Immunogenicity and Vaccine Shedding After 1 or 2 Doses of rVSVΔG-ZEBOV-GP Ebola Vaccine (ERVEBO®): Results From a Phase 2, Randomized, Placebo-controlled Trial in Children and Adults.

BACKGROUND: The rVSVΔG-ZEBOV-GP vaccine (ERVEBO®) is a single-dose, live-attenuated, recombinant vesicular stomatitis virus vaccine indicated for the prevention of Ebola virus disease (EVD) caused by Zaire ebolavirus in individuals 12 months of age and older. METHODS: The Partnership for Research on Ebola VACcination (PREVAC) is a multicenter, phase 2, randomized, double-blind, placebo-controlled trial of 3 vaccine strategies in healthy children (ages 1-17) and adults, with projected 5 years of follow-up (NCT02876328). Using validated assays (GP-ELISA and PRNT), we measured antibody responses after 1-dose rVSVΔG-ZEBOV-GP, 2-dose rVSVΔG-ZEBOV-GP (given on Day 0 and Day 56), or placebo. Furthermore, we quantified vaccine virus shedding in a subset of children's saliva using RT-PCR. RESULTS: In total, 819 children and 783 adults were randomized to receive rVSVΔG-ZEBOV-GP (1 or 2 doses) or placebo. A single dose of rVSVΔG-ZEBOV-GP increased antibody responses by Day 28 that were sustained through Month 12. A second dose of rVSVΔG-ZEBOV-GP given on Day 56 transiently boosted antibody concentrations. In vaccinated children, GP-ELISA titers were superior to placebo and non-inferior to vaccinated adults. Vaccine virus shedding was observed in 31.7% of children, peaking by Day 7, with no shedding observed after Day 28 post-dose 1 or any time post-dose 2. CONCLUSIONS: A single dose of rVSVΔG-ZEBOV-GP induced robust antibody responses in children that was non-inferior to the responses induced in vaccinated adults. Vaccine virus shedding in children was time-limited and only observed after the first dose. Overall, these data support the use of rVSVΔG-ZEBOV-GP for the prevention of EVD in at-risk children. Clinical Trials Registration. The study is registered at ClinicalTrials.gov (NCT02876328), the Pan African Clinical Trials Registry (PACTR201712002760250), and the European Clinical Trials Register (EudraCT number: 2017-001798-18).

Prevalence of malaria and helminth infections in rural communities in northern Sierra Leone, a baseline study to inform Ebola vaccine study protocols.

INTRODUCTION: Recurrent parasitic infections may influence the immune response to vaccines. In the Partnership for Research on Ebola VACcinations extended follow-UP and clinical research capacity build-UP (PREVAC-UP) study being undertaken in Mambolo, northern Sierra Leone, participants are being followed up to assess the potential impact of exposure to malaria and/or helminth infections on long-term immune response to two Ebola vaccines. To support the development of the assays that will be used in this evaluation, a parasitological survey was conducted in Mambolo between November 2019 and February 2020. METHODS: Healthy individuals aged ≥1 year who were resident in Mambolo Chiefdom were selected using a stratified sampling approach and questionnaires were administered to explore their sociodemographic characteristics. Microscopy was used to detect malaria parasites, intestinal helminths and urinary schistosome infections. Rapid blood tests were used to detect infections with Onchocerca volvulus and Wuchereria bancrofti. We estimated the overall prevalence of these infections and used adjusted logistic regression models to explore risk factors for malaria and hookworm infection. RESULTS: Eight hundred and fifteen (815) residents, 50.9% of whom were female were surveyed. Overall, 309 (39.1%) of 791 persons tested for malaria had a positive blood slide; Plasmodium falciparum was the dominant species. Helminth infection was detected in 122 (15.0%) of 815 stool samples including three mixed infections. The helminth infections comprised 102 (12.5%) cases of hookworm, 11 (1.3%) cases of Trichuris trichiura, 10 (1.2%) cases of Schistosoma mansoni and two (0.2%) cases of Ascaris lumbricoides. Being male (OR = 2.01, 95% CI 1.15-3.50) and residing in a non-riverine community (OR = 4.02, 95%CI 2.32-6.98) were the factors associated with hookworm infection. Onchocerca volvulus and Wuchereria bancrofti infections were found in 3.3% and 0.4% of participants respectively. CONCLUSION: Malaria and hookworm are the most prevalent parasite infections and those most likely to influence long-term immune response to Ebola vaccines among the trial participants.

Suramin and suramin analogues inhibit merozoite surface protein-1 secondary processing and erythrocyte invasion by the malaria parasite Plasmodium falciparum.

Malarial merozoites invade erythrocytes; and as an essential step in this invasion process, the 42-kDa fragment of Plasmodium falciparum merozoite surface protein-1 (MSP142) is further cleaved to a 33-kDa N-terminal polypeptide (MSP133) and an 19-kDa C-terminal fragment (MSP119) in a secondary processing step. Suramin was shown to inhibit both merozoite invasion and MSP142 proteolytic cleavage. This polysulfonated naphthylurea bound directly to recombinant P. falciparum MSP142 (Kd = 0.2 microM) and to Plasmodium vivax MSP142 (Kd = 0.3 microM) as measured by fluorescence enhancement in the presence of the protein and by isothermal titration calorimetry. Suramin bound only slightly less tightly to the P. vivax MSP133 (Kd = 1.5 microM) secondary processing product (fluorescence measurements), but very weakly to MSP119 (Kd approximately 15 mM) (NMR measurements). Several residues in MSP119 were implicated in the interaction with suramin using NMR measurements. A series of symmetrical suramin analogues that differ in the number of aromatic rings and substitution patterns of the terminal naphthylamine groups was examined in invasion and processing assays. Two classes of analogue with either two or four bridging rings were found to be active in both assays, whereas two other classes without bridging rings were inactive. We propose that suramin and related compounds inhibit erythrocyte invasion by binding to MSP1 and by preventing its cleavage by the secondary processing protease. The results indicate that enzymatic events during invasion are suitable targets for drug development and validate the novel concept of an inhibitor binding to a macromolecular substrate to prevent its proteolysis by a protease.

A single malaria merozoite serine protease mediates shedding of multiple surface proteins by juxtamembrane cleavage.

Erythrocyte invasion by the malaria merozoite is accompanied by the regulated discharge of apically located secretory organelles called micronemes. Plasmodium falciparum apical membrane antigen-1 (PfAMA-1), which plays an indispensable role in invasion, translocates from micronemes onto the parasite surface and is proteolytically shed in a soluble form during invasion. We have previously proposed, on the basis of incomplete mass spectrometric mapping data, that PfAMA-1 shedding results from cleavage at two alternative positions. We now show conclusively that the PfAMA-1 ectodomain is shed from the merozoite solely as a result of cleavage at a single site, just 29 residues away from the predicted transmembrane-spanning sequence. Remarkably, this cleavage is mediated by the same membrane-bound parasite serine protease as that responsible for shedding of the merozoite surface protein-1 (MSP-1) complex, an abundant, glycosylphosphatidylinositol-anchored multiprotein complex. Processing of MSP-1 is essential for invasion. Our results indicate the presence on the merozoite surface of a multifunctional serine sheddase with a broad substrate specificity. We further demonstrate that translocation and shedding of PfAMA-1 is an actin-independent process.