Clinical expression and antigenic profiles of a Plasmodium vivax vaccine candidate: merozoite surface protein 7 (PvMSP-7)

Plasmodium vivax transcriptomics: What is new?

Malaria is the leading human parasitosis and is transmitted through the bite of anopheline mosquitoes infected with parasites of the genus Plasmodium spp. Among the seven species that cause malaria in humans, Plasmodium vivax is the most prevalent species in Latin America. In recent years, there have been an increasing number of reports of clinical complications caused by P. vivax infections, which were previously neglected and underestimated. P. vivax biology remains with large gaps. The emergence of next-generation sequencing technology has ensured a breakthrough in species knowledge. Coupled with this, the deposition of the P. vivax Sal-1 reference genome allowed an increase in transcriptomics projects by accessing messenger RNA. Thus, the regulation of differential gene expression according to the parasite life stage was verified, and several expressed genes were linked to different biological functions. Today, with the progress associated with RNA sequencing technologies, it is possible to detect nuances and obtain robust results. Discoveries provided by transcriptomic studies allow us to understand topics such as RNA expression and regulation and proteins and metabolic pathways involved during different stages of the parasite life cycle. The information obtained enables a better comprehension of immune system evasion mechanisms; invasion and adhesion strategies used by the parasite; as well as new vaccine targets, potential molecular markers, and others therapeutic targets. In this review, we provide new insights into P. vivax biology by summarizing recent findings in transcriptomic studies.

Identification of novel Plasmodium vivax proteins associated with protection against clinical malaria

As progress towards malaria elimination continues, the challenge posed by the parasite species Plasmodium vivax has become more evident. In many regions co-endemic for P. vivax and Plasmodium falciparum, as transmission has declined the proportion of cases due to P. vivax has increased. Novel tools that directly target P. vivax are thus warranted for accelerated elimination. There is currently no advanced vaccine for P. vivax and only a limited number of potential candidates in the pipeline. In this study we aimed to identify promising P. vivax proteins that could be used as part of a subunit vaccination approach. We screened 342 P. vivax protein constructs for their ability to induce IgG antibody responses associated with protection from clinical disease in a cohort of children from Papua New Guinea. This approach has previously been used to successfully identify novel candidates. We were able to confirm previous results from our laboratory identifying the proteins reticulocyte binding protein 2b and StAR-related lipid transfer protein, as well as at least four novel candidates with similar levels of predicted protective efficacy. Assessment of these P. vivax proteins in further studies to confirm their potential and identify functional mechanisms of protection against clinical disease are warranted.

The first complete genome of the simian malaria parasite Plasmodium brasilianum

Naturally occurring human infections by zoonotic Plasmodium species have been documented for P. knowlesi, P. cynomolgi, P. simium, P. simiovale, P. inui, P. inui-like, P. coatneyi, and P. brasilianum. Accurate detection of each species is complicated by their morphological similarities with other Plasmodium species. PCR-based assays offer a solution but require prior knowledge of adequate genomic targets that can distinguish the species. While whole genomes have been published for P. knowlesi, P. cynomolgi, P. simium, and P. inui, no complete genome for P. brasilianum has been available. Previously, we reported a draft genome for P. brasilianum, and here we report the completed genome for P. brasilianum. The genome is 31.4 Mb in size and comprises 14 chromosomes, the mitochondrial genome, the apicoplast genome, and 29 unplaced contigs. The chromosomes consist of 98.4% nucleotide sites that are identical to the P. malariae genome, the closest evolutionarily related species hypothesized to be the same species as P. brasilianum, with 41,125 non-synonymous SNPs (0.0722% of genome) identified between the two genomes. Furthermore, P. brasilianum had 4864 (82.1%) genes that share 80% or higher sequence similarity with 4970 (75.5%) P. malariae genes. This was demonstrated by the nearly identical genomic organization and multiple sequence alignments for the merozoite surface proteins msp3 and msp7. We observed a distinction in the repeat lengths of the circumsporozoite protein (CSP) gene sequences between P. brasilianum and P. malariae. Our results demonstrate a 97.3% pairwise identity between the P. brasilianum and the P. malariae genomes. These findings highlight the phylogenetic proximity of these two species, suggesting that P. malariae and P. brasilianum are strains of the same species, but this could not be fully evaluated with only a single genomic sequence for each species.

