Study of TBX-3400 in Patients With Stage III and IV Melanoma Resistant or Refractory to Immune Checkpoint Inhibitors

Inclusion Criteria: Patients must meet all of the following inclusion criteria to be eligible for participation in the study: 1. Histopathologically confirmed diagnosis of advanced, unresectable or metastatic malignant melanoma 2. Male or female patients age 18 or older 3. Previously treated with checkpoint inhibitor therapy either alone or in combination with either stable disease or progressive disease per RECIST version 1.1 (there is no minimum treatment duration for patients who have progressive disease while on checkpoint inhibitor therapy) 4. Measurable or evaluable disease by RECIST version 1.1 5. Capable of understanding and complying with protocol requirements 6. A life expectancy of greater than 24 weeks at Screening 7. ECOG Performance Status of 0 to 2 8. Written informed consent from the patient or the patient's legally acceptable representative prior to the initiation of any study procedures 9. Adequate bone marrow, liver, and renal function as defined below: * hemoglobin ≥8.0 g/dL (transfusions allowed) * absolute neutrophil count ≥1500/µL * platelet count ≥100,000/µL (transfusions allowed) * alanine transaminase and aspartate transaminase ≤3.0 times the upper limit of normal (ULN), or ≤5 times ULN for patients with known hepatic metastases * total serum bilirubin ≤1.5 x the ULN; ≤2.0 x the ULN if liver metastases are present; patients with a known history of Gilbert's syndrome (≤3.0 x the ULN) and/or isolated elevations of indirect bilirubin are eligible for study participation * estimated glomerular filtration rate ≥50 mL/min/1.73 m\^2 (using Cockcroft Gault formula) Exclusion Criteria: Patients who meet any of the following criteria will not be eligible for participation in the study: 1. Pregnant or breast feeding 2. Developed immune-related toxicity while on prior checkpoint inhibitor therapy that has not yet returned to Grade 1 or better 3. Require systemic pharmacologic doses of corticosteroids at or above the equivalent of 10 mg/day of prednisone; replacement doses, topical, ophthalmologic and inhalational steroids are permitted 4. Active, symptomatic central nervous system (CNS) metastases. Patients with CNS metastases are eligible for the trial if the metastases have been treated by surgery and/or radiotherapy and the patient is off corticosteroids and is neurologically stable for at least 7 days prior to screening 5. Any concurrent uncontrolled illness, including mental illness or substance abuse which in the opinion of the investigator would make the patient unable to cooperate or participate in the trial 6. Severe uncontrolled cardiac disease within 3 months of study entry, including unstable or new onset angina, myocardial infarction or cerebrovascular accident 7. Women of childbearing potential who are unable or unwilling to use an acceptable method of contraception 8. Known infection with human immunodeficiency virus (HIV) that is not well controlled on anti-retroviral therapy as defined by HIV RNA more than 400 copies/mL or severely symptomatic 9. Presence of Hepatitis B and/or Hepatitis C active infection 10. Symptomatic congestive heart failure, defined as New York Heart Association Class II or higher