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Patel PN, Tolia N. Structural vaccinology of malaria transmission-blocking vaccines. Expert Rev Vaccines 2021; 20:199-214. [PMID: 33430656 PMCID: PMC11077433 DOI: 10.1080/14760584.2021.1873135] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 12/16/2020] [Indexed: 02/06/2023]
Abstract
Introduction: The development of effective vaccines remains a major health priority to combat the global burden of malaria, a life-threatening disease caused by Plasmodium parasites. Transmission-blocking vaccines (TBVs) elicit antibodies that neutralize the sexual stages of the parasite in blood meals ingested by the Anopheles mosquito, interrupting parasite development in the vector host and preventing disease spread to other individuals.Areas covered: The P. falciparum gametocyte surface antigens Pfs230, Pfs48/45, and Pfs47, the parasite ookinete surface protein Pfs25, and the male gametocyte specific protein PfHAP2 are leading TBV candidates, some of which are in clinical development. The recent expansion of methodology to study monoclonal antibodies isolated directly from humans and animal models, coupled with effective measures for parasite neutralization, has provided unprecedented insight into TBV efficacy and development.Expert opinion: Available structural and functional data on antigen-monoclonal antibody (Ag-mAb) complexes, as well as epitope classification studies, have identified neutralizing epitopes that may aid vaccine development and improve protection. Here, we review the clinical prospects of TBV candidates, progress in the development of novel vaccine strategies for TBVs, and the impact of structural vaccinology in TBV design.
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Affiliation(s)
- Palak N Patel
- Host-Pathogen Interactions and Structural Vaccinology Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Niraj Tolia
- Host-Pathogen Interactions and Structural Vaccinology Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA
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2
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Attenuation Methods for Live Vaccines. Methods Mol Biol 2020. [PMID: 32959252 DOI: 10.1007/978-1-0716-0795-4_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/27/2023]
Abstract
Vaccination was developed by Edward Jenner in 1796. Since then, vaccination and vaccine development research has been a hotspot of research in the scientific community. Various ways of vaccine development are successfully employed in mass production of vaccines. One of the most successful ways to generate vaccines is the method of virulence attenuation in pathogens. The attenuated strains of viruses, bacteria, and parasites are used as vaccines which elicit robust immune response and confers protection against virulent pathogens. This chapter brings together the most common and efficient ways of generating live attenuated vaccine strains in viruses, bacteria, and parasites.
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3
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Kengne-Ouafo JA, Sutherland CJ, Binka FN, Awandare GA, Urban BC, Dinko B. Immune Responses to the Sexual Stages of Plasmodium falciparum Parasites. Front Immunol 2019; 10:136. [PMID: 30804940 PMCID: PMC6378314 DOI: 10.3389/fimmu.2019.00136] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 01/16/2019] [Indexed: 11/13/2022] Open
Abstract
Malaria infections remain a serious global health problem in the world, particularly among children and pregnant women in Sub-Saharan Africa. Moreover, malaria control and elimination is hampered by rapid development of resistance by the parasite and the vector to commonly used antimalarial drugs and insecticides, respectively. Therefore, vaccine-based strategies are sorely needed, including those designed to interrupt disease transmission. However, a prerequisite for such a vaccine strategy is the understanding of both the human and vector immune responses to parasite developmental stages involved in parasite transmission in both man and mosquito. Here, we review the naturally acquired humoral and cellular responses to sexual stages of the parasite while in the human host and the Anopheles vector. In addition, updates on current anti-gametocyte, anti-gamete, and anti-mosquito transmission blocking vaccines are given. We conclude with our views on some important future directions of research into P. falciparum sexual stage immunity relevant to the search for the most appropriate transmission-blocking vaccine.
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Affiliation(s)
- Jonas A Kengne-Ouafo
- West African Centre for Cell Biology of Infectious Pathogens, University of Ghana, Accra, Ghana
| | - Colin J Sutherland
- Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Fred N Binka
- Department of Epidemiology and Biostatistics, School of Public Health, University of Health and Allied Sciences, Ho, Ghana
| | - Gordon A Awandare
- West African Centre for Cell Biology of Infectious Pathogens, University of Ghana, Accra, Ghana
| | - Britta C Urban
- Faculty of Biological Sciences, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Bismarck Dinko
- Department of Biomedical Sciences, School of Basic and Biomedical Sciences, University of Health and Allied Sciences, Ho, Ghana
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4
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Khamsehnejad MI, Djadid ND, Raz A. Identification, Molecular Characterization, and In Silico Structural Analysis of Carboxypeptidase B2 of Anopheles stephensi. JOURNAL OF MEDICAL ENTOMOLOGY 2019; 56:72-85. [PMID: 30124910 DOI: 10.1093/jme/tjy127] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Indexed: 06/08/2023]
Abstract
Malaria is a vector-borne infectious disease that is considered a priority of the World Health Organization due to its enormous impacts on global health. Plasmodium spp. (Haemosporida: Plasmodiidae), Anopheles spp. (Diptera: Culicidae), and a suitable host are the key elements for malaria transmission. To disrupt the parasitic life cycle of malaria or prevent its transmission, these three key elements should be targeted by effective control strategies. Development of vaccines that interrupt malaria transmission is one of the solutions that has been recommended to the countries that aim to eliminate malaria. With respect to the important role of Anopheles stephensi in malaria transmission and involvement of Anopheles carboxypeptidase B1 in sexual parasite development, we characterized the second member of cpb gene family (cpbAs2) of An. Stephensi to provide some basic information and evaluate significance of cpbAs2's role in complementing sexual plasmodium development role of cpbAs1. The cpbAs2 mRNA sequence was characterized by 3' and 5' RACE and the structural features of its coded protein were studied by in silico modeling. The coding sequence and gene structure of cpbAs2 were determined empirically and compared with the in silico predictions from the An. stephensi genome sequencing project. Furthermore, homology modeling revealed that its structure is very similar to the structurally important domains of procarboxypeptidase B2 in humans. This study provides basic molecular and structural information about another member of the cpb gene family of An. stephensi. The reported results are informative and necessary for evaluation of the role of this gene in sexual parasite development by future studies.
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Affiliation(s)
- Mahdokht Ilbeigi Khamsehnejad
- Malaria and Vector Research Group (MVRG), Biotechnology Research Center (BRC), Pasteur Institute of Iran (PII), Pasteur Avenue, Tehran, Iran
| | - Navid Dinparast Djadid
- Malaria and Vector Research Group (MVRG), Biotechnology Research Center (BRC), Pasteur Institute of Iran (PII), Pasteur Avenue, Tehran, Iran
| | - Abbasali Raz
- Malaria and Vector Research Group (MVRG), Biotechnology Research Center (BRC), Pasteur Institute of Iran (PII), Pasteur Avenue, Tehran, Iran
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5
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Abstract
Evidence accumulated through the years clearly indicates that antiparasite immune responses can efficiently control malaria parasite infection at all development stages, and under certain circumstances they can prevent parasite infection. Translating these findings into vaccines or immunotherapeutic interventions has been difficult in part because of the extraordinary biological complexity of this parasite, which has several developmental stages expressing unique sets of stage-specific genes and multiple antigens, most of which are antigenically diverse. Nevertheless, in the last 30 years major advances have resulted in characterization of a number of vaccine candidates, exploration of the repertoire of host immune responses to the various parasite stages, and also identification of significant hurdles that need to be overcome. Most important, these advances strengthened the concept that the induction of host immune responses that target all developmental stages of Plasmodium can efficiently control or abrogate Plasmodium infections and strongly support the notion that an effective vaccine can be developed. This vaccine would be a critical component for programs aimed at controlling or eradicating malaria.
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Affiliation(s)
- Carole A Long
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institute of Health, Rockville, Maryland 20852
| | - Fidel Zavala
- Departmentof Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205
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6
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Lempereur L, Larcombe SD, Durrani Z, Karagenc T, Bilgic HB, Bakirci S, Hacilarlioglu S, Kinnaird J, Thompson J, Weir W, Shiels B. Identification of candidate transmission-blocking antigen genes in Theileria annulata and related vector-borne apicomplexan parasites. BMC Genomics 2017; 18:438. [PMID: 28583072 PMCID: PMC5460460 DOI: 10.1186/s12864-017-3788-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 05/11/2017] [Indexed: 01/11/2023] Open
Abstract
Background Vector-borne apicomplexan parasites are a major cause of mortality and morbidity to humans and livestock globally. The most important disease syndromes caused by these parasites are malaria, babesiosis and theileriosis. Strategies for control often target parasite stages in the mammalian host that cause disease, but this can result in reservoir infections that promote pathogen transmission and generate economic loss. Optimal control strategies should protect against clinical disease, block transmission and be applicable across related genera of parasites. We have used bioinformatics and transcriptomics to screen for transmission-blocking candidate antigens in the tick-borne apicomplexan parasite, Theileria annulata. Results A number of candidate antigen genes were identified which encoded amino acid domains that are conserved across vector-borne Apicomplexa (Babesia, Plasmodium and Theileria), including the Pfs48/45 6-cys domain and a novel cysteine-rich domain. Expression profiling confirmed that selected candidate genes are expressed by life cycle stages within infected ticks. Additionally, putative B cell epitopes were identified in the T. annulata gene sequences encoding the 6-cys and cysteine rich domains, in a gene encoding a putative papain-family cysteine peptidase, with similarity to the Plasmodium SERA family, and the gene encoding the T. annulata major merozoite/piroplasm surface antigen, Tams1. Conclusions Candidate genes were identified that encode proteins with similarity to known transmission blocking candidates in related parasites, while one is a novel candidate conserved across vector-borne apicomplexans and has a potential role in the sexual phase of the life cycle. The results indicate that a ‘One Health’ approach could be utilised to develop a transmission-blocking strategy effective against vector-borne apicomplexan parasites of animals and humans. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-3788-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Laetitia Lempereur
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK.,Present address: Laboratory of Parasitology and Parasitic Diseases, Department of Infectious and Parasitic Diseases, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium
| | - Stephen D Larcombe
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK
| | - Zeeshan Durrani
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK.,Present address: School of Veterinary Science, University of Liverpool, Chester High Road, Neston, CH64 7TE,, UK
| | - Tulin Karagenc
- Faculty of Veterinary Medicine, Department of Parasitology, Adnan Menderes University, Batı Kampus, Işıklı, Aydın, Turkey
| | - Huseyin Bilgin Bilgic
- Faculty of Veterinary Medicine, Department of Parasitology, Adnan Menderes University, Batı Kampus, Işıklı, Aydın, Turkey
| | - Serkan Bakirci
- Faculty of Veterinary Medicine, Department of Parasitology, Adnan Menderes University, Batı Kampus, Işıklı, Aydın, Turkey
| | - Selin Hacilarlioglu
- Faculty of Veterinary Medicine, Department of Parasitology, Adnan Menderes University, Batı Kampus, Işıklı, Aydın, Turkey
| | - Jane Kinnaird
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK
| | - Joanne Thompson
- Institute of Immunology and Infection Research, School of Biological Sciences, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Edinburgh, EH9 3FL, UK
| | - William Weir
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK
| | - Brian Shiels
- Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, G61 1QH, Scotland, UK.
