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PLoS Pathogens Mar 2024Placental accumulation of Plasmodium falciparum infected erythrocytes results in maternal anemia, low birth weight, and pregnancy loss. The parasite protein VAR2CSA...
Placental accumulation of Plasmodium falciparum infected erythrocytes results in maternal anemia, low birth weight, and pregnancy loss. The parasite protein VAR2CSA facilitates the accumulation of infected erythrocytes in the placenta through interaction with the host receptor chondroitin sulfate A (CSA). Antibodies that prevent the VAR2CSA-CSA interaction correlate with protection from placental malaria, and VAR2CSA is a high-priority placental malaria vaccine antigen. Here, structure-guided design leveraging the full-length structures of VAR2CSA produced a stable immunogen that retains the critical conserved functional elements of VAR2CSA. The design expressed with a six-fold greater yield than the full-length protein and elicited antibodies that prevent adhesion of infected erythrocytes to CSA. The reduced size and adaptability of the designed immunogen enable efficient production of multiple variants of VAR2CSA for use in a cocktail vaccination strategy to increase the breadth of protection. These designs form strong foundations for the development of potent broadly protective placental malaria vaccines.
Topics: Humans; Pregnancy; Female; Placenta; Malaria Vaccines; Malaria, Falciparum; Antibodies, Protozoan; Malaria; Plasmodium falciparum; Antigens, Protozoan; Chondroitin Sulfates; Erythrocytes
PubMed: 38437239
DOI: 10.1371/journal.ppat.1011879 -
The Lancet. Global Health Apr 2024Malaria accounts for over half a million child deaths annually. WHO recommends RTS,S/AS01 to prevent malaria in children living in moderate-to-high malaria transmission...
Integration of the RTS,S/AS01 malaria vaccine into the Essential Programme on Immunisation in western Kenya: a qualitative longitudinal study from the health system perspective.
BACKGROUND
Malaria accounts for over half a million child deaths annually. WHO recommends RTS,S/AS01 to prevent malaria in children living in moderate-to-high malaria transmission regions. We conducted a qualitative longitudinal study to investigate the contextual and dynamic factors shaping vaccine delivery and uptake during a pilot introduction in western Kenya.
METHODS
The study was conducted between Oct 3, 2019, and Mar 24, 2022. We conducted participant and non-participant observations and in-depth interviews with health-care providers, health managers, and national policymakers at three timepoints using an iterative approach and observations of practices and processes of malaria vaccine delivery. Transcripts were coded by content analysis using the consolidated framework for implementation research, to which emerging themes were added deductively and categorised into challenges and opportunities.
FINDINGS
We conducted 112 in-depth interviews with 60 participants (25 health-care providers, 27 managers, and eight policy makers). Health-care providers highlighted limitations in RTS,S/AS01 integration into routine immunisation services due to the concurrent pilot evaluation and temporary adaptations for health reporting. Initial challenges related to the complexity of the four-dose schedule (up to 24-months); however, self-efficacy increased over time as the health-care providers gained experience in vaccine delivery. Low uptake of the fourth dose remained a challenge. Health managers cited insufficient trained immunisation staff and inadequate funding for supervision. Confidence in the vaccine increased among all participant groups owing to reductions in malaria frequency and severity.
INTERPRETATION
Integration of RTS,S/AS01 into immunisation services in western Kenya presented substantial operational challenges most of which were overcome in the first 2 years, providing important lessons for other countries. Programme expansion is feasible with intensive staff training and retention, enhanced supervision, and defaulter-tracing to ensure uptake of all doses.
FUNDING
PATH via World Health Organization; Gavi, the Vaccine Alliance; The Global Fund; and Unitaid.
Topics: Child; Humans; Infant; Malaria Vaccines; Malaria, Falciparum; Kenya; Longitudinal Studies; Malaria; Vaccination
PubMed: 38430916
DOI: 10.1016/S2214-109X(24)00013-5 -
Malaria Journal Feb 2024Plasmodium vivax Duffy binding protein (PvDBP) is a merozoite surface protein located in the micronemes of P. vivax. The invasion of human reticulocytes by P. vivax...
