Mepolizumab in Nasal Polyposis

Inclusion: A subject will be eligible for inclusion in this study only if all of the following criteria apply: 1. Subjects have a diagnosis of severe bilateral nasal polyposis at the screening visit and Visit 1 (i.e. at end of run-in period) which meets the definition of the situation indicative of the need for surgery as described in Decision Table 1 in Appendix 3. 2. Subjects must have had at least one previous surgery for the removal of nasal polyps. 3. Subjects must have an history of refractory response to steroid therapy as shown by being deemed potentially eligible for surgery despite having been on a regular/continuous course of nasal corticosteroids for the treatment of nasal polyposis for at least 3 months and/or have received a short course of oral steroids in the past for nasal polyp treatment. 4. Male or female between 18 and 70 years of age, inclusive at time of signing informed consent. 5. BMI within the range 19.0 to 31.0 kg/m2 (inclusive). 6. Subjects must be free of any clinically significant disease that would interfere with the study schedule or procedures or compromise his/her safety. 7. Subjects with concurrent asthma must be maintained on no more than 10mg/day of Prednisolone or the equivalent. 8. Female subjects of childbearing potential must agree to use one of the contraception methods listed in Section 8.1. This criterion must be followed from 1 month prior to first dose of study medication until four months after last dose of study medication. Females of non -childbearing potential are defined as pre-menopausal females with a documented tubal ligation or hysterectomy; or postmenopausal defined as 12 months of spontaneous amenorrhea. Females on hormone replacement therapy (HRT) and whose menopausal status is in doubt will be required to use one of the contraception methods in Section 8.1 if they wish to continue their HRT during the study (from 1 month prior to first dose of study medication until four months after last dose of study medication). Otherwise, they must discontinue HRT to allow confirmation of post-menopausal status prior to study enrollment. For most forms of HRT, at least 2- 4 weeks will elapse between the cessation of therapy and the blood draw; this interval depends on the type and dosage of HRT. Following confirmation of their post-menopausal status, they can resume use of HRT during the study without use of a contraceptive method. 9. Male subjects must agree to use one of the contraception methods listed in Section 8.1. This criterion must be followed from the time of the first dose of study medication until four months after last dose of study medication. 10. Subjects are capable of giving written informed consent, which includes agreeing to be compliant with the study requirements and restrictions listed in the consent form. 11. Subjects are willing and available to complete the study and all measurements. 12. Subjects are capable of reading, comprehending, and writing the local language at a sufficient level to complete study related materials. Exclusion: A subject will not be eligible for inclusion in this study if any of the following criteria apply: 1. As a result of medical interview, physical examination, or screening investigation the physician responsible considers the subject unfit for the study. 2. Subjects requiring oral corticosteroids at a dose greater than 10mg Prednisolone or equivalent during the study will be terminated from the study. 3. Subjects who have had an asthma exacerbation requiring admission to hospital within 4 weeks of Screening. 4. Subjects who have received immunotherapy within the previous 12 months. 5. Subjects with a positive pre-study drug/alcohol screen. A minimum list of drugs that will be screened for include amphetamines, barbiturates, cocaine, opiates, cannabinoids and benzodiazepines. 6. Subjects with a known medical history of Hepatitis B, Hepatitis C, or HIV infection. 7. Subjects with a history or suspicion of drug abuse or alcohol abuse within the last 6 months. 8. Subjects who are currently receiving, or have received within 3 months prior to first mepolizumab dose, chemotherapy, radiotherapy or investigational medications/therapies. 9. Subjects with one or more of the following abnormal laboratory values:

• Serum creatinine ≥ 3 times institutional ULN
• AST or/ALT ≥ 5 times institutional ULN
• Platelet count < 50,000/μL 10. Subjects with a 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 GSK Medical Monitor, contraindicates their participation. Aspirin-sensitive subjects are acceptable. 11. Subjects with a history of allergic reaction to anti-IL-5 or other antibody therapy. 12. Pregnant females as determined by positive serum pregnancy test at screening or positive urine pregnancy test prior to each dosing occasion. 13. Breastfeeding/Lactating females. 14. Subjects who currently smoke or have smoked in the last 6 months. 15. Subjects who are unwilling or unable to follow the procedures outlined in the protocol.