Effect of Belimumab on Antibody Titers in Primary APS Patients

This is a single center, randomized controlled trial in Ruijin Hospital. The enrolled patients will be randomized in a 1: 1 ratio to receive either SOC+Belimumab or SOC treatment. Belimumab is administered intravenously at a dose of 10mg/kg once a month for 18 months.

Inclusion criteria

• Age ≥ 18 years old.
• Positive for high-titer antiphospholipid antibodies according to the criteria of the "EULAR Guidelines for the Treatment of Antiphospholipid Syndrome in Adults" published in 2019.
• Stable APS regimen according to EULAR recommendations for antiphospholipid syndrome.
• Female patients who are not pregnant, breastfeeding, of childbearing potential, or not using contraception.

Exclusion criteria

• Patients with a history of malignant tumor in the past 5 years, except for basal cell carcinoma or squamous cell carcinoma of skin or cervical carcinoma in situ treated locally, and there is no evidence of metastasis within 3 years;
• Patients with a history of primary immunodeficiency;
• Serious lack of IgG (IgG level < 400 mg/dL);
• IgA deficiency (IgA level < 10 mg/dL);
• Patients with a current history of infection;
• Patients with a current history of drug or alcohol abuse or dependence, or have a history of drug or alcohol abuse or dependence within 365 days before day 0;
• HIV test is historically positive or HIV screening is positive;
• Hepatitis status;
• Patients with a history of allergic reaction caused by injection of contrast agent, human or mouse protein or monoclonal antibody;
• Patients with other abnormal laboratory values with clinical significance;
• If women with reproductive potential (WCBP) are included, please refer to the following special instructions;
• Patients with concurrent major medical or mental illnesss;
• Patients with diseases of liver, kidney, heart and other important organs,blood and Endocrine system;
• Patients who have been vaccinated with live vaccine in the last month;
• Patients who have participated in any clinical trial within 28 days before the initial screening and/or within 5 times of the half-life of the study compound (whichever is longer);
• Patients who use B-cell targeted therapy drugs within one year, such as rituximab or epratuzumab;
• Patients who use tumor necrosis factor inhibitor and interleukin receptor blocker within one year;
• Patients who use Intravenous gamma globulin (IVIG) and prednisone ≥100mg/d for more than 14 days within one year or plasma exchange;
• Patients with active infection (such as herpes zoster, HIV infection, active tuberculosis, etc.) during the screening period;
• Patients with depression or suicidal thoughts;
• Other conditions that the investigator considers would make the candidate unsuitable for the study.