Malaria Vaccine Candidate Research Articles

Characterization of T and B cell epitopes in PvCyRPA by studying the naturally acquired immune response in Brazilian Amazon communities

Plasmodium vivax, a challenging species to eliminate, causes millions of malaria cases globally annually. Developing an effective vaccine is crucial in the fight against vivax malaria, but considering the limited number of studies focusing on the identification and development of P. vivax-specific vaccine candidates, exploring new antigens is an urgent need. The merozoite protein CyRPA is essential for P. falciparum growth and erythrocyte invasion and corresponds to a promising candidate antigen. In P. vivax, a single study with multiple vaccine candidates indicates PvCyRPA with strong association with protection, outperforming classic malaria vaccine candidates. However, little is known about the specific naturally acquired response in the Americas, as well as the antigen epitope mapping. For this reason, we aimed to investigate the cellular and humoral immune response elicited against PvCyRPA in Brazilian endemic areas to identify the existence of immunodominant regions and the potential of this protein as a single or even a multi-stage specific malaria vaccine candidate for P. vivax. The results demonstrated that PvCyRPA is naturally immunogenic in Brazilian Amazon individuals previously exposed to malaria, which presented anti-PvCyRPA cytophilic antibodies. Moreover, our data show that the protein also possesses important immunogenic regions with an overlap of B and T cell epitopes. These data reinforce the possibility of including PvCyRPA in vaccine formulations for P. vivax.

Specific antibody responses to Qβ-displayed Plasmodium falciparum-derived UB05 and MSP3 proteins in mother-neonate couples.

Malaria blood-stage parasite is a critical pathogenic stage responsible for serious adverse outcomes in pregnant women and their neonates. Immunoglobulin G (IgG) antibody responses specific to various asexual blood-stage antigens were well reported in non-pregnant individuals. However, little is still known during placental malaria. To assess the antibody responses specific to Plasmodium falciparum-derived MSP3 and UB05 malaria vaccine candidates in mother-neonate couples, mother's peripheral blood and neonate's cord blood samples were collected at delivery. After malaria diagnostic, plasma levels of IgG and IgG subclass responses specific to UB05, MSP3 and UB05-MSP3 were determined using ELISA. As outcomes, both mothers and neonates had significantly higher IgG responses to UB05 and UB05-MSP3 compared to anti-MSP3 IgG (p < 0.05), irrespective of malaria status. Significant negative correlations were observed between IgG levels specific to the three antigens and parasitaemia (p < 0.01). Anti-UB05 and anti-UB05-MSP3 IgG levels in neonates showed a significant positive correlation with the corresponding mothers' antibodies (rs = 0.25 with p = 0.04; rs = 0.31 with p = 0.01, respectively). UB05MSP3-specific IgG3 and IgG1 subclass responses were significantly higher than the IgG4 subclass (p < 0.01). The neonates IgG1 and IgG3 levels positively correlated with the corresponding antibody subclasses of mothers. These findings suggest an association between UB05 and UB05-MSP3-specific antibody responses and malaria control during pregnancy. Maternal-foetal transfer of MSP3 and UB05-specific IgG occurs during pregnancy, suggesting the interest in the future malaria vaccination strategies in pregnant women to generate early protective immunity in baby against malaria.

Natural selection on apical membrane antigen 1 (AMA1) of an emerging zoonotic malaria parasite Plasmodium inui

