Impact of RTS,S/AS02A and RTS,S/AS01B on Genotypes of P. falciparum in Adults Participating in a Malaria Vaccine Clinical Trial

Objective

RTS,S, a candidate vaccine for malaria, is a recombinant protein expressed in yeast containing part of the circumsporozoite protein (CSP) sequence of 3D7 strain of Plasmodium falciparum linked to the hepatitis B surface antigen in a hybrid protein. The RTS,S antigen is formulated with GSK Biologicals'' proprietary Adjuvant Systems AS02_A or AS01_B. A recent trial of the RTS,S/AS02_A and RTS,S/AS01_B vaccines evaluated safety, immunogenicity and impact on the development of parasitemia of the two formulations. Parasite isolates from this study were used to determine the molecular impact of RTS,S/AS02_A and RTS,S/AS01_B on the multiplicity of infection (MOI) and the csp allelic characteristics of subsequent parasitemias.

Design

The distribution of csp sequences and the MOI of the infecting strains were examined at baseline and in break-through infections from vaccinated individuals and from those receiving a non-malarial vaccine.

Setting

The study was conducted in Kombewa District, western Kenya.

Participants

Semi-immune adults from the three study arms provided isolates at baseline and during break-through infections.

Outcome

Parasite isolates used for determining MOI and divergence of csp T cell–epitopes were 191 at baseline and 87 from break-through infections.

Results

Grouping recipients of RTS,S/AS01_A and RTS,S/AS02_B together, vaccine recipients identified as parasite-positive by microscopy contained significantly fewer parasite genotypes than recipients of the rabies vaccine comparator (median in pooled RTS,S groups: 3 versus 4 in controls, P = 0.0313). When analyzed separately, parasitaemic individuals in the RTS,S/AS01_B group, but not the RTS,S/AS02_A group, were found to have significantly fewer genotypes than the comparator group. Two individual amino acids found in the vaccine construct (Q339 in Th2R and D371 in Th3R) were observed to differ in incidence between vaccine and comparator groups but in different directions; parasites harboring Q339 were less common among pooled RTS,S/AS vaccine recipients than among recipients of rabies vaccine, whereas parasites with D371 were more common among the RTS,S/AS groups.

Conclusions

It is concluded that both RTS,S/AS vaccines reduce multiplicity of infection. Our results do not support the hypothesis that RTS,S/AS vaccines elicit preferential effects against pfcsp alleles with sequence similarity to the 3D7 pfcsp sequence employed in the vaccine construct.     

Randomized Controlled Trial of RTS,S/AS02D and RTS,S/AS01E Malaria Candidate Vaccines Given According to Different Schedules in Ghanaian Children

Background

The target delivery channel of RTS,S candidate malaria vaccines in malaria-endemic countries in Africa is the World Health Organisation Expanded Program on Immunization. As an Adjuvant System, age de-escalation and schedule selection step, this study assessed 3 schedules of RTS,S/AS01_E and RTS,S/AS02_D in infants and young children 5–17 months of age in Ghana.

Methodology

A Phase II, partially-blind randomized controlled study (blind to vaccine, not to schedule), of 19 months duration was conducted in two (2) centres in Ghana between August 2006 and May 2008. Subjects were allocated randomly (1∶1∶1∶1∶1∶1) to one of six study groups at each study site, each defining which vaccine should be given and by which schedule (0,1-, 0,1,2- or 0,1,7-months). For the 0,1,2-month schedule participants received RTS,S/AS01_E or rabies vaccine at one center and RTS,S/AS01_E or RTS,S/AS02_D at the other. For the other schedules at both study sites, they received RTS,S/AS01_E or RTS,S/AS02_D. The primary outcome measure was the occurrence of serious adverse events until 10 months post dose 1.

Results

The number of serious adverse events reported across groups was balanced. One child had a simple febrile convulsion, which evolved favourably without sequelae, considered to be related to RTS,S/AS01_E vaccination. Low grade reactions occurred slightly more frequently in recipients of RTS,S/AS than rabies vaccines; grade 3 reactions were infrequent. Less local reactogenicity occurred with RTS,S/AS01_E than RTS,S/AS02_D. Both candidate vaccines were highly immunogenic for anti-circumsporozoite and anti-Hepatitis B Virus surface antigen antibodies. Recipients of RTS,S/AS01_E compared to RTS,S/AS02_D had higher peak anti-circumsporozoite antibody responses for all 3 schedules. Three dose schedules were more immunogenic than 2 dose schedules. Area under the curve analyses for anti-circumsporozoite antibodies were comparable between the 0,1,2- and 0,1,7-month RTS,S/AS01_E schedules.

