RTS,S/AS01 vaccine (Mosquirix™): an overview

Pseudovirus Nanoparticles Displaying Plasmodium Circumsporozoite Proteins Elicited High Titers of Sporozoite-Binding Antibody

BACKGROUND

malaria caused by Plasmodium parasites remains a public health threat. The circumsporozoite proteins (CSPs) of Plasmodium sporozoite play a key role in Plasmodium infection, serving as an excellent vaccine target.

METHODS

using a self-assembled S60 nanoparticle platform, we generated pseudovirus nanoparticles (PVNPs) displaying CSPs, named S-CSPs, for enhanced immunogenicity.

RESULTS

purified Hisx6-tagged or tag-free S-CSPs self-assembled into PVNPs that consist of a norovirus S60 inner shell and multiple surface-displayed CSPs. The majority of the PVNPs measured ~27 nm with some size variations, and their three-dimensional structure was modeled. The PVNP-displayed CSPs retained their glycan receptor-binding function. A mouse immunization study showed that PVNPs induced a high antibody response against CSP antigens and the PVNP-immunized mouse sera stained the CSPs of Plasmodium sporozoites at high titer.

CONCLUSIONS AND DISCUSSION

the PVNP-displayed CSPs retain their authentic antigenic feature and receptor-binding function. The CSP-specific antibody elicited by the S-CSP PVNPs binds original CSPs and potentially inhibits the attachment of Plasmodium sporozoites to their host cells, a key step for liver invasion by the sporozoites. Thus, S-CSP PVNPs may be an excellent vaccine candidate against malaria caused by Plasmodium parasites.

Bibliometric analysis of parasite vaccine research from 1990 to 2019

Bibliometric and bibliographic analyses are popular tools for investigating publication metrics and thematic transitions in an expanding codex of biomedical literature. Bibliometric techniques have been employed in parasitology and vaccinology, with only a few malaria-specific literature analyses being reported specifically on parasite vaccines. The pursuit of parasite prophylactics is an important, global endeavour both medically and economically. As such, a comprehensive understanding of the research topics would be a valuable tool in assessing the current status and future directions of parasite vaccine development. Consequently, this study investigated parasite vaccinology from 1990 to 2019 by analysing literature exported from the Web of Science and Dimensions databases using two, commonly used, bibliometric programs: SciMAT and VOSviewer. The results of this study show the common, emerging, and transient themes within the discipline, and where the future lies as vaccine development moves further into the age of omics and informatics.

Plasmodium knowlesi (Pk) Malaria: A Review & Proposal of Therapeutically Rational Exchange (T-REX) of Pk-Resistant Red Blood Cells

Plasmodium knowlesi (Pk) causes zoonotic malaria and is known as the "fifth human malaria parasite". Pk malaria is an emerging threat because infections are increasing and can be fatal. While most infections are in Southeast Asia (SEA), especially Malaysia, travelers frequently visit this region and can present with Pk malaria around the world. So, clinicians need to know (1) patients who present with fever after recent travel to SEA might be infected with Pk and (2) Pk is often misdiagnosed as P. malariae (which typically causes less severe malaria). Here we review the history, pathophysiology, clinical features, diagnosis, and treatment of Pk malaria. Severe disease is most common in adults. Signs and symptoms can include fever, abdominal pain, jaundice, acute kidney injury, acute respiratory distress syndrome, hyponatremia, hyperparasitemia, and thrombocytopenia. Dengue is one of the diseases to be considered in the differential. Regarding pathophysiologic mechanisms, when Pk parasites invade mature red blood cells (RBCs, i.e., normocytes) and reticulocytes, changes in the red blood cell (RBC) surface can result in life-threatening cytoadherence, sequestration, and reduced RBC deformability. Since molecular mechanisms involving the erythrocytic stage are responsible for onset of severe disease and lethal outcomes, it is biologically plausible that manual exchange transfusion (ET) or automated RBC exchange (RBCX) could be highly beneficial by replacing "sticky" parasitized RBCs with uninfected, deformable, healthy donor RBCs. Here we suggest use of special Pk-resistant donor RBCs to optimize adjunctive manual ET/RBCX for malaria. "Therapeutically-rational exchange transfusion" (T-REX) is proposed in which Pk-resistant RBCs are transfused (instead of disease-promoting RBCs). Because expression of the Duffy antigen on the surface of human RBCs is essential for parasite invasion, T-REX of Duffy-negative RBCs-also known as Fy(a-b-) RBCs-could replace the majority of the patient's circulating normocytes with Pk invasion-resistant RBCs (in a single procedure lasting about 2 h). When sequestered or non-sequestered iRBCs rupture-in a 24 h Pk asexual life cycle-the released merozoites cannot invade Fy(a-b-) RBCs. When Fy(a-b-) RBC units are scarce (e.g., in Malaysia), clinicians can consider the risks and benefits of transfusing plausibly Pk-resistant RBCs, such as glucose-6-phosphate dehydrogenase deficient (G6PDd) RBCs and Southeast Asian ovalocytes (SAO). Patients typically require a very short recovery time (<1 h) after the procedure. Fy(a-b-) RBCs should have a normal lifespan, while SAO and G6PDd RBCs may have mildly reduced half-lives. Because SAO and G6PDd RBCs come from screened blood donors who are healthy and not anemic, these RBCs have a low-risk for hemolysis and do not need to be removed after the patient recovers from malaria. T-REX could be especially useful if (1) antimalarial medications are not readily available, (2) patients are likely to progress to severe disease, or (3) drug-resistant strains emerge. In conclusion, T-REX is a proposed optimization of manual ET/RBCX that has not yet been utilized but can be considered by physicians to treat Pk malaria patients.

Safety and immunogenicity of BK-SE36/CpG malaria vaccine in healthy Burkinabe adults and children: a phase 1b randomised, controlled, double-blinded, age de-escalation trial

Background

BK-SE36/CpG is a recombinant blood-stage malaria vaccine candidate based on the N-terminal Plasmodium falciparum serine repeat antigen5 (SE36), adsorbed to aluminium hydroxide gel and reconstituted, prior to administration, with synthetic oligodeoxynucleotides bearing CpG motifs. In healthy Japanese adult males, BK-SE36/CpG was well tolerated. This study assessed its safety and immunogenicity in healthy malaria-exposed African adults and children.

Methods

A double-blind, randomised, controlled, age de-escalating clinical trial was conducted in an urban area of Ouagadougou, Burkina Faso. Healthy participants (n=135) aged 21-45 years (Cohort 1), 5-10 years (Cohort 2) and 12-24 months (Cohort 3) were randomised to receive three vaccine doses (Day 0, 28 and 112) of BK-SE36/CpG or rabies vaccine by intramuscular injection.

Results

One hundred thirty-four of 135 (99.2%) subjects received all three scheduled vaccine doses. Vaccinations were well tolerated with no related Grade 3 (severe) adverse events (AEs). Pain/limitation of limb movement, headache in adults and fever in younger children (all mild to moderate in intensity) were the most frequently observed local and systemic AEs. Eighty-three of BK-SE36/CpG (91%) recipients and 37 of control subjects (84%) had Grade 1/2 events within 28 days post vaccination. Events considered by the investigator to be vaccine related were experienced by 38% and 14% of subjects in BK-SE36/CpG and control arms, respectively. Throughout the trial, six Grade 3 events (in 4 subjects), not related to vaccination, were recorded in the BK-SE36/CpG arm: 5 events (in 3 subjects) within 28 days of vaccination. All serious adverse events (SAEs) (n=5) were due to severe malaria (52-226 days post vaccination) and not related to vaccination. In all cohorts, BK-SE36/CpG arm had higher antibody titres after Dose 3 than after Dose 2. Younger cohorts had stronger immune responses (12-24-month-old > 5-10 years-old > 21-45 years-old). Sera predominantly reacted to peptides that lie in intrinsically unstructured regions of SE36. In the control arm, there were no marked fold changes in antibody titres and participants' sera reacted poorly to all peptides spanning SE36.

Conclusion

BK-SE36/CpG was well-tolerated and immunogenic. These results pave the way for further proof-of-concept studies to demonstrate vaccine efficacy.

Clinical trial registration

https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=1921, PACTR201701001921166.