Apical membrane antigen 1 (AMA1) of malaria parasites plays an important role in host cell invasion. Antibodies to AMA1 can inhibit malaria merozoite invasion of erythrocytes while vaccine-induced specific cytotoxic T cell responses to this protein are associated with clinical protection. Polymorphisms in AMA1 of Plasmodium falciparum (PfAMA1) and P. vivax (PvAMA1) are of concern for vaccine development. To date, little is known about sequence diversity in ama1 of P. inui (Piama1), an emerging zoonotic malaria parasite. In this study, 80 complete Piama1 coding sequences were obtained from 57 macaques in Thailand that defined 60 haplotypes clustering in two phylogenetic lineages. In total, 74 nucleotide substitutions were identified and distributed unevenly across the gene. Blockwise analysis of the rates of synonymous (dS) and nonsynonymous (dN) nucleotide substitutions did not show a significant deviation from neutrality among Thai isolates. However, significantly negative Tajima’s D values were detected in domain I and the loop region of domain II, implying purifying selection. Codon-based analysis of dN/dS has identified 12 and 14 codons under positive and negative selections, respectively. Meanwhile, 85 amino acid substitutions were identified among 80 Thai and 11 non-Thai PiAMA1 sequences. Of these, 48 substituted residues had a significant alteration in physicochemical properties, suggesting positive selection. More than half of these positively selected amino acids (32 of 48) corresponded to the predicted B-cell or T-cell epitopes, suggesting that selective pressure could be mediated by host immunity. Importantly, 14 amino acid substitutions were singletons and predicted to be deleterious that could be subject to ongoing purifying selection or elimination. Besides genetic drift and natural selection, intragenic recombination identified in domain II could generate sequence variation in Piama1. It is likely that malarial ama1 exhibits interspecies differences in evolutionary histories. Knowledge of the sequence diversity of the Piama1 locus further provides an evolutionary perspective of this important malaria vaccine candidate.

Genetic structure of apical membrane antigen-1 in Plasmodium falciparum isolates from Pakistan.

Plasmodium falciparum apical membrane antigen-1 (PfAMA-1) is a major candidate for the blood-stage malaria vaccine. Genetic polymorphisms of global pfama-1suggest that the genetic diversity of the gene can disturb effective vaccine development targeting this antigen. This study was conducted to explore the genetic diversity and gene structure of pfama-1 among P. falciparum isolates collected in the Khyber Pakhtunkhwa (KP) province of Pakistan. A total of 19 full-length pfama-1 sequences were obtained from KP-Pakistan P. falciparum isolates, and genetic polymorphism and natural selection were investigated. KP-Pakistan pfama-1 exhibited genetic diversity, wherein 58 amino acid changes were identified, most of which were located in ectodomains, and domains I, II, and III. The amino acid changes commonly found in the ectodomain of global pfama-1 were also detected in KP-Pakistan pfama-1. Interestingly, 13 novel amino acid changes not reported in the global population were identified in KP-Pakistan pfama-1. KP-Pakistan pfama-1 shared similar levels of genetic diversity with global pfama-1. Evidence of natural selection and recombination events were also detected in KP-Pakistan pfama-1.

Natural malaria infection elicits rare but potent neutralizing antibodies to the blood-stage antigen RH5

Plasmodium falciparum reticulocyte-binding protein homolog 5 (RH5) is the most advanced blood-stage malaria vaccine candidate and is being evaluated for efficacy in endemic regions, emphasizing the need to study the underlying antibody response to RH5 during natural infection, which could augment or counteract responses to vaccination. Here, we found that RH5-reactive B cells were rare, and circulating immunoglobulin G (IgG) responses to RH5 were short-lived in malaria-exposed Malian individuals, despite repeated infections over multiple years. RH5-specific monoclonal antibodies isolated from eight malaria-exposed individuals mostly targeted non-neutralizing epitopes, in contrast to antibodies isolated from five RH5-vaccinated, malaria-naive UK individuals. However, MAD8-151 and MAD8-502, isolated from two malaria-exposed Malian individuals, were among the most potent neutralizers out of 186 antibodies from both cohorts and targeted the same epitopes as the most potent vaccine-induced antibodies. These results suggest that natural malaria infection may boost RH5-vaccine-induced responses and provide a clear strategy for the development of next-generation RH5 vaccines.

Malaria vaccines: a new era of prevention and control.

