Safety, tolerability, and immunogenicity of inactivated poliovirus vaccine with or without E.coli double mutant heat-labile toxin (dmLT) adjuvant in healthy adults; a phase 1 randomized study.

BACKGROUND: Inactivated trivalent poliovirus vaccine (IPV) induces humoral immunity, which protects against paralytic poliomyelitis but does not induce sufficient mucosal immunity to block intestinal infection. We assessed the intestinal immunity in healthy adults in Belgium conferred by a co-formulation of IPV with the mucosal adjuvant double mutant Labile Toxin (dmLT) derived from Escherichia coli. METHODS: Healthy fully IPV-vaccinated 18-45-year-olds were randomly allocated to three groups: on Day 1 two groups received one full dose of IPV (n = 30) or IPV + dmLT (n = 30) in a blinded manner, and the third received an open-label dose of bivalent live oral polio vaccine (bOPV types 1 and 3, n = 20). All groups received a challenge dose of bOPV on Day 29. Participants reported solicited and unsolicited adverse events (AE) using study diaries. Mucosal immune responses were measured by fecal neutralization and IgA on Days 29 and 43, with fecal shedding of challenge viruses measured for 28 days. Humoral responses were measured by serum neutralizing antibody (NAb). RESULTS: Solicited and unsolicited AEs were mainly mild-to-moderate and transient in all groups, with no meaningful differences in rates between groups. Fecal shedding of challenge viruses in both IPV groups exceeded that of the bOPV group but was not different between IPV and IPV + dmLT groups. High serum NAb responses were observed in both IPV groups, alongside modest levels of fecal neutralization and IgA. CONCLUSIONS: Addition of dmLT to IPV administered intramuscularly neither affected humoral nor intestinal immunity nor decreased fecal virus shedding following bOPV challenge. The tolerability of the dose of dmLT used in this study may allow higher doses to be investigated for impact on mucosal immunity. Registered on ClinicalTrials.gov - NCT04232943.

A phase IIA extension study evaluating the effect of booster vaccination with a fractional dose of RTS,S/AS01E in a controlled human malaria infection challenge.

BACKGROUND: We previously demonstrated that RTS,S/AS01B and RTS,S/AS01E vaccination regimens including at least one delayed fractional dose can protect against Plasmodium falciparum malaria in a controlled human malaria infection (CHMI) model, and showed inferiority of a two-dose versus three-dose regimen. In this follow-on trial, we evaluated whether fractional booster vaccination extended or induced protection in previously protected (P-Fx) or non-protected (NP-Fx) participants. METHODS: 49 participants (P-Fx: 25; NP-Fx: 24) received a fractional (1/5th dose-volume) RTS,S/AS01E booster 12 months post-primary regimen. They underwent P. falciparum CHMI three weeks later and were then followed for six months for safety and immunogenicity. RESULTS: Overall vaccine efficacy against re-challenge was 53% (95% CI: 37-65%), and similar for P-Fx (52% [95% CI: 28-68%]) and NP-Fx (54% [95% CI: 29-70%]). Efficacy appeared unaffected by primary regimen or previous protection status. Anti-CS (repeat region) antibody geometric mean concentrations (GMCs) increased post-booster vaccination. GMCs were maintained over time in primary three-dose groups but declined in the two-dose group. Protection after re-challenge was associated with higher anti-CS antibody responses. The booster was well-tolerated. CONCLUSIONS: A fractional RTS,S/AS01E booster given one year after completion of a primary two- or three-dose RTS,S/AS01 delayed fractional dose regimen can extend or induce protection against CHMI. CLINICAL TRIAL REGISTRATION: NCT03824236. linked to this article can be found on the Research Data as well as Figshare https://figshare.com/s/ee025150f9d1ac739361.

A Randomized Clinical Trial to Compare Plasmodium falciparum Gametocytemia and Infectivity After Blood-Stage or Mosquito Bite-Induced Controlled Malaria Infection.

