Characterisation of the opposing effects of G6PD deficiency on cerebral malaria and severe malarial anaemia.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is believed to confer protection against Plasmodium falciparum malaria, but the precise nature of the protective effecthas proved difficult to define as G6PD deficiency has multiple allelic variants with different effects in males and females, and it has heterogeneous effects on the clinical outcome of P. falciparum infection. Here we report an analysis of multiple allelic forms of G6PD deficiency in a large multi-centre case-control study of severe malaria, using the WHO classification of G6PD mutations to estimate each individual's level of enzyme activity from their genotype. Aggregated across all genotypes, we find that increasing levels of G6PD deficiency are associated with decreasing risk of cerebral malaria, but with increased risk of severe malarial anaemia. Models of balancing selection based on these findings indicate that an evolutionary trade-off between different clinical outcomes of P. falciparum infection could have been a major cause of the high levels of G6PD polymorphism seen in human populations

Investigating the evolutionary link between malaria and autoimmunity: a large scale immunogenetic study in two West African populations.

AIM. Despite equivalent exposure to infection and comparable use of protective measures, the Fulani of West Africa have been shown to mount stronger immune responses to Plasmodium falciparum antigens and to be less susceptible to infection and mild disease than sympatric populations (Modiano et al. 1996, PNAS). The Fulani also show a higher response to other pathogens, and both their Th1 and Th2 responses are enhanced, suggesting that their resistance to malaria could result from a generally stronger immune activation. Key genes related to T regulatory cell function are indeed down-regulated in the Fulani (Torcia et al. 2008 PNAS). This disorder of immune homeostasis could be driven by genetic factors positively selected by P. falciparum and may underlie the higher susceptibility of the Fulani to diseases with autoimmune pathogenesis reported in the literature (Fish et al. 1987, Diabetologia; Mahe et al. 1996, Br J Dermatol; Brieger et al. 1997, Trop Med Int Health). The general aim of the proposed investigation is to explore the genetic basis of the lower susceptibility to malaria observed in the Fulani, and in particular to evaluate the role of autoimmunity loci. MATERIALS AND METHODS. To investigate this hypothesis, we conducted a large-scale epidemiological study in rural villages of Burkina Faso inhabited by Fulani, Mossi and Rimaibe communities. The field study lasted 2 years (2007-8) and consisted in a combination of cross sectional and longitudinal surveys. At each survey we collected parasitological (P. falciparum index and parasite density), clinical (fever, anemia, spleen size) and serological data (IgG levels against P. falciparum and self antigens). We genotyped 363 Single Nucleotide Polymorphisms (SNPs) on 2186 samples using the Sequenom System, based on allele-specific primer extension and MALDI-TOF Mass Spectrometry. SNPs included polymorphisms previously shown to be involved in resistance to severe malaria, in resistance to infection and/or in antibody production, as well as polymorphisms at autoimmunity loci. We conducted population genetic analyses and genetic association analysis with parasitological, clinical and serological phenotypes using the free software package R. RESULTS. Principal component analysis revealed that Mossi and Rimaibe (Non-Fulani) are not genetically distinct among themselves, whereas the Fulani are a clearly distinct group, in agreement with data obtained on HLA class I-II alleles (Modiano et al. 2001, Tissue Antigens; Lulli et al. 2009, Hum Immunol). We therefore compared allele frequencies and calculated Fst, a measure of population genetic differentiation, between Fulani and Non-Fulani. We observed that the proportion of autoimmunity SNPs with Fst>0.05 (indicating moderate/high differentiation and corresponding to at least a two-fold difference in allele frequency) is 20%, versus 10% shown by other loci (p=0.03). Genetic association analysis of susceptibility to infection and infection levels showed association signals among genes involved in resistance to severe malaria (TNF, DDC, ABO, IFNG-IL22, GNAS, MECP2, G6PD). Furthermore we observed strong signals of association, both in Fulani and Non-Fulani, in the 5q31 region of the genome, which has been previously linked to P. falciparum infection levels (Rihet et al. 1998, Am J Hum Genet; Mangano et al. 2008, Genes Immun). Finally, association signals were also observed among genes related to T regulatory cell function and/or involved in autoimmunity (TGFBR3, CD25, FCGR2A, CR1, IL1R1L-IL18RAP, IL1A-IL1B, IL21, BLK, ORMDL3, TGFB1). CONCLUSIONS. The results of our investigation support the hypothesis that malaria has exerted a selective pressure on the immune system and has affected is evolution, and provide evidence that common gene regulatory networks could underlie susceptibility to malaria and to immunological disorders such as autoimmune diseases

Investigating the genetic basis of the lower susceptibility to malaria shown by the Fulani of West-Africa.

Despite equivalent exposure to infection and comparable use of protective measures, the Fulani of West Africa have been shown to mount stronger immune responses to Plasmodium falciparum antigens and to be less susceptible to infection and mild disease than sympatric populations. The Fulani also show a higher response to other pathogens, and both their Th1 and Th2 responses are enhanced, suggesting that their resistance to malaria could result from a generally stronger immune activation. Key genes related to T regulatory cell function are indeed down-regulated in the Fulani. This disorder of immune homeostasis could be driven by genetic factors positively selected by P. falciparum and may underlie the reported higher susceptibility of the Fulani to autoimmune diseases. In order to investigate the genetic basis of the lower susceptibility to malaria shown by the Fulani we conducted a large-scale epidemiological study in Burkina Faso consisting of a combination of cross-sectional and longitudinal surveys. We genotyped 363 Single Nucleotide Polymorphisms (SNPs) on 2186 samples, by Sequenom MassArray System. SNPs included polymorphisms previously shown to be involved in resistance to severe malaria, in resistance to infection or in antibody production (www.malariagen.net), as well as polymorphisms at autoimmunity loci. We will show results of: i) inter-ethnic comparison of malaria susceptibility phenotypes; ii) population genetics analysis; iii) genetic association analysis with parasitological, clinical and immunological phenotypes

Investigating the genetic basis of the Fulani’s lower susceptibility to malaria: the role of autoimmunity loci.

