Exosomes are small membrane vesicles originating from late endosomes and 
secreted by hematopoietic and epithelial cells in culture. Exosome proteic and 
lipid composition is unique and might shed some light into exosome biogenesis 
and function. Exosomes secreted from professional antigen-presenting cells 
(i.e., B lymphocytes and dendritic cells) are enriched in MHC class I and II 
complexes, costimulatory molecules, and hsp70-90 chaperones, and have therefore 
been more extensively studied for their immunomodulatory capacities in vitro and 
in vivo. This review will present the main biological features pertaining to 
tumor or DC-derived exosomes, will emphasize their immunostimulatory function, 
and will discuss their implementation in cancer immunotherapy.