Immune Profiling of Refractory cSLE Exposed to CD3×CD19 BiTE

Inclusion Criteria: * Participants must meet all of the following criteria: 1. Age ≥ 5 years. 2. Diagnosis of systemic lupus erythematosus (SLE) confirmed according to the 2019 EULAR/ACR classification criteria. 3. Refractory or persistently active SLE, defined by clinical evaluation and meeting at least one of the following conditions: <!-- --> 1. Inadequate response to prior standard treatments, including oral glucocorticoids, antimalarial agents, conventional immunosuppressants (cyclophosphamide, mycophenolate mofetil, azathioprine, methotrexate, cyclosporine, tacrolimus, sirolimus, leflunomide), and biologic therapies (telitacicept, belimumab, rituximab). 2. Moderate to high disease activity, such as a SLEDAI score ≥ 6. 4.Receiving CD3×CD19 bispecific T-cell engager (BiTE) therapy as part of routine clinical management, with traceable dosing information and treatment timeline. 5.Availability of peripheral blood samples collected before and/or after CD3×CD19 BiTE exposure, obtained during routine clinical assessment or prospective follow-up, that are suitable for immunologic analyses. 6.Prior informed consent obtained in a related clinical study or clinical care context that explicitly permits the storage and secondary use of biological samples and associated clinical data for disease-related scientific research, including prospective analyses during subsequent follow-up; and willingness of the child to cooperate with study follow-up procedures, as appropriate. Exclusion Criteria: Participants meeting any of the following criteria will be excluded: 1. Inability to obtain peripheral blood samples of adequate quality for immunologic analyses, including insufficient sample volume, severe hemolysis, or failure to meet predefined cell viability criteria. 2. Presence of acute severe infection, acute organ decompensation, or other acute medical conditions that may substantially interfere with immune profiling analyses. 3. Significant risk associated with blood sampling, such as severe anemia, serious coagulation disorders, or other conditions deemed by the investigator to pose unacceptable risk for phlebotomy. 4. Inability to obtain essential clinical data required for immune-clinical correlation analyses (e.g., disease activity scores, complement levels, autoantibody results, or renal parameters). 5. Refusal of the legal guardian to allow participation or withdrawal of permission for use of biological samples, or lack of assent from the child when applicable. 6. Any other condition that, in the opinion of the investigator, may compromise study completion, data integrity, or participant safety.