Safety Study of Tezepelumab (AMG 157) in Healthy Adults and Adults with Atopic Dermatitis

- 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/m^2, inclusive - Subject must have normal or clinically acceptable physical examination, clinical laboratory tests and electrocardiogram (ECG) results - For Part B, subject must have active atopic dermatitis (AD) affecting ≥ 10% body surface area; Eczema Area and Severity Index (EASI) score ≥ 15, aged between 18 and 60 years, inclusive and BMI between 18 and 35 kg/m^2, inclusive

- 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 (except for Part B below) - Subject has known type I/II diabetes - Subject used nonprescription drugs within 14 days prior to randomization and during the study - Subject used any cytotoxic or immunosuppressive drugs with 30 days or 5 half-lives prior to randomization and during the study - Subject previously received a monoclonal antibody - Subject donated blood or had loss of blood of equal to or greater than 500 mL with 2 months of screening - Subject positive for human immunodeficiency virus antibodies, hepatitis B surface antigen, or hepatitis C antibodies - Subject has any condition that might compromise informed consent or compliance to the protocol - 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, ultraviolet [UV] A, 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 nonsteroidal anti-inflammatory drugs [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. - Subject who smokes more than 10 cigarettes per day within the 6 months prior to randomization and during the study.