Fc gamma receptor 3B (FCGR3B-c.233C>A-rs5030738) polymorphism modifies the protective effect of malaria specific antibodies in Ghanaian children

Malaria elimination in Ghana: recommendations for reactive case detection strategy implementation in a low endemic area of Asutsuare, Ghana

BACKGROUND

Progress toward malaria elimination is increasing as many countries near zero indigenous malaria cases. In settings nearing elimination, interventions will be most effective at interrupting transmission when targeted at the residual foci of transmission. These foci may be missed due to asymptomatic infections. To solve this problem, the World Health Organization recommends reactive case detection (RACD). This case study was conducted to identify individuals with asymptomatic malaria, their predisposing risk factors and recommend RACD in Asutsuare, Ghana based on literature review and a cross sectional study.

METHODS

The study involved a search on PubMed and Google Scholar of literature published between 1st January, 2009-14th August, 2023 using the search terms "malaria" in "Asutsuare". Furthermore, structured questionnaires were administered to one hundred individuals without symptoms of malaria and screened using rapid diagnostic test (RDT) kits, microscopy and real-time polymerase chain reaction (rt-PCR). Malaria prevalence based on the three diagnostic techniques as well as potential malaria risk factors were assessed through questionnaires in a cross-sectional study.

RESULTS

Cumulatively, sixty-four (64) studies (Google Scholar, 57 and PubMed, 7) were reviewed and 22 studies included in the literature on malaria in Asutsuare, Ghana. Significant risk factors were occupation, distance from a house to a waterbody, age group and educational level. Out of the 100 samples, 3 (3%) were positive by RDT, 6 (6%) by microscopy and 9 (9%) by rt-PCR. Ages 5-14.9 years had the highest mean malaria parasite densities of 560 parasites/µl with Plasmodium falciparum as the dominant species in 4 participants. Moreover, in the age group ≥ 15, 2 participants (1 each) harboured P. falciparum and Plasmodium malariae parasites. RDT had a higher sensitivity (76.54%; CI95 66.82-85.54) than rt-PCR (33.33%; CI95 4.33-77.72), while both rt-PCR and RDT were observed to have a higher specificity (92.55; CI95 85.26-96.95) and (97.30; CI95 93.87-99.13), respectively in the diagnosis of malaria.

CONCLUSION

In Asutsuare, Ghana, a low endemic area, the elimination of malaria may require finding individuals with asymptomatic infections. Given the low prevalence of asymptomatic individuals identified in this study and as repleted in the literature review, which favours RACD, Asutsuare is a possible setting receptive for RACD implementation.

A Non-Coding Fc Gamma Receptor Cis-Regulatory Variant within the 1q23 Gene Cluster Is Associated with Plasmodium falciparum Infection in Children Residing in Burkina Faso

Antibodies play a crucial role in activating protective immunity against malaria by interacting with Fc-gamma receptors (FcγRs). Genetic variations in genes encoding FcγRs can affect immune cell responses to the parasite. In this study, our aim was to investigate whether non-coding variants that regulate FcγR expression could influence the prevalence of Plasmodium falciparum infection. Through bioinformatics approaches, we selected expression quantitative trait loci (eQTL) for FCGR2A, FCGR2B, FCGR2C, FCGR3A, and FCGR3B genes encoding FcγRs (FCGR), in whole blood. We prioritized two regulatory variants, rs2099684 and rs1771575, located in open genomic regions. These variants were identified using RegVar, ImmuNexUT, and transcription factor annotations specific to immune cells. In addition to these, we genotyped the coding variants FCGR2A/rs1801274 and FCGR2B/rs1050501 in 234 individuals from a malaria-endemic area in Burkina Faso. We conducted age and family-based analyses to evaluate associations with the prevalence of malarial infection in both children and adults. The analysis revealed that the regulatory rs1771575-CC genotype was predicted to influence FCGR2B/FCGR2C/FCGR3A transcripts in immune cells and was the sole variant associated with a higher prevalence of malarial infection in children. In conclusion, this study identifies the rs1771575 cis-regulatory variant affecting several FcγRs in myeloid and neutrophil cells and associates it with the inter-individual capacity of children living in Burkina Faso to control malarial infection.

