Sirolimus Monotherapy in the Treatment of Antiphospholipid Antibody Related Thrombocytopenia

The goal of this clinical trial is to evaluate the efficacy and safety of sirolimus in patients with anti-phospholipid antibody-associated thrombocytopenia. In the 6-month randomized, double-blind, placebo-controlled phase, participants will receive either sirolimus 1 mg once daily or matching placebo. Participants will be followed at 2 weeks, 1 month, 3 months, and 6 months after enrollment. Participants who do not achieve the primary endpoint at 6 months may enter a 3-month open-label extension and receive sirolimus 1.5 mg once daily, with follow-up through month 9. The main question is whether sirolimus improves the overall response rate at 6 months compared with placebo. Primary outcome: \- Overall response rate at 6 months Secondary outcomes: * Overall response rate at 1 month and 3 months * Complete response rate at 6 months * Partial response rate at 6 months * Change in anti-phospholipid antibody titers at 6 months * Change in oral glucocorticoid dosage at 6 months Exploratory outcomes: * Proportion and reasons for early discontinuation during the double-blind phase * Among participants who do not achieve the primary endpoint at 6 months and enter the open-label extension, overall response rate, complete response rate, partial response rate, and safety outcomes after 3 months of open-label treatment