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7
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Accelerated and long term stability study of Pfs25-EPA conjugates adjuvanted with Alhydrogel®. Vaccine 2017; 35:3232-3238. [PMID: 28479180 DOI: 10.1016/j.vaccine.2017.04.067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 04/07/2017] [Accepted: 04/23/2017] [Indexed: 11/22/2022]
Abstract
Pfs25, a Plasmodium falciparum surface protein expressed during zygote and ookinete stages in infected mosquitoes, is a lead transmission-blocking vaccine candidate against falciparum malaria. To enhance immunogenicity, recombinant Pfs25 was chemically conjugated to recombinant nontoxic Pseudomonas aeruginosa ExoProtein A (rEPA) in conformance with current good manufacturing practices (cGMP), and formulated with the alum adjuvant Alhydrogel. In order to meet the regulatory requirements for a phase 1 human clinical trial, the vaccine product was extensively evaluated for stability at an initial time point and through the clinical trial period annually. Because basic quality control methods to characterize alum-based vaccines remain unavailable, a thermal forced degradation study was performed prior to the initial evaluation to identify the methods suitable to detect the quality of vaccine formulations. Our results show that the vaccine product Pfs25-EPA formulated on Alhydrogel is in conformance with regulatory guidelines and suitable for human trials.
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8
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Gebru T, Ajua A, Theisen M, Esen M, Ngoa UA, Issifou S, Adegnika AA, Kremsner PG, Mordmüller B, Held J. Recognition of Plasmodium falciparum mature gametocyte-infected erythrocytes by antibodies of semi-immune adults and malaria-exposed children from Gabon. Malar J 2017; 16:176. [PMID: 28446190 PMCID: PMC5406886 DOI: 10.1186/s12936-017-1827-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Accepted: 04/19/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Transmission of malaria from man to mosquito depends on the presence of gametocytes, the sexual stage of Plasmodium parasites in the infected host. Naturally acquired antibodies against gametocytes exist and may play a role in controlling transmission by limiting the gametocyte development in the circulation or by interrupting gamete development and fertilization in the mosquito following ingestion. So far, most studies on antibody responses to sexual stage antigens have focused on a subset of gametocyte-surface antigens, even though inhibitory Ab responses to other gametocyte antigens might also play a role in controlling gametocyte density and fertility. Limited information is available on natural antibody response to the surfaces of gametocyte-infected erythrocytes. METHODS Ab responses to surface antigens of erythrocytes infected by in vitro differentiated Plasmodium falciparum mature gametocytes were investigated in sera of semi-immune adults and malaria-exposed children. In addition, the effect of immunization with GMZ2, a blood stage malaria vaccine candidate, and the effect of intestinal helminth infection on the development of immunity to gametocytes of P. falciparum was evaluated in malaria-exposed children and adults from Gabon. Serum samples from two Phase I clinical trials conducted in Gabon were analysed by microscopic and flow-cytometric immunofluorescence assay. RESULTS Adults had a higher Ab response compared to children. Ab reactivity was significantly higher after fixation and permeabilization of parasitized erythrocytes. Following vaccination with the malaria vaccine candidate GMZ2, anti-gametocyte Ab concentration decreased in adults compared to baseline. Ab response to whole asexual stage antigens had a significant but weak positive correlation to anti-gametocyte Ab responses in adults, but not in children. Children infected with Ascaris lumbricoides had a significantly higher anti-gametocyte Ab response compared to non-infected children. CONCLUSION The current data suggest that antigens exposed on the gametocyte-infected red blood cells are recognized by serum antibodies from malaria-exposed children and semi-immune adults. This anti-gametocyte immune response may be influenced by natural exposure and vaccination. Modulation of the natural immune response to gametocytes by co-infecting parasites should be investigated further and may have an important impact on malaria control strategies.
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Affiliation(s)
- Tamirat Gebru
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon.,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon.,Department of Medical Laboratory Sciences, College of Medical and Health Sciences, Haramaya University, Harar, Ethiopia
| | - Anthony Ajua
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany
| | - Michael Theisen
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark.,Center for Medical Parasitology at Department of International Health, Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark
| | - Meral Esen
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon.,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon
| | - Ulysse Ateba Ngoa
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon.,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon.,Department of Parasitology, Leiden University Medical Center, Leiden, The Netherlands
| | - Saadou Issifou
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Fondation pour la Recherche Scientifique (FORS), Cotonou, Benin
| | - Ayola A Adegnika
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon.,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon.,Department of Parasitology, Leiden University Medical Center, Leiden, The Netherlands
| | - Peter G Kremsner
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon.,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon
| | - Benjamin Mordmüller
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany.,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany.,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon.,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon
| | - Jana Held
- Institute of Tropical Medicine, University of Tübingen, Wilhelmstraße 27, 72074, Tübingen, Germany. .,German Centre for Infection Research (DZIF), Partner Site Tübingen, Germany. .,Centre de Recherches Médicales de Lambaréné (CERMEL), Lambaréné, Gabon. .,German Centre for Infection Research (DZIF), Partner Site Lambaréné, Gabon.
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9
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Londono-Renteria B, Grippin C, Cardenas JC, Troupin A, Colpitts TM. Human C5a Protein Participates in the Mosquito Immune Response Against Dengue Virus. JOURNAL OF MEDICAL ENTOMOLOGY 2016; 53:505-512. [PMID: 26843451 PMCID: PMC4892811 DOI: 10.1093/jme/tjw003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Accepted: 01/11/2016] [Indexed: 06/05/2023]
Abstract
Dengue virus (DENV) is transmitted by Aedes spp mosquitoes during a bloodmeal uptake. The bloodmeal consists of host cells, immune factors, and possibly blood-borne pathogens, such as arboviruses. Human cells and immune-related factors, like the complement system, can remain active in the bloodmeal and may be able to interact with pathogens in the mosquito. Previous studies have shown that active complement proteins impact Plasmodium parasite viability in the Anopheles midgut. Thus, we investigated the effects of the human complement on DENV infection in the midgut of Aedes aegypti. Our findings indicate that mosquitoes receiving DENV mixed with normal non-inactivated human serum showed significantly lower viremia than those fed with heat-inactivated serum. This implies that human complement may act to limit DENV infection in the mosquito midgut. In addition, we found that human complement C5a protein was able to directly communicate with mosquito cells, affecting the cell antiviral response against DENV. Our results also show that human C5a protein is able to interact with several membrane-bound mosquito proteins. Together these results suggest an important role of human complement protein in DENV transmission.
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Affiliation(s)
- Berlin Londono-Renteria
- Department of Pathology, Microbiology and Immunology, University of South Carolina School of Medicine, Columbia, SC, 29209 (; ),
| | - Crystal Grippin
- Department of Tropical Medicine, Tulane University School of Public Health and Tropical Medicine, New Orleans, LA, 70130 , and
| | - Jenny C Cardenas
- Microbiology and Clinical Laboratory, Hospital San Juan de Dios, Los Patios - Norte de Santander, Colombia
| | - Andrea Troupin
- Department of Pathology, Microbiology and Immunology, University of South Carolina School of Medicine, Columbia, SC, 29209 (; )
| | - Tonya M Colpitts
- Department of Pathology, Microbiology and Immunology, University of South Carolina School of Medicine, Columbia, SC, 29209 (; )
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10
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Nikolaeva D, Draper SJ, Biswas S. Toward the development of effective transmission-blocking vaccines for malaria. Expert Rev Vaccines 2015; 14:653-80. [PMID: 25597923 DOI: 10.1586/14760584.2015.993383] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The continued global burden of malaria can in part be attributed to a complex lifecycle, with both human hosts and mosquito vectors serving as transmission reservoirs. In preclinical models of vaccine-induced immunity, antibodies to parasite sexual-stage antigens, ingested in the mosquito blood meal, can inhibit parasite survival in the insect midgut as judged by ex vivo functional studies such as the membrane feeding assay. In an era of renewed political momentum for malaria elimination and eradication campaigns, such observations have fueled support for the development and implementation of so-called transmission-blocking vaccines. While leading candidates are being evaluated using a variety of promising vaccine platforms, the field is also beginning to capitalize on global '-omics' data for the rational genome-based selection and unbiased characterization of parasite and mosquito proteins to expand the candidate list. This review covers the progress and prospects of these recent developments.
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Affiliation(s)
- Daria Nikolaeva
- The Jenner Institute, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Headington, Oxford OX3 7DQ, UK
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11
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Sala KA, Nishiura H, Upton LM, Zakutansky SE, Delves MJ, Iyori M, Mizutani M, Sinden RE, Yoshida S, Blagborough AM. The Plasmodium berghei sexual stage antigen PSOP12 induces anti-malarial transmission blocking immunity both in vivo and in vitro. Vaccine 2014; 33:437-45. [PMID: 25454088 DOI: 10.1016/j.vaccine.2014.11.038] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 11/19/2014] [Accepted: 11/20/2014] [Indexed: 01/15/2023]
Abstract
Anti-malarial transmission-blocking vaccines (TBVs) aim to inhibit the transmission of Plasmodium from humans to mosquitoes by targeting the sexual/ookinete stages of the parasite. Successful use of such interventions will subsequently result in reduced cases of malarial infection within a human population, leading to local elimination. There are currently only five lead TBV candidates under examination. There is a consequent need to identify novel antigens to allow the formulation of new potent TBVs. Here we describe the design and evaluation of a potential TBV (BDES-PbPSOP12) targeting Plasmodium berghei PSOP12 based on the baculovirus dual expression system (BDES), enabling expression of antigens on the surface of viral particles and within infected mammalian cells. In silico studies have previously suggested that PSOP12 (Putative Secreted Ookinete Protein 12) is expressed within the sexual stages of the parasite (gametocytes, gametes and ookinetes), and is a member of the previously characterized 6-Cys family of plasmodial proteins. We demonstrate that PSOP12 is expressed within the sexual/ookinete forms of the parasite, and that sera obtained from mice immunized with BDES-PbPSOP12 can recognize the surface of the male and female gametes, and the ookinete stages of the parasite. Immunization of mice with BDES-PbPSOP12 confers modest but significant transmission-blocking activity in vivo by active immunization (53.1% reduction in oocyst intensity, 10.9% reduction in oocyst prevalence). Further assessment of transmission-blocking potency ex vivo shows a dose-dependent response, with up to a 76.4% reduction in intensity and a 47.2% reduction in prevalence observed. Our data indicates that PSOP12 in Plasmodium spp. could be a potential new TBV target candidate, and that further experimentation to examine the protein within human malaria parasites would be logical.
