Anti-CD19 CAR-Engineered NK Cells in the Treatment of Relapsed/Refractory Acute Lymphoblastic Leukemia

CAR-NK-CD19 Cells, 1-3×10\^7 /KG, treatment follows a lymphodepletion. Drug: Fludarabine Recommendation: 25-30 mg/m2 (D-5\~D-3), determined by tumor burden at baseline. Drug: Cyclophosphamide Recommendation: 250-300 mg/m2 (D-5\~D-3), determined by tumor burden at baseline.