Characterization of anti-BCMA-Exo-Btz. (A) Flow sorting of anti-BCMA⁺ monocytes. (B) Size distribution of anti-BCMA-Exo and anti-BCMA-Exo-Btz determined by dynamic light scattering. (C) CD81 and CD63 expressions of anti-BCMA-Exo and anti-BCMA-Exo-Btz by western blot. (D) Representative transmission electron microscopy image of anti-BCMA-Exo and anti-BCMA-Exo-Btz. (E-F) The expression of anti-BCMA on the surface of anti-BCMA-Exo-Btz membrane was detected by nano-flow cytometry (E) and colloidal gold immunoelectron microscopy (F). Scale bar, 100 nm. (G) The loading of Btz into exosomes was detected by fourier transform infrared spectrometer. (H) The loading efficiency and encapsulation efficiency of Btz into exosomes.