ATRA for Management of Primary ITP

Inclusion Criteria: * Primary ITP if aged ⩾18 years; * With an average of two platelet counts ⩾1 day apart of \<30×10\^9/L during screening and no single platelet count \>35×10\^9/L within 2 weeks before study treatment; * Patients who have previously received at least one first-line standard therapy for ITP (corticosteroid and/or intravenous immunoglobulin) with unsustained efficacy, relapse, intolerance to standard therapy, or insufficient response. Exclusion Criteria: * Pregnant or lactating women, and who were possibly pregnant, planning to become pregnant, or who had partners planning to become pregnant; * With active malignancy or a history of malignant tumor; * Having experienced severe bacterial, viral, fungal or parasitic infection within the past 4 weeks; * With a history of symptomatic herpes zoster infection within 12 weeks prior to screening; * Active or chronic HBV, HCV or HIV infection; * Evidence of active tuberculosis; or previous evidence of active tuberculosis without appropriate and documented treatment; or household contact with patients with active tuberculosis without appropriate and documented tuberculosis prophylaxis; * Receipt of live vaccines within the past 12 weeks, or planned live vaccination during the study period; * Prior ATRA therapy; * History of solid organ transplant or planned surgery; * Myelodysplastic syndrome, aplastic anemia or myelofibrosis; * Patients with other diseases were undergoing treatment with immunosuppressants; * Clinic…