Conclusions

Both candidate malaria vaccines were well tolerated. Anti-circumsporozoite responses were greater with RTS,S/AS01_E than RTS,S/AS02_D and when 3 rather than 2 doses were given. This study supports the selection of RTS,S/AS01_E and a 3 dose schedule for further development in children and infants.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00360230","term_id":"NCT00360230"}}NCT00360230     

A Randomized Trial Assessing the Safety and Immunogenicity of AS01 and AS02 Adjuvanted RTS,S Malaria Vaccine Candidates in Children in Gabon

Background

The malaria vaccine candidate antigen RTS,S includes parts of the pre-erythrocytic stage circumsporozoite protein fused to the Hepatitis B surface antigen. Two Adjuvant Systems are in development for this vaccine, an oil-in water emulsion – based formulation (AS02) and a formulation based on liposomes (AS01).

Methods & Principal Findings

In this Phase II, double-blind study ({"type":"clinical-trial","attrs":{"text":"NCT00307021","term_id":"NCT00307021"}}NCT00307021), 180 healthy Gabonese children aged 18 months to 4 years were randomized to receive either RTS,S/AS01_E or RTS,S/AS02_D, on a 0–1–2 month vaccination schedule. The children were followed-up daily for six days after each vaccination and monthly for 14 months. Blood samples were collected at 4 time-points. Both vaccines were well tolerated. Safety parameters were distributed similarly between the two groups. Both vaccines elicited a strong specific immune response after Doses 2 and 3 with a ratio of anti-CS GMT titers (AS02_D/AS01_E) of 0.88 (95% CI: 0.68–1.15) post-Dose 3. After Doses 2 and 3 of experimental vaccines, anti-CS and anti-HBs antibody GMTs were higher in children who had been previously vaccinated with at least one dose of hepatitis B vaccine compared to those not previously vaccinated.

Conclusions

RTS,S/AS01_E proved similarly as well tolerated and immunogenic as RTS,S/AS02_D, completing an essential step in the age de-escalation process within the RTS,S clinical development plan.

Trial Registration

ClinicalTrials.gov. {"type":"clinical-trial","attrs":{"text":"NCT00307021","term_id":"NCT00307021"}}NCT00307021     

Induction of Plasmodium falciparum-specific CD4+ T cells and memory B cells in Gabonese children vaccinated with RTS,S/AS01(E) and RTS,S/AS02(D)

The recombinant circumsporozoite protein (CS) based vaccine, RTS,S, confers protection against Plasmodium falciparum infection in controlled challenge trials and in field studies. The RTS,S recombinant antigen has been formulated with two adjuvant systems, AS01 and AS02, which have both been shown to induce strong specific antibody responses and CD4 T cell responses in adults. As infants and young children are particularly susceptible to malaria infection and constitute the main target population for a malaria vaccine, we have evaluated the induction of adaptive immune responses in young children living in malaria endemic regions following vaccination with RTS,S/AS01(E) and RTS,S/AS02(D). Our data show that a CS-specific memory B cell response is induced one month after the second and third vaccine dose and that CS-specific antibodies and memory B cells persist up to 12 months after the last vaccine injection. Both formulations also induced low but significant amounts of CS-specific IL-2(+) CD4(+) T cells one month after the second and third vaccine dose, upon short-term in vitro stimulation of whole blood cells with peptides covering the entire CS derived sequence in RTS,S. These results provide evidence that both RTS,S/AS01(E) and RTS,S/AS02(D) induced adaptive immune responses including antibodies, circulating memory B cells and CD4(+) T cells directed against P. falciparum CS protein. TRIAL REGISTRATION: ClinicalTrials.gov NCT00307021.     

Malaria: deploying a candidate vaccine (RTS,S/AS02A) for an old scourge of humankind.

