Large Scale systematic priorization of Plasmodium vivax blood stage vaccine antigens

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Summary Despite recent progress in reducing severe disease in sub-Saharan Africa, malaria remains one of the largest global public health burdens and a leading cause of mortality in children in low and middle income countries. There is an urgent need for an effective malaria vaccine because resistance has emerged to every antimalarial drug that has been publicly released to date. Vaccines against Plasmodium falciparum, the major cause of malaria in Africa, have received extensive support and are showing encouraging signs, but vaccine research for Plasmodium vivax, the major cause of malaria outside of Africa, has to date been extremely limited. This proposal will use the lessons from P. falciparum vaccine development, which for too long focussed on a limited number of candidates and did not make use of the full depth of available genomic sequence information. The central objective is to carry out the first comprehensive reverse vaccinology assessment of P. vivax blood stage antigens, combining advanced genomic and cellular techniques with ex vivo phenotyping assays. An established eukaryotic protein expression system will be used to express a library of >200 P. vivax blood stage vaccine candidates, which will be selected based on gene expression, biophysical characteristics and genomic diversity criteria. All expression constructs will be made freely available to the research community to aid global P. vivax vaccine and biology research efforts. The expressed proteins will be screened for antibody binding to confirm correct folding, and used in erythrocyte and receptor binding assays to prioritise targets for further study. Polyclonal antibodies will be raised against 100 targets and used in ex vivo P. vivax invasion phenotyping assays, to identify antibodies that block parasite invasion or growth. P. vivax parasites from both South America and Southeast Asia will be used at this stage of screening, introducing antigenic diversity at the earliest stage of target prioritization, another important lesson from P. falciparum vaccine development where strain-specific inhibitory responses derailed several promising candidates. Antibodies that provide cross- strain inhibition will be tested in combination to identify >4 highly effective and synergistic candidates for future development and potential clinical testing. The proposal will radically change the scale and pace of P. vivax vaccine development, and will produce resources of broad utility to the malaria research community.