Subjects will be assigned to one of nine sequential groups A, B, C, D, E, F, G, H, or I. In each group, 6 subjects will be randomized to ASP015K and 2 subjects will be randomized to placebo. Subjects in group F will participate in two treatment periods. Subjects in the first treatment period of group F will have a single study drug dose administered in the fasted state. Subjects in the second treatment period of group F will have a single study drug dose administered immediately following a standard FDA recommended high-fat breakfast.