Ageing of Plasmodium falciparum malaria sporozoites alters their motility, infectivity and reduces immune activation in vitro

BACKGROUND

Sporozoites (SPZ), the infective form of Plasmodium falciparum malaria, can be inoculated into the human host skin by Anopheline mosquitoes. These SPZ migrate at approximately 1 µm/s to find a blood vessel and travel to the liver where they infect hepatocytes and multiply. In the skin they are still low in number (50-100 SPZ) and vulnerable to immune attack by antibodies and skin macrophages. This is why whole SPZ and SPZ proteins are used as the basis for most malaria vaccines currently deployed and undergoing late clinical testing. Mosquitoes typically inoculate SPZ into a human host between 14 and 25 days after their previous infective blood meal. However, it is unknown whether residing time within the mosquito affects SPZ condition, infectivity or immunogenicity. This study aimed to unravel how the age of P. falciparum SPZ in salivary glands (14, 17, or 20 days post blood meal) affects their infectivity and the ensuing immune responses.

METHODS

SPZ numbers, viability by live/dead staining, motility using dedicated sporozoite motility orienting and organizing tool software (SMOOT), and infectivity of HC-04.j7 liver cells at 14, 17 and 20 days after mosquito feeding have been investigated. In vitro co-culture assays with SPZ stimulated monocyte-derived macrophages (MoMɸ) and CD8+ T-cells, analysed by flow cytometry, were used to investigate immune responses.

RESULTS

SPZ age did not result in different SPZ numbers or viability. However, a markedly different motility pattern, whereby motility decreased from 89% at day 14 to 80% at day 17 and 71% at day 20 was observed (p ≤ 0.0001). Similarly, infectivity of day 20 SPZ dropped to ~ 50% compared with day 14 SPZ (p = 0.004). MoMɸ were better able to take up day 14 SPZ than day 20 SPZ (from 7.6% to 4.1%, p = 0.03) and displayed an increased expression of pro-inflammatory CD80, IL-6 (p = 0.005), regulatory markers PDL1 (p = 0.02), IL-10 (p = 0.009) and cytokines upon phagocytosis of younger SPZ. Interestingly, co-culture of these cells with CD8+ T-cells revealed a decreased expression of activation marker CD137 and cytokine IFNγ compared to their day 20 counterparts. These findings suggest that older (day 17-20) P. falciparum SPZ are less infectious and have decreased immune regulatory potential.

CONCLUSION

Overall, this data is a first step in enhancing the understanding of how mosquito residing time affects P. falciparum SPZ and could impact the understanding of the P. falciparum infectious reservoir and the potency of whole SPZ vaccines.

No Remdesivir Resistance Observed in the Phase 3 Severe and Moderate COVID-19 SIMPLE Trials

Remdesivir (RDV) is a broad-spectrum nucleotide analog prodrug approved for the treatment of COVID-19 in hospitalized and non-hospitalized patients with clinical benefit demonstrated in multiple Phase 3 trials. Here we present SARS-CoV-2 resistance analyses from the Phase 3 SIMPLE clinical studies evaluating RDV in hospitalized participants with severe or moderate COVID-19 disease. The severe and moderate studies enrolled participants with radiologic evidence of pneumonia and a room-air oxygen saturation of ≤94% or >94%, respectively. Virology sample collection was optional in the study protocols. Sequencing and related viral load data were obtained retrospectively from participants at a subset of study sites with local sequencing capabilities (10 of 183 sites) at timepoints with detectable viral load. Among participants with both baseline and post-baseline sequencing data treated with RDV, emergent Nsp12 substitutions were observed in 4 of 19 (21%) participants in the severe study and none of the 2 participants in the moderate study. The following 5 substitutions emerged: T76I, A526V, A554V, E665K, and C697F. The substitutions T76I, A526V, A554V, and C697F had an EC50 fold change of ≤1.5 relative to the wildtype reference using a SARS-CoV-2 subgenomic replicon system, indicating no significant change in the susceptibility to RDV. The phenotyping of E665K could not be determined due to a lack of replication. These data reveal no evidence of relevant resistance emergence and further confirm the established efficacy profile of RDV with a high resistance barrier in COVID-19 patients.

Intradermal delivery of the third dose of the mRNA-1273 SARS-CoV-2 vaccine: safety and immunogenicity of a fractional booster dose

OBJECTIVES

The aim of this study was to assess the safety and immunogenicity of a dose-sparing fractional intradermal (ID) booster strategy with the mRNA-1273 COVID-19 vaccine.

METHODS

COVID-19 naive adults aged 18-30 years were recruited from a previous study on primary vaccination regimens that compared 20 μg ID vaccinations with 100 μg intramuscular (IM) vaccinations with mRNA-1273 as the primary vaccination series. Participants previously immunized with ID regimens were randomly assigned (1:1) to receive a fractional ID booster dose (20 μg) or the standard-of-care intramuscular (IM) booster dose (50 μg) of the mRNA-1273 vaccine, 6 months after completing their primary series (ID-ID and ID-IM group, respectively). Participants that had received a full dose IM regimen as the primary series, received the IM standard-of-care booster dose (IM-IM group). In addition, COVID-19 naive individuals aged 18-40 years who had received an IM mRNA vaccine as the primary series were recruited from the general population to receive a fractional ID booster dose (IM-ID group). Immunogenicity was assessed using IgG anti-spike antibody responses and neutralizing capacity against SARS-CoV-2. Cellular immune responses were measured in a sub-group. Safety and tolerability were monitored.

RESULTS

In January 2022, 129 participants were included in the study. Fractional ID boosting was safe and well tolerated, with fewer systemic adverse events compared with IM boosting. At day 28 post-booster, anti-spike S1 IgG geometric mean concentrations were 9106 (95% CI, 7150-11 597) binding antibody units (BAU)/mL in the IM-IM group and 4357 (3003-6322) BAU/mL; 6629 (4913-8946) BAU/mL; and 5264 (4032-6873) BAU/mL in the ID-IM, ID-ID, and IM-ID groups, respectively.

DISCUSSION

Intradermal boosting provides robust immune responses and is a viable dose-sparing strategy for mRNA COVID-19 vaccines. The favourable side-effect profile supports its potential to reduce vaccine hesitancy. Fractional dosing strategies should be considered early in the clinical development of future mRNA vaccines to enhance vaccine availability and pandemic preparedness.

Coagulation and inflammatory response after intramuscular or intradermal mRNA-1273 SARS-CoV-2 vaccine: secondary analysis of a randomized trial

Background

Fractional-dosed intradermal (i.d.) vaccination produces antibody concentrations above the proposed proxy for protection against severe disease as compared with intramuscular (i.m.) vaccination and may be associated with a decreased prothrombotic effect.

Objectives

To assess changes in coagulation following standard dosed i.m. or fractional-dosed i.d. (one-fifth of i.m.) mRNA-1273 SARS-CoV-2 vaccine and to determine the association between the inflammatory response and coagulation.

Methods

This study was embedded in a randomized controlled trial assessing the immunogenicity of an i.d. fractional-dosed mRNA-1273 vaccine. Healthy participants, aged 18 to 30 years, were randomized (2:1) to receive either 2 doses of i.d. or i.m. vaccine. Blood was drawn prior to first and second vaccination doses and 1 and 2 weeks after the second dose. The outcomes were changes in coagulation parameters (primary endpoint peak height of the thrombin generation curve) and inflammation (high-sensitivity C-reactive protein [hs-CRP]).

Results

One hundred twenty-three participants were included (81 i.d.; 42 i.m.). Peak height increased after vaccination (i.m., 28.8 nmol; 95% CI, 6.3-63.8; i.d., 17.3 nmol; 95% CI, 12.5-47.2) and recovered back to baseline within 2 weeks. I.m. vaccination showed a higher inflammatory response compared with i.d. vaccination (extra increase hs-CRP, 0.92 mg/L; 95% CI, 0.2-1.7). Change in endogenous thrombin potential was associated with change in hs-CRP (beta, 28.0; 95% CI, 7.6-48.3).

Conclusion

A transient increase in coagulability after mRNA-1273 SARS-CoV-2 vaccination occurred, which was associated with the inflammatory response. While i.d. administration showed antibody concentrations above the proposed proxy for protection against severe disease, it was associated with less systemic inflammation. Hence, i.d. vaccination may be safer.

