Open-Label Extension Of Intravenous Mepolizumab In Patients With Hypereosinophilic Syndrome

Inclusion criteria:

- Signed informed consent.

- Subjects who have participated in Study MHE100185 and have been administered at least
2 doses of study medication.

- Not pregnant or nursing

- Of non-childbearing potential (i.e., women who had a hysterectomy, are
post-menopausal which is defined as 1 year without menses, have both ovaries
surgically removed, or have current documented tubule ligation); or

- Of childbearing potential (i.e., women with functional ovaries and no documented
impairment of oviductal or uterine function that would cause sterility). This
category includes women with oligomenorrhoea [even severe], women who are
perimenopausal or have just begun to menstruate. These women must have a negative
serum pregnancy test at the Screening Visit, and agree to one of the following:1).
Complete abstinence from intercourse from 2 weeks prior to administration of the
first dose of investigational product until 3 months after the last dose of
investigational product; Or 2). Consistent and correct use of one of the following
acceptable methods of birth control for one month prior to the start of the
investigation product and three months after the last dose:Male partner who is
sterile prior to the female subject's entry into the study and is the sole sexual
partner for the female subjects; Implants of levonorgestrel;Injectable
progestogen;Any intrauterine device (IUD) with a documented failure rate of less than
1% per year; Oral contraceptives (either combined or progestogen only)

Exclusion criteria:

- Has developed life-threatening or other serious illness or clinical manifestation
deemed inappropriate for inclusion in study per the principal investigator

- Has any of the following abnormal laboratory values at the Week36/EW Visit of Study
MHE100185: • Serum creatinine ≥3 times institutional upper limit normal (ULN); • AST
or/ALT ≥5 times institutional ULN; • Platelet count < 50,000/uL

- Has developed abnormal cardiac functions, as the following, within past 3 months:•
Left ventricular ejection fraction (LVEF) < 20%; • NYHA class IIIb or IV; • Angina or
acute myocardial infarction

- Has developed allergic reaction to Study MHE100185 investigational product Use of an
investigational drug as concurrent medication

- Does not complete Week36/EW Visit assessments required in Study MHE100185

- Has completed or been terminated from Study MHE100185 for more than 1 month

- Recent history or suspicion of current drug abuse or alcohol abuse within the last 6
months

- Positive pregnancy test at the Week36/EW Visit of Study MHE100185