Particle-based platforms for malaria vaccines

Recombinant subunit vaccines in general are poor immunogens likely due to the small size of pep-tides and proteins, combined with the lack or reduced presentation of repetitive motifs and missing complementary signal(s) for optimal triggering of the immune response. Therefore, recombinant sub-unit vaccines require enhancement by vaccine delivery vehicles in order to attain adequate protective immunity. Particle-based delivery platforms, including particulate antigens and particulate adjuvants,are promising delivery vehicles for modifying the way in which immunogens are presented to both theinnate and adaptive immune systems. These particle delivery platforms can also co-deliver non-specific immunostimodulators as additional adjuvants. This paper reviews efforts and advances of the Particle-based delivery platforms in development of vaccines against malaria, a disease that claims over 600,000lives per year, most of them are children under 5 years of age in sub-Sahara Africa

The challenges of Plasmodium vivax human malaria infection models for vaccine development

Controlled Human Malaria Infection models (CHMI) have been critical to advancing new vaccines for malaria. Stringent and safe preparation of a challenge agent is key to the success of any CHMI. Difficulty producing the Plasmodium vivax parasite in vitro has limited production of qualified parasites for CHMI as well as the functional assays required to screen and down-select candidate vaccines for this globally distributed parasite. This and other challenges to P. vivax CHMI (PvCHMI), including scientific, logistical, and ethical obstacles, are common to P. vivax research conducted in both non-endemic and endemic countries, with additional hurdles unique to each. The challenges of using CHMI for P. vivax vaccine development and evaluation, lessons learned from previous and ongoing clinical trials, and the way forward to effectively perform PvCHMI to support vaccine development, are discussed

Asymptomatic Plasmodium vivax infections induce robust IgG responses to multiple blood-stage proteins in a low-transmission region of western Thailand

BACKGROUND: Thailand is aiming to eliminate malaria by the year 2024. Plasmodium vivax has now become the dominant species causing malaria within the country, and a high proportion of infections are asymptomatic. A better understanding of antibody dynamics to P. vivax antigens in a low-transmission setting, where acquired immune responses are poorly characterized, will be pivotal for developing new strategies for elimination, such as improved surveillance methods and vaccines. The objective of this study was to characterize total IgG antibody levels to 11 key P. vivax proteins in a village of western Thailand. METHODS: Plasma samples from 546 volunteers enrolled in a cross-sectional survey conducted in 2012 in Kanchanaburi Province were utilized. Total IgG levels to 11 different proteins known or predicted to be involved in reticulocyte binding or invasion (ARP, GAMA, P41, P12, PVX_081550, and five members of the PvRBP family), as well as the leading pre-erythrocytic vaccine candidate (CSP) were measured using a multiplexed bead-based assay. Associations between IgG levels and infection status, age, and spatial location were explored. RESULTS: Individuals from a low-transmission region of western Thailand reacted to all 11 P. vivax recombinant proteins. Significantly greater IgG levels were observed in the presence of a current P. vivax infection, despite all infected individuals being asymptomatic. IgG levels were also higher in adults (18 years and older) than in children. For most of the proteins, higher IgG levels were observed in individuals living closer to the Myanmar border and further away from local health services. CONCLUSIONS: Robust IgG responses were observed to most proteins and IgG levels correlated with surrogates of exposure, suggesting these antigens may serve as potential biomarkers of exposure, immunity, or both

Antigen-Displaying Lipid-Enveloped PLGA Nanoparticles as Delivery Agents for a Plasmodium vivax Malaria Vaccine

The parasite Plasmodium vivax is the most frequent cause of malaria outside of sub-Saharan Africa, but efforts to develop viable vaccines against P. vivax so far have been inadequate. We recently developed pathogen-mimicking polymeric vaccine nanoparticles composed of the FDA-approved biodegradable polymer poly(lactide-co-glycolide) acid (PLGA) “enveloped” by a lipid membrane. In this study, we sought to determine whether this vaccine delivery platform could be applied to enhance the immune response against P. vivax sporozoites. A candidate malaria antigen, VMP001, was conjugated to the lipid membrane of the particles, and an immunostimulatory molecule, monophosphoryl lipid A (MPLA), was incorporated into the lipid membranes, creating pathogen-mimicking nanoparticle vaccines (VMP001-NPs). Vaccination with VMP001-NPs promoted germinal center formation and elicited durable antigen-specific antibodies with significantly higher titers and more balanced Th1/Th2 responses in vivo, compared with vaccines composed of soluble protein mixed with MPLA. Antibodies raised by NP vaccinations also exhibited enhanced avidity and affinity toward the domains within the circumsporozoite protein implicated in protection and were able to agglutinate live P. vivax sporozoites. These results demonstrate that these VMP001-NPs are promising vaccines candidates that may elicit protective immunity against P. vivax sporozoites.United States. Dept. of Defense (contract W911NF-07-D-0004)Ragon Institute of MGH, MIT and Harvar