Regulatory workshop on challenge strain development and GMP manufacture - A stakeholder meeting report

Within the Innovative Health Initiative (IHI) Inno4Vac CHIMICHURRI project, a regulatory workshop was organised on the development and manufacture of challenge agent strains for Controlled Human Infection Model (CHIM) studies. Developers are often uncertain about which GMP requirements or regulatory guidelines apply but should be guided by the 2022 technical white paper "Considerations on the Principles of Development and Manufacturing Qualities of Challenge Agents for Use in Human Infection Models" (published by hVIVO, Wellcome Trust, HIC-Vac consortium members). Where those recommendations cannot be met, regulators advise following the "Principles of GMP" until definitive guidelines are available. Sourcing wild-type virus isolates is a significant challenge for developers. Still, it is preferred over reverse genetics challenge strains for several reasons, including implications and regulations around genetically modified organisms (GMOs). Official informed consent guidelines for collecting isolates are needed, and the characterisation of these isolates still presents risks and uncertainty. Workshop topics included ethics, liability, standardised clinical endpoints, selection criteria, sharing of challenge agents, and addressing population heterogeneity concerning vaccine response and clinical course. The organisers are confident that the workshop discussions will contribute to advancing ethical, safe, and high-quality CHIM studies of influenza, RSV and C. difficile, including adequate regulatory frameworks.

Immunogenicity and reactogenicity of intradermal mRNA-1273 SARS-CoV-2 vaccination: a non-inferiority, randomized-controlled trial

Fractional dosing can be a cost-effective vaccination strategy to accelerate individual and herd immunity in a pandemic. We assessed the immunogenicity and safety of primary intradermal (ID) vaccination, with a 1/5th dose compared with the standard intramuscular (IM) dose of mRNA-1273 in SARS-CoV-2 naïve persons. We conducted an open-label, non-inferiority, randomized controlled trial in the Netherlands between June and December 2021. One hundred and fifty healthy and SARS-CoV-2 naïve participants, aged 18-30 years, were randomized (1:1:1) to receive either two doses of 20 µg mRNA-1273 ID with a standard needle (SN) or the Bella-mu® needle (BM), or two doses of 100 µg IM, 28 days apart. The primary outcome was non-inferiority in seroconversion rates at day 43 (D43), defined as a neutralizing antibody concentration threshold of 465 IU/mL, the lowest response in the IM group. The non-inferiority margin was set at -15%. Neutralizing antibody concentrations at D43 were 1789 (95% CI: 1488-2150) in the IM and 1263 (951-1676) and 1295 (1020-1645) in the ID-SN and ID-BM groups, respectively. The absolute difference in seroconversion proportion between fractional and standard-dose groups was -13.95% (-24.31 to -3.60) for the ID-SN and -13.04% (-22.78 to -3.31) for the ID-BM group and exceeded the predefined non-inferiority margin. Although ID vaccination with 1/5th dose of mRNA-1273 did not meet the predefined non-inferior criteria, the neutralizing antibody concentrations in these groups are far above the proposed proxy for protection against severe disease (100 IU/mL), justifying this strategy in times of vaccine scarcity to accelerate mass protection against severe disease.

Protective efficacy of short-term infection with Necator americanus hookworm larvae in healthy volunteers in the Netherlands: a single-centre, placebo-controlled, randomised, controlled, phase 1 trial

BACKGROUND

Vaccine development against hookworm is hampered by the absence of the development of protective immunity in populations repeatedly exposed to hookworm, limiting identification of mechanisms of protective immunity and new vaccine targets. Immunisation with attenuated larvae has proven effective in dogs and partial immunity has been achieved using an irradiated larvae model in healthy volunteers. We aimed to investigate the protective efficacy of immunisation with short-term larval infection against hookworm challenge.

METHODS

We did a single-centre, placebo-controlled, randomised, controlled, phase 1 trial at Leiden University Medical Center (Leiden, Netherlands). Healthy volunteers (aged 18-45 years) were recruited using advertisements on social media and in publicly accessible areas. Volunteers were randomly assigned (2:1) to receive three short-term infections with 50 infectious Necator americanus third-stage filariform larvae (50L3) or placebo. Infection was abrogated with a 3-day course of albendazole 400 mg, 2 weeks after each exposure. Subsequently all volunteers were challenged with two doses of 50L3 at a 2-week interval. The primary endpoint was egg load (geometric mean per g faeces) measured weekly between weeks 12 and 16 after first challenge, assessed in the per-protocol population, which included all randomly assigned volunteers with available data on egg counts at week 12-16 after challenge. This study is registered with ClinicalTrials.gov, NCT03702530.

FINDINGS

Between Nov 8 and Dec 14, 2018, 26 volunteers were screened, of whom 23 enrolled in the trial. The first immunisation was conducted on Dec 18, 2018. 23 volunteers were randomly assigned (15 to the intervention group and eight to the placebo group). Egg load after challenge was lower in the intervention group than the placebo group (geometric mean 571 eggs per g [range 372-992] vs 873 eggs per g [268-1484]); however, this difference was not statistically significant (p=0·10). Five volunteers in the intervention group developed a severe skin rash, which was associated with 40% reduction in egg counts after challenge (geometric mean 742 eggs per g [range 268-1484] vs 441 eggs per g [range 380-520] after challenge; p=0·0025) and associated with higher peak IgG1 titres.

INTERPRETATION

To our knowledge, this is the first study to describe a protective effect of short-term exposure to hookworm larvae and show an association with skin response, eosinophilic response, and IgG1. These findings could inform future hookworm vaccine development.

FUNDING

Dioraphte Foundation.

Strategic and scientific contributions of human challenge trials for vaccine development: facts versus fantasy

The unprecedented speed of delivery of SARS-CoV-2 pandemic vaccines has redefined the limits for all vaccine development. Beyond the aspirational 100-day timeline for tomorrow's hypothetical pandemic vaccines, there is a sense of optimism that development of other high priority vaccines can be accelerated. Early in the COVID-19 pandemic, an intense and polarised academic and public discourse arose concerning the role of human challenge trials for vaccine development. A case was made for human challenge trials as a powerful tool to establish early proof-of-concept of vaccine efficacy in humans, inform vaccine down selection, and address crucial knowledge gaps regarding transmission, pathogenesis, and immune protection. We review the track record of human challenge trials contributing to the development of vaccines for 19 different pathogens and discuss relevant limitations, barriers, and pitfalls. This Review also highlights opportunities for efforts to broaden the scope and boost the effects of human challenge trials, to accelerate all vaccine development.

Safety and infectivity of female cercariae in Schistosoma-naïve, healthy participants: a controlled human Schistosoma mansoni infection study

BACKGROUND

A controlled human infection model for schistosomiasis (CHI-S) can speed up vaccine development and provides insight into early immune responses following schistosome exposure. Recently, we established CHI-S model using single-sex male-only Schistosoma mansoni (Sm) cercariae in Schistosoma-naïve individuals. Given important differences in antigenic profile and human immune responses to schistosomes of different sex, we pioneered a single-sex female-only CHI-S model for future use in vaccine development.

METHODS

We exposed 13 healthy, Schistosoma-naïve adult participants to 10 (n = 3) or 20 (n = 10) female cercariae and followed for 20 weeks, receiving treatment with praziquantel (PZQ) 60 mg/kg at week 8 and 12 after exposure.

FINDINGS

The majority (11/13) participants reported rash and/or itch at the site of exposure, 5/13 had transient symptoms of acute schistosomiasis. Exposure to 20 cercariae led to detectable infection, defined as serum circulating anodic antigen levels >1.0 pg/mL, in 6/10 participants. Despite two rounds of PZQ treatment, 4/13 participants showed signs of persistent infection. Additional one- or three-day PZQ treatment (1 × 60 mg/kg and 3 × 60 mg/kg) or artemether did not result in cure, but over time three participants self-cured. Antibody, cellular, and cytokine responses peaked at week 4 post infection, with a mixed Th1, Th2, and regulatory profile. Cellular responses were (most) discriminative for symptoms.

INTERPRETATION

Female-only infections exhibit similar clinical and immunological profiles as male-only infections but are more resistant to PZQ treatment. This limits future use of this model and may have important implications for disease control programs.

FUNDING

European Union's Horizon 2020 (grant no. 81564).

Causal chemoprophylactic activity of cabamiquine against Plasmodium falciparum in a controlled human malaria infection: a randomised, double-blind, placebo-controlled study in the Netherlands

BACKGROUND

Cabamiquine is a novel antimalarial that inhibits Plasmodium falciparum translation elongation factor 2. We investigated the causal chemoprophylactic activity and dose-exposure-response relationship of single oral doses of cabamiquine following the direct venous inoculation (DVI) of P falciparum sporozoites in malaria-naive, healthy volunteers.

