Inclusion Criteria:

• Subject must sign an Institutional Review Board (IRB) approved informed consent form before any study specific procedures
• Subjects must be aged between 18 and 45 years, inclusive (Part A only)
• Female subjects must be of non-reproductive potential
• Male subjects with partners of childbearing potential should inform their partner of their participation in this clinical study and use highly effective methods of birth control during the study
• Healthy subjects must have a body mass index (BMI) between 18 to 32 kg/m2, inclusive
• Subject must have normal or clinically acceptable physical examination, clinical laboratory tests and electrocardiogram (ECG) results
• For Part B, Subject must have active AD affecting ≥10% body surface area; EASI score ≥15, aged between 18 and 60 years, inclusive and BMI between 18 and 35 kg/m2, inclusive

Exclusion Criteria:

• Subject who has history or evidence of a clinically significant disorder, condition or disease that, in the opinion of the Investigator in consultation with the Amgen physician, would pose a risk to subject safety or interfere with the study evaluation, procedures or completion
• Subject who has evidence of any active or suspected bacterial, viral, fungal or parasitic infections within the past 30 days prior to randomization
• Subject who has known positive tuberculin skin test or recent (within 6 months from randomization) exposure to an individual with active tuberculosis
• Subject who has history of malignancy within 5 years before randomization
• Subject who has history of significant dermatological conditions (except for atopic dermatitis in Part B)
• Subject who has previously received any investigational drug (or is currently using an investigational device) within 30 days prior to randomization
• Subject who has tested positive for drugs and/or alcohol use at screening or before randomization
• Female subjects who are pregnant or lactating
• Subject who has used nicotine or tobacco containing products during 6 months before randomization and during the study
• For atopic dermatitis subjects in Part B (Cohorts 9 and 10) only, additional exclusion criteria are as follows: Subject who has concurrent skin disease (eg, acne) of such severity in the study area that it could interfere with study evaluation; Subject who has active or recent skin infections (within 7 days of randomization); Subject who has received phototherapy (eg, UVA, UVB) known or suspected to have an effect on AD within 6 weeks prior to randomization; Subject who has received corticosteroids by other than topical, inhaled or intranasal delivery within 4 weeks prior to randomization; Subject who has been treated with topical calcineurin inhibitors within 14 days prior to randomization; Subject who uses any medications that interfere with blood coagulation (eg NSAIDs) or wound healing within 7 days or 5 half-lives (whichever is longer) prior to enrolling into the study and for the duration of the study.