This study is checking how safe and effective a new medicine, **APG777**, is for people with a skin condition called *Atopic Dermatitis (AD)*, which makes the skin red and itchy. The study has two parts, and each person can only be in one part. The study lasts up to 106 weeks (about 2 years) and includes different phases like screening, treatment, and follow-up. In Part A, they test if the medicine works. In Part B, they figure out how much medicine to give and how often. If you have moderate-to-severe AD and have not responded well to other treatments, you might be eligible. However, if you’ve been in a study with APG777 before or used certain treatments recently, you won't qualify.

• The study can last up to 106 weeks, which includes screening and treatment phases.
• Participants will need to visit for screening, treatment, and follow-up.
• People with certain medical histories may not be eligible for this study.