CD63 and influenza: For our study, we opted for a two-step exosome purification method that included precipitation reagent-based exosome enrichment, followed by CD63 antibody based immuno-magnetic isolation, as there is no evidence from the literature that RSV virions contain this particular molecule38,39, and because RSV assembles and egress cells through a pathway similar to influenza, which has been shown to be devoid of CD63 and other tetraspannins40.