This clinical trial is focused on studying Atopic Dermatitis, a condition that causes the skin to become red, itchy, and inflamed. The study will evaluate a new treatment called APG777, which is a solution for injection. The purpose of the study is to assess the safety and effectiveness of APG777 in patients with moderate-to-severe Atopic Dermatitis. Participants in the study will receive either the APG777 treatment or a placebo, which is a substance with no active medication.

The study is divided into two parts. In Part A, the effectiveness of APG777 will be compared to the placebo after 16 weeks of treatment. In Part B, three different doses of APG777 will be tested against the placebo, also over a 16-week period. Throughout the study, participants will receive regular injections and attend scheduled visits to monitor their progress and any side effects. The study aims to provide valuable information on how well APG777 works and its safety profile over time.

Participants will be monitored for changes in their skin condition, including the severity and area affected by eczema, which is a common symptom of Atopic Dermatitis. The study will also track any adverse events or side effects that may occur during the treatment period. The overall duration of the study is expected to last up to 106 weeks, allowing researchers to gather comprehensive data on the long-term effects of APG777.