RNA is now known to travel outside cells to tissues around the body. Researchers are working out whether they can exploit this extracellular RNA to detect and treat disease.

The molecule best known for its part in translating genetic code into protein-assembly instructions is finding a new role in medicine. RNA, once thought to exist only in cells, is now known to travel to tissues all over the body through the blood, under the protection of tiny lipid sacs known as extracellular vesicles. The study of this extracellular RNA (exRNA) has led to a quiet revolution in biology, as scientists endeavour to understand why cells release RNA, and how the molecules might be used to improve the detection and treatment of disease.

Eavesdropping on the cellular communications encoded by exRNA could reveal early signs of diseases such as cancer. Various ways to track these extracellular snippets in body fluids are under development. On the therapeutic front, RNA-carrying vesicles might offer a safer and simpler alternative to stem-cell therapy for cardiovascular, neurological and immunological disorders. In particular, researchers are focusing on how to use vesicles that contain RNA to deliver drugs across the barrier that separates the bloodstream and the brain. These natural vesicles have several advantages over the engineered nanoparticles that have received much more research attention.

Beyond the potential clinical applications, exRNA could have intriguing implications for diet. One provocative study that linked RNA in what we eat to gene expression has kick-started vigorous efforts to learn the language in which our food speaks to us. The link, however, remains unproven. Related efforts are focusing on how RNA in breast milk affects infant health.

In plants, a clearer understanding of the biological importance of exRNA is leading to methods to genetically modify some food plants to make them less vulnerable to disease. And researchers across a range of biomedical fields are investigating how best to use exRNA.

 （Nature 582, S1 (2020)）