Inclusion Criteria:  Chronic AD for at least 2 years before the screening visit and confirmed according to American Academy of Dermatology Consensus at the time of the screening visit. EASI score ≥ 20 at both the screening and baseline visits. Participant with an EASI score of 18-19 at the screening visit only may be reevaluated once within 48 hours. IGA score ≥ 3 (based on the IGA scale ranging from 0 to 4, in which 3 is moderate and 4 is severe) at both the screening and baseline visits. AD involvement ≥ 10% of BSA at both the screening and baseline visits. Documented history by a physician (within 6 months before the screening visit) of inadequate response to topical medications or use of systemic therapies for control of the disease. Agree to apply a moisturizer throughout the study from the screening visit; agree to apply an authorized TCS, with or without TCI, from the screening visit and throughout the study as determined appropriate by the investigator.  Documented history of one of the following, where CsA treatment should not be continued/restarted or participant is not currently a candidate for CsA treatment:  Inadequate response to CsA with previous exposure (defined as flare of AD during CsA tapering from a maximum of 6 weeks of high dose [5 mg/kg/day] to maintenance dose [2 to 3 mg/kg/day] or a flare after a minimum of 3 months on maintenance dose). Flare is defined as increase in signs and/or symptoms leading to escalation of therapy (ie, increase in dose, switch to a higher-potency topical corticosteroids [TCS] or start of another systemic nonsteroidal immunosuppressive drug), or Previous requirement for CsA at doses > 5 mg/kg/day, or duration beyond those specified in the prescribing information (> 1 year) Intolerance and/or unacceptable toxicity (eg, elevated creatinine, elevated liver function tests, uncontrolled hypertension, paresthesia, headache, nausea, hypertrichosis) with previous CsA exposure CsA is medically inadvisable due to medical contraindication, use of prohibited medications, risk of AEs (eg, serious infection) or toxicity (eg, renal or liver damage), or hypersensitivity to CsA or excipients, in the opinion of the investigator  Acceptable documentation includes patient records with information on CsA prescription and treatment outcome, other prohibitive medications/medical history, or written documentation of the conversation with the participant's treating physician, if different than the investigator, as applicable.  Other protocol defined inclusion criteria could apply.  Exclusion Criteria:  Body weight < 30 kg.  One or more of the following criteria at screening or baseline:  Exacerbation of asthma requiring hospitalization in the preceding 12 months. Asthma that has not been well controlled (i.e, symptoms occurring on > 2 days per week, nighttime awakenings 2 or more times per week, or some interference with normal activities) during the preceding 3 months. Asthma Control Test (ACT) ≤ 19 (only for subjects with a history of asthma). Peak expiratory flow (PEF) < 80% of the predicted value. Current medical history of chronic obstructive pulmonary disease and/or chronic bronchitis. Positive serology results (hepatitis B surface antigen [HBsAg] or hepatitis B core antibody [HBcAb], hepatitis C [HCV] antibody with positive HCV RNA, or human immunodeficiency virus [HIV] antibody) at the screening visit. Presence of confounding skin conditions that may interfere with study assessments. Planned or expected major surgical procedure during the clinical study. Other protocol defined exclusion criteria could apply.