Multi-center, randomized, double blind, parallel-arm, placebo controlled trial to determine whether mepolizumab is more effective than placebo for improving symptoms of dysphagia and decreasing esophageal eosinophil counts in adults and adolescents with active eosinophilic esophagitis (EoE) after an initial 3 month treatment course, and will also assess the impact of an additional 3 months of treatment.

This is a multi-center, randomized, double blind, parallel-arm, placebo controlled trial of mepolizumab. After the first 3 month blinded phase, there will be a second 3 month blinded phase where all patients receive active medication, but the dose will be lower in the subjects initially randomized to the placebo arm.

In the first arm, subjects will receive mepolizumab 300 mg SQ monthly for 3 months. In the second arm, subjects will receive a placebo SQ injection monthly for 3 months. Both groups will have the injection administered under direct observation in a Clinical & Translational Research Center (CTRC) or other clinic to ensure proper administration and compliance. Each visit will also provide an opportunity for symptom questionnaires to be completed and for blood samples to be drawn. After 3 months (the time point where the primary outcome is assessed), all subjects initially randomized to active treatment will continue with mepolizumab dosing 300 mg SQ monthly, and will remain blinded. All subjects initially randomized to placebo will receive mepolizumab 100mg SQ monthly, and will remain blinded. Of note, no dietary changes, changes in baseline Proton Pump Inhibitor (PPI) medication dose, changes in inhaled or intranasal steroid doses, or administration or oral, topical/swallowed, or systemic steroids will be allowed during the study period. Subjects will undergo endoscopy after the first blinded phase (at 3 months) and after the second blinded phase (after 6 months).

Inclusion Criteria:

• Age 16-75

• Diagnosis of EoE (eosinophilic esophagitis) as per consensus guidelines (including PPI non-response)*

• Active eosinophilia on esophageal biopsy, with a peak count of least 15 EOS/hpf (eosinophils per high power field) from at least one esophageal level.

• Biopsies from the stomach and duodenum that have ruled out alternative etiologies in all children and in adults with abnormal endoscopic findings or when other gastric or small intestinal conditions are clinical possibilities. If these samples have been obtained during a previous endoscopic evaluation and in the judgement of the site-Investigator the patient has not had a clinically significant change that would merit repeat gastric/duodenal biopsies, then prior normal gastric and duodenal biopsies are acceptable to exclude alternate etiologies.

• Active symptoms of dysphagia with more than 3 episodes of dysphagia over a period of 2 weeks during the screening period, and an Eosinophilic Esophagitis Symptom Activity Index (EEsAI; see below for details) score of ≥ 27 at baseline.

• Able to read, comprehend, and sign consent form.

• Have maintained a stable diet for 6 weeks prior to enrollment.

• Able to maintain a stable diet throughout the duration of the study period.

• Female subjects of childbearing potential who have had their first menses agree to use a highly effective method of birth control during the study and for 30 days after the last dose of study drug. Female subjects with reproductive potential who are using systemic contraceptives (e.g., oral contraceptives, injectable contraceptives, implantable/insertable hormonal contraceptive products, or transdermal patches) to prevent pregnancy must have stable use for ≥28 days prior to screening.

  • PPI non-response is defined as >15 eos/hpf after at least 6 weeks of high dose administration (40mg total per day or higher) of any approved PPI medication or documented evidence of intolerance or allergy to PPIs. The length of the PPI trial period or documented intolerance/allergy will be determined according to the local clinical standard of care.

Exclusion Criteria:

• Esophageal dilation within 8 weeks of the screening endoscopy.
• Inability to pass a standard upper endoscope (8-10mm) due to esophageal narrowing or stricturing.
• Swallowed/topical steroids for EoE within 4 weeks of the screening endoscopy, or a course of systemic corticosteroids within 8 weeks of the screening endoscopy.
• Not having maintained a stable diet for at least 6 weeks preceding the screening endoscopy.
• Initiation, discontinuation, or change of dose regimen of PPIs; leukotriene inhibitors; or nasal, inhaled, and/or orally administered topical corticosteroids for any condition (such as gastroesophageal reflux disease, asthma, or allergic rhinitis) within the 8 weeks prior to the qualifying esophagogastroduodenoscopy (EGD).
• Presence of concomitant eosinophilic gastritis (EG), eosinophilic gastroenteritis (EGE), eosinophilic colitis (EC), Crohn's disease, ulcerative colitis, or celiac disease.
• History of malignancy within 5 years prior to screening, except completely treated in situ carcinoma of the cervix and completely treated non-metastatic squamous or basal cell carcinoma of the skin.
• History of achalasia.
• Prior esophageal surgery.
• History of bleeding disorder or esophageal varices.
• Active parasitic infection or suspicion of an active parasitic infection, which, in the opinion of the site-Investigator, has not been previously evaluated or treated. Subjects presenting with signs of active parasitic infection or suspicion of active parasitic infection as assessed by current diarrhea and/or blood or mucus in stool will be referred to their clinical physician for further testing to rule out parasitic infection.
• Any other active infections judged at the discretion of the site-Investigator.
• Any other medical or psychological condition that, in the opinion of the site-investigator, may present an unreasonable risk to the study patient as a result of his/her participation in this clinical trial, may make patient's participation unreliable, or may interfere with study assessments. The specific justification for patients excluded under this criterion will be noted in study documents.
• Patient or his/her immediate family is a member of the investigational team.
• Pregnancy or breastfeeding.
• Women of children bearing potential who are not on highly-effective contraception.

Baseline through Month 6 post treatment assessments

Adverse events were captured from time of consent (prior to group assignment) through Month 6.