Malaria killed over 600,000 people in 2022, a death toll that has not improved since 2015. Additionally, parasites and mosquitoes resistant to existing interventions are spreading across Africa and other regions. Vaccines offer hope to reduce the mortality burden: the first licensed malaria vaccines, RTS,S and R21, will be widely deployed in 2024 and should substantially reduce childhood deaths. In this Review, we provide an overview of the malaria problem and the Plasmodium parasite, then describethe RTS,S and R21 vaccines (the first vaccines for any human parasitic disease), summarizing their benefits and limitations. We explore next-generation vaccines designed using new knowledge of malaria pathogenesis and protective immunity, which incorporate antigens and platforms to elicit effective immune responses against different parasite stages in human or mosquito hosts. We describe a decision-making process that prioritizes malaria vaccine candidates for development in a resource-constrained environment. Future vaccines might improve upon the protective efficacy of RTS,S or R21 for children, or address the wider malaria scourge by preventing pregnancy malaria, reducing the burden of Plasmodium vivax or accelerating malaria elimination.

Diversity and selection analyses identify transmission-blocking antigens as the optimal vaccine candidates in Plasmodium falciparum

A highly effective vaccine for malaria remains an elusive target, at least in part due to the under-appreciated natural parasite variation. This study aimed to investigate genetic and structural variation, and immune selection of leading malaria vaccine candidates across the Plasmodium falciparum's life cycle. We analysed 325P.falciparum whole genome sequences from Zambia, in addition to 791 genomes from five other African countries available in the MalariaGEN Pf3k Database. Ten vaccine antigens spanning three life-history stages were examined for genetic and structural variations, using population genetics measures, haplotype network analysis, and 3D structure selection analysis. Among the ten antigens analysed, only three in the transmission-blocking vaccine category display P. falciparum 3D7 as the dominant haplotype. The antigens AMA1, CSP, MSP119 and CelTOS, are much more diverse than the other antigens, and their epitope regions are under moderate to strong balancing selection. In contrast, Rh5, a blood stage antigen, displays low diversity yet slightly stronger immune selection in the merozoite-blocking epitope region. Except for CelTOS, the transmission-blocking antigens Pfs25, Pfs48/45, Pfs230, Pfs47, and Pfs28 exhibit minimal diversity and no immune selection in epitopes that induce strain-transcending antibodies, suggesting potential effectiveness of 3D7-based vaccines in blocking transmission. These findings offer valuable insights into the selection of optimal vaccine candidates against P.falciparum. Based on our results, we recommend prioritising conserved merozoite antigens and transmission-blocking antigens. Combining these antigens in multi-stage approaches may be particularly promising for malaria vaccine development initiatives. Purdue Department of Biological Sciences; Puskas Memorial Fellowship; National Institute of Allergy and Infectious Diseases (U19AI089680).

Increased of Spleen White Pulp Diameter Post Dbl2β-Pfemp1 Recombinant Protein Injection in Wistar Rats: Pre-Clinical Study for Malaria Vaccine Development

Malaria is a major infectious disease worldwide, and vaccination is essential for disease control. The Plasmodium falciparum Erythrocyte Membrane Protein-1 (PfEMP1) is a potential malaria vaccine candidate due to its involvement in pathogenesis. Injection of DBL2β-PfEMP1 recombinant protein in animal models induces IgG and CD4+ production and inhibits binding with host endothelial receptors. This study aimed to analyze the spleen immune response by measuring the white pulp diameter. The experimental study used Wistar rats (Rattus norvegicus) that were divided into four groups, a control group and three treatment groups, which were injected with 100, 150, and 200 μg of DBL2β-PfEMP1 protein. Injection was done thrice with three-week intervals (days 0, 21, and 42). On day 56, rats were euthanized, and spleens were prepared for histology examination. The white pulp diameter increased along with increasing the dose of protein. The ANOVA test showed a significant difference between groups (p=0.001). The posthoc Bonferroni test showed a significant difference between the control and the 150 and 200 μg groups and the 100 μg and 200 μg groups. In conclusion, the DBL2β-PfEMP1 recombinant protein injection increased the spleen white pulp diameter in Wistar rats, and the 200 μg dose resulted in the highest increase.

