Compassionate Use of Mepolizumab in Subjects With Hypereosinophilic Syndrome (HES)

• Change in end organ assessments; peripheral blood eosinophil levels; disease control; and HES medications.
• Assessment of mepolizumab dosing requirements as measured by time between doses.

It is thought that from the efficacy and safety information to date, it is possible that subjects with severe or life-threatening HES, and limited treatment options (unresponsive or intolerant to available HES medication), may benefit from mepolizumab treatment. Such subjects will not be able to access mepolizumab through the aforementioned clinical trials due to the severity of their disease. Waiting for regulatory approval would delay access. It is this population of subjects in whom there is a clear unmet medical need, and in whom the benefit to risk ratio is thought appropriate, who will be considered for compassionate use of mepolizumab. This view is echoed by the physicians caring for subjects with HES.

GSK will sponsor this compassionate use trial of mepolizumab to provided access to treatment in subjects determined by their treating physicians to have life threatening HES and in who there is documented failure to at least 3 standard therapies used to treat HES.

Inclusion criteria:

• ≥ 12 years of age
• Has life-threatening HES as defined by ther treating physician's documented view that likelihood of death is high unless the course of the disease is interrupted.
• Meets the diagnostic criteria for Hyper Eosinophilic Syndrome as defined by:

Eosinophilia >1500/ul for at least 6 months with evidence of symptoms and signs of organ system involvement or dysfunction that can be directly related to eosinophilia (with no evidence of parasitic, allergic or other recognized causes of eosinophilia such as connective tissues disease, malignancy) or Eosinophilia of >1500/ul for less than 6 months who meet the other criteria for HES accompanied by clear evidence of eosinophil tissue infiltration and with exclusion for secondary causes of eosinophilia as above.

• Has life-threatening HES disease, as defined above, with documented failure (lack of efficacy or a contra-indication) to at least 3 standard therapies (corticosteroids, cytotoxic agents, immunomodulatory therapy and Imatinib mesylate) at the appropriate duration and dose.

Exclusion Criteria:

• Subjects without HES but with other conditions associated with eosinophilic pathological process such as Churg-Strauss, Wegner's Granulomatosis, atopic disorders, hypersensitivity reactions to parasitic infections, eosinophilic gastroenteropathies, will not be eligible for this compassionate use program which is restricted to life-threatening HES.
• Female subjects of child -bearing potential who are not using an effective method of contraception:

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 (vasectomy with documentation of azoospermia) prior to the female subject's entry into the study and is the sole sexual partner for the female subjects; abstinence, implants of levonorgestrel; injectable progestogen; any intrauterine device (IUD) or intrauterine system (IUS) with a documented failure rate of less than 1% per year; estrogenic vaginal ring, percutaneous contraceptive patches, oral contraceptives (either combined or progestogen only); Double-barrier method:condom and an occlusive cap (diaphragm or cervical/vault caps) with a vaginal spermicidal agent (foam/gel/film/cream/suppository).

• Pregnant or lactating females unless meets Inclusion criteria
• Subjects with severe/life-threatening underlying disease unrelated to HES unrelated to HES where life expectancy is estimated to be less than 3 months.
• Subjects with known lymphoma, eosinophilic leukaemia or pre-leukemia, hematological malignancy advanced and/or metastatic tumors, subjects receiving chemotherapy, radiotherapy and IL-2 due to potential risk of driving tumor growth with use or withdrawal of mepolizumab.
• Subjects with history of serious adverse event or allergic reaction to anti-IL5 or other antibody therapy or known or suspected hypersensitivity to any component of the investigational product (mepolizumab).
• Subjects with current drug or alcohol abuse where uncertain compliance with medication causes safety risk.
• subject currently receiving any other investigational product or other investigational intervention.