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Affiliation(s)
- K A Sala
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, South Kensington, London SW7 2AZ, UK
| | - H Nishiura
- Laboratory of Vaccinology and Applied Immunology, School of Pharmacy, Kanazawa University, Ishikawa, Japan
| | - L M Upton
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, South Kensington, London SW7 2AZ, UK
| | - S E Zakutansky
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, South Kensington, London SW7 2AZ, UK
| | - M J Delves
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, South Kensington, London SW7 2AZ, UK
| | - M Iyori
- Laboratory of Vaccinology and Applied Immunology, School of Pharmacy, Kanazawa University, Ishikawa, Japan
| | - M Mizutani
- Laboratory of Vaccinology and Applied Immunology, School of Pharmacy, Kanazawa University, Ishikawa, Japan
| | - R E Sinden
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, South Kensington, London SW7 2AZ, UK; Jenner Institute, The University of Oxford, Roosevelt Road, Oxford OX9 2PP, UK
| | - S Yoshida
- Laboratory of Vaccinology and Applied Immunology, School of Pharmacy, Kanazawa University, Ishikawa, Japan
| | - A M Blagborough
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, South Kensington, London SW7 2AZ, UK.
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12
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Woo MK, Kim KA, Kim J, Oh JS, Han ET, An SSA, Lim CS. Sequence polymorphisms in Pvs48/45 and Pvs47 gametocyte and gamete surface proteins in Plasmodium vivax isolated in Korea. Mem Inst Oswaldo Cruz 2014; 108:S0074-02762013000300359. [PMID: 23778662 DOI: 10.1590/s0074-02762013000300015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Accepted: 10/09/2012] [Indexed: 11/22/2022] Open
Abstract
Nucleotide sequence analyses of the Pvs48/45 and Pvs47 genes were conducted in 46 malaria patients from the Republic of Korea (ROK) (n = 40) and returning travellers from India (n = 3) and Indonesia (n = 3). The domain structures, which were based on cysteine residue position and secondary protein structure, were similar between Plasmodium vivax (Pvs48/45 and Pvs47) and Plasmodium falciparum (Pfs48/45 and Pfs47). In comparison to the Sal-1 reference strain (Pvs48/45, PVX_083235 and Pvs47, PVX_083240), Korean isolates revealed seven polymorphisms (E35K, H211N, K250N, D335Y, A376T, I380T and K418R) in Pvs48/45. These isolates could be divided into five haplotypes with the two major types having frequencies of 47.5% and 20%, respectivelfy. In Pvs47, 10 polymorphisms (F22L, F24L, K27E, D31N, V230I, M233I, E240D, I262T, I273M and A373V) were found and they could be divided into four haplotypes with one major type having a frequency of 75%. The Pvs48/45 isolates from India showed a unique amino acid substitution site (K26R). Compared to the Sal-1 and ROK isolates, the Pvs47 isolates from travellers returning from India and Indonesia had amino acid substitutions (S57T and I262K). The current data may contribute to the development of the malaria transmission-blocking vaccine in future clinical trials.
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Affiliation(s)
- Mi Kyung Woo
- Korea University Guro Hospital, Department of Laboratory Medicine, Seoul, Korea
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13
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Limited genetic diversity and purifying selection in Iranian Plasmodium falciparum Generative Cell Specific 1 (PfGCS1), a potential target for transmission-blocking vaccine. INFECTION GENETICS AND EVOLUTION 2014; 22:150-6. [PMID: 24462906 DOI: 10.1016/j.meegid.2014.01.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 01/02/2014] [Accepted: 01/04/2014] [Indexed: 11/24/2022]
Abstract
Among vaccines, those that have an impact on transmission are in priority for malaria elimination and eradication. One of the new identified transmission-blocking vaccine (TBV) candidate antigens is Generative Cell Specific 1 (GCS1) located on the male gametocytes of Plasmodium species. Since the antigenic diversity could hamper vaccine development, it is essential to determine the gene diversity of gcs1 in global malaria-endemic areas in order to develop efficient TBVs. Therefore, in this study, nucleotide diversity and selection in the Plasmodium falciparum GCS1 (PfGCS1) antigen were analyzed in 36 Iranian clinical isolates by using PCR sequencing in order to provide useful information on this TBV candidate antigen. For this purpose, successful sequence analysis was carried out in 36 isolates. The results showed three single-nucleotide polymorphisms including one synonymous (G1475A) and two non-synonymous (A697G and G1479A) mutations leading to 3 distinct haplotypes with different frequencies: GCS1-A (N184/D445, 16.7%), GCS1-B (S184/D445, 63.9%), and GCS1-C (N184/N445, 19.4%). The overall nucleotide diversity (π) for all 36 sequences of Iranian pfgcs1 was 0.00066±0.00012, and the dN-dS value (-0.00028) was negative, suggesting the possible action of purifying selection in this gene. Epitope mapping prediction of PfGCS1 antigen showed that most of the potential linear and conformational B-cell epitopes are located in conserved regions. However, N184S and D445N mutations were also involved in linear and conformational B-cell epitopes, respectively that should be considered in vaccine design. In conclusion, the present study showed a very low genetic diversity of pfgcs1 gene among Iranian isolates. Considering PfGCS1 as a conserved TBV candidate, our data provides valuable information to develop a PfGCS1-based TBV.
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14
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VOGT-GEISSE KATIA, LORENZO CHRISTINA, FENG ZHILAN. IMPACT OF AGE-DEPENDENT RELAPSE AND IMMUNITY ON MALARIA DYNAMICS. J BIOL SYST 2014. [DOI: 10.1142/s0218339013400019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
An age-structured mathematical model for malaria is presented. The model explicitly includes the human and mosquito populations, structured by chronological age of humans. The infected human population is divided into symptomatic infectious, asymptomatic infectious and asymptomatic chronic infected individuals. The original partial differential equation (PDE) model is reduced to an ordinary differential equation (ODE) model with multiple age groups coupled by aging. The basic reproduction number [Formula: see text] is derived for the PDE model and the age group model in the case of general n age groups. We assume that infectiousness of chronic infected individuals gets triggered by bites of even susceptible mosquitoes. Our analysis points out that this assumption contributes greatly to the [Formula: see text] expression and therefore needs to be further studied and understood. Numerical simulations for n = 2 age groups and a sensitivity/uncertainty analysis are presented. Results suggest that it is important not only to consider asymptomatic infectious individuals as a hidden cause for malaria transmission, but also asymptomatic chronic infections (>60%), which often get neglected due to undetectable parasite loads. These individuals represent an important reservoir for future human infectiousness. By considering age-dependent immunity types, the model helps generate insight into effective control measures, by targeting age groups in an optimal way.
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Affiliation(s)
- KATIA VOGT-GEISSE
- Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, Indiana 47907, USA
| | - CHRISTINA LORENZO
- Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, Indiana 47907, USA
| | - ZHILAN FENG
- Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, Indiana 47907, USA
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15
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Transmission-blocking interventions eliminate malaria from laboratory populations. Nat Commun 2013; 4:1812. [PMID: 23652000 PMCID: PMC3674233 DOI: 10.1038/ncomms2840] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Accepted: 04/05/2013] [Indexed: 12/02/2022] Open
Abstract
Transmission-blocking interventions aim to reduce the prevalence of infection in endemic communities by targeting Plasmodium within the insect host. Although many studies have reported the successful reduction of infection in the mosquito vector, direct evidence that there is an onward reduction in infection in the vertebrate host is lacking. Here we report the first experiments using a population, transmission-based study of Plasmodium berghei in Anopheles stephensi to assess the impact of a transmission-blocking drug upon both insect and host populations over multiple transmission cycles. We demonstrate that the selected transmission-blocking intervention, which inhibits transmission from vertebrate to insect by only 32%, reduces the basic reproduction number of the parasite by 20%, and in our model system can eliminate Plasmodium from mosquito and mouse populations at low transmission intensities. These findings clearly demonstrate that use of transmission-blocking interventions alone can eliminate Plasmodium from a vertebrate population, and have significant implications for the future design and implementation of transmission-blocking interventions within the field. Transmission-blocking interventions aim to interrupt progression of Plasmodium parasites from the vertebrate host to the mosquito. Blagborough et al. demonstrate that only partially reducing transmission can be sufficient to eliminate experimental Plasmodium infection in successive mosquito and mice populations when biting rates are low.
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16
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Patra KP, Vinetz JM. New ultrastructural analysis of the invasive apparatus of the Plasmodium ookinete. Am J Trop Med Hyg 2012; 87:412-7. [PMID: 22802443 DOI: 10.4269/ajtmh.2012.11-0609] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Invasion of the mosquito midgut by the Plasmodium ookinete determines the success of transmission of malaria parasites from humans to mosquitoes and therefore, is a potential target for molecular intervention. Here, we show higher-resolution ultrastructural details of developing and mature P. gallinaceum ookinetes than previously available. Improved fixation and processing methods yielded substantially improved transmission electron micrographs of ookinetes, particularly with regard to visualization of subcellular secretory and other organelles. These new images provide new insights into the synthesis and function of vital invasive machinery focused on the following features: apical membrane protrusions presumptively used for attachment and protein secretion, dark spherical bodies at the apical end of the mature ookinete, and the presence of a dense array of micronemes apposed to microtubules at the apical end of the ookinete involved in constitutive secretion. This work advances understanding of the molecular and cellular details of the Plasmodium ookinete and provides the basis of future, more detailed mechanistic experimentation on the biology of the Plasmodium ookinete.
