Use of reconstituted influenza virus virosomes as an immunopotentiating delivery system for a peptide‐based vaccine

Immunopotentiating reconstituted influenza virosomes (IRIV) were used as a delivery system for the synthetic peptide‐based malaria vaccine SPf66. The reduced SPf66 peptide molecules containing terminal cysteine residues were covalently attached to phosphatidylethanolamine with the heterobifunctional crosslinker γ‐maleimidobutyric acid N‐hydroxysuccinimide ester. The SPf66‐phosphatidylethanolamine was incorporated into IRIV and BALB/c mice were immunized twice by intramuscular injection with peptide‐loaded virosomes. Titres of elicited anti‐SPf66 IgG were determined by ELISA. These titres were significantly higher and the required doses of antigen were lower, when mice had been preimmunized with a commercial whole virus influenza vaccine. After preimmunization with the influenza vaccine, SPf66‐IRIV elicited far more consistently anti‐SPf66 antibody responses than SPf(66) n adsorbed to alum. MoAb produced by four B cell hybridoma clones derived from a SPf66‐IRIV‐immunized mouse cross‐reacted with Plasmodium falciparum blood stage parasites in immunofluorescence assays. All four MoAbs were specific for the merozoite surface protein‐1 (MSP‐1)‐derived 83.1 portion of SPf66. Sequencing of their functionally rearranged κ light chain variable region genes demonstrated that the four hybridomas were generated from clonally related splenic B cells. Biomolecular interaction analyses (BIA) together with these sequencing data provided evidence for the selection of somatically mutated affinity‐matured B cells upon repeated immunization with SPf66‐IRIV. The results indicate that IRIV are a suitable delivery system for synthetic peptide vaccines and thus have a great potential for the design of molecularly defined combined vaccines targeted against multiple antigens and development stages of one parasite, as well as against multiple pathogens.