Safety Study of CC-93538 in Adult and Adolescent Participants With Eosinophilic Esophagitis

Inclusion Criteria:

• Previously participated in prior clinical study CC-93538-EE-001 and either:

1. Subject experienced a severe EoE flare requiring endoscopic intervention and/orconcomitant rescue therapy during the Induction Phase and has completed Week 24of the Induction Phase; OR

2. Subject completed the Induction Phase and does not qualify for entry to theMaintenance Phase for reasons other than a severe EoE flare; OR

3. Subject experienced a severe EoE flare requiring endoscopic intervention and/orconcomitant rescue therapy during the Maintenance Phase and completed Week 48of the Maintenance Phase; OR

4. Subject completed Week 48 of the Maintenance Phase

• OR Subject must have participated in Study CC-93538-DDI-001 and completedassessments through the end of treatment visit

• Demonstrated ≥ 80% and ≤ 120% overall compliance with required investigationalproduct dosing during the prior studies.

• Did not permanently discontinue investigational product in the prior studies and/ordid not experience any clinically significant adverse events related toInvestigational Product that would preclude further dosing in the opinion of theInvestigator.

• Females of childbearing potential must have a negative pregnancy test prior to thefirst dose of open-label CC-93538 and agree to practice a highly effective method ofcontraception (as defined in the prior study) until 5 months after the last dose ofopen-label CC-93538.

Exclusion Criteria:

• Clinical or endoscopic evidence of other diseases or conditions that may affect orconfound the histologic, endoscopic, or clinical symptom evaluation for this study.

• Active Helicobacter pylori infection or esophageal varices.

• Evidence of immunosuppression, or of having received systemic immunosuppressive orimmunomodulating drugs within 5 drug half-lives prior to open-label extension study (OLE) Day 1. Use of these agents is prohibited during the study.

• Treatment with oral or sublingual immunotherapy within 6 months of OLE Day 1. Use ofthese agents is prohibited during the study.

• Received an investigational product, other than that administered in theCC-93538-EE-001 or CC-93538-DDI-001 studies, within 5 half-lives prior to OLE Day 1 (includes investigational product received during an interventional trial forCOVID-19). Those vaccinated with an investigational COVID-19 vaccine during theCC-93538-EE-001 or CC-93538-DDI-001 studies are not eligible to participate, unlessallowed following a discussion with the Clinical Trial Physician.

• Received a live attenuated vaccine within one month prior to OLE Day 1; oranticipates the need for a live attenuated vaccine at any time throughout the courseof this study.

• Any disease that would affect the conduct of the protocol or interpretation of thestudy results, or would put a patient at risk by participating in the study (e.g.colitis, celiac disease, Mendelian disorder associated with EoE, severe uncontrolledasthma, infection causing eosinophilia, hypereosinophilic syndrome, orcardiovascular condition, or neurologic or psychiatric illness that could compromisethe participant's ability to accurately document symptoms of EoE; newly diagnosedmalignancy, lymphoproliferative disease, or clinically significant laboratoryabnormality).

• Active parasitic/helminthic infection or a suspected parasitic/helminthic infectionsor chronic infection (viral hepatitis, tuberculosis, or HIV)

• Has had idiopathic anaphylaxis or major immunologic reaction to an immunoglobulin-Gcontaining agent; or any known hypersensitivity to any ingredient in CC-93538.

• Females who are pregnant or lactating.