A Safety and Tolerability Study of Otelixizumab in Thyroid Eye Disease

Inclusion Criteria: * Male or female between 18 and 75 years of age inclusive * 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 \[in questionable cases a blood sample with simultaneous follicle stimulating hormone (FSH) \> 40 mIU/ml and estradiol \<40 pg/ml (\<140 pmol/L) is confirmatory\]. * Child-bearing potential and agrees to use one of the agreed contraception methods listed in the protocol for an appropriate period of time to sufficiently minimize the risk of pregnancy at that point. Female subjects must agree to use contraception for at least 2 weeks prior to dosing and for at least 6 months after the last dose. * Male subjects must agree to use one of the contraception methods listed in the protocol. This criterion must be followed from the time of the first dose of study medication until at least 60 days after the last dose. * Blood test of liver function within normal range * Body mass index within 18.5 - 35 kg/m2 inclusive * Capable of giving informed consent and agreement to comply with the study restrictions * 12-lead ECG within normal limits * fT4 blood levels within reference range for at least 2 months * Active Graves' Ophthalmopathy (GO) with a Clinical Activity Score (CAS) of \>/= 3 out of 7 * Moderately severe GO (as defined by EUGOGO guidelines) * No previous immunosuppressive treatment for GO * Subject is seropositive for EBV with \<10,000 copies of EBV DNA per 10\^6 lymphocytes (qPCR) or seronegative with no evidence of acute EBV infection (asymptomatic, negative EBV IgM and EBV viral load of \<10,000 per 10\^6 lymphocytes) * The subject has no current or prior malignancy, other than non-melanoma skin cancer (subject must have had fewer than 5 occurrences of non-melanoma skin cancer, and the last occurrence must not be within 3 months of study entry) Exclusion Criteria: * A positive pre-study Hepatitis B surface antigen or positive Hepatitis C antibody result within 3 months of screening * Current or chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones) * Positive pre-study drug/alcohol screen. A minimum list of drugs that will be screened for include amphetamines, barbiturates, cocaine, opiates, cannabinoids and benzodiazepines * Positive test for HIV antibody * Positive test for syphilis * History of regular alcohol consumption within 6 months of the study defined as: * an average weekly intake of greater than 21 units or an average daily intake of greater than 3 units (males), or * an average weekly intake of greater than 14 units or an average daily intake of greater than 2 units (females) * Participation in a clinical trial and has received an investigational product within the following time period prior to the first dosing day in the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer) or planning to take any investigational drug for the planned duration of study participation (6 months after the last dose of study drug) * Exposure to more than four new chemical entities within 12 months prior to the first dosing day * History of sensitivity to any of the study medications, or components thereof or a history of drug or other allergy that, in the opinion of the investigator or GSK Medical Monitor, contraindicates their participation * Where participation in the study would result in donation of blood or blood products in excess of 500 mL within a 56 day period * Pregnant females as determined by positive (serum or urine) hCG test at screening or prior to dosing, or lactating females * Currently receiving or has received corticosteroids or other immunosuppressive agents within the last 3 months * Evidence of optic neuropathy and/or corneal breakdown * Immunization with a vaccine within 30 days before the first dose of study drug or requires a vaccine within 30 days after the last dose of study drug * A CD4+ lymphocyte count outside the range of 0.53 - 1.76 × 109/L during screening * Significant systemic infection during the 6 weeks before the first dose of study drug * Received a course of oral antibiotics within 2 weeks of dosing day one * History of recurrent or chronic infection * Subject has had a splenectomy * Subjects with a screening chest X-ray suggestive of TB without documentation of adequate TB treatment * Any major surgical procedure within the 8 weeks before signing the consent form, or planning to undergo any such surgery within the 3 months after the last dose of study drug * Clinically significant cardiovascular and/or cerebrovascular disease * Predisposition to thromboembolic disease, or thromboembolic event (excluding superficial) in past 12 months * Uncontrolled medical conditions: Significant concurrent, uncontrolled medical condition including, but not limited to renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, cerebral psychiatric disease, or evidence of demyelinating disease * A condition or situation that, in the investigator's judgment, is likely to cause the subject to be unable or unwilling to participate in study procedures or to complete all scheduled assessments * Clinically significant abnormal laboratory values during the Screening period, other than those due to GO. Abnormal values are permitted if, upon re-test, the abnormality was resolved * Unwillingness or inability to follow the procedures outlined in the protocol * Mentally or legally incapacitated