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Background For blood-stage malaria vaccine development, the in vitro growth inhibition assay (GIA) has been widely used to evaluate functionality of vaccine-induced antibodies (Ab), and Plasmodium falciparum reticulocyte-binding protein homolog 5 (RH5) is a leading blood-stage antigen. However, precision, also called “error of assay (EoA)”, in GIA readouts and the source of EoA has not been evaluated systematically. Methods In the Main GIA experiment, 4 different cultures of P. falciparum 3D7 parasites were prepared with red blood cells (RBC) collected from 4 different donors. For each culture, 7 different anti-RH5 Ab (either monoclonal or polyclonal Ab) were tested by GIA at two concentrations on three different days (168 data points). To evaluate sources of EoA in % inhibition in GIA (%GIA), a linear model fit was conducted including donor (source of RBC) and day of GIA as independent variables. In addition, 180 human anti-RH5 polyclonal Ab were tested in a Clinical GIA experiment, where each Ab was tested at multiple concentrations in at least 3 independent GIAs using different RBCs (5,093 data points). The standard deviation (sd) in %GIA and in GIA50 (Ab concentration that gave 50%GIA) readouts, and impact of repeat assays on 95% confidence interval (95%CI) of these readouts was estimated. Results The Main GIA experiment revealed that the RBC donor effect was much larger than the day effect, and an obvious donor effect was also observed in the Clinical GIA experiment. Both %GIA and log-transformed GIA50 data reasonably fit a constant sd model, and sd of %GIA and log-transformed GIA50 measurements were calculated as 7.54 and 0.206, respectively. Taking the average of three repeat assays (using three different RBCs) reduces the 95%CI width in %GIA or in GIA50 measurements by ~ half compared to a single assay. Conclusions The RBC donor effect (donor-to-donor variance on the same day) in GIA was much bigger than the day effect (day-to-day variance using the same donor’s RBC) at least for the RH5 Ab evaluated in this study; thus, future GIA studies should consider the donor effect. In addition, the 95%CI for %GIA and GIA50 shown here help when comparing GIA results from different samples/groups/studies; therefore, this study supports future malaria blood-stage vaccine development.

BackgroundRH5 is the leading blood-stage candidate antigen for inclusion in aPlasmodium falciparummalaria vaccine, however, its safety profile and ability to induce functional immune responses in a malaria-endemic population are unknown. Characterising safety and immunogenicity is key to refine and progress next-generation RH5-based blood-stage malaria vaccines to field efficacy assessment.MethodsA Phase 1b, single-center, dose-escalation, age de-escalation, double-blind, randomized, controlled trial was conducted in Bagamoyo, Tanzania. Healthy adults (18-35 years), young children (1-6 years) and infants (6-11 months) were recruited to receive a priming dose of viral-vectored ChAd63 RH5 (or rabies control vaccine) followed by a booster dose of MVA RH5 (or rabies control vaccine) 8 weeks later. The primary outcomes were the number of solicited and unsolicited adverse events following vaccination and the number of serious adverse events over the whole study period. Secondary outcomes included quantitative and qualitative measures of the anti-RH5 immune response. All participants receiving at least one dose of vaccine were included in the primary analyses.FindingsBetween 12thApril and 25thOctober 2018 a total of 63 adults, children and infants were recruited and primed and 60 of these were boosted, all completing six months of follow-up post-priming vaccination. Vaccinations were well-tolerated with participants reporting predominantly mild reactogenicity, with profiles comparable between ChAd63 RH5, MVA RH5 and rabies vaccine groups, and across the age groups. No serious adverse events were reported during the study period. RH5-specific T cell, B cell and serum antibody responses were induced by vaccination. Higher anti-RH5 serum IgG responses were observed post-boost in the 1-6 year old children (median 93 µg/mL; range: 31-508 µg/mL) and infants (median 149 µg/mL; range: 29-352 µg/mL) as compared to adults (median 14 µg/mL; range: 9-15 µg/mL). These contracted over time post-boost, but the same hierarchy of responses across the age groups was maintained to end of follow-up at 16 weeks post-boost (day 168). Vaccine-induced anti-RH5 antibodies were functional showing growth inhibition activity (GIA)in vitroagainstP. falciparumblood-stage parasites. The highest levels were observed in the 6-11 month old infants, with 6/11 showing >60% GIA following dilution of total IgG to 2.5 mg/mL (median 61%; range: 41-78%).InterpretationThe ChAd63-MVA RH5 vaccine regimen shows an acceptable safety and reactogenicity profile and encouraging immunogenicity in children and infants residing in a malaria-endemic area. The levels of functional GIA observed in the RH5 vaccinated 6-11 month old infants are the highest levels reported to-date following human vaccination. These data support onward clinical development of RH5-based blood-stage vaccines that aim to protect against clinical malaria in young African infants.FundingMedical Research Council, London, United Kingdom.Trial RegistrationISRCTN registry: 47448832 and ClinicalTrials.gov:NCT03435874.

