Inclusion Criteria:
1. Participants must fully understand the trial content, procedures, and potential adverse reactions, and voluntarily sign a written informed consent form (ICF).
2. Age at signing the ICF must be ≥ 18 years (including the boundary value), regardless of gender.
3. Confirmed diagnosis of primary ITP for at least 3 months at screening.
4. Previous treatment with corticosteroids.
5. At the last ITP treatment, participants experienced loss of remission, no remission, relapse after remission, or intolerance.
6. Platelet count \<30×10⁹/L at screening with clinical assessment indicating treatment necessity
7. Participants must have adequate organ function
8. Clinically stable condition with World Health Organization (WHO) bleeding scale grade 0-1
9. Female participants of childbearing potential or male participants with fertile partners must refrain from sperm/ova donation from ICF signing until 12 weeks after last dose and agree to protocol-specified contraceptive measures
Exclusion Criteria:
1. Diagnosis of secondary thrombocytopenia or concomitant autoimmune hemolytic anemia
2. Received platelet transfusion, whole blood transfusion, plasma exchange, or any other emergency treatment drugs within 14 days prior to the first infusion of SHR-2173
3. Received immunosuppressants (other than corticosteroids) such as Janus kinase \[JAK\] inhibitors or Bruton tyrosine kinase \[BTK\] inhibitors within either 5 times the drug elimination half-life or 14 days prior to the first infusion of SHR-2173 (whichever is longer)
4. Previous treatment with SHR-2173
5. Screening prothrombin time or activated partial thromboplastin time outside the normal range; concurrent coagulation disorders and/or receiving antiplatelet or anticoagulant medications (e.g., warfarin, clopidogrel, novel oral anticoagulants), except for low-dose acetylsalicylic acid
6. History of any thrombotic or embolic events within 12 months prior to the first administration, or clinical symptoms and history suggesting thrombophilia
7. Current life-threatening bleeding (related to thrombocytopenia) or expected to require emergency treatment within one week after randomization
8. Active viral, bacterial, or other infections (including tuberculosis \[TB\]) requiring systemic treatment at screening, or SARS-CoV-2 infection during screening, or history of clinically significant recurrent infections
9. Received live or attenuated live vaccines within 8 weeks prior to the first administration of SHR-2173, or planned to receive live/attenuated vaccinations during the trial
10. Received live or attenuated live vaccines within 8 weeks prior to the first administration of SHR-2173, or planned to receive live/attenuated vaccinations during the trial
11. Diagnosis of myelodysplastic syndrome; history of or current malignancy within 5 years prior to screening (except for cured non-melanoma skin cancer, in situ carcinoma \[e.g., cervical, breast, bladder, prostate cancer\], and cancers in complete remission for at least 5 years with no evidence of recurrence)
12. Previous splenectomy
13. Previous allogeneic stem cell or organ transplantation (except for corneal transplantation ≥ 3 months prior to screening); known or suspected history of immunosuppression
14. Planned surgery during the dosing period
15. Any severe and/or unstable pre-existing medical, psychiatric, or other conditions that the investigator judges may interfere with patient safety, obtaining informed consent, or compliance with study procedures
16. Allergic constitution (e.g., allergies to two or more drugs, foods, or pollens) or known hypersensitivity (immediate or delayed) or atopic reactions to the study drug (including excipients, monoclonal antibodies)
17. Concurrent participation in other investigational studies within either 30 days prior to enrollment or 5 half-lives of the investigational drug (whichever is longer)
18. Females who are lactating or pregnant (positive serum or urine β-human chorionic gonadotropin \[hCG\]) at screening or on Day 1 of Week 1 prior to administration
