The Virosome concept in influenza vaccines

Reconstituted influenza virus envelopes (virosomes) represent efficient influenza vaccines inducing high antibody titers upon intramuscular adminsitration. Virosomes are reconstituted viral envelopes which retain the cell entry and membrane fusion characteristics of native influenza virus. Here, we show that virosomes, by virtue of their membrane fusion activity, have the capacity to deliver a virosome-encapsulated protein antigen (ovalbumin, OVA) to the cytosol of cultured murine bone-marrow-derived dendritic cells (DCs) and thus to the MHC class I presentation pathway. Accordingly, immunization of mice with OVA-containing virosomes resulted in efficient priming of an OVA-specific class I MHC-restricted cytotoxic T lymphocyte (CTL) response. These results indicate that virosomes have the capacity to prime a broad immune response, inducing not only humoral but also cellular immunity.