Human blood neutrophils generate ROS through FcγR-signaling to mediate protection against febrile P. falciparum malaria

Blood phagocytes, such as neutrophils and monocytes, generate reactive oxygen species (ROS) as a part of host defense response against infections. We investigated the mechanism of Fcγ-Receptor (FcγR) mediated ROS production in these cells to understand how they contribute to anti-malarial immunity. Plasmodium falciparum merozoites opsonized with naturally occurring IgG triggered both intracellular and extracellular ROS generation in blood phagocytes, with neutrophils being the main contributors. Using specific inhibitors, we show that both FcγRIIIB and FcγRIIA acted synergistically to induce ROS production in neutrophils, and that NADPH oxidase 2 and the PI3K intracellular signal transduction pathway were involved in this process. High levels of neutrophil ROS were also associated with protection against febrile malaria in two geographically diverse malaria endemic regions from Ghana and India, stressing the importance of the cooperation between anti-malarial IgG and neutrophils in triggering ROS-mediated parasite killing as a mechanism for naturally acquired immunity against malaria.

Fc Gamma Receptor IIIB NA1/NA2/SH Polymorphisms Are Associated with Malaria Susceptibility and Antibody Levels to P. falciparum Merozoite Antigens in Beninese Children

This paper aimed to investigate the influence of polymorphisms in the FCGR2A gene encoding R131H FcgRIIA variants and in the FCGR3B gene (108G > C, 114C > T, 194 A > G, 233C > A, 244 G > A and 316G > A) encoding FcgRIIIB-NA1, -NA2 and -SH variants on malaria susceptibility and antibody responses against P. falciparum merozoite antigens in Beninese children. An active malaria follow-up was conducted in infants from birth to 24 months of age in Allada, Benin. FCGR3B exon 3 was sequenced and FCGR2A exon 4 was genotyped. Antibodies directed to GLURP and MSP3 were quantified by ELISA. Association studies were performed using mixed-effect models. Individual carriage of FCGR3B 194 AA genotype was associated with a high number of malaria infections and a low level of IgG1 against MSP3 and GLURP-R0. High parasitemia and increased malaria infections were observed in infants carrying the FCGR3B*05 108C-114T-194A-233C-244A-316A haplotype. A reduced risk of malaria infections and low parasitemia were related to the carriages of the FCGR3B 108C-114T-194G-233C-244G-316A (FCGR3B*06), FCGR3B 108C−114T−194G−233A−244A−316A (FCGR3B*03 encoding for FcgRIIIB-SH) haplotypes and FCGR3B 297 TT genotype. Our results highlight the impact of FCGR3B polymorphisms on the individual susceptibility to malaria and antibody responses against MSP3 and GLURP in Beninese children.

Polymorphisms in Fc Gamma Receptors and Susceptibility to Malaria in an Endemic Population

Repeated infections by Plasmodium falciparum result in a humoral response that could reduce disease symptoms and prevent the development of clinical malaria. The principal mechanism underlying this humoral response is that immunoglobulin G (IgG) binds directly to the parasites, thus causing their neutralization. However, the action of antibodies alone is not always sufficient to eliminate pathogens from an organism. One key element involved in the recognition of IgG that plays a crucial role in the destruction of the parasites responsible for spreading malaria is the family of Fc gamma receptors. These receptors are expressed on the surface of immune cells. Several polymorphisms have been detected in the genes encoding these receptors, associated with susceptibility or resistance to malaria in different populations. In this review, we describe identified polymorphisms within the family of Fc gamma receptors and the impact of these variations on the response of a host to infection as well as provide new perspectives for the design of an effective vaccine for malaria.

Evaluating the predictive performance of malaria antibodies and FCGR3B gene polymorphisms on Plasmodium falciparum infection outcome: a prospective cohort study

Background

Malaria antigen-specific antibodies and polymorphisms in host receptors involved in antibody functionality have been associated with different outcomes of Plasmodium falciparum infections. Thus, to identify key prospective malaria antigens for vaccine development, there is the need to evaluate the associations between malaria antibodies and antibody dependent host factors with more rigorous statistical methods. In this study, different statistical models were used to evaluate the predictive performance of malaria-specific antibodies and host gene polymorphisms on P. falciparum infection in a longitudinal cohort study involving Ghanaian children.

Methods

Models with different functional forms were built using known predictors (age, sickle cell status, blood group status, parasite density, and mosquito bed net use) and malaria antigen-specific immunoglobulin (Ig) G and IgG subclasses and FCGR3B polymorphisms shown to mediate antibody-dependent cellular functions. Malaria antigens studied were Merozoite surface proteins (MSP-1 and MSP-3), Glutamate Rich Protein (GLURP)-R0, R2, and the Apical Membrane Antigen (AMA-1). The models were evaluated through visualization and assessment of differences between the Area Under the Receiver Operating Characteristic Curve and Brier Score estimated by suitable internal cross-validation designs.

Results

This study found that the FCGR3B-c.233C>A genotype and IgG against AMA1 were relatively better compared to the other antibodies and FCGR3B genotypes studied in classifying or predicting malaria risk among children.