Despite equivalent exposure to infection and comparable use of protective measures, the Fulani of West Africa have been shown to mount stronger immune responses to Plasmodium falciparum antigens and to be less susceptible to infection and mild disease than sympatric populations. The Fulani also show a higher response to other pathogens, and both their Th1 and Th2 responses are enhanced, suggesting that their resistance to malaria could result from a generally stronger immune activation. Key genes related to T regulatory cell function are indeed down-regulated in the Fulani. This disorder of immune homeostasis could be driven by genetic factors positively selected by P. falciparum and may underlie the higher susceptibility of the Fulani to diseases with autoimmune pathogenesis reported in the literature. The general aim of our investigation is to explore the genetic basis of the lower susceptibility to malaria observed in the Fulani, and in particular to evaluate the role of autoimmunity loci. We conducted a large-scale epidemiological study in rural villages of Burkina Faso inhabited by Fulani, Mossi and Rimaibe communities. The field study lasted 2 years (2007-8) and consisted in a combination of cross sectional and longitudinal surveys. At each survey we collected relevant parasitological and clinical data. Serological data (IgG levels against P. falciparum and self antigens) were generated by ELISA on plasma samples from the first survey. We genotyped 363 Single Nucleotide Polymorphisms (SNPs) on 2186 samples using the Sequenom System. Principal component analysis revealed that Mossi and Rimaibe (Non-Fulani) are not genetically distinct among themselves, whereas the Fulani are a clearly distinct group. We therefore compared allele frequencies and calculated Fst between Fulani and Non-Fulani. We observed that the proportion of autoimmunity SNPs with Fst>0.05 (indicating moderate/high differentiation and corresponding to at least a two-fold difference in allele frequency) is 20% versus 10% shown by other loci. Genetic association analysis of susceptibility to infection showed, both in Fulani and Non-Fulani, signals of association among genes: i) involved in resistance to severe malaria (ABO, DDC, G6PD, GNAS, IFNG-IL22, MECP2, TNF); ii) lying in the 5q31 region of the genome, which has been previously linked to P. falciparum infection levels (IRF1); iii) related to T regulatory cell function and/or involved in autoimmunity (BLK, CD25, CR1, FCGR2A, IL1A-IL1B, IL1R1L-IL18RAP, IL21, ORMDL3, TGFB1, TGFBR3). These results support the hypothesis that malaria has exerted a selective pressure on the immune system and has affected its evolution, and suggest that common gene regulatory networks could underlie susceptibility to malaria and to immunological disorders such as autoimmune diseases

First field efficacy trial of the ChAd63 MVA ME-TRAP vectored malaria vaccine candidate in 5-17 months old infants and children

Background Heterologous prime boost immunization with chimpanzee adenovirus 63 (ChAd63) and Modified Vaccinia Virus Ankara (MVA) vectored vaccines is a strategy previously shown to provide substantial protective efficacy against P. falciparum infection in United Kingdom adult Phase IIa sporozoite challenge studies (approximately 20–25% sterile protection with similar numbers showing clear delay in time to patency), and greater point efficacy in a trial in Kenyan adults. Methodology We conducted the first Phase IIb clinical trial assessing the safety, immunogenicity and efficacy of ChAd63 MVA ME-TRAP in 700 healthy malaria exposed children aged 5–17 months in a highly endemic malaria transmission area of Burkina Faso. Results ChAd63 MVA ME-TRAP was shown to be safe and immunogenic but induced only moderate T cell responses (median 326 SFU/106 PBMC (95% CI 290–387)) many fold lower than in previous trials. No significant efficacy was observed against clinical malaria during the follow up period, with efficacy against the primary endpoint estimate by proportional analysis being 13.8% (95%CI -42.4 to 47.9) at sixth month post MVA ME-TRAP and 3.1% (95%CI -15.0 to 18.3; p = 0.72) by Cox regression. Conclusions This study has confirmed ChAd63 MVA ME-TRAP is a safe and immunogenic vaccine regimen in children and infants with prior exposure to malaria. But no significant protective efficacy was observed in this very highly malaria-endemic setting

Resistance to malaria through structural variation of red blood cell invasion receptors

Plasmodium falciparum invades erythrocytes via interactions with proteins on the host cell surface. By analyzing genome sequence data from human populations, including 1269 African individuals, we identify a diverse array of large copy number variants affecting the erythrocyte invasion receptor genes GYPA and GYPB. We find that a nearby association with severe malaria is explained by a complex structural rearrangement that involves the loss of GYPB and gain of two hybrid genes, each with a GYPB extracellular domain and GYPA intracellular domain. This variant reduces the risk of severe malaria by 40% and has recently risen in frequency in parts of Kenya. We show that the structural variant encodes the Dantu blood group antigen, a serologically distinct red cell phenotype. Thus structural variation of erythrocyte invasion receptors is associated with natural resistance to severe malaria