Yoanne D. Mouwenda

Helminth-driven immunomodulation contributes to immune heterogeneity in tropical environments. Whether it can be reversed by BCG revaccination, an inducer of trained immunity, remains unknown. We applied high-dimensional mass cytometry to profile immune variation in Ugandan adolescents across contrasting rural–urban and Schistosoma mansoni ( Sm ) exposure settings, before and four weeks after BCG revaccination. We studied untreated rural Sm ⁺ individuals, rural individuals who became Sm ^– following praziquantel treatment, and urban Sm ^– individuals. At baseline, rural, particularly Sm ⁺ , participants exhibited immune signatures of chronic stimulation and exhaustion, including expanded CD11c ⁺ T-bet ⁺ B, CRTH2 ^hi CD4 ⁺ T, and HLA-DR ⁺ CD38 ⁺ CD8 ⁺ T cells, alongside reduced NK cells with cytotoxic potential (CD16 ⁺ , NKp46 ⁺ , KLRG1 ^hi ) and non-classical/intermediate monocytes, contrasting with urban participants. Consistent with these phenotypic differences, polyclonal stimulation elicited broadly attenuated cytokine responses in rural, versus urban, individuals. Four weeks post-BCG, rural–urban immune divergence narrowed. Cytotoxic and inflammatory innate compartments, including CD16 ⁺ /NKp46 ⁺ /KLRG1 ^hi NK cells and non-classical/intermediate monocytes, expanded, predominantly in rural Sm ⁺ individuals. Adaptive phenotypes associated with chronic stimulation and immune exhaustion, such as CRTH2 ^hi CD4 ⁺ T and CD11c ⁺ T-bet ⁺ B-cell subsets, declined, indicating partial reversal of helminth-driven immunomodulation. These findings suggest that BCG can reprogram immune profiles shaped by chronic helminth exposure, highlighting substantial immune plasticity in schistosomiasis-endemic settings.

Cellular metabolism is a key determinant of immune cell function. Here we found that CD14⁺ monocytes from Sub‐Saharan Africans produce higher levels of IL‐10 following TLR‐4 stimulation and are bioenergetically distinct from monocytes from Europeans. Through metabolomic profiling, we identified the higher IL‐10 production to be driven by increased baseline production of NADPH oxidase‐dependent reactive oxygen species, supported by enhanced pentose phosphate pathway activity. Together, these data indicate that NADPH oxidase‐derived ROS is a metabolic checkpoint in monocytes that governs their inflammatory profile and uncovers a metabolic basis for immunological differences across geographically distinct populations.

Vaccination of malaria-naive volunteers with a high dose of Plasmodium falciparum sporozoites chemoattenuated by chloroquine (CQ) (PfSPZ-CVac [CQ]) has previously demonstrated full protection against controlled human malaria infection (CHMI). However, lower doses of PfSPZ-CVac [CQ] resulted in incomplete protection. This provides the opportunity to understand the immune mechanisms needed for better vaccine-induced protection by comparing individuals who were protected with those not protected. Using mass cytometry, we characterized immune cell composition and responses of malaria-naive European volunteers who received either lower doses of PfSPZ-CVac [CQ], resulting in 50% protection irrespective of the dose, or a placebo vaccination, with everyone becoming infected following CHMI. Clusters of CD4 ⁺ and γδ T cells associated with protection were identified, consistent with their known role in malaria immunity. Additionally, EMRA CD8 ⁺ T cells and CD56 ⁺ CD8 ⁺ T cell clusters were associated with protection. In a cohort from a malaria-endemic area in Gabon, these CD8 ⁺ T cell clusters were also associated with parasitemia control in individuals with lifelong exposure to malaria. Upon stimulation with P . falciparum –infected erythrocytes, CD4 ⁺ , γδ, and EMRA CD8 ⁺ T cells produced IFN-γ and/or TNF, indicating their ability to mediate responses that eliminate malaria parasites.

