Japanese Phase 1 Study of Mepolizumab

Inclusion Criteria: * Healthy Japanese as determined by a responsible and experienced physician, based on a medical evaluation including medical history, physical examination, laboratory tests and cardiac monitoring. 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 * Japanese defined as being born in Japan, having four ethnic Japanese grandparents, holding a Japanese passport or identity papers and being able to speak Japanese. Japanese subjects should also have lived outside Japan for less than 10 years. * Male between 20 and 55 years of age inclusive, at the time of signing the informed consent. * Body weight equal or more than 45.0 kg and BMI within the range between 18.5 and 29.0 kg/m2 (inclusive). * Capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form. * At screening, QTCF\<450 msec; or QTcF \< 480 msec in subjects with Bundle Branch Block. * AST, ALT, alkaline phosphatase and bilirubin equal or less than 1.5xULN (isolated bilirubin \>1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin \<35%). 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). * A positive pre-study drug/alcohol screen. * A positive test for HIV antibody. * 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. One unit is equivalent to a 285 mL glass or full strength beer or 425 mL schooner or light beer or 1 (30 mL) measure of spirits or 1 glass (100 mL) of wine (NHMRC Guidelines \[NHMRC, 2001\]) * The subject has participated 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). * Exposure to more than four new chemical entities within 12 months prior to the first dosing day. * Use of prescription or non-prescription drugs, including vitamins, herbal and dietary supplements (including St John's Wort) within 7 days (or 14 days if the drug is a potential enzyme inducer) or 5 half-lives (whichever is longer) prior to the first dose of study medication, unless in the opinion of the Investigator and GSK Medical Monitor the medication will not interfere with the study procedures or compromise subject safety. * 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. * Unwillingness or inability to follow the procedures outlined in the protocol. * Subject is mentally or legally incapacitated. * Subjects with a smoking history of \>10 cigarettes per day in the last 3 months. * The subject's systolic blood pressure is outside the range of 90-140 mmHg, or diastolic blood pressure is outside the range of 45-90 mmHg or systolic blood pressure drop from supine to standing of \>30 mmHg, or heart rate is outside the range of 40-100 bpm for subjects at Screening and pre-dose on Day 1. * Exposure to live vaccine within the four weeks prior to screening or with intention to receive live vaccine during the study