The purpose of this study is to evaluate the safety, tolerability and pharmacokinetics of IBI356 in Healthy Participants and in Atopic Dermatitis Patients

Inclusion Criteria:

1. Healthy participants:

   1. Aged 18 to 45 years,
   2. Weight 50 to 120 kgs,
   3. Good physical and mental health based on medical history, physical examination, clinical laboratory, ECG, and vital signs, as judged by the Investigator.
   4. No child-bearing potential during the trial and within 6 months after SAD doses, and adequate contraceptive measures can be taken.

2. Atopic dermatitis:

   1. Aged 18 to 75 years,
   2. body mass index (BMI): 18.0 - 32.0 kg/m2,
   3. Atopic Dermatitis (AD) for 1 year or longer at Baseline,
   4. Eczema Area and Severity Index (EASI) of 16 or higher at baseline,
   5. Investigator Global Assessment (IGA) of 3 or 4 at baseline,
   6. AD involvement of 10 percent or more of body surface area at Baseline,
   7. Documented history, within 1 year before Baseline, of either inadequate response to topical treatments or inadvisability of topical treatments,
   8. Must have applied a stable dose of topical bland emollient at least twice daily for at least 7 consecutive days before Baseline.

Exclusion Criteria:

1. History of relevant drug allergies.

2. Has any condition that, in the opinion of the investigator, would make participation not be in the best interest (for example, compromise the well-being) of the participant or that could prevent, limit, or confound the protocol-specified assessments

3. Healthy participants:

   1. History of alcohol abuse or drug addiction within 1 year before screen,
   2. Positive drug and alcohol screen at screening.

4. Atopic dermatitis:

   1. Having used any of the following treatments within 4 weeks before the baseline visit, or any condition that, in the opinion of the investigator, was likely to require Immunosuppressive/ immunomodulating drugs treatment(s) during the first 4 weeks of study treatment:
   2. Treatment with topical corticosteroids (TCS) or topical calcineurin inhibitors (TCI) within 1 week before the baseline visit.