Omalizumab to Mepolizumab Switch Study in Severe Eosinophilic Asthma Patients

Inclusion Criteria:

- At least 12 years of age at the time of signing the informed consent. For those
countries where local regulations permit enrolment of adults only, subject recruitment
will be restricted to those who are >= 18 years of age.

- Asthma: A physician diagnosis of asthma for >=2 years that meets the National Heart
and Lung Institute guidelines.

- Forced expiratory volume in 1 second (FEV1): Persistent airflow obstruction as
indicated by: For subjects >=18 years of age at Visit 1, a pre-bronchodilator FEV1
<80% predicted recorded at Visit 1, For subjects 12-17 years of age at Visit 1, a
pre-bronchodilator FEV1 <90% predicted recorded at Visit 1 or FEV1/ Forced Vital
Capacity (FVC) ratio <0.8 recorded at Visit 1

- Eosinophilic asthma: Airway inflammation characterized as eosinophilic in nature as
indicated by one of the following: A peripheral blood eosinophil count of >=300
cells/microliter (uL) that is related to asthma demonstrated in the past 12 months
prior to Visit 1 or a peripheral blood eosinophil count of >=150 cells/uL at Visit 1
that is related to asthma.

- Inhaled Corticosteroid: 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). For 18 years of age and older: ICS
dose must be >=880 microgram (ug)/day fluticasone propionate (FP) (ex-actuator) or
equivalent daily. For ICS/ Long-Acting Beta-2-Agonists (LABA) combination
preparations, the highest approved maintenance dose in the local country will meet
this ICS criterion. For subjects 12-17 years of age at Visit 1: ICS dose must be >=440
ug/day fluticasone propionate (FP) (ex-actuator) or equivalent daily, For ICS/LABA
combination preparations, the highest approved maintenance dose in the local country
will meet this ICS criterion.

- Controller Medication: 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. [e.g., LABA,
leukotriene receptor antagonist (LTRA), or theophylline.]

- Asthma symptoms not optimally controlled: An ACQ-5 score of >=1.5 recorded at Visit 1.

- Omalizumab Treatment: Receiving omalizumab, based on weight and IgE levels, for at
least the 4 months prior to Visit 1.

- Exacerbation history: Previously confirmed history of two or more exacerbations
requiring treatment with systemic corticosteroids (intramuscular, intravenous, or
oral) in the 12 months prior to Visit 1 despite the use of high-dose ICS. For subjects
receiving omalizumab for >=8 months, at least one exacerbation must have occurred
while on omalizumab treatment. For subjects receiving maintenance oral
corticosteroids, the corticosteroid treatment for the exacerbations must have been a
two-fold dose increase or greater.

- Male or eligible Female: Females: a) Non-reproductive potential defined as
:Pre-menopausal females with one of the following: Documented tubal ligation,
Documented hysteroscopic tubal occlusion procedure with follow-up confirmation of
bilateral tubal occlusion, Hysterectomy, Documented Bilateral Oophorectomy,
Postmenopausal defined as 12 months of spontaneous amenorrhea [in questionable cases a
blood sample with simultaneous follicle stimulating hormone (FSH) and estradiol levels
consistent with menopause (refer to laboratory reference ranges for confirmatory
levels)]. Females on hormone replacement therapy (HRT) and whose menopausal status is
in doubt will be required to use one of the highly effective contraception methods 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 enrolment. b)
Reproductive potential and agrees to follow one of the options listed in the Modified
List of Highly Effective Methods for Avoiding Pregnancy in Females of Reproductive
Potential (FRP) from 30 days prior to the first dose of study medication and until at
least five terminal half-lives or until any continuing pharmacologic effect has ended,
whichever is longer, after the last dose of study medication and completion of the
Exit visit/Early Withdrawal visit.The investigator is responsible for ensuring that
subjects understand how to properly use these methods of contraception.

- Capable of giving signed informed consent which includes compliance with the
requirements and restrictions listed in the consent form and in this protocol.

Exclusion Criteria:

- Concurrent Respiratory Disease: Presence of a known pre-existing, clinically important
lung condition other than asthma. This includes current infection, bronchiectasis,
pulmonary fibrosis, bronchopulmonary aspergillosis, or diagnoses of emphysema or
chronic bronchitis (chronic obstructive pulmonary disease other than asthma) or a
history of lung cancer.