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Affiliation(s)
- Kailash P Patra
- Division of Infectious Diseases, Department of Medicine, University of California at San Diego, La Jolla, CA 92093-0741, USA.
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17
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Abstract
Here we describe a series of methods that can be used to assess the activities of "vaccines," drugs, and genetically modified vectors, for their abilities to inhibit transmission of Plasmodium from its vertebrate to its mosquito hosts. The selection of method to be used is determined by the purpose of the experiment, which can include the determination of the site/time of activity, and/or the potential reduction in transmission achieved.
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18
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Goodman AL, Blagborough AM, Biswas S, Wu Y, Hill AV, Sinden RE, Draper SJ. A viral vectored prime-boost immunization regime targeting the malaria Pfs25 antigen induces transmission-blocking activity. PLoS One 2011; 6:e29428. [PMID: 22216279 PMCID: PMC3247263 DOI: 10.1371/journal.pone.0029428] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Accepted: 11/29/2011] [Indexed: 11/18/2022] Open
Abstract
The ookinete surface protein Pfs25 is a macrogamete-to-ookinete/ookinete stage antigen of Plasmodium falciparum, capable of exerting high-level anti-malarial transmission-blocking activity following immunization with recombinant protein-in-adjuvant formulations. Here, this antigen was expressed in recombinant chimpanzee adenovirus 63 (ChAd63), human adenovirus serotype 5 (AdHu5) and modified vaccinia virus Ankara (MVA) viral vectored vaccines. Two immunizations were administered to mice in a heterologous prime-boost regime. Immunization of mice with AdHu5 Pfs25 at week 0 and MVA Pfs25 at week 10 (Ad-MVA Pfs25) resulted in high anti-Pfs25 IgG titers, consisting of predominantly isotypes IgG1 and IgG2a. A single priming immunization with ChAd63 Pfs25 was as effective as AdHu5 Pfs25 with respect to ELISA titers at 8 weeks post-immunization. Sera from Ad-MVA Pfs25 immunized mice inhibited the transmission of P. falciparum to the mosquito both ex vivo and in vivo. In a standard membrane-feeding assay using NF54 strain P. falciparum, oocyst intensity in Anopheles stephensi mosquitoes was significantly reduced in an IgG concentration-dependent manner when compared to control feeds (96% reduction of intensity, 78% reduction in prevalence at a 1 in 5 dilution of sera). In addition, an in vivo transmission-blocking effect was also demonstrated by direct feeding of immunized mice infected with Pfs25DR3, a chimeric P. berghei line expressing Pfs25 in place of endogenous Pbs25. In this assay the density of Pfs25DR3 oocysts was significantly reduced when mosquitoes were fed on vaccinated as compared to control mice (67% reduction of intensity, 28% reduction in prevalence) and specific IgG titer correlated with efficacy. These data confirm the utility of the adenovirus-MVA vaccine platform for the induction of antibodies with transmission-blocking activity, and support the continued development of this alternative approach to transmission-blocking malaria subunit vaccines.
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Affiliation(s)
- Anna L Goodman
- The Jenner Institute, University of Oxford, Oxford, United Kingdom.
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19
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Arévalo-Herrera M, Solarte Y, Marin C, Santos M, Castellanos J, Beier JC, Valencia SH. Malaria transmission blocking immunity and sexual stage vaccines for interrupting malaria transmission in Latin America. Mem Inst Oswaldo Cruz 2011; 106 Suppl 1:202-11. [PMID: 21881775 PMCID: PMC4830685 DOI: 10.1590/s0074-02762011000900025] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Accepted: 07/13/2011] [Indexed: 11/22/2022] Open
Abstract
Malaria is a vector-borne disease that is considered to be one of the most serious public health problems due to its high global mortality and morbidity rates. Although multiple strategies for controlling malaria have been used, many have had limited impact due to the appearance and rapid dissemination of mosquito resistance to insecticides, parasite resistance to multiple antimalarial drug, and the lack of sustainability. Individuals in endemic areas that have been permanently exposed to the parasite develop specific immune responses capable of diminishing parasite burden and the clinical manifestations of the disease, including blocking of parasite transmission to the mosquito vector. This is referred to as transmission blocking (TB) immunity (TBI) and is mediated by specific antibodies and other factors ingested during the blood meal that inhibit parasite development in the mosquito. These antibodies recognize proteins expressed on either gametocytes or parasite stages that develop in the mosquito midgut and are considered to be potential malaria vaccine candidates. Although these candidates, collectively called TB vaccines (TBV), would not directly stop malaria from infecting individuals, but would stop transmission from infected person to non-infected person. Here, we review the progress that has been achieved in TBI studies and the development of TBV and we highlight their potential usefulness in areas of low endemicity such as Latin America.
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20
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Mlambo G, Kumar N, Yoshida S. Functional immunogenicity of baculovirus expressing Pfs25, a human malaria transmission-blocking vaccine candidate antigen. Vaccine 2010; 28:7025-9. [PMID: 20709008 DOI: 10.1016/j.vaccine.2010.08.022] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 07/19/2010] [Accepted: 08/02/2010] [Indexed: 11/19/2022]
Abstract
We have focused on development of a novel vaccine vector based on "Baculophage", a baculovirus display system for expression of proteins on the surface of the viral envelope, as a non-pathogenic and non-vertebrate insect virus. In the present study, recombinant baculovirus (AcNPV-Pfs25surf) were generated, which displayed Pfs25, a potent Plasmodium falciparum transmission-blocking vaccine candidate. Both intranasal and intramuscular immunizations of mice with AcNPV-Pfs25surf induced high levels of Pfs25-specific antibodies, which strongly reacted with ookinetes of transgenic Plasmodium berghei expressing Pfs25 (TrPfs25Pb). Importantly, sera obtained from immunized rabbits exhibited a significant transmission-blocking effect (>90% reduction in infection intensity) in standard membrane feeding assay using P. falciparum gametocytes. Additionally, active immunization (both intranasal and intramuscular routes) of mice followed by challenge using TrPfs25Pb demonstrated an effective transmission-blocking response, with an 83% (intranasal) and ∼95% (intramuscular) reduction in oocyst intensity, respectively. Thus, the baculovirus-based vaccines offer a promising new alternative to current human vaccine delivery platforms for the development of malaria multi-stage vaccines.
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Affiliation(s)
- Godfree Mlambo
- Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 N Wolfe Street, Baltimore, MD 21205, USA
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21
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Blagborough AM, Yoshida S, Sattabongkot J, Tsuboi T, Sinden RE. Intranasal and intramuscular immunization with Baculovirus Dual Expression System-based Pvs25 vaccine substantially blocks Plasmodium vivax transmission. Vaccine 2010; 28:6014-20. [PMID: 20637303 DOI: 10.1016/j.vaccine.2010.06.100] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 06/28/2010] [Accepted: 06/29/2010] [Indexed: 12/20/2022]
Abstract
We have recently developed a new experimental vaccine vector system based on Autographa californica nucleopolyhedrosis virus (AcNPV) termed the "Baculovirus Dual Expression System", which drives expression of vaccine candidate antigens by a dual promoter that consists of tandemly arranged baculovirus-derived polyhedrin and mammalian-derived CMV promoters. The present study used this system to generate a Plasmodium vivax transmission-blocking immunogen (AcNPV-Dual-Pvs25). AcNPV-Dual-Pvs25 not only displayed Pvs25 on the AcNPV envelope, exhibiting aspects of its native three-dimensional structure, but also expressed appropriately immunogenic protein upon transduction of mammalian cells. Both intranasal and intramuscular immunization of mice with AcNPV-Dual-Pvs25 induced high Pvs25-specific antibody titres, notably of IgG1, IgG2a and IgG2b isotypes, indicating a mixed Th1/Th2 response. Importantly, sera obtained from subcutaneously immunized rabbits exhibited a significant transmission-blocking effect (96% reduction in infection intensity, 24% reduction in prevalence) when challenged with human blood infected with P. vivax gametocytes using the standard membrane feeding assay. Additionally, active immunization (both intranasal and intramuscular routes) of mice followed by challenge using a transgenic P. berghei line expressing Pvs25 in place of native Pbs25 and Pbs28 (clone Pvs25DR3) demonstrates a strong transmission-blocking response, with a 92.1% (intranasal) and 83.8% (intramuscular) reduction in oocyst intensity. Corresponding reductions in prevalence of infection were observed (88.4% and 75.5% respectively). This study offers a novel tool for the development of malarial transmission-blocking vaccines against the sexual stages of the parasite, using the Baculovirus Dual Expression System that functions as both a subunit, and DNA based vaccine.
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Affiliation(s)
- Andrew M Blagborough
- Division of Cell and Molecular Biology, Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, Imperial College Road, London SW7 2AZ, UK.
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22
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Plasmodium berghei HAP2 induces strong malaria transmission-blocking immunity in vivo and in vitro. Vaccine 2009; 27:5187-94. [DOI: 10.1016/j.vaccine.2009.06.069] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Revised: 06/16/2009] [Accepted: 06/21/2009] [Indexed: 01/10/2023]
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23
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Gholizadeh S, Djadid ND, Basseri HR, Zakeri S, Ladoni H. Analysis of von Willebrand factor A domain-related protein (WARP) polymorphism in temperate and tropical Plasmodium vivax field isolates. Malar J 2009; 8:137. [PMID: 19549316 PMCID: PMC2709902 DOI: 10.1186/1475-2875-8-137] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Accepted: 06/23/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The identification of key molecules is crucial for designing transmission-blocking vaccines (TBVs), among those ookinete micronemal proteins are candidate as a general class of malaria transmission-blocking targets. Here, the sequence analysis of an extra-cellular malaria protein expressed in ookinetes, named von Willebrand factor A domain-related protein (WARP), is reported in 91 Plasmodium vivax isolates circulating in different regions of Iran. METHODS Clinical isolates were collected from north temperate and southern tropical regions in Iran. Primers have been designed based on P. vivax sequence (ctg_6991) which amplified a fragment of about 1044 bp with no size variation. Direct sequencing of PCR products was used to determine polymorphism and further bioinformatics analysis in P. vivax sexual stage antigen, pvwarp. RESULTS Amplified pvwarp gene showed 886 bp in size, with no intron. BLAST analysis showed a similarity of 98-100% to P. vivax Sal-I strain; however, Iranian isolates had 2 bp mismatches in 247 and 531 positions that were non-synonymous substitution [T (ACT) to A (GCT) and R (AGA) to S (AGT)] in comparison with the Sal-I sequence. CONCLUSION This study presents the first large-scale survey on pvwarp polymorphism in the world, which provides baseline data for developing WARP-based TBV against both temperate and tropical P. vivax isolates.