Malaria is an infectious disease caused by the protist Plasmodium spp. and it currently kills more than one million people annually. The burden of malaria is concentrated in sub-Saharan Africa, India, and Southeast Asia. The parasite's resistance to commonly used anti-malarial drugs has worsened the situation in the poorest countries. The World Health Organization (WHO) estimates that more than 100 countries suffer from endemic malaria episodes. In addition to numerous control measures and treatments, several vaccines are at different research stages and trials. We have assayed RTS,S/AS02A, a pre-erythrocytic candidate vaccine that has shown promising protection levels in phase IIb trials in Mozambique. The vaccine is directed against the sporozoite form of the parasite, which is injected by the mosquito Anopheles spp. The vaccine induces a strong antibody response and stimulates Th1 cells-a subset of helper T cells that participates in cell-mediated immunity. Recent interest by international funding agencies has provided new inputs into initiatives and programs to fight malaria, which, under normal welfare and adequate social development conditions, is a curable disease.     

T cell responses to the RTS,S/AS01(E) and RTS,S/AS02(D) malaria candidate vaccines administered according to different schedules to Ghanaian children

Background

The Plasmodium falciparum pre-erythrocytic stage candidate vaccine RTS,S is being developed for protection of young children against malaria in sub-Saharan Africa. RTS,S formulated with the liposome based adjuvant AS01_E or the oil-in-water based adjuvant AS02_D induces P. falciparum circumsporozoite (CSP) antigen-specific antibody and T cell responses which have been associated with protection in the experimental malaria challenge model in adults.

Methods

This study was designed to evaluate the safety and immunogenicity induced over a 19 month period by three vaccination schedules (0,1-, 0,1,2- and 0,1,7-month) of RTS,S/AS01_E and RTS,S/AS02_D in children aged 5–17 months in two research centers in Ghana. Control Rabies vaccine using the 0,1,2-month schedule was used in one of two study sites.

Results

Whole blood antigen stimulation followed by intra-cellular cytokine staining showed RTS,S/AS01_E induced CSP specific CD4 T cells producing IL-2, TNF-α, and IFN-γ. Higher T cell responses were induced by a 0,1,7-month immunization schedule as compared with a 0,1- or 0,1,2-month schedule. RTS,S/AS01_E induced higher CD4 T cell responses as compared to RTS,S/AS02_D when given on a 0,1,7-month schedule.

Conclusions

These findings support further Phase III evaluation of RTS,S/AS01_E. The role of immune effectors and immunization schedules on vaccine protection are currently under evaluation.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00360230","term_id":"NCT00360230"}}NCT00360230     

A Statistical Interaction between Circumsporozoite Protein-Specific T Cell and Antibody Responses and Risk of Clinical Malaria Episodes following Vaccination with RTS,S/AS01E

The candidate malaria vaccine RTS,S/AS01_E provides significant but partial protection from clinical malaria. On in vitro circumsporozoite protein (CSP) peptide stimulation and intra-cellular cytokine staining of whole blood taken from 407 5–17 month-old children in a phase IIb trial of RTS,S/AS01_E, we identified significantly increased frequencies of two CSP-specific CD4+ T cells phenotypes among RTS,S/AS01_E vaccinees (IFNγ-IL2+TNF− and IFNγ-IL2+TNF+ CD4+ T cells), and increased frequency of IFNγ-IL2-TNF+ CD4+ T cells after natural exposure. All these T cells phenotypes were individually associated with reductions in the risk of clinical malaria, but IFNγ-IL2-TNF+ CD4+ T cells independently predicted reduced risk of clinical malaria on multi-variable analysis (HR = 0.29, 95% confidence intervals 0.15–0.54, p<0.0005). Furthermore, there was a strongly significant synergistic interaction between CSP-specific IFNγ-IL2-TNF+ CD4+ T cells and anti-CSP antibodies in determining protection against clinical malaria (p = 0.002). Vaccination strategies that combine potent cellular and antibody responses may enhance protection against malaria.     

Avidity of Anti-Circumsporozoite Antibodies following Vaccination with RTS,S/AS01E in Young Children

Background

The nature of protective immune responses elicited by immunization with the candidate malaria vaccine RTS,S is still incompletely understood. Antibody levels correlate with protection against malaria infection, but considerable variation in outcome is unexplained (e.g., children may experience malaria despite high anti-circumsporozoite [CS] titers).

