Drugs/interventions and mechanisms: • CAR-T cell therapy (adoptive cellular gene therapy): patient receives commercial CAR-Ts that recognize tumor antigen (e.g., CD19) to kill malignant B cells. • Exploratory reparative approaches (tested in vitro/in vivo, not given to patients): allogeneic mesenchymal stromal cells (MSC, cell therapy) and MSC-derived extracellular vesicles (MSC-EV, biologic/exosome therapy) aimed at immunomodulation, reduction of inflammation, and trophic support to repair the bone marrow (BM) niche and restore hematopoiesis. Cells/pathways targeted: • Malignant B cells (DLBCL) by CAR-T. • BM hematopoietic niche: stromal/mesenchymal cells, endothelial support, and hematopoietic stem/progenitor cells. • Macrophages activated by CAR-T/tumor interaction and cytokine-mediated inflammatory pathways (CRS-associated mediators).