Blood-stage malaria vaccine candidate RH5.1/Matrix-M in healthy Tanzanian adults and children; an open-label, non-randomised, first-in-human, single-centre, phase 1b trial

A blood-stage Plasmodium falciparum malaria vaccine would provide a second line of defence to complement partially effective or waning immunity conferred by the approved pre-erythrocytic vaccines. RH5.1 is a soluble protein vaccine candidate for blood-stage P falciparum, formulated with Matrix-M adjuvant to assess safety and immunogenicity in a malaria-endemic adult and paediatric population for the first time. We did a non-randomised, phase 1b, single-centre, dose-escalation, age de-escalation, first-in-human trial of RH5.1/Matrix-M in Bagamoyo, Tanzania. We recruited healthy adults (aged 18-45 years) and children (aged 5-17 months) to receive the RH5.1/Matrix-M vaccine candidate in the following three-dose regimens: 10 μg RH5.1 at 0, 1, and 2 months (Adults 10M), and the higher dose of 50 μg RH5.1 at 0 and 1 month and 10 μg RH5.1 at 6 months (delayed-fractional third dose regimen; Adults DFx). Children received either 10 μg RH5.1 at 0, 1, and 2 months (Children 10M) or 10 μg RH5.1 at 0, 1, and 6 months (delayed third dose regimen; Children 10D), and were recruited in parallel, followed by children who received the dose-escalation regimen (Children DFx) and children with higher malaria pre-exposure who also received the dose-escalation regimen (High Children DFx). All RH5.1 doses were formulated with 50 μg Matrix-M adjuvant. Primary outcomes for vaccine safety were solicited and unsolicited adverse events after each vaccination, along with any serious adverse events during the study period. The secondary outcome measures for immunogenicity were the concentration and avidity of anti-RH5.1 serum IgG antibodies and their percentage growth inhibition activity (GIA) in vitro, as well as cellular immunogenicity to RH5.1. All participants receiving at least one dose of vaccine were included in the primary analyses. This trial is registered at ClinicalTrials.gov, NCT04318002, and is now complete. Between Jan 25, 2021, and April 15, 2021, we recruited 12 adults (six [50%] in the Adults 10M group and six [50%] in the Adults DFx group) and 48 children (12 each in the Children 10M, Children 10D, Children DFx, and High Children DFx groups). 57 (95%) of 60 participants completed the vaccination series and 55 (92%) completed 22 months of follow-up following the third vaccination. Vaccinations were well-tolerated across both age groups. There were five serious adverse events involving four child participants during the trial, none of which were deemed related to vaccination. RH5-specific T cell and serum IgG antibody responses were induced by vaccination and purified total IgG showed in vitro GIA against P falciparum. We found similar functional quality (ie, GIA per μg RH5-specific IgG) across all age groups and dosing regimens at 14 days after the final vaccination; the concentration of RH5.1-specific polyclonal IgG required to give 50% GIA was 14·3 μg/mL (95% CI 13·4-15·2). 11 children were vaccinated with the delayed third dose regimen and showed the highest median anti-RH5 serum IgG concentration 14 days following the third vaccination (723 μg/mL [IQR 511-1000]), resulting in all 11 who received the full series showing greater than 60% GIA following dilution of total IgG to 2·5 mg/mL (median 88% [IQR 81-94]). The RH5.1/Matrix-M vaccine candidate shows an acceptable safety and reactogenicity profile in both adults and 5-17-month-old children residing in a malaria-endemic area, with all children in the delayed third dose regimen reaching a level of GIA previously associated with protective outcome against blood-stage P falciparum challenge in non-human primates. These data support onward efficacy assessment of this vaccine candidate against clinical malaria in young African children. The European and Developing Countries Clinical Trials Partnership; the UK Medical Research Council; the UK Department for International Development; the National Institute for Health and Care Research Oxford Biomedical Research Centre; the Division of Intramural Research, National Institute of Allergy and Infectious Diseases; the US Agency for International Development; and the Wellcome Trust.