In endemic settings it is known that natural malaria immunity is gradually acquired following repeated exposures. Here we sought to assess whether similar acquisition of blood-stage malaria immunity would occur following repeated parasite exposure by controlled human malaria infection (CHMI). We report the findings of repeat homologous blood-stageClinicalTrials.gov, identifier NCT03906474, NCT02927145.

The peer commentaries on our Target Article, “Promoting Ethical Payment in Human Infection Challenge Studies,” (Fernandez Lynch et al. 2021) offer a number of insights that will help advance the co...

Falciparum malaria is clinically heterogeneous and the relative contribution of parasite and host in shaping disease severity remains unclear. We explored the interaction between inflammation and parasite variant surface antigen (VSA) expression, asking whether this relationship underpins the variation observed in controlled human malaria infection (CHMI). We uncovered marked heterogeneity in the host response to blood challenge; some volunteers remained quiescent, others triggered interferon-stimulated inflammation and some showed transcriptional evidence of myeloid cell suppression. Significantly, only inflammatory volunteers experienced hallmark symptoms of malaria. When we tracked temporal changes in parasite VSA expression to ask whether variants associated with severe disease rapidly expand in naive hosts, we found no transcriptional evidence to support this hypothesis. These data indicate that parasite variants that dominate severe malaria do not have an intrinsic growth or survival advantage; instead, they presumably rely upon infection-induced changes in their within-host environment for selection.

To prepare for potential human infection challenge studies (HICS) involving SARS-CoV-2, this report offers an expert analysis of ethical approaches to paying research participants in these studies, as well as HICS more broadly. The report first provides an overarching ethical framework for research payment that divides payment into reimbursement, compensation, and incentive, focusing on fairness and promoting adequate recruitment and retention as counterweights to ethical concerns about undue inducement. It then describes variables relevant to applying this framework to any type of study, including the prospect of direct medical benefit, early participant withdrawal, study setting and location, pandemic circumstances, study budget, and participant perspectives. We conclude that there is no need for a unique payment framework specific to HICS or SARS-CoV-2 HICS, but that there may be features of particular relevance to ethical payment for these studies. Participants have varied motivations for enrolling in HICS, including financial considerations, altruism, and other interests, but undue inducement does not seem to be a significant problem based on available evidence. Payment in these studies should reflect the nature of participant confinement, anticipated discomfort from induced infection, risks and uncertainty, participant motivations, and the need to recruit from certain populations, as relevant. Where HICS involve significant risks and highly contingent social value, special review confirming the ethical permissibility of these studies can help promote confidence in the ethical permissibility of offers of payment to participate in them. We do not propose specific payment amounts for potential SARS-CoV-2 HICS, as these will be highly variable based on the relevant factors described in the report. Instead, we note that it is reasonable to start from payments offered in other similar studies, while adopting a systematic approach based on the ethical framework herein, as reflected in a pragmatic payment worksheet describing goals, coverage, factors to consider, and potential benchmarks.

Grimwade et al highlight the current lack of a universal, standardised approach to the payment of participants taking part in controlled human infection model (CHIM) studies.1 As they discuss, payment for these studies is controversial, with many voicing arguments for and against higher payments, particularly for those studies which involve significant burdens to the participant. The main concerns about overpayment relate to the concepts of undue inducement or coercion, whereas underpayment raises concern about exploitation and unfair treatment. In many healthy volunteer trials compensation for travel, time and inconvenience are generally accepted as fair payment, but payment for risk is less accepted, with a belief that non-therapeutic studies should only incur minimal risks, so payment for risk should not be necessary.2 This paper argues that payment for risk should be included for CHIM studies. Their findings among members of the UK public and CHIM experts from a variety of centres suggest that there is support for greater risks being associated with higher payments for participants. The amount of compensation offered by a trial has to be approved by an ethics committee/institutional review board (IRB), and some research suggests that IRB members have concerns about higher payments being offered, with only approximately one-third agreeing that payment should be offered for risk.3 Without agreement and clear guidance for calculating compensation for these types of trial, there is bound to be …