Mitigating the effects of climate change on human health with vaccines and vaccinations

Climate change represents an unprecedented threat to humanity and will be the ultimate challenge of the 21st century. As a public health consequence, the World Health Organization estimates an additional 250,000 deaths annually by 2030, with resource-poor countries being predominantly affected. Although climate change's direct and indirect consequences on human health are manifold and far from fully explored, a growing body of evidence demonstrates its potential to exacerbate the frequency and spread of transmissible infectious diseases. Effective, high-impact mitigation measures are critical in combating this global crisis. While vaccines and vaccination are among the most cost-effective public health interventions, they have yet to be established as a major strategy in climate change-related health effect mitigation. In this narrative review, we synthesize the available evidence on the effect of climate change on vaccine-preventable diseases. This review examines the direct effect of climate change on water-related diseases such as cholera and other enteropathogens, helminthic infections and leptospirosis. It also explores the effects of rising temperatures on vector-borne diseases like dengue, chikungunya, and malaria, as well as the impact of temperature and humidity on airborne diseases like influenza and respiratory syncytial virus infection. Recent advances in global vaccine development facilitate the use of vaccines and vaccination as a mitigation strategy in the agenda against climate change consequences. A focused evaluation of vaccine research and development, funding, and distribution related to climate change is required.

Malaria vaccine-related adverse events among children under 5 in sub-Saharan Africa: systematic review and meta-analysis protocol

INTRODUCTION

The RTS,S vaccine has been approved for use in children under 5 living in moderate to high malaria transmission areas. However, clinically important adverse events have been reported in countries in sub-Saharan Africa. This systematic review aims to assess the frequency, severity and clinical importance of vaccine-related adverse events.

METHODS AND ANALYSIS

This systematic review protocol has been prepared following robust methods and reported in line with the Preferred Reporting Items for Systematic reviews and Meta-Analyses for protocols guidelines. We will search PubMed, CINAHL, LILACS, Google Scholar, SCOPUS, WEB OF SCIENCE, Cochrane library, HINARI, African Journals Online, Trip Pro and TOXNET from 2000 to 30 September 2023, without language restrictions. We will also search conference proceedings, dissertations, World Bank Open Knowledge Repository, and WHO, PATH, UNICEF, Food and Drugs Authorities and European Medicines Agency databases, preprint repositories and reference lists of relevant studies for additional studies. Experts in the field will be contacted for unpublished or published studies missed by our searches. At least two reviewers will independently select studies and extract data using pretested tools and assess risk of bias in the included studies using the Cochrane risk of bias tool. Any disagreements will be resolved through discussion between the reviewers. Heterogeneity will be explored graphically, and statistically using the I2 statistic. We will conduct random-effects meta-analysis when heterogeneity is appreciable, and express dichotomous outcomes (serious adverse events, cerebral malaria and febrile convulsion) as risk ratio (RR) with their 95% CI. We will perform subgroup analysis to assess the impact of heterogeneity and sensitivity analyses to test the robustness of the effect estimates. The overall level of evidence will be assessed using Grading of Recommendations Assessment, Development and Evaluation.

ETHICS AND DISSEMINATION

Ethical approval is not required for a systematic review. The findings of this study will be disseminated through stakeholder forums, conferences and peer-review publications.

PROSPERO REGISTRATION NUMBER

CRD42021275155.

Genetic diversity and in silico analysis of Plasmodium knowlesi Serine Repeat Antigen (SERA) 3 antigen 2 in Malaysia

Plasmodium knowlesi is the leading cause of malaria in Malaysia. Serine Repeat Antigens (SERAs) have an essential role in the parasite life cycle. However, genetic characterization on P. knowlesi SERA3 Ag2 (PkSERA3 Ag2) is lacking. In the present study, nucleotide diversity, natural selection, and haplotypes of PkSERA3 Ag2 in clinical samples from Peninsular Malaysia and Malaysian Borneo were investigated. A total of 50 P. knowlesi clinical samples were collected from Peninsular Malaysia and Malaysian Borneo. The PkSERA3 Ag2 gene was amplified using PCR, and subsequently cloned and sequenced. Genetic diversity, haplotype, natural selection as well as genetic structure and differentiation of PkSERA3 Ag2 were analysed. In addition, in silico analyses were performed to identify repeat motifs, B-cell epitopes, and antigenicity indices of the protein. Analysis of 114 PkSERA3 Ag2 sequences revealed high nucleotide diversity of the gene in Malaysia. A codon-based Z-test indicated that the gene underwent purifying selection. Haplotype and population structure analyses identified two distinct PkSERA3 Ag2 clusters (K = 2, ΔK = 721.14) but no clear genetic distinction between PkSERA3 Ag2 from Peninsular Malaysia and Malaysian Borneo. FST index indicated moderate differentiation of the gene. In silico analyses revealed unique repeat motifs among PkSERA3 Ag2 isolates. Moreover, the amino acid sequence of PkSERA3 Ag2 exhibited potential B-cell epitopes and possessed high antigenicity indices. These findings enhance the understanding of PkSERA3 Ag2 gene as well as its antigenic properties. Further validation is necessary to ascertain the utility of PkSERA3 Ag2 as a serological marker for P. knowlesi infection.

An Overview of Recent Developments in the Application of Antigen Displaying Vaccine Platforms: Hints for Future SARS-CoV-2 VLP Vaccines

Recently, a great effort has been devoted to studying attenuated and subunit vaccine development against SARS-CoV-2 since its outbreak in December 2019. It is known that diverse virus-like particles (VLPs) are extensively employed as carriers to display various antigenic and immunostimulatory cargo modules for vaccine development. Single or multiple antigens or antigenic domains such as the spike or nucleocapsid protein or their variants from SARS-CoV-2 could also be incorporated into VLPs via either a genetic or chemical display approach. Such antigen display platforms would help screen safer and more effective vaccine candidates capable of generating a strong immune response with or without adjuvant. This review aims to provide valuable insights for the future development of SARS-CoV-2 VLP vaccines by summarizing the latest updates and perspectives on the vaccine development of VLP platforms for genetic and chemical displaying antigens from SARS-CoV-2.

Evaluation of 4-Aminoquinoline Hydrazone Analogues as Potential Leads for Drug-Resistant Malaria

The emergence of resistance to first-line antimalarial drugs calls for the development of new therapies for drug-resistant malaria. The efficacy of quinoline-based antimalarial drugs has prompted the development of novel quinolines. A panel of 4-aminoquinoline hydrazone analogues were tested on the multidrug-resistant K1 strain of Plasmodium falciparum: IC50 values after a 48 h cycle ranged from 0.60 to 49 µM, while the 72 h cycle ranged from 0.026 to 0.219 μM. Time-course assays were carried out to define the activity of the lead compounds, which inhibited over 50% growth in 24 h and 90% growth in 72 h. Cytotoxicity assays with HepG2 cells showed IC50 values of 0.87-11.1 μM, whereas in MDBK cells, IC50 values ranged from 1.66 to 11.7 μM. High selectivity indices were observed for the lead compounds screened at 72 h on P. falciparum. Analyses of stage specificity revealed that the ring stages of the parasite life cycle were most affected. Based on antimalarial efficacy and in vitro safety profiles, lead compound 4-(2-benzylidenehydrazinyl)-6-methoxy-2-methylquinoline 2 was progressed to drug combination studies for the detection of synergism, with a combinatory index of 0.599 at IC90 for the combination with artemether, indicating a synergistic antimalarial activity. Compound 2 was screened on different strains of P. falciparum (3D7, Dd2), which maintained similar activity to K1, suggesting no cross-resistance between multidrug resistance and sensitive parasite strains. In vivo analysis with 2 showed the suppression of parasitaemia with P. yoelii NL (non-lethal)-treated mice (20 mg/kg and 5 mg/kg).

mRNA vaccine against malaria tailored for liver-resident memory T cells

Malaria is caused by Plasmodium species transmitted by Anopheles mosquitoes. Following a mosquito bite, Plasmodium sporozoites migrate from skin to liver, where extensive replication occurs, emerging later as merozoites that can infect red blood cells and cause symptoms of disease. As liver tissue-resident memory T cells (Trm cells) have recently been shown to control liver-stage infections, we embarked on a messenger RNA (mRNA)-based vaccine strategy to induce liver Trm cells to prevent malaria. Although a standard mRNA vaccine was unable to generate liver Trm or protect against challenge with Plasmodium berghei sporozoites in mice, addition of an agonist that recruits T cell help from type I natural killer T cells under mRNA-vaccination conditions resulted in significant generation of liver Trm cells and effective protection. Moreover, whereas previous exposure of mice to blood-stage infection impaired traditional vaccines based on attenuated sporozoites, mRNA vaccination was unaffected, underlining the potential for such a rational mRNA-based strategy in malaria-endemic regions.