Inhibition of Plasmodium knowlesi merozoite invasion into human erythrocytes by antibodies raised against the parasite's secreted protein with altered thrombospondin repeat (SPATR).

The Plasmodium secreted protein with an altered thrombospondin repeat (SPATR) has been known to play an important role in the malaria parasite's invasion into host erythrocytes. This protein is immunogenic and has been considered as one of the potential vaccine candidates against malaria parasite infection. Thus far, only a handful immunological studies have been carried out on P. knowlesi SPATR (PkSPATR), and none of these studies investigated the immunoprotective properties of the protein. In the present study, the ability of anti-PkSPATR antibodies to inhibit invasion of human erythrocytes was assessed in an in vitro merozoite invasion inhibition assay. The antibodies were harvested from the serum of a rabbit which was immunised with recombinat PkSPATR. Results from the merozoite invasion inhibition assay revealed significant antibody invasion inhibitory activity in a concentration dependent manner (concentration range: 0.375 - 3.00 mg/ml) with inhibition rate ranging from 20% to 32%. Future studies, such as anti-PkSPATR antibodies inhibitory effect on sporozoite invasion of human liver cells, need to be carried out to assess the potential of PkSPATR as a knowlesi malaria vaccine candidate.

Evaluation of naturally acquired immune responses against novel pre-erythrocytic Plasmodium vivax proteins in a low endemic malaria population located in the Peruvian Amazon Basin

BackgroundPlasmodium vivax represents the most geographically widespread human malaria parasite affecting civilian and military populations in endemic areas. Targeting the pre-erythrocytic (PE) stage of the parasite life cycle is especially appealing for developing P. vivax vaccines as it would prevent disease and transmission. Here, naturally acquired immunity to a panel of P. vivax PE antigens was explored, which may facilitate vaccine development and lead to a better understanding of naturally acquired PE immunity.MethodsTwelve P. vivax PE antigens orthologous to a panel of P. falciparum antigens previously identified as highly immunogenic in protected subjects after immunization with radiation attenuated sporozoites (RAS) were used for evaluation of humoral and cellular immunity by ELISA and IFN-γ ELISpot. Samples from P. vivax infected individuals (n = 76) from a low endemic malaria region in the Peruvian Amazon Basin were used.ResultsIn those clinical samples, all PE antigens evaluated showed positive IgG antibody reactivity with a variable prevalence of 58–99% in recently P. vivax diagnosed patients. The magnitude of the IgG antibody response against PE antigens was lower compared with blood stage antigens MSP1 and DBP-II, although antibody levels persisted better for PE antigens (average decrease of 6% for PE antigens and 43% for MSP1, p < 0.05). Higher IgG antibodies was associated with one or more previous malaria episodes only for blood stage antigens (p < 0.001). High IgG responders across PE and blood stage antigens showed significantly lower parasitaemia compared to low IgG responders (median 1,921 vs 4,663 par/µl, p < 0.05). In a subgroup of volunteers (n = 17),positive IFN-γ T cell response by ELISPOT was observed in 35% vs 9–35% against blood stage MSP1 and PE antigens, respectively, but no correlation with IgG responses.ConclusionsThese results demonstrate clear humoral and T cell responses against P. vivax PE antigens in individuals naturally infected with P. vivax. These data identify novel attractive PE antigens suitable for use in the potential development and selection of new malaria vaccine candidates which can be used as a part of malaria prevention strategies in civilian and military populations living in P. vivax endemic areas.