Conclusions

The data supports the P. falciparum, AMA1 as an important malaria vaccine antigen, while FCGR3B-c.233C>A under the additive and dominant models of inheritance could be an important modifier of the effect of malaria protective antibodies.

Peripheral Merozoite Surface Proteins Are Targets of Naturally Acquired Immunity against Malaria in both India and Ghana

Development of a successful blood-stage vaccine against Plasmodium falciparum malaria remains a high priority. Immune-epidemiological studies are effective tools for the identification of antigenic targets of naturally acquired immunity (NAI) against malaria. However, differences in study design and methodology may compromise interstudy comparisons. Here, we assessed antibody responses against intact merozoites and a panel of 24 recombinant merozoite antigens in longitudinal cohort studies of Ghanaian (n = 115) and Indian (n = 121) populations using the same reagents and statistical methods. Anti-merozoite antibodies were associated with NAI in both the Indian (hazard ratio [HR] = 0.41, P = 0.020) and the Ghanaian (HR = 0.17, P < 0.001) participants. Of the 24 antigen-specific antibodies quantified, 12 and 8 were found to be protective in India and Ghana, respectively. Using least absolute shrinkage and selection operator (LASSO) regression, a powerful variable subselection technique, we identified subsets of four (MSP6, MSP3.7, MSPDBL2, and Pf12) and five (cMSP3^3D7, MSP3.3, MSPDBL1, GLURP-R2, and RALP-1) antigens that explained NAI better than the individual antibodies in India (HR = 0.18, P < 0.001) and Ghana (HR = 0.31, P < 0.001), respectively. IgG1 and/or IgG3 subclasses against five antigens from these subsets were associated with protection. Through this comparative study, maintaining uniformity of reagents and methodology, we demonstrate that NAI across diverse geographic regions may result from antibodies to multiple antigenic targets that constitute the peripheral merozoite surface protein complexes.

Cytophilic Antibodies Against Key Plasmodium falciparum Blood Stage Antigens Contribute to Protection Against Clinical Malaria in a High Transmission Region of Eastern India

Background

The collection of clinical data from a tribal population in a malaria-endemic area of India suggests the occurrence of naturally acquired immunity (NAI) against Plasmodium falciparum malaria.

Methods

Quantity and functionality of immunoglobulin G (IgG) antibodies against intact merozoites and recombinant proteins were assessed in a 13-month longitudinal cohort study of 121 individuals, 3-60 years of age.

Results

Opsonic phagocytosis of merozoites activity was strongly associated (hazard ratio [HR] = 0.34; 95% confidence interval [CI] = .18-.66; P = .0013) with protection against febrile malaria. Of the different IgG subclasses, only IgG3 antibodies against intact whole merozoites was significantly associated with protection against febrile malaria (HR = 0.47; 95% CI = .26-.86; P = .01). Furthermore, a combination of IgG3 antibody responses against Pf12, MSP3.7, MSP3.3, and MSP2FC27 was strongly associated with protection against febrile malaria (HR = 0.15; 95% CI, .06-.37; P = .0001).

Conclusions

These data suggest that NAI may, at least in part, be explained by opsonic phagocytosis of merozoites and IgG3 responses against whole merozoites, and in particular to a combination of 4 antigens is critical in this population. These results may have implications in the development of a subunit malaria vaccine. Opsonic phagocytosis of Plasmodium falciparum merozoites was associated with protection against clinical malaria in an India population. Antibody profiling identified four merozoite antigens (Pf12, MSP3.7, MSP3.3, and MSP2) as targets of protective Immunoglobuline G3 antibodies.

Neutrophils and Malaria

Neutrophils are abundant in the circulation and are one of the immune system's first lines of defense against infection. There has been substantial work carried out investigating the role of neutrophils in malaria and it is clear that during infection neutrophils are activated and are capable of clearing malaria parasites by a number of mechanisms. This review focuses on neutrophil responses to human malarias, summarizing evidence which helps us understand where neutrophils are, what they are doing, how they interact with parasites as well as their potential role in vaccine mediated immunity. We also outline future research priorities for these, the most abundant of leukocytes.

Fcγ-receptor polymorphisms associated with clinical symptoms in patients with immunoglobulin G subclass deficiency

BACKGROUND

Immunoglobulin G subclass deficiencies (IgGsd) are associated with recurrent respiratory tract infections. Immunoglobulin substitution therapy may be needed to prevent chronic lung tissue damage but tools for identifying the patients that will benefit from this treatment are still insufficient. Some FcγR polymorphisms seem to predispose for an increased risk for infections. In this study we wanted to evaluate if the FcγR-profile differs between individuals with IgGsd and a control population.

METHODS

Single nucleotide polymorphisms (SNPs) of FcγRIIa, FcγRIIIa and FcγRIIc in 36 IgGsd patients and 192 controls with similar sex and geographical distribution were analyzed by TaqMan allelic discrimination assay or Sanger sequencing.