Methods and Findings

We measured the avidity index (AI) of the anti-CS antibodies raised in subgroup of 5–17 month old children in Kenya who were vaccinated with three doses of RTS,S/AS01_E between March and August 2007. We evaluated the association between the AI and the subsequent risk of clinical malaria. We selected 19 cases (i.e., with clinical malaria) and 42 controls (i.e., without clinical malaria), matching for anti-CS antibody levels and malaria exposure. We assessed their sera collected 1 month after the third dose of the vaccine, in March 2008 (range 4–10 months after the third vaccine), and at 12 months after the third vaccine dose. The mean AI was 45.2 (95% CI: 42.4 to 48.1), 45.3 (95% CI: 41.4 to 49.1) and 46.2 (95% CI; 43.2 to 49.3) at 1 month, in March 2008 (4–10 months), and at 12 months after the third vaccination, respectively (p = 0.9 by ANOVA test for variation over time). The AI was not associated with protection from clinical malaria (OR = 0.90; 95% CI: 0.49 to 1.66; p = 0.74). The AI was higher in children with high malaria exposure, as measured using the weighted local prevalence of malaria, compared to those with low malaria exposure at 1 month post dose 3 (p = 0.035).

Conclusion

Our data suggest that in RTS,S/AS01_E-vaccinated children residing in malaria endemic countries, the avidity of anti-circumsporozoite antibodies, as measured using an elution ELISA method, was not associated with protection from clinical malaria. Prior natural malaria exposure might have primed the response to RTS,S/AS01_E vaccination.     

Estimated impact of RTS,S/AS01 malaria vaccine allocation strategies in sub-Saharan Africa: A modelling study

BackgroundThe RTS,S/AS01 vaccine against Plasmodium falciparum malaria infection completed phase III trials in 2014 and demonstrated efficacy against clinical malaria of approximately 36% over 4 years for a 4-dose schedule in children aged 5–17 months. Pilot vaccine implementation has recently begun in 3 African countries. If the pilots demonstrate both a positive health impact and resolve remaining safety concerns, wider roll-out could be recommended from 2021 onwards. Vaccine demand may, however, outstrip initial supply. We sought to identify where vaccine introduction should be prioritised to maximise public health impact under a range of supply constraints using mathematical modelling.Methods and findingsUsing a mathematical model of P. falciparum malaria transmission and RTS,S vaccine impact, we estimated the clinical cases and deaths averted in children aged 0–5 years in sub-Saharan Africa under 2 scenarios for vaccine coverage (100% and realistic) and 2 scenarios for other interventions (current coverage and World Health Organization [WHO] Global Technical Strategy targets). We used a prioritisation algorithm to identify potential allocative efficiency gains from prioritising vaccine allocation among countries or administrative units to maximise cases or deaths averted. If malaria burden at introduction is similar to current levels—assuming realistic vaccine coverage and country-level prioritisation in areas with parasite prevalence >10%—we estimate that 4.3 million malaria cases (95% credible interval [CrI] 2.8–6.8 million) and 22,000 deaths (95% CrI 11,000–35,000) in children younger than 5 years could be averted annually at a dose constraint of 30 million. This decreases to 3.0 million cases (95% CrI 2.0–4.7 million) and 14,000 deaths (95% CrI 7,000–23,000) at a dose constraint of 20 million, and increases to 6.6 million cases (95% CrI 4.2–10.8 million) and 38,000 deaths (95% CrI 18,000–61,000) at a dose constraint of 60 million. At 100% vaccine coverage, these impact estimates increase to 5.2 million cases (95% CrI 3.5–8.2 million) and 27,000 deaths (95% CrI 14,000–43,000), 3.9 million cases (95% CrI 2.7–6.0 million) and 19,000 deaths (95% CrI 10,000–30,000), and 10.0 million cases (95% CrI 6.7–15.7 million) and 51,000 deaths (95% CrI 25,000–82,000), respectively. Under realistic vaccine coverage, if the vaccine is prioritised sub-nationally, 5.3 million cases (95% CrI 3.5–8.2 million) and 24,000 deaths (95% CrI 12,000–38,000) could be averted at a dose constraint of 30 million. Furthermore, sub-national prioritisation would allow introduction in almost double the number of countries compared to national prioritisation (21 versus 11). If vaccine introduction is prioritised in the 3 pilot countries (Ghana, Kenya, and Malawi), health impact would be reduced, but this effect becomes less substantial (change of <5%) if 50 million or more doses are available. We did not account for within-country variation in vaccine coverage, and the optimisation was based on a single outcome measure, therefore this study should be used to understand overall trends rather than guide country-specific allocation.ConclusionsThese results suggest that the impact of constraints in vaccine supply on the public health impact of the RTS,S malaria vaccine could be reduced by introducing the vaccine at the sub-national level and prioritising countries with the highest malaria incidence.

