Abstract
BackgroundIn clinical trials, immunopotentiating reconstituted influenza virosomes (IRIVs) have shown great potential as a versatile antigen delivery platform for synthetic peptides derived from Plasmodium falciparum antigens. This study describes the immunogenicity of a virosomally-formulated recombinant fusion protein comprising domains of the two malaria vaccine candidate antigens MSP3 and GLURP.MethodsThe highly purified recombinant protein GMZ2 was coupled to phosphatidylethanolamine and the conjugates incorporated into the membrane of IRIVs. The immunogenicity of this adjuvant-free virosomal formulation was compared to GMZ2 formulated with the adjuvants Montanide ISA 720 and Alum in three mouse strains with different genetic backgrounds.ResultsIntramuscular injections of all three candidate vaccine formulations induced GMZ2-specific antibody responses in all mice tested. In general, the humoral immune response in outbred NMRI mice was stronger than that in inbred BALB/c and C57BL/6 mice. ELISA with the recombinant antigens demonstrated immunodominance of the GLURP component over the MSP3 component. However, compared to the Al(OH)3-adjuvanted formulation the two other formulations elicited in NMRI mice a larger proportion of anti-MSP3 antibodies. Analyses of the induced GMZ2-specific IgG subclass profiles showed for all three formulations a predominance of the IgG1 isotype. Immune sera against all three formulations exhibited cross-reactivity with in vitro cultivated blood-stage parasites. Immunofluorescence and immunoblot competition experiments showed that both components of the hybrid protein induced IgG cross-reactive with the corresponding native proteins.ConclusionA virosomal formulation of the chimeric protein GMZ2 induced P. falciparum blood stage parasite cross-reactive IgG responses specific for both MSP3 and GLURP. GMZ2 thus represents a candidate component suitable for inclusion into a multi-valent virosomal malaria vaccine and influenza virosomes represent a versatile antigen delivery system suitable for adjuvant-free immunization with recombinant proteins.
Highlights
In clinical trials, immunopotentiating reconstituted influenza virosomes (IRIVs) have shown great potential as a versatile antigen delivery platform for synthetic peptides derived from Plasmodium falciparum antigens
Development of anti-GMZ2 IgG responses in mice In order to examine whether an adjuvant-free IRIV formulation of the recombinant hybrid protein GMZ2 elicits P. falciparum cross-reactive antibody responses, highly purified GMZ2 was chemically coupled to phosphatidylethanolamine and attached to the surface of IRIVs
Sera collected 3 weeks after the second immunization were assessed for IgG antibody titres specific for GMZ2 and its individual Glutamate Rich Protein (GLURP) and Merozoite Surface Protein 3 (MSP3) components by ELISA (Figure 2)
Summary
In clinical trials, immunopotentiating reconstituted influenza virosomes (IRIVs) have shown great potential as a versatile antigen delivery platform for synthetic peptides derived from Plasmodium falciparum antigens. This study describes the immunogenicity of a virosomally-formulated recombinant fusion protein comprising domains of the two malaria vaccine candidate antigens MSP3 and GLURP. One of the leading candidates for an anti-falciparum vaccine is GMZ2, a fusion protein consisting of the N-terminal portion of the Glutamate Rich Protein (GLURP) genetically fused to a C-terminal fragment of Merozoite Surface Protein 3 (MSP3) [4]. Data supporting MSP3 and GLURP as vaccine candidates rely on in vitro and in vivo preclinical models and on immuno-epidemiological studies demonstrating a statistically significant association between protection from clinical malaria and antigen recognition by exposed individuals [5,6,7,8,9,10,11,12,13]
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