Ando Guindo

A Field Trial to Assess a Blood-Stage Malaria Vaccine

BACKGROUND Blood-stage malaria vaccines are intended to prevent clinical disease. The malaria vaccine FMP2.1/AS02(A), a recombinant protein based on apical membrane antigen 1 (AMA1) from the 3D7 strain of Plasmodium falciparum, has previously been shown to have immunogenicity and acceptable safety in Malian adults and children. METHODS In a double-blind, randomized trial, we immunized 400 Malian children with either the malaria vaccine or a control (rabies) vaccine and followed them for 6 months. The primary end point was clinical malaria, defined as fever and at least 2500 parasites per cubic millimeter of blood. A secondary end point was clinical malaria caused by parasites with the AMA1 DNA sequence found in the vaccine strain. RESULTS The cumulative incidence of the primary end point was 48.4% in the malaria-vaccine group and 54.4% in the control group; efficacy against the primary end point was 17.4% (hazard ratio for the primary end point, 0.83; 95% confidence interval [CI], 0.63 to 1.09; P=0.18). Efficacy against the first and subsequent episodes of clinical malaria, as defined on the basis of various parasite-density thresholds, was approximately 20%. Efficacy against clinical malaria caused by parasites with AMA1 corresponding to that of the vaccine strain was 64.3% (hazard ratio, 0.36; 95% CI, 0.08 to 0.86; P=0.03). Local reactions and fever after vaccination were more frequent with the malaria vaccine. CONCLUSIONS On the basis of the primary end point, the malaria vaccine did not provide significant protection against clinical malaria, but on the basis of secondary results, it may have strain-specific efficacy. If this finding is confirmed, AMA1 might be useful in a multicomponent malaria vaccine. (Funded by the National Institute of Allergy and Infectious Diseases and others; ClinicalTrials.gov number, NCT00460525.).

Impact of Trimethoprim-Sulfamethoxazole Prophylaxis on Falciparum Malaria Infection and Disease

BACKGROUND Trimethoprim-sulfamethoxazole (TS) prophylaxis is recommended for persons living with human immunodeficiency virus infection and acquired immunodeficiency syndrome in Africa. TS and the antimalarial combination sulfadoxine-pyrimethamine (SP) share mechanisms of action and resistance patterns, and concerns about the impact of TS resistance on SP efficacy have contributed to reluctance to implement TS prophylaxis in Africa. METHODS To determine whether TS prophylaxis impairs SP efficacy for treatment of uncomplicated falciparum malaria, we conducted a randomized, controlled, open-label study of TS prophylaxis. Two hundred and forty children 5-15 years old were randomized in a 2 : 1 fashion to receive either thrice-weekly TS for 12 weeks or no prophylaxis and were treated with SP for subsequent episodes of malaria. The incidence of malaria, SP efficacy, and the prevalence of parasite mutations that confer antifolate drug resistance were measured. RESULTS TS prophylaxis had a 99.5% protective efficacy against episodes of clinical malaria, with 97% efficacy against infection. Four SP treatment failures occurred in the control group, and none occurred in the TS group. No evidence was seen for selection by TS of antifolate resistance-conferring mutations in parasite dihydrofolate reductase or dihydropteroate synthase during subclinical infections. CONCLUSIONS In this setting of low antifolate resistance, TS was highly effective in preventing falciparum malaria infection and disease and did not appear to select for SP-resistant parasites.

Safety and immunogenicity of an AMA1 malaria vaccine in Malian children: results of a phase 1 randomized controlled trial.