Alexandra Hogan and colleagues explore strategies to optimize vaccine allocation for maximum public health benefit in the face of potential supply constraints.     

Simulated impact of RTS,S/AS01 vaccination programs in the context of changing malaria transmission

Introduction

The RTS,S/AS01 pre-erythrocytic malaria vaccine is in phase III clinical trials. It is critical to anticipate where and how it should be implemented if trials are successful. Such planning may be complicated by changing levels of malaria transmission.

Methods/results

Computer simulations were used to examine RTS,S/AS01 impact, using a vaccine profile based on phase II trial results, and assuming that protection decays only slowly. Settings were simulated in which baseline transmission (in the absence of vaccine) was fixed or varied between 2 and 20 infectious mosquito bites per person per annum (ibpa) over ten years. Four delivery strategies were studied: routine infant immunization (EPI), EPI plus infant catch-up, EPI plus school-based campaigns, and EPI plus mass campaigns. Impacts in changing transmission settings were similar to those in fixed settings. Assuming a persistent effect of vaccination, at 2 ibpa, the vaccine averted approximately 5–7 deaths per 1000 doses of vaccine when delivered via mass campaigns, but the benefit was less at higher transmission levels. EPI, catch-up and school-based strategies averted 2–3 deaths per 1000 doses in settings with 2 ibpa. In settings where transmission was decreasing or increasing, EPI, catch-up and school-based strategies averted approximately 3–4 deaths per 1000 doses.

Discussion

Where transmission is changing, it appears to be sufficient to consider simulations of pre-erythrocytic vaccine impact at a range of initial transmission levels. At 2 ibpa, mass campaigns averted the most deaths and reduced transmission, but this requires further study. If delivered via EPI, RTS,S/AS01 could avert approximately 6–11 deaths per 1000 vaccinees in all examined settings, similar to estimates for pneumococcal conjugate vaccine in African infants. These results support RTS,S/AS01 implementation via EPI, for example alongside vector control interventions, providing that the phase III trials provide support for our assumptions about efficacy.     

Phase 1/2a Trial of Plasmodium vivax Malaria Vaccine Candidate VMP001/AS01B in Malaria-Naive Adults: Safety,Immunogenicity, and Efficacy

Background

A vaccine to prevent infection and disease caused by Plasmodium vivax is needed both to reduce the morbidity caused by this parasite and as a key component in efforts to eradicate malaria worldwide. Vivax malaria protein 1 (VMP001), a novel chimeric protein that incorporates the amino- and carboxy- terminal regions of the circumsporozoite protein (CSP) and a truncated repeat region that contains repeat sequences from both the VK210 (type 1) and the VK247 (type 2) parasites, was developed as a vaccine candidate for global use.

Methods

We conducted a first-in-human Phase 1 dose escalation vaccine study with controlled human malaria infection (CHMI) of VMP001 formulated in the GSK Adjuvant System AS01_B. A total of 30 volunteers divided into 3 groups (10 per group) were given 3 intramuscular injections of 15μg, 30μg, or 60μg respectively of VMP001, all formulated in 500μL of AS01_B at each immunization. All vaccinated volunteers participated in a P. vivax CHMI 14 days following the third immunization. Six non-vaccinated subjects served as infectivity controls.

Results

The vaccine was shown to be well tolerated and immunogenic. All volunteers generated robust humoral and cellular immune responses to the vaccine antigen. Vaccination did not induce sterile protection; however, a small but significant delay in time to parasitemia was seen in 59% of vaccinated subjects compared to the control group. An association was identified between levels of anti-type 1 repeat antibodies and prepatent period.

Significance

This trial was the first to assess the efficacy of a P. vivax CSP vaccine candidate by CHMI. The association of type 1 repeat-specific antibody responses with delay in the prepatency period suggests that augmenting the immune responses to this domain may improve strain-specific vaccine efficacy. The availability of a P. vivax CHMI model will accelerate the process of P. vivax vaccine development, allowing better selection of candidate vaccines for advancement to field trials.     