Preliminary studies on the immunogenicity of a prime-and-trap malaria vaccine in nonhuman primates

Development of next-generation vaccines against Plasmodium falciparum (Pf) is a priority. Many malaria vaccines target the pre-erythrocytic sporozoite (SPZ) and liver stages. These include subunit vaccines based on the Pf circumsporozoite protein (CSP) and attenuated PfSPZ vaccines. However, these strategies require 3-4 doses and have not achieved optimal efficacy against field-transmitted malaria. Prime-and-trap is a recently developed two-step heterologous vaccine strategy that combines priming with DNA encoding CSP followed by a single dose of attenuated SPZ. This strategy aims to induce CD8+ T cells that can eliminate parasites in the liver. Prior data has demonstrated that prime-and-trap with P. yoelii CSP and PySPZ was immunogenic and protective in mice. Here we report preliminary data on the immunogenicity of PfCSP prime and PfSPZ trap vaccine in rhesus macaques. This vaccine induced PfCSP-specific antibodies and T cell responses in all animals. However, response magnitude differed between individuals, suggesting further study is required.

Malaria Genomics, Vaccine Development, and Microbiome

Recent advances in malaria genetics and genomics have transformed many aspects of malaria research in areas of molecular evolution, epidemiology, transmission, host-parasite interaction, drug resistance, pathogenicity, and vaccine development. Here, in addition to introducing some background information on malaria parasite biology, parasite genetics/genomics, and genotyping methods, we discuss some applications of genetic and genomic approaches in vaccine development and in studying interactions with microbiota. Genetic and genomic data can be used to search for novel vaccine targets, design an effective vaccine strategy, identify protective antigens in a whole-organism vaccine, and evaluate the efficacy of a vaccine. Microbiota has been shown to influence disease outcomes and vaccine efficacy; studying the effects of microbiota in pathogenicity and immunity may provide information for disease control. Malaria genetics and genomics will continue to contribute greatly to many fields of malaria research.

Chemical and biological conjugation strategies for the development of multivalent protein vaccine nanoparticles

The development of subunit vaccine platforms has been of considerable interest due to their good safety profile and ability to be adapted to new antigens, compared to other vaccine typess. Nevertheless, subunit vaccines often lack sufficient immunogenicity to fully protect against infectious diseases. A wide variety of subunit vaccines have been developed to enhance antigen immunogenicity by increasing antigen multivalency, as well as stability and delivery properties, via presentation of antigens on protein nanoparticles. Increasing multivalency can be an effective approach to provide a potent humoral immune response by more strongly engaging and clustering B cell receptors (BCRs) to induce activation, as well as increased uptake by antigen presenting cells and their subsequent T cell activation. Proper orientation of antigen on protein nanoparticles is also considered a crucial factor for enhanced BCR engagement and subsequent immune responses. Therefore, various strategies have been reported to decorate highly repetitive surfaces of protein nanoparticle scaffolds with multiple copies of antigens, arrange antigens in proper orientation, or combinations thereof. In this review, we describe different chemical bioconjugation methods, approaches for genetic fusion of recombinant antigens, biological affinity tags, and enzymatic conjugation methods to effectively present antigens on the surface of protein nanoparticle vaccine scaffolds.

Secondary metabolites of the leaves of Tricalysia atherura N. Hallé (Rubiaceae) and their potential antiplasmodial activity

One monoterpene indole alkaloid, atheruramine (1) bearing an ether bridge linking, one hydrobenzoin derivative, tricalydioloside (2) and two ursane-type triterpenes, atherurosides (A and B) (3 and 4) were isolated from the leaves of Tricalysia atherura, together with eight known compounds. The structures of these new compounds were elucidated on the basis of the results of spectroscopic analysis, and the relative configurations of compounds 1-3 were established by NOE difference. Four of the metabolites were screened in vitro against both chloroquine (CQ)-sensitive (3D7) and -resistant (Dd2) strains of Plasmodium falciparum; they were found to exhibit moderate activity against chloroquine-resistant (Dd2) (IC50 64.99-92.29 μg/mL). Meanwhile, crude extract possesses high antiplasmodial activity against both 3D7 and Dd2 strains of P. falciparum (IC50 4.39-7.54 μg/mL) and high selectivity indices values (SI > 10) and was found to be safe.

Reduced polymorphism of Plasmodium vivax early transcribed membrane protein (PvETRAMP) 11.2

BACKGROUND

ETRAMP11.2 (PVX_003565) is a well-characterized protein with antigenic potential. It is considered to be a serological marker for diagnostic tools, and it has been suggested as a potential vaccine candidate. Despite its immunological relevance, the polymorphism of the P. vivax ETRAMP11.2 gene (pvetramp11.2) remains undefined. The genetic variability of an antigen may limit the effectiveness of its application as a serological surveillance tool and in vaccine development and, therefore, the aim of this study was to investigate the genetic diversity of pvetramp11.2 in parasite populations from Amazonian regions and worldwide. We also evaluated amino acid polymorphism on predicted B-cell epitopes. The low variability of the sequence encoding PvETRAMP11.2 protein suggests that it would be a suitable marker in prospective serodiagnostic assays for surveillance strategies or in vaccine design against P. vivax malaria.

METHODS

The pvetramp11.2 of P. vivax isolates collected from Brazil (n = 68) and Peru (n = 36) were sequenced and analyzed to assess nucleotide polymorphisms, allele distributions, population differentiation, genetic diversity and signature of selection. In addition, sequences (n = 104) of seven populations from different geographical regions were retrieved from the PlasmoDB database and included in the analysis to study the worldwide allele distribution. Potential linear B-cell epitopes and their polymorphisms were also explored.

RESULTS

The multiple alignments of 208 pvetramp11.2 sequences revealed a low polymorphism and a marked geographical variation in allele diversity. Seven polymorphic sites and 11 alleles were identified. All of the alleles were detected in isolates from the Latin American region and five alleles were detected in isolates from the Southeast Asia/Papua New Guinea (SEA/PNG) region. Three alleles were shared by all Latin American populations (H1, H6 and H7). The H1 allele (reference allele from Salvador-1 strain), which was absent in the SEA/PNG populations, was the most represented allele in populations from Brazil (54%) and was also detected at high frequencies in populations from all other Latin America countries (range: 13.0% to 33.3%). The H2 allele was the major allele in SEA/PNG populations, but was poorly represented in Latin America populations (only in Brazil: 7.3%). Plasmodium vivax populations from Latin America showed a marked inter-population genetic differentiation (fixation index [Fst]) in contrast to SEA/PNG populations. Codon bias measures (effective number of codons [ENC] and Codon bias index [CBI]) indicated preferential use of synonymous codons, suggesting selective pressure at the translation level. Only three amino acid substitutions, located in the C-terminus, were detected. Linear B-cell epitope mapping predicted two epitopes in the Sal-1 PvETRAMP11.2 protein, one of which was fully conserved in all of the parasite populations analyzed.

CONCLUSIONS

We provide an overview of the allele distribution and genetic differentiation of ETRAMP11.2 antigen in P. vivax populations from different endemic areas of the world. The reduced polymorphism and the high degree of protein conservation supports the application of PvETRAMP11.2 protein as a reliable antigen for application in serological assays or vaccine design. Our findings provide useful information that can be used to inform future study designs.

Kinetic and Structural Characterization of Trypanosoma cruzi Hypoxanthine-Guanine-Xanthine Phosphoribosyltransferases and Repurposing of Transition-State Analogue Inhibitors

Over 70 million people are currently at risk of developing Chagas Disease (CD) infection, with more than 8 million people already infected worldwide. Current treatments are limited and innovative therapies are required. Trypanosoma cruzi, the etiological agent of CD, is a purine auxotroph that relies on phosphoribosyltransferases to salvage purine bases from their hosts for the formation of purine nucleoside monophosphates. Hypoxanthine-guanine-xanthine phosphoribosyltransferases (HGXPRTs) catalyze the salvage of 6-oxopurines and are promising targets for the treatment of CD. HGXPRTs catalyze the formation of inosine, guanosine, and xanthosine monophosphates from 5-phospho-d-ribose 1-pyrophosphate and the nucleobases hypoxanthine, guanine, and xanthine, respectively. T. cruzi possesses four HG(X)PRT isoforms. We previously reported the kinetic characterization and inhibition of two isoforms, TcHGPRTs, demonstrating their catalytic equivalence. Here, we characterize the two remaining isoforms, revealing nearly identical HGXPRT activities in vitro and identifying for the first time T. cruzi enzymes with XPRT activity, clarifying their previous annotation. TcHGXPRT follows an ordered kinetic mechanism with a postchemistry event as the rate-limiting step(s) of catalysis. Its crystallographic structures reveal implications for catalysis and substrate specificity. A set of transition-state analogue inhibitors (TSAIs) initially developed to target the malarial orthologue were re-evaluated, with the most potent compound binding to TcHGXPRT with nanomolar affinity, validating the repurposing of TSAIs to expedite the discovery of lead compounds against orthologous enzymes. We identified mechanistic and structural features that can be exploited in the optimization of inhibitors effective against TcHGPRT and TcHGXPRT concomitantly, which is an important feature when targeting essential enzymes with overlapping activities.

