A Phase I Study of HXN5003 in Healthy Participants and Patients With Moderate-to-Severe Atopic Dermatitis

Inclusion Criteria: 1. Participants must be able to understand and comply with the study requirements and voluntarily sign the informed consent form (ICF). 2. (Healthy Participants) Male or female participants aged 18 to 50 years (inclusive) at the time of signing the ICF. 3. (Healthy Participants) Male participants weighing ≥ 50.0 kg and female participants weighing ≥ 45.0 kg, with a body mass index (BMI) between 19.0 and 26.0 kg/m² (inclusive). 4. (Patients with AD) Male or female participants aged 18 to 70 years (inclusive) 5. (Patients with AD) Participants must have documented AD history, moderate-to-severe disease, and inadequate response to topical therapy at screening. Exclusion Criteria: 1. Presence of any clinically significant disease at randomization, as judged by the investigator. 2. History of severe drug allergy or systemic anaphylactic reactions, such as anaphylactic shock, laryngeal edema, etc. 3. Known or suspected history of immunosuppression, or history of invasive opportunistic infections, including infections that are unusually frequent, recurrent, or prolonged in duration as judged by the investigator, even after resolution of the infection. 4. Participants who have resided long-term in regions with high prevalence of Human Herpesvirus-8 (HHV-8), such as Africa or the Mediterranean coastal areas. 5. History of malignancy or malignant disease, with the exception of surgically excised cutaneous squamous cell carcinoma in situ, basal cell carcinoma, and cervical carcinoma in situ that have been in complete remission for more than 5 years without any evidence of recurrence. 6. Female participants who are breastfeeding or pregnant, or women of childbearing potential with a positive serum pregnancy test result at screening. 7. Participants with a chronic active infection or a condition that would seriously interfere with study drug administration at baseline within 4 weeks prior to randomization; or a superficial skin infection requiring treatment within 1 week prior to randomization; or an acute illness within 48 hours prior to randomization. 8. (Patients with AD) Other than AD, A history of clinically significant disease which is poorly controlled or could pose a safety risk to the participant or confound the safety assessment, as judged by the Investigator to compromise participant safety in the study. 9. (Patients with AD) Positive results in any of the following infectious disease screening tests: 1）History of active tuberculosis, or positive result at screening (T-SPOT.TB or QuantiFERON-TB Gold); 2）Positive for hepatitis B; 3）Positive hepatitis C antibody; 4）Positive Treponema pallidum antibody; 5）History of HIV infection, or positive HIV antibody.