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Affiliation(s)
- Saber Gholizadeh
- Biotechnology Research Center (BRC), Pasteur Institute of Iran (PII), Tehran, Iran.
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24
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Sutherland CJ. Surface antigens of Plasmodium falciparum gametocytes--a new class of transmission-blocking vaccine targets? Mol Biochem Parasitol 2009; 166:93-8. [PMID: 19450726 DOI: 10.1016/j.molbiopara.2009.03.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2008] [Revised: 03/07/2009] [Accepted: 03/10/2009] [Indexed: 10/21/2022]
Abstract
The re-establishment of elimination and eradication on the malaria control agenda has led to calls for renewed effort in the development of parasite transmission-blocking interventions. Vaccines are ideally suited to this task, but progress towards an anti-gamete transmission-blocking vaccine, designed to act on parasites in blood-fed mosquitoes, has been slow. Recent work has confirmed that the surface of the gametocyte-infected erythrocyte presents antigens to the host immune system, and elicits specific humoral immune responses to these antigens, termed gametocyte surface antigens (GSAs). Likely candidate molecules, including antigens encoded by sub-telomeric multi-gene families, are discussed, and a hypothetical group of parasite molecules involved in spatial and temporal signal transduction in the human host is proposed, the tropins and circadins. The next steps for development of anti-gametocyte transmission-blocking vaccines for P. falciparum and the other human malaria species are considered.
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Affiliation(s)
- Colin J Sutherland
- HPA Malaria Reference Laboratory, Department of Infectious & Tropical Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom.
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25
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Zakeri S, Razavi S, Djadid ND. Genetic diversity of transmission blocking vaccine candidate (Pvs25 and Pvs28) antigen in Plasmodium vivax clinical isolates from Iran. Acta Trop 2009; 109:176-80. [PMID: 18950597 DOI: 10.1016/j.actatropica.2008.09.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Revised: 09/09/2008] [Accepted: 09/17/2008] [Indexed: 11/29/2022]
Abstract
The leading candidates for a Transmission Blocking Vaccine (TBV) in Plasmodium vivax parasite are the ookinete surface protein 25 (Pvs25) and Pvs28, which their phase I clinical trial is ongoing. Therefore, we carried out survey of polymorphisms of the pvs25 and pvs28 genes in P. vivax populations that are circulating in the two malaria areas of contrasting endemicity in Iran, before field application of the TBV. To characterize the polymorphisms of pvs25 and pvs28 genes, 50 isolates were analyzed by sequencing method and their gene structure was compared with parasite populations from India, Bangladesh, Indonesia, Thailand, Mexico and Brazil. Three mutations were detected in pvs25 and pvs28 including Q87K, E97Q, I130T and M52L, T65K, T140S with two and four distinct haplotypes, in comparison with the Sal I sequence type, respectively. Both haplotypes of Pvs25 were found among northern and southern P. vivax isolates; however, only two and three of the Pvs28 variants were observed among the northern and southern isolates, respectively. In conclusion, the present results show the limited sequence polymorphism of the pvs25 and pvs28 genes among field P. vivax population in Iran. These results highly encourage with respect to applicability of Pvs25 and Pvs28-based vaccine against P. vivax infection in the region, where these parasites are prevalent, whether these occur in the temperate or tropical zones.
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MESH Headings
- Amino Acid Sequence
- Amino Acid Substitution/genetics
- Animals
- Antigens, Protozoan/chemistry
- Antigens, Protozoan/genetics
- Antigens, Surface/chemistry
- Antigens, Surface/genetics
- Clinical Trials as Topic
- DNA, Protozoan/chemistry
- DNA, Protozoan/genetics
- Genetic Variation
- Haplotypes
- Humans
- Iran
- Malaria Vaccines/chemistry
- Malaria Vaccines/genetics
- Malaria Vaccines/immunology
- Malaria, Vivax/immunology
- Malaria, Vivax/parasitology
- Molecular Sequence Data
- Mutation, Missense
- Plasmodium vivax/genetics
- Plasmodium vivax/isolation & purification
- Sequence Analysis, DNA
- Sequence Homology
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Affiliation(s)
- Sedigheh Zakeri
- Malaria and Vector Research Group (MVRG), Biotechnology Research Center, Pasteur Institute of Iran, Tehran, Iran.
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26
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Correctly folded Pfs48/45 protein of Plasmodium falciparum elicits malaria transmission-blocking immunity in mice. Proc Natl Acad Sci U S A 2008; 105:4301-5. [PMID: 18332422 DOI: 10.1073/pnas.0800459105] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Malaria kills >1 million people each year, in particular in sub-Saharan Africa. Although asexual forms are directly responsible for disease and death, sexual stages account for the transmission of Plasmodium parasites from human to the mosquito vector and therefore the spread of the parasite in the population. Development of a malaria vaccine is urgently needed to reduce morbidity and mortality. Vaccines against sexual stages of Plasmodium falciparum are meant to decrease the force of transmission and consequently reduce malaria burden. Pfs48/45 is specifically expressed in sexual stages and is a well established transmission-blocking (TB) vaccine candidate. However, production of correctly folded recombinant Pfs48/45 protein with display of its TB epitopes has been a major challenge. Here, we show the production of a properly folded Pfs48/45 C-terminal fragment by simultaneous coexpression with four periplasmic folding catalysts in Escherichia coli. This C-terminal fragment fused to maltose binding protein was produced at medium scale with >90% purity and a stability over at least a 9-month period. It induces uniform and high antibody titers in mice and elicits functional TB antibodies in standard membrane feeding assays in 90% of the immunized mice. Our data provide a clear perspective on the clinical development of a Pfs48/45-based TB malaria vaccine.
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27
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Murine model for assessment of Plasmodium falciparum transmission-blocking vaccine using transgenic Plasmodium berghei parasites expressing the target antigen Pfs25. Infect Immun 2008; 76:2018-24. [PMID: 18316385 DOI: 10.1128/iai.01409-07] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Currently, there is no animal model for Plasmodium falciparum challenge to evaluate malaria transmission-blocking vaccines based on the well-established Pfs25 target antigen. The biological activity of transmission-blocking antibodies is typically assessed using an assay known as the membrane feeding assay (MFA). It is an in vitro method that involves mixing antibodies with cultured P. falciparum gametocytes and feeding them to mosquitoes through an artificial membrane followed by assessment of infection in the mosquitoes. We genetically modified Plasmodium berghei to express Pfs25 and demonstrated that the transgenic parasites (TrPfs25Pb) are susceptible to anti-Pfs25 antibodies during mosquito-stage development. The asexual growth kinetics and mosquito infectivity of TrPfs25Pb were comparable to those of wild-type parasites, and TrPfs25Pb displayed Pfs25 on the surface of ookinetes. Immune sera from nonhuman primates immunized with a Pfs25-based vaccine when passively transferred to mice blocked transmission of TrPfs25Pb to Anopheles stephensi. Furthermore, mice immunized with Pfs25 DNA vaccine and challenged with TrPfs25Pb displayed reduced malaria transmission compared to mice immunized with wild-type plasmid. These studies describe development of an animal malaria model alternative to the in vitro MFA and show that the model can facilitate P. falciparum transmission-blocking vaccine evaluation based on the target antigen Pfs25. We believe that an animal model to test transmission-blocking vaccines would be superior to the MFA, since there may be additional immune factors that synergize the transmission-blocking activity of antibodies in vivo.
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28
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Dubovsky F, Malkin E. Malaria vaccines. Vaccines (Basel) 2008. [DOI: 10.1016/b978-1-4160-3611-1.50056-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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LeBlanc R, Vasquez Y, Hannaman D, Kumar N. Markedly enhanced immunogenicity of a Pfs25 DNA-based malaria transmission-blocking vaccine by in vivo electroporation. Vaccine 2007; 26:185-92. [PMID: 18054817 DOI: 10.1016/j.vaccine.2007.10.066] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2007] [Revised: 10/19/2007] [Accepted: 10/29/2007] [Indexed: 11/29/2022]
Abstract
Pfs25 is a promising target antigen for the development of a malaria transmission-blocking vaccine and prior research has demonstrated induction of high and functionally effective antibodies in mice with IM injection of Pfs25 encoding DNA plasmid. Likewise, Pfs25 DNA vaccine was immunogenic in rhesus macaques but required a protein boost to elicit significant transmission-blocking antibodies. The translation of these encouraging findings to human clinical trials has been impeded largely by the relatively poor immunogenicity of DNA plasmids in larger animals. In vivo electroporation (EP) has revealed significant enhancement of the potency of DNA plasmids. The results reported here compared the immunogenicity and functional transmission-blocking effects of immunization with DNA plasmid (25 microg) by the traditional IM route compared to coupling the IM injection (0.25, 2.5 and 25 microg doses) with in vivo EP. Significantly, a 0.25 microg dose of DNA plasmid, when administered with EP, induced antibody titers (1:160,000) and functional transmission-blocking effects that were equivalent to those achieved by a one hundred fold higher (25 microg) dose of DNA plasmid given without EP. At a 25.0 microg DNA dose with or without EP there was sufficient antigenic stimulation to result in effective antibody titers; however EP method yielded antibody titer of 1:1,280,000 as compared to only 1:160,000 titer without EP. This observed two log reduction in the amount of DNA plasmid required to induce significant transmission-blocking effects makes a compelling argument in favor of further evaluation of DNA vaccines by in vivo EP method in larger animals. Further experiments in non-human primates and eventually in phase I human trials will determine if the use of EP will induce effective and sustained malaria transmission-blocking effects at acceptable doses of plasmid DNA.
