SG301-SC Injection Safety Study in Subjects With Primary ITP Patients

Inclusion criteria

• Aged 18-75 years, any gender.
• Voluntarily signed informed consent and able to comply with study procedures.
• Clinically diagnosed with primary immune thrombocytopenia (ITP) per 2019 ASH Guidelines, international consensus statements, or 2025 Chinese Guidelines for Adult ITP Diagnosis and Treatment; disease duration ≥ 3 months.
• Experienced treatment failure or relapse after prior first-line therapy (glucocorticoids and/or IVIG).
• ≥2 platelet assessments ≥3 days apart before first dosing: mean platelet count <30×10⁹/L, no single value >35×10⁹/L.
• ECOG performance status 0-2.
• On stable-dose maintenance therapy for ≥4 weeks pre-first dose, with stability expected throughout the trial.
• Screening lab parameters meeting criteria below:

• Liver function: AST and ALT ≤3×ULN; total bilirubin ≤1.5×ULN.
• Renal function: eGFR ≥30 mL/min (CKD-EPI equation).
• CBC (no RBC transfusions, IL-11, EPO or colony-stimulating factors within 2 weeks before testing): hemoglobin ≥90 g/L, absolute neutrophil count ≥1.5×10⁹/L.
• Participants or partners with childbearing potential must use effective contraception during the study and for 6 months after last study drug administration.

Exclusion criteria

• Prior treatment targeting CD38, including but not limited to monoclonal antibodies, bispecific antibodies and antibody-drug conjugates.
• Secondary thrombocytopenia or concurrent autoimmune hemolytic anemia.
• History of thromboembolism within 12 months prior to randomization, or severe bleeding events (hemoptysis, massive gastrointestinal hemorrhage, intracranial hemorrhage, etc.).
• Anticoagulants or antiplatelet agents (e.g., aspirin) administered within 4 weeks before randomization.
• Emergency ITP therapies (methylprednisolone, platelet transfusion, IVIG, TPO-RA, etc.) received within 4 weeks before randomization.
• Oral immunosuppressants other than azathioprine, cyclosporine A and mycophenolate mofetil (e.g., tacrolimus, sirolimus) within 4 weeks pre-randomization; anti-CD20 mAbs (e.g., rituximab) within 3 months pre-randomization.
• Splenectomy performed within 6 months before randomization.
• Diagnosis of myelodysplastic syndrome; history of malignancy within 5 years pre-randomization (excluding cervical carcinoma in situ, basal cell skin carcinoma, etc.).
• Participation in another clinical trial within 4 weeks or 5 half-lives pre-randomization (whichever is longer), except placebo-controlled trials.
• History of severe recurrent or chronic infection; active systemic infection requiring IV antibiotics, antivirals, antiparasitics or antifungals within 4 weeks pre-randomization (excluding prophylaxis); acute infection; superficial skin infection within 1 week pre-randomization.
• Major surgery within 12 weeks pre-randomization, unhealed wounds, ulcers or fractures, or planned major surgery during the study.
• Severe cardiovascular or cerebrovascular diseases, including but not limited to: myocardial infarction, unstable angina or stroke within 6 months pre-randomization; NYHA Class III/IV heart failure; screening QTcF >480 ms or familial long QT syndrome; uncontrolled hypertension (resting SBP ≥160 mmHg and/or DBP ≥95 mmHg).
• HIV infection, active hepatitis B or hepatitis C.
• Confirmed active syphilis or Mycobacterium tuberculosis infection.
• Known hypersensitivity to monoclonal antibodies (prior Grade ≥3 allergic reactions per CTCAE v6.0) or excipients of investigational product.
• Live or attenuated live vaccines administered within 4 weeks pre-randomization or planned during the study.
• History of solid organ transplantation (heart, lung, kidney, liver, etc.) or hematopoietic stem cell/bone marrow transplantation.
• Lactating females.
• Any condition judged by the investigator to interfere with subject compliance or trial participation.