METHODS

This was a phase 1b, randomised, double-blind, placebo-controlled, adaptive, dose-finding, single-centre study performed in Leiden, Netherlands. Malaria-naive, healthy adults aged 18-45 years were divided into five cohorts and randomly assigned (3:1) to receive cabamiquine or placebo. Randomisation was done by an independent statistician using codes in a permuted block schedule with a block size of four. Participants, investigators, and study personnel were masked to treatment allocation. A single, oral dose regimen of cabamiquine (200, 100, 80, 60, or 30 mg) or matching placebo was administered either at 2 h (early liver-stage) or 96 h (late liver-stage) after DVI. The primary endpoints based on a per-protocol analysis set were the number of participants who developed parasitaemia within 28 days of DVI, time to parasitaemia, number of participants with documented parasite blood-stage growth, clinical symptoms of malaria, and exposure-efficacy modelling. The impact of cabamiquine on liver stages was evaluated indirectly by the appearance of parasitaemia in the blood. The Clopper-Pearson CI (nominal 95%) was used to express the protection rate. The secondary outcomes were safety and tolerability, assessed in those who had received DVI and were administered one dose of the study intervention. The trial was prospectively registered on ClinicalTrials.gov (NCT04250363).

FINDINGS

Between Feb 17, 2020 and April 29, 2021, 39 healthy participants were enrolled (early liver-stage: 30 mg [n=3], 60 mg [n=6], 80 mg [n=6], 100 mg [n=3], 200 mg [n=3], pooled placebo [n=6]; late liver-stage: 60 mg [n=3], 100 mg [n=3], 200 mg [n=3], pooled placebo [n=3]). A dose-dependent causal chemoprophylactic effect was observed, with four (67%) of six participants in the 60 mg, five (83%) of six participants in the 80 mg, and all three participants in the 100 and 200 mg cabamiquine dose groups protected from parasitaemia up to study day 28, whereas all participants in the pooled placebo and 30 mg cabamiquine dose group developed parasitaemia. A single, oral dose of 100 mg cabamiquine or higher provided 100% protection against parasitaemia when administered during early or late liver-stage malaria. The median time to parasitaemia in those with early liver-stage malaria was prolonged to 15, 22, and 24 days for the 30, 60, and 80 mg dose of cabamiquine, respectively, compared with 10 days for the pooled placebo. All participants with positive parasitaemia showed documented blood-stage parasite growth, apart from one participant in the pooled placebo group and one participant in the 30 mg cabamiquine group. Most participants did not exhibit any malaria symptoms in both the early and late liver-stage groups, and those reported were mild in severity. A positive dose-exposure-efficacy relationship was established across exposure metrics. The median maximum concentration time was 1-6 h, with a secondary peak observed between 6 h and 12 h in all cabamiquine dose groups (early liver-stage). All cabamiquine doses were safe and well tolerated. Overall, 26 (96%) of 27 participants in the early liver-stage group and ten (83·3%) of 12 participants in the late liver-stage group reported at least one treatment-emergent adverse event (TEAE) with cabamiquine or placebo. Most TEAEs were of mild severity, transient, and resolved without sequelae. The most frequently reported cabamiquine-related TEAE was headache. No dose-related trends were observed in the incidence, severity, or causality of TEAEs.

INTERPRETATION

The results from this study show that cabamiquine has a dose-dependent causal chemoprophylactic activity. Together with previously demonstrated activity against the blood stages combined with a half-life of more than 150 h, these results indicate that cabamiquine could be developed as a single-dose monthly regimen for malaria prevention.

FUNDING

The healthcare business of Merck KGaA, Darmstadt, Germany.

Chemically augmented malaria sporozoites display an altered immunogenic profile

Despite promising results in malaria-naïve individuals, whole sporozoite (SPZ) vaccine efficacy in malaria-endemic settings has been suboptimal. Vaccine hypo-responsiveness due to previous malaria exposure has been posited as responsible, indicating the need for SPZ vaccines of increased immunogenicity. To this end, we here demonstrate a proof-of-concept for altering SPZ immunogenicity, where supramolecular chemistry enables chemical augmentation of the parasite surface with a TLR7 agonist-based adjuvant (SPZ-SAS(CL307)). In vitro, SPZ-SAS(CL307) remained well recognized by immune cells and induced a 35-fold increase in the production of pro-inflammatory IL-6 (p < 0.001). More promisingly, immunization of mice with SPZ-SAS(CL307) yielded improved SPZ-specific IFN-γ production in liver-derived NK cells (percentage IFN-γ+ cells 11.1 ± 1.8 vs. 9.4 ± 1.5%, p < 0.05), CD4+ T cells (4.7 ± 4.3 vs. 1.8 ± 0.7%, p < 0.05) and CD8+ T cells (3.6 ± 1.4 vs. 2.5 ± 0.9%, p < 0.05). These findings demonstrate the potential of using chemical augmentation strategies to enhance the immunogenicity of SPZ-based malaria vaccines.

Establishing a single-sex controlled human Schistosoma mansoni infection model for Uganda: protocol for safety and dose-finding trial

Control of schistosomiasis depends on a single drug, praziquantel, with variable cure rates, high reinfection rates, and risk of drug resistance. A vaccine could transform schistosomiasis control. Preclinical data show that vaccine development is possible, but conventional vaccine efficacy trials require high incidence, long-term follow-up, and large sample size. Controlled human infection studies (CHI) can provide early efficacy data, allowing the selection of optimal candidates for further trials. A Schistosoma CHI has been established in the Netherlands but responses to infection and vaccines differ in target populations in endemic countries. We aim to develop a CHI for Schistosoma mansoni in Uganda to test candidate vaccines in an endemic setting. This is an open-label, dose-escalation trial in two populations: minimal, or intense, prior Schistosoma exposure. In each population, participants will be enrolled in sequential dose-escalating groups. Initially, three volunteers will be exposed to 10 cercariae. If all show infection, seven more will be exposed to the same dose. If not, three volunteers in subsequent groups will be exposed to higher doses (20 or 30 cercariae) following the same algorithm, until all 10 volunteers receiving a particular dose become infected, at which point the study will be stopped for that population. Volunteers will be followed weekly after infection until CAA positivity or to 12 weeks. Once positive, they will be treated with praziquantel and followed for one year. The trial registry number is ISRCTN14033813 and all approvals have been obtained. The trial will be subjected to monitoring, inspection, and/or audits.

Perspective on Schistosomiasis Drug Discovery: Highlights from a Schistosomiasis Drug Discovery Workshop at Wellcome Collection, London, September 2022

In September 2022, the Drug Discovery Unit at the University of Dundee, UK, organised an international meeting at the Wellcome Collection in London to explore the current clinical situation and challenges associated with treating schistosomiasis. The aim of this meeting was to discuss the need for new treatments in view of the clinical situation and to ascertain what the key requirements would be for any potential new anti-schistosomals. This information will be essential to inform ongoing drug discovery efforts for schistosomiasis. We also discussed the potential drug discovery pathway and associated criteria for progressing compounds to the clinic. To date, praziquantel (PZQ) is the only drug available to treat all species causing schistosomiasis, but it is often unable to completely clear parasites from an infected patient, partially due to its inactivity against juvenile worms. PZQ-mediated mass drug administration campaigns conducted in endemic areas (e.g., sub-Saharan Africa, where schistosomiasis is primarily prevalent) have contributed to reducing the burden of disease but will not eliminate the disease as a public health problem. The potential for Schistosoma to develop resistance towards PZQ, as the sole treatment available, could become a concern. Consequently, new anthelmintic medications are urgently needed, and this Perspective aims to capture some of the learnings from our discussions on the key criteria for new treatments.

Pulmonary inflammation promoted by type-2 dendritic cells is a feature of human and murine schistosomiasis

Schistosomiasis is a parasitic disease affecting over 200 million people in multiple organs, including the lungs. Despite this, there is little understanding of pulmonary immune responses during schistosomiasis. Here, we show type-2 dominated lung immune responses in both patent (egg producing) and pre-patent (larval lung migration) murine Schistosoma mansoni (S. mansoni) infection. Human pre-patent S. mansoni infection pulmonary (sputum) samples revealed a mixed type-1/type-2 inflammatory cytokine profile, whilst a case-control study showed no significant pulmonary cytokine changes in endemic patent infection. However, schistosomiasis induced expansion of pulmonary type-2 conventional dendritic cells (cDC2s) in human and murine hosts, at both infection stages. Further, cDC2s were required for type-2 pulmonary inflammation in murine pre-patent or patent infection. These data elevate our fundamental understanding of pulmonary immune responses during schistosomiasis, which may be important for future vaccine design, as well as for understanding links between schistosomiasis and other lung diseases.

Imaging as a (pre)clinical tool in parasitology

Imaging of parasites is central to diagnosis of many parasitic diseases and has thus far played an important role in the development of antiparasitic strategies. The development of novel imaging technologies has revolutionized medicine in fields other than parasitology and has also opened up new avenues for the visualization of parasites. Here we review the role imaging technology has played so far in parasitology and how it may spur further advancement. We point out possibilities to improve current microscopy-based diagnostic methods and how to extend them with radiological imaging modalities. We also highlight in vivo tracking of parasites as a readout for efficacy of new antiparasitic strategies and as a source of fundamental insights for rational design.

