Fig. 1

A schematic of exosome formation. Exosome formation is divided into two main pathways: ‘classical’ and ‘direct’. The ‘direct pathway’ involves exosome formation via direct exocytosis of vesicles, such as MVs originating from the external budding of the plasma membrane. The ‘classical pathway’ requires the re-activation of endosomes that originated from the internal budding of the plasma membrane. This pathway results in MVE. Following the active packaging of their components, MVE can fuse with the plasma membrane, and exosomes will then be released to the extracellular space. Exosomes are composed of a lipid bilayer and contain non-coding miRNAs, transmembrane and cytoplasmic proteins, and single-stranded and double-stranded DNA sequences. Exosomes contain proteins such as tetraspanins, ALIX, class-I and -II MHC molecules, and tumor-derived neo-antigens. ALIX: ALG-2 interacting protein X; ESCRT: Endosomal sorting complexes required for transport; LE/MVB: late endosome/multivesicular body; ILV: Intralumenal vesicle; MHC: Major histocompatibility complex; MVE: multi-vesicular endosomes; NEF: Negative Regulatory Factor. Figure adapted from [25]