A Phase I Clinical Study to Evaluate SM17 in Chinese Healthy Subjects and Patients With Moderate to Severe Atopic Dermatitis

Inclusion Criteria: Healthy Volunteers： * Male or Female，19\~55 years old * BMI ≥18.5 and \<28.0 kg/m² at the screening visit, with body weight ≥50 kg for males and ≥45 kg for females * Non-smokers or former smokers who have quit for at least 6 months, with a smoking history of \<10 pack-years for former smokers at the screening visit. No history of alcohol consumption or light alcohol consumption prior to the screening visit. * No abnormalities or abnormalities of no clinical significance (NCS) in vital signs, physical examination, laboratory tests, or electrocardiogram (ECG) results during the screening period, QTcF \<450 msec for male and QTcF \<470 msec for female subjects. * Use one medically approved contraceptive method during the trial and for 6 months after the trial ends (specific methods see Appendix 1); No plans to donate sperm/ova during the trial and for 6 months after the trial ends. * informed consent. Eligible patients must have a history of inadequate response or intolerance to treatment with topical AD medications. * Male or female, 18 \~70 years old * Atopic dermatitis (Hanifin \& Rajka) at the screening visit with eczema symptoms reported over 1year * Eczema Area and Severity Index (EASI) score ≥16 at the screening and baseline visits * Investigator's Global Assessment (IGA) score ≥3 at the screening and baseline visits * ≥10% body surface area (BSA) of AD involvement at the screening and baseline visits * Baseline pruritus numerical rating scale (NRS) weekly average score ≥4 * Documented recent history (within 6 months before the screening visit) of inadequate response to topical AD medication(s) or for whom topical treatments are medically inadvisable (e.g. intolerance, because of important side effects, or safety risks) * Have applied a stable dose of topical bland emollient (moisturizer) at least twice daily for at least 7 consecutive days immediately before randomization * Willing and able to comply with all clinic visits and study-related procedures * Able to understand and complete study-related questionnaires * Signed written informed consent Exclusion Criteria: Healthy volunteers: * Presence of psychiatric or legal incapacity, significant emotional problems at the screening visit, or anticipation of such issues during the study period. * Regular alcohol consumption within 6 months prior to screening. * History or evidence of any clinically significant medical condition, situation, or disease. * Any laboratory parameter meeting the following criteria: 1. Total bilirubin (TBIL) \>1.5 × upper limit of normal (ULN) 2. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \>2 × ULN 3. Serum creatinine (Cr) \>1.5 × ULN 4. White blood cell count below the lower limit of normal (LLN), deemed clinically significant and unsuitable for inclusion by the investigator at screening or baseline. * History or current diagnosis of cardiovascular/cerebrovascular disease. * Prior hospitalization for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. * Evidence of any active or suspected bacterial, viral, fungal, or parasitic infection within 4 weeks prior to screening. Subjects deemed at high risk for parasitic diseases are also excluded. * Known diagnosis of Type I/II diabetes mellitus or prediabetes. * Administration of live (attenuated) vaccines within 1 month prior to first dose. * History of any malignancy within 5 years prior to screening (except successfully treated carcinoma in situ of the cervix or surgically excised non-melanoma skin cancer). * Any known history of primary or secondary immunodeficiency disorders. * Positive drug urine screen or alcohol consumption within 48 hours prior to screening. * History or presence of hypersensitivity or idiosyncratic reactions to protein therapies, drugs, any component of SM17, or related compounds. * Active infection including: Tuberculosis (TB), Hepatitis B, Hepatitis C, Human Immunodeficiency Virus. * Use of any prescription or non-prescription medication within 14 days or 5 half-lives (whichever longer) prior to first SM17 dose. * Tattoos, scars at/near the infusion site, or any other condition potentially interfering with infusion site examination, per investigator assessment. * Blood/plasma donation (≥500 mL) or significant blood loss within 2 months prior to screening; planned donation during study. Bone marrow donation within 3 months prior to first dose. * Inability to undergo protocol-required visits/procedures per investigator/subject knowledge. * Current/recent participation in another investigational drug/device study. AD patients: * Pregnant or breastfeeding women, or women planning to become pregnant or breastfeed during the study * Laboratory abnormality for serum hemoglobulin, WBC, neutrophils, platelet, ALT/AST, TBIL, serum creatinine at screening or baseline * HIV/HBV/HCV/TB positive * ECG abnormality with clinical significance * History of concomitant diseases: VKC/AKC, other skin diseases, active chronic or acute infection requiring treatment with systemic medications, malignancy within 5 yrs, other major diseases * History of acute allergies, or known allergies to composition of monoclonal antibodies or excipients * Treatments within 4 weeks before the baseline visit, or is likely to require such treatment(s) during the study treatment: * systemic corticosteroids, Janus kinase inhibitors * other immunosuppressive/immunomodulating drugs (cyclosporine, mycophenolate-mofetil, IFN-γ,, azathioprine, MTX..) * traditional Chinese medicine * Treatment with TCS, TCI, PDE-4 inhibitor, or other topical AD medications within 1 week before baseline * New treatment of anti-histamine or ICS within 1 week before baseline ( stable doses of anti-histamine or ICS is allowed during study) * Treatment with biologics, within 5 half-lives (if known) or 16 weeks prior to baseline visit, whichever is longer