BCR signaling regulates exosome secretion and exosome microRNA expression in CLL. (A) CD19⁺ CLL cells were purified and cultured in AIM V medium with or without α-IgM stimulation for 24 hours. CLL-derived exosomes were isolated from cell culture supernatant, and the exosome concentration was measured by NTA. α-IgM stimulation significantly increased exosome secretion from CLL cells (*P = .013). (B) CD19⁺ CLL cells were isolated and first treated with or without 1 μM ibrutinib for 1 hour and then washed to remove the drug. Cells were then stimulated with α-IgM for 24 hours, and exosomes were isolated from the supernatant for measurement of exosome concentration by NTA. In the 7 of 12 CLL cells that responded to α-IgM stimulation (*P = .011), ibrutinib treatment decreased α-IgM-induced exosome release (P = .064). (C) Exosome microRNA was also isolated from the supernatant of cells incubated with or without α-IgM, and analyzed for miR-150 and miR-155 expression. Both miR-150 and miR-155 showed significantly higher levels of expression after α-IgM stimulation (*P = .042 and *P = .014, respectively).