A Systematic Review of Human Challenge Trials, Designs, and Safety

BACKGROUND

Few studies have assessed participant safety in human challenge trials (HCTs). Key questions regarding HCTs include how risky such trials have been, how often adverse events (AEs) and serious adverse events (SAEs) occur, and whether risk mitigation measures have been effective.

METHODS

A systematic search of PubMed and PubMed Central for articles reporting on results of HCTs published between 1980 and 2021 was performed and completed by 7 October 2021.

RESULTS

Of 2838 articles screened, 276 were reviewed in full. A total of 15 046 challenged participants were described in 308 studies that met inclusion criteria; 286 (92.9%) of these studies reported mitigation measures used to minimize risk to the challenge population. Among 187 studies that reported on SAEs, 0.2% of participants experienced at least 1 challenge-related SAE. Among 94 studies that graded AEs by severity, challenge-related AEs graded "severe" were reported by between 5.6% and 15.8% of participants. AE data were provided as a range to account for unclear reporting. Eighty percent of studies published after 2010 were registered in a trials database.

CONCLUSIONS

HCTs are increasingly common and used for an expanding list of diseases. Although AEs occur, severe AEs and SAEs are rare. Reporting has improved over time, though not all papers provide a comprehensive report of relevant health impacts. We found very few severe symptoms or SAEs in studies that reported them, but many HCTs did not report relevant safety data. This study was preregistered on PROSPERO as CRD42021247218.

Quantifying the Impact of Signal-to-background Ratios on Surgical Discrimination of Fluorescent Lesions

PURPOSE

Surgical fluorescence guidance has gained popularity in various settings, e.g., minimally invasive robot-assisted laparoscopic surgery. In pursuit of novel receptor-targeted tracers, the field of fluorescence-guided surgery is currently moving toward increasingly lower signal intensities. This highlights the importance of understanding the impact of low fluorescence intensities on clinical decision making. This study uses kinematics to investigate the impact of signal-to-background ratios (SBR) on surgical performance.

METHODS

Using a custom grid exercise containing hidden fluorescent targets, a da Vinci Xi robot with Firefly fluorescence endoscope and ProGrasp and Maryland forceps instruments, we studied how the participants' (N = 16) actions were influenced by the fluorescent SBR. To monitor the surgeon's actions, the surgical instrument tip was tracked using a custom video-based tracking framework. The digitized instrument tracks were then subjected to multi-parametric kinematic analysis, allowing for the isolation of various metrics (e.g., velocity, jerkiness, tortuosity). These were incorporated in scores for dexterity (Dx), decision making (DM), overall performance (PS) and proficiency. All were related to the SBR values.

RESULTS

Multi-parametric analysis showed that task completion time, time spent in fluorescence-imaging mode and total pathlength are metrics that are directly related to the SBR. Below SBR 1.5, these values substantially increased, and handling errors became more frequent. The difference in Dx and DM between the targets that gave SBR < 1.50 and SBR > 1.50, indicates that the latter group generally yields a 2.5-fold higher Dx value and a threefold higher DM value. As these values provide the basis for the PS score, proficiency could only be achieved at SBR > 1.55.

CONCLUSION

By tracking the surgical instruments we were able to, for the first time, quantitatively and objectively assess how the instrument positioning is impacted by fluorescent SBR. Our findings suggest that in ideal situations a minimum SBR of 1.5 is required to discriminate fluorescent lesions, a substantially lower value than the SBR 2 often reported in literature.

Sporozoite immunization: innovative translational science to support the fight against malaria

INTRODUCTION

Malaria, a devastating febrile illness caused by protozoan parasites, sickened 247,000,000 people in 2021 and killed 619,000, mostly children and pregnant women in sub-Saharan Africa. A highly effective vaccine is urgently needed, especially for Plasmodium falciparum (Pf), the deadliest human malaria parasite.

AREAS COVERED

Sporozoites (SPZ), the parasite stage transmitted by Anopheles mosquitoes to humans, are the only vaccine immunogen achieving >90% efficacy against Pf infection. This review describes >30 clinical trials of PfSPZ vaccines in the U.S.A., Europe, Africa, and Asia, based on first-hand knowledge of the trials and PubMed searches of 'sporozoites,' 'malaria,' and 'vaccines.'

EXPERT OPINION

First generation (radiation-attenuated) PfSPZ vaccines are safe, well tolerated, 80-100% efficacious against homologous controlled human malaria infection (CHMI) and provide 18-19 months protection without boosting in Africa. Second generation chemo-attenuated PfSPZ are more potent, 100% efficacious against stringent heterologous (variant strain) CHMI, but require a co-administered drug, raising safety concerns. Third generation, late liver stage-arresting, replication competent (LARC), genetically-attenuated PfSPZ are expected to be both safe and highly efficacious. Overall, PfSPZ vaccines meet safety, tolerability, and efficacy requirements for protecting pregnant women and travelers exposed to Pf in Africa, with licensure for these populations possible within 5 years. Protecting children and mass vaccination programs to block transmission and eliminate malaria are long-term objectives.

Chemically Enhanced Immunogenicity of Bacteria by Supramolecular Functionalization with an Adjuvant

Many pathogens blunt immune responses because they lack immunogenic structural features, which typically results in disease. Here, we show evidence suggesting that pathogen immunogenicity can be chemically enhanced. Using supramolecular host-guest chemistry, we complexed onto the surface of a poorly immunogenic bacterium (Staphylococcus aureus) a TLR7 agonist-based adjuvant. "Adjuvanted" bacteria were readily recognized by macrophages and induced a more pro-inflammatory immunophenotype. Future applications of this concept could yield treatment modalities that bolster the immune system's response to pathogenic microbes.

A comparison of two Fendrix hepatitis B vaccination schedules in patients with inflammatory bowel disease

Systemic immunosuppressive therapy (IS) renders patients with inflammatory bowel disease (IBD) vulnerable to fulminant hepatitis B virus (HBV) infection. Seroprotection against HBV through a full vaccination scheme is preferably obtained before IS is initiated, but often conflicts with the clinical need to initiate therapy rapidly. Consequently, the vast majority of patients will use IS during booster vaccinations. In this retrospective cohort study, we examined the serological response after a modified vaccination schedule which includes an initial double dose of Fendrix in patients with IBD and compared the results with the serological responses of patients with IBD who received the standard schedule. Seroprotection rates were 86.2 % and 88.9 % in the modified and standard schedule groups respectively. One-third of patients obtained seroprotection after only one double dose vaccine. A double dose may be considered in patients with IBD at high short-term risk of HBV infection when a rapid protective response is warranted.

Immune Determinants of Viral Clearance in Hospitalised COVID-19 Patients: Reduced Circulating Naïve CD4+ T Cell Counts Correspond with Delayed Viral Clearance

Virus-specific cellular and humoral responses are major determinants for protection from critical illness after SARS-CoV-2 infection. However, the magnitude of the contribution of each of the components to viral clearance remains unclear. Here, we studied the timing of viral clearance in relation to 122 immune parameters in 102 hospitalised patients with moderate and severe COVID-19 in a longitudinal design. Delayed viral clearance was associated with more severe disease and was associated with higher levels of SARS-CoV-2-specific (neutralising) antibodies over time, increased numbers of neutrophils, monocytes, basophils, and a range of pro-inflammatory cyto-/chemokines illustrating ongoing, partially Th2 dominating, immune activation. In contrast, early viral clearance and less critical illness correlated with the peak of neutralising antibodies, higher levels of CD4 T cells, and in particular naïve CD4+ T cells, suggesting their role in early control of SARS-CoV-2 possibly by proving appropriate B cell help. Higher counts of naïve CD4+ T cells also correlated with lower levels of MIF, IL-9, and TNF-beta, suggesting an indirect role in averting prolonged virus-induced tissue damage. Collectively, our data show that naïve CD4+ T cell play a critical role in rapid viral T cell control, obviating aberrant antibody and cytokine profiles and disease deterioration. These data may help in guiding risk stratification for severe COVID-19.

