• Any sex or gender who is 18 to 65 years old

• Body weight of 50 to 125 kg and body mass index (BMI) between 18.5 and 35 kg/m2

• Considered in good general health based on medical history, physical exam, 12-lead ECG, screening clinical laboratory findings, and vital signs

• Negative pregnancy test for subjects of child-bearing potential

• Use of highly effective forms of birth control

• Any sex or gender who is 18 to 65 years old

• Body weight of 50 to 125 kg and BMI between 18.5 and 40 kg/m2

• Clinically confirmed diagnosis of active AD

• At least a 1-year history of AD and had no significant flares in AD for at least 4 weeks before Screening

• Baseline weekly mean of daily PP-NRS ≥ 7 at Day 1

• EASI score of ≥ 7 at Screening and Day 1

• vIGA-AD score of ≥ 3 at Screening and Day 1

• Use of topical bland emollient (moisturizer) once or twice daily for at least 5 of the 7 days immediately before Day 1 and agrees to continue using that same emollient at the same frequency throughout the study

• Negative pregnancy test for subjects of child-bearing potential

• Use of highly effective forms of birth control

• Any sex or gender who is 18 to 85 years old

• Body weight of 50 to 125 kg, inclusive, and BMI between 18.5 and 40 kg/m2

• Has had chronic pruritus for at least 6 months and is unresponsive to at least a 2-week course of emollient use.

• Chronic pruritus that affects at least 2 of the following body areas: legs, arms, or trunk

• A single PP-NRS score of ≥ 5 in the 24-hour period prior to the Screening visit

• Baseline weekly mean of daily PP-NRS ≥ 7 at Day 1

• Use of a stable dose of topical bland emollient (moisturizer) once or twice daily for at least 2 weeks before Day 1 and agrees to continue using that same emollient at the same frequency throughout the study

• Negative pregnancy test for subjects of child-bearing potential

• Use of highly effective forms of birth control

⁃ Parts 1 \& 2 (Healthy Volunteers) Exclusion Criteria:

• Any clinically significant underlying illness.

• History of malignancy within 5 years of Screening, except adequately treated basal carcinoma or in situ carcinoma of the cervix.

• History of major surgery within 8 weeks prior to Day 1

• History of asthma requiring regular use of a bronchodilator or a daily maintenance therapy

• History of hypersensitivity (including anaphylaxis) to a biologic medication, vaccine, an immunoglobulin product (plasma-derived or recombinant, eg, monoclonal antibody), or to any of the IP excipients (sucrose, polysorbate 80, or histidine)

• Active hepatitis B virus (HBV) or hepatitis C virus (HCV) or is positive for HIV

• Active or latent tuberculosis infection

• Smoking more than 20 cigarettes (or cigars, cigarillos, or e-cigarettes equivalent) per day

• History of drug or alcohol abuse

• Laboratory values outside of the normal range