Memory CD8+ T cell-mediated protection against liver-stage malaria

Nearly half of the world's population is at risk of malaria, a disease caused by the protozoan parasite Plasmodium, which is estimated to cause more than 240,000,000 infections and kill more than 600,000 people annually. The emergence of Plasmodia resistant to chemoprophylactic treatment highlights the urgency to develop more effective vaccines. In this regard, whole sporozoite vaccination approaches in murine models and human challenge studies have provided substantial insight into the immune correlates of protection from malaria. From these studies, CD8+ T cells have come to the forefront, being identified as critical for vaccine-mediated liver-stage immunity that can prevent the establishment of the symptomatic blood stages and subsequent transmission of infection. However, the unique biological characteristics required for CD8+ T cell protection from liver-stage malaria dictate that more work must be done to design effective vaccines. In this review, we will highlight a subset of studies that reveal basic aspects of memory CD8+ T cell-mediated protection from liver-stage malaria infection.

[Vaccination against malaria]

Vaccination against malaria is an old dream that reemerged in 2015 with the European Medicines Agency's favourable opinion on a first antimalarial vaccine, RTS,S/ AS01. Six years later, the World Health Organization (WHO) is advising a wide deployment of this vaccine in sub-Saharan Africa and in regions with high and moderate transmission where Plasmodium falciparum circulates. This follows favourable results from the pilot programme in Ghana, Kenya and Malawi involving over 800,000 children since 2019. This article addresses the objectives and main vaccine candidates targeting the different stages of parasite development, highlighting the progress and limitations of these different approaches. The RTS,S saga has been a milestone in vaccine development, with a first-generation vaccine recommended by the WHO for use in children over 5 months of age in sub-Saharan Africa and other areas of moderate to high transmission of P. falciparum malaria, in combination with other prevention measures. Research efforts continue to better understand the correlates of protection. With advances in vaccine platforms, new multi-antigen, multi-stage, and even multi-species approaches might emerge and brighten the horizon for malaria control.

Trends of the Global, Regional and National Incidence, Mortality, and Disability-Adjusted Life Years of Malaria, 1990-2019: An Analysis of the Global Burden of Disease Study 2019

Background

Malaria remains a substantial concern in the realm of public health on a worldwide level. Using information from the global burden of disease (GBD) 2019 for 204 countries and territories between 1990 and 2019, we assessed the burden of malaria.

Methods

Data on malaria were derived from the GBD 2019 study between 1990 and 2019. We evaluated the number of incidence, deaths, disability-adjusted life years (DALYs), age-standardized incidence rates (ASIR), age-standardized mortality rates (ASMR), and age-standardized DALY rates (ASDR), examining them across variables such as age, year, gender, country, region, and socio-demographic index (SDI).

Results

The burden of malaria decreased globally between 1990 and 2019. There were 2313.57×10⁵ incident cases and 6.43×10⁵ deaths in 2019, contributing to 464.38×10⁵ DALYs. Largest incident cases were observed in Western Sub-Saharan Africa [1151.72 (95% UI: 890.01-1527.17)] ×10⁵ in 2019. The only region where deaths increased between 1990 and 2019 was Western Sub-Saharan Africa. ASRs of malaria are distributed heterogeneously in different regions. The highest ASIR was observed in Central Sub-Saharan Africa [21,557.65 (95% UI: 16,639.4-27,491.48)] in 2019. From 1990 to 2019, the ASMR of malaria declined. Compared to other age cohorts, the ASIR, ASMR, and ASDR for children aged between 1 to 4 years were found to be higher. Worst-affected regions by malaria infection were the low-middle SDI region and low SDI region.

Conclusion

Malaria threatens global public health, especially in Central Sub-Saharan Africa and Western Sub-Saharan Africa. Children 1-4 years old continue to bear the most significant burden of malaria. The study's results will guide efforts to reduce malaria's impact on the global population.

Purine containing carbonucleoside phosphonate analogues as novel chemotype for Plasmodium falciparum Inhibition

The nucleotidase ISN1 is a potential therapeutic target of the purine salvage pathway of the malaria parasite Plasmodium falciparum. We identified PfISN1 ligands by in silico screening of a small library of nucleos(t)ide analogues and by thermal shift assays. Starting from a racemic cyclopentyl carbocyclic phosphonate scaffold, we explored the diversity on the nucleobase moiety and also proposed a convenient synthetic pathway to access the pure enantiomers of our initial hit (compound (±)-2). 2,6-Disubstituted purine containing derivatives such as compounds 1, (±)-7e and β-L-(+)-2 showed the most potent inhibition of the parasite in vitro, with low micromolar IC₅₀ values. These results are remarkable considering the anionic nature of nucleotide analogues, which are known to lack activity in cell culture experiments due to their scarce capacity to cross cell membranes. For the first time, we report the antimalarial activity of a carbocyclic methylphosphonate nucleoside with an L-like configuration.

Molecular engineering tools for the development of vaccines against infectious diseases: current status and future directions

INTRODUCTION

The escalating global changes have fostered conditions for the expansion and transmission of diverse biological factors, leading to the rise of emerging and reemerging infectious diseases. Complex viral infections, such as COVID-19, influenza, HIV, and Ebola, continue to surface, necessitating the development of effective vaccine technologies.

AREAS COVERED

This review article highlights recent advancements in molecular biology, virology, and genomics that have propelled the design and development of innovative molecular tools. These tools have promoted new vaccine research platforms and directly improved vaccine efficacy. The review summarizes the cutting-edge molecular engineering tools used in creating novel vaccines and explores the rapidly expanding molecular tools landscape and potential directions for future vaccine development.

EXPERT OPINION

The strategic application of advanced molecular engineering tools can address conventional vaccine limitations, enhance the overall efficacy of vaccine products, promote diversification in vaccine platforms, and form the foundation for future vaccine development. Prioritizing safety considerations of these novel molecular tools during vaccine development is crucial.

Research Progress of Aluminum Phosphate Adjuvants and Their Action Mechanisms

Although hundreds of different adjuvants have been tried, aluminum-containing adjuvants are by far the most widely used currently. It is worth mentioning that although aluminum-containing adjuvants have been commonly applied in vaccine production, their acting mechanism remains not completely clear. Thus far, researchers have proposed the following mechanisms: (1) depot effect, (2) phagocytosis, (3) activation of pro-inflammatory signaling pathway NLRP3, (4) host cell DNA release, and other mechanisms of action. Having an overview on recent studies to increase our comprehension on the mechanisms by which aluminum-containing adjuvants adsorb antigens and the effects of adsorption on antigen stability and immune response has become a mainstream research trend. Aluminum-containing adjuvants can enhance immune response through a variety of molecular pathways, but there are still significant challenges in designing effective immune-stimulating vaccine delivery systems with aluminum-containing adjuvants. At present, studies on the acting mechanism of aluminum-containing adjuvants mainly focus on aluminum hydroxide adjuvants. This review will take aluminum phosphate as a representative to discuss the immune stimulation mechanism of aluminum phosphate adjuvants and the differences between aluminum phosphate adjuvants and aluminum hydroxide adjuvants, as well as the research progress on the improvement of aluminum phosphate adjuvants (including the improvement of the adjuvant formula, nano-aluminum phosphate adjuvants and a first-grade composite adjuvant containing aluminum phosphate). Based on such related knowledge, determining optimal formulation to develop effective and safe aluminium-containing adjuvants for different vaccines will become more substantiated.

Mechanism of small molecule inhibition of Plasmodium falciparum myosin A informs antimalarial drug design

Malaria results in more than 500,000 deaths per year and the causative Plasmodium parasites continue to develop resistance to all known agents, including different antimalarial combinations. The class XIV myosin motor PfMyoA is part of a core macromolecular complex called the glideosome, essential for Plasmodium parasite mobility and therefore an attractive drug target. Here, we characterize the interaction of a small molecule (KNX-002) with PfMyoA. KNX-002 inhibits PfMyoA ATPase activity in vitro and blocks asexual blood stage growth of merozoites, one of three motile Plasmodium life-cycle stages. Combining biochemical assays and X-ray crystallography, we demonstrate that KNX-002 inhibits PfMyoA using a previously undescribed binding mode, sequestering it in a post-rigor state detached from actin. KNX-002 binding prevents efficient ATP hydrolysis and priming of the lever arm, thus inhibiting motor activity. This small-molecule inhibitor of PfMyoA paves the way for the development of alternative antimalarial treatments.