Plasmodium vivax HAP2 genetic diversity and population structure from worldwide clinical samples. A potential Transmission-Blocking malaria vaccine candidate

BackgroundMalaria infections due to Plasmodium vivax are increasingly becoming a significant public health problem and are directly impacting malaria elimination efforts in many countries. Recent functional studies have shown that a pre-fertilising antigen; gamete membrane fusion protein HAP2/Generative Cell specific 1 (GCS1) domain significantly reduces the formation of P. vivax oocysts in mosquitos, implying that it could be developed as a transmission-blocking vaccine. MethodsIn this study, the genetic diversity, natural selection, haplotype network analysis and population structure of PvHAP2/GCS1 full-length gene using worldwide samples from 16 countries are determined and the implications for its use as a potential vaccine candidate against P. vivax are discussed. ResultsThe study revealed low levels of nucleotide diversity (π ∼ 0.003, SNPs = 95) and purifying selection for the full-length PvHAP2 gene indicating functional constraints. Among the 95 SNPs (65 synonymous and 30 non-synonymous), 15 non-synonymous substitutions were localised to the C-terminal domain of the protein (674a.a − 862a.a) majority of these non-synonymous substitutions were from two countries of Central Africa i.e. Cameroon and Gabon. Phylogeographic haplotype network analysis indicated that a major haplotype (Hap_2, n = 34) is shared among countries from Asian countries and South American countries. Population structure analysis using a robust Bayesian algorithm indicated the existence of two sub-populations of PvHAP2/GCS1 among the worldwide samples. ConclusionThis study suggests that, due to low genetic diversity across 15 countries, and shared haplotype identified, the HAP2 gene can be a good target for vaccine development as a transmission-blocking vaccine with the potential to provide strain-transcending immunity. The C-terminal region from two countries from Central Africa (Cameroon and Gabon) identified high number of non-synonymous substitutions, which may indicate new adaption of parasites from these countries. However, more detailed field based studies with a larger sample size from these countries are needed.

IgG and IgM responses to the Plasmodium falciparum asexual stage antigens reflect respectively protection against malaria during pregnancy and infanthood.

Plasmodium falciparum malaria is a public health issue mostly seen in tropical countries. Until now, there is no effective malaria vaccine against antigens specific to the blood-stage of P. falciparum infection. Because the pathogenesis of malarial disease results from blood-stage infection, it is essential to identify the most promising blood-stage vaccine candidate antigens under natural exposure to malaria infection. A cohort of 400 pregnant women and their infants was implemented in South Benin. An active and passive protocol of malaria surveillance was established during pregnancy and infancy to precisely ascertain malaria infections during the follow-up. Twenty-eight antibody (Ab) responses specific to seven malaria candidate vaccine antigens were repeatedly quantified during pregnancy (3 time points) and infancy (6 time points) in order to study the Ab kinetics and their protective role. Abs were quantified by ELISA and logistic, linear and cox-proportional hazard model were performed to analyse the associations between Ab responses and protection against malaria in mothers and infants, taking into account socio-economic factors and for infants an environmental risk of exposure. The levels of IgM against MSP1, MSP2 and MSP3 showed an early protective response against the onset of symptomatic malaria infections starting from the 18th month of life, whereas no association was found for IgG responses during infancy. In women, some IgG responses tend to be associated with a protection against malaria risk along pregnancy and at delivery, among them IgG3 against GLURP-R0 and IgG2 against MSP1. The main finding suggests that IgM should be considered in vaccine designs during infanthood. Investigation of the functional role played by IgM in malaria protection needs further attention.

Evaluation of the precision of the Plasmodium knowlesi growth inhibition assay for Plasmodium vivax Duffy-binding protein-based malaria vaccine development

