A Study to Investigate Belimumab for the Treatment of Chronic Immune Thrombocytopenia.

Inclusion Criteria: * Male or female,18-75 years old * Chronic ITP for a minimum of 6 months with a platelet count \<75,000/uL at screening and a platelet count \<75,000/uL 2 to 6 months before screening * Stable either on no treatment or on a stable dose of corticosteroids (10 milligrams(mg)/day prednisone or prednisone equivalent or less) and/or azathioprine (100mg/day or less) for a minimum of 30 days before screening * Single QTc \<450 milliseconds (msec); or QTc \<480 msec in subjects with Bundle Branch Block * A female subject is eligible to participate if she is not pregnant or nursing and at least one of the following conditions apply: a. Non-childbearing potential defined as pre-menopausal females with a documented tubal ligation or hysterectomy; or postmenopausal defined as 12 months of spontaneous amenorrhea. b.Child-bearing potential and agrees to use one of the contraception methods listed in the protocol Exclusion Criteria: * Diagnosis of ITP is secondary to other conditions * Treated with any B cell targeted therapy at any time * Have received any of the following within 364 days prior to Day 0: Abatacept, A biologic investigational agent other than B cell targeted therapy * Have received any of the following within 180 days prior to Day 0: Intravenous (IV) cyclophosphamide, 3 or more courses of systemic corticosteroids for concomitant conditions * Have received any of the following within 90 days prior to Day 0: High dose corticosteroid for treatment of ITP, Splenectomy, plasmapheresis * Have received any of the following within 60 days, 5 half-lives or twice the duration of the biological effect of belimumab before Day 0: A non-biologic investigational agent, any other immunosuppressive/immunomodulatory agent with the exception of azathioprine and corticosteroids, Eltrombopag, romiplostim, any steroid injection * Have received any of the following within 30 days before Screening: Intravenous immunoglobulin, Corticosteroids greater than 10mg/day (prednisone or prednisone equivalent) or azathioprine more than 100 mg/day, Changes to corticosteroid or azathioprine therapy * Have received a live vaccine within 30 days before Day 0 * Subject could be at risk of haemorrhage that threatens a vital organ * History of a major organ transplant or hematopoietic stem cell/marrow transplant * History of malignant neoplasm within the last 5 years, except for adequately treated cancers of the skin (basal or squamous cell) or carcinoma in situ of the uterine cervix * Required management of infections, as follows: Currently on any suppressive therapy for a chronic infection, Hospitalisation for treatment of infection within 60 days before Day 0, Use of parenteral antibiotics within 60 days before Day 0 * Significant unstable or uncontrolled acute or chronic diseases not due to ITP or planned surgical procedure or a history of any other medical disease, laboratory abnormality, or condition that makes the subject unsuitable for the study * Positive screening Hepatitis C antibody result or Hepatitis B (HB) infection * Positive test for Human Immunodeficiency Virus (HIV) antibody at screening or historically * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) greater or equal to 2x upper limit of normal (ULN); alkaline phosphatase and bilirubin \>1.5xULN (isolated bilirubin \>1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin is \<35%) * IgA deficiency (IgA \<10mg/dL) * Abnormal lab results * Lymphocyte count \<500/mm3 * History of sensitivity to any of the study medications, or components thereof or a history of drug or other allergy including a previous anaphylactic reaction to parenteral administration contrast agents, human or murine proteins or monoclonal antibodies * Evidence of serious suicide risk * Current drug or alcohol abuse or dependence * Where participation in the study would result in donation of blood or blood products \>500 mL within a 56 day period