It is disclosed herein that cultured primary placental human trophoblast (PHT) cells are highly resistant to infection by a number of disparate viruses, and confer this resistance to non-placental recipient cells by exosome-mediated delivery of microRNAs (miRs). PHT cells express high levels of unique, primate-specific miRNAs, expressed from the chromosome 19 miRNA cluster (C19MC). It is further disclosed herein that C19MC miRNAs are packaged within PHT-derived exosomes and attenuate viral replication in recipient cells by inducing autophagy. Thus, provided herein are methods of inhibiting, treating or preventing microbial infections by administering one or more miRs of the C19MC. Also provided are methods of inducing autophagy in a cell by contacting the cell with one or more miRs of the C19MC.
