This is an exploratory, open-label, single-arm clinical study designed to evaluate the safety, tolerability, and preliminary efficacy of QT-219CX. QT-219CX is a universal allogeneic chimeric antigen receptor T-cell (CAR-T) product targeting both CD19 and BCMA. The study targets subjects with refractory B-cell-related autoimmune diseases, including systemic lupus erythematosus (SLE), multi-drug resistant nephrotic syndrome (NS), IgA nephropathy (IgAN), systemic sclerosis (SSc), and ANCA-associated vasculitis (AAV) .The research is divided into two phases: a dose-escalation phase and a dose-expansion phase. Dose Escalation: Utilizes a standard "3+3" design to evaluate potential recommended dose(RD) and identify dose-limiting toxicities (DLTs) .Treatment Procedure: Eligible subjects will receive a lymphodepleting conditioning regimen followed by a single intravenous infusion of QT-219CX .Primary Objectives: The primary goals are to evaluate the safety profile, including the incidence of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), and to assess clinical response rates at 90 days post-infusion .Follow-up: Subjects will be monitored for pharmacokinetics (cell expansion), pharmacodynamics (B-cell depletion), and long-term safety for up to two years .