Exosome-based cancer vaccines

Exosomes are 30-100-nm membrane vesicles originating from late endosomes and secreted by hematopoietic and epithelial cells in culture. The exosome protein and lipid composition is very unique and might shed some light on exosome biogenesis and function. Exosomes secreted from professional antigen-presenting cells (APCs), i.e., B-lymphocytes and dendritic cells, are enriched in major histocompatibility complex (MHC) class I and II complexes, co-stimulatory molecules and heat shock protein Hsp70-90 chaperones, and have therefore been extensively studied for their immunomodulatory activity in vitro and in vivo. The first pilot phase I trials using exosome-based vaccines in cancer patients have just ended. This review will present the major biological features of exosomes, emphasizing their immunostimulatory functions in mice and humans, and will discuss their possible implementation in the immunotherapy of cancer.