A Study to Assess the Safety, Tolerability and Pharmacokinetics of ASP015K

Subjects will be confined to the clinical research unit for 19 days. Subjects will receive a follow-up phone call to asses safety 1 to 5 days after being discharged from the study. Subjects will receive study drug twice per day (BID) on days 1 to 13 of the 14 day treatment period, and will receive a single dose of study drug on the morning of day 14 of the treatment period.