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The genetically attenuated malaria vaccine PfSPZ-GA1 is safe, immunogenic, and has suboptimal protective efficacy in people.

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.

Abstract Background Controlled human hookworm infections could significantly contribute to the development of a hookworm vaccine. However, current models are hampered by low and unstable egg output, reducing generalizability and increasing sample sizes. This study aims to investigate the safety, tolerability and egg output of repeated exposure to hookworm larvae. Methods Twenty-four healthy volunteers were randomized double blind to one, two or three doses of 50 Necatoramericanus L3 larvae at 2-week intervals. Volunteers were monitored weekly and were treated with albendazole at week 20. Results There was no association between larval dose and number or severity of adverse events. Geomean egg loads stabilized at 697, 1668 and 1914 eggs per gram feces for the 1x50L3, 2x50L3 and 3x50L3 group respectively. Bayesian statistical modelling showed that egg count variability relative to the mean was reduced with a second infectious dose, however the third dose did not increase egg load or decrease variability. We therefore suggest 2x50L3 as an improved challenge dose. Model-based simulations indicates increased frequency of stool sampling optimizes power of hypothetical vaccine trials. Discussion Repeated infection with hookworm larvae increased egg counts to levels comparable to the field and reduced relative variability in egg output without aggravating adverse events.

Four healthy volunteers were infected with 50 Necator americanus infective larvae (L3) in a controlled human hookworm infection trial and followed for 52 weeks. The kinetics of fecal egg counts in volunteers was assessed with Bayesian multilevel analysis, which revealed an increase between weeks 7 and 13, followed by an egg density plateau of about 1000 eggs/g of feces. Variation in egg counts was minimal between same-day measurements but varied considerably between days, particularly during the plateau phase. These analyses pave the way for the controlled human hookworm model to accelerate drug and vaccine efficacy studies.