A Clinical Study on the Safety and Efficacy of CAR19-BCMA Dual-target CAR-T Cell Therapy for Relapsed/Refractory Plasma Cell Neoplasms and Lymphomas/Leukemias With Plasmacytic Differentiation

CAR19BCMA-T cells Each subject will be infused with single dose of CD19BCMA-CAR-T cells. A classic "3+3" dose escalation will be employed. The low dose is 1×10\^6 /kg, the medium dose is 2×10\^6 /kg, and the high dose is 3×10\^6 /kg.

Drug: Fludarabine Fludarabine will be given at a dose of 30 mg/m2/day intravenously (IV) for 3 days prior to the infusion of CD19BCMA-CAR-T cells. Drug: Cyclophosphamide Cyclophosphamide will be given at a dose of 300 mg/m2/day intravenously (IV) for 3 days prior to the infusion of CD19BCMA-CAR-T cells.