Protective RNA nanovaccines against Mycobacterium avium subspecies hominissuis

The induction of an effective immune response is critical for the success of mRNA-based therapeutics. Here, we developed a nanoadjuvant system compromised of Quil-A and DOTAP (dioleoyl 3 trimethylammonium propane), hence named QTAP, for the efficient delivery of mRNA vaccine constructs into cells. Electron microscopy indicated that the complexation of mRNA with QTAP forms nanoparticles with an average size of 75 nm and which have ~90% encapsulation efficiency. The incorporation of pseudouridine-modified mRNA resulted in higher transfection efficiency and protein translation with low cytotoxicity than unmodified mRNA. When QTAP-mRNA or QTAP alone transfected macrophages, pro-inflammatory pathways (e.g., NLRP3, NF-kb, and MyD88) were upregulated, an indication of macrophage activation. In C57Bl/6 mice, QTAP nanovaccines encoding Ag85B and Hsp70 transcripts (QTAP-85B+H70) were able to elicit robust IgG antibody and IFN- ɣ, TNF-α, IL-2, and IL-17 cytokines responses. Following aerosol challenge with a clinical isolate of M. avium ss. hominissuis (M.ah), a significant reduction of mycobacterial counts was observed in lungs and spleens of only immunized animals at both 4- and 8-weeks post-challenge. As expected, reduced levels of M. ah were associated with diminished histological lesions and robust cell-mediated immunity. Interestingly, polyfunctional T-cells expressing IFN- ɣ, IL-2, and TNF- α were detected at 8 but not 4 weeks post-challenge. Overall, our analysis indicated that QTAP is a highly efficient transfection agent and could improve the immunogenicity of mRNA vaccines against pulmonary M. ah, an infection of significant public health importance, especially to the elderly and to those who are immune compromised.

The αTSR Domain of Plasmodium Circumsporozoite Protein Bound Heparan Sulfates and Elicited High Titers of Sporozoite Binding Antibody After Displayed by Nanoparticles

Introduction

Malaria is a devastating infectious illness caused by protozoan Plasmodium parasites. The circumsporozoite protein (CSP) on Plasmodium sporozoites binds heparan sulfate proteoglycan (HSPG) receptors for liver invasion, a critical step for prophylactic and therapeutic interventions.

Methods

In this study, we characterized the αTSR domain that covers region III and the thrombospondin type-I repeat (TSR) of the CSP using various biochemical, glycobiological, bioengineering, and immunological approaches.

Results

We found for the first time that the αTSR bound heparan sulfate (HS) glycans through support by a fused protein, indicating that the αTSR is a key functional domain and thus a vaccine target. When the αTSR was fused to the S domain of norovirus VP1, the fusion protein self-assembled into uniform S₆₀-αTSR nanoparticles. Three-dimensional structure reconstruction revealed that each nanoparticle consists of an S₆₀ nanoparticle core and 60 surface displayed αTSR antigens. The nanoparticle displayed αTSRs retained the binding function to HS glycans, indicating that they maintained authentic conformations. Both tagged and tag-free S₆₀-αTSR nanoparticles were produced via the Escherichia coli system at high yield by scalable approaches. They are highly immunogenic in mice, eliciting high titers of αTSR-specific antibody that bound specifically to the CSPs of Plasmodium falciparum sporozoites at high titer.

Discussion and Conclusion

Our data demonstrated that the αTSR is an important functional domain of the CSP. The S₆₀-αTSR nanoparticle displaying multiple αTSR antigens is a promising vaccine candidate potentially against attachment and infection of Plasmodium parasites.

Acceptance, availability, and feasibility of RTS, S/AS01 malaria vaccine: A review

INTRODUCTION

In malaria-stricken regions, malaria continues to be one of the primary causes of mortality for children. The number of malaria-related fatalities has drastically decreased because of artemisinin-based pharmacological regimens.

METHODS

Two independent researchers did a comprehensive literature search using PubMed/MEDLINE and Google Scholar from its inception to September 2022.

RESULTS

After evaluating RTS, S/AS01 for its safety, effectiveness, and feasibility, the European Medicines Agency (EMA) issued a favorable conclusion. It was suggested that the RTS, S malaria vaccine be used extensively by the World Health Organization on October 6, 2021. The successful pilot program testing the malaria vaccine in Ghana, Kenya, and Malawi served as the basis for this proposal.

CONCLUSION

Several challenges need to be addressed to ensure the success of vaccination programs. From the acceptability perspective, issues such as inadequate community engagement, concerns about side effects, and issues with the delivery and quality of healthcare services can affect the acceptance of the vaccine. From the feasibility standpoint, factors such as lack of transportation or long distances to healthcare facilities and the perception of completion of the vaccination calendar can affect the feasibility of the vaccine. Lastly, the availability of the vaccine is also a major concern as it may not be readily available to meet the demands.

What Do We Know about Surface Proteins of Chicken Parasites Eimeria?

Poultry is the first source of animal protein for human consumption. In a changing world, this sector is facing new challenges, such as a projected increase in demand, higher standards of food quality and safety, and reduction of environmental impact. Chicken coccidiosis is a highly widespread enteric disease caused by Eimeria spp. which causes significant economic losses to the poultry industry worldwide; however, the impact on family poultry holders or backyard production-which plays a key role in food security in small communities and involves mainly rural women-has been little explored. Coccidiosis disease is controlled by good husbandry measures, chemoprophylaxis, and/or live vaccination. The first live vaccines against chicken coccidiosis were developed in the 1950s; however, after more than seven decades, none has reached the market. Current limitations on their use have led to research in next-generation vaccines based on recombinant or live-vectored vaccines. Next-generation vaccines are required to control this complex parasitic disease, and for this purpose, protective antigens need to be identified. In this review, we have scrutinised surface proteins identified so far in Eimeria spp. affecting chickens. Most of these surface proteins are anchored to the parasite membrane by a glycosylphosphatidylinositol (GPI) molecule. The biosynthesis of GPIs, as well as the role of currently identified surface proteins and interest as vaccine candidates has been summarised. The potential role of surface proteins in drug resistance and immune escape and how these could limit the efficacy of control strategies was also discussed.

Antimalarial potential of Moringa oleifera Lam. (Moringaceae): A review of the ethnomedicinal, pharmacological, toxicological, and phytochemical evidence

Several regions of the world frequently use the species Moringa oleifera Lam. (Moringaceae) in traditional medicine. This situation is even more common in African countries. Many literature reports point to the antimalarial potential of this species, indicating the efficacy of its chemical compounds against malaria-causing parasites of the genus Plasmodium. From this perspective, the present study reviews the ethnobotanical, pharmacological, toxicological, and phytochemical (flavonoids) evidence of M. oleifera, focusing on the treatment of malaria. Scientific articles were retrieved from Google Scholar, PubMed^®, ScienceDirect^®, and SciELO databases. Only articles published between 2002 and 2022 were selected. After applying the inclusion and exclusion criteria, this review used a total of 72 articles. These documents mention a large use of M. oleifera for the treatment of malaria in African and Asian countries. The leaves (63%) of this plant are the main parts used in the preparation of herbal medicines. The in vivo antimalarial activity of M. oleifera was confirmed through several studies using polar and nonpolar extracts, fractions obtained from the extracts, infusion, pellets, and oils obtained from this plant and tested in rodents infected by the following parasites of the genus Plasmodium: P. berghei, P. falciparum, P. yoelii, and P. chabaudi. Extracts obtained from M. oleifera showed no toxicity in preclinical tests. A total of 46 flavonoids were identified in the leaves and seeds of M. oleifera by different chromatography and mass spectrometry methods. Despite the scarcity of research on the antimalarial potential of compounds isolated from M. oleifera, the positive effects against malaria-causing parasites in previous studies are likely to correlate with the flavonoids that occur in this species.

Malaria vaccines: the 60-year journey of hope and final success-lessons learned and future prospects

BACKGROUND

The world has made great strides towards beating malaria, although about half of the world population is still exposed to the risk of contracting malaria. Developing an effective malaria vaccine was a huge challenge for medical science. In 2021 the World Health Organization (WHO) approved the first malaria vaccine, RTS,S/AS01 vaccine (Mosquirix™), for widespread use. This review highlights the history of development, and the different approaches and types of malaria vaccines, and the literature to date. It covers the developmental stages of RTS,S/AS01 and recommends steps for its deployment. The review explores other potential vaccine candidates and their status, and suggests options for their further development. It also recommends future roles for vaccines in eradicating malaria. Questions remain on how RTS,S vaccine will work in widespread use and how it can best be utilized to benefit vulnerable communities.

CONCLUSION

Malaria vaccines have been in development for almost 60 years. The RTS,S/AS01 vaccine has now been approved, but cannot be a stand-alone solution. Development should continue on promising candidates such as R21, PfSPZ and P. vivax vaccines. Multi-component vaccines may be a useful addition to other malaria control techniques in achieving eradication of malaria.

