980. Specific Immune Response Against the Plasmodium falciparum CS Protein Mediated by Baculovirus Vectors

Abstract

Top of pageAbstract Malaria is the most common tropical disease worldwide. More than 300 million people are infected and about 2-3 million die annually. The most pathogenic form, Malaria tropica, is caused by Plasmodium falciparum. This enormous world-health problem is compounded by parasites becoming resistant to drugs which are commonly used for treatment and also the complete lack of an effective vaccine. Recombinant baculovirus vectors derived from the Autographa californica nuclear polyhedrosis virus (AcNPV) are commonly used as a tool for high-level expression of recombinant proteins of interest in insect cells. Baculovirus vectors can mediate an immune response against an antigen when it is displayed on the viral surface, or when it is expressed from the baculovirus backbone using promoters which are active in mammalian cells. Their ability to accommodate very large inserts of foreign DNA, the lack of a preexisting/neutralizing immunity to baculoviruses in humans and the easy generation of high titer virus stocks are further clear advantages of this vector system for the delivery of a vaccine. In order to use baculoviruses for an induction of a specific immune response we inserted a P. falciparum circumsporozoite (CS) protein expression cassette, driven by the strong CMV promoter, into the baculoviral genome (AcNPV-CSFVI). An expression of the CS protein in antigen presenting cells (APC) should activate CD8+ T cells via MHC I presentation. The display of a second, recombinant CS peptide in the viral envelope was achieved by fusion of the CS gene to the main baculovirus surface protein gp64 (AcNPV-CS/gp64). This envelope-modified baculovirus mimics the parasite to induce CD4+ T cells and CS specific antibodies following uptake into APC and antigen presentation by MHC II. A third vector (AcNPV-CSFVI-CS/gp64) was constructed to combine expression and presentation of CS antigens in mammalian cells. Expression of the CS protein upon infection of a mouse muscle cell line with AcNPV-CSFVI or AcNPV-CSFVI-CS/gp64 was confirmed by Western blotting with CS specific antibodies. For vaccination studies, BALB/c mice were injected intramuscularly with 5|[times]|108 pfu of AcNPV-CSFVI, AcNPV-CS/gp64, AcNPV-CSFVI-CS/gp64 or 10 ug recombinant CS protein and boosted after 3 weeks with the same dose. Data of IgG1/IgG2a serum ELISAs showed high CS specific antibody titers for mice injected with AcNPV-CS/gp64. Whereas infection with AcNPV-CSFVI could induce only low levels of antibodies, the combined expression and presentation of CS antigens (AcNPV-CSFVI-CS/gp64) could elicit an even higher IgG2a response. Frequencies of CS specific CD4+ and CD8+ T cells will be analyzed by ELIspot and data will be presented. Our current efforts are aimed towards targeting baculoviruses infection to dendritic cells by incorporation of specific receptor ligands into the viral envelope.