Longitudinal evaluation of interactions between variable PfEMP1 virulence genes, the anti-PfEMP1 antibody repertoire, and outcomes of naturally occurring Plasmodium falciparum infections - ABSTRACT: Immunity to Plasmodium falciparum eventually develops in malaria endemic areas, preventing innumerable cases of malaria. Unfortunately, this takes years of repeated infections, partly due to sequence variation in P. falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1 proteins are exported to the surface of infected red blood cells where they bind to host receptors, allowing parasites to evade splenic clearance, enabling symptomatic disease and persistent infections. Each parasite contains ~60 variable (var) genes encoding PfEMP1 proteins and regularly switches which var is expressed during infections to avoid host antibodies, allowing P. falciparum infections to attain high parasite density and cause symptomatic disease (often treated) or to persist for a year or longer if not treated. These persistent, asymptomatic infections are the rule rather than the exception in most endemic settings and are the primary driver of transmission. Our central premise is that naturally acquired antibody responses to a small subset of key PfEMP1 epitopes, such as those involved in binding host receptors, are largely responsible for protection from symptomatic disease, control of parasite density, and clearance of persistent infections. Confirming this hypothesis and identifying novel epitopes of clinical importance would greatly facilitate the development of vaccines and monoclonal antibodies aimed at decreasing malarial morbidity and mortality. Understanding the role of the antibody response to PfEMP1 in preventing disease and clearing infections requires characterization of expressed var genes and profiling of the anti-PfEMP1 antibody response. We are uniquely positioned to generate such data and test our hypotheses by leveraging a cohort of Ugandan children and adults with available clinical data, molecular data on parasitemia and clonal dynamics, and frequently collected plasma and cryopreserved parasites. We will apply novel methods for var gene sequence assembly and granular assessment of the antibody response to complete the following aims, evaluating interactions between the host antibody response, var gene expression, and clinically relevant outcomes at the onset of infection (Aim 1) and during persistent infections (Aim 2). Both aims will test relevant hypotheses on malaria biology and immunity and identify novel PfEMP1 epitopes of importance by integrating longitudinal data on the anti-PfEMP1 antibody response - using an established bead array and novel PhIP-seq assay - var gene expression from RNA sequencing, and in vivo outcomes from our existing cohort. In Aim 1, we will determine associations between the anti-PfEMP1 antibody response, initial var gene expression, and outcomes of incident P. falciparum infection in a Ugandan cohort. In Aim 2, we will determine associations between the anti-PfEMP1 antibody response, changes in var gene expression during persistent infections, and host clearance of asymptomatic infections in a Ugandan cohort. Upon successful completion of this project, we will have clarified the role of anti-PfEMP1 antibodies in improving infection outcomes, identified key PfEMP1 epitopes, and laid the groundwork for future structural and functional work.
