This study is a first-in-human, 3-part, multi-center, Phase 1, randomized, double-blind, placebo-controlled study with RPT193 in up to 64 healthy male and female subjects and 30 male and female patients with atopic dermatitis. RPT193 is an orally-available, potent, and selective antagonist of CCR4.

Selected Inclusion Criteria:

Parts A & B (COMPLETED ENROLLMENT):

• Healthy male or female
• 18-55 years of age, inclusive
• At least 50 kg in weight
• BMI: 18.0-30.0 kg/m2, inclusive

Part C (COMPLETED ENROLLMENT):

• Male or female with atopic dermatitis
• 18-65 years of age, inclusive
• BMI between 18.0 (inclusive) and <40.0 kg/m2
• Body surface area (BSA) with AD involvement ≥10%
• Eczema Area and Severity Index (EASI) score ≥12
• Validated Investigator's Global Assessment (vIGA) ≥3
• History of inadequate response to treatment with topical medications, such as corticosteroids or calcineurin inhibitors, or patients for whom topical treatments are otherwise medically inadvisable

Selected Exclusion Criteria:

Parts A & B (COMPLETED ENROLLMENT):

• Use of tobacco products within 60 days prior to drug administration
• History of alcohol abuse or drug addiction
• Positive drug and alcohol screen
• Participation in a drug study within 60 days prior to drug administration
• Donation or loss of more than 100 mL of blood within 60 days prior to drug administration.
• Donation or loss of more than 1.5 liters of blood (for male subjects) / more than 1.0 liters of blood (for female subjects) in the 10 months prior to drug administration.

Part C (COMPLETED ENROLLMENT):

• Any serious and/or uncontrolled medical condition
• History of alcohol abuse or drug addiction
• Positive drug and alcohol screen