A Study to Compare the Pharmacokinetics of Mepolizumab as a Liquid Drug in a Safety Syringe or an Autoinjector Versus Lyophilised Drug

Inclusion Criteria

- 18 years of age and over at the time of signing the informed consent.

- Healthy as determined by the investigator or medically qualified designee based on a
medical evaluation including medical history, physical examination, vital signs,
laboratory tests, and cardiac monitoring. A subject with a clinical abnormality or
laboratory parameter(s) which is/are not specifically listed in the inclusion or
exclusion criteria, outside the reference range for the population being studied may
be included only if the investigator agrees and documents that the finding is unlikely
to introduce additional risk factors and will not interfere with the study procedures
or ability to interpret study results.

- Body weight >=50 kg and body mass index (BMI) within the range 19.0-30 kg/square
meter(m^2) (inclusive)

- Male or Female: A female subject is eligible to participate if she is not pregnant (as
confirmed by a negative human chorionic gonadotrophin (hCG) test), not lactating, and
at least one of the following conditions applies: Non-reproductive potential defined
as: pre-menopausal females with documented tubal ligation; documented hysteroscopic
tubal occlusion procedure with follow-up; confirmation of bilateral tubal occlusion;
hysterectomy; documented bilateral oophorectomy; post- menopausal females. Subject is
of 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 16 weeks after the administration of the single dose of study medication.

- Capable of giving signed informed consent which includes compliance with the
requirements and restrictions listed in the consent form and in the protocol. The
subject must be able to understand and communicate in the native language of the site,
e.g. German in German sites.

Exclusion Criteria

- Alanine transaminase >1.5x upper limit of normal (ULN)

- Bilirubin >1.5xULN (isolated bilirubin >1.5x ULN is acceptable if bilirubin is
fractionated and direct bilirubin <35%).

- Current or chronic history of liver disease, or known hepatic or biliary abnormalities
(with the exception of Gilbert's syndrome or asymptomatic gallstones)

- QTc corrected by Fridericia's (QTcF) formula>450 milliseconds (msec)

- Any clinically relevant abnormality identified at the screening medical assessment
(physical examination/medical history), clinical laboratory tests, or 12-lead
electrocardiogram.

- 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) before the first dose
of study medication and until study completion, unless in the opinion of the
investigator and GlaxoSmithKline Medical Monitor the medication will not interfere
with the study procedures or compromise subject safety.

- History of regular alcohol consumption within 6 months of the study defined as: an
average weekly intake of >14 units for females and >21 units for males. One unit is
equivalent to 8 grams of alcohol: a half-pint (~240 milliliter [mL]) of beer, 1 glass
(125 mL) of wine or 1 (25 mL) measure of spirits.

- Urinary nicotine levels indicative of smoking or history or regular use of tobacco- or
nicotine-containing products within 6 months prior to screening. Limit of >500
nanogram/mL.

- Involved in any activities likely to result in any significant decrease or increase in
body weight during the study period (e.g. 'crash' dieting, bodybuilding).

- 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.

- Presence of hepatitis B surface antigen (HBsAg), positive hepatitis C antibody test
result at screening or within 3 months prior to first dose of study treatment.

- A positive test for human immunodeficiency virus antibody.

- Subjects with known, pre-existing helminthes infestation within 6 months prior to Day
1.

- Where participation in the study would result in donation of blood or blood products
in excess of 500 mL within 3 months.

- 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.

- A positive pre-study drug/alcohol screen.

- A vulnerable subject. Defined as individuals whose willingness to volunteer in a
clinical trial may be unduly influenced by the expectation, whether justified or not,
of benefits associated with participation, or of a retaliatory response from senior
members of a hierarchy in case of refusal to participate.

- Subjects who work for the Sponsor, contract research organization, or one of the study
centers.