Summary Background Development of an effective vaccine against the pathogenic blood-stage infection of human malaria has proved challenging, and no candidate vaccine has affected blood-stage parasitemia following controlled human malaria infection (CHMI) with blood-stage Plasmodium falciparum. Methods We undertook a phase I/IIa clinical trial in healthy adults in the United Kingdom of the RH5.1 recombinant protein vaccine, targeting the P. falciparum reticulocyte-binding protein homolog 5 (RH5), formulated in AS01B adjuvant. We assessed safety, immunogenicity, and efficacy against blood-stage CHMI. Trial registered at ClinicalTrials.gov, NCT02927145. Findings The RH5.1/AS01B formulation was administered using a range of RH5.1 protein vaccine doses (2, 10, and 50 μg) and was found to be safe and well tolerated. A regimen using a delayed and fractional third dose, in contrast to three doses given at monthly intervals, led to significantly improved antibody response longevity over ∼2 years of follow-up. Following primary and secondary CHMI of vaccinees with blood-stage P. falciparum, a significant reduction in parasite growth rate was observed, defining a milestone for the blood-stage malaria vaccine field. We show that growth inhibition activity measured in vitro using purified immunoglobulin G (IgG) antibody strongly correlates with in vivo reduction of the parasite growth rate and also identify other antibody feature sets by systems serology, including the plasma anti-RH5 IgA1 response, that are associated with challenge outcome. Conclusions Our data provide a new framework to guide rational design and delivery of next-generation vaccines to protect against malaria disease. Funding This study was supported by USAID, UK MRC, Wellcome Trust, NIAID, and the NIHR Oxford-BRC., Graphical abstract, Highlights The RH5.1/AS01B vaccine is safe, well tolerated, and immunogenic in healthy adults A delayed fractional third dose significantly improves antibody response longevity In vivo blood-stage P. falciparum growth rate is significantly lower in vaccinees In vitro IgG-mediated growth inhibition activity is associated with challenge outcome, Context and significance A highly effective vaccine against the human malaria parasite Plasmodium falciparum is urgently needed. One vaccine strategy aims to prevent parasite growth in the blood, protecting against clinical disease; however, this has proved exceptionally challenging. Here we show that a candidate vaccine (reticulocyte-binding protein homolog 5.1 [RH5.1]/AS01B) is safe in a phase I/IIa clinical trial and identify a vaccination regimen that improves the durability of the human antibody response, which is critical for long-term protection. Following experimental challenge of vaccinated adults with malaria, we observed that the vaccine could reduce parasite growth in the blood and identified immune responses that could predict how well the vaccine performs. These data will help guide the design of improved vaccines in the future., Minassian et al. report that the RH5.1/AS01B vaccine against blood-stage Plasmodium falciparum malaria is safe and immunogenic in a phase I/IIa clinical trial. They demonstrate a significantly reduced blood-stage parasite growth rate in vaccinees following controlled human malaria infection and identify that in vitro antibody-mediated growth inhibition activity is associated with challenge outcome.

Summary Interactions between B cells and CD4+ T follicular helper (Tfh) cells are key determinants of humoral responses. Using samples from clinical trials performed with the malaria vaccine candidate antigen Plasmodium falciparum merozoite protein (PfRH5), we compare the frequency, phenotype, and gene expression profiles of PfRH5-specific circulating Tfh (cTfh) cells elicited by two leading human vaccine delivery platforms: heterologous viral vector prime boost and protein with AS01B adjuvant. We demonstrate that the protein/AS01B platform induces a higher-magnitude antigen-specific cTfh cell response and that this correlates with peak anti-PfRH5 IgG concentrations, frequency of PfRH5-specific memory B cells, and antibody functionality. Furthermore, our data indicate a greater Th2/Tfh2 skew within the polyfunctional response elicited following vaccination with protein/AS01B as compared to a Th1/Tfh1 skew with viral vectors. These data highlight the impact of vaccine platform on the cTfh cell response driving humoral immunity, associating a high-magnitude, Th2-biased cTfh response with potent antibody production., Graphical abstract, Highlights CD4 Tfh comparison in malaria vaccine trials using leading human vaccine platforms Protein/AS01B drives stronger antigen-specific Tfh responses than viral vectors Greater T(f)h2 skewing of antigen-specific CD4 T cells in protein/AS01B vaccinees Antigen-specific CD4 T(fh) cell parameters correlate with functional antibody, Nielsen et al. evaluate the induction of antigen-specific T follicular helper cell responses in human malaria vaccine trials using protein/adjuvant (AS01B) or heterologous viral vector platforms. They demonstrate that protein/AS01B drives a higher-magnitude polyfunctional response with greater skewing toward a Th2 phenotype, associated with superior production of neutralizing antibodies.

Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) is a leading asexual blood-stage vaccine candidate for malaria. In preparation for clinical trials, a full-length PfRH5 protein vaccine called “RH5.1” was produced as a soluble product under cGMP using the ExpreS2 platform (based on a Drosophila melanogaster S2 stable cell line system). Following development of a high-producing monoclonal S2 cell line, a master cell bank was produced prior to the cGMP campaign. Culture supernatants were processed using C-tag affinity chromatography followed by size exclusion chromatography and virus-reduction filtration. The overall process yielded >400 mg highly pure RH5.1 protein. QC testing showed the MCB and the RH5.1 product met all specified acceptance criteria including those for sterility, purity, and identity. The RH5.1 vaccine product was stored at −80 °C and is stable for over 18 months. Characterization of the protein following formulation in the adjuvant system AS01B showed that RH5.1 is stable in the timeframe needed for clinical vaccine administration, and that there was no discernible impact on the liposomal formulation of AS01B following addition of RH5.1. Subsequent immunization of mice confirmed the RH5.1/AS01B vaccine was immunogenic and could induce functional growth inhibitory antibodies against blood-stage P. falciparum in vitro. The RH5.1/AS01B was judged suitable for use in humans and has since progressed to phase I/IIa clinical trial. Our data support the future use of the Drosophila S2 cell and C-tag platform technologies to enable cGMP-compliant biomanufacture of other novel and “difficult-to-express” recombinant protein-based vaccines., Malaria: Successful clinical trial preparation for blood-stage vaccine A vaccine candidate for blood-stage malaria has overcome previous hurdles to enter clinical trials. The protein PfRH5 is an essential blood-stage infection facilitator of malarial parasite Plasmodium falciparum, and a promising target for vaccine strategies. Unfortunately, efforts to produce the protein in an immunogenic, clinically-viable way have been met with difficulty. Here, researchers led by Simon Draper, from the UK’s Jenner Institute, used a fruit fly expression system to produce over 400 mg of high-purity protein. Formulated with an immunity-boosting adjuvant, the vaccine elicited antibodies in mice that proved inhibitory to blood-stage P. falciparum during in vitro assays. The PfRH5 vaccine candidate and its adjuvant have been approved for a clinical trial in the UK, and the authors hope that the expression system used may be beneficial in the expression of other ‘difficult’ proteins.

SummaryMany viral infections that cause minor illness in younger adults can lead to significant mortality and morbidity in older people, particularly as co-morbidities tend to accumulate with increased age. Respiratory and gastrointestinal viruses are ubiquitous and frequently cause outbreaks, with major impact on those in care homes or residential accommodation. Advances in medicine have opened the way for increased impact of the herpes viruses (varicella zoster virus, herpes simplex virus, Epstein–Barr virus and cytomegalovirus), as immune systems are manipulated. People are also leading more active lives in older age; human immunodeficiency virus (HIV) will be increasingly prevalent, as those living with HIV grow older in good health. In addition, new diagnoses of HIV, viral hepatitis and travel-related infections will present to those working in health care of older people. This review article of viral infections aims to highlight relevant pathology, with specific reference to management in older people.

Viral vectored vaccines using chimpanzee adenoviruses and Modified Vaccinia Ankara (MVA) vectors have demonstrated efficacy against Ebolavirus challenge in non-human primates. This Phase 1 trial was designed to assess the safety and immunogenicity of 2 novel Ebolavirus vaccines in healthy UK adults: the monovalent chimpanzee adenovirus 3 vector encoding Zaire Ebolavirus glycoprotein (ChAd3-EBO Z) and the multivalent MVA encoding multiple filoviral proteins (MVA-BN® Filo).

T-cell responses against highly conserved influenza antigens have been previously associated with protection. However, these immune responses are poorly maintained following recovery from influenza infection and are not boosted by inactivated influenza vaccines. We have previously demonstrated the safety and immunogenicity of two viral vectored vaccines, modified vaccinia virus Ankara (MVA) and the chimpanzee adenovirus ChAdOx1 expressing conserved influenza virus antigens, nucleoprotein (NP) and matrix protein-1 (M1). We now report on the safety and long-term immunogenicity of multiple combination regimes of these vaccines in young and older adults.We conducted a Phase I open-label, randomized, multi-center study in 49 subjects aged 18-46years and 24 subjects aged 50years or over. Following vaccination, adverse events were recorded and the kinetics of the T cell response determined at multiple time points for up to 18months.Both vaccines were well tolerated. A two dose heterologous vaccination regimen significantly increased the magnitude of pre-existing T-cell responses to NP and M1 after both doses in young and older adults. The fold-increase and peak immune responses after a single MVA-NP+M1 vaccination was significantly higher compared to ChAdOx1 NP+M1. In a mixed regression model, T-cell responses over 18months were significantly higher following the two dose vaccination regimen of MVA/ChAdOx1 NP+M1.A two dose heterologous vaccination regimen of MVA/ChAdOx1 NP+M1 was safe and immunogenic in young and older adults, offering a promising vaccination strategy for inducing long-term broadly cross-reactive protection against influenza A.Medical Research Council UK, NIHR BMRC Oxford.