This is a first-in-human, single ascending dose study of 9MW3811, the primary objective of which is to evaluate the safety and tolerability of 9MW3811 in healthy adult participants.

The single ascending dose study will comprise 4 dose cohorts of 8 healthy participants each. In each cohort, participants will be randomized to receive 9MW3811 or placebo by 6:2.

Inclusion Criteria:

1. Male or female participants between 18 and 55 years of age, inclusive.
2. Male body weight ≥50.0 kg, or female body weight ≥45.0 kg, and body mass index (BMI) between 18.0 and 30.0 kg/m2, inclusive.
3. In good health determined by the investigator based on a medical evaluation, including a detailed medical and surgical history, as well as a complete physical examination including vital signs, 12-lead ECG, laboratory evaluations.

Exclusion Criteria:

1. Clinically significant histories determined by the investigator of cardiovascular, hepatic, renal, gastrointestinal, neurological, respiratory, hematological, endocrinological, immunological, metabolic, and musculoskeletal abnormalities.
2. Having any history of an allergy to biological agents or any components of study drug; those who have a history of allergies and judged by the investigator to be ineligible for enrolment.
3. Use of any prescription medication 14 days prior to dosing or over-the-counter medication, vitamins, and/or herbal medicines 7 days prior to dosing (Excluding oral contraception, occasional paracetamol, ibuprofen and standard dose of multivitamins at the discretion of the PI or designee)
4. Participants who have been vaccinated within 4 weeks prior to screening or who are scheduled to be vaccinated during the study
5. Participants who received immunosuppressants except for previous use of inhaled or nasal corticosteroids 4 weeks earlier before administration or any oral corticosteroids 8 weeks earlier before administration, and who had received a single dose of monoclonal antibodies for any reason within 1 year prior to screening
6. Participants with one or more clinically significant positive test results of hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) antibody or human immunodeficiency virus (HIV) antibody
7. History of drug abuse including narcotic and psychiatric drugs within 6 months prior to screening or a positive drug abuse test result at baseline (Morphine, Methamphetamine, Tetrahydrocannabinol acid, Cocaine)
8. Participants with a positive SARS-CoV-2 test prior to admission (polymerase chain reaction (PCR) and/or rapid antigen testing (RAT), per site policy and PI discretion)