Immunological profiles associated with distinct parasitemic states in volunteers undergoing malaria challenge in Gabon

Controlled human malaria infection (CHMI) using cryopreserved non-attenuated Plasmodium falciparum sporozoites (PfSPZ) offers a unique opportunity to investigate naturally acquired immunity (NAI). By analyzing blood samples from 5 malaria-naïve European and 20 African adults with lifelong exposure to malaria, before, 5, and 11 days after direct venous inoculation (DVI) with Sanaria^R PfSPZ Challenge, we assessed the immunological patterns associated with control of microscopic and submicroscopic parasitemia. All (5/5) European individuals developed parasitemia as defined by thick blood smear (TBS), but 40% (8/20) of the African individuals controlled their parasitemia, and therefore remained thick blood smear-negative (TBS⁻ Africans). In the TBS⁻ Africans, we observed higher baseline frequencies of CD4⁺ T cells producing interferon-gamma (IFNγ) that significantly decreased 5 days after PfSPZ DVI. The TBS⁻ Africans, which represent individuals with either very strong and rapid blood-stage immunity or with immunity to liver stages, were stratified into subjects with sub-microscopic parasitemia (TBS^-PCR⁺) or those with possibly sterilizing immunity (TBS⁻PCR⁻). Higher frequencies of IFNγ⁺TNF⁺CD8⁺ γδ T cells at baseline, which later decreased within five days after PfSPZ DVI, were associated with those who remained TBS⁻PCR⁻. These findings suggest that naturally acquired immunity is characterized by different cell types that show varying strengths of malaria parasite control. While the high frequencies of antigen responsive IFNγ⁺CD4⁺ T cells in peripheral blood keep the blood-stage parasites to a sub-microscopic level, it is the IFNγ⁺TNF⁺CD8⁺ γδ T cells that are associated with either immunity to the liver-stage, or rapid elimination of blood-stage parasites.

Ethical and practical considerations arising from community consultation on implementing controlled human infection studies using Schistosoma mansoni in Uganda

Issues related to controlled human infection studies using Schistosoma mansoni (CHI-S) were explored to ensure the ethical and voluntary participation of potential CHI-S volunteers in an endemic setting in Uganda. We invited volunteers from a fishing community and a tertiary education community to guide the development of informed consent procedures. Consultative group discussions were held to modify educational materials on schistosomiasis, vaccines and the CHI-S model and similar discussions were held with a test group. With both groups, a mock consent process was conducted. Fourteen in-depth key informant interviews and three group discussions were held to explore perceptions towards participating in a CHI-S. Most of the participants had not heard of the CHI-S. Willingness to take part depended on understanding the study procedures and the consenting process. Close social networks were key in deciding to take part. The worry of adverse effects was cited as a possible hindrance to taking part. Volunteer time compensation was unclear for a CHI-S. Potential volunteers in these communities are willing to take part in a CHI-S. Community engagement is needed to build trust and time must be taken to share study procedures and ensure understanding of key messages.

COVID-19 vaccine dose sparing: strategies to improve vaccine equity and pandemic preparedness

Despite tremendous efforts, worldwide COVID-19 vaccination coverage is lagging. Dose-sparing strategies for COVID-19 vaccines can increase vaccine availability to address the global crisis. Several clinical trials evaluating dose sparing are currently underway. However, to rapidly provide solid scientific justification for different dose-sparing strategies, joint coordinated action involving both public and private parties is needed. In this Viewpoint, we provide examples of approaches to vaccine dose-sparing that have previously been evaluated in clinical trials to improve vaccine availability and reflect on the origin of their funding. With a focus on the current COVID-19 pandemic, we stress the need for expedited testing of vaccine dose-sparing strategies in endemic or epidemic infectious diseases. However, we argue that the establishment of a mechanism through which dose-sparing opportunities are systematically identified, scientifically tested, and ultimately implemented will prove to be valuable beyond the current pandemic for infectious diseases product development and pandemic preparedness in the future.

Assessment of Risks Associated With Severe Acute Respiratory Syndrome Coronavirus 2 Experimental Human Infection Studies

Controlled human infection (CHI) models for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been proposed as a tool to accelerate the development of vaccines and drugs. Such models carry inherent risks. Participants may develop severe disease or complications after deliberate infection. Prolonged isolation may negatively impact their well-being. Through secondary infection of study personnel or participant household contacts, the experimental virus strain may cause a community outbreak. We identified risks associated with such a SARS-CoV-2 CHI model and assessed their likelihood and impact and propose strategies that mitigate these risks. In this report, we show that risks can be minimized with proper risk mitigation strategies; the residual risk, however, should be weighed carefully against the scientific and social values of such a CHI model.

A double-blind, placebo-controlled phase 1/2a trial of the genetically attenuated malaria vaccine PfSPZ-GA1

Immunization with attenuated Plasmodium sporozoites can induce protection against malaria infection, as shown by Plasmodium falciparum (Pf) sporozoites attenuated by radiation in multiple clinical trials. As alternative attenuation strategy with a more homogeneous population of Pf sporozoites (PfSPZ), genetically engineered Plasmodium berghei sporozoites (SPZ) lacking the genes b9 and slarp induced sterile protection against malaria in mice. Consequently, PfSPZ-GA1 Vaccine, a Pf identical double knockout (Pf∆b9∆slarp), was generated as a genetically attenuated malaria parasite vaccine and tested for safety, immunogenicity, and preliminary efficacy in malaria-naïve Dutch volunteers. Dose-escalation immunizations up to 9.0 × 10⁵ PfSPZ of PfSPZ-GA1 Vaccine were well tolerated without breakthrough blood-stage infection. Subsequently, groups of volunteers were immunized three times by direct venous inoculation with cryopreserved PfSPZ-GA1 Vaccine (9.0 × 10⁵ or 4.5 × 10⁵ PfSPZ, N = 13 each), PfSPZ Vaccine (radiation-attenuated PfSPZ, 4.5 × 10⁵ PfSPZ, N = 13), or normal saline placebo at 8-week intervals, followed by exposure to mosquito bite controlled human malaria infection (CHMI). After CHMI, 3 of 25 volunteers from both PfSPZ-GA1 groups were sterilely protected, and the remaining 17 of 22 showed a patency ≥9 days (median patency in controls, 7 days; range, 7 to 9). All volunteers in the PfSPZ Vaccine control group developed parasitemia (median patency, 9 days; range, 7 to 12). Immunized groups exhibited a significant, dose-related increase in anti-Pf circumsporozoite protein (CSP) antibodies and Pf-specific interferon-γ (IFN-γ)-producing T cells. Although no definite conclusion can be drawn on the potential strength of protective efficacy of PfSPZ-GA1 Vaccine, the favorable safety profile and induced immune responses by PfSPZ-GA1 Vaccine warrant further clinical evaluation.

Interventional nuclear medicine: "click" chemistry as an in vivo targeting strategy for imaging microspheres and bacteria

AIM

Pre-targeting is a proven strategy for in vivo delivery of a diagnostic or therapeutic payload. The pre-targeting concept can be realized through various conjugation strategies, one of which is based on copper-free "click" chemistry. Copper-free click reactions have shown in vivo potential for imaging and radionuclide therapy, but this conjugation strategy has not yet been explored in combination with microspheres or unicellular organisms. This study aims to evaluate the in vivo efficacy of strain-promoted azide-alkyne cycloaddition (SPAAC) reactions to achieve imaging and targeting of azide-functionalized macro-aggregated albumin (MAA) microspheres and Staphylococcus aureus bacteria.

METHODS

MAA microspheres (diameter 10-90 μm) were functionalized with a biorthogonal Cy5 fluorophore, bearing an azide functionality (N3), to generate MAA-Cy5-N3. S. aureus (diameter ∼1 μm) were functionalized with 99mTc-UBI29-41-Cy5-N3, generating S. aureus-99mTc-UBI29-41-Cy5-N3. In situ and in vitro click conjugation on the -N3 moieties was studied for 20 h using a radioactivity-based assay and fluorescence microscopy. For in vivo validation, both primary entities, radiolabeled with 99mTc, were deposited into the microvasculature of the liver via intrasplenic injections. Secondary targeting was realized following the intravenous administration of indium-111-radiolabeled diethylenetriaminepentaacetic acid-dibenzocyclooctyne (111In-DTPA-DBCO). To assess click reaction efficiency in vivo, 99mTc and 111In-biodistributions were measured (SPECT and %ID g-1). Use of 111In-DTPA-DBCO in mice without MAA deposits or mice infected with non-functionalized S. aureus served as controls. Ex vivo confocal fluorescence imaging was carried out in excised tissues to confirm the presence of functionalized MAA and bacteria.

RESULTS

In vitro data confirmed effective click reactions on both the MAA particles and the bacterial membrane. SPECT imaging and biodistribution studies revealed significantly (p < 0.05) increased accumulation of 111In-DTPA-DBCO at the sites where MAA-Cy5-N3 (7.5 ± 1.5%ID g-1vs. 3.5 ± 0.5%ID g-1 in control mice) and S. aureus-99mTc-UBI29-41-Cy5-N3 (9.3 ± 1.3%ID g-1vs. 6.0 ± 0.5%ID g-1 in control mice) resided. Ex vivo fluorescence imaging confirmed the presence of either functionalized MAA or S. aureus in excised spleens and livers of mice.

