A phase 0, exploratory study of the pharmacodynamics of a single intratumoral dose of IMCgp100, a monoclonal T cell receptor anti-CD3 scFv fusion protein, in subjects with advanced unresectable melanoma to assess the safety and pharmacodynamic properties of single intratumoral doses of IMCgp100 in the setting of advanced unresectable melanoma. Six patients will be enrolled to complete the study over approximately 12-15 months.