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Affiliation(s)
- Ralph LeBlanc
- Johns Hopkins Malaria Research Institute, Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA
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30
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Pradel G. Proteins of the malaria parasite sexual stages: expression, function and potential for transmission blocking strategies. Parasitology 2007; 134:1911-29. [PMID: 17714601 DOI: 10.1017/s0031182007003381] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SUMMARYThe sexual phase of the malaria pathogen,Plasmodium falciparum, culminates in fertilization within the midgut of the mosquito and represents a crucial step in the completion of the parasite's life-cycle and transmission of the disease. Two decades ago, the first sexual stage-specific surface proteins were identified, among themPfs230,Pfs48/45, andPfs25, which were of scientific interest as candidates for the development of transmission blocking vaccines. A decade later, gene information gained from the sequencing of theP. falciparumgenome led to the identification of numerous additional sexual-stage proteins with antigenic properties and novel enzymes that putatively possess regulatory functions during sexual-stage development. This review aims to summarize the sexual-stage proteins identified to date, to compare their stage specificities and expression patterns and to highlight novel regulative mechanisms of sexual differentiation. The prospective candidacy of select sexual-stage proteins as targets for transmission blocking strategies will be discussed.
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Affiliation(s)
- G Pradel
- University of Würzburg, Research Center for Infectious Diseases, Röntgenring 11, 97070 Würzburg, Germany.
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31
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Lavazec C, Boudin C, Lacroix R, Bonnet S, Diop A, Thiberge S, Boisson B, Tahar R, Bourgouin C. Carboxypeptidases B of Anopheles gambiae as targets for a Plasmodium falciparum transmission-blocking vaccine. Infect Immun 2007; 75:1635-42. [PMID: 17283100 PMCID: PMC1865713 DOI: 10.1128/iai.00864-06] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Anopheles gambiae is the major African vector of Plasmodium falciparum, the most deadly species of human malaria parasite and the most prevalent in Africa. Several strategies are being developed to limit the global impact of malaria via reducing transmission rates, among which are transmission-blocking vaccines (TBVs), which induce in the vertebrate host the production of antibodies that inhibit parasite development in the mosquito midgut. So far, the most promising components of a TBV are parasite-derived antigens, although targeting critical mosquito components might also successfully block development of the parasite in its vector. We previously identified A. gambiae genes whose expression was modified in P. falciparum-infected mosquitoes, including one midgut carboxypeptidase gene, cpbAg1. Here we show that P. falciparum up-regulates the expression of cpbAg1 and of a second midgut carboxypeptidase gene, cpbAg2, and that this up-regulation correlates with an increased carboxypeptidase B (CPB) activity at a time when parasites establish infection in the mosquito midgut. The addition of antibodies directed against CPBAg1 to a P. falciparum-containing blood meal inhibited CPB activity and blocked parasite development in the mosquito midgut. Furthermore, the development of the rodent parasite Plasmodium berghei was significantly reduced in mosquitoes fed on infected mice that had been immunized with recombinant CPBAg1. Lastly, mosquitoes fed on anti-CPBAg1 antibodies exhibited reduced reproductive capacity, a secondary effect of a CPB-based TBV that could likely contribute to reducing Plasmodium transmission. These results indicate that A. gambiae CPBs could constitute targets for a TBV that is based upon mosquito molecules.
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Affiliation(s)
- C Lavazec
- Unité de Biologie et Génétique du Paludisme, Institut Pasteur, 25 rue du Dr Roux, 75015 Paris, France
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32
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Tsai CW, Duggan PF, Shimp RL, Miller LH, Narum DL. Overproduction of Pichia pastoris or Plasmodium falciparum protein disulfide isomerase affects expression, folding and O-linked glycosylation of a malaria vaccine candidate expressed in P. pastoris. J Biotechnol 2006; 121:458-70. [PMID: 16274825 DOI: 10.1016/j.jbiotec.2005.08.025] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Revised: 08/09/2005] [Accepted: 08/24/2005] [Indexed: 11/28/2022]
Abstract
Production of recombinant malaria proteins in the methylotrophic yeast Pichia pastoris has been difficult due to constraints in transcription, translation and/or post-translation controls. Use of codon-optimized genes has resolved many of the transcriptional controls; however, efforts to overcome translational and post-translational modifications involving disulfide bond formation and glycosylation have been mostly restricted to knocking-out putative N-linked glycosylation sites. We report now on the effect of overproduction of P. pastoris protein disulfide isomerase (PpPDI) and Plasmodium falciparum (PfPDI) on production of a disulfide-rich P. falciparum transmission-blocking vaccine candidate, Pfs25. Pfs25 is expressed in P. pastoris as two isoforms (A and B); the A form has been selected for Phase I human studies. Overproduction of PpPDI in the P. pastoris Pfs25 production clone markedly enhanced the expression level of Pfs25(A) and (B) by 3-fold, while overproduction of PfPDI increased the proportion of Pfs25(A) compared to (B). The resultant Pfs25 products were purified and fully characterized biochemically. In addition to differences in production levels, the mass spectra of PpPDI-Pfs25(A) compared to Pfs25(A) and PfPDI-Pfs25(A) were different due to the pattern and level of O-linked glycosylation. The overproduction of PpPDI or PfPDI provides new platforms for expression of disulfide-rich malaria proteins.
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Affiliation(s)
- Chiawei W Tsai
- Malaria Vaccine Development Branch, National Institute of Allergy and Infectious Disease, National Institutes of Health, 5640 Fishers Lane, Rockville, MD 20852, USA
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33
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Arévalo-Herrera M, Solarte Y, Yasnot MF, Castellanos A, Rincón A, Saul A, Mu J, Long C, Miller L, Herrera S. Induction of transmission-blocking immunity in Aotus monkeys by vaccination with a Plasmodium vivax clinical grade PVS25 recombinant protein. Am J Trop Med Hyg 2006; 73:32-7. [PMID: 16291764 DOI: 10.4269/ajtmh.2005.73.32] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Aotus monkeys were used to determine the immunogenicity of Pvs25 protein expressed in the zygote/ookinete surface. Animals were immunized in three times with 100 microg of Pvs25 formulated in Montanide ISA-720. Antibodies to Pvs25 detected by an enzyme-linked immunosorbent assay appeared by day 30 after the first immunization, with a peak of antibodies levels on day 150. These antibodies were still detectable on day 300. Plasma samples on day 150 from experimental group were able to completely block the development of the parasite in Anopheles albimanus mosquitoes artificially fed with human isolates of Plasmodium vivax. Immunized Aotus monkeys were infected with blood forms of the P. vivax Salvador I strain and no boosting effect of blood infection on titers of antibodies to Pvs25 was observed despite the presence of infective gametocytes. In conclusion, Pvs25 protein formulated in Montanide ISA-720 induces efficient and long-lasting transmission-blocking antibodies that cannot be boosted by parasite infection.
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MESH Headings
- Animals
- Anopheles
- Antibodies, Protozoan/blood
- Antigens, Protozoan/administration & dosage
- Antigens, Protozoan/genetics
- Antigens, Protozoan/immunology
- Antigens, Surface/administration & dosage
- Antigens, Surface/genetics
- Antigens, Surface/immunology
- Cebidae
- Humans
- Immune Sera/immunology
- Malaria Vaccines/administration & dosage
- Malaria Vaccines/genetics
- Malaria Vaccines/immunology
- Malaria, Vivax/immunology
- Malaria, Vivax/prevention & control
- Malaria, Vivax/transmission
- Mannitol/administration & dosage
- Mannitol/analogs & derivatives
- Mannitol/immunology
- Oleic Acids/administration & dosage
- Oleic Acids/immunology
- Plasmodium vivax/immunology
- Recombinant Proteins/administration & dosage
- Recombinant Proteins/genetics
- Recombinant Proteins/immunology
- Vaccination
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34
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Young JA, Fivelman QL, Blair PL, de la Vega P, Le Roch KG, Zhou Y, Carucci DJ, Baker DA, Winzeler EA. The Plasmodium falciparum sexual development transcriptome: a microarray analysis using ontology-based pattern identification. Mol Biochem Parasitol 2005; 143:67-79. [PMID: 16005087 DOI: 10.1016/j.molbiopara.2005.05.007] [Citation(s) in RCA: 242] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2005] [Revised: 04/29/2005] [Accepted: 05/20/2005] [Indexed: 01/24/2023]
Abstract
The sexual stages of malarial parasites are essential for the mosquito transmission of the disease and therefore are the focus of transmission-blocking drug and vaccine development. In order to better understand genes important to the sexual development process, the transcriptomes of high-purity stage I-V Plasmodium falciparum gametocytes were comprehensively profiled using a full-genome high-density oligonucleotide microarray. The interpretation of this transcriptional data was aided by applying a novel knowledge-based data-mining algorithm termed ontology-based pattern identification (OPI) using current information regarding known sexual stage genes as a guide. This analysis resulted in the identification of a sexual development cluster containing 246 genes, of which approximately 75% were hypothetical, exhibiting highly-correlated, gametocyte-specific expression patterns. Inspection of the upstream promoter regions of these 246 genes revealed putative cis-regulatory elements for sexual development transcriptional control mechanisms. Furthermore, OPI analysis was extended using current annotations provided by the Gene Ontology Consortium to identify 380 statistically significant clusters containing genes with expression patterns characteristic of various biological processes, cellular components, and molecular functions. Collectively, these results, available as part of a web-accessible OPI database (http://carrier.gnf.org/publications/Gametocyte), shed light on the components of molecular mechanisms underlying parasite sexual development and other areas of malarial parasite biology.
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Affiliation(s)
- Jason A Young
- Department of Cell Biology ICND202, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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35
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van Dijk MR, Douradinha B, Franke-Fayard B, Heussler V, van Dooren MW, van Schaijk B, van Gemert GJ, Sauerwein RW, Mota MM, Waters AP, Janse CJ. Genetically attenuated, P36p-deficient malarial sporozoites induce protective immunity and apoptosis of infected liver cells. Proc Natl Acad Sci U S A 2005; 102:12194-9. [PMID: 16103357 PMCID: PMC1189305 DOI: 10.1073/pnas.0500925102] [Citation(s) in RCA: 211] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Indexed: 11/18/2022] Open
Abstract
Immunization with Plasmodium sporozoites that have been attenuated by gamma-irradiation or specific genetic modification can induce protective immunity against subsequent malaria infection. The mechanism of protection is only known for radiation-attenuated sporozoites, involving cell-mediated and humoral immune responses invoked by infected hepatocytes cells that contain long-lived, partially developed parasites. Here we analyzed sporozoites of Plasmodium berghei that are deficient in P36p (p36p(-)), a member of the P48/45 family of surface proteins. P36p plays no role in the ability of sporozoites to infect and traverse hepatocytes, but p36p(-) sporozoites abort during development within the hepatocyte. Immunization with p36p(-) sporozoites results in a protective immunity against subsequent challenge with infectious wild-type sporozoites, another example of a specifically genetically attenuated sporozoite (GAS) conferring protective immunity. Comparison of biological characteristics of p36p(-) sporozoites with radiation-attenuated sporozoites demonstrates that liver cells infected with p36p(-) sporozoites disappear rapidly as a result of apoptosis of host cells that may potentiate the immune response. Such knowledge of the biological characteristics of GAS and their evoked immune responses are essential for further investigation of the utility of an optimized GAS-based malaria vaccine.
