A Phase I Study Evaluating the Safety, Tolerability, PK and PD in Healthy Chinese Volunteers

Inclusion Criteria: 1. Han Chinese male or female subjects, and his/her biological parents and grandparents are of Han Chinese ethnicity. 2. Body weight ≥ 50kg with BMI ≥19.0 and \<=24.0 kg/m2 at screening and baseline visit. 3. Generally, in good health with no clinically significant abnormalities as determined by medical history, physical examination, 12-lead ECG and clinical laboratory tests. Exclusion Criteria: 1. Subject has a total IgG level of \< 700mg/dL at screening. 2. Subject has an active infection or has had a serious infection within 6 weeks prior to Day -1 or infection requiring oral anti-infective agents within 2 weeks prior to Day-1, or subject had a febrile illness or symptomatic, viral, bacterial, or fungal infection within 1 week prior to admission (Day -1). 3. History of relevant allergy/hypersensitivity (including allergy to study drug or its excipients). 4. Any laboratory values outside the reference range that are of clinical significance according to investigator's clinical judgement. 5. Subject has estimated creatinine clearance ≤ 80 mL/min calculated by Cockcroft Gault formula at screening. 6. Subject has any ECG abnormality defined in the protocol (a single repeat will be allowed for eligibility determination) at screening or Day -1: 7. Positive HIV test result at screening. 8. Positive testing for HBs Antigen and/or a positive Hepatitis C antibody test result at screening. 9. Subject has a positive T-cell interferon-γ release assay (TIGRA) result 10. Subjects who had immunization within 4 weeks before screening; or subjects who plan to have immunization during the study and within 12 weeks after dosing of the study drug. 11. For female subjects, positive pregnancy test at screening or Day -1, or planning to become pregnant from screening until 90 days after the dosing of the study drug. 12. Lactating female subjects.