Alphavirus Replicon Particles Are Highly Immunogenic in the Murine Malaria Model by Homologous or Heterologous Immunization

We evaluated the immunogenicity of virus-like replicon particles (VRP) derived from an attenuated strain of the alphavirus Venezuelan equine encephalitis virus, encoding two pre-erythrocytic Plasmodium yoelii antigens, in mice. Three immunizing doses were superior to two, and the subcutaneous route was comparable to intramuscular and more immunogenic than intradermal, at doses between 5x10 5 � 5x10 8 IU. VRP vaccines were capable of overcoming the tradi- tionally low immunogenicity of the PyHEP17 antigen when delivered as a DNA vaccine, particularly evident with regard to enhancing specific IgG responses. Furthermore, a heterologous VRP prime and poxvirus boost regimen induced a sig- nificant enhancement of IFN- responses as compared with homologous VRP or DNA immunization, which was equal or greater to that induced by DNA prime followed by poxvirus boost. These data demonstrate the potential of VRP as a vac- cine delivery system to enhance protective immune responses to malaria.