A Single Oral Dose Study of ASP015K in Healthy Volunteers Assessing the Relative Bioavailability Across Three Tablet Strengths From a New Formulation of ASP015K

Inclusion Criteria: * Subject weighs at least 45 kg and has a body mass index (BMI) of 18-32 kg/m2 * Male subject agrees to sexual abstinence, is surgically sterile or is using a medically acceptable method to prevent pregnancy and agrees to continue using this method until 90 days after the last dose of study drug administration * Male subject agrees to not donate sperm until 90 days after the dose of study drug administration * Female subject is surgically sterile or is post-menopausal and is not pregnant and is not lactating * Subject's 12-lead electrocardiogram (ECG) is normal * Subject must be capable of swallowing multiple tablets Exclusion Criteria: * Subject has a previous history of any clinically significant gastro-intestinal, neurological, renal, hepatic, pulmonary, metabolic, cardiovascular, psychiatric, endocrine, hematological disorder or disease, malignancy excluding non-melanoma skin cancer or any other medical condition * Subject has had major GI surgery (such as colectomy, cholecystectomy, etc) * Subject has a history of consuming more than 14 units of alcoholic beverages per week or has a history of alcoholism or drug/chemical/ substance abuse within past 2 years * Subject has/had a symptomatic, viral, bacterial (including upper respiratory infection), or fungal (non-cutaneous) infection within 1 week * Subject has a positive test for hepatitis C antibody, or positive test for hepatitis B surface antigen (HBsAg), or positive hepatitis B core antibody * Subject has a history of the human immunodeficiency virus (HIV) antibody * Subject has a positive tuberculosis (TB) skin test, Quantiferon Gold test or T-SPOT® test * Subject received any vaccine within 60 days * Subject received an experimental agent within 30 days * Subject has an absolute neutrophil count (ANC) \< 2500 cells/mm3 * Subject has had any significant blood loss, donated one unit (450 mL) of blood or more, or received a transfusion of any blood or blood products within 60 days or donated plasma within 7 days * Subject has a history of smoking or has used tobacco-containing products and nicotine or nicotine-containing products in the past six months