Determination of surface protein expression on CLL exosomes by flow cytometry. (A) Purified CLL exosomes from plasma were first bound to beads with a size that can be detected by direct sorting. Then the exosome-bead complex was stained with fluorophore-conjugated primary antibodies or matched isotype controls and analyzed by flow cytometry. CLL exosomes expressed abundant levels of CD63, CD9, and CD37 but not CD41, CD3, or CD56. (B) The dot plots present a range of expression of each surface antigen on exosomes isolated from 12 CLL patients.