BACKGROUND
Plasmodium vivax Duffy binding protein (PvDBP) is a merozoite surface protein located in the micronemes of P. vivax. The invasion of human reticulocytes by P. vivax merozoites depends on the parasite DBP binding domain engaging Duffy Antigen Receptor for Chemokine (DARC) on these red blood cells (RBCs). PvDBPII shows high genetic diversity which is a major challenge to its use in the development of a vaccine against vivax malaria.
METHODS
A cross-sectional study was conducted from February 2021 to September 2022 in five study sites across Ethiopia. A total of 58 blood samples confirmed positive for P. vivax by polymerase chain reaction (PCR) were included in the study to determine PvDBPII genetic diversity. PvDBPII were amplified using primers designed from reference sequence of P. vivax Sal I strain. Assembling of sequences was done using Geneious Prime version 2023.2.1. Alignment and phylogenetic tree constructions using MEGA version 10.1.1. Nucleotide diversity and haplotype diversity were analysed using DnaSP version 6.12.03, and haplotype network was generated with PopART version 1.7.
RESULTS
The mean age of the participants was 25 years, 5 (8.6%) participants were Duffy negatives. From the 58 PvDBPII sequences, seven haplotypes based on nucleotide differences at 8 positions were identified. Nucleotide diversity and haplotype diversity were 0.00267 ± 0.00023 and 0.731 ± 0.036, respectively. Among the five study sites, the highest numbers of haplotypes were identified in Arbaminch with six different haplotypes while only two haplotypes were identified in Gambella. The phylogenetic tree based on PvDBPII revealed that parasites of different study sites shared similar genetic clusters with few exceptions. Globally, a total of 39 haplotypes were identified from 223 PvDBPII sequences representing different geographical isolates obtained from NCBI archive. The nucleotide and haplotype diversity were 0.00373 and 0.845 ± 0.015, respectively. The haplotype prevalence ranged from 0.45% to 27.3%. Two haplotypes were shared among isolates from all geographical areas of the globe.
CONCLUSIONS
PvDBPII of the Ethiopian P. vivax isolates showed low nucleotide but high haplotype diversity, this pattern of genetic variability suggests that the population may have undergone a recent expansion. Among the Ethiopian P. vivax isolates, almost half of the sequences were identical to the Sal-I reference sequence. However, there were unique haplotypes observed in the Ethiopian isolates, which does not share with isolates from other geographical areas. There were two haplotypes that were common among populations across the globe. Categorizing population haplotype frequency can help to determine common haplotypes for designing an effective blood-stage vaccine which will have a significant role for the control and elimination of P. vivax.
Topics: Humans; Adult; Plasmodium vivax; Phylogeny; Ethiopia; Cross-Sectional Studies; Selection, Genetic; Protozoan Proteins; Antigens, Protozoan; Malaria, Vivax; Haplotypes; Vaccines; Nucleotides; Genetic Variation
PubMed: 38395885
DOI: 10.1186/s12936-024-04887-1 -
Vaccine Mar 2024Two malaria transmission-blocking vaccine (TBV) candidates, R0.6C and ProC6C, have completed preclinical development including the selection of adjuvants, Alhydrogel®...
Two malaria transmission-blocking vaccine (TBV) candidates, R0.6C and ProC6C, have completed preclinical development including the selection of adjuvants, Alhydrogel® with or without the saponin based adjuvant Matrix-M™. Here, we report on the final drug product (formulation) design of R0.6C and ProC6C and evaluate their safety and biochemical stability in preparation for preclinical and clinical pharmacy handling. The point-of-injection stability studies demonstrated that both the R0.6C and ProC6C antigens are stable on Alhydrogel in the presence or absence of Matrix-M for up to 24 h at room temperature. As this is the first study to combine Alhydrogel and Matrix-M for clinical use, we also evaluated their potential interactions. Matrix-M adsorbs to Alhydrogel, while not displacing the > 95 % adsorbed protein. The R0.6C and ProC6C formulations were found to be safe and well tolerated in repeated dose toxicity studies in rabbits generating high levels of functional antibodies that blocked infection of mosquitoes. Further, the R0.6C and ProC6C drug products were found to be stable for minimally 24 months when stored at 2-8 °C, with studies ongoing through 36 months. Together, this data demonstrates the safety and suitability of the L. lactis expression system as well as supports the clinical testing of the R0.6C and ProC6C malaria vaccine candidates in First-In-Human clinical trials.
