. Osier, KEMRI-CGMRC, Defining the merozoite targets of protective immunity against Plasmodium falciparum malaria through multi-centre cohort studies

Malaria is still a major public health problem for many parts of sub-Saharan Africa. The World Health Organization estimates that nearly ninety children under the age of five years die from malaria each hour, in this region. Many tools can be used to control malaria including, insecticide-treated bed-nets, rapidly acting and effective medications, and better control of mosquitoes. Although these have been used in Africa with varying degrees of success, many experts now agree that novel measures will be needed to achieve better control, and move towards elimination. Vaccines have historically been the most effective and cost-effective public health tools against infectious diseases.

There is currently no licensed malaria vaccine. The most promising vaccine so far is still being tested in clinical trials but early data show that it only offers 30% protection against clinical episodes of malaria. Whilst this marks significant progress, there is an urgent need to improve on this vaccine efficacy. The conviction that it will be possible to develop an effective malaria vaccine comes partly from observations of disease patterns in areas that experience a lot of malaria. Young children under the age of five are susceptible to severe and complicated forms of malaria, while older children and young adults experience only milder forms of the illness, and gradually remain symptom-free despite being infected.

How is this immunity acquired? Studies conducted over fifty years ago showed that antibodies taken from adults who had become immune to malaria could be used to successfully treat individuals hospitalized with malaria. We know that antibodies act by binding to specific molecules on microbes or infecting agents, thus halting their progress. With advances in technology, we have now been able to identify the thousands of proteins that make up a malaria parasite. What we have failed to do is to identify which of these thousands of proteins are the targets of the protective antibodies. Previous studies have concentrated only on a small number of antigens, in small studies, used varied methodologies, and not taken into account the wide differences in malaria transmission intensity that affect antibody measurements. For these reasons, it is still not clear which parasite proteins induce protective antibodies.

I propose to overcome these shortcomings in four main ways. First, I will test a large number of parasite proteins, selecting only those that are plausible biological targets by virtue of being exposed to antibodies in the body. Second, I will study antibody responses in samples collected from multiple sites in sub-Saharan Africa (sSA) that are representative of the varying levels of malaria transmission experienced on the continent. Third, I will conduct a very large study using blood samples that have already been collected from the different sites. This has three important advantages: i) the study will be sufficiently large, allowing me to test antibody responses to many parasite proteins with the confidence that any protective associations identified are not due to chance, ii) all assays and analyses will be performed in an identical manner, allowing us to directly compare data from individual sites, iii) the study will be extremely cost-effective, avoiding the prohibitive costs that would be required to set up and longitudinally monitor children in multiple sites in Africa. Finally, I will examine the mechanisms of action of the antibodies directed against the parasite proteins that we find to be important.

This study will therefore be the most comprehensive to date with regards to number of specific parasite proteins tested, generalizability of results across sSA, and supported by the demonstration of antibody mechanisms of action for the best candidates. This information will be extremely valuable for the development of the next generation of malaria vaccines.

The development of an effective malaria vaccine remains an important research priority as the global malaria control agenda moves from reductions in morbidity and mortality, to elimination. Whilst our understanding of the molecular complexity of Plasmodium falciparum has grown tremendously in the last decade, this has not as yet been paralleled with equivalent strides in deciphering the targets of, and mechanisms underlying naturally acquired immunity. I hypothesize that this stems from i) failure to examine more than a handful of potential immune targets ii) failure to conduct sufficiently large studies with statistical power to investigate hundreds of associations iii) failure to take into account the wide variation in malaria transmission intensity observed in sub-Saharan Africa (SSA) and iv) failure to marry protective association studies with demonstration of immune effector mechanisms.

I believe we are now in a position to tackle these shortcomings and propose to do the following: i) systematically analyze antibody responses to at least 120 distinct surface-exposed or associated merozoite proteins, and invasion ligands, ii) conduct a cohort study statistically powered to analyze multiple responses and combinations of responses - this will be achieved cost-effectively by re-using previously collected serum samples and epidemiological data from established cohorts in Africa, iii) standardizing the antigens tested, laboratory assays and analytical approaches iv) concurrently assessing antigen-specific antibody-dependent mechanisms of action.

This will be the most definitive cohort study to date and provide strong evidence for or against malaria vaccine candidates. Demonstration of function will further strengthen the evidence, allowing for rational prioritization of the best candidates.

Economic and Societal Impact
Malaria and non-malaria researchers will benefit directly or indirectly from knowledge gained through this project as it will contribute significantly to worldwide efforts to address a major public health issue affecting sub-Saharan Africa and other resource-poor tropical countries. For researchers involved directly in malaria vaccine development, this project will provide additional high quality evidence for vaccine candidates that might be considered for the next generation of malaria vaccines. This project brings together South-South researchers to find solutions to a major and shared health problem facing the African continent. It will provide a prime example of equitable of North-South and South-South partnerships in which research is driven from and directly addresses priority health problems of people in Africa, while drawing on the technical expertise and financial support of partners in the North. At the home African Institution, research capacity will be directly enhanced through the specialized training members of the ARL's research group will receive at the Sanger Institute. This expertise is currently lacking and will be transferred back to other researchers within the home African Institution during the lifetime of the award.

Through this award, the knowledge base of local communities will be enhanced, thereby fostering a culture that appreciates and understands the benefits and value of basic science research. Of particular importance is creating a greater awareness that although the returns on this type of research are generally not realized in the short-term, the potential long-term benefits can make a real difference to the lives of many. This is well illustrated through the impact that the extended programme on immunization (EPI) has had on the health and wellbeing of children and families in Africa and around the world. Enhancing the knowledge base of local communities also encourages participation in this kind of research, promotes basic science research as a tangible and viable career option for younger generations within the community and promotes goodwill between researchers and local communities, towards the common goal of improved health.