Q&A: What are exosomes, exactly?

Exosomes are extracellular vesicles first described as such 30 years ago and since implicated in cell-cell communication and the transmission of disease states, and explored as a means of drug discovery. Yet fundamental questions about their biology remain unanswered. Here I explore what exosomes are, highlight the difficulties in studying them and explain the current definition and some of the outstanding issues in exosome biology.