Subjects will be enrolled in 1 of 3 dose cohorts (low, medium and high). Each cohort will consist of 8 subjects with a 3:1 randomization ratio for ASP015K to placebo. Subjects will be confined to the clinic for study procedures until day 4 (5 days). After all subjects in a dose cohort have completed study procedures through day 4, a decision will be made whether or not dosing and enrollment of the next dose cohort should occur, which will only take place after a review of the safety and tolerability data through day 4 of the most recent dose cohort and any additional reported adverse events (AEs) for previously dosed cohorts.