BACKGROUND: For malaria elimination efforts, it is important to better understand parasite transmission to mosquitoes and develop models for early-clinical evaluation of transmission-blocking interventions. METHODS: In a randomized open-label trial, 24 participants were infected by bites from Plasmodium falciparum 3D7-infected mosquitoes (mosquito bite [MB]; n = 12) or by induced blood-stage malaria (IBSM) with the same parasite line (n = 12). After subcurative piperaquine treatment, asexual parasite and gametocytes kinetics were assessed, and mosquito feeding experiments were performed. RESULTS: Study procedures were well tolerated. The median peak gametocyte density was 1304/mL (interquartile range, 308-1607/mL) after IBSM, compared with 14/mL (10-64/mL) after MB inoculation (P < .001), despite similar peak asexual parasite densities (P = .48). Peak gametocyte density was correlated with preceding pfap2-g transcripts, indicative of gametocyte commitment (ρ = 0.62; P = .002). Direct feeding assays resulted in mosquito infections from 9 of 12 participants after IBSM versus 0 of 12 after MB inoculation (P < .001). CONCLUSIONS: We observed a striking effect of inoculation method on gametocyte production, suggesting higher gametocyte commitment after IBSM. Our direct comparison of MB and IBSM establishes the controlled human malaria infection transmission model, using intravenous administration of P. falciparum-infected erythrocytes as a model for early-clinical evaluation of interventions that aim to interrupt malaria transmission. CLINICAL TRIAL REGISTRATION: NCT03454048.

A Phase IIa Controlled Human Malaria Infection and Immunogenicity Study of RTS,S/AS01E and RTS,S/AS01B Delayed Fractional Dose Regimens in Malaria-Naive Adults.

BACKGROUND: A previous RTS,S/AS01B vaccine challenge trial demonstrated that a 3-dose (0-1-7-month) regimen with a fractional third dose can produce high vaccine efficacy (VE) in adults challenged 3 weeks after vaccination. This study explored the VE of different delayed fractional dose regimens of adult and pediatric RTS,S/AS01 formulations. METHODS: A total of 130 participants were randomized into 5 groups. Four groups received 3 doses of RTS,S/AS01B or RTS,S/AS01E on a 0-1-7-month schedule, with the final 1 or 2 doses being fractional (one-fifth dose volume). One group received 1 full (month 0) and 1 fractional (month 7) dose of RTS,S/AS01E. Immunized and unvaccinated control participants underwent Plasmodium falciparum-infected mosquito challenge (controlled human malaria infection) 3 months after immunization, a timing chosen to potentially discriminate VEs between groups. RESULTS: The VE of 3-dose formulations ranged from 55% (95% confidence interval, 27%-72%) to 76% (48%-89%). Groups administered equivalent formulations of RTS,S/AS01E and RTS,S/AS01B demonstrated comparable VE. The 2-dose group demonstrated lower VE (29% [95% confidence interval, 6%-46%]). All regimens were well tolerated and immunogenic, with trends toward higher anti-circumsporozoite antibody titers in participants protected against infection. CONCLUSIONS: RTS,S/AS01E can provide VE comparable to an equivalent RTS,S/AS01B regimen in adults, suggesting a universal formulation may be considered. Results also suggest that the 2-dose regimen is inferior to the 3-dose regimens evaluated. CLINICAL TRIAL REGISTRATION: NCT03162614.

Combining antimalarial drugs and vaccine for malaria elimination campaigns: a randomized safety and immunogenicity trial of RTS,S/AS01 administered with dihydroartemisinin, piperaquine, and primaquine in healthy Thai adult volunteers.

