Exosome mimicry by a HAVCR1–NPC1 pathway of endosomal fusion mediates hepatitis A virus infection

Cell-to-cell communication by exosomes controls normal and pathogenic processes 1,2 . Viruses can spread in exosomes and thereby avoid immune recognition 3 . While biogenesis, binding and uptake of exosomes are well characterized 4,5 , delivery of exosome cargo into the cytoplasm is poorly understood 3 . We report that the phosphatidylserine receptor HAVCR1 (refs. 6,7 ) and the cholesterol transporter NPC1 (ref. 8 ) participate in cargo delivery from exosomes of hepatitis A virus (HAV)-infected cells (exo-HAV) by clathrin-mediated endocytosis. Using CRISPR-Cas9 knockout technology, we show that these two lipid receptors, which interact in the late endosome 9 , are necessary for the membrane fusion and delivery of RNA from exo-HAV into the cytoplasm. The HAVCR1-NPC1 pathway, which Ebola virus exploits to infect cells 9 , mediates HAV infection by exo-HAV, which indicates that viral infection via this exosome mimicry mechanism does not require an envelope glycoprotein. The capsid-free viral RNA in the exosome lumen, but not the endosomal uncoating of HAV particles contained in the exosomes, is mainly responsible for exo-HAV infectivity as assessed by methylene blue inactivation of non-encapsidated RNA. In contrast to exo-HAV, infectivity of HAV particles is pH-independent and requires HAVCR1 or another as yet unidentified receptor(s) but not NPC1. Our findings show that envelope-glycoprotein-independent fusion mechanisms are shared by exosomes and viruses, and call for a reassessment of the role of envelope glycoproteins in infection.