RESULTS

In the IgGsd-group, homozygous frequency for FcγRIIa-R/R131 (low-binding capacity isoform) was higher (p = .03) as well as for non-classical FcγRIIc-ORF (p = .03) and classical FcγRIIc-ORF tended (p = .07) to be more common compared to the controls. There was no difference between the groups regarding FcγRIIIa.

CONCLUSION

The gene for classical FcγRIIc-ORF tended to be more frequent in individuals with immunoglobulin G subclass deficiency and the genes for non-classical FcγRIIc-ORF as well as low-binding capacity receptor FcγRIIa-R/R131 were more frequent. Further studies on the FcγR polymorphisms may pave way for identifying individuals that will benefit from immunoglobulin substitution.

Molecular and Functional Characterization of Fcγ Receptor IIIb-Ligand Interaction: Implications for Neutrophil-Mediated Immune Mechanisms in Malaria

The Fcγ receptor IIIb (FcγRIIIb) is a low-affinity receptor of IgG and is essential in neutrophil-mediated effector functions. Different allelic forms of FcγRIIIb carrying human neutrophil antigen (HNA-1a, -1b, -1c, and -1d) have been identified. Here, we have generated stable transfected HEK293 cell lines expressing HNA-1aa, -1bb, and -1bc. Of these, cells expressing HNA-1bc interacted significantly stronger (binding affinities, 2.277 versus 0.743) with human IgG than cells expressing the HNA-1aa or -1bb alloforms. The higher affinity of IgG toward the HNA-1c alloform was confirmed using neutrophils derived from German blood donors. Neutrophils from HNA-1abc-phenotyped individuals bound IgG significantly stronger (1.825 versus 0.903) than did neutrophils from HNA-1ab-typed individuals. These findings were confirmed by surface plasmon resonance (SPR) analysis demonstrating that recombinant HNA-1bc had a higher affinity (dissociation constant [Kd ], 7.24 × 10-6 M) than recombinant HNA-1bb (Kd , 1.15 × 10-5 M) against normal IgG. Finally, we demonstrated that Plasmodium falciparum merozoites opsonized with human IgG affinity purified against P. falciparum glutamate-rich protein (GLURP) enhanced stronger reactive oxygen species (ROS) emission in neutrophils obtained from HNA-1abc donors than in neutrophils from HNA-1ab donors. Collectively, these results indicate that the amino acid substitution Ala78Asp resulting in the HNA-1c allotype leads to higher affinity toward human IgG, enhancement of neutrophil activation, and possibly effective clearance of malaria by intracellular ROS.

TCRβ-expressing macrophages induced by a pathogenic murine malaria correlate with parasite burden and enhanced phagocytic activity

Macrophages express a wide array of invariant receptors that facilitate host defense and mediate pathogenesis during pathogen invasion. We report on a novel population of CD11b^highCD14⁺F4/80⁺ macrophages that express TCRβ. This population expands dramatically during a Plasmodium berghei ANKA infection and sequesters in the brain during experimental cerebral malaria. Importantly, measurement of TCRβ transcript and protein levels in macrophages in wildtype versus nude and Rag1 knockout mice establishes that the observed expression is not a consequence of passive receptor expression due to phagocytosis or trogocytosis of peripheral T cells or nonspecific antibody staining to an Fc receptor or cross reactive epitope. We also demonstrate that TCRβ on brain sequestered macrophages undergoes productive gene rearrangements and shows preferential Vβ usage. Remarkably, there is a significant correlation in the proportion of macrophages that express TCRβ and peripheral parasitemia. In addition, presence of TCRβ on the macrophage also correlates with a significant increase (1.9 fold) in the phagocytosis of parasitized erythrocytes. By transcriptional profiling, we identify a novel set of genes and pathways that associate with TCRβ expression by the macrophage. Expansion of TCRβ-expressing macrophages points towards a convergence of the innate and adaptive immune responses where both arms of the immune system cooperate to modulate the host response to malaria and possibly other infections.

Naturally Acquired Antibody Responses to a Synthetic Malaria Antigen AS202.11

Background

A major challenge to malaria vaccine development is identification of protective epitopes and respective protective immune responses.

Objective

To characterize naturally acquired Immunoglobulin G (IgG) responses to the synthetic peptide AS202.11, a malaria vaccine candidate.

Methodology

This community based cross-sectional study enrolled 320 participants aged 1 year and above. Demographic information was recorded through interviews. Detection of P. falciparum infection was done by microscopy, malaria rapid diagnostic test, and polymerase chain reaction. ELISA was used to detect IgG antibody. Data was analyzed using STATA.

