PBMC (Peripheral Blood Mononuclear Cells) /Lymphocyte SPECT (Single Photon Emission Computerized Tomography) Imaging in Crohn's Disease

Inclusion A subject will be eligible for inclusion in this study only if all of the following criteria apply: Part A only: 1. Healthy as determined by a responsible and experienced physician, based on a medical evaluation including medical history, physical examination, vital signs, ECG, complete blood count and clinical chemistry. A subject with a clinical abnormality or laboratory parameters outside the reference range for the population being studied may be included only if the investigator and the GSK Medical Monitor agree that the finding is unlikely to introduce additional risk factors and will not interfere with the study procedures. Part A and B: 2. Male or female over 18 years of age inclusive, at the time of signing the informed consent. 3. A female subject is eligible to participate if she is of: • Non-childbearing potential defined as pre-menopausal females with a documented tubal ligation or hysterectomy; or postmenopausal defined as 12 months of spontaneous amenorrhea \[in questionable cases a blood sample with simultaneous follicle stimulating hormone (FSH) \> 40 MlU/ml and estradiol \< 40 pg/ml (\<140 pmol/L) is confirmatory\]. Females on hormone replacement therapy (HRT) and whose menopausal status is in doubt will be required to use one of the contraception methods in Section 8.1 if they wish to continue their HRT during the study. Otherwise, they must discontinue HRT to allow confirmation of post-menopausal status prior to study enrollment. For most forms of HRT, at least 2-4 weeks will elapse between the cessation of therapy and the blood draw; this interval depends on the type and dosage of HRT. Following confirmation of their post-menopausal status, they can resume use of HRT during the study without use of a contraceptive method. Part B only: 4. A history of CD for at least 3 months with a diagnosis confirmed by radiologic, endoscopic or histological assessment. 5. Moderate to severe CD as evidenced by an elevated retrospective CDAI score (of ≥150) and 1 or more of the following: * CRP (of ≥5 mg/L); or * recent (within 4 weeks before the screening visit) evidence of active CD by CT scan, MRI scan or endoscopy. Scans must be part of the patients routine care and should not be conducted as a screening test for this study. 6. Radiographic (barium, CT, MRI) or endoscopic evidence of small bowel involvement (if a patient has had a surgical intervention, evidence of small bowel involvement must have been obtained after the procedure). Exclusion A subject will not be eligible for inclusion in this study if any of the following criteria apply: Part A and B: 1. Known or positive infection with hepatitis B, hepatitis C or HIV. 2. The subject has participated in a clinical trial and has received an investigational product within the following time period prior to Day 1 of the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer). 3. Previous inclusion in a research and/or medical protocol involving nuclear medicine, PET or radiological investigations with significant radiation burden (a significant radiation burden being defined as ICRP category IIb or above: no more than 10 mSv in addition to natural background radiation, in the previous 3 years including the dose from this study). Part B only: 4. Patients with active Crohn's disease with small bowel involvement who are not yet receiving treatment for whom it is judged inappropriate to defer initiating steroid or other treatment for up to 13 days (the maximum interval from screening to last imaging session). 5. Patients who are corticosteroid dependent for whom it is judged inappropriate to defer increasing the dose of steroids or initiating other treatment for up to 13 days (the maximum interval from screening to last imaging session). 6. Patients who are refractory to steroids or immunosuppressants or anti-TNFs for whom it is judged inappropriate to defer change of medical management or surgical intervention for up to 13 days (the maximum interval from screening to last imaging session). 7. The subject is taking \>20mg/day Prednisolone or a prednisolone equivalent during the 4 weeks prior to screening 8. The subject received treatment natalizumab within 12 weeks prior to study entry; 9. The subject has Hb\<10 g/l or Lymphocyte count \<10\^9 /l 10. Known C. difficile infection, or a clinical suspicion of a pathogenic bowel infection (including significant infection due to fistula). 11. Suspected or diagnosed intra-abdominal abscess or bowel perforation 12. The subjects has had bowel surgery (other than appendectomy) within 12 weeks prior to randomization or is likely to require abdominal surgery within 1 month of screening 13. Concurrent illness, infection or disability (including malignancies or neoplastic disease of the bowel) that may affect the interpretation of clinical data, or otherwise contraindicates participation in this clinical study (e.g., an unstable cardiovascular, autoimmune, renal, hepatic, pulmonary, endocrine, metabolic, gastrointestinal, hematologic, psychiatric or neurological condition).