Inclusion Criteria:  Stage IV or unresectable Stage III advanced melanoma Prior treatment with at least 2 months of anti-PD-(L)1 agent Measurable disease at baseline Tumor available for biopsy  Exclusion Criteria:  History of allergy or severe hypersensitivity to biologic agents History of Grade 3-4 immune-related adverse events leading to discontinuation of prior immunotherapy Prior treatment with ipilimumab or other CTLA-4 antagonists