Results

The overall AS202.11 IgG seropositivity was 78.8% (73.9–82.9). Seropositivity by age categories was ≤12 years [74.3% (67.4–80.2)], 13–40 years [85.3% (76.5–91.1)], and >40 years [82.6% (68.7–91.1)]. Compared to the ≤ 12-year-old group, aORs for the other groups were 2.22 (1.14–4.32), p = 0.019, and 1.87 (0.81–4.35), p = 0.143, for the 13–40-year-old and >40-year-old groups, respectively. The 13–40-year-old group had more seropositive individuals compared to the ≤ 12-year-old group.

Conclusion

We report a high degree of recognition of AS202.11 by IgG elicited by field P. falciparum strains, suggesting its close similarity to native P. falciparum antigens and possible suitability of the peptide as a future malaria vaccine candidate.

The GMZ2 malaria vaccine: from concept to efficacy in humans

INTRODUCTION

GMZ2 is a recombinant protein consisting of conserved domains of GLURP and MSP3, two asexual blood-stage antigens of Plasmodium falciparum, and is designed with the aim of mimicking naturally acquired anti-malarial immunity. The rationale for combining these two antigens is based on a series of immune epidemiological studies from geographically diverse malaria endemic regions; functional in vitro studies; and pre-clinical studies in rodents and New World monkeys. GMZ2 adjuvanted with alhydrogel® (alum) was well tolerated and immunogenic in three phase 1 studies. The recently concluded phase 2 trial of GMZ2/alum, involving 1849 participants 12 to 60 month of age in four countries in West, Central and Eastern Africa, showed that GMZ2 is well tolerated and has some, albeit modest, efficacy in the target population. Areas covered: PubMed ( www.ncbi.nlm.nih.gov/pubmed ) was searched to review the progress and future prospects for clinical development of GMZ2 sub-unit vaccine. We will focus on discovery, naturally acquired immunity, functional activity of specific antibodies, sequence diversity, production, pre-clinical and clinical studies. Expert commentary: GMZ2 is well tolerated and has some, albeit modest, efficacy in the target population. More immunogenic formulations should be developed.

Identification of Fc Gamma Receptor Glycoforms That Produce Differential Binding Kinetics for Rituximab

Fc gamma receptors (FcγR) bind the Fc region of antibodies and therefore play a prominent role in antibody-dependent cell-based immune responses such as ADCC, CDC and ADCP. The immune effector cell activity is directly linked to a productive molecular engagement of FcγRs where both the protein and glycan moiety of antibody and receptor can affect the interaction and in the present study we focus on the role of the FcγR glycans in this interaction. We provide a complete description of the glycan composition of Chinese hamster ovary (CHO) expressed human Fcγ receptors RI (CD64), RIIa_{Arg131/His131} (CD32a), RIIb (CD32b) and RIIIa_{Phe158/Val158} (CD16a) and analyze the role of the glycans in the binding mechanism with IgG. The interactions of the monoclonal antibody rituximab with each FcγR were characterized and we discuss the CHO-FcγRIIIa_{Phe158/Val158} and CHO-FcγRI interactions and compare them to the equivalent interactions with human (HEK293) and murine (NS0) produced receptors. Our results reveal clear differences in the binding profiles of rituximab, which we attribute in each case to the differences in host cell-dependent FcγR glycosylation. The glycan profiles of CHO expressed FcγRI and FcγRIIIa_{Phe158/Val158} were compared with the glycan profiles of the receptors expressed in NS0 and HEK293 cells and we show that the glycan type and abundance differs significantly between the receptors and that these glycan differences lead to the observed differences in the respective FcγR binding patterns with rituximab. Oligomannose structures are prevalent on FcγRI from each source and likely contribute to the high affinity rituximab interaction through a stabilization effect. On FcγRI and FcγRIIIa large and sialylated glycans have a negative impact on rituximab binding, likely through destabilization of the interaction. In conclusion, the data show that the IgG1-FcγR binding kinetics differ depending on the glycosylation of the FcγR and further support a stabilizing role of FcγR glycans in the antibody binding interaction.

Naturally Acquired Antibodies Target the Glutamate-Rich Protein on Intact Merozoites and Predict Protection Against Febrile Malaria

Background

Plasmodium species antigens accessible at the time of merozoite release are likely targets of biologically functional antibodies.

Methods

Immunoglobulin G (IgG) antibodies against intact merozoites were quantified in the plasma of Ghanaian children from a longitudinal cohort using a novel flow cytometry-based immunofluorescence assay. Functionality of these antibodies, as well as glutamate-rich protein (GLURP)-specific affinity-purified IgG from malaria hyperimmune Liberian adults, was assessed by the opsonic phagocytosis (OP) assay.