Introduction: RTS,S/AS01 is currently the most advanced malaria vaccine but provides incomplete, short-term protection. It was developed for use within the expanded program on immunizations (EPI) for African children. Another use could be adding mass RTS,S/AS01 vaccination to the integrated malaria elimination strategy in the Greater Mekong Subregion (GMS), where multidrug-resistant P.falciparum strains have emerged and spread. Prior to evaluating RTS,S/AS01 in large-scale trials we assessed whether the vaccine, administered with and without antimalarial drugs, is safe and immunogenic in Asian populations.Methods: An open-label, randomized, controlled phase 2 trial was conducted in healthy, adult Thai volunteers. Seven vaccine regimens with and without antimalarial drugs (dihydroartemisinin-piperaquine plus a single low dose primaquine) were assessed. Antibody titres against the PfCSP full-length (NANP) 6, PfCSP anti-C-term, PfCSP full-length (N + C-Terminal) were measured by standard enzyme-linked immunosorbent assays. Liquid chromatography was used to measure piperaquine, primaquine and carboxy-primaquine concentrations.Results: 193 volunteers were enrolled and 186 study participants completed the 6 months follow-up period. One month after the last vaccination all study participants had seroconverted to the PfCSP (NANP)6, and the PfCSP Full Length (N + C-Terminal). More than 90% had seroconverted to the Pfanti-C-Term CSP. There was no indication that drug concentrations were influenced by vaccine regimens or the antibody levels by the drug regimens. Adverse events were similarly distributed between the seven treatment groups. No serious adverse events attributable to the study interventions were detected.Conclusion: This study found that RTS,S/AS01 with and without dihydroartemisinin-piperaquine plus a single low dose primaquine was safe and immunogenic in a healthy, adult Asian population.

Safety and efficacy of novel malaria vaccine regimens of RTS,S/AS01B alone, or with concomitant ChAd63-MVA-vectored vaccines expressing ME-TRAP.

We assessed a combination multi-stage malaria vaccine schedule in which RTS,S/AS01B was given concomitantly with viral vectors expressing multiple-epitope thrombospondin-related adhesion protein (ME-TRAP) in a 0-month, 1-month, and 2-month schedule. RTS,S/AS01B was given as either three full doses or with a fractional (1/5th) third dose. Efficacy was assessed by controlled human malaria infection (CHMI). Safety and immunogenicity of the vaccine regimen was also assessed. Forty-one malaria-naive adults received RTS,S/AS01B at 0, 4 and 8 weeks, either alone (Groups 1 and 2) or with ChAd63 ME-TRAP at week 0, and modified vaccinia Ankara (MVA) ME-TRAP at weeks 4 and 8 (Groups 3 and 4). Groups 2 and 4 received a fractional (1/5th) dose of RTS,S/AS01B at week 8. CHMI was delivered by mosquito bite 11 weeks after first vaccination. Vaccine efficacy was 6/8 (75%), 8/9 (88.9%), 6/10 (60%), and 5/9 (55.6%) of subjects in Groups 1, 2, 3, and 4, respectively. Immunological analysis indicated significant reductions in anti-circumsporozoite protein antibodies and TRAP-specific T cells at CHMI in the combination vaccine groups. This reduced immunogenicity was only observed after concomitant administration of the third dose of RTS,S/AS01B with the second dose of MVA ME-TRAP. The second dose of the MVA vector with a four-week interval caused significantly higher anti-vector immunity than the first and may have been the cause of immunological interference. Co-administration of ChAd63/MVA ME-TRAP with RTS,S/AS01B led to reduced immunogenicity and efficacy, indicating the need for evaluation of alternative schedules or immunization sites in attempts to generate optimal efficacy.

A randomized feasibility trial comparing four antimalarial drug regimens to induce Plasmodium falciparum gametocytemia in the controlled human malaria infection model.

