PROJECT SUMMARY/ABSTRACT
With repeated Plasmodium infections, children eventually gain the ability to tolerate Plasmodium parasitemia
without developing symptoms. However, preventing malaria with effective chemoprevention may delay
development of this clinical immunity, such that children are at increased risk of more severe disease following
cessation. Although mechanisms controlling development of clinical immunity remain unclear, effector and
regulatory CD4+ T cells play a critical role in orchestrating a coordinated immune response to pathogens
including malaria. Plasmodium-specific Type 1 regulatory CD4+ T cells (Tr1) are a specialized, tolerogenic CD4
subset that expand following Plasmodium infection in humans and mice, although genetic mechanisms that
support Tr1 differentiation and maintenance remain unresolved. It also remains unclear whether these
represent clonal expansions, contribute to a stable memory pool, and/or play a role in mediating clinical
immunity to subsequent Plasmodium infections. We hypothesize that clonal populations of Plasmodium-
specific Tr1 cells expand following Plasmodium infection, are critical mediators of clinical immunity to
repeated infection, and are limited by effective chemoprevention. To test our hypotheses, we will leverage
two extraordinary and complementary cohorts to longitudinally and comprehensively analyze the CD4+ T cell
response in children. In Aim 1, we will analyze samples already obtained from children enrolled in the
Ugandan International Centers of Excellence in Malaria cohorts before, during, and at multiple time points
following a single and repeated malaria infection. We will study CD4+ T cell population dynamics within the
same child over time using innovative single cell transcriptomic and epigenomic approaches that we have
optimized. We will predict genes and other genetic loci that support or suppress Tr1 responses in children, and
determine associations with antibody responses and clinical phenotypes of infection. In Aim 2, we will analyze
samples collected as part of the Modifying Immunity in Children with Dihydroartemisin-Piperaquine (MIC-DroP)
clinical trial, in which 924 infants are being randomized to receive artemisinin-based chemoprevention vs.
placebo from birth to 2 years of age, then followed to 4 years of age. We will determine whether preventing
repeated infection interferes with Tr1 development, and whether specific malaria-specific CD4+ T cell
populations correlate with clinical outcomes following the cessation of chemoprevention. Finally, to
complement the pediatric studies, in Aim 3 we will perform studies of experimental re-infection and
chemoprevention in mice, since these systems permit detailed analysis of CD4+ T cell dynamics in the first few
hours and days after a reinfection event, and can assess organ-specific CD4+ responses in both the spleen
and liver. This study of Plasmodium-specific CD4+ T cell dynamics in humans and mice will provide critical
insight into how the adaptive immune system tolerates foreign antigens, and lay the foundation for the
development of therapeutic strategies aimed at reducing disease severity and/or enhancing parasite clearance.