CONCLUSION

Copper-free click chemistry between a DBCO moiety and Cy5-N3-functionalized microspheres or bacterial entities in the liver can be used to realize in vivo imaging and targeting.

Immunological Considerations for Schistosoma Vaccine Development: Transitioning to Endemic Settings

Despite mass drug administration programmes with praziquantel, the prevalence of schistosomiasis remains high. A vaccine is urgently needed to control transmission of this debilitating disease. As some promising schistosomiasis vaccine candidates are moving through pre-clinical and clinical testing, we review the immunological challenges that these vaccine candidates may encounter in transitioning through the clinical trial phases in endemic settings. Prior exposure of the target population to schistosomes and other infections may impact vaccine response and efficacy and therefore requires considerable attention. Schistosomes are known for their potential to induce T-reg/IL-10 mediated immune suppression in populations which are chronically infected. Moreover, endemicity of schistosomiasis is focal whereby target and trial populations may exhibit several degrees of prior exposure as well as in utero exposure which may increase heterogeneity of vaccine responses. The age dependent distribution of exposure and development of acquired immunity, and general differences in the baseline immunological profile, adds to the complexity of selecting suitable trial populations. Similarly, prior or concurrent infections with other parasitic helminths, viral and bacterial infections, may alter immunological responses. Consequently, treatment of co-infections may benefit the immunogenicity of vaccines and may be considered despite logistical challenges. On the other hand, viral infections leave a life-long immunological imprint on the human host. Screening for serostatus may be needed to facilitate interpretation of vaccine responses. Co-delivery of schistosome vaccines with PZQ is attractive from a perspective of implementation but may complicate the immunogenicity of schistosomiasis vaccines. Several studies have reported PZQ treatment to induce both transient and long-term immuno-modulatory effects as a result of tegument destruction, worm killing and subsequent exposure of worm antigens to the host immune system. These in turn may augment or antagonize vaccine immunogenicity. Understanding the complex immunological interactions between vaccine, co-infections or prior exposure is essential in early stages of clinical development to facilitate phase 3 clinical trial design and implementation policies. Besides well-designed studies in different target populations using schistosome candidate vaccines or other vaccines as models, controlled human infections could also help identify markers of immune protection in populations with different disease and immunological backgrounds.

Cyclodextrin/Adamantane-Mediated Targeting of Inoculated Bacteria in Mice

Cyclodextrin (CD)-based host–guest interactions with adamantane (Ad) have demonstrated use for functionalizing living cells in vitro. The next step in this supramolecular functionalization approach is to explore the concept to deliver chemical cargo to living cells in vivo, e.g., inoculated bacteria, in order to study their dissemination. We validated this concept in two rodent Staphylococcus aureus models. Bacteria (1 × 10⁸ viable S. aureus) were inoculated by (1) intramuscular injection or (2) intrasplenic injection followed by dissemination throughout the liver. The bacteria were prefunctionalized with ^99mTc-UBI_29–41-Ad₂ (primary vector), which allowed us to both determine the bacterial load and create an in vivo target for the secondary host-vector (24 h post-inoculation). The secondary vector, i.e., chemical cargo delivery system, made use of a ¹¹¹In-Cy5_0.5CD₉PIBMA₃₉ polymer that was administered intravenously. Bacteria-specific cargo delivery as a result of vector complexation was evaluated by dual-isotope SPECT imaging and biodistribution studies (¹¹¹In), and by fluorescence (Cy5); these evaluations were performed 4 h post-injection of the secondary vector. Mice inoculated with nonfunctionalized S. aureus and mice without an infection served as controls. Dual-isotope SPECT imaging demonstrated that ¹¹¹In-Cy5_0.5CD₉PIBMA₃₉ colocalized with ^99mTc-UBI_29–41-Ad₂-labeled bacteria in both muscle and liver. In inoculated muscle, a 2-fold higher uptake level (3.2 ± 1.0%ID/g) was noted compared to inoculation with nonfunctionalized bacteria (1.9 ± 0.4%ID/g), and a 16-fold higher uptake level compared to noninfected muscle (0.2 ± 0.1%ID/g). The hepatic accumulation of the host-vector was nearly 10-fold higher (27.1 ± 11.1%ID/g) compared to the noninfected control (2.7 ± 0.3%ID/g; p < 0.05). Fluorescence imaging of the secondary vector corroborated SPECT-imaging and biodistribution findings. We have demonstrated that supramolecular host–guest complexation can be harnessed to achieve an in vivo cargo delivery strategy, using two different bacterial models in soft tissue and liver. This proof-of-principle study paves a path toward developing innovative drug delivery concepts via cell functionalization techniques.

Specificity of the Point-of-Care Urine Strip Test for Schistosoma Circulating Cathodic Antigen (POC-CCA) Tested in Non-Endemic Pregnant Women and Young Children

The point-of-care urine based strip test for the detection of circulating cathodic antigen (POC-CCA) in schistosome infections is a frequently used tool for diagnosis and mapping of Schistosoma mansoni in school-aged children. Because of its ease of use, the test is increasingly applied to adults and preschool-aged children (PSAC), but its performance has not been specifically evaluated in these target groups. Recent observations have raised concerns about possible reduced specificity, in particular in pregnant women (PW) and PSAC. We thus explored specificity of the POC-CCA urine strip test (Rapid Medical Diagnostics, Pretoria, South Africa) in a non-endemic, nonexposed population of 47 healthy nonpregnant adults (NPAs), 52 PW, and 58 PSAC. A total of 157 urines were tested with POC-CCA, of which five (10.6%) NPAs, 17 (32.7%) PW, and 27 (46.5%) PSAC were positive. The highest scores were found in the youngest babies, with an infant of 9 months being the oldest positive case. On measuring pH, it appeared that all POC-CCA strongly positive urines were acidic (pH range 5-5.5), whereas addition of pH-neutral buffer to a subsample reversed the false positivity. We conclude that the POC-CCA test has reduced specificity in PW and infants younger than 9 months, but that the false positivity might be eliminated by modifications in the buffers used in the test.

Building momentum for malaria vaccine research and development: key considerations

To maintain momentum towards improved malaria control and elimination, a vaccine would be a key addition to the intervention toolkit. Two approaches are recommended: (1) promote the development and short to medium term deployment of first generation vaccine candidates and (2) support innovation and discovery to identify and develop highly effective, long-lasting and affordable next generation malaria vaccines.

Dynamics of the bacterial gut microbiota during controlled human infection with Necator americanus larvae

Hookworms are soil-transmitted helminths that use immune-evasive strategies to persist in the human duodenum where they are responsible for anemia and protein loss. Given their location and immune regulatory effects, hookworms likely impact the bacterial microbiota. However, microbiota studies struggle to deconvolute the effect of hookworms from confounders such as coinfections and malnutrition. We thus used an experimental human hookworm infection model to explore temporal changes in the gut microbiota before and during hookworm infection. Volunteers were dermally exposed to cumulative dosages of 50, 100 or 150 L3 Necator americanus larvae. Fecal samples were collected for microbiota profiling through 16S rRNA gene amplicon sequencing at weeks zero, four, eight, fourteen and twenty. During the acute infection phase (trial week zero to eight) no changes in bacterial diversity were detected. During the established infection phase (trial week eight to twenty), bacterial richness (Chao1, p = .0174) increased significantly over all volunteers. No relation was found between larval dosage and diversity, stability or relative abundance of individual bacterial taxa. GI symptoms were associated with an unstable microbiota during the first eight weeks and rapid recovery at week twenty. Barnesiella, amongst other taxa, was more abundant in volunteers with more GI symptoms throughout the study. In conclusion, this study showed that clinical GI symptoms following N. americanus infection are associated with temporary microbiota instability and relative abundance of specific bacterial taxa. These results suggest a possible role of hookworm-induced enteritis on microbiota stability.

Judging the social value of controlled human infection studies

In controlled human infection (CHI) studies, investigators deliberately infect healthy individuals with pathogens in order to study mechanisms of disease or obtain preliminary efficacy data on investigational vaccines and medicines. CHI studies offer a fast and cost-effective way of generating new scientific insights, prioritizing investigational products for clinical testing, and reducing the risk that large numbers of people are exposed to ineffective or harmful substances in research or in practice. Yet depending on the pathogen, CHI studies can involve significant risks or burdens for participants, pose risks to individuals or communities not involved in the research, and lead to public controversy. It is therefore essential to ensure that the risks of CHI studies are justified by their social value-that is, their potential to generate benefits for society-and that public trust can be maintained. In this paper, we aim to clarify how research sponsors, research ethics committees and other reviewers should judge the social value of CHI studies. We develop a list of relevant considerations for making social value judgments based on the standard view of social value. We then use this list to discuss the example of potentially conducting dengue virus CHI studies in endemic settings. We argue that dengue virus CHI studies in endemic settings would fall on the higher end of the spectrum of social value, mostly because of their potential to redirect all fields of future dengue research. Drawing on this discussion, we derive several general recommendations for how reviewers should judge the social value of CHI studies.