Background: Malaria elimination strategies require a thorough understanding of parasite transmission from human to mosquito. A clinical model to induce gametocytes to understand their dynamics and evaluate transmission-blocking interventions (TBI) is currently unavailable. Here, we explore the use of the well-established Controlled Human Malaria Infection model (CHMI) to induce gametocyte carriage with different antimalarial drug regimens. Methods: In a single centre, open-label randomised trial, healthy malaria-naive participants (aged 18­35 years) were infected with Plasmodium falciparum by bites of infected Anopheles mosquitoes. Participants were randomly allocated to four different treatment arms (n = 4 per arm) comprising low-dose (LD) piperaquine (PIP) or sulfadoxine-pyrimethamine (SP), followed by a curative regimen upon recrudescence. Male and female gametocyte densities were determined by molecular assays. Results: Mature gametocytes were observed in all participants (16/16, 100%). Gametocytes appeared 8.5­12 days after the first detection of asexual parasites. Peak gametocyte densities and gametocyte burden was highest in the LD-PIP/SP arm, and associated with the preceding asexual parasite biomass (p=0.026). Male gametocytes had a mean estimated circulation time of 2.7 days (95% CI 1.5­3.9) compared to 5.1 days (95% CI 4.1­6.1) for female gametocytes. Exploratory mosquito feeding assays showed successful sporadic mosquito infections. There were no serious adverse events or significant differences in the occurrence and severity of adverse events between study arms (p=0.49 and p=0.28). Conclusions: The early appearance of gametocytes indicates gametocyte commitment during the first wave of asexual parasites emerging from the liver. Treatment by LD-PIP followed by a curative SP regimen, results in the highest gametocyte densities and the largest number of gametocyte-positive days. This model can be used to evaluate the effect of drugs and vaccines on gametocyte dynamics, and lays the foundation for fulfilling the critical unmet need to evaluate transmission-blocking interventions against falciparum malaria for downstream selection and clinical development. Funding: Funded by PATH Malaria Vaccine Initiative (MVI). Clinical trial number: NCT02836002.

The parasite that causes malaria, named Plasmodium falciparum, has a life cycle that involves both humans and mosquitoes. Starting in the saliva of female Anopheles mosquitoes, it enters a person's bloodstream when the insects feed. It then moves to the person's liver, where it infects liver cells and matures into a stage known as schizonts. The schizonts then divide to form thousands of so-called merozoites, which burst out of the liver cells and into the bloodstream. The merozoites infect red blood cells, producing more schizonts and yet more merozoites, which continue the infection. To complete its life cycle, the parasite must return to a mosquito. Some of the parasites in the person's blood transform into male and female cells called gametocytes that are taken up by a mosquito when it feeds on that person. Inside the mosquito, male and female parasites reproduce to create the next generation of parasites. The new parasites then move to the mosquito's salivary glands, ready to begin another infection. Stopping the parasite being transmitted from humans to mosquitoes will stop the spread of malaria in the population. Yet it has proven difficult to study this part of the life cycle from natural infections. Here, Reuling et al. report a new method for generating gametocytes in human volunteers that will enable closer study of the biology of malaria transmission. The method is developed using the Controlled Human Malaria Infection (CHMI) model. Healthy volunteers without a history of malaria are bitten by mosquitoes infected with malaria parasites. Shortly afterwards, the volunteers are given a drug treatment to control and reduce their symptoms. The gametocytes form during this phase of the infection. At the end of the experiment, all the volunteers receive a final treatment that completely cures the infection. Reuling et al. recruited 16 volunteers and assigned them to four groups at random. Each group received a different drug regime. Roughly a week after the mosquito bites, all participants showed malaria parasites in their blood, and between 8.5 and 12 days later, mature gametocytes started to appear. This early appearance suggests that the parasites start to transform into gametocytes when they first emerge from the liver. The experiment also revealed that female gametocytes stay in the blood for a longer period than their male counterparts. These results are proof of principle for a new way to investigate malaria infection. The new model provides a controlled method for studying P. falciparum gametocytes in people. In the future, it could help to test the impact of drugs and vaccines on gametocytes. Understanding more about these parasites' biology could lead to treatments that block malaria transmission.

Salivary Blockade Protects the Lower Respiratory Tract of Mice from Lethal Influenza Virus Infection.