Malaria Morbidity in High and Seasonal Malaria Transmission Area of Burkina Faso

Background

Malariometric parameters are often primary endpoints of efficacy trials of malaria vaccine candidates. This study aims to describe the epidemiology of malaria prior to the conduct of a series of drug and vaccine trials in a rural area of Burkina Faso.

Methods

Malaria incidence was prospectively evaluated over one year follow-up among two cohorts of children aged 0–5 years living in the Saponé health district. The parents of 1089 children comprising a passive case detection cohort were encouraged to seek care from the local health clinic at any time their child felt sick. Among this cohort, 555 children were randomly selected for inclusion in an active surveillance sub-cohort evaluated for clinical malaria during twice weekly home visits. Malaria prevalence was evaluated by cross-sectional survey during the low and high transmission seasons.

Results

Number of episodes per child ranged from 0 to 6 per year. Cumulative incidence was 67.4% in the passive and 86.2% in the active cohort and was highest among children 0–1 years. Clinical malaria prevalence was 9.8% in the low and 13.0% in the high season (p>0.05). Median days to first malaria episode ranged from 187 (95% CI 180–193) among children 0–1 years to 228 (95% CI 212, 242) among children 4–5 years. The alternative parasite thresholds for the malaria case definition that achieved optimal sensitivity and specificity (70–80%) were 3150 parasites/µl in the high and 1350 parasites/µl in the low season.

Conclusion

Clinical malaria burden was highest among the youngest age group children, who may represent the most appropriate target population for malaria vaccine candidate development. The pyrogenic threshold of parasitaemia varied markedly by season, suggesting a value for alternative parasitaemia levels in the malaria case defintion. Regional epidemiology of malaria described, Sapone area field centers are positioned for future conduct of malaria vaccine trials.     

Circumsporozoite-specific T cell responses in children vaccinated with RTS,S/AS01E and protection against P falciparum clinical malaria

Background

RTS,S/AS01_E is the lead candidate pre-erythrocytic malaria vaccine. In Phase IIb field trials the safety profile was acceptable and the efficacy was 53% (95%CI 31%–72%) for protecting children against clinical malaria caused by P. falciparum. We studied CS-specific T cell responses in order to identify correlates of protection.

Methods and Findings

We used intracellular cytokine staining (for IL2, IFNγ, and TNFα), ex-vivo ELISPOTs (IFNγ and IL2) and IFNγ cultured ELISPOT assays to characterize the CS-specific cellular responses in 407 children (5–17 months of age) in a phase IIb randomized controlled trial of RTS,S/AS01_E ({"type":"clinical-trial","attrs":{"text":"NCT00380393","term_id":"NCT00380393"}}NCT00380393). RTS,S/ AS01_E vaccinees had higher frequencies of CS-specific CD4+ T cells producing IFNγ, TNFα or IL2 compared to control vaccinees. In a multivariable analysis TNFα⁺ CD4⁺ T cells were independently associated with a reduced risk for clinical malaria among RTS,S/AS01_E vaccinees (HR = 0.64, 95%CI 0.49–0.86, p = 0.002). There was a non-significant tendency towards reduced risk among control vaccinees (HR = 0.80, 95%CI 0.62–1.03, p = 0.084), albeit with lower CS-specific T cell frequencies and higher rates of clinical malaria. When data from both RTS,S/AS01_E vaccinees and control vaccinees were combined (with adjusting for vaccination group), the HR was 0.74 (95%CI 0.62–0.89, p = 0.001). After a Bonferroni correction for multiple comparisons (n-18), the finding was still significant at p = 0.018. There was no significant correlation between cultured or ex vivo ELISPOT data and protection from clinical malaria. The combination of TNFα⁺ CD4⁺ T cells and anti-CS antibody statistically accounted for the protective effect of vaccination in a Cox regression model.

Conclusions

RTS,S/AS01_E induces CS-specific Th1 T cell responses in young children living in a malaria endemic area. The combination of anti-CS antibody concentrations titers and CS-specific TNFα⁺ CD4⁺ T cells could account for the level of protection conferred by RTS,S/AS01_E. The correlation between CS-specific TNFα⁺ CD4⁺ T cells and protection needs confirmation in other datasets.     

