High-efficiency incorporation of functional influenza virus glycoproteins into recombinant vesicular stomatitis viruses.

We derived recombinant vesicular stomatitis virus (VSV) expressing either influenza virus hemagglutinin (HA) or neuraminidase (NA) glycoproteins from extra genes inserted in the viral genome. The HA protein was expressed from a site downstream of the VSV glycoprotein (G) gene, while NA protein was expressed from a site upstream of the VSV G gene. The HA protein was expressed at lower levels than the VSV G protein, while the NA protein was expressed at higher levels, as expected from the gradient of VSV transcription that follows the gene order. The HA and NA proteins were transported to the cell surface and were functional as demonstrated by hemadsorption, hemolysis, and NA assays. Biochemical analysis showed that both HA and NA proteins were incorporated into VSV particles at high levels, although there was a preference for incorporation of the VSV G protein over either of the influenza virus proteins. Immunoelectron microscopy of the recombinants showed that the particles derived from the recombinants were mosaics carrying both the VSV G protein and the influenza virus membrane glycoproteins. These results extend earlier studies showing incorporation of the cellular glycoprotein CD4 and two other viral glycoproteins into VSV particles. Our results indicate that there is significant space in the VSV membrane that can accommodate foreign membrane proteins and that the foreign protein can represent as much as 35% of the total protein in the viral envelope. Incorporation of foreign proteins into VSV virions can, in many cases, occur passively in the absence of specific incorporation signals.