Topics: Animals; Rabbits; Aluminum Hydroxide; Antibodies, Protozoan; Antigens, Protozoan; Malaria Vaccines; Malaria, Falciparum; Plasmodium falciparum; Protozoan Proteins
PubMed: 38388238
DOI: 10.1016/j.vaccine.2024.02.043 -
Vaccine Mar 2024Plasmodium vivax malaria is increasingly recognized as a major global health problem and the socio-economic impact of P.vivax-induced burden is huge. Vaccine development...
Plasmodium vivax malaria is increasingly recognized as a major global health problem and the socio-economic impact of P.vivax-induced burden is huge. Vaccine development against P. vivax malaria has been hampered by the lack of an in vitro culture system and poor access to P. vivax sporozoites. The recent generation of Plasmodium falciparum parasites that express a functional P. vivax AMA1 molecule has provided a platform for in vitro evaluation of PvAMA1 as a potential blood stage vaccine. Three so-called PvAMA1 Diversity Covering (DiCo) proteins were designed to assess their potential to induce a functional and broad humoral immune response to the polymorphic PvAMA1 molecule. Rabbits were immunized with the mixture of three, Pichia-produced, PvAMA1 DiCo proteins, as well as with 2 naturally occurring PvAMA1 alleles. For these three groups, the experimental adjuvant raffinose fatty acid sulfate ester (RFASE) was used, while in a fourth group the purified main mono-esterified constituent (RSL10) of this adjuvant was used. Animals immunized with the mixture of the three PvAMA1 DiCo proteins in RFASE showed high anti-PvAMA1 antibody titers against three naturally occurring PvAMA1variants while also high growth-inhibitory capacity was observed against P. falciparum parasites expressing PvAMA1. This supports further clinical development of the PvAMA1 DiCo mixture as a potential malaria vaccine. However, as the single allele PvAMA1 SalI-group showed similar characteristics in antibody titer and inhibition levels as the PvAMA1 DiCo mixture-group, this raises the question whether a mixture is really necessary to overcome the polymorphism in the vaccine candidate. RFASE induced strong humoral responses, as did the animals immunized with the purified component, RSL10. This suggests that RSL10 is the active ingredient. However, one of the RSL10-immunized animal showed a delayed response, necessitating further research into the clinical development of RSL10.
Topics: Animals; Rabbits; Protozoan Proteins; Plasmodium vivax; Raffinose; Sulfates; Membrane Proteins; Antigens, Protozoan; Adjuvants, Immunologic; Malaria, Falciparum; Plasmodium falciparum; Malaria, Vivax; Malaria Vaccines; Parasites; Antibodies, Protozoan
PubMed: 38365484
DOI: 10.1016/j.vaccine.2024.02.029 -
Microbiology Spectrum Apr 2024During blood-stage infection, parasites are constantly exposed to a range of extracellular stimuli, including host molecules and drugs such as artemisinin derivatives,...
