Antiangiogenic effects of modified exosomes in vivo. (A) Exosomal miR-340 expression levels in young BMSC exosomes, older BMSC exosomes, and miR-340 exosomes were quantified by reverse transcription polymerase chain reaction (young BMSC exosomes vs older BMSC exosomes; *P < .01, young BMSC exosomes vs miR-340 exosomes; **P < .001, Student t test). Values represent the mean ± SD. (B-C) Recipient cells were treated with exosomes directly transfected with Cy3-miR-340 mimics. Cy3-miR-340 signals were detected in the cytoplasm of RPMI8226-HR cells (B) and HUVECs (C). Nuclear and cytoplasmic staining were performed with DAPI (blue) and Calcein AM (green), respectively. Scale bar, 25 µm. (D) A mixture of Matrigel and 4 × 10⁶ RPMI8226-HR cells was admixed with older BMSC exosomes directly transfected with miR-340 mimics (miR-340 exosomes; 4 × 10⁷ particles per 200 µL Matrigel), miR-365 mimics (miR-365 exosomes; 4 × 10⁷ particles per 200 µL Matrigel), or negative control miR (control miR exosomes). The Matrigel mixture was injected subcutaneously into nude mice. Three weeks after implantation, the Matrigel plugs were harvested. Paraffin-embedded sections of Matrigel plugs were stained with hematoxylin and eosin and then subjected to immunostaining for CD31 (red). Scale bar, 500 µm. (E) Quantification of vessel density in Matrigel plugs by pixel density. Both mir-340 and miR-365 exosomes inhibited tumor angiogenesis in Matrigel plugs in comparison with the control (*P < .001 vs control, Student t test, n = 6). Values represent the mean ± SD. Exo, exosomes.