It is possible to model the progression of influenza virus from the upper respiratory tract to the lower respiratory tract in the mouse using viral inoculum delivered in a restricted manner to the nose. In this model, infection with the A/Udorn/307/72 (Udorn) strain of virus results ultimately in high viral titers in both the trachea and lungs. In contrast, the A/Puerto Rico/8/34 (PR8) strain causes an infection that is almost entirely limited to the nasal passages. The factors that govern the progression of virus down the respiratory tract are not well understood. Here, we show that, while PR8 virus grows to high titers in the nose, an inhibitor present in the saliva blocks further progression of infection to the trachea and lungs and renders an otherwise lethal dose of virus completely asymptomatic. In vitro, the salivary inhibitor was capable of potent neutralization of PR8 virus and an additional 20 strains of type A virus and two type B strains that were tested. The exceptions were Udorn virus and the closely related H3N2 strains A/Port Chalmers/1/73 and A/Victoria/3/75. Characterization of the salivary inhibitor showed it to be independent of sialic acid and other carbohydrates for its function. This and other biochemical properties, together with its virus strain specificity and in vivo function, indicate that the mouse salivary inhibitor is a previously undescribed innate inhibitory molecule that may have evolved to provide pulmonary protection of the species from fatal influenza virus infection.IMPORTANCE Influenza A virus occasionally jumps from aquatic birds, its natural host, into mammals to cause outbreaks of varying severity, including pandemics in humans. Despite the laboratory mouse being used as a model to study influenza virus pathogenesis, natural outbreaks of influenza have not been reported in the species. Here, we shed light on one mechanism that might allow mice to be protected from influenza in the wild. We show that virus deposited in the mouse upper respiratory tract will not progress to the lower respiratory tract due to the presence of a potent inhibitor of the virus in saliva. Containing inhibitor-sensitive virus to the upper respiratory tract renders an otherwise lethal infection subclinical. This knowledge sheds light on how natural inhibitors may have evolved to improve survival in this species.

Safety and Reproducibility of a Clinical Trial System Using Induced Blood Stage Plasmodium vivax Infection and Its Potential as a Model to Evaluate Malaria Transmission.

BACKGROUND: Interventions to interrupt transmission of malaria from humans to mosquitoes represent an appealing approach to assist malaria elimination. A limitation has been the lack of systems to test the efficacy of such interventions before proceeding to efficacy trials in the field. We have previously demonstrated the feasibility of induced blood stage malaria (IBSM) infection with Plasmodium vivax. In this study, we report further validation of the IBSM model, and its evaluation for assessment of transmission of P. vivax to Anopheles stephensi mosquitoes. METHODS: Six healthy subjects (three cohorts, n = 2 per cohort) were infected with P. vivax by inoculation with parasitized erythrocytes. Parasite growth was monitored by quantitative PCR, and gametocytemia by quantitative reverse transcriptase PCR (qRT-PCR) for the mRNA pvs25. Parasite multiplication rate (PMR) and size of inoculum were calculated by linear regression. Mosquito transmission studies were undertaken by direct and membrane feeding assays over 3 days prior to commencement of antimalarial treatment, and midguts of blood fed mosquitoes dissected and checked for presence of oocysts after 7-9 days. RESULTS: The clinical course and parasitemia were consistent across cohorts, with all subjects developing mild to moderate symptoms of malaria. No serious adverse events were reported. Asymptomatic elevated liver function tests were detected in four of six subjects; these resolved without treatment. Direct feeding of mosquitoes was well tolerated. The estimated PMR was 9.9 fold per cycle. Low prevalence of mosquito infection was observed (1.8%; n = 32/1801) from both direct (4.5%; n = 20/411) and membrane (0.9%; n = 12/1360) feeds. CONCLUSION: The P. vivax IBSM model proved safe and reliable. The clinical course and PMR were reproducible when compared with the previous study using this model. The IBSM model presented in this report shows promise as a system to test transmission-blocking interventions. Further work is required to validate transmission and increase its prevalence. TRIAL REGISTRATION: Anzctr.org.au ACTRN12613001008718.

