The purpose of this research study is to investigate if KY1005 results in improvement of eczema when given to participants with moderate to severe disease. Side effects of KY1005 will also be explored.

Phase 2a, randomized, double-blinded, placebo-controlled study to evaluate the efficacy, safety and tolerability of two doses of KY1005 in adults with moderate to severe atopic dermatitis whose disease cannot be adequately controlled with topical medications or for whom topical treatment is medically inadvisable.

Inclusion Criteria:

• Adults (greater than or equal to [>=] 18 years but less than [<] 75 years of age) with Atopic Dermatitis (AD) for 1 year or longer at Baseline (Day 1; prior to first administration of Investigational Medicinal Product [IMP]).
• Eczema Area and Severity Index (EASI) of 12 or higher at the Screening Visit and 16 or higher at Baseline.
• validated Investigator Global Assessment (vIGA) of 3 or 4 at Baseline.
• AD involvement of 10 percent or more of body surface area at Baseline.
• Documented history, within 6 months prior to Baseline, of either inadequate response to topical treatments or inadvisability of topical treatments.
• Must have applied a stable dose of topical bland emollient (simple moisturizer, no additives [e.g., urea]) at least twice daily for at least 7 consecutive days before Baseline.
• Able and willing to comply with requested study visits/telephone visits and procedures.
• Able and willing to provide punch biopsy of both lesional and non-lesional skin at Baseline.
• Able and willing to provide written informed consent.

Exclusion Criteria:

• Recent treatment within specific time windows before the baseline visit for the management of atopic dermatitis such as topical or systemic corticosteroids, biologic or investigational therapies and/or phototherapy.
• Known history of or suspected significant current immunosuppression, including history of invasive opportunistic infections despite infection resolution or otherwise recurrent infections of abnormal frequency or prolonged duration.
• Basal and squamous cell skin cancer in the last 3 years prior to Baseline. Any other malignancies in the last 5 years prior to Baseline (excluding in situ cervical carcinoma).
• Severe concomitant illness that would in the Investigator's opinion inhibit the participant's participation in the study, including for example, but not limited to, renal disease, neurological conditions, heart failure and pulmonary disease.
• Laboratory values at the Screening Visit:
• a. Serum creatinine > 1.6 milligrams per deciliter (mg/dL) (141 micromole per liter [mcmol/L]) in female participants and > 1.9 mg/dL (168 mcmol/L) in male participants;
• b. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 1.5 × upper limit of normal (ULN);
• c. Platelet count < 100*10^9/L;
• d. Haemoglobin (Hb): Male < 13.5 g/dL and Female <12 g/dL;
• e. White blood cell count (WBCC) < 3.0*10^9/L;
• f. Absolute neutrophil count < 2.0*10^9/L;
• g. Absolute lymphocyte count < 0.5*10^9/L;
• h. Total bilirubin > ULN.
• Participation in any other clinical study, including non-interventional studies.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org