Inclusion Criteria:

- Histologically or cytologically confirmed diagnosis of unresectable Stage III or
metastatic MEL not amenable to local therapy

- Participants must have progressive disease after the most recent treatment regimen

- Must consent to allow correlative studies and should have available tumor tissue

- Radiographically measurable disease

- Eastern Cooperative Oncology Group Performance Status of 0 or 1

Exclusion criteria:

- Chemotherapy, radiation therapy, or biological therapy within four weeks prior to the
first dose of study drug, or not recovered from the AEs due to cancer therapies
administered more than four weeks earlier

- Participating or has participated in a study of an investigational agent or using an
investigational device within 30 days of the first dose of study drug

- Expected to require any other form of systemic or localized antineoplastic therapy
while on study

- Chronic systemic steroid therapy within two weeks before the planned date for first
dose randomized treatment or on any other form of immunosuppressive medication

- Known history of any other than the current malignancy excepting adequately treated
basal or squamous cell carcinoma of the skin, superficial bladder cancer, in situ
cervical cancer, breast cancer, or other in situ cancers

- Known active central nervous system (CNS) metastases and/or carcinomatous meningitis

- Active autoimmune disease or a documented history of autoimmune disease or syndrome
that requires systemic steroids or immunosuppressive agents

- Prior treatment with any other anti-programmed cell death (PD) agent

- Active infection requiring systemic therapy

- Known history of Human Immunodeficiency Virus (HIV)

- Active Hepatitis B or Hepatitis C

- Regular user (including recreational use of) illicit drugs or had a recent history
(within the last year) of substance abuse (including alcohol)

- Pregnant or breastfeeding, or expecting to conceive or father children within the
projected duration of the study.