Abstract

BackgroundPlasmodium falciparum is transmitted from person to person by Anopheles mosquitoes after completing its sexual reproductive cycle within the infected mosquito. An efficacious vaccine holds the potential to interrupt development of the parasite in the mosquito leading to control and possibly eradication of malaria. A multi-component, R0.10C, was developed comprising P. falciparum glutamate-rich protein (R0) fused in frame to a correctly folded fragment of Pfs48/45 (10C). Here, a series of novel adjuvants were screened for their ability to elicit transmission-blocking (TB) antibodies.MethodsThe recombinant fusion protein R0.10C was produced in Lactococcus lactis and purified by affinity-chromatography on a monoclonal antibody (mAb 85RF45.1) against a major epitope for TB antibodies (epitope 1) harboured on R0.10C. Immune-purified R0.10C was mixed with a series of adjuvants and tested in mice and rats.ResultsIn general, all R0.10C formulations elicited high levels of antibodies recognizing native Pfs48/45 in macrogametes/zygotes. TB activity of anti-R0.10C antisera was assessed in the standard membrane-feeding assay (SMFA). Potency of different adjuvant/R0.10C combinations was tested in mice and rats using aluminium hydroxide (Alum), Alum with micellar and emulsion formulations of a synthetic TLR4 agonist, Glucopyranosyl Lipid Adjuvant (GLA), stable emulsion (SE)/GLA, AbISCO-100 and Freund’s adjuvant (as reference). All formulations produced high antibody titres recognizing the native Pfs48/45 protein in macrogametes/zygotes. Interestingly, the GLA-Alum combination adjuvant was the most potent inducer of TB antibodies based on serum collected after two immunizations. In agreement with previous observations, biological activity in the SMFA correlated well with the level of anti-Pfs48/45 antibodies.ConclusionThe combined data provide a strong basis for entering the next phase of clinical grade R0.10C production and testing.

Highlights

  • Plasmodium falciparum is transmitted from person to person by Anopheles mosquitoes after complet‐ ing its sexual reproductive cycle within the infected mosquito

  • With the renewed focus on malaria eradication, transmission blocking malaria vaccines (TBMV) which induce antibodies that target the sexual stages of the parasite have become a focus of malaria vaccine research

  • Irrespective of the mechanism, it has been shown in ex vivo assays that there is a strong correlation between levels of Pfs48/45-specific antibodies in sera from malaria-endemic areas and TB activity in the standard membrane feeding assay (SMFA) [9,10,11]

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Summary

Introduction

Plasmodium falciparum is transmitted from person to person by Anopheles mosquitoes after complet‐ ing its sexual reproductive cycle within the infected mosquito. An efficacious vaccine holds the potential to interrupt development of the parasite in the mosquito leading to control and possibly eradication of malaria. With the renewed focus on malaria eradication, transmission blocking malaria vaccines (TBMV) which induce antibodies that target the sexual stages of the parasite have become a focus of malaria vaccine research. Pfs48/45 is essential for male gamete fertility in Plasmodium [7] and anti-Pfs48/45 antibodies have been found to prevent zygote development in the standard membrane feeding assay (SMFA) [8]. Irrespective of the mechanism, it has been shown in ex vivo assays that there is a strong correlation between levels of Pfs48/45-specific antibodies in sera from malaria-endemic areas and TB activity in the SMFA [9,10,11]

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