Results

Opsonic phagocytosis activity was strongly associated (hazard ratio [HR] = 0.46; 95% confidence interval [CI] = .30-.73; P = .0008) with protection against febrile malaria. Of the antimerozoite-specific antibodies, only IgG3 was significantly associated with both OP and protection (HR = 0.53; 95% CI = .34-.84; Pcorrected = .03) against febrile malaria. Similarly, GLURP-specific antibodies previously shown to be protective against febrile malaria in this same cohort were significantly associated with OP activity in this study. GLURP-specific antibodies recognized merozoites and also mediated OP activity.

Conclusions

These findings support previous studies that found OP of merozoites to be associated with protection against malaria and further shows IgG3 and GLURP antibodies are key in the OP mechanism, thus giving further impetus for the development of malaria vaccines targeting GLURP.

The role of Fc receptors in HIV prevention and therapy

Over the past decade, a wealth of experimental evidence has accumulated supporting the importance of Fc receptor (FcR) ligation in antibody-mediated pathology and protection in many disease states. Here we present the diverse evidence base that has accumulated as to the importance of antibody effector functions in the setting of HIV prevention and therapy, including clinical correlates, genetic associations, viral evasion strategies, and a rapidly growing number of compelling animal model experiments. Collectively, this work identifies antibody interactions with FcR as important to both therapeutic and prophylactic strategies involving both passive and active immunity. These findings mirror those in other fields as investigators continue to work toward identifying the right antibodies and the right effectors to be present at the right sites at the right time.

A phase 2b randomized, controlled trial of the efficacy of the GMZ2 malaria vaccine in African children

BACKGROUND

GMZ2 is a recombinant protein malaria vaccine, comprising two blood-stage antigens of Plasmodium falciparum, glutamate-rich protein and merozoite surface protein 3. We assessed efficacy of GMZ2 in children in Burkina Faso, Gabon, Ghana and Uganda.

METHODS

Children 12-60months old were randomized to receive three injections of either 100μg GMZ2 adjuvanted with aluminum hydroxide or a control vaccine (rabies) four weeks apart and were followed up for six months to measure the incidence of malaria defined as fever or history of fever and a parasite density ⩾5000/μL.

RESULTS

A cohort of 1849 children were randomized, 1735 received three doses of vaccine (868 GMZ2, 867 control-vaccine). There were 641 malaria episodes in the GMZ2/Alum group and 720 in the control group. In the ATP analysis, vaccine efficacy (VE), adjusted for age and site was 14% (95% confidence interval [CI]: 3.6%, 23%, p-value=0.009). In the ITT analysis, age-adjusted VE was 11.3% (95% CI 2.5%, 19%, p-value=0.013). VE was higher in older children. In GMZ2-vaccinated children, the incidence of malaria decreased with increasing vaccine-induced anti-GMZ2 IgG concentration. There were 32 cases of severe malaria (18 in the rabies vaccine group and 14 in the GMZ2 group), VE 27% (95% CI -44%, 63%).

CONCLUSIONS

GMZ2 is the first blood-stage malaria vaccine to be evaluated in a large multicenter trial. GMZ2 was well tolerated and immunogenic, and reduced the incidence of malaria, but efficacy would need to be substantially improved, using a more immunogenic formulation, for the vaccine to have a public health role.

Antibody levels against GLURP R2, MSP1 block 2 hybrid and AS202.11 and the risk of malaria in children living in hyperendemic (Burkina Faso) and hypo-endemic (Ghana) areas

Background

Differences in parasite transmission intensity influence the process of acquisition of host immunity to Plasmodium falciparum malaria and ultimately, the rate of malaria related morbidity and mortality. Potential vaccines being designed to complement current intervention efforts therefore need to be evaluated against different malaria endemicity backgrounds.

Methods

The associations between antibody responses to the chimeric merozoite surface protein 1 block 2 hybrid (MSP1 hybrid), glutamate-rich protein region 2 (GLURP R2) and the peptide AS202.11, and the risk of malaria were assessed in children living in malaria hyperendemic (Burkina Faso, n = 354) and hypo-endemic (Ghana, n = 209) areas. Using the same reagent lots and standardized protocols for both study sites, immunoglobulin (Ig) M, IgG and IgG sub-class levels to each antigen were measured by ELISA in plasma from the children (aged 6–72 months). Associations between antibody levels and risk of malaria were assessed using Cox regression models adjusting for covariates.