Effect of Codon Optimization on Expression Levels of a Functionally Folded Malaria Vaccine Candidate in Prokaryotic and Eukaryotic Expression Systems

We have produced two synthetic genes that code for the F2 domain located within region II of the 175-kDa Plasmodium falciparum erythrocyte binding antigen (EBA-175) to determine the effects of codon alteration on protein expression in homologous and heterologous host systems. EBA-175 plays a key role in the process of merozoite invasion into erythrocytes through a specific receptor-ligand interaction. The F2 domain of EBA-175 is the ligand that binds to the glycophorin A receptor on human erythrocytes and is therefore a target of vaccine development efforts. We designed synthetic genes based on P. falciparum, Escherichia coli, and Pichia codon usage and expressed recombinant F2 in E. coli and Pichia pastoris. Compared to the expression of the native F2 sequence, conversion to prokaryote (E. coli)- or eukaryote (Pichia)-based codon usage dramatically improved the levels of recombinant protein expression in both E. coli and P. pastoris. The majority of the protein expressed in E. coli, however, was produced as inclusion bodies. The protein expressed in P. pastoris, on the other hand, was expressed as a secreted, soluble protein. The P. pastoris-produced protein was superior to that produced in E. coli based on its ability to bind to red blood cells. Consistent with these observations, the antibodies generated against the Pichia-produced protein prevented the binding of recombinant EBA to red blood cells. These antibodies recognize EBA-175 present on merozoites as well as in sporozoites by immunofluorescence. Our results suggest that the Pichia-based EBA-F2 vaccine construct has further potential to be developed for clinical use

How high is high enough?

<p>In two studies assessing efficacy of the VMP001 vaccine, higher anti-type 1 repeat antibodies were associated with a positive outcome after sporozoite challenge. Protected <i>Aotus</i> (left panel; [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005164#pntd.0005164.ref010" target="_blank">10</a>]) and humans with a delay to parasitemia (middle panel; [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005164#pntd.0005164.ref007" target="_blank">7</a>]) had significantly higher anti-type 1 repeat antibodies. In rhesus monkeys, CSV-S,S, a particulate formulation, generated significantly higher antibodies against the type 1 repeat compared to its soluble counterpart VMP001 (right panel; [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005164#pntd.0005164.ref009" target="_blank">9</a>]). These data raise the question—how high do the anti-repeat titers need to be in order to protect humans post-challenge? (Horizontal line within the box and whisker graphs represents the median values. Geometric mean titer values are listed below each group.)</p

Development of a Chimeric \u3ci\u3ePlasmodium berghei\u3c/i\u3e Strain Expressing the Repeat Region of the \u3ci\u3eP. vivax\u3c/i\u3e Circumsporozoite Protein for \u3ci\u3eIn Vivo\u3c/i\u3e Evaluation of Vaccine Efficacy

The development of vaccine candidates against Plasmodium vivax—the most geographically widespread human malaria species— is challenged by technical difficulties, such as the lack of in vitro culture systems and availability of animal models. Chimeric rodent Plasmodium parasites are safe and useful tools for the preclinical evaluation of new vaccine formulations. We report the successful development and characterization of chimeric Plasmodium berghei parasites bearing the type I repeat region of P. vivax circumsporozoite protein (CSP). The P. berghei-P. vivax chimeric strain develops normally in mosquitoes and produces highly infectious sporozoites that produce patent infection in mice that are exposed to the bites of as few as 3 P. berghei-P. vivax-infected mosquitoes. Using this transgenic parasite, we demonstrate that monoclonal and polyclonal antibodies against P. vivax CSP strongly inhibit parasite infection and thus support the notion that these antibodies play an important role in protective immunity. The chimeric parasites we developed represent a robust model for evaluating protective immune responses against P. vivax vaccines based on CSP

Genome-Wide Expression Profiling in Malaria Infection Reveals Transcriptional Changes Associated with Lethal and Nonlethal Outcomes

High-density oligonucleotide microarrays are widely used to study gene expression in cells exposed to a variety of pathogens. This study addressed the global genome-wide transcriptional activation of genes in hosts infected in vivo, which result in radically different clinical outcomes. We present an analysis of the gene expression profiles that identified a set of host biomarkers which distinguish between lethal and nonlethal blood stage Plasmodium yoelii malaria infections. Multiple biological replicates sampled during the course of infection were used to establish statistically valid sets of differentially expressed genes. These genes that correlated with the intensity of infection were used to identify pathways of cellular processes related to metabolic perturbations, erythropoiesis, and B-cell immune responses and other innate and cellular immune responses. The transcriptional apparatus that controls gene expression in erythropoiesis was also differentially expressed and regulated the expression of target genes involved in the host's response to malaria anemia. The biological systems approach provides unprecedented opportunities to explore the pathophysiology of host-pathogen interactions in experimental malaria infection and to decipher functionally complex networks of gene and protein interactions