Protective immunity against influenza A virus induced by immunization withDNA plasmid containing influenza M gene

DNA vaccination is characterized by its preferential induction of the cytot oxic T cell lymphocyte (CTL) response and is expected to be a useful means of protection against viral infection. We examined the protective effect of an expression plasmid (pME18S-M) containing M1 and M2 genes of influenza A /PR/8/34. We detected the CTL activity by introducing these plasmids into B ALB/c mice by either the intramuscular or the intranasal route. The influen za-specific antibody response was also induced, although its neutralizing e ffect against influenza virus was not observed. From 70 to 80% protection w as observed in the mice immunized with the pME18S-M plasmid followed by let hal infection with influenza viruses of the A/WSN/33 and A/PR/8/34 strains, whereas all mice without the plasmid vaccination failed to survive. This p rotective activity was significantly weakened when the CD8(+) cells of thes e immunized mice were eliminated by several injections of anti-CD8 antibody . The protective activity was also weakened when anti-CD4 antibody was inje cted in the early phase of DNA vaccination. These data suggest that the pME 18S-M plasmid is useful as a DNA vaccine for overcoming highly mutational i nfluenza viruses. (C) 2001 Elsevier Science Ltd. All rights reserved.