- Malignancy: A current malignancy or previous history of cancer in remission for less
than 12 months prior to screening (subjects that had localized carcinoma of the skin
which was resected for cure will not be excluded).

- Liver disease: Subjects must not be enrolled in the study if :At screening (Visit 1)
Alanine Transaminase (ALT) >2x Upper Limit of Normal (ULN); and bilirubin >1.5xULN
(isolated bilirubin >1.5xULN is acceptable if bilirubin is fractionated and direct
bilirubin <35%) Current active liver or biliary disease (with the exception of
Gilbert's syndrome or asymptomatic gallstones or otherwise stable chronic liver
disease per investigator assessment). Stable chronic liver disease should generally be
defined by the absence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia,
oesophageal or gastric varices, or persistent jaundice, or cirrhosis.

- Hepatitis status: Diagnosis of chronic hepatitis B, as evidenced by positive Hepatitis
B surface antigen (HBsAg) at Visit 1. Chronic stable hepatitis C (e.g.,positive
hepatitis C antibody test result at screening (Visit 1) or within 3 months prior to
first dose of study treatment) are acceptable if subject otherwise meets entry
criteria.

- Cardiovascular: Subjects who have severe or clinically significant cardiovascular
disease uncontrolled with standard treatment. Including but not limited to: a) known
ejection fraction of <30% or b) severe heart failure meeting New York Heart
Association Class IV classification or c) hospitalised in the 12 months prior to Visit
1 for severe heart failure meeting New York Heart Association Class III or d) angina
diagnosed less than 3 months prior to Visit 1 or at Visit 1

- Subjects with QT interval corrected (QTc) > 450 milliseconds (msec) or QTc > 480 msec
in subjects with Bundle Branch Block at screening Visit 1.The QTc is the QT interval
corrected for heart rate according to Bazett's formula (QTcB), Fridericia's formula
(QTcF), and/or another method, machine-read or manually over-read. The specific
formula that will be used to determine eligibility and discontinuation for an
individual subject should be determined prior to initiation of the study. In other
words, several different formulae cannot be used to calculate the QTc for an
individual subject and then the lowest QTc value used to include or discontinue the
subject from the trial.For purposes of data analysis, QTcB, QTcF, another QT
correction formula, or a composite of available values of QTc will be used.

- Other Concurrent Medical Conditions: Subjects who have known, pre-existing, clinically
significant endocrine, autoimmune, metabolic, neurological, renal, gastrointestinal,
hepatic, haematological or any other system abnormalities that are uncontrolled with
standard treatment.

- Eosinophilic Diseases: Subjects with other conditions that could lead to elevated
eosinophils such as Hypereosinophilic Syndromes, including Churg-Strauss Syndrome
(Eosinophilic Granulomatosis with Polyangiitis [EGPA]), or Eosinophilic Esophagitis.
Subjects with a known, pre-existing parasitic infestation within 6 months prior to
Visit 1 are also to be excluded.

- Immunodeficiency: A known immunodeficiency (e.g., human immunodeficiency virus [HIV]),
other than that explained by the use of corticosteroids taken as therapy for asthma.

- Other Monoclonal Antibodies: Subjects who have received any monoclonal antibody (other
than omalizumab) to treat inflammatory disease within 5 half-lives of Visit 1.

- Smoking history: Current smokers or former smokers with a smoking history of >=10 pack
years (number of pack years = (number of cigarettes per day / 20) x number of years
smoked). A former smoker is defined as a subject who quit smoking at least 6 months
prior to Screening Visit 1.

- Alcohol/Substance Abuse: A history (or suspected history) of alcohol misuse or
substance abuse within 2 years prior to Visit 1.

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

- Hypersensitivity: Subjects with allergy/intolerance to a monoclonal antibody or
biologic. 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 Medical Monitor, contraindicates their participation.

- Investigator opinion: Omalizumab treatment has provided significant clinical benefit
despite experiencing 2 exacerbations in the past 12 months, and potential benefit from
a switch to mepolizumab would not outweigh the potential harm after omalizumab
withdrawal for the subject.

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

- Investigational Medications: 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, prior to Screening (V1) (this also includes investigational
formulations of marketed products).

- Pregnancy: Subjects who are pregnant or breastfeeding. Patients should not be enrolled
if they plan to become pregnant during the time of study participation.