Characterization of exo-AAV8 vector preparations and in vitro transduction efficiency. (A) Concentration and mean particle size of an exo-AAV8 vector expressing luciferase. Representative plot generated from the average of three 90-second videos. (B) Western blot for the AAV8 capsid proteins VP1, VP2, and VP3, and for the exosomal markers TSG101 and CD9. (C-D) Cryo-transmission electron microscopy of exo-AAV8 (C) and standard AAV8 (D) vectors. Arrows indicate AAV particles; #, membrane of the exosome with the characteristic lipid bilayer; *, carbon support film. (E-F) In vitro transduction of HUH-7 and HHL5 liver cell lines. Analysis performed 24 hours posttransduction. Data are shown as mean of 3 independent experiments ± standard error of the mean (SEM). **P < .01; ***P < .001; unpaired Student t test. (G) HUH-7 cells transduced with exo- or standard vectors at an MOI of 25 000 and stained with the ADK8/9 antibody (intact AAV particles, in green; Alexa-Fluor 488) 1 hour postinfection. Green arrows show representative positive signal for AAV particles. Dapi, 4′,6-diamidino-2-phenylindole; MW, molecular weight marker; RLU, relative light unit.