We currently have a very limited understanding of the factors, either genetic or immune-related, conferring
protection to clinical Plasmodium vivax (Pv) malaria. Deciphering the mechanisms underlying such protection
would allow the design of tailored intervention strategies for the elimination of Pv. Production of anti-Pv Duffy
Binding Protein (DBP) binding-inhibitory antibodies (BIabs) is associated to functional and protective
immunity against Pv malaria. Only a minority of individuals develops such antibodies and the mechanisms
enabling their production are unknown. Individuals not producing BIabs can still be protected against Pv
clinical malaria indicating that additional immunological and/or genetic factors can confer protection.
Leveraging a longitudinal cohort we have constituted in endemic area of Cambodia, we have identified
individuals displaying remarkable clinical protection against Pv and the overall goal of this proposal aims
at characterizing the factors enabling such protection. The first specific aim (SA1) will be to understand
the factors that drive the production of anti-PvDBP BIabs and therefore further clinical protection against Pv.
By phenotyping and functionally characterizing DBP-specific CD4+ T cells and B cells in naturally infected
participants with characterized amounts of BIabs, we will have a better understanding of the adaptive immune
response of individuals leading to the production of naturally-acquired anti-PvDBP BIabs. On the other hand,
by characterizing the PvDBP allelic polymorphism and isoforms produced by isolates collected from
individuals with various levels of BIabs, we will determine if parasite genetic factors are also contributing to
the acquisition of BIabs. The second and third SA will be to decipher the genetic (SA2) or immune (SA3)
factors leading to protection against Pv malaria for individuals not producing anti-PvDBP BIabs. In SA2, we
will compare the gene expression profiles and genotypes of parasites isolated from chronically-infected
asymptomatic individuals and from symptomatic treatment-seeking patients to identify parasite factors
differentiating these two drastically different clinical outcomes. We will also determine the human erythrocyte
proteins’ polymorphism of individuals displaying contrasted clinical outcome of infection to identify host
genetic factors conferring protection. Any host polymorphism identified will be functionally tested in vitro for
Pv invasion/development alterations. In SA3, we will identify host immune factors associated to protection
from clinical Pv malaria. Using the same patient cohort as SA2, we will study ex vivo and in vitro the immune
responses in Pv-infected patients. Using single cell cultures of antigen-specific B cells, we aim to identify
novel humoral targets on the Pv merozoite or iRBC that could be involved in conferring protection from clinical
Pv malaria trough blockade of invasion or alternative antibody effector functions.
