Kenneth W. Witwer, PhD, is an associate professor of molecular and comparative pathobiology and neurology at the Johns Hopkins University School of Medicine. Dr. Witwer studies extracellular vesicles (sacks filled with proteins and other molecules) and extracellular RNA (molecules involved in cell-to-cell communication) in neurodegenerative and infectious diseases. The various interests of his laboratory include single-particle analysis and studies of biomarkers -- objective measures of disease -- and transfer of extracellular RNA by extracellular vesicles. Dr. Witwer has helped to lead standardization initiatives of the International Society for Extracellular Vesicles (ISEV), serves as ISEV's executive chair for science and meetings and has been an external scientific advisor to the NIH (National Institutes of Health) Common Fund's Extracellular RNA Communication Consortium.