Results

There was a significant association between GLURP R2 IgG3 and reduced risk of malaria after adjusting age of children in both the Burkinabe (hazard ratio 0.82; 95 % CI 0.74–0.91, p < 0.0001) and the Ghanaian (HR 0.48; 95 % CI 0.25–0.91, p = 0.02) cohorts. MSP1 hybrid IgM was associated (HR 0.85; 95 % CI 0.73–0.98, p = 0.02) with reduced risk of malaria in Burkina Faso cohort while IgG against AS202.11 in the Ghanaian children was associated with increased risk of malaria (HR 1.29; 95 % CI 1.01–1.65, p = 0.04).

Conclusion

These findings support further development of GLURP R2 and MSP1 block 2 hybrid, perhaps as a fusion vaccine antigen targeting malaria blood stage that can be deployed in areas of varying transmission intensity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1146-4) contains supplementary material, which is available to authorized users.

Polymorphisms in B Cell Co-Stimulatory Genes Are Associated with IgG Antibody Responses against Blood-Stage Proteins of Plasmodium vivax

The development of an effective immune response can help decrease mortality from malaria and its clinical symptoms. However, this mechanism is complex and has significant inter-individual variation, most likely owing to the genetic contribution of the human host. Therefore, this study aimed to investigate the influence of polymorphisms in genes involved in the costimulation of B-lymphocytes in the naturally acquired humoral immune response against proteins of the asexual stage of Plasmodium vivax. A total of 319 individuals living in an area of malaria transmission in the Brazilian Amazon were genotyped for four SNPs in the genes CD40, CD40L, BLYS and CD86. In addition, IgG antibodies against P. vivax apical membrane antigen 1 (PvAMA–1), Duffy binding protein (PvDBP) and merozoite surface protein 1 (PvMSP–1₁₉) were detected by ELISA. The SNP BLYS –871C>T was associated with the frequency of IgG responders to PvAMA–1 and PvMSP–1₁₉. The SNP CD40 –1C>T was associated with the IgG response against PvDBP, whereas IgG antibody titers against PvMSP–1₁₉ were influenced by the polymorphism CD86 +1057G>A. These data may help to elucidate the immunological aspects of vivax malaria and consequently assist in the design of malaria vaccines.

Genome-wide association study of antibody responses to Plasmodium falciparum candidate vaccine antigens

We conducted a genome-wide association study (GWAS) of antibody responses directed to three Plasmodium falciparum vaccine candidate antigens (MSP1, MSP2 and GLURP) previously associated with different patterns of protection against malaria infection in Senegalese children. A total of 174 950 single-nucleotide polymorphisms (SNPs) were tested for association with immunoglobulin G1 (IgG1) responses directed to MSP1 and to GLURP and with IgG3 responses to MSP2 FC27 and to MSP2 3D7. We first performed a single-trait analysis with each antibody response and then a multiple-trait analysis in which we analyzed simultaneously the three immune responses associated with the control of clinical malaria episodes. Suggestive associations (P<1 × 10(-4)) were observed for 25 SNPs in MSP1 antibody response analysis or in multiple-trait analysis. According to the strength of their observed associations and their functional role, the following genes are of particular interest: RASGRP3 (2p22.3, P=7.6 × 10(-6)), RIMS1 (6q13, P=2.0 × 10(-5)), MVB12B (9q33.3, P=8.9 × 10(-5)) and GNPTAB (12q23.2, P=7.4 × 10(-5)). Future studies will be required to replicate these findings in other African populations. This work will contribute to the elucidation of the host genetic factors underlying variable immune responses to P. falciparum.

Recent advances in recombinant protein-based malaria vaccines

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Protein-based vaccines remain the cornerstone approach for B cell and antibody induction against leading target malaria antigens.

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Advances in antigen selection, immunogen design and epitope-focusing are advancing the field.

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New heterologous expression platforms are enabling cGMP production of next-generation protein vaccines.

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Next-generation antigens, protein-based immunogens and virus-like particle (VLP) delivery platforms are in clinical development.

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Protein-based vaccines will form part of a highly effective multi-component/multi-stage/multi-antigen subunit formulation against malaria.

Plasmodium parasites are the causative agent of human malaria, and the development of a highly effective vaccine against infection, disease and transmission remains a key priority. It is widely established that multiple stages of the parasite's complex lifecycle within the human host and mosquito vector are susceptible to vaccine-induced antibodies. The mainstay approach to antibody induction by subunit vaccination has been the delivery of protein antigen formulated in adjuvant. Extensive efforts have been made in this endeavor with respect to malaria vaccine development, especially with regard to target antigen discovery, protein expression platforms, adjuvant testing, and development of soluble and virus-like particle (VLP) delivery platforms. The breadth of approaches to protein-based vaccines is continuing to expand as innovative new concepts in next-generation subunit design are explored, with the prospects for the development of a highly effective multi-component/multi-stage/multi-antigen formulation seeming ever more likely. This review will focus on recent progress in protein vaccine design, development and/or clinical testing for a number of leading malaria antigens from the sporozoite-, merozoite- and sexual-stages of the parasite's lifecycle–including PfCelTOS, PfMSP1, PfAMA1, PfRH5, PfSERA5, PfGLURP, PfMSP3, Pfs48/45 and Pfs25. Future prospects and challenges for the development, production, human delivery and assessment of protein-based malaria vaccines are discussed.