The interaction of malaria parasites with their human host is extensively studied, yet only few studies reported how P. falciparum infection affects urinary metabolite profiles and how this is associated with immunity. We present a longitudinal study of the urinary metabolic profiles of twenty healthy Africans with lifelong exposure to malaria and five malaria-naïve Europeans, who were all challenged with direct venous inoculation of live P. falciparum sporozoïtes (PfSPZ) and followed up until they developed symptoms or became thick blood smear positive (TBS). Urine samples were collected before and at 2, 5, 9 and 11 days post challenge and were analysed. Upon infection, all Europeans became TBS positive, while Africans showed either a delay in time to parasitaemia or controlled infection. Our metabolic data showed that Europeans and Africans had distinct alterations in metabolite patterns, with changes mostly seen on days 5 and 9 post PfSPZ infection, and more prominently in Europeans. Within the African group, the levels of formate, urea, trimethylamine, threonine, choline, myo-inositol and acetate were significantly higher in TBS positive whereas the levels of pyruvate, 3-methylhistidine and dimethylglycine were significantly lower in individuals who remained TBS negative. Notably, before inoculation with PfSPZ, a group of metabolites including phenylacetylglutamine can potentially be used to predict parasitaemia control among Africans. Taken together, this study highlights the difference in urinary metabolic changes in response to malaria infection as a consequence of lifelong exposure to malaria and that change detectable before challenge might predict the control of parasitaemia in malaria-endemic areas.

Metabolomics provides a powerful tool to study physiological changes in response to various perturbations such as vaccination. We explored whether metabolomic changes could be seen after vaccination in a phase I trial where Gabonese adults living either in rural or semi-urban areas received the subunit hookworm vaccine candidates (Na-GST-1 and Na-APR-1 (M74) adjuvanted with Alhydrogel plus GLA-AF (n = 24) or the hepatitis B vaccine (n = 8) as control. Urine samples were collected and assayed using targeted ¹H NMR spectroscopy. At baseline, a set of metabolites significantly distinguished rural from semi-urban individuals. The pre- and post-vaccination comparisons indicated significant changes in few metabolites but only one day after the first vaccination. There was no relationship with immunogenicity. In conclusion, in a small phase 1 trial, urinary metabolomics could distinguish volunteers with different environmental exposures and reflected the safety of the vaccines but did not show a relationship to immunogenicity.

Two hookworm vaccine candidates, Na-GST-1 and Na-APR-1, formulated with Glucopyranosyl Lipid A (GLA-AF) adjuvant, have been shown to be safe, well tolerated, and to induce antibody responses in a Phase 1 clinical trial (Clinicaltrials.gov NCT02126462) conducted in Gabon. Here, we characterized T cell responses in 24 Gabonese volunteers randomized to get vaccinated three times with Na-GST-1 and Na-APR-1 at doses of 30μg (n = 8) or 100μg (n = 10) and as control Hepatitis B (n = 6). Blood was collected pre- and post-vaccination on days 0, 28, and 180 as well as 2-weeks after each vaccine dose on days 14, 42, and 194 for PBMCs isolation. PBMCs were stimulated with recombinant Na-GST-1 or Na-APR-1, before (days 0, 28 and 180) and two weeks after (days 14, 42 and 194) each vaccination and used to characterize T cell responses by flow and mass cytometry. A significant increase in Na-GST-1 -specific CD4⁺ T cells producing IL-2 and TNF, correlated with specific IgG antibody levels, after the third vaccination (day 194) was observed. In contrast, no increase in Na-APR-1 specific T cell responses were induced by the vaccine. Mass cytometry revealed that, Na-GST-1 cytokine producing CD4⁺ T cells were CD161⁺ memory cells expressing CTLA-4 and CD40-L. Blocking CTLA-4 enhanced the cytokine response to Na-GST-1. In Gabonese volunteers, hookworm vaccine candidate, Na-GST-1, induces detectable CD4⁺ T cell responses that correlate with specific antibody levels. As these CD4⁺ T cells express CTLA-4, and blocking this inhibitory molecules resulted in enhanced cytokine production, the question arises whether this pathway can be targeted to enhance vaccine immunogenicity.

Controlled human infections provide opportunities to study the interaction between the immune system and malaria parasites, which is essential for vaccine development. Here, we compared immune signatures of malaria-naive Europeans and of Africans with lifelong malaria exposure using mass cytometry, RNA sequencing and data integration, before and 5 and 11 days after venous inoculation with Plasmodium falciparum sporozoites. We observed differences in immune cell populations, antigen-specific responses and gene expression profiles between Europeans and Africans and among Africans with differing degrees of immunity. Before inoculation, an activated/differentiated state of both innate and adaptive cells, including elevated CD161⁺CD4⁺ T cells and interferon-γ production, predicted Africans capable of controlling parasitemia. After inoculation, the rapidity of the transcriptional response and clusters of CD4⁺ T cells, plasmacytoid dendritic cells and innate T cells were among the features distinguishing Africans capable of controlling parasitemia from susceptible individuals. These findings can guide the development of a vaccine effective in malaria-endemic regions.