Design and pre-clinical profiling of a Plasmodium falciparum MSP-3 derived component for a multi-valent virosomal malaria vaccine.
BACKGROUND
Clinical profiling of two components for a synthetic peptide-based virosomal malaria vaccine has yielded promising results, encouraging the search for additional components for inclusion in a final multi-valent vaccine formulation. This report describes the immunological characterization of linear and cyclized synthetic peptides comprising amino acids 211-237 of Plasmodium falciparum merozoite surface protein (MSP-3).


METHODS
These peptides were coupled to phosphatidylethanolamine (PE); the conjugates were intercalated into immunopotentiating reconstituted influenza virosomes (IRIVs) and then used for immunizations in mice to evaluate their capacity to elicit P. falciparum cross-reactive antibodies.


RESULTS
While all MSP-3-derived peptides were able to elicit parasite-binding antibodies, stabilization of turn structures by cyclization had no immune-enhancing effect. Therefore, further pre-clinical profiling was focused on FB-12, a PE conjugate of the linear peptide. Consistent with the immunological results obtained in mice, all FB-12 immunized rabbits tested seroconverted and consistently elicited antibodies that interacted with blood stage parasites. It was observed that a dose of 50 microg was superior to a dose of 10 microg and that influenza pre-existing immunity improved the immunogenicity of FB-12 in rabbits. FB-12 production was successfully up-scaled and the immunogenicity of a vaccine formulation, produced according to the rules of Good Manufacturing Practice (GMP), was tested in mice and rabbits. All animals tested developed parasite-binding antibodies. Comparison of ELISA and IFA titers as well as the characterization of a panel of anti-FB-12 monoclonal antibodies indicated that at least the majority of antibodies specific for the virosomally formulated synthetic peptide were parasite cross-reactive.


CONCLUSIONS
These results reconfirm the suitability of IRIVs as a carrier/adjuvant system for the induction of strong humoral immune responses against a wide range of synthetic peptide antigens. The virosomal formulation of the FB-12 peptidomimetic is suitable for use in humans and represents a candidate component for a virosomal multi-valent malaria subunit vaccine.
Tamborrini
Marco
M
Swiss Tropical Institute, Molecular Immunology, CH-4002 Basel, Switzerland. gerd.pluschke@unibas.ch.
Mueller
Markus S
MS
Stoffel
Sabine A
SA
Westerfeld
Nicole
N
Vogel
Denise
D
Boato
Francesca
F
Zurbriggen
Rinaldo
R
Robinson
John A
JA
Pluschke
Gerd
G
D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D000953:Antigens, Protozoan / Q000276:immunology*; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods; D006801:Humans; D016778:Malaria, Falciparum / Q000517:prevention & control*; D051379:Mice; D008807:Mice, Inbred BALB C; D009975:Orthomyxoviridae / Q000737:chemistry; D010456:Peptides, Cyclic / Q000276:immunology; D010963:Plasmodium falciparum / Q000276:immunology*; D015800:Protozoan Proteins / Q000276:immunology*; D011817:Rabbits; D022223:Vaccines, Subunit / Q000276:immunology; D022721:Vaccines, Virosome / Q000276:immunology; D014764:Viral Proteins / Q000276:immunology / Q000378:metabolism
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D002352:Carrier Proteins; D010456:Peptides, Cyclic; D015800:Protozoan Proteins; D022223:Vaccines, Subunit; D022721:Vaccines, Virosome; D014764:Viral Proteins; C089133:merozoite surface protein 3, Plasmodium