Effect of Remdesivir vs Standard Care on Clinical Status at 11 Days in Patients With Moderate COVID-19: A Randomized Clinical Trial

IMPORTANCE

Remdesivir demonstrated clinical benefit in a placebo-controlled trial in patients with severe coronavirus disease 2019 (COVID-19), but its effect in patients with moderate disease is unknown.

OBJECTIVE

To determine the efficacy of 5 or 10 days of remdesivir treatment compared with standard care on clinical status on day 11 after initiation of treatment.

DESIGN, SETTING, AND PARTICIPANTS

Randomized, open-label trial of hospitalized patients with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and moderate COVID-19 pneumonia (pulmonary infiltrates and room-air oxygen saturation >94%) enrolled from March 15 through April 18, 2020, at 105 hospitals in the United States, Europe, and Asia. The date of final follow-up was May 20, 2020.

INTERVENTIONS

Patients were randomized in a 1:1:1 ratio to receive a 10-day course of remdesivir (n = 197), a 5-day course of remdesivir (n = 199), or standard care (n = 200). Remdesivir was dosed intravenously at 200 mg on day 1 followed by 100 mg/d.

MAIN OUTCOMES AND MEASURES

The primary end point was clinical status on day 11 on a 7-point ordinal scale ranging from death (category 1) to discharged (category 7). Differences between remdesivir treatment groups and standard care were calculated using proportional odds models and expressed as odds ratios. An odds ratio greater than 1 indicates difference in clinical status distribution toward category 7 for the remdesivir group vs the standard care group.

RESULTS

Among 596 patients who were randomized, 584 began the study and received remdesivir or continued standard care (median age, 57 [interquartile range, 46-66] years; 227 [39%] women; 56% had cardiovascular disease, 42% hypertension, and 40% diabetes), and 533 (91%) completed the trial. Median length of treatment was 5 days for patients in the 5-day remdesivir group and 6 days for patients in the 10-day remdesivir group. On day 11, patients in the 5-day remdesivir group had statistically significantly higher odds of a better clinical status distribution than those receiving standard care (odds ratio, 1.65; 95% CI, 1.09-2.48; P = .02). The clinical status distribution on day 11 between the 10-day remdesivir and standard care groups was not significantly different (P = .18 by Wilcoxon rank sum test). By day 28, 9 patients had died: 2 (1%) in the 5-day remdesivir group, 3 (2%) in the 10-day remdesivir group, and 4 (2%) in the standard care group. Nausea (10% vs 3%), hypokalemia (6% vs 2%), and headache (5% vs 3%) were more frequent among remdesivir-treated patients compared with standard care.

CONCLUSIONS AND RELEVANCE

Among patients with moderate COVID-19, those randomized to a 10-day course of remdesivir did not have a statistically significant difference in clinical status compared with standard care at 11 days after initiation of treatment. Patients randomized to a 5-day course of remdesivir had a statistically significant difference in clinical status compared with standard care, but the difference was of uncertain clinical importance.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04292730.

Money-oriented risk-takers or deliberate decision-makers: a cross-sectional survey study of participants in controlled human infection trials

OBJECTIVE

To quantitatively investigate the motivations, decision-making and experience of participants in controlled human infection (CHI) studies.

DESIGN

Cross-sectional descriptive survey study.

SETTING

Previous participants of CHI studies at the Leiden Controlled Human Infection Center, control group of students from Leiden University.

PARTICIPANTS

61 previous participants and 156 controls.

MEASUREMENTS

Ranking of motivational and decisional factors, risk propensity score and multiple-choice questions on experience of trial participation and ethical aspects of CHI studies.

RESULTS

Motivating factors for participants were contributing to science (81%), contributing to research that may benefit developing countries (72%) and the financial compensation (63%). For 51% of participants, a reason other than financial compensation was the most important motivational factor. Participants considered trust in the study team (70%), time investment (63%), severity of symptoms (54%), chance of developing symptoms (54%) and whether it is an easy way to make money (54%) in their decision to participate. Most CHI participants (84%) were proud of their participation, would advise others to participate (89%) and would participate in a similar trial again (85%). CHI participants had a higher risk propensity score than students (estimated difference 0.9, p<0.001).

CONCLUSION

Although financial compensation is important, the motivations for participants in a CHI study are diverse and participants make a balanced appraisal of risks and burden before participating.

First-in-human administration of a live-attenuated RSV vaccine lacking the G-protein assessing safety, tolerability, shedding and immunogenicity: a randomized controlled trial

BACKGROUND

Human respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in early infancy and in elderly. A pediatric vaccine against RSV would not only prevent morbidity and mortality amongst infants and young children but could also reduce transmission to elderly. The RSVΔG vaccine consists of a live-attenuated RSV that lacks the G attachment protein. RSVΔG is severely impaired in binding to host cells and exhibits reduced infectivity in preclinical studies. Intranasal immunization of cotton rats with RSVΔG vaccine protected against replication of wildtype RSV, without inducing enhanced disease.

METHODS

We performed a first-in-human trial with primary objective to evaluate safety and shedding of RSVΔG (6.5 log₁₀ CCID₅₀) after intranasal administration. Healthy adults aged between 18 and 50, with RSV neutralizing serum titers below 9.6 log₂, received a single dose of either vaccine or placebo (n = 48, ratio 3:1). In addition to safety and tolerability, nasal viral load, and systemic and humoral immune responses were assessed at selected time points until 4 weeks after immunization.

RESULTS

Intranasal administration of RSVΔG was well tolerated with no findings of clinical concern. No infectious virus was detected in nasal wash samples. Similar to other live-attenuated RSV vaccines, neutralizing antibody response following inoculation was limited in seropositive adults.

CONCLUSIONS

A single dose of 6.5 log₁₀ CCID₅₀ of RSVΔG was safe and well-tolerated in seropositive healthy adults. RSVΔG was sufficiently attenuated but there were no signs of induction of antibodies. Safety and immunogenicity can now be explored in children and eventually in seronegative infants. Clinical trial register: NTR7173/EudraCT number 2016-002437-30.

Antigen-based diagnosis of Schistosoma infection in travellers: a prospective study

BACKGROUND

Travellers infected with Schistosoma spp. might be pauci- or even asymptomatic on first presentation. Therefore, schistosomiasis may remain undiagnosed in this population. Active infection, as evidenced by the presence of the tissue-dwelling worm, can be demonstrated via the detection of adult worm-derived circulating anodic antigen (CAA) utilising a robust well-described lateral flow-(LF) based test applying background-free up-converting reporter particles (UCP). In this prospective study, we assessed the diagnostic value of serum and urine UCP-LF CAA test in comparison with two Schistosoma-specific serological assays detecting antibodies against adult worm antigen-immuno fluorescence assay (AWA-IFA) and against soluble egg antigen-enzyme-linked immunosorbent assay (SEA-ELISA) antigens in travellers.

METHODS

Samples were collected from 106 Dutch travellers who reported freshwater contact in sub-Saharan Africa and who were recruited up to 2 years after return. Subjects were asked to complete a detailed questionnaire on travel history, water contact, signs and symptoms compatible with schistosomiasis.

RESULTS

Two travellers were positive by serum CAA and an additional one by urine CAA. A total of 22/106 (21%) samples were antibody positive by AWA-IFA and 9/106 (9%) by SEA-ELISA. At follow-up 6 weeks and 6 months after praziquantel treatment, all seropositives remained antibody positive whereas CAA was cleared. Seropositivity could not be predicted by the type of fresh water-related activity, country visited or symptoms reported.

CONCLUSION

The low number of UCP-LF CAA positives suggests that in travellers, active infections often do not establish or have very low worm burden. Based on our high seroconversion rates, we conclude that the AWA-IFA assay is the most sensitive test to detect schistosome exposure. Given the lack of predictive symptoms or risk factors, we recommend schistosomiasis screening at least by serology in all travellers with reported freshwater contact in high-endemic areas.

A Supramolecular Platform Technology for Bacterial Cell Surface Modification

In an era of antimicrobial resistance, a better understanding of the interaction between bacteria and the sentinel immune system is needed to discover new therapeutic targets for combating bacterial infectious disease. Sentinel immune cells such as macrophages phagocytose intact bacteria and thereby initiate ensuing immune responses. The bacterial surface composition is a key element that determines the macrophage signaling. To study the role of the bacterial cell surface composition in immune recognition, we developed a platform technology for altering bacterial surfaces in a controlled manner with versatile chemical scaffolds. We show that these scaffolds are efficiently loaded onto both Gram-positive and -negative bacteria and that their presence does not impair the capacity of monocyte-derived macrophages to phagocytose bacteria and subsequently signal to other components of the immune system. We believe this technology thus presents a useful tool to study the role of bacterial cell surface composition in disease etiology and potentially in novel interventions utilizing intact bacteria for vaccination.

