Liposomes enhance the immunogenicity of reconstituted influenza virus A/PR/8 envelopes and the formation of protective antibody by influenza virus A/Sichuan/87 (H3N2) surface antigen.

Reconstituted influenza virus (A/PR/8 strain) envelopes (RIVE) and influenza virus (A/Sichuan/87 (H3N2) strain) surface antigens were entrapped in dehydration-rehydration vesicles (DRV liposomes) composed of egg phosphatidylcholine (PC) or distearoyl phosphatidylcholine (DSPC DRV) and equimolar (32 mumol) cholesterol. Entrapment values for RIVE were 31.2 (PC) and 29.4% (DSPC DRV) of the material used. Corresponding entrapment values for the A/Sichuan/87 strain antigens were 40.7 and 39.3%. Balb/c mice injected intramuscularly with PC or DSPC DRV liposomes containing 0.1 and 1.0 microgram RIVE exhibited primary (higher dose only) and secondary responses (IgG1) which were significantly higher than those obtained in mice injected with identical amounts of non-entrapped RIVE. Significantly higher secondary responses were also observed for the IgG2a and IgG2b subclasses. In experiments designed to assess the effectiveness of DRV liposomes as a carrier of influenza virus antigens in a potential vaccine, hamsters were immunized intramuscularly with 0.1, 0.5 and 5.0 micrograms of free or liposome-entrapped influenza A/Sichuan/87 surface antigens. Results showed increased haemagglutination inhibition (HI) antibody levels in terms of both primary (0.5 and 5.0 micrograms doses) and secondary (all doses) responses in the sera of animals treated with the liposomal formulations. DSPC compared with PC DRV exhibited greater adjuvanticity when the lower doses of antigens were used.