Humoral immune responses against the malaria vaccine candidate antigen Plasmodium vivax AMA-1 and IL-4 gene polymorphisms in individuals living in an endemic area of the Brazilian Amazon

BACKGROUND

Several studies have recently demonstrated that the immune responses against malaria is governed by different factors, including the genetic components of the host. The IL-4 gene appears to be a strong candidate factor because of its role in the regulation of the Th2 response. The present study investigated the role of IL-4 polymorphisms in the development of IgG antibodies against PvAMA-1 and the IL-4 levels in individuals infected with Plasmodium vivax in a malaria endemic area in the Brazilian Amazon.

METHODS

The study sample included 83 patients who were diagnosed with P. vivax infection using thick smear and confirmed by nested-PCR. The IL-4 -590C>T and IL-4 -33C>T polymorphisms were genotyped by PCR-RFLP, and the intron 3 VNTR was genotyped by PCR. A standardised ELISA protocol was used to measure the total IgG against PvAMA-1. The cytokine/chemokine levels were measured using a Milliplex multiplex assay (Millipore). All of the subjects were genotyped with 48 ancestry informative markers to determine the proportions of African, European and Amerindian ancestry using STRUCTURE software.

RESULTS

Of the 83 patients, 60 (73%) produced IgG antibodies against PvAMA-1. A significant decrease in the percentage of respondents was observed among the primo-infected individuals. No significant differences were observed in the frequencies of genotypes and haplotypes among individuals who were positive or negative for IgG antibodies against PvAMA-1. Furthermore, no significant correlation was observed between the IL-4 polymorphisms, antibody levels, IL-4 levels, and parasitemia.

CONCLUSIONS

This study indicated that the polymorphisms identified in the IL-4 gene are not likely to play a role in the regulation of the antibody response against PvAMA-1 and IL-4 production in vivax malaria.

Antibody-Dependent Cellular Inhibition Is Associated With Reduced Risk Against Febrile Malaria in a Longitudinal Cohort Study Involving Ghanaian Children

The antibody-dependent respiratory burst and opsonic phagocytosis assays have been associated with protection against malaria; however, other mechanisms may also be involved. The antibody-dependent cellular inhibition (ADCI) assay is yet to be correlated with protection in longitudinal cohort studies (LCS). We investigated the relationship between ADCI activity of immunoglobulin G before malaria season and risk of malaria in a LCS involving Ghanaian children. High ADCI activity was significantly associated with reduced risk against malaria. Findings here suggest a potential usefulness of the ADCI assay as a correlate of protection to guide malaria vaccine studies.

High-throughput tri-colour flow cytometry technique to assess Plasmodium falciparum parasitaemia in bioassays

BACKGROUND

Unbiased flow cytometry-based methods have become the technique of choice in many laboratories for high-throughput, accurate assessments of malaria parasites in bioassays. A method to quantify live parasites based on mitotracker red CMXRos was recently described but consistent distinction of early ring stages of Plasmodium falciparum from uninfected red blood cells (uRBC) remains a challenge.

METHODS

Here, a high-throughput, three-parameter (tri-colour) flow cytometry technique based on mitotracker red dye, the nucleic acid dye coriphosphine O (CPO) and the leucocyte marker CD45 for enumerating live parasites in bioassays was developed. The technique was applied to estimate the specific growth inhibition index (SGI) in the antibody-dependent cellular inhibition (ADCI) assay and compared to parasite quantification by microscopy and mitotracker red staining. The Bland-Altman analysis was used to compare biases between SGI estimated by the tri-colour staining technique, mitotracker red and by microscopy.

RESULTS

CPO allowed a better separation between early rings and uRBCs compared to mitotracker red resulting in a more accurate estimate of total parasitaemia. The tri-colour technique is rapid, cost effective and robust with comparable sensitivity to microscopy and capable of discriminating between live and dead and/or compromised parasites. Staining for CD45 improved parasitaemia estimates in ADCI assay since high numbers of leucocytes interfered with the accurate identification of parasitized RBC. The least bias (-1.60) in SGI was observed between the tri-colour and microscopy.

CONCLUSION

An improved methodology for high-throughput assessment of P. falciparum parasitaemia under culture conditions that could be useful in different bioassays, including ADCI and growth inhibition assays has been developed.