A Randomized Controlled Trial to Investigate Safety and Variability of Egg Excretion After Repeated Controlled Human Hookworm Infection

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-blindly, to 1, 2, or 3 doses of 50 Necator americanus 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. Geometric mean egg loads stabilized at 697, 1668, and 1914 eggs per gram feces for the 1 × 50L3, 2 × 50L3, and 3 × 50L3 group, respectively. Bayesian statistical modeling 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 2 × 50L3 as an improved challenge dose. Model-based simulations indicates increased frequency of stool sampling optimizes the power of hypothetical vaccine trials.

CONCLUSIONS

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.

CLINICAL TRIALS REGISTRATION

NCT03257072.

Screening of a library of recombinant Schistosoma mansoni proteins with sera from murine and human controlled infections identifies early serological markers

Background

Schistosomiasis is a major global health problem caused by blood-dwelling parasitic worms, which is currently tackled primarily by mass administration of the drug praziquantel. Appropriate drug treatment strategies are informed by diagnostics that establish the prevalence and intensity of infection, which, in regions of low transmission, should be highly sensitive.

Methods

To identify sensitive new serological markers of Schistosoma mansoni infections, we have compiled a recombinant protein library of parasite cell-surface and secreted proteins expressed in mammalian cells.

Results

Together with a time series of sera samples from volunteers experimentally infected with a defined number of male parasites, we probed this protein library to identify several markers that can detect primary infections with as low as 10 parasites and as early as 5 weeks postinfection.

Conclusions

These new markers could be further explored as valuable tools to detect ongoing and previous S mansoni infections, including in endemic regions where transmission is low.

New Insights Into the Kinetics and Variability of Egg Excretion in Controlled Human Hookworm Infections

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.

Risk assessment for the implementation of controlled human Schistosoma mansoni infection trials in Uganda

Schistosomiasis is a parasitic infection highly prevalent in sub-Saharan Africa, and a significant cause of morbidity; it is a priority for vaccine development. A controlled human infection model for Schistosoma mansoni (CHI-S) with potential to accelerate vaccine development has been developed among naïve volunteers in the Netherlands. Because responses both to infections and candidate vaccines are likely to differ between endemic and non-endemic settings, we propose to establish a CHI-S in Uganda where Schistosoma mansoni is endemic. As part of a “road-map” to this goal, we have undertaken a risk assessment. We identified risks related to importing of laboratory vector snails and schistosome strains from the Netherlands to Uganda; exposure to natural infection in endemic settings concurrently with CHI-S studies, and unfamiliarity of the community with the nature, risks and rationale for CHI. Mitigating strategies are proposed. With careful implementation of the latter, we believe that CHI-S can be implemented safely in Uganda. Our reflections are presented here to promote feedback and discussion.

Sensitive diagnostic tools and targeted drug administration strategies are needed to eliminate schistosomiasis

Although preventive chemotherapy has been instrumental in reducing schistosomiasis incidence worldwide, serious challenges remain. These problems include the omission of certain groups from campaigns of mass drug administration, the existence of persistent disease hotspots, and the risk of recrudescent infections. Central to these challenges is the fact that the diagnostic tools currently used to establish the burden of infection are not sensitive enough, especially in low-endemic settings, which results in underestimation of the true prevalence of active Schistosoma spp infections. This central issue necessitates that the current schistosomiasis control strategies recommended by WHO are re-evaluated and, possibly, adapted. More targeted interventions and novel approaches have been used to estimate the prevalence of schistosomiasis, such as establishing infection burden by use of precision mapping, which provides high resolution spatial information that delineates variations in prevalence within a defined geographical area. Such information is instrumental in guiding targeted intervention campaigns. However, the need for highly accurate diagnostic tools in such strategies is a crucial factor that is often neglected. The availability of highly sensitive diagnostic tests also opens up the possibility of applying strategies of sample pooling to reduce the cost of control programmes. To interrupt the transmission of, and eventually eliminate, schistosomiasis, better local targeting of preventive chemotherapy, in combination with highly sensitive diagnostic tools, is crucial.

Efficacy of single versus four repeated doses of praziquantel against Schistosoma mansoni infection in school-aged children from Côte d'Ivoire based on Kato-Katz and POC-CCA: An open-label, randomised controlled trial (RePST)

Background

Preventive chemotherapy with praziquantel (PZQ) is the cornerstone of schistosomiasis control. However, a single dose of PZQ (40 mg/kg) does not cure all infections. Repeated doses of PZQ at short intervals might increase efficacy in terms of cure rate (CR) and intensity reduction rate (IRR). Here, we determined the efficacy of a single versus four repeated treatments with PZQ on Schistosoma mansoni infection in school-aged children from Côte d’Ivoire, using two different diagnostic tests.

Methods

An open-label, randomized controlled trial was conducted from October 2018 to January 2019. School-aged children with a confirmed S. mansoni infection based on Kato-Katz (KK) and point-of-care circulating cathodic antigen (POC-CCA) urine cassette test were randomly assigned to receive either a single or four repeated doses of PZQ, administered at two-week intervals. The primary outcome was the difference in CR between the two treatment arms, measured by triplicate KK thick smears 10 weeks after the first treatment. Secondary outcomes included CR estimated by POC-CCA, IRR by KK and POC-CCA, and safety of repeated PZQ administration.

Principal findings

During baseline screening, 1,022 children were assessed for eligibility of whom 153 (15%) had a detectable S. mansoni infection, and hence, were randomized to the standard treatment group (N = 70) and the intense treatment group (N = 83). Based on KK, the CR was 42% (95% confidence interval (CI) 31–52%) in the standard treatment group and 86% (95% CI 75–92%) in the intense treatment group. Observed IRR was 72% (95% CI 55–83%) in the standard treatment group and 95% (95% CI 85–98%) in the intense treatment group. The CR estimated by POC-CCA was 18% (95% CI 11–27%) and 36% (95% CI 26–46%) in the standard and intense treatment group, respectively. Repeated PZQ treatment did not result in a higher number of adverse events.

Conclusion/significance

The observed CR using KK was significantly higher after four repeated treatments compared to a single treatment, without an increase in adverse events. Using POC-CCA, the observed CR was significantly lower than measured by KK, indicating that PZQ may be considerably less efficacious as concluded by KK. Our findings highlight the need for reliable and more accurate diagnostic tools, which are essential for monitoring treatment efficacy, identifying changes in transmission, and accurately quantifying the intensity of infection in distinct populations. In addition, the higher CR in the intense treatment group suggests that more focused and intense PZQ treatment can help to advance schistosomiasis control.

Trial registration

www.clinicaltrials.govNCT02868385.

The previously established efficacy of the widely used drug praziquantel (PZQ) against schistosomiasis might have been overestimated due to the use of inaccurate diagnostic methods. Repeated PZQ treatment at short intervals in areas with ongoing transmission could more effectively target non-susceptible schistosomula as they will have matured into drug susceptible worms within a few weeks. In the current study, we aimed to determine the cure rate (CR) of repeated PZQ, measured by the Kato-Katz (KK) technique and the point-of-care circulating cathodic antigen (POC-CCA) test, respectively. An open-label, randomized controlled trial was conducted assigning 153 school-aged children with a confirmed Schistosoma mansoni infection to two groups, one receiving a single PZQ treatment, while the second group received four repeated PZQ treatments, given at two-week intervals. Based on the KK test, the CR was significantly higher after four repeated treatments compared to a single treatment. When using POC-CCA, a diagnostic method that has not been utilized before in studies assessing the efficacy of four repeated PZQ treatments, the CR was much lower, even after four repeated PZQ treatments. Our results indicate that worms are still present after multiple PZQ treatments and that PZQ might be less efficacious than previously published.

Are placebo controls necessary in controlled human infection trials for vaccines?

Controlled human infection trials, whereby a small group of healthy participants is deliberately exposed to a pathogen under controlled circumstances, can provide preliminary data for vaccine efficacy and for the selection of the most promising candidate vaccines for field trials. Because of the potential harm to participants through the deliberate exposure to a pathogen, the use of smaller groups minimises the cumulative risk. As such, a control group that receives a placebo vaccine followed by controlled exposure to a pathogen should be scientifically well justified. As these types of trials are designed to generate consistent infection rates and thus comparable outcomes across populations and trial sites, data from past studies (historical data) could be used as a valid alternative to placebo groups. In this Personal View, we review this option and highlight the considerations for choosing historical data as a suitable control. For the widespread application of this method, responsibility for the centralisation and sharing of data from controlled human infection trials lies with the scientific community.