Recent data indicate increasing disease burden and importance of Plasmodium vivax (Pv) malaria. A robust assay will be essential for blood-stage Pv vaccine development. Results of the in vitro growth inhibition assay (GIA) with transgenic P. knowlesi (Pk) parasites expressing the Pv Duffy-binding protein region II (PvDBPII) correlate with in vivo protection in the first PvDBPII controlled human malaria infection (CHMI) trials, making the PkGIA an ideal selection tool once the precision of the assay is defined. To determine the precision in percentage of inhibition in GIA (%GIA) and in GIA50 (antibody concentration that gave 50 %GIA), ten GIAs with transgenic Pk parasites were conducted with four different anti-PvDBPII human monoclonal antibodies (mAbs) at concentrations of 0.016 to 2 mg/mL, and three GIAs with eighty anti-PvDBPII human polyclonal antibodies (pAbs) at 10 mg/mL. A significant assay-to-assay variation was observed, and the analysis revealed a standard deviation (SD) of 13.1 in the mAb and 5.94 in the pAb dataset for %GIA, with a LogGIA50 SD of 0.299 (for mAbs). Moreover, the ninety-five percent confidence interval (95 %CI) for %GIA or GIA50 in repeat assays was calculated in this investigation. The error range determined in this study will help researchers to compare PkGIA results from different assays and studies appropriately, thus supporting the development of future blood-stage malaria vaccine candidates, specifically second-generation PvDBPII-based formulations.

Targeting Plasmodium Life Cycle with Novel Parasite Ligands as Vaccine Antigens.

The WHO reported an estimated 249 million malaria cases and 608,000 malaria deaths in 85 countries in 2022. A total of 94% of malaria deaths occurred in Africa, 80% of which were children under 5. In other words, one child dies every minute from malaria. The RTS,S/AS01 malaria vaccine, which uses the Plasmodium falciparum circumsporozoite protein (CSP) to target sporozoite infection of the liver, achieved modest efficacy. The Malaria Vaccine Implementation Program (MVIP), coordinated by the WHO and completed at the end of 2023, found that immunization reduced mortality by only 13%. To further reduce malaria death, the development of a more effective malaria vaccine is a high priority. Three malaria vaccine targets being considered are the sporozoite liver infection (pre-erythrocytic stage), the merozoite red blood cell infection (asexual erythrocytic stage), and the gamete/zygote mosquito infection (sexual/transmission stage). These targets involve specific ligand-receptor interactions. However, most current malaria vaccine candidates that target two major parasite population bottlenecks, liver infection, and mosquito midgut infection, do not focus on such parasite ligands. Here, we evaluate the potential of newly identified parasite ligands with a phage peptide-display technique as novel malaria vaccine antigens.

Positive-unlabeled learning identifies vaccine candidate antigens in the malaria parasite Plasmodium falciparum

Malaria vaccine development is hampered by extensive antigenic variation and complex life stages of Plasmodium species. Vaccine development has focused on a small number of antigens, many of which were identified without utilizing systematic genome-level approaches. In this study, we implement a machine learning-based reverse vaccinology approach to predict potential new malaria vaccine candidate antigens. We assemble and analyze P. falciparum proteomic, structural, functional, immunological, genomic, and transcriptomic data, and use positive-unlabeled learning to predict potential antigens based on the properties of known antigens and remaining proteins. We prioritize candidate antigens based on model performance on reference antigens with different genetic diversity and quantify the protein properties that contribute most to identifying top candidates. Candidate antigens are characterized by gene essentiality, gene ontology, and gene expression in different life stages to inform future vaccine development. This approach provides a framework for identifying and prioritizing candidate vaccine antigens for a broad range of pathogens.

Previous Malaria Exposures and Immune Dysregulation: Developing Strategies To Improve Malaria Vaccine Efficacy in Young Children.

After several decades in development, two malaria vaccines based on the same antigen and with very similar constructs and adjuvants, RTS,S/AS01 (RTS,S) and R21/Matrix-M (R21), were recommended by the WHO for widespread vaccination of children. These vaccines are much-needed additions to malaria control programs that, when used in conjunction with other control measures, will help to accelerate reductions in malaria morbidity and mortality. Although R21 is not yet available, RTS,S is currently being integrated into routine vaccine schedules in some areas. However, the efficacy of RTS,S is partial, short-lived, and varies widely according to age and geographic location. It is not clear why RTS,S induces protection in some individuals and not others, what the immune mechanisms are that favor protective immunity with RTS,S, and how immune mechanisms are influenced by host and environmental factors. Several studies suggest that higher levels of previous malaria exposure negatively impact RTS,S clinical efficacy. In this article, we summarize data suggesting that previous malaria exposures negatively impact the efficacy of RTS,S and other malaria vaccine candidates. We highlight recent evidence suggesting that increasing malaria exposure impairs the generation of functional antibody responses to RTS,S. Finally, we discuss how investigation of clinical and immune factors associated with suboptimal responses to RTS,S can be used to develop strategies to optimize RTS,S, which will remain relevant to R21 and next-generation vaccines.

