Enveloped virus is the major virus form produced during productive infection with the modified vaccinia virus Ankara strain

Modified vaccinia virus Ankara (MVA) is a highly attenuated virus strain th at may be useful as a vaccine vector. Ultrastructural examination of purifi ed MVA showed that most of the viral particles are enveloped in contrast to the Copenhagen strain (COP). In CsCl gradients, the majority of the MVA pa rticles displayed a light buoyant density characteristic of the enveloped f orm. Consistent with these results, MVA particles were poorly labeled with antibodies against the surface of intracellular mature virus but strongly l abeled with antibodies against an envelope antigen. Furthermore, MVA was mo re resistant than the COP strain to neutralization by mouse anti-COP antibo dies. These results suggest that the MVA strain may be particularly suitabl e for the engineering of envelope proteins and that MVA may be able to resi st the humoral immunity displayed by previously vaccinated individuals. (C) 2000 Academic Press.