Efficacy and Safety Study of Mepolizumab Adjunctive Therapy in Subjects With Severe Uncontrolled Refractory Asthma

Inclusion Criteria:

- Able to give written informed consent prior to participation in the study

- At least 12 years of age at visit 1 and a minimum weight of 45 kilogram (kg)

- A well-documented requirement for regular treatment with high dose inhaled
corticosteroid (ICS) in the 12 months prior to Visit 1 with or without maintenance
oral corticosteroids (OCS)

- Current treatment with an additional controller medication, besides ICS, for at least
3 months or a documented failure in the past 12 months of an additional controller
medication for at least 3 successive months

- Prior documentation of eosinophilic asthma or high likelihood of eosinophilic asthma

- At Visit 1, a pre-bronchodilator FEV1 <80% (for subjects >= 18 years of age), a
pre-bronchodilator FEV1 <90% or FEV1:FVC ratio <0.8 (for subjects 12-17 years of age).

- Previously confirmed history of two or more exacerbations requiring treatment with
systemic CS

- Male or Eligible Female (females of childbearing potential must commit to consistent
and correct use of an acceptable method of birth control)

- French subjects will be included only if either affiliated to or a beneficiary of a
social security category.

Exclusion Criteria:

- Current smokers or former smokers with a smoking history of >=10 pack years

- Presence of a known pre-existing, clinically important lung condition other than
asthma

- A current malignancy or previous history of malignancy in less than 12 months

- Known, pre-existing, unstable liver disease cirrhosis and known biliary abnormalities

- Known, pre-existing severe or clinically significant cardiovascular disease

- known, pre-existing other concurrent clinically significant medical conditions that
are uncontrolled with standard treatment

- Subjects with any eosinophilic diseases

- QTc(F) ≥450msec or QTc(F) ≥480 msec

- A history of alcohol/substance abuse

- Subject with known immunodeficiency

- Subjects who have received omalizumab within 130 days of Visit 1 or any monoclonal
antibody (other than Xolair) to treat inflammatory disease within 5 half-lives of
Visit 1

- Subjects who have received treatment with an investigational drug within the past 30
days or five terminal phase half-lives of the drug whichever is longer

- Subjects with allergy/intolerance to a monoclonal antibody or biologic.

- Subjects who are pregnant or breastfeeding

- Subjects who have known evidence of lack of adherence to controller medications and/or
ability to follow physician's recommendations

- Previously participated in any study with mepolizumab and received investigational
product (including placebo)