Inclusion Criteria:

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

• Subject experienced a severe EoE flare requiring endoscopic intervention and/or concomitant rescue therapy during the Induction Phase and has completed Week 24 of the Induction Phase; OR
• Subject completed the Induction Phase and does not qualify for entry to the Maintenance Phase for reasons other than a severe EoE flare; OR
• Subject experienced a severe EoE flare requiring endoscopic intervention and/or concomitant rescue therapy during the Maintenance Phase and completed Week 48 of the Maintenance Phase; OR
• Subject completed Week 48 of the Maintenance Phase; OR
• Subject must have participated in Study CC-93538-DDI-001 and completed assessments
• through the end of treatment visit.

- Demonstrated ≥ 80% and ≤ 120% overall compliance with required investigational product dosing during the prior studies.

- Did not permanently discontinue investigational product in the prior studies and/or did not experience any clinically significant adverse events related to Investigational Product that would preclude further dosing in the opinion of the
Investigator.

- Female subject of childbearing potential must agree to practice a highly effective method of contraception. Highly effective methods of contraception are those that alone or in combination result in a failure rate of a Pearl index of less than 1% per year when used consistently and correctly. A female of childbearing potential (FCBP) is a female who:

• has achieved menarche at some point; and
• has not undergone a hysterectomy or bilateral oophorectomy or bilateral salpingectomy; or
• has not been naturally postmenopausal (amenorrhea following cancer therapy does not rule out childbearing potential) for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months).
• An FCBP must:
  • Have 2 negative pregnancy tests as verified by the Investigator prior to starting study therapy in Study CC-93538-EE-001 or Study CC-93538-DDI-001 and an additional negative result prior to continuing study therapy in the OLE. She must agree to ongoing pregnancy testing during the course of the study and through the Final 16-week Safety Follow-up Visit. This applies even if the subject practices true abstinence* from heterosexual contact;
  • Either commit to true abstinence* from heterosexual contact (which must be reviewed on a monthly basis and source documented) or agree to use, and be able to comply with, highly effective contraception without interruption throughout the study and for 5 months after the last dose of IP. Acceptable methods of birth control in this study are the following and as applicable per national and local regulations (birth control must be effective by the time the FCBP subject is randomized into the study [e.g., hormonal contraception should be initiated at least 28 days before randomization]):  combined hormonal (estrogen and progestogen containing) contraception, which may be oral, intravaginal, or transdermal Note: Intravaginal and transdermal combined hormonal contraception are not approved in Japan and would therefore not be an acceptable method of contraception for subjects enrolled in this region.
  • progestogen-only hormonal contraception associated with inhibition of ovulation, which may be oral, injectable, or implantable Note: progestogen-only hormonal contraception is not approved in Japan and would therefore not be an acceptable method of contraception for subjects enrolled in this region;
  • placement of an intrauterine device (IUD);
  • placement of an intrauterine hormone-releasing system (IUS);
  • bilateral tubal ligation; or bilateral tubal occlusion (if an implantable device was recently placed, the subject must use an additional effective method of birth control until full occlusion has been confirmed and documented);
  • vasectomized partner (vasectomized partner is a highly effective birth control method provided that the partner is the sole sexual partner of the FCBP and has received medical assessment of the surgical success);
  • sexual abstinence.

Exclusion Criteria:

- Clinical or endoscopic evidence of other diseases or conditions that may affect or confound 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 or immunomodulating 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 of these agents is prohibited during the study.

- Received an investigational product, other than that administered in the CC-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 for COVID-19). Those vaccinated with an investigational COVID-19 vaccine during the CC-93538-EE-001 or CC-93538-DDI-001 studies are not eligible to participate, unless
allowed following a discussion with the Clinical Trial Physician.

- Received a live attenuated vaccine within one month prior to OLE Day 1; or anticipates the need for a live attenuated vaccine at any time throughout the course of this study.

- Any disease that would affect the conduct of the protocol or interpretation of the study results, or would put a patient at risk by participating in the study (e.g., colitis, celiac disease, Mendelian disorder associated with EoE, severe uncontrolled
asthma, infection causing eosinophilia, hypereosinophilic syndrome, or cardiovascular condition, or neurologic or psychiatric illness that could compromise the participant's ability to accurately document symptoms of EoE; newly diagnosed malignancy, lymphoproliferative disease, or clinically significant laboratory abnormality).

- Active parasitic/helminthic infection or a suspected parasitic/helminthic infections or chronic infection (viral hepatitis, tuberculosis, or HIV).

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

- Females who are pregnant or lactating.

Eligibility last updated 12/27/23. Questions regarding updates should be directed to the study team contact.