This is a single-center, randomized, parallel-group, open-label clinical study designed to compare the bioavailability and safety of SHR-1703 Injection administered subcutaneously using a pre-filled safety syringe (PFS) or a pre-filled autoinjector (AI) in healthy participants.

A total of 84 healthy participants are planned to be enrolled and randomized in a 1:1 ratio to either the PFS group or the AI group. Participants in the PFS group will receive a single subcutaneous injection of SHR-1703 Injection using a pre-filled safety syringe, while participants in the AI group will receive a single subcutaneous injection of SHR-1703 Injection using a pre-filled autoinjector.

Inclusion Criteria:

1. Aged 18-55 years at ICF signing.
2. Screening BMI 19-26 kg/m², weight 50-80 kg.
3. Normal or NCS findings at screening/baseline: physical exam, lab tests (CBC, blood chemistry, UA, coagulation), ECG, abdominal ultrasound, chest X-ray.
4. Investigator-assessed absence of diseases that could significantly impact the study or pose additional health risks; stable health expected, no medical intervention needed. Clinically significant lab abnormalities may be retested within 1 week if justified; retest results determine eligibility.
5. Females of childbearing potential and males with female partners of childbearing potential must avoid sperm/egg donation, have no pregnancy plan, and use appropriate contraception from ICF signing through 14 months post-last dose (see Section 13.1.2).
6. No heavy smoking (<5 cigarettes/day) or alcohol abuse (≤15 g/day [e.g., 450 mL beer, 150 mL wine, or 50 mL low-alcohol liquor], ≤2×/week) within 6 months pre-screening; no drug abuse history. Negative drug screen and alcohol breath test at baseline.

Exclusion Criteria:

1. AST, ALT, or bilirubin > ULN at screening/baseline.
2. eGFR < 90 mL/min/1.73m² at screening/baseline.
3. Clinically significant abnormal blood pressure (SBP >140 or <90 mmHg; DBP >90 or <60 mmHg) at screening/baseline.
4. Positive for HBsAg, HBcAb with HBV-DNA > ULN, HIV-Ab, syphilis serology, or HCV-Ab at screening.
5. Suspected or confirmed active tuberculosis (clinical symptoms or imaging evidence within 3 months).
6. QTcF > 450 ms on repeated 12-lead ECG at screening/baseline.
7. Participation in another drug/device clinical trial within 3 months prior to screening (defined as signed ICF and received study drug/device, or still in follow-up or within 5 half-lives of prior investigational drug, whichever is longer).
8. Use of any prescription drugs, OTC drugs, or herbal medicines within 1 month prior to dosing (except routine vitamins ≤100% RDA or occasional paracetamol ≤2 g/day for ≤5 days/month), or less than 5 half-lives washout.
9. Major trauma or surgery within 6 months prior to screening, or planned surgery during the study.
10. Blood donation or significant blood loss (≥400 mL) within 1 month, or blood transfusion within 2 months prior to screening.
11. Receipt or planned receipt of live (attenuated) vaccine within 1 month prior to dosing or during the study.
12. Suspected or confirmed parasitic infection within 6 months prior to screening.
13. Pregnant or breastfeeding women, or positive pregnancy test (HCG).
14. Investigator or site personnel directly involved in the study.
15. Any other condition deemed by the investigator to preclude study participation or increase risk to the participant.