Safety of the malaria vaccine candidate, RTS,S/AS01E in 5 to 17 month old Kenyan and Tanzanian Children

The malaria vaccine candidate, RTS,S/AS01(E), showed promising protective efficacy in a trial of Kenyan and Tanzanian children aged 5 to 17 months. Here we report on the vaccine's safety and tolerability. The experimental design was a Phase 2b, two-centre, double-blind (observer- and participant-blind), randomised (1∶1 ratio) controlled trial. Three doses of study or control (rabies) vaccines were administered intramuscularly at 1 month intervals. Solicited adverse events (AEs) were collected for 7 days after each vaccination. There was surveillance and reporting for unsolicited adverse events for 30 days after each vaccination. Serious adverse events (SAEs) were recorded throughout the study period which lasted for 14 months after dose 1 in Korogwe, Tanzania and an average of 18 months post-dose 1 in Kilifi, Kenya. Blood samples for safety monitoring of haematological, renal and hepatic functions were taken at baseline, 3, 10 and 14 months after dose 1. A total of 894 children received RTS,S/AS01(E) or rabies vaccine between March and August 2007. Overall, children vaccinated with RTS,S/AS01(E) had fewer SAEs (51/447) than children in the control group (88/447). One SAE episode in a RTS,S/AS01(E) recipient and nine episodes among eight rabies vaccine recipients met the criteria for severe malaria. Unsolicited AEs were reported in 78% of subjects in the RTS,S/AS01(E) group and 74% of subjects in the rabies vaccine group. In both vaccine groups, gastroenteritis and pneumonia were the most frequently reported unsolicited AE. Fever was the most frequently observed solicited AE and was recorded after 11% of RTS,S/AS01(E) doses compared to 31% of doses of rabies vaccine. The candidate vaccine RTS,S/AS01(E) showed an acceptable safety profile in children living in a malaria-endemic area in East Africa. More data on the safety of RTS,S/AS01(E) will become available from the Phase 3 programme.     

Antigen-specific IL-2 secretion correlates with NK cell responses after immunization of Tanzanian children with the RTS,S/AS01 malaria vaccine

RTS,S/AS01, a vaccine targeting pre-erythrocytic stages of Plasmodium falciparum, is undergoing clinical trials. We report an analysis of cellular immune response to component Ags of RTS,S-hepatitis B surface Ag (HBs) and P. falciparum circumsporozoite (CS) protein-among Tanzanian children in a phase IIb RTS,S/AS01(E) trial. RTS,S/AS01 (E) vaccinees make stronger T cell IFN-γ, CD69, and CD25 responses to HBs peptides than do controls, indicating that RTS,S boosts pre-existing HBs responses. T cell CD69 and CD25 responses to CS and CS-specific secreted IL-2 were augmented by RTS,S vaccination. Importantly, more than 50% of peptide-induced IFN-γ(+) lymphocytes were NK cells, and the magnitude of the NK cell CD69 response to HBs peptides correlated with secreted IL-2 concentration. CD69 and CD25 expression and IL-2 secretion may represent sensitive markers of RTS,S-induced, CS-specific T cells. The potential for T cell-derived IL-2 to augment NK cell activation in RTS,S-vaccinated individuals, and the relevance of this for protection, needs to be explored further.     

Safety, immunogenicity and duration of protection of the RTS,S/AS02(D) malaria vaccine: one year follow-up of a randomized controlled phase I/IIb trial

Background

The RTS,S/AS02_D vaccine has been shown to have a promising safety profile, to be immunogenic and to confer protection against malaria in children and infants.

Methods and Findings

We did a randomized, controlled, phase I/IIb trial of RTS,S/AS02_D given at 10, 14 and 18 weeks of age staggered with routine immunization vaccines in 214 Mozambican infants. The study was double-blind until the young child completed 6 months of follow-up over which period vaccine efficacy against new Plasmodium falciparum infections was estimated at 65.9% (95% CI 42.6–79.8, p<0.0001). We now report safety, immunogenicity and estimated efficacy against clinical malaria up to 14 months after study start. Vaccine efficacy was assessed using Cox regression models. The frequency of serious adverse events was 32.7% in the RTS,S/AS02_D and 31.8% in the control group. The geometric mean titers of anti-circumsporozoite antibodies declined from 199.9 to 7.3 EU/mL from one to 12 months post dose three of RTS,S/AS02_D, remaining 15-fold higher than in the control group. Vaccine efficacy against clinical malaria was 33% (95% CI: −4.3–56.9, p = 0.076) over 14 months of follow-up. The hazard rate of disease per 2-fold increase in anti-CS titters was reduced by 84% (95% CI 35.1–88.2, p = 0.003).

