The purpose of this research study is to see if the study drug, CT-011, is safe to give and if it helps people with melanoma that has spread to other areas of their body. CT-011 is a monoclonal antibody. Monoclonal antibodies are a type of drug that is typically given by infusion into a vein (intravenously). Monoclonal antibodies are antibodies made in a lab instead of by the immune system which then recruit the immune system to help fight cancer cells.

All final eligible subjects will receive an intravenous infusion of CT-011. This study will test two dose levels of the study drug:

Group 1: Patients in this group will be given the study drug at dose level 1 (1.5 mg/kg).

Group 2: Patients in this group will be given the study drug at dose level 2 (6.0 mg/kg).

Each group will be given the study drug through an IV (a needle put into a vein in the arm) on day 1. After day 1, the study drug will be given every other week. Patients may be given a total of up to 27 study drug infusions for about 12 months while they are in the study. Approximately 100 patients will participate in this study.

Inclusion Criteria:

1. Participants must have a histologically or cytologically documented diagnosis of metastatic melanoma.
2. Participants age is 18 years or older.
3. Stage IV disease that is clearly progressive since last therapy
4. ECOG performance status of 0 or 1.

Exclusion Criteria:

1. Patients with uveal melanoma.
2. Active autoimmune disease, symptoms or conditions except for vitiligo, type I diabetes, treated thyroiditis, asymptomatic laboratory evidence of autoimmune disease (eg: + ANA, +RF, antithyroglobulin antibodies) or mild arthritis requiring no therapy or manageable with NSAIDs.
3. Prior use of anti PD-1, anti PD-L1 or PD-L2 therapy.
4. More than 3 prior lines of treatment for metastatic melanoma including approved and investigational treatments.
5. Women of child bearing potential who are pregnant

Note: This is only a partial list of eligibility criteria.