Safety and immunogenicity of RTS,S/AS01 malaria vaccine in infants and children with WHO stage 1 or 2 HIV disease: a randomised, double-blind, controlled trial.

BACKGROUND: Malaria remains a major global public health concern, especially in sub-Saharan Africa. The RTS,S/AS01 malaria candidate vaccine was reviewed by the European Medicines Agency and received a positive scientific opinion; WHO subsequently recommended pilot implementation in sub-Saharan African countries. Because malaria and HIV overlap geographically, HIV-infected children should be considered for RTS,S/AS01 vaccination. We therefore aimed to assess the safety of RTS,S/AS01 in HIV-infected children at two sites in western Kenya. METHODS: We did a randomised, double-blind, controlled trial at the clinical trial sites of the Kenya Medical Research Institute (KEMRI)-Walter Reed Army Institute of research in Kisumu and the KEMRI/US Centers for Disease Control and Prevention in Siaya. Eligible participants were infants and children aged from 6 weeks to 17 months with WHO stage 1 or 2 HIV disease (documented positive by DNA PCR), whether or not they were receiving antiretroviral therapy (ART). We randomly assigned participants (1:1) to receive three doses of either RTS,S/AS01 or rabies vaccine (both 0·5 mL per dose by intramuscular injection), given once per month at 0, 1, and 2 months. We did the treatment allocation using a web-based central randomisation system stratified by age (6 weeks-4 months, 5-17 months), and by baseline CD4% (<10, 10-14, 15-19, and ≥20). Data were obtained in an observer-blind manner, and the vaccine recipient, their parent or carer, the funder, and investigators responsible for the assessment of endpoints were all masked to treatment allocation (only staff responsible for the preparation and administration of the vaccines were aware of the assignment and these individuals played no other role in the study). We provided ART, even if the participants were not receiving ART before the study, and daily co-trimoxazole for prevention of opportunistic infections. The primary outcome was the occurrence of serious adverse events until 14 months after dose 1 of the vaccine, assessed in the intention-to-treat population. This trial was registered at ClinicalTrials.gov, number NCT01148459. FINDINGS: Between July 30, 2010, and May 24, 2013, we enrolled 200 children to our study and randomly assigned 99 to receive RTS,S/AS01 and 101 to receive rabies vaccine. 177 (89%) of the 200 children enrolled completed 14 months of follow-up. Serious adverse events were noted in 41 (41·4%, 95% CI 31·6-51·8) of 99 RTS,S/AS01 recipients and 37 (36·6%, 27·3-46·8) of 101 rabies-vaccine recipients (relative risk 1·1, 95% CI 0·8-1·6). 20 (20·2%, 95% CI 12·8-29·5) of 99 RTS,S/AS01 recipients and 12 (11·9%, 6·3-19·8) of 101 rabies-vaccine recipients had at least one serious adverse event within 30 days after vaccination, mainly pneumonia, febrile convulsions, and salmonella sepsis. Five (5·1%, 95% CI 1·7-11·4) of 99 RTS,S/AS01 recipients and four (4·0%, 1·1-9·8) of 101 rabies-vaccine recipients died, but no deaths were deemed related to vaccination. Mortality was associated with five cases of pneumonia (1% RTS,S/AS01 recipients vs 3% rabies-vaccine recipients), five cases of gastroenteritis (3% RTS,S/AS01 recipients vs 2% rabies-vaccine recipients), five cases of malnutrition (2% RTS,S/AS01 recipients vs 3% rabies-vaccine recipients), one case of sepsis (1% rabies-vaccine recipients), one case of Haemophilus influenza meningitis (1% rabies-vaccine recipients), and one case of tuberculosis (1% RTS,S/AS01 recipients). INTERPRETATION: RTS, S/AS01 was well tolerated when given to children with WHO clinical stage 1 or 2 HIV disease along with high antiretroviral and co-trimoxazole use. Children with HIV disease could be included in future RTS,S/AS01 vaccination programmes. FUNDING: GlaxoSmithKline Biologicals SA and PATH Malaria Vaccine Initiative.