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Affiliation(s)
- Melissa R van Dijk
- Department of Parasitology, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands
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36
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Malkin EM, Durbin AP, Diemert DJ, Sattabongkot J, Wu Y, Miura K, Long CA, Lambert L, Miles AP, Wang J, Stowers A, Miller LH, Saul A. Phase 1 vaccine trial of Pvs25H: a transmission blocking vaccine for Plasmodium vivax malaria. Vaccine 2005; 23:3131-8. [PMID: 15837212 PMCID: PMC10994215 DOI: 10.1016/j.vaccine.2004.12.019] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2004] [Revised: 12/20/2004] [Accepted: 12/28/2004] [Indexed: 11/19/2022]
Abstract
Plasmodium vivax is responsible for the majority of malaria cases outside of Africa, and results in substantial morbidity. Transmission blocking vaccines are a potentially powerful component of a multi-faceted public health approach to controlling or eliminating malaria. We report the first phase 1 clinical trial of a P. vivax transmission blocking vaccine in humans. The Pvs25H vaccine is a recombinant protein derived from the Pvs25 surface antigen of P. vivax ookinetes. The protein was expressed in Saccharomyces cerevisiae, purified, and adsorbed onto Alhydrogel. Ten volunteers in each of three dose groups (5, 20, or 80 microg) were vaccinated by intramuscular injection in an open-label study at 0, 28 and 180 days. No vaccine-related serious adverse events were observed. The majority of adverse events causally related to vaccination were mild or moderate in severity. Injection site tenderness was the most commonly observed adverse event. Anti-Pvs25H antibody levels measured by ELISA peaked after the third vaccination. Vaccine-induced antibody is functionally active as evidenced by significant transmission blocking activity in the membrane feeding assay. Correlation between antibody concentration and degree of inhibition was observed. Pvs25H generates transmission blocking immunity in humans against P. vivax demonstrating the potential of this antigen as a component of a transmission blocking vaccine.
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Affiliation(s)
- Elissa M Malkin
- Malaria Vaccine Development Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 5640 Fishers Lane, Twinbrook 1, Room 1123, Rockville, MD 20852, USA.
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37
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van der Kolk M, De Vlas SJ, Saul A, van de Vegte-Bolmer M, Eling WM, Sauerwein RW, Sauerwein W. Evaluation of the standard membrane feeding assay (SMFA) for the determination of malaria transmission-reducing activity using empirical data. Parasitology 2005; 130:13-22. [PMID: 15700753 DOI: 10.1017/s0031182004006067] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Host responses to the transmittable stages of the malaria parasite may reduce transmission effectively. Transmission-reducing activity (TRA) of human serum can be determined as a percentage, using the Standard Membrane Feeding Assay (SMFA). This laboratory assay was evaluated using the results of 121 experiments with malaria-endemic sera among which many repeated measurements were obtained. The assay consists of the feeding of Anopheles stephensi mosquitoes with cultured Plasmodium falciparum gametocytes, mixed with human red blood cells, and control and experimental sera. The TRA of individual sera was determined by the comparison of oocyst densities between these sera. Bootstrap data on oocyst densities in individual mosquitoes in control feeds were used to construct confidence limits for TRA percentages of serum feeds. Low (<20%) and high TRA (>90%) values for individual sera were usually reproduced in a second experiment, whereas this was more difficult for values between 20% and 90%. The observed variability of TRA values is explained in part by the variability in oocyst density per mosquito. Oocyst densities in control feeds varied more between experiments than within experiments and showed a slight decline over the 3 years of experiments. Reproducibility of TRA of field sera was low (20%) between experiments, but much higher (61 %) within experiments. A minimum of 35 oocysts per mosquito in control feeds gave optimal reproducibility (44%) between experiments. We recommend that (1) sera are compared within an experiment, or (2) assays are only analysed where controls have at least 35 oocysts per mosquito. The SMFA is under the recommended conditions appropriate for the study of factors that may influence TRA, e.g. transmission blocking vaccines.
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Affiliation(s)
- M van der Kolk
- UMC Nijmegen, Medical Microbiology, 6500 HB Nijmegen, The Netherlands.
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38
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Sattabongkot J, Tsuboi T, Zollner GE, Sirichaisinthop J, Cui L. Plasmodium vivax transmission: chances for control? Trends Parasitol 2004; 20:192-8. [PMID: 15099559 DOI: 10.1016/j.pt.2004.02.001] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Jetsumon Sattabongkot
- Entomology Department, USAMC Armed Forces Research Institute of Medical Sciences, 315/6 Rajavithi Road, Bangkok 10400, Thailand.
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39
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Doerig C. Protein kinases as targets for anti-parasitic chemotherapy. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2004; 1697:155-68. [PMID: 15023358 DOI: 10.1016/j.bbapap.2003.11.021] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2003] [Accepted: 11/12/2003] [Indexed: 11/19/2022]
Abstract
Parasitic protozoa infecting humans have a staggering impact on public health, especially in the developing world. Furthermore, several protozoan species are major pathogens of domestic animals and have a considerable impact on food production. In many instances, the parasites have developed resistance against available chemotherapeutic agents, making the search for alternative drugs a priority. In line with the current interest in protein kinases inhibitors as potential drugs against a variety of diseases, the possibility that protein kinases may represent targets for novel anti-parasitic agents is being explored. Research into parasite protein kinases has benefited greatly from genome and EST sequencing projects, with the genomes of a few species fully sequenced (notably that of the human malaria parasite Plasmodium falciparum) and several more under way. The overall picture that emerged from research in this area shows that the phylogenetic isolation of parasitic protozoa is reflected by atypical structural and functional properties of many of their protein kinase homologues. Likewise, evidence is emerging, which suggests that the organisation of some otherwise well-conserved signal transduction pathways is divergent in some parasitic species. The differences between protein kinases of a parasite and their homologues in its host cell suggest that specific inhibition of the former can be achieved. The development of anti-parasitic drugs based on protein kinase inhibition is being pursued following two avenues: one consists of screening chemical libraries on recombinant enzymes; several protein kinases from parasitic protozoa are now available for this approach. The second approach relies on the identification of the molecular targets of kinase inhibitors which display anti-parasitic properties. This has led to promising developments in a few instances, in particular regarding PKG as a drug target against Eimeria and Toxoplasma, and purvalanol B, a purine-based CDK inhibitor which appears to affect unexpected targets in several protozoan parasites. The recent resolution of the structure of a Plasmodium protein kinase complexed with small inhibitory molecules opens the way to a rational approach towards the design of anti-parasitic drugs based on kinase inhibition.
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Affiliation(s)
- Christian Doerig
- Wellcome Centre for Molecular Parasitology, University of Glasgow, INSERM, 56 Dumbarton Road, Glasgow G11 6NU, Scotland, UK.
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40
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Li F, Templeton TJ, Popov V, Comer JE, Tsuboi T, Torii M, Vinetz JM. Plasmodium ookinete-secreted proteins secreted through a common micronemal pathway are targets of blocking malaria transmission. J Biol Chem 2004; 279:26635-44. [PMID: 15069061 DOI: 10.1074/jbc.m401385200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mosquito midgut ookinete stage of the malaria parasite, Plasmodium, possesses microneme secretory organelles that mediate locomotion and midgut wall egress to establish sporogonic stages and subsequent transmission. The purpose of this study was 2-fold: 1) to determine whether there exists a single micronemal population with respect to soluble and membrane-associated secreted proteins; and 2) to evaluate the ookinete micronemal proteins chitinase (PgCHT1), circumsporozoite and TRAP-related protein (CTRP), and von Willebrand factor A domain-related protein (WARP) as immunological targets eliciting sera-blocking malaria parasite infectivity to mosquitoes. Indirect immunofluorescence localization studies in Plasmodium gallinaceum using specific antisera showed that all three proteins are distributed intracellularly with a similar granular cytoplasmic appearance and with focal concentration of PgCHT1 and PgCTRP, but not PgWARP, at the ookinete apical end. Immunogold double-labeling electron microscopy, using antisera against the membrane-associated protein CTRP and the soluble WARP, showed that these two proteins co-localized to the same micronemal population. Within the microneme CTRP was associated peripherally at the microneme membrane, whereas PgCHT1 and WARP were diffuse within the micronemal lumen. Sera produced against Plasmodium falciparum WARP significantly reduced the infectivity of P. gallinaceum to Aedes aegypti and P. falciparum to Anopheles mosquitoes. Antisera against PgCTRP and PgCHT1 also significantly reduced the infectivity of P. gallinaceum for A. aegypti. These results support the concept that ookinete micronemal proteins may constitute a general class of malaria transmission-blocking vaccine candidates.
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Affiliation(s)
- Fengwu Li
- Division of Infectious Diseases, Department of Medicine, University of California, San Diego, La Jolla, California 92093-0640, USA
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41
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Coban C, Ishii KJ, Stowers AW, Keister DB, Klinman DM, Kumar N. Effect of CpG oligodeoxynucleotides on the immunogenicity of Pfs25, a Plasmodium falciparum transmission-blocking vaccine antigen. Infect Immun 2004; 72:584-8. [PMID: 14688140 PMCID: PMC344005 DOI: 10.1128/iai.72.1.584-588.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Antibodies directed against Pfs25, a protein present on the surface of zygotes and ookinetes of Plasmodium falciparum, completely block pathogen transmission. We evaluated the immunomodulatory effect of CpG oligodeoxynucleotides (ODN) on the immunogenicity of recombinant Pfs25 (rPfs25) formulated in alum (Al). Immunization of mice with rPfs25 plus CpG ODN improved both the antibody titer (a 30-fold-higher antibody response than that with rPfs25-Al alone) and avidity. Coadministration of CpG ODN dramatically enhanced the titer of immunoglobulin G2A (IgG2a) compared to the titer of the IgG1-dominant response caused by rPfs25-Al alone, and the sera from the CpG ODN-coadministered group completely blocked the transmission of P. falciparum parasites to mosquitoes, as determined by membrane feeding assays. However, transmission-blocking experiments revealed that blocking efficacy was dependent on high-titer antibody levels, independent of isotypes. These results suggest that CpG ODN can be used as an adjuvant to enhance the immunogenicity of rPfs25 as a malaria transmission-blocking vaccine.