Conclusion

The RTS,S/AS02_D malaria vaccine administered to young infants has a good safety profile and remains efficacious over 14 months. A strong association between anti-CS antibodies and risk of clinical malaria has been described for the first time. The results also suggest a decrease of both anti-CS antibodies and vaccine efficacy over time.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00197028","term_id":"NCT00197028"}}NCT00197028     

Rare B(A)02/O01 was found in Sichuan again: a case report

B(A) is a rare ABO blood subgroup. Here we reported a B(A)02/O01 case. One 25-year-old female patient showed inconsistent forward and reverse blood grouping results based on micro-column gel agglutination assay. PCR-SSP and PCR-SBT based genotyping indicated that the patient was B(A)02/O01 heterozygous.     

Genetic Variation in the Plasmodium falciparum Circumsporozoite Protein in India and Its Relevance to RTS,S Malaria Vaccine

RTS,S is the most advanced malaria vaccine candidate, currently under phase-III clinical trials in Africa. This Plasmodium falciparum vaccine contains part of the central repeat region and the complete C-terminal T cell epitope region (Th2R and Th3R) of the circumsporozoite protein (CSP). Since naturally occurring polymorphisms at the vaccine candidate loci are critical determinants of the protective efficacy of the vaccines, it is imperative to investigate these polymorphisms in field isolates. In this study we have investigated the genetic diversity at the central repeat, C-terminal T cell epitope (Th2R and Th3R) and N-terminal T cell epitope regions of the CSP, in P. falciparum isolates from Madhya Pradesh state of India. These isolates were collected through a 5-year prospective study aimed to develop a well-characterized field-site for the future evaluation of malaria vaccine in India. Our results revealed that the central repeat (63 haplotypes, n = 161) and C-terminal Th2R/Th3R epitope (24 haplotypes, n = 179) regions were highly polymorphic, whereas N-terminal non-repeat region was less polymorphic (5 haplotypes, n = 161) in this population. We did not find any evidence of the role of positive natural selection in maintaining the genetic diversity at the Th2R/Th3R regions of CSP. Comparative analysis of the Th2R/Th3R sequences from this study to the global isolates (n = 1160) retrieved from the GenBank database revealed two important points. First, the majority of the sequences (∼61%, n = 179) from this study were identical to the Dd2/Indochina type, which is also the predominant Th2R/Th3R haplotype in Asia (∼59%, n = 974). Second, the Th2R/Th3R sequences in Asia, South America and Africa are geographically distinct with little allele sharing between continents. In conclusion, this study provides an insight on the existing polymorphisms in the CSP in a parasite population from India that could potentially influence the efficacy of RTS,S vaccine in this region.     

Field Evaluation of a Push-Pull System to Reduce Malaria Transmission

Malaria continues to place a disease burden on millions of people throughout the tropics, especially in sub-Saharan Africa. Although efforts to control mosquito populations and reduce human-vector contact, such as long-lasting insecticidal nets and indoor residual spraying, have led to significant decreases in malaria incidence, further progress is now threatened by the widespread development of physiological and behavioural insecticide-resistance as well as changes in the composition of vector populations. A mosquito-directed push-pull system based on the simultaneous use of attractive and repellent volatiles offers a complementary tool to existing vector-control methods. In this study, the combination of a trap baited with a five-compound attractant and a strip of net-fabric impregnated with micro-encapsulated repellent and placed in the eaves of houses, was tested in a malaria-endemic village in western Kenya. Using the repellent delta-undecalactone, mosquito house entry was reduced by more than 50%, while the traps caught high numbers of outdoor flying mosquitoes. Model simulations predict that, assuming area-wide coverage, the addition of such a push-pull system to existing prevention efforts will result in up to 20-fold reductions in the entomological inoculation rate. Reductions of such magnitude are also predicted when mosquitoes exhibit a high resistance against insecticides. We conclude that a push-pull system based on non-toxic volatiles provides an important addition to existing strategies for malaria prevention.