Safety and High Level Efficacy of the Combination Malaria Vaccine Regimen of RTS,S/AS01B With Chimpanzee Adenovirus 63 and Modified Vaccinia Ankara Vectored Vaccines Expressing ME-TRAP.

BACKGROUND: The need for a highly efficacious vaccine against Plasmodium falciparum remains pressing. In this controlled human malaria infection (CHMI) study, we assessed the safety, efficacy and immunogenicity of a schedule combining 2 distinct vaccine types in a staggered immunization regimen: one inducing high-titer antibodies to circumsporozoite protein (RTS,S/AS01B) and the other inducing potent T-cell responses to thrombospondin-related adhesion protein (TRAP) by using a viral vector. METHOD: Thirty-seven healthy malaria-naive adults were vaccinated with either a chimpanzee adenovirus 63 and modified vaccinia virus Ankara-vectored vaccine expressing a multiepitope string fused to TRAP and 3 doses of RTS,S/AS01B (group 1; n = 20) or 3 doses of RTS,S/AS01B alone (group 2; n = 17). CHMI was delivered by mosquito bites to 33 vaccinated subjects at week 12 after the first vaccination and to 6 unvaccinated controls. RESULTS: No suspected unexpected serious adverse reactions or severe adverse events related to vaccination were reported. Protective vaccine efficacy was observed in 14 of 17 subjects (82.4%) in group 1 and 12 of 16 subjects (75%) in group 2. All control subjects received a diagnosis of blood-stage malaria parasite infection. Both vaccination regimens were immunogenic. Fourteen protected subjects underwent repeat CHMI 6 months after initial CHMI; 7 of 8 (87.5%) in group 1 and 5 of 6 (83.3%) in group 2 remained protected. CONCLUSIONS: The high level of sterile efficacy observed in this trial is encouraging for further evaluation of combination approaches using these vaccine types. CLINICAL TRIALS REGISTRATION: NCT01883609.

Demonstration of the Blood-Stage Plasmodium falciparum Controlled Human Malaria Infection Model to Assess Efficacy of the P. falciparum Apical Membrane Antigen 1 Vaccine, FMP2.1/AS01.

BACKGROUND: Models of controlled human malaria infection (CHMI) initiated by mosquito bite have been widely used to assess efficacy of preerythrocytic vaccine candidates in small proof-of-concept phase 2a clinical trials. Efficacy testing of blood-stage malaria parasite vaccines, however, has generally relied on larger-scale phase 2b field trials in malaria-endemic populations. We report the use of a blood-stage P. falciparum CHMI model to assess blood-stage vaccine candidates, using their impact on the parasite multiplication rate (PMR) as the primary efficacy end point. METHODS: Fifteen healthy United Kingdom adult volunteers were vaccinated with FMP2.1, a protein vaccine that is based on the 3D7 clone sequence of apical membrane antigen 1 (AMA1) and formulated in Adjuvant System 01 (AS01). Twelve vaccinees and 15 infectivity controls subsequently underwent blood-stage CHMI. Parasitemia was monitored by quantitative real-time polymerase chain reaction (PCR) analysis, and PMR was modeled from these data. RESULTS: FMP2.1/AS01 elicited anti-AMA1 T-cell and serum antibody responses. Analysis of purified immunoglobulin G showed functional growth inhibitory activity against P. falciparum in vitro. There were no vaccine- or CHMI-related safety concerns. All volunteers developed blood-stage parasitemia, with no impact of the vaccine on PMR. CONCLUSIONS: FMP2.1/AS01 demonstrated no efficacy after blood-stage CHMI. However, the model induced highly reproducible infection in all volunteers and will accelerate proof-of-concept testing of future blood-stage vaccine candidates. CLINICAL TRIALS REGISTRATION: NCT02044198.

