Liposome-mediated DNA vaccination.

Numerous reports have indicated that intramuscular injection of antigen-coding naked plasmid DNA can trigger humoral and cell-mediated protective immunity against infection. This follows DNA uptake by muscle fibres, leading to the expression and extracellular release of the antigen. Here it is shown for the first time that intramuscular immunization of mice with pRc/CMV HBS (encoding the S region of hepatitis B antigen; HBsAg) entrapped into positively charged (cationic) liposomes leads to greatly improved humoral and cell-mediated immunity. These cationic liposome-entrapped DNA vaccines generate titres of anti-HBsAg IgG1 antibody isotype in excess of 100-fold higher and increased levels of both IFN-gamma and IL-4 when compared with naked DNA or DNA complexed with preformed similar (cationic) liposomes. It is likely that immunization with liposome-entrapped plasmid DNA involves antigen-presenting cells locally or in the regional draining lymph nodes.