled or topical steroids, or adrenal replacement dose of corticosteroids at dose ≤ 10 mg/day prednisone equivalent are permitted. 12. Use of another investigational agent (drug or vaccine not marketed for any indication) 28 days or before administration of Study Treatment. If the investigational agent is a monoclonal antibody then within 3 months before administration of Study Treatment. 13. Pregnant or breast-feeding women. 14. Second malignancy unless in remission for 2 years or locally curable cancers that have been treated with curative intent with no evidence of recurrence, such as: • Basal or squamous cell skin cancer • Superficial bladder cancer • Carcinoma in situ of cervix or breast • Incidental prostate cancer • Non melanomatous skin cancer • Carcinoma in situ of the cervix treated with curative intent • Prostate cancer treated with curative intent with serum prostate specific antigen (PSA) < 2.0 ng/mL 15. Patients with medical conditions requiring administration of strong cytochrome P450 (CYP), CYP3A4 Inducers and Inhibitors. 16. Uncontrolled adrenal insufficiency or active chronic liver disease. 17. Has received approved live vaccine/live attenuated vaccines within 30 days of planned Cycle 1 Day 1. Inactivated viral vaccines or vaccines based upon subviral component are allowed. however intranasal influenza vaccines (e.g. Flu-Mist) are not allowed. COVID-19 vaccination should be administered at least 7 days before Cycle 1 Day 1. 18. Underlying medical conditions that, in the Investigator’s opinion, will make the administration of Study Treatment hazardous or obscure the interpretation of toxicity determination or AEs. 19. Unwilling or unable to comply with procedures required in this protocol.