Safety Monitoring in Group A Meningococcal Conjugate Vaccine Trials: Description, Challenges, and Lessons.

BACKGROUND: The determination of the safety profile of any vaccine is critical to its widespread use in any population. In addition, the application of international guidelines to fit local context could be a challenging but important step toward obtaining quality safety data. METHODS: In clinical studies of PsA-TT (MenAfriVac), safety was monitored immediately after vaccination, at 4-7 days for postimmunization local and systemic reactions, within 28 days for adverse events, and throughout the duration of study for serious adverse events. Initial and ongoing training of sites' staff were undertaken during the studies, and a data and safety monitoring board reviewed all the data during and after the studies. RESULTS: The safety of PsA-TT was evaluated according to international standards despite obvious challenges in remote areas where these studies were conducted. These challenges included the need for uniformity of methods, timely reporting in the context of frequent communication problems, occurrence of seasonal diseases such as malaria and rotavirus diarrhea, and healthcare systems that required improvement. CONCLUSIONS: The trials of PsA-TT highlighted the value of a robust vaccine development plan and design so that lessons learned in initial studies were incorporated into the subsequent ones, initial training and periodic retraining, strict monitoring of all procedures, and continuous channel of communication with all stakeholders that enabled the application of international requirements to local settings, with high quality of data.

Design of a Phase III cluster randomized trial to assess the efficacy and safety of a malaria transmission blocking vaccine.

Vaccines interrupting Plasmodium falciparum malaria transmission targeting sexual, sporogonic, or mosquito-stage antigens (SSM-VIMT) are currently under development to reduce malaria transmission. An international group of malaria experts was established to evaluate the feasibility and optimal design of a Phase III cluster randomized trial (CRT) that could support regulatory review and approval of an SSM-VIMT. The consensus design is a CRT with a sentinel population randomly selected from defined inner and buffer zones in each cluster, a cluster size sufficient to assess true vaccine efficacy in the inner zone, and inclusion of ongoing assessment of vaccine impact stratified by distance of residence from the cluster edge. Trials should be conducted first in areas of moderate transmission, where SSM-VIMT impact should be greatest. Sample size estimates suggest that such a trial is feasible, and within the range of previously supported trials of malaria interventions, although substantial issues to implementation exist.

Heterogeneity of freshly isolated human tonsil dendritic cells demonstrated by intracellular markers, phagocytosis, and membrane dye transfer.

BACKGROUND: Heterogeneity within human dendritic cells (DCs) has been described but its functional relationships to cells of macrophage lineage and its role in human immunodeficiency virus (HIV) infection in vivo remain unclear. METHODS: Tonsil macrophages and DCs were isolated from low-density cells by negative selection and DCs were sorted into myeloid and plasmacytoid populations using antibodies to CD11c or CD123. Phagocytosis of latex beads and uptake of dye-labeled target cells were compared by flow cytometry and CD68 and S-100 by immunofluorescence on cytospins of sorted cells. RESULTS: Bead uptake and membrane dye transfer were found in both blood and tonsil CD11c(+) DCs and in CD14(+) cells particularly from blood monocytes. CD11c(-) DCs were poorly phagocytic but took up fluorescent dye from intact, necrotic or apoptotic cells. Tonsil DCs and macrophages expressed both CD68 and S-100 but CD11c(-) DCs expressed CD68 only. CONCLUSIONS: Freshly isolated CD11c(+) tonsil DCs are similar to CD14(+) macrophages in phagocytic function but the poorly phagocytic CD11c(-) DCs can also take up membrane from target cells. The intracellular markers commonly used to identify DCs and macrophages in situ do not identify accurately the CD11c(-) DC subset nor do they distinguish tonsil macrophages from DCs.