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Affiliation(s)
- Cevayir Coban
- Department of Molecular Microbiology and Immunology, Malaria Research Institute, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA
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42
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Bhatnagar RK, Arora N, Sachidanand S, Shahabuddin M, Keister D, Chauhan VS. Synthetic propeptide inhibits mosquito midgut chitinase and blocks sporogonic development of malaria parasite. Biochem Biophys Res Commun 2003; 304:783-7. [PMID: 12727225 DOI: 10.1016/s0006-291x(03)00682-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Incessant transmission of the parasite by mosquitoes makes most attempts to control malaria fail. Blocking of parasite transmission by mosquitoes therefore is a rational strategy to combat the disease. Upon ingestion of blood meal mosquitoes secrete chitinase into the midgut. This mosquito chitinase is a zymogen which is activated by the removal of a propeptide from the N-terminal. Since the midgut peritrophic matrix acts as a physical barrier, the activated chitinase is likely to contribute to the further development of the malaria parasite in the mosquito. Earlier it has been shown that inhibiting chitinase activity in the mosquito midgut blocked sporogonic development of the malaria parasite. Since synthetic propeptides of several zymogens have been found to be potent inhibitors of their respective enzymes, we tested propeptide of mosquito midgut chitinase as an inhibitor and found that the propeptide almost completely inhibited the recombinant or purified native Anopheles gambiae chitinase. We also examined the effect of the inhibitory peptide on malaria parasite development. The result showed that the synthetic propeptide blocked the development of human malaria parasite Plasmodium falciparum in the African malaria vector An. gambiae and avian malaria parasite Plasmodium gallinaceum in Aedes aegypti mosquitoes. This study implies that the expression of inhibitory mosquito midgut chitinase propeptide in response to blood meal may alter the mosquito's vectorial capacity. This may lead to developing novel strategies for controlling the spread of malaria.
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Affiliation(s)
- Raj K Bhatnagar
- International Center for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, P.O. Box 10504, New Delhi 1100 67, India.
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43
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Dalton JP, Brindley PJ, Knox DP, Brady CP, Hotez PJ, Donnelly S, O'Neill SM, Mulcahy G, Loukas A. Helminth vaccines: from mining genomic information for vaccine targets to systems used for protein expression. Int J Parasitol 2003; 33:621-40. [PMID: 12782060 DOI: 10.1016/s0020-7519(03)00057-2] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The control of helminth diseases of people and livestock continues to rely on the widespread use of anti-helminthic drugs. However, concerns with the appearance of drug resistant parasites and the presence of pesticide residues in food and the environment, has given further incentive to the goal of discovering molecular vaccines against these pathogens. The exponential rate at which gene and protein sequence information is accruing for many helminth parasites requires new methods for the assimilation and analysis of the data and for the identification of molecules capable of inducing immunological protection. Some promising vaccine candidates have been discovered, in particular cathepsin L proteases from Fasciola hepatica, aminopeptidases from Haemonchus contortus, and aspartic proteases from schistosomes and hookworms, all of which are secreted into the host tissues or into the parasite intestine where they play important roles in host-parasite interactions. Since secreted proteins, in general, are exposed to the immune system of the host they represent obvious candidates at which vaccines could be targeted. Therefore, in this article, we consider the potential values and uses of algorithms for characterising cDNAs amongst the collated helminth genomic information that encode secreted proteins, and methods for their selective isolation and cloning. We also review the variety of prokaryotic and eukaryotic cell expression systems that have been employed for the production and downstream purification of recombinant proteins in functionally active form, and provide an overview of the parameters that must be considered if these recombinant proteins are to be commercialised as vaccine therapeutics in humans and/or animals.
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Affiliation(s)
- John P Dalton
- School of Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland.
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44
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Zou L, Miles AP, Wang J, Stowers AW. Expression of malaria transmission-blocking vaccine antigen Pfs25 in Pichia pastoris for use in human clinical trials. Vaccine 2003; 21:1650-7. [PMID: 12639486 DOI: 10.1016/s0264-410x(02)00701-6] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In previously published studies, Saccharomyces cerevisiae recombinant protein expression systems have been employed to express the malaria parasite antigen Pfs25, a candidate transmission-blocking vaccine antigen against Plasmodium falciparum malaria. However, despite having been in two Phase 1 trials, the recombinant Pfs25 so produced (previously called TBV25H) exists as a mixture of two monomeric protein conformational forms, Pfs25H-A and Pfs25H-B. In this study, we optimized the expression and purification of the two Pfs25H conformers in S. cerevisiae, and characterized their biochemical and antigenic properties, immunogenicities, and transmission-blocking activities. Pfs25H-A is apparently homogeneous, and has the correct conformation as measured by monoclonal antibody recognition. It is, however, expressed at a low yield of only 0.19mg/l. By contrast, Pfs25H-B is produced as a heterogeneous population of molecules that do not seem to have the correct conformation. Nonetheless, both forms appear equally effective in their ability to produce transmission-blocking antibodies in mice. To address the low yield seen with S. cerevisiae, we also expressed Pfs25 in Pichia pastoris. P. pastoris is apparently superior to S. cerevisiae in producing higher yield, immunologically more potent, biologically more active Pfs25H-A.
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Affiliation(s)
- Lanling Zou
- Malaria Vaccine Development Unit, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA
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Abstract
Insects' resistance to infectious agents is essential for their own survival and also for the health of the plant, animal and human populations with which they closely interact. Several of the major human diseases are spread by insects and are rapidly expanding as a result of the development of insecticide resistance in vectors and drug resistance in parasites. A vector insects' permissiveness to a pathogen, and hence the spread of the disease, will largely depend on the compatibility of the molecular interactions between the two species and the capability of the insect immune system to recognize and kill the pathogen. The innate immune system comprises a variety of components and mechanisms that can discriminate between different microorganisms and mount specific responses to control pathogenic infections. An impressive body of knowledge on the insects' innate immunity has been generated from studies in the model organism Drosophila. These studies are now guiding the exploration of the immune system in the vector mosquito of human malaria, Anopheles, and its implication in the elimination of parasites. Anopheles immune responses have been linked to parasite losses and some refractory mosquitoes can kill all parasites through specific defence mechanisms. The recently sequenced Drosophila and Anopheles genomes provide a detailed and comparative view on their immune gene repertoires that in combination with post-genomic analyses is used to further dissect the complex mechanisms of Plasmodium killing in the mosquito.
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Affiliation(s)
- George Dimopoulos
- Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College of Science, Technology and Medicine, SW7 2AZ London, UK.
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46
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Carter R. Spatial simulation of malaria transmission and its control by malaria transmission blocking vaccination. Int J Parasitol 2002; 32:1617-24. [PMID: 12435446 DOI: 10.1016/s0020-7519(02)00190-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A simple, visual representation of spatial aspects of malaria transmission in successive snap-shots in time, is presented. The spatial components of the simulation involve (i) the identification of mosquito vector breeding sites of defined shape and area, (ii) the identification of a zone of malaria transmission determined by the shapes and areas of the vector breeding sites and the distance from these sites that the mosquitoes disperse, (iii) a human population dispersed in relation to the malaria transmission zone, (iv) perimeters around each individual human within which his or her infection can be transmitted by the local vector mosquitoes. The intensity of transmission within a malaria transmission zone is given by a number which is the number of new cases of malaria that each existing case will distribute through the human population within the duration of an infection. The simulation has been used here to examine the effects of vaccination against malaria transmission. Different levels of vaccine coverage are represented under endemic and epidemic malaria. The consequences of full or partial coverage of a zone of malaria transmission are also examined. The results are numerically compatible with the predictions of previous simple mathematical simulations of malaria transmission and interventions. The present simulation allows the nature of malaria transmission and the effects of interventions to be communicated easily and directly to an audience. It could have practical value in discussions of malaria control strategies with health planners.
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Affiliation(s)
- Richard Carter
- Division of Biological Sciences, ICAPB, University of Edinburgh, UK.
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Kongkasuriyachai D, Kumar N. Functional characterisation of sexual stage specific proteins in Plasmodium falciparum. Int J Parasitol 2002; 32:1559-66. [PMID: 12435440 DOI: 10.1016/s0020-7519(02)00184-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The various stages of the malaria parasites in the vertebrate host and in the mosquito vector offer numerous candidates for vaccine and drug development. However, the biological complexity of the parasites and the interaction with the immune system of the host continue to frustrate all such efforts thus far. While most of the targets for drug and vaccine design have focused on the asexual stages, the sexual stages of the parasite are critical for transmission and maintenance of parasites among susceptible vertebrate hosts. Sexual stage parasites undergo a series of morphological and biochemical changes during their development, accompanied by a co-ordinated cascade of a distinct expression pattern of sexual stage specific proteins. Mechanisms underlying the developmental switch from asexual parasite to sexual parasite still remain elusive. Methods that can break the malaria transmission cycle thus occupy a central place in the overall malaria control strategies. This paper provides a review of genes expressed in sexually differentiated Plasmodium. In the past few years, a molecular approach based on targeted gene disruption has revealed fascinating biological roles for many of the sexual stage gene products. In addition, we will briefly discuss other functional genomic approaches employed to study not only sexual but also other aspects of host-parasite biology.
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Affiliation(s)
- Darin Kongkasuriyachai
- Johns Hopkins Malaria Research Institute, Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
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Moore SA, Surgey EGE, Cadwgan AM. Malaria vaccines: where are we and where are we going? THE LANCET. INFECTIOUS DISEASES 2002; 2:737-43. [PMID: 12467689 DOI: 10.1016/s1473-3099(02)00451-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Malaria is still killing over one million people each year and its incidence is increasing. The need for an effective vaccine is greater than ever. A major difficulty with vaccine research is that the malaria parasite presents thousands of antigens to the human immune system that vary throughout its life cycle. Identifying those that may prove to be vaccine targets is complicated and time consuming. Most vaccines are targeted at individual stages of the malaria life cycle, although it is likely that only the development of a multistage vaccine will offer complete protection to both visitors to, and residents of, a malaria-endemic area. With the development of a successful vaccine other issues such as cost, distribution, education, and compliance will have to be addressed. This review describes some of the current vaccine candidates for immunising against malaria.
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