During blood-stage infection, parasites are constantly exposed to a range of extracellular stimuli, including host molecules and drugs such as artemisinin derivatives, the mainstay of artemisinin-based combination therapies currently used as first-line treatment worldwide. Partial resistance of to artemisinin has been associated with mutations in the propeller domain of the gene, resulting in a fraction of ring stages that are able to survive exposure to artemisinin through a temporary growth arrest. Here, we investigated whether the growth arrest in ring-stage parasites reflects a general response to stress. We mimicked a stressful environment by exposing parasites to chloroquine or dihydroartemisinin (DHA). We observed that early ring-stage parasites pre-exposed to a stressed culture supernatant exhibited a temporary growth arrest and a reduced susceptibility to DHA, as assessed by the ring-stage survival assay, irrespective of their genotype. These data suggest that temporary growth arrest of early ring stages may be a constitutive, -independent survival mechanism in .IMPORTANCE ring stages have the ability to sense the extracellular environment, regulate their growth, and enter a temporary growth arrest state in response to adverse conditions such as drug exposure. This temporary growth arrest results in reduced susceptibility to artemisinin . The signal responsible for this process is thought to be small molecules (less than 3 kDa) released by stressed mature-stage parasites. These data suggest that Pfkelch13-dependent artemisinin resistance and the growth arrest phenotype are two complementary but unrelated mechanisms of ring-stage survival in . This finding provides new insights into the field of antimalarial drug resistance by highlighting the extracellular compartment and cellular communication as an understudied mechanism.
Topics: Animals; Plasmodium falciparum; Parasites; Artemisinins; Antimalarials; Malaria, Falciparum; Drug Resistance; Protozoan Proteins
PubMed: 38363132
DOI: 10.1128/spectrum.03500-23 -
Frontiers in Microbiology 2024Leishmaniasis is a neglected tropical disease caused by protozoan parasites of the genus. Despite the efforts to control and treat the disease, it still remains a major...
Leishmaniasis is a neglected tropical disease caused by protozoan parasites of the genus. Despite the efforts to control and treat the disease, it still remains a major public health problem in many countries. Synthetic biology is a rapidly evolving interdisciplinary field that combines biology, engineering, and computer science to design and construct novel biological systems. In recent years, synthetic biology approaches have shown great promise for developing new and effective strategies to combat leishmaniasis. In this perspective, we summarize the recent advances in the use of synthetic biology for the development of vaccines, diagnostic tools, and novel therapeutics for leishmaniasis.
PubMed: 38362504
DOI: 10.3389/fmicb.2024.1338749 -
Parasites & Vectors Feb 2024Cryptosporidium spp. are common protozoa causing diarrhea in humans and animals. There are currently only one FDA-approved drug and no vaccines for cryptosporidiosis,...
BACKGROUND
Cryptosporidium spp. are common protozoa causing diarrhea in humans and animals. There are currently only one FDA-approved drug and no vaccines for cryptosporidiosis, largely due to the limited knowledge of the molecular mechanisms involved in the invasion of the pathogens. Previous studies have shown that GP60, which is cleaved into GP40 and GP15 after expression, is an immunodominant mucin protein involved in the invasion of Cryptosporidium. The protein is highly O-glycosylated, and recombinant proteins expressed in prokaryotic systems are non-functional. Therefore, few studies have investigated the function of GP40 and GP15.
METHODS
To obtain recombinant GP40 with correct post-translational modifications, we used CRISPR/Cas9 technology to insert GP40 and GP15 into the UPRT locus of Toxoplasma gondii, allowing heterologous expression of Cryptosporidium proteins. In addition, the Twin-Strep tag was inserted after GP40 for efficient purification of GP40.
RESULTS
Western blotting and immunofluorescent microscopic analyses both indicated that GP40 and GP15 were stably expressed in T. gondii mutants. GP40 localized not only in the cytoplasm of tachyzoites but also in the parasitophorous vacuoles, while GP15 without the GPI anchor was expressed only in the cytoplasm. In addition, a large amount of recTgGP40 was purified using Strep-TactinXT supported by a visible band of ~ 50 kDa in SDS-PAGE.
CONCLUSIONS
The establishment of a robust and efficient heterologous expression system of GP40 in T. gondii represents a novel approach and concept for investigating Cryptosporidium mucins, overcoming the limitations of previous studies that relied on unstable transient transfection, which involved complex steps and high costs.
Topics: Humans; Animals; Cryptosporidium parvum; Toxoplasma; Cryptosporidium; Cryptosporidiosis; Protozoan Proteins; Mucins; Glycoproteins
PubMed: 38360646
DOI: 10.1186/s13071-024-06159-y -
The Lancet. Infectious Diseases May 2024The R21/Matrix-M vaccine has demonstrated high efficacy against Plasmodium falciparum clinical malaria in children in sub-Saharan Africa. Using trial data, we aimed to...
