PROJECT SUMMARY Malaria continues to be responsible for substantial childhood mortality in Africa despite current control efforts. Developing an effective vaccine for malaria elimination is constrained by knowledge gaps in both naturally- acquired and vaccine-induced immunity. Existing vaccine candidates elicit antibodies against the target antigen but the associations between antibody functional activity and level and duration of protection are unknown. Additionally novel blood-stage antigens that could be used in future vaccines aimed at preventing symptomatic malaria have emerged (some are polymorphic), that need to be further investigated. Preferred antigens should elicit antibody functional activity that is: i) boosted with natural infection; ii) long-lasting; iii) correlated with protection; iv) not highly strain-specific, i.e., effective against a diversity of isolates. Our study aims to clarify these unknowns focusing on 12 understudied blood-stage antigens (and the alleles of those polymorphic antigens) to inform selection of antigens that could be potential vaccine candidates. Prior studies of naturally-acquired antibody immunity have largely quantified antibody magnitude to specific proteins and have typically been limited to quantifying immune responses infrequently or at a single time-point. Because the immune profiles of individuals are dynamic and a function of exposure to infection that cannot be synchronized at the beginning of a study, these largely cross-sectional measurements obscure outcomes of interest. Furthermore, prior studies predominantly measured only magnitude of IgG responses; few have assessed the range and breath of functional activities of antibodies, and the impact of antigen polymorphisms on functional antibody activities. The expertise of our study team, combined with access to samples collected during a longitudinal study with intensive follow-up and a comprehensive study approach, provides an opportunity to address these questions and elucidate the importance of these antigens in acquired immunity to malaria. Our study will be based on a cohort of children and adults who were seen monthly over two years in which subjects had repeated clinical and/or sub clinical malaria infections. Studying this cohort will enable us to gain new insights into the durability and boosting over time of functional antibody activity against blood-stage antigens upon natural exposure to malaria. We will also evaluate the cross-reactivity or strain-specificity of functional antibodies against alternative alleles of polymorphic antigens. Finally, we will evaluate antigens (and alleles) against which functional antibody activity is correlated with protection from symptomatic malaria and high density parasitemia, and we will seek signatures of functional responses that can accurately discriminate protected and unprotected subjects. These correlates of protection will provide endpoints for evaluating future vaccines. This may have implications for strategies to improve vaccine efficacy and implementation.

PROJECT NARRATIVE Development of an effective vaccine to combat malaria is hampered by knowledge gaps in malaria immunity. The general objective of our study is to inform selection of antigens for evaluation as potential vaccine candidates and establish approaches and principals that can be applied in future larger studies. We will use data from parasite genetics, new analytical approaches, and antibody functional activity targeting novel antigens that have promise as future vaccine candidates.