DNA vaccination with both the haemagglutinin and fusion proteins but not the nucleocapsid protein protects against experimental measles virus infection

Plasmids that expressed the nucleocapsid, haemagglutinin and fusion protein s of measles virus (MV) were used to immunize cotton rats (Sigmodon hispidu s) against intranasal MV infection, After immunization with all three plasm ids, T cell responses and MV-specific antibodies were induced. A reduction in virus titre was observed in lung tissue from animals immunized with plas mids expressing the viral glycoproteins. Histologically, however, a moderat e peribronchitis was observed after immunization with the plasmid expressin g the fusion protein whereas, after immunization with plasmids expressing h aemagglutinin or both glycoproteins, only mild or focal peribronchitis was seen. Immunization with the nucleocapsid did not reduce virus titres, proba bly because of the failure to induce neutralizing antibodies. A disadvantag e of plasmid immunization was its inefficacy in the presence of MV-specific 'maternal' antibodies. This indicates that genetic immunization has to be improved to be a useful alternative vaccine against measles.