Safety assessment of anti-BCMA-Exo-Btz. (A) Red blood cells (RBCs), PBMCs, monocytes, and PBMCs except monocytes (PBMC-monocyte) were exposed to varying concentrations of 1, 2, 4, and 8 mg/mL anti-BCMA-Exo loaded with Btz for 48 and 72 hours, and the cell viability were detected. (B) H&E staining of the tissue of heart, kidney, lung, liver, and spleen. Scale bar, 200 μm. H&E, hematoxylin and eosin.