Background The objective was to evaluate the safety, reactogenicity and immunogenicity of the AMA-1-based blood-stage malaria vaccine FMP2.1/AS02A in adults exposed to seasonal malaria. Methodology/Principal Findings A phase 1 double blind randomized controlled dose escalation trial was conducted in Bandiagara, Mali, West Africa, a rural town with intense seasonal transmission of Plasmodium falciparum malaria. The malaria vaccine FMP2.1/AS02A is a recombinant protein (FMP2.1) based on apical membrane antigen-1 (AMA-1) from the 3D7 clone of P. falciparum, adjuvanted with AS02A. The comparator vaccine was a cell-culture rabies virus vaccine (RabAvert). Sixty healthy, malaria-experienced adults aged 18–55 y were recruited into 2 cohorts and randomized to receive either a half dose or full dose of the malaria vaccine (FMP2.1 25 µg/AS02A 0.25 mL or FMP2.1 50 µg/AS02A 0.5 mL) or rabies vaccine given in 3 doses at 0, 1 and 2 mo, and were followed for 1 y. Solicited symptoms were assessed for 7 d and unsolicited symptoms for 30 d after each vaccination. Serious adverse events were assessed throughout the study. Titers of anti-AMA-1 antibodies were measured by ELISA and P. falciparum growth inhibition assays were performed on sera collected at pre- and post-vaccination time points. Transient local pain and swelling were common and more frequent in both malaria vaccine dosage groups than in the comparator group. Anti-AMA-1 antibodies increased significantly in both malaria vaccine groups, peaking at nearly 5-fold and more than 6-fold higher than baseline in the half-dose and full-dose groups, respectively. Conclusion/Significance The FMP2.1/AS02A vaccine had a good safety profile, was well-tolerated, and was highly immunogenic in malaria-exposed adults. This malaria vaccine is being evaluated in Phase 1 and 2 trials in children at this site. Trial Registration ClinicalTrials.gov NCT00308061

Dynamics of polymorphism in a malaria vaccine antigen at a vaccine-testing site in Mali.

Background Malaria vaccines based on the 19-kDa region of merozoite surface protein 1 (MSP-119) derived from the 3D7 strain of Plasmodium falciparum are being tested in clinical trials in Africa. Knowledge of the distribution and natural dynamics of vaccine antigen polymorphisms in populations in which malaria vaccines will be tested will guide vaccine design and permit distinction between natural fluctuations in genetic diversity and vaccine-induced selection. Methods and Findings Using pyrosequencing, six single-nucleotide polymorphisms in the nucleotide sequence encoding MSP-119 were genotyped from 1,363 malaria infections experienced by 100 children who participated in a prospective cohort study in Mali from 1999 to 2001. The frequencies of 14 MSP-119 haplotypes were compared over the course of the malaria transmission season for all three years, in three age groups, and in consecutive infections within individuals. While the frequency of individual MSP-119 haplotypes fluctuated, haplotypes corresponding to FVO and FUP strains of P. falciparum (MSP-119 haplotypes QKSNGL and EKSNGL, respectively) were most prevalent during three consecutive years and in all age groups with overall prevalences of 46% (95% confidence interval [CI] 44%–49%) and 36% (95% CI 34%–39%), respectively. The 3D7 haplotype had a lower overall prevalence of 16% (95% CI 14%–18%). Multiplicity of infection based on MSP-119 was higher at the beginning of the transmission season and in the oldest individuals (aged ≥11 y). Three MSP-119 haplotypes had a reduced frequency in symptomatic infections compared to asymptomatic infections. Analyses of the dynamics of MSP-119 polymorphisms in consecutive infections implicate three polymorphisms (at positions 1691, 1700, and 1701) as being particularly important in determining allele specificity of anti-MSP-119 immunity. Conclusions Parasites with MSP-119 haplotypes different from that of the leading vaccine strain were consistently the most prevalent at a vaccine trial site. If immunity elicited by an MSP-1-based vaccine is allele-specific, a vaccine based on either the FVO or FUP strain might have better initial efficacy at this site. This study, to our knowledge the largest of its kind to date, provides molecular information needed to interpret population responses to MSP-1-based vaccines and suggests that certain MSP-119 polymorphisms may be relevant to cross-protective immunity.

