Inclusion Criteria:
* Age ≥18 years, male or female.
* Before enrollment, the subjects have been clinically diagnosed with primary immune thrombocytopenia for no less than three months according to the American Society of Hematology guidelines 2011 Evidence-Based Practice Guideline (Neunert et al. 2011) or the International Consensus Report for the Investigation and Management of Primary Immune Thrombocytopenia (Provan et al. 2010), as applicable locally.
* Patients have failed glucocorticoid therapy (either due to inefficacy, efficacy could not be maintained, or relapse). Patients were required to have a response history (PLT≥50×10\^9/L) to standard first-line treatment of ITP (glucocorticoid and/or intravenous immunoglobulin).
* Subjects with a platelet count of \<30×10\^9/L within the 24 hours prior to the first dose of the study drug; The mean platelet count of at least two separate assessments (at least 1 week apart) \<30×10\^9/L during the screening visit, and no platelet count \> 35×10\^9/L.
* ECOG performance status score of ≤2.
* Enrollment of subjects receiving maintenance therapy with a stable dosage is permitted, including glucocorticoids (≤0.5 mg/kg of prednisone or equivalent) or TPO receptor agonists. However, at the time of enrollment, subjects are restricted to using only one concomitant medication with a stable dose, and the concomitant medication must have been stable for a minimum of 4 weeks prior to the initial infusion of the study drug.
* For fertile female patients, a negative pregnancy test result is required. Fertile female and male patients must use effective contraception separately during the study and for 4 or 6 months after the cessation of study drug treatment.
* Subjects comprehensively understand and can adhere to the study protocol requirements and willingly signed the informed consent form.
Exclusion Criteria:
* Subjects with a known allergy to anti-CD38 monoclonal antibodies or excipients, or those who have previously received anti-CD38 monoclonal antibodies with ineffective therapeutic outcomes.
* Subjects who are diagnosed with autoimmune hemolytic anemia or various secondary thrombocytopenic disorders.
* Subjects with history of any thrombotic or embolic events or extensive and severe bleeding, such as hemoptysis, major upper gastrointestinal bleeding, intracranial hemorrhage, or the presence of sepsis or other irregular bleeding within the 12 months preceding the initiation of the first dose of study drug.
* Subjects who have participated in any other investigational drug studies (including vaccine studies) or been exposed to other investigational drugs within the first 4 weeks or 5 half-lives (whichever was longer) prior to the first dose of study drug.
* Subjects who have used anticoagulants or any agents with antiplatelet effects, such as aspirin, within 3 weeks prior to the first dose of study drug.
* Subjects who have received emergency treatment for ITP (e.g., methylprednisolone, platelet transfusion, intravenous immunoglobulin infusion, or thrombopoietin receptor agonist therapy) within 2 weeks prior to the first dose of study drug.
* Subjects who have been treated with medications including azathioprine, danazol, dapsone, cyclosporine A, tacrolimus, and sirolimus within 4 weeks prior to the first dose of study drug. Subjects who have receive anti-CD20 monoclonal antibodies such as rituximab, or medications including cyclophosphamide and vindesine within 6 months prior to the first dose of study drug.
* Subjects who have undergone splenectomy within 6 months prior to the first dose of study drug.
* Subjects who have received live vaccines within 4 weeks prior to the first dose of study drug, or plan to receive any live vaccines during the course of the study.
* Subjects who are diagnosed with Myelodysplastic syndromes (MDS); Subjects with a with a history of malignancy within the 5 years prior to screening (excluding completely cured in situ cervical cancer and non-metastatic skin squamous cell carcinoma or basal cell carcinoma).
* Subjects who have undergone allogeneic stem cell transplantation or organ transplantation.
* Subjects with a clinically significant medical history, as perceived by investigators, that will pose risks to subjects' safety during the study or potentially affect the safety or efficacy analyses, includes major clinical histories such as circulatory system abnormalities, endocrine system abnormalities, nervous system diseases, blood system diseases, immune system diseases, mental diseases and metabolic abnormalities and so on. e.g., subjects with acute myocardial infarction, unstable angina pectoris, or severe arrhythmias (multifocal ventricular premature contractions, ventricular tachycardia, or ventricular fibrillation) within the 6 months before screening ; New York Heart Association (NYHA) class III-IV heart failure; subjects who were known to have had moderate or severe persistent asthma or chronic obstructive pulmonary disease within the 5 years prior to screening, or whose condition was currently poorly controlled;
* Subjects with a history of severe recurrent or chronic infections, or acute infections requiring systemic treatment with antibiotics, antiviral drugs, antiparasitic drugs, anti-amoebic drugs, or antifungal drugs within 4 weeks prior to the first dose and during the screening period, or superficial skin infections requiring systemic treatment within one week prior to the first dose of study drug. Notably, after the resolution of the infection, the subject may be re-screened.
* Subjects with a history of known or suspected immunosuppression, including invasive opportunistic infections such as histoplasmosis, listeriosis, coccidioidomycosis, pneumocystis pneumonia, and aspergillosis, even if the infection has resolved; or unusually frequent, recurrent, or prolonged infections (as judged by the investigator).
* Significant laboratory abnormalities during screening included:
1. Alanine aminotransferase or aspartate aminotransferase greater than three times the upper limit of normal (ULN).
2. Total bilirubin greater than 1.5 times the ULN (note: subjects diagnosed with Gilbert syndrome based on medical records should not be excluded based on this criterion).
3. absolute neutrophil count \< 1500/mm3.
4. hemoglobin \< 9g/dL; IgG \< 500 mg/dL.
f) lymphocyte count \< 500/mm3. g) Creatinine clearance (CrCl) \< 30 mL/min (i.e., CrCl ≥30 mL/min is allowed)
* Positive for HIV antibodies or syphilis antibodies.
* Subjects test positive for Hepatitis B surface antigen (HBsAg) or subjects test positive for hepatitis B core antibody and HBV-DNA (through polymerase chain reaction testing), or subjects test positive for hepatitis C virus antibody and HCV-RNA during the screening period. Subjects with positive hepatitis B core antibody but negative HBV-DNA can be enrolled, with HBV-DNA monitoring every 4 weeks.
* Pregnant or lactating women, or those intending to conceive or breastfeed during the study; and male partners intending to induce pregnancy during the study.
* Any other conditions unsuitable for participation in this study, as assessed by the investigator.