Design and characterization of chimeric Rabies-SARS-CoV-2 virus-like particles for vaccine purposes

Due to the high number of doses required to achieve adequate coverage in the context of COVID-19 pandemics, there is a great need for novel vaccine developments. In this field, there have been research approaches that focused on the production of SARS-CoV-2 virus-like particles. These are promising vaccine candidates as their structure is similar to that of native virions but they lack the genome, constituting a biosafe alternative. In order to produce these structures using mammal cells, it has been established that all four structural proteins must be expressed. Here we report the generation and characterization of a novel chimeric virus-like particle (VLP) that can be produced by the expression of a single novel fusion protein that contains SARS-CoV-2 spike (S) ectodomain fused to rabies glycoprotein membrane anchoring region in HEK293 cells. This protein is structurally similar to native S and can autonomously bud forming enveloped VLPs that resemble native virions both in size and in morphology, displaying S ectodomain and receptor binding domain (RBD) on their surface. As a proof of concept, we analyzed the immunogenicity of this vaccine candidate in mice and confirmed the generation of anti-S, anti-RBD, and neutralizing antibodies. KEY POINTS: • A novel fusion rabies glycoprotein containing S ectodomain was designed. • Fusion protein formed cVLPs that were morphologically similar to SARS-CoV-2 virions. • cVLPs induced anti-S, anti-RBD, and neutralizing antibodies in mice.

Current advances in nanodrug delivery systems for malaria prevention and treatment

Malaria is a life-threatening, blood-borne disease with over two hundred million cases throughout the world and is more prevalent in Sub-Saharan Africa than anywhere else in the world. Over the years, several treatment agents have been developed for malaria; however, most of these active pharmaceutical ingredients exhibit poor aqueous solubility and low bioavailability and may result in drug-resistant parasites, thus increasing malaria cases and eventually, deaths. Factors such as these in therapeutics have led to a better appreciation of nanomaterials. The ability of nanomaterials to function as drug carriers with a high loading capacity and targeted drug delivery, good biocompatibility, and low toxicity renders them an appealing alternative to conventional therapy. Nanomaterials such as dendrimers and liposomes have been demonstrated to be capable of enhancing the efficacy of antimalarial drugs. This review discusses the recent development of nanomaterials and their benefits in drug delivery for the potential treatment of malaria.

Antimalarial drugs: what's new in the patents?

INTRODUCTION

The efficacy of current therapeutic warheads in preventing malaria transmission or treating the disease is often hampered by the emergence of drug-resistance. No effective vaccines are available to date, and novel drugs able to counteract drug-resistant forms of malaria and/or to target multiple stages of the parasite's lifecycle are urgently needed.

AREAS COVERED

This review covers patents that protect antimalarial small molecules bearing the artemisinin or other chemical scaffolds, as well as vaccines, that have been published in the period 2015-2022. Literature was searched in public databases of articles and patents. Patents protecting small molecules that prevent malaria transmission are not discussed herein.

EXPERT OPINION

Significant progress has been made in the design of antimalarial agents. Most of these candidates have been tested in standardized strains, with the use of Plasmodium clinical isolates for testing still underdeveloped. Several compounds have been profiled in in vivo mouse models of malaria, including humanised mice. Despite having different efficacy, these new molecules might further progress the field and hopefully will advance to clinical development soon.

Malaria therapeutics: are we close enough?

Malaria is a vector-borne parasitic disease caused by the apicomplexan protozoan parasite Plasmodium. Malaria is a significant health problem and the leading cause of socioeconomic losses in developing countries. WHO approved several antimalarials in the last 2 decades, but the growing resistance against the available drugs has worsened the scenario. Drug resistance and diversity among Plasmodium strains hinder the path of eradicating malaria leading to the use of new technologies and strategies to develop effective vaccines and drugs. A timely and accurate diagnosis is crucial for any disease, including malaria. The available diagnostic methods for malaria include microscopy, RDT, PCR, and non-invasive diagnosis. Recently, there have been several developments in detecting malaria, with improvements leading to achieving an accurate, quick, cost-effective, and non-invasive diagnostic tool for malaria. Several vaccine candidates with new methods and antigens are under investigation and moving forward to be considered for clinical trials. This article concisely reviews basic malaria biology, the parasite's life cycle, approved drugs, vaccine candidates, and available diagnostic approaches. It emphasizes new avenues of therapeutics for malaria.

A Critical Review on Human Malaria and Schistosomiasis Vaccines: Current State, Recent Advancements, and Developments

Malaria and schistosomiasis are two major parasitic diseases that remain leading causes of morbidity and mortality worldwide. Co-infections of these two parasites are common in the tropics, where both diseases are endemic. The clinical consequences of schistosomiasis and malaria are determined by a variety of host, parasitic, and environmental variables. Chronic schistosomiasis causes malnutrition and cognitive impairments in children, while malaria can cause fatal acute infections. There are effective drugs available to treat malaria and schistosomiasis. However, the occurrence of allelic polymorphisms and the rapid selection of parasites with genetic mutations can confer reduced susceptibility and lead to the emergence of drug resistance. Moreover, the successful elimination and complete management of these parasites are difficult due to the lack of effective vaccines against Plasmodium and Schistosoma infections. Therefore, it is important to highlight all current vaccine candidates undergoing clinical trials, such as pre-erythrocytic and erythrocytic stage malaria, as well as a next-generation RTS,S-like vaccine, the R21/Matrix-M vaccine, that conferred 77% protection against clinical malaria in a Phase 2b trial. Moreover, this review also discusses the progress and development of schistosomiasis vaccines. Furthermore, significant information is provided through this review on the effectiveness and progress of schistosomiasis vaccines currently under clinical trials, such as Sh28GST, Sm-14, and Sm-p80. Overall, this review provides insights into recent progress in malarial and schistosomiasis vaccines and their developmental approaches.

Lipid-based colloidal nanoparticles for applications in targeted vaccine delivery

Bioactive molecules and their effects have been influenced by their solubility and administration route. In many therapeutic reagents, the performance of therapeutics is dependent on physiological barriers in the human body and delivery efficacy. Therefore, an effective and stable therapeutic delivery promotes pharmaceutical advancement and suitable biological usage of drugs. In the biological and pharmacological industries, lipid nanoparticles (LNPs) have emerged as a potential carrier to deliver therapeutics. Since studies reported doxorubicin-loaded liposomes (Doxil®), LNPs have been applied to numerous clinical trials. Lipid-based nanoparticles, including liposomes, solid lipid nanoparticles (SLNs), and nanostructured lipid nanoparticles, have also been developed to deliver active ingredients in vaccines. In this review, we present the type of LNPs used to develop vaccines with attractive advantages. We then discuss messenger RNA (mRNA) delivery for the clinical application of mRNA therapeutic-loaded LNPs and recent research trend of LNP-based vaccine development.

The mRNA Vaccine Technology Era and the Future Control of Parasitic Infections

Despite intensive long-term efforts, with very few exceptions, the development of effective vaccines against parasitic infections has presented considerable challenges, given the complexity of parasite life cycles, the interplay between parasites and their hosts, and their capacity to escape the host immune system and to regulate host immune responses. For many parasitic diseases, conventional vaccine platforms have generally proven ill suited, considering the complex manufacturing processes involved and the costs they incur, the inability to posttranslationally modify cloned target antigens, and the absence of long-lasting protective immunity induced by these antigens. An effective antiparasite vaccine platform is required to assess the effectiveness of novel vaccine candidates at high throughput. By exploiting the approach that has recently been used successfully to produce highly protective COVID mRNA vaccines, we anticipate a new wave of research to advance the use of mRNA vaccines to prevent parasitic infections in the near future. This article considers the characteristics that are required to develop a potent antiparasite vaccine and provides a conceptual foundation to promote the development of parasite mRNA-based vaccines. We review the recent advances and challenges encountered in developing antiparasite vaccines and evaluate the potential of developing mRNA vaccines against parasites, including those causing diseases such as malaria and schistosomiasis, against which vaccines are currently suboptimal or not yet available.

