Trial type: Observational. Population: Adults receiving approved anti‑CD19 CAR‑T therapies. Drugs/interventions: Second‑generation CAR‑T cell products (autologous, genetically engineered T‑lymphocyte therapy, “living drug”): tisagenlecleucel, axicabtagene ciloleucel, brexucabtagene autoleucel (lisocabtagene maraleucel anticipated). Mechanism of action: Patient T cells are transduced to express a chimeric antigen receptor that binds CD19 on B cells, triggering HLA‑independent activation and cytotoxic killing, expected on‑target effects include B‑cell aplasia, risks include CRS and ICANS. Targets (cells/pathways): CD19+ malignant B cells, assessment of tumor resistance (e.g., antigen loss/alteration) via ctDNA VAF kinetics, immune microenvironment via single‑cell RNA‑seq of peripheral blood CAR+ and CAR− T‑cell subsets and myeloid cells, mapping cytokine/inflammatory pathways and cellular states linked to efficacy and toxicity.