BACKGROUND
The R21/Matrix-M vaccine has demonstrated high efficacy against Plasmodium falciparum clinical malaria in children in sub-Saharan Africa. Using trial data, we aimed to estimate the public health impact and cost-effectiveness of vaccine introduction across sub-Saharan Africa.
METHODS
We fitted a semi-mechanistic model of the relationship between anti-circumsporozoite protein antibody titres and vaccine efficacy to data from 3 years of follow-up in the phase 2b trial of R21/Matrix-M in Nanoro, Burkina Faso. We validated the model by comparing predicted vaccine efficacy to that observed over 12-18 months in the phase 3 trial. Integrating this framework within a mathematical transmission model, we estimated the cases, malaria deaths, and disability-adjusted life-years (DALYs) averted and cost-effectiveness over a 15-year time horizon across a range of transmission settings in sub-Saharan Africa. Cost-effectiveness was estimated incorporating the cost of vaccine introduction (dose, consumables, and delivery) relative to existing interventions at baseline. We report estimates at a median of 20% parasite prevalence in children aged 2-10 years (PfPR) and ranges from 3% to 65% PfPR.
FINDINGS
Anti-circumsporozoite protein antibody titres were found to satisfy the criteria for a surrogate of protection for vaccine efficacy against clinical malaria. Age-based implementation of a four-dose regimen of R21/Matrix-M vaccine was estimated to avert 181 825 (range 38 815-333 491) clinical cases per 100 000 fully vaccinated children in perennial settings and 202 017 (29 868-405 702) clinical cases per 100 000 fully vaccinated children in seasonal settings. Similar estimates were obtained for seasonal or hybrid implementation. Under an assumed vaccine dose price of US$3, the incremental cost per clinical case averted was $7 (range 4-48) in perennial settings and $6 (3-63) in seasonal settings and the incremental cost per DALY averted was $34 (29-139) in perennial settings and $30 (22-172) in seasonal settings, with lower cost-effectiveness ratios in settings with higher PfPR.
INTERPRETATION
Introduction of the R21/Matrix-M malaria vaccine could have a substantial public health benefit across sub-Saharan Africa.
FUNDING
The Wellcome Trust, the Bill & Melinda Gates Foundation, the UK Medical Research Council, the European and Developing Countries Clinical Trials Partnership 2 and 3, the NIHR Oxford Biomedical Research Centre, and the Serum Institute of India, Open Philanthropy.
Topics: Humans; Cost-Benefit Analysis; Malaria Vaccines; Malaria, Falciparum; Burkina Faso; Models, Theoretical; Child, Preschool; Public Health; Plasmodium falciparum; Child; Protozoan Proteins; Antibodies, Protozoan; Vaccine Efficacy; Infant; Male; Female
PubMed: 38342107
DOI: 10.1016/S1473-3099(23)00816-2 -
Frontiers in Immunology 2024Attenuated sporozoites provide a valuable model for exploring protective immunity against the malarial liver stage, guiding the design of highly efficient vaccines to... (Review)
Review
Attenuated sporozoites provide a valuable model for exploring protective immunity against the malarial liver stage, guiding the design of highly efficient vaccines to prevent malaria infection. Liver tissue-resident CD8 T cells (CD8 Trm cells) are considered the host front-line defense against malaria and are crucial to developing prime-trap/target strategies for pre-erythrocytic stage vaccine immunization. However, the spatiotemporal regulatory mechanism of the generation of liver CD8 Trm cells and their responses to sporozoite challenge, as well as the protective antigens they recognize remain largely unknown. Here, we discuss the knowledge gap regarding liver CD8 Trm cell formation and the potential strategies to identify predominant protective antigens expressed in the exoerythrocytic stage, which is essential for high-efficacy malaria subunit pre-erythrocytic vaccine designation.
Topics: Humans; CD8-Positive T-Lymphocytes; Malaria; Liver; Malaria Vaccines; Immunization
PubMed: 38318178
DOI: 10.3389/fimmu.2024.1344941