24-Week Induction Study of APT-1011 in Adult Subjects With Eosinophilic Esophagitis (EoE) (FLUTE 3)

Inclusion Criteria:

1. Adult male or female ≥18 years of age at the time of informed consent

2. Each subject must read, understand, and provide consent on the ICF for this studyand be willing and able to adhere to study-related treatment regimens, procedures,and visit schedule

3. Diagnosis or presumptive diagnosis of EoE that is confirmed during the Screeningperiod by histology that demonstrates ≥15 peak eos/HPF. In order to ensure that adiagnosis can be made, at least 6 biopsies should be taken in total from bothproximal and distal esophageal mucosal areas (at least 3 each). Mid-esophagealbiopsies are not required (optional). HPF will be defined as a standard area of 235square microns in a microscope with 40x lens (0.3 mm^2) and 22 mm ocular.

4. Esophagogastroduodenoscopies and biopsies are to be obtained during theScreening period

5. Biopsies will be read by a central pathologist

6. Esophagogastroduodenoscopies and biopsies performed outside the study will notbe accepted to meet eligibility criteria

7. Optional biopsies may be taken and processed locally for local use, only wherespecified in the local ICF. If serious pathology is unexpectedly encounteredbiopsies of such lesions must be processed locally

8. Have a subject-reported history of ≥6 episodes to a maximum of 30 episodes ofdysphagia in a 14-consecutive-day period within 18 days prior to baseline

9. Completion of the evening eDiary on at least 11 out of the 14-consecutive-dayobservation period during the 4-week run-in period (Baseline Symptom Assessment).Theminimum requirement of 11 days need not be consecutive.

Exclusion Criteria:

1. Have known contraindication, hypersensitivity, or intolerance to corticosteroids

2. Have a contraindication to, or factors that substantially increase the risk of, EGDprocedure or esophageal biopsy or have narrowing of the esophagus that precludes EGDwith a standard (8-10 mm) endoscope

3. Have history of an esophageal stricture requiring dilatation within the 12 weeksprior to Screening

4. Have any physical, mental, or social condition or history of illness or laboratoryabnormality that in the Investigator's judgment might interfere with studyprocedures or the ability of the subject to adhere to and complete the study orincrease the safety risk to the subject such as uncontrolled diabetes orhypertension

5. History of recurrent or current oral or esophageal mucosal infection due to inhaledor nasal corticosteroids

6. Have any mouth or dental condition that prevents normal eating (excluding braces)

7. Have any condition affecting the esophageal mucosa or altering esophageal motilityother than EoE, including erosive esophagitis (grade B or higher as per the LosAngeles Classification of Gastroesophageal Reflux Disease; hiatus hernia longer than 3 cm, Barrett's esophagus, and achalasia)

8. Use of systemic (oral or parenteral) corticosteroids within 30 days beforeScreening, use of swallowed corticosteroids within 30 days before Screening

9. Initiation of either inhaled or nasal corticosteroids or high-potency dermal topicalcorticosteroids within 30 days before Screening

10. Use of calcineurin inhibitors or purine analogues (azathioprine, 6-mercaptopurine)in the 12 weeks before Screening

11. Use of potent cytochrome P450 (CYP) 3A4 inhibitors (e.g., ritonavir andketoconazole) in the 4 weeks before Screening

12. Initiation of an elimination diet or elemental diet within 30 days before Screening (diet must remain stable after signing ICF)

13. Abnormal ACTH stimulation defined as a serum cortisol level <16 μg/dL (440 nmol/L)at 60 minutes with ACTH stimulation test using 250 μg cosyntropin

14. Use of biologic immunomodulators, including dupilumab for EoE, with dose lastadministered within 6 months before Screening (allergy desensitization injection ororal therapies allowed as long as the course of therapy is not altered during thestudy period)

15. Subjects who have initiated, discontinued, or changed dosage regimen of histamine H2receptor antagonists, antacids or antihistamines, leukotriene inhibitors, or sodiumcromolyn within 4 weeks before qualifying endoscopy during Screening. If alreadyreceiving these drugs, the dosage must remain constant throughout the study

16. Subjects who have initiated PPIs within 8 weeks before qualifying endoscopy. Ifalready receiving PPIs, the dosage regimen must remain constant throughout the study

17. Have gastrointestinal bleeding or documented active peptic ulcer within 4 weeksprior to Screening or entering a new study period

18. Have chronic infection such as prior or active tuberculosis, active chicken pox ormeasles, or absence of prior measles, mumps, and rubella vaccine. Subjects withtuberculosis exposure or who live in, or travel to, high endemic areas should beassessed locally for tuberculosis before consideration for the study

19. Immunosuppression or immunodeficiency disorder

20. Current malignancy or malignancy within 3 years of Screening, with the exception ofskin cancers other than melanoma. Subjects in remission for at least 3 yearspost-treatment may be enrolled.

21. Have a history or presence of Crohn's disease, celiac disease, or other inflammatorydisease of the gastrointestinal tract, including non-EoE eosinophilicgastrointestinal disorders (EGIDs)

22. Have current drug abuse in the opinion of the Investigator

23. Have current alcohol abuse in the opinion of the Investigator

24. Female subjects who are pregnant, breastfeeding, or planning to become pregnantduring the study

25. Sexually active females of childbearing potential who do not agree to follow highlyeffective contraceptive methods through the End of Study visit

26. Have received an investigational product as part of a clinical trial within 30 days (or 5 half-lives, whichever is longest) of Screening. Subjects who are currentlyparticipating in observational studies or enrolled in patient registries are allowedin this study

27. Have participated in a prior study with investigational product APT-1011