Next Generation Sequencing to Detect Variation in the Plasmodium falciparum Circumsporozoite Protein

The malaria vaccine RTS,S/AS01, based on immunogenic regions of the Plasmodium falciparum circumsporozoite protein (CSP), has partial efficacy against clinical malaria in African children. Understanding how sequence diversity in CSP T- and B-cell epitopes relates to naturally acquired and vaccine-induced immunity may be useful in efforts to improve the efficacy of CSP-based vaccines. However, limitations in sequencing technology have precluded thorough evaluation of diversity in the immunogenic regions of this protein. In this study, 454, a next generation sequencing technology, was evaluated as a method for assessing diversity in these regions. Portions of the circumsporozoite gene (cs) were sequenced both by 454 and Sanger sequencing from samples collected in a study in Bandiagara, Mali. 454 detected more single nucleotide polymorphisms and haplotypes in the T-cell epitopes than Sanger sequencing, and it was better able to resolve genetic diversity in samples with multiple infections; however, it failed to generate sequence for the B-cell epitopes.

Extended Safety, Immunogenicity and Efficacy of a Blood-Stage Malaria Vaccine in Malian Children: 24-Month Follow-Up of a Randomized, Double-Blinded Phase 2 Trial

Background The FMP2.1/AS02A candidate malaria vaccine was tested in a Phase 2 study in Mali. Based on results from the first eight months of follow-up, the vaccine appeared well-tolerated and immunogenic. It had no significant efficacy based on the primary endpoint, clinical malaria, but marginal efficacy against clinical malaria in secondary analyses, and high allele-specific efficacy. Extended follow-up was conducted to evaluate extended safety, immunogenicity and efficacy. Methods A randomized, double-blinded trial of safety, immunogenicity and efficacy of the candidate Plasmodium falciparum apical membrane antigen 1 (AMA1) vaccine FMP2.1/AS02A was conducted in Bandiagara, Mali. Children aged 1–6 years were randomized in a 1∶1 ratio to receive FMP2.1/AS02A or control rabies vaccine on days 0, 30 and 60. Using active and passive surveillance, clinical malaria and adverse events as well as antibodies against P. falciparum AMA1 were monitored for 24 months after the first vaccination, spanning two malaria seasons. Findings 400 children were enrolled. Serious adverse events occurred in nine participants in the FMP2.1/AS02A group and three in the control group; none was considered related to study vaccination. After two years, anti-AMA1 immune responses remained significantly higher in the FMP2.1/AS02A group than in the control group. For the entire 24-month follow-up period, vaccine efficacy was 7.6% (p = 0.51) against first clinical malaria episodes and 9.9% (p = 0.19) against all malaria episodes. For the final 16-month follow-up period, vaccine efficacy was 0.9% (p = 0.98) against all malaria episodes. Allele-specific efficacy seen in the first malaria season did not extend into the second season of follow-up. Interpretation Allele-specific vaccine efficacy was not sustained in the second malaria season, despite continued high levels of anti-AMA1 antibodies. This study presents an opportunity to evaluate correlates of partial protection against clinical malaria that waned during the second malaria season. Trial Registration Clinicaltrials.gov NCT00460525 NCT00460525

Spatio-temporal analysis of malaria within a transmission season in Bandiagara, Mali

