The objective of this study is to evaluate the safety and tolerability of multiple intravenous (IV) infusions of KHK4083 in subjects with moderate or severe atopic dermatitis.

Inclusion Criteria:

1. Voluntary written informed consent to participate in the study
2. Atopic dermatitis diagnosed according to the Definition and Diagnostic Criteria for Atopic Dermatitis (Guidelines for Management of Atopic Dermatitis 2016) established by the Japanese Dermatological Association
3. Moderate or severe (≥4.5) symptoms of atopic dermatitis at screening, according to the Rajka & Langeland Severity Index
4. Investigator Global Assessment(IGA) ≥3 (moderate) at screening

Exclusion Criteria:

1. Any of the following clinically significant concurrent illnesses:

   • Type 1 diabetes
   • Poorly controlled type 2 diabetes (HbA1c >8.5%)
   • Congestive heart failure (class II to IV of the New York Heart Association classification)
   • Myocardial infarction within 1 year
   • Unstable angina pectoris within 1 year
   • Poorly controlled hypertension (systolic pressure >150 mm Hg or diastolic pressure >90 mm Hg at screening)
   • Severe chronic lung diseases requiring oxygen therapy
   • Multiple sclerosis or other demyelinating diseases
   • Active malignancies, or onset or a history of treatment of malignancies within 5 years prior to informed consent (except for resected or surgically cured epithelial carcinoma of the uterine cervix, cutaneous basal cell carcinoma, cutaneous squamous cell carcinoma, or ductal carcinoma)

2. Current or past history of clinically significant cardiovascular, liver, renal, respiratory, hematologic, central nervous system, psychiatric, or autoimmune diseases/disorders other than those in 1)

3. Alcohol dependence, or drug dependence or a positive result for any of the drug abuse test items

4. Past or current history of drug allergy

5. Any clinically significant infection requiring hospitalization or IV administration of antibiotics within 8 weeks prior to pre-enrollment

6. Any planned surgical treatment during the study

7. Any skin disease that may affect the clinical symptom assessment

8. Pregnant or lactating women, or women willing to have a child during the study period