Antibody response to malaria vaccine candidates in pregnant women with Plasmodium falciparum and Schistosoma haematobium infections.

Malaria in pregnancy has severe consequences for the mother and foetus. Antibody response to specific malaria vaccine candidates (MVC) has been associated with a decreased risk of clinical malaria and its outcomes. We studied Plasmodium falciparum (Pf) and Schistosoma haematobium (Sh) infections and factors that could influence antibody responses to MVC in pregnant women. A total of 337 pregnant women receiving antenatal care (ANC) and 139 for delivery participated in this study. Pf infection was detected by qPCR and Sh infection using urine filtration method. Antibody levels against CSP, AMA-1, GLURP-R0, VAR2CSA and Pfs48/45 MVC were quantified by ELISA. Multivariable linear regression models identified factors associated with the modulation of antibody responses. The prevalence of Pf and Sh infections was 27% and 4% at ANC and 7% and 4% at delivery. Pf infection, residing in Adidome and multigravidae were positively associated with specific IgG response to CSP, AMA-1, GLURP-R0 and VAR2CSA. ITN use and IPTp were negatively associated with specific IgG response to GLURP-R0 and Pfs48/45. There was no association between Sh infection and antibody response to MVC at ANC or delivery. Pf infections in pregnant women were positively associated with antibody response to CSP, GLURP-R0 and AMA-1. Antibody response to GLURP-R0 and Pfs48/45 was low for IPTp and ITN users. This could indicate a lower exposure to Pf infection and low malaria prevalence observed at delivery.

Nano-differential scanning fluorimetry as a tool for the assessment of refolded antibody fragments: A case study for anti-Pfs25 single-chain antibodies

Differential Scanning Fluorimetry (DSF) is a valuable and versatile tool in the field of protein and antibody stability studies, providing valuable insights into their thermal stability, and aiding in the optimization of experimental conditions for various applications. Antibody fragments provide armamentarium for researchers and practitioners across various fields, enabling advancements in medicine, diagnostics, research, and industrial applications. In the present study, single-chain antibodies derived from mAb 4B7 and mAb 1245 were expressed in E. coli, refolded, and checked for their binding with the antigen - Pfs25 (transmission-blocking malaria vaccine candidate). We used nano-DSF as a valuable tool to assess thermal stability, consequently aiding in predicting the correct folding of single-chain antibodies.. Employing nano-DSF as a checkpoint enables the determination of whether to proceed with functional and binding studies on the refolded single-chain antibodies.

Persistence of Anti-SE36 Antibodies Induced by the Malaria Vaccine Candidate BK-SE36/CpG in 5-10-Year-Old Burkinabe Children Naturally Exposed to Malaria.

Information on the dynamics and decline/persistence of antibody titres is important in vaccine development. A recent vaccine trial in malaria-exposed, healthy African adults and children living in a malaria hyperendemic and seasonal area (Ouagadougou, Burkina Faso) was the first study in which BK-SE36/CpG was administered to different age groups. In 5- to 10-year-old children, the risk of malaria infection was markedly lower in the BK-SE36/CpG arm compared to the control arm. We report here data on antibody titres measured in this age-group after the high malaria transmission season of 2021 (three years after the first vaccine dose was administered). At Year 3, 83% of children had detectable anti-SE36 total IgG antibodies. Geometric mean antibody titres and the proportion of children with detectable anti-SE36 antibodies were markedly higher in the BK-SE36/CpG arm than the control (rabies) arm. The information obtained in this study will guide investigators on future vaccine/booster schedules for this promising blood-stage malaria vaccine candidate.