BackgroundHeterogeneous patterns of malaria transmission are thought to be driven by factors including host genetics, distance to mosquito breeding sites, housing construction, and socio-behavioural characteristics. Evaluation of local transmission epidemiology to characterize malaria risk is essential for planning malaria control and elimination programmes. The use of geographical information systems (GIS) techniques has been a major asset to this approach. To assess time and space distribution of malaria disease in Bandiagara, Mali, within a transmission season, data were used from an ongoing malaria incidence study that enrolled 300 participants aged under six years old”.MethodsChildren’s households were georeferenced using a handheld global position system. Clinical malaria was defined as a positive blood slide for Plasmodium falciparum asexual stages associated with at least one of the following signs: headache, body aches, fever, chills and weakness. Daily rainfall was measured at the local weather station.Landscape features of Bandiagara were obtained from satellite images and field survey. QGIS™ software was used to map malaria cases, affected and non-affected children, and the number of malaria episodes per child in each block of Bandiagara. Clusters of high or low risk were identified under SaTScan® software according to a Bernoulli model.ResultsFrom June 2009 to May 2010, 296 clinical malaria cases were recorded. Though clearly temporally related to the rains, Plasmodium falciparum occurrence persisted late in the dry season. Two “hot spots” of malaria transmission also found, notably along the Yamé River, characterized by higher than expected numbers of malaria cases, and high numbers of clinical episodes per child. Conversely, the north-eastern sector of the town had fewer cases despite its proximity to a large body of standing water which was mosquito habitat.ConclusionThese results confirm the existence of a marked spatial heterogeneity of malaria transmission in Bandiagara, providing support for implementation of targeted interventions.

Association of HLA alleles with Plasmodium falciparum severity in Malian children

Pre-erythrocytic immunity to Plasmodium falciparum malaria is likely to be mediated by T-cell recognition of malaria epitopes presented on infected host cells via class I and II major histocompatibility complex (MHC) antigens. To test for associations of human leukocyte antigen (HLA) alleles with disease severity, we performed high-resolution typing of HLA class I and II loci and compared the distributions of alleles of HLA-A, -B, -C and -DRB1 loci in 359 Malian children of Dogon ethnicity with uncomplicated or severe malaria. We observed that alleles A*30:01 and A*33:01 had higher frequency in the group of patients with cerebral disease compared to patients with uncomplicated disease [A*30:01: gf = 0.2031 vs gf = 0.1064, odds ratio (OR) = 3.17, P = 0.004, confidence interval (CI) (1.94–5.19)] and [A*33:01: gf = 0.0781 vs gf = 0.0266, 4.21, P = 0.005, CI (1.89–9.84)], respectively. The A*30:01 and A*33:01 alleles share some sequence motifs and A*30:01 appears to have a unique peptide binding repertoire compared to other A*30 group alleles. Computer algorithms predicted malaria peptides with strong binding affinity for HLA-A*30:01 and HLA-A*33:01 but not to closely related alleles. In conclusion, we identified A*30:01 and A*33:01 as potential susceptibility factors for cerebral malaria, providing further evidence that polymorphism of MHC genes results in altered malaria susceptibility.

Variation in the Circumsporozoite Protein of Plasmodium falciparum: Vaccine Development Implications

The malaria vaccine candidate RTS,S/AS01 is based on immunogenic regions of Plasmodium falciparum circumsporozoite protein (CSP) from the 3D7 reference strain and has shown modest efficacy against clinical disease in African children. It remains unclear what aspect(s) of the immune response elicited by this vaccine are protective. The goals of this study were to measure diversity in immunogenic regions of CSP, and to identify associations between polymorphism in CSP and the risk of P. falciparum infection and clinical disease. The present study includes data and samples from a prospective cohort study designed to measure incidence of malaria infection and disease in children in Bandiagara, Mali. A total of 769 parasite-positive blood samples corresponding to both acute clinical malaria episodes and asymptomatic infections experienced by 100 children were included in the study. Non-synonymous SNP data were generated by 454 sequencing for the T-cell epitopes, and repeat length data were generated for the B-cell epitopes of the cs gene. Cox proportional hazards models were used to determine the effect of sequence variation in consecutive infections occurring within individuals on the time to new infection and new clinical malaria episode. Diversity in the T-cell epitope-encoding regions Th2R and Th3R remained stable throughout seasons, between age groups and between clinical and asymptomatic infections with the exception of a higher proportion of 3D7 haplotypes found in the oldest age group. No associations between sequence variation and hazard of infection or clinical malaria were detected. The lack of association between sequence variation and hazard of infection or clinical malaria suggests that naturally acquired immunity to CSP may not be allele-specific.