A Study to Assess the Bioavailability of ASP015K

Inclusion Criteria: * Subject weighing at least 45 kg and BMI of 18-32 kg/m2 * Subject must demonstrate their ability to swallow an empty size 000 capsule * Subject agrees to sexual abstinence, is surgically sterile (with documentation provided by a healthcare professional), or is using a medically acceptable method to prevent pregnancy during the study * Subject has a normal 12-lead ECG * Subject is medically healthy, with no clinically significant medical history or abnormalities Exclusion Criteria: * Subject has ever sought advice from, or been referred to, a General Practitioner (GP) or counselor for abuse or misuse of alcohol, non medical drugs, medicinal drugs or other substance abuse e.g. solvents * Subject is currently using or has had previous use of Class A drugs such as opiates, cocaine, ecstasy, lysergic acid diethylamide (LSD) and intravenous amphetamines * The subject has a positive drugs of abuse test result * The subject regularly consumes alcohol \>21 units per week * The subject is a current smoker or has smoked within the last 12 months * The subject has clinically significant abnormal biochemistry, hematology or urinalysis * The subject has a history of gastrointestinal surgery (with the exception of appendectomy unless it was performed within the previous 12 months) * The subject has a history of clinically significant cardiovascular, renal, hepatic, respiratory and particularly gastrointestinal disease, especially peptic ulceration, gastrointestinal bleeding, ulcerative colitis, Crohn's Disease or Irritable Bowel Syndrome * The subject has had radiation exposure from clinical trials exceeding 5 mSv in the last twelve months or 10 mSv in the last five years * The subject has a history of adverse reaction or allergy to study drug or its excipients The subject suffers from hayfever they must not have or be expecting to have symptoms during the study * The subject has had acute diarrhoea or constipation in the 7 days before the first study day * The subject has the presence of non-removable metal objects such as metal plates, screws, etc, in the abdominal region of the body (with the exception of sterilisation clips) * The subject has a positive Hepatitis B virus (HBV), Hepatitis C virus (HCV) or Human Immunodeficiency virus HIV results * The subject has had treatment with prescription drugs or complementary and alternative medicines within 14 days prior to study drug administration, or over the counter medication within 7 days prior to study drug administration * The subject has/had a symptomatic, viral, bacterial, or fungal infection within 1 week prior to clinic check in * The subject has been vaccinated within the last 90 days * The subject has participated in a clinical research study involving investigational drugs or dosage forms within the previous 90 days * The 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 90 days or donated plasma within 7 days prior to clinic admission * The subject has a past history of tuberculosis or absence of evidence of successful TB immunization as assessed at clinical examination of the Bacille Calmette-Guérin (BCG) scar * The subject has a past history of recurrent herpes simplex or varicella zoster infections