SARS-CoV-2 spike-ferritin-nanoparticle adjuvanted with ALFQ induces long-lived plasma cells and cross-neutralizing antibodies

This study demonstrates the impact of adjuvant on the development of T follicular helper (Tfh) and B cells, and their influence on antibody responses in mice vaccinated with SARS-CoV-2-spike-ferritin-nanoparticle (SpFN) adjuvanted with either Army Liposome Formulation containing QS-21 (SpFN + ALFQ) or Alhydrogel® (SpFN + AH). SpFN + ALFQ increased the size and frequency of germinal center (GC) B cells in the vaccine-draining lymph nodes and increased the frequency of antigen-specific naive B cells. A single vaccination with SpFN + ALFQ resulted in a higher frequency of IL-21-producing-spike-specific Tfh and GC B cells in the draining lymph nodes and spleen, S-2P protein-specific IgM and IgG antibodies, and elicitation of robust cross-neutralizing antibodies against SARS-CoV-2 variants as early as day 7, which was enhanced by a second vaccination. This was associated with the generation of high titer, high avidity binding antibodies. The third vaccination with SpFN + ALFQ elicited high levels of neutralizing antibodies against the Omicron variant. No cross-neutralizing antibodies against Omicron were induced with SpFN + AH. These findings highlight the importance of ALFQ in orchestrating early induction of antigen-specific Tfh and GC B cell responses and long-lived plasma cells in the bone marrow. The early engagement of S-2P specific naive B cells and high titer IgM antibodies shape the development of long-term neutralization breadth.

Targeting plasmodium α-tubulin-1 to block malaria transmission to mosquitoes

Plasmodium ookinetes use an invasive apparatus to invade mosquito midguts, and tubulins are the major structural proteins of this apical complex. We examined the role of tubulins in malaria transmission to mosquitoes. Our results demonstrate that the rabbit polyclonal antibodies (pAb) against human α-tubulin significantly reduced the number of P. falciparum oocysts in Anopheles gambiae midguts, while rabbit pAb against human β-tubulin did not. Further studies showed that pAb, specifically against P. falciparum α-tubulin-1, also significantly limited P. falciparum transmission to mosquitoes. We also generated mouse monoclonal antibodies (mAb) using recombinant P. falciparum α-tubulin-1. Out of 16 mAb, two mAb, A3 and A16, blocked P. falciparum transmission with EC50 of 12 μg/ml and 2.8 μg/ml. The epitopes of A3 and A16 were determined to be a conformational and linear sequence of EAREDLAALEKDYEE, respectively. To understand the mechanism of the antibody-blocking activity, we studied the accessibility of live ookinete α-tubulin-1 to antibodies and its interaction with mosquito midgut proteins. Immunofluorescent assays showed that pAb could bind to the apical complex of live ookinetes. Moreover, both ELISA and pull-down assays demonstrated that insect cell-expressed mosquito midgut protein, fibrinogen-related protein 1 (FREP1), interacts with P. falciparum α-tubulin-1. Since ookinete invasion is directional, we conclude that the interaction between Anopheles FREP1 protein and Plasmodium α-tubulin-1 anchors and orients the ookinete invasive apparatus towards the midgut PM and promotes the efficient parasite infection in the mosquito.

VelcroVax: a "Bolt-On" Vaccine Platform for Glycoprotein Display

Having varied approaches to the design and manufacture of vaccines is critical in being able to respond to worldwide needs and newly emerging pathogens. Virus-like particles (VLPs) form the basis of two of the most successful licensed vaccines (against hepatitis B virus [HBV] and human papillomavirus). They are produced by recombinant expression of viral structural proteins, which assemble into immunogenic nanoparticles. VLPs can be modified to present unrelated antigens, and here we describe a universal "bolt-on" platform (termed VelcroVax) where the capturing VLP and the target antigen are produced separately. We utilize a modified HBV core (HBcAg) VLP with surface expression of a high-affinity binding sequence (Affimer) directed against a SUMO tag and use this to capture SUMO-tagged gp1 glycoprotein from the arenavirus Junín virus (JUNV). Using this model system, we have solved the first high-resolution structures of VelcroVax VLPs and shown that the VelcroVax-JUNV gp1 complex induces superior humoral immune responses compared to the noncomplexed viral protein. We propose that this system could be modified to present a range of antigens and therefore form the foundation of future rapid-response vaccination strategies. IMPORTANCE The hepatitis B core protein (HBc) forms noninfectious virus-like particles, which can be modified to present a capturing molecule, allowing suitably tagged antigens to be bound on their surface. This system can be adapted and provides the foundation for a universal "bolt-on" vaccine platform (termed VelcroVax) that can be easily and rapidly modified to generate nanoparticle vaccine candidates.

Platforms, advances, and technical challenges in virus-like particles-based vaccines

Viral infectious diseases threaten human health and global stability. Several vaccine platforms, such as DNA, mRNA, recombinant viral vectors, and virus-like particle-based vaccines have been developed to counter these viral infectious diseases. Virus-like particles (VLP) are considered real, present, licensed and successful vaccines against prevalent and emergent diseases due to their non-infectious nature, structural similarity with viruses, and high immunogenicity. However, only a few VLP-based vaccines have been commercialized, and the others are either in the clinical or preclinical phases. Notably, despite success in the preclinical phase, many vaccines are still struggling with small-scale fundamental research owing to technical difficulties. Successful production of VLP-based vaccines on a commercial scale requires a suitable platform and culture mode for large-scale production, optimization of transduction-related parameters, upstream and downstream processing, and monitoring of product quality at each step. In this review article, we focus on the advantages and disadvantages of various VLP-producing platforms, recent advances and technical challenges in VLP production, and the current status of VLP-based vaccine candidates at commercial, preclinical, and clinical levels.

Emerging adjuvants for intradermal vaccination

The majority of vaccines have been delivered into the muscular tissue. Skin contains large amounts of antigen-presenting cells and has been recognized as a more immunogenic site for vaccine delivery. Intradermal delivery has been approved to improve influenza vaccine efficacy and spare influenza vaccine doses. In response to the recent monkeypox outbreak, intradermal delivery has been also approved to stretch the limited monkeypox vaccine doses to immunize more people at risk. Incorporation of vaccine adjuvants is promising to further increase intradermal vaccine efficacy and spare more vaccine doses. Yet, intradermal vaccination is associated with more significant local reactions than intramuscular vaccination. Thus, adjuvants suitable to boost intradermal vaccination need to have a good local safety without inducing overt local reactions. This review introduces currently approved adjuvants in licensed human vaccines and their relative reactogenicity for intradermal delivery and then introduces emerging chemical and physical adjuvants with a good local safety to boost intradermal vaccination. The rational to develop physical adjuvants, the types of physical adjuvants, and the unique advantages of physical adjuvants to boost intradermal vaccination are also introduced in this review.

Immunodominant T cell peptides from four candidate malarial antigens as biomarkers of protective immunity against malaria

A malaria vaccine with high efficacy and capable of inducing sterile immunity against malaria within genetically diverse populations is urgently needed to complement ongoing disease control and elimination efforts. Parasite-specific IFN-γ and granzyme B-secreting CD8 + T cells have been identified as key mediators of protection and the rapid identification of malaria antigen targets that elicit these responses will fast-track the development of simpler, cost-effective interventions. This study extends our previous work which used peripheral blood mononuclear cells (PBMCs) from adults with life-long exposure to malaria parasites to identify immunodominant antigen-specific peptide pools composed of overlapping 15mer sequences spanning full length proteins of four malarial antigens. Our current study aimed to identify CD8 + T cell epitopes within these previously identified positive peptide pools. Cryopreserved PBMCs from 109 HLA-typed subjects were stimulated with predicted 9-11mer CD8 + T cell epitopes from P. falciparum circumsporozoite protein (CSP), apical membrane antigen 1 (AMA1), thrombospondin related anonymous protein (TRAP) and cell traversal for ookinetes and sporozoites (CelTOS) in FluoroSpot assays. A total of 135 epitopes out of 297 tested peptides from the four antigens were experimentally identified as positive for IFN-γ and/or granzyme B production in 65 of the 109 subjects. Forty-three of 135 epitopes (32 %) were promiscuous for HLA binding, with 31 of these promiscuous epitopes (72 %) being presented by HLA alleles that fall within at least two different HLA supertypes. Furthermore, about 52 % of identified epitopes were conserved when the respective sequences were aligned with those from 16 highly diverse P. falciparum parasite strains. In summary, we have identified a number of conserved epitopes, immune responses to which could be effective against multiple P. falciparum parasite strains in genetically diverse populations.

Immunogenicity of Wild Type and Mutant Hepatitis B Surface Antigen Virus-like Particles (VLPs) in Mice with Pre-Existing Immunity against the Wild Type Vector

Virus-like particles (VLPs), composed of the small hepatitis B virus surface antigen (HBsAgS), are the antigenic components of the hepatitis B virus (HBV) vaccine and represent the backbones for a chimeric anti-malaria vaccine and various vaccine candidates. Biological vectors have to face pre-existing anti-vector immune responses due to previous immune exposure. Vector recognition after natural infections or vaccinations can result in unwarranted outcomes, with compromising effects on clinical outcomes. In order to evaluate the impact of a pre-existing anti-HBsAgS immune response, we developed mutant VLPs composed of subunits with reduced HBsAgS-specific antigenicity. The insertion of a Plasmodium falciparum circumsporozoite protein (CSP)-derived epitope as a read-out allowed the assessment of wild type (wt) and mutant VLPs in the context of a pre-existing immune response. Mutant and wt VLP platforms with a CSP-epitope insert are immunogenic and have the ability to generate anti-CSP antibody responses in both naïve BALB/c mice and mice with a pre-existing anti-HBsAgS immune response, but with superior anti-CSP responses in mice with a pre-existing immunity. The data indicate that previous HBsAgS exposure facilitates enhanced antibody responses against foreign epitopes delivered by the HBsAgS platform, and, in this context, the state of immune sensitization alters the outcome of subsequent vaccinations.

