Extracellular vesicles are tiny membrane bound particles released by virtually all cell types. They include exosomes that originate from intracellular compartments and microvesicles that bud directly from the plasma membrane. Once thought to be cellular waste, they are now recognized as key mediators of communication between cells and tissues.

These vesicles carry proteins, lipids, metabolites, DNA and diverse RNA species, including microRNAs and long non coding RNAs. Their cargo reflects the state of the cell that produced them, for example its activation, stress level or malignancy. When extracellular vesicles fuse with or are taken up by recipient cells, they can reprogram gene expression, alter metabolism, modulate immune responses and influence cell survival, migration and differentiation.

Because they circulate in blood and other body fluids and protect their contents from degradation, extracellular vesicles are promising non invasive biomarkers. They are being studied for early detection, prognosis and treatment monitoring in cancer, neurodegenerative diseases, cardiovascular and metabolic disorders, and infections. Disease specific changes in vesicle number, origin and molecular cargo have been repeatedly observed.

Extracellular vesicles are also being developed as therapeutic tools. Their natural biocompatibility, low immunogenicity and ability to cross biological barriers make them attractive for targeted drug delivery, including to the brain. Engineered vesicles can be loaded with small molecules, nucleic acids or proteins and directed to specific cell types using surface ligands.

Major challenges remain, such as standardizing isolation and characterization methods, improving purity and yield, and understanding in vivo biodistribution and safety. Nonetheless, extracellular vesicles are emerging as central players in physiology, pathology and precision medicine.