The successful treatment of melanoma with immune checkpoint inhibitors, such as anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and Programmed cell death protein 1 (PD-1) antibodies, has altered our thinking and approach to immunotherapy for solid tumors. Despite these advances, only a portion of patients experience a durable response suggesting that there is room for improvement via enhanced immunomodulatory approaches. Anti-CTLA-4 (Ipilimumab) significantly improves overall survival and achieves long-lasting complete responses in some melanoma patients, the number of patients that achieve durable clinical benefit is limited and could be improved by a combined immunomodulatory approach. The objectives of this study are to assess the safety and efficacy of combined treatment with Ipilimumab and all-trans retinoic acid (ATRA) in melanoma patients. We hypothesize that combined treatment with Ipilimumab and ATRA will improve patient responses, increase tumor antigen-specific T cell responses, and decrease immunosuppressive myeloid-derived suppressor cells (MDSCs) in melanoma patients compared to patients treated with Ipilimumab alone.