Plasmodium vivax vaccine: What is the best way to go?

Malaria is one of the most devastating human infectious diseases caused by Plasmodium spp. parasites. A search for an effective and safe vaccine is the main challenge for its eradication. Plasmodium vivax is the second most prevalent Plasmodium species and the most geographically distributed parasite and has been neglected for decades. This has a massive gap in knowledge and consequently in the development of vaccines. The most significant difficulties in obtaining a vaccine against P. vivax are the high genetic diversity and the extremely complex life cycle. Due to its complexity, studies have evaluated P. vivax antigens from different stages as potential targets for an effective vaccine. Therefore, the main vaccine candidates are grouped into preerythrocytic stage vaccines, blood-stage vaccines, and transmission-blocking vaccines. This review aims to support future investigations by presenting the main findings of vivax malaria vaccines to date. There are only a few P. vivax vaccines in clinical trials, and thus far, the best protective efficacy was a vaccine formulated with synthetic peptide from a circumsporozoite protein and Montanide ISA-51 as an adjuvant with 54.5% efficacy in a phase IIa study. In addition, the majority of P. vivax antigen candidates are polymorphic, induce strain-specific and heterogeneous immunity and provide only partial protection. Nevertheless, immunization with recombinant proteins and multiantigen vaccines have shown promising results and have emerged as excellent strategies. However, more studies are necessary to assess the ideal vaccine combination and test it in clinical trials. Developing a safe and effective vaccine against vivax malaria is essential for controlling and eliminating the disease. Therefore, it is necessary to determine what is already known to propose and identify new candidates.

Host-parasite interactions during Plasmodium infection: Implications for immunotherapies

Malaria is a global infectious disease that remains a leading cause of morbidity and mortality in the developing world. Multiple environmental and host and parasite factors govern the clinical outcomes of malaria. The host immune response against the Plasmodium parasite is heterogenous and stage-specific both in the human host and mosquito vector. The Plasmodium parasite virulence is predominantly associated with its ability to evade the host's immune response. Despite the availability of drug-based therapies, Plasmodium parasites can acquire drug resistance due to high antigenic variations and allelic polymorphisms. The lack of licensed vaccines against Plasmodium infection necessitates the development of effective, safe and successful therapeutics. To design an effective vaccine, it is important to study the immune evasion strategies and stage-specific Plasmodium proteins, which are targets of the host immune response. This review provides an overview of the host immune defense mechanisms and parasite immune evasion strategies during Plasmodium infection. Furthermore, we also summarize and discuss the current progress in various anti-malarial vaccine approaches, along with antibody-based therapy involving monoclonal antibodies, and research advancements in host-directed therapy, which can together open new avenues for developing novel immunotherapies against malaria infection and transmission.

Similarities and differences of chemical compositions and physical and functional properties of adjuvant system 01 and army liposome formulation with QS21

A vaccine adjuvant known as Adjuvant System 01 (AS01) consists of liposomes containing a mixture of natural congeners of monophosphoryl lipid A (MPL^®) obtained from bacterial lipopolysaccharide, and a tree saponin known as QS21. Two vaccines containing AS01 as the adjuvant have been licensed, including a malaria vaccine (Mosquirix^®) approved by World Health. Organization and European Medicines Agency for use in sub-Saharan Africa, and a shingles vaccine (Shingrix^®) approved by the U.S. Food and Drug Administration. The success of the AS01 vaccine adjuvant has led to the development of another liposomal vaccine adjuvant, referred to as Army Liposome Formulation with QS21 (ALFQ). Like AS01, ALFQ consists of liposomes containing monophosphoryl lipid A (as a synthetic molecule known as 3D-PHAD^®) and QS21 as adjuvant constituents, and the polar headgroups of the liposomes of AS01 and ALFQ are similar. We compare here AS01 with ALFQ with respect to their similar and different liposomal chemical structures and physical characteristics with a goal of projecting some of the likely mechanisms of safety, side effects, and mechanisms of adjuvanticity. We hypothesize that some of the side effects exhibited in humans after injection of liposome-based vaccines might be caused by free fatty acid and lysophospholipid released by enzymatic attack of liposomal phospholipid by phospholipase A₂ at the injection site or systemically after injection.

Characterization of a novel Plasmodium falciparum merozoite surface antigen and potential vaccine target

Introduction

Detailed analyses of genetic diversity, antigenic variability, protein localization and immunological responses are vital for the prioritization of novel malaria vaccine candidates. Comprehensive approaches to determine the most appropriate antigen variants needed to provide broad protection are challenging and consequently rarely undertaken.

Methods

Here, we characterized PF3D7_1136200, which we named Asparagine-Rich Merozoite Antigen (ARMA) based on the analysis of its sequence, localization and immunogenicity. We analyzed IgG and IgM responses against the common variants of ARMA in independent prospective cohort studies in Burkina Faso (N = 228), Kenya (N = 252) and Mali (N = 195) using a custom microarray, Div-KILCHIP.

Results

We found a marked population structure between parasites from Africa and Asia. African isolates shared 34 common haplotypes, including a dominant pair although the overall selection pressure was directional (Tajima's D = -2.57; Fu and Li's F = -9.69; P < 0.02). ARMA was localized to the merozoite surface, IgG antibodies induced Fc-mediated degranulation of natural killer cells and strongly inhibited parasite growth in vitro. We found profound serological diversity, but IgG and IgM responses were highly correlated and a hierarchical clustering analysis identified only three major serogroups. Protective IgG and IgM antibodies appeared to target both cross-reactive and distinct epitopes across variants. However, combinations of IgG and IgM antibodies against selected variants were associated with complete protection against clinical episodes of malaria.

Discussion

Our systematic strategy exploits genomic data to deduce the handful of antigen variants with the strongest potential to induce broad protection and may be broadly applicable to other complex pathogens for which effective vaccines remain elusive.

Humoral Immune Responses to P. falciparum Circumsporozoite Protein (Pfcsp) Induced by the RTS, S Vaccine - Current Update

Malaria vaccines targeting the circumsporozoite protein (CSP) of the P. falciparum parasite have been overall relatively promising. RTS, S is a pre-erythrocytic recombinant protein-based malaria vaccine that targets CSP. RTS, S effectiveness shows some limited success regardless of its 58% efficacy for severe disease. P. falciparum circumsporozoite protein (Pfcsp) has stood to be the main candidate protein for most pre-erythrocytic stage vaccines. Studies on the structural and biophysical characteristics of antibodies specific to CSP (anti-CSP) are underway to achieve fine specificity with the CSP polymorphic regions. More recent studies have proposed the use of different kinds of monoclonal antibodies, the use of appropriate adjuvants, ideal vaccination dose and frequency, and improved targeting of particular epitopes for the robust production of functional antibodies and high complement-fixing activity as other potential methods for achieving long-lasting RTS, S. This review highlights recent findings regarding humoral immune responses to CSP elicited by RTS, S vaccine.

Vaccine approaches for antigen capture by liposomes

INTRODUCTION

Liposomes have been used as carriers for vaccine adjuvants and antigens due to their inherent biocompatibility and versatility as delivery vehicles. Two vial admixture of protein antigens with liposome-formulated immunostimulatory adjuvants has become a broadly used clinical vaccine preparation approach. Compared to freely soluble antigens, liposome-associated forms can enhance antigen delivery to antigen-presenting cells and co-deliver antigens with adjuvants, leading to improved vaccine efficacy.

AREAS COVERED

Several antigen-capture strategies for liposomal vaccines have been developed for proteins, peptides, and nucleic acids. Specific antigen delivery methodologies are discussed, including electrostatic adsorption, encapsulation inside the liposome aqueous core, and covalent and non-covalent antigen capture.

EXPERT OPINION

Several commercial vaccines include active lipid components, highlighting an increasingly prominent role of liposomes and lipid nanoparticles in vaccine development. Utilizing liposomes to associate antigens offers potential advantages, including antigen and adjuvant dose-sparing, co-delivery of antigen and adjuvant to immune cells, and enhanced immunogenicity. Antigen capture by liposomes has demonstrated feasibility in clinical testing. New antigen-capture techniques have been developed and appear to be of interest for vaccine development.