Vaccine requirements for sustained cellular immunity to an intracellular parasitic infection

The humoral immunity induced by many viral and bacterial vaccines mediates protection that is maintained over a long period of time. In contrast, for other intracellular infections (such as with Leishmania major or Mycobacter ium tuberculosis) for which cell-mediated immunity is required for protecti on, the mechanisms for developing durable responses after vaccination have not been well defined. Here we demonstrate that vaccination with plasmid DN A encoding a specific leishmanial antigen is more effective than leishmania l protein plus recombinant IL-12 in eliciting long-term immunity capable of controlling L. major infection. We also show that leishmanial protein plus IL-12 DNA produces an immunity that lasts much longer than does immunity e licited by leishmanial protein plus IL-12 protein, indicating that the pers istence of IL-12 may be the essential determinant in maintaining durable ce ll-mediated immune responses for an intracellular parasitic infection.