Rapid Response to Pandemic Threats: Immunogenic Epitope Detection of Pandemic Pathogens for Diagnostics and Vaccine Development Using Peptide Microarrays

Emergence and re-emergence of pathogens bearing the risk of becoming a pandemic threat are on the rise. Increased travel and trade, growing population density, changes in urbanization, and climate have a critical impact on infectious disease spread. Currently, the world is confronted with the emergence of a novel coronavirus SARS-CoV-2, responsible for yet more than 800 000 deaths globally. Outbreaks caused by viruses, such as SARS-CoV-2, HIV, Ebola, influenza, and Zika, have increased over the past decade, underlining the need for a rapid development of diagnostics and vaccines. Hence, the rational identification of biomarkers for diagnostic measures on the one hand, and antigenic targets for vaccine development on the other, are of utmost importance. Peptide microarrays can display large numbers of putative target proteins translated into overlapping linear (and cyclic) peptides for a multiplexed, high-throughput antibody analysis. This enabled for example the identification of discriminant/diagnostic epitopes in Zika or influenza and mapping epitope evolution in natural infections versus vaccinations. In this review, we highlight synthesis platforms that facilitate fast and flexible generation of high-density peptide microarrays. We further outline the multifaceted applications of these peptide array platforms for the development of serological tests and vaccines to quickly encounter pandemic threats.

Exploration of Plasmodium vivax merozoite surface proteins 1 and 7 genetic diversity in Brazilian Amazon and Rio de Janeiro Atlantic Forest

Plasmodium vivax merozoite surface proteins (PvMSP) 1 and 7 are considered vaccine targets. Genetic diversity knowledge is crucial to assess their potential as immunogens and to provide insights about population structure in different epidemiological contexts. Here, we investigate the variability of pvmsp-1₄₂, pvmsp-7E, and pvmsp-7F genes in 227 samples from the Brazilian Amazon (BA) and Rio de Janeiro Atlantic Forest (AF). pvmsp-1₄₂ has 63 polymorphisms - 57 nonsynonymous - generating a nucleotide diversity of π = 0.009 in AF, and π = 0.018 in BA. In pvmsp-7E, 134 polymorphisms - 103 nonsynonymous - generate the nucleotide diversity of π = 0.027 in AF, and π = 0.042 in BA. The pvmsp-7F has only two SNPs - A610G and A1054T -, with nucleotide diversity of π = 0.0004 in AF, and π = 0.0007 in BA. The haplotype diversity of pvmsp-1₄₂, pvmsp-7E, and pvmsp-7F genes is 0.997, 1.00, and 0.649, respectively. None of the pvmsp-1₄₂ or pvmsp-7E sequences are identical to the Salvador 1 strain's sequence. Conversely, most of pvmsp-7F sequences (94/48%) are identical to Sal-1. We evaluated eight B-cell epitopes in pvmsp-7E, four of them showed higher nucleotide diversity compared to pvmsp-7E's epitopes. Positive selection was detected in pvmsp-1₄₂, pvmsp-7E central region, and pvmsp-7F with Tajima's D. In pvmsp-7E, the significant nucleotide and haplotype diversities with low genetic differentiation, could be indicative of balancing selection. The genetic differentiation of pvmsp-1₄₂ (0.315) and pvmsp-7F (0.354) genes between AF and BA regions is significant, which is not the case for pvmsp-7E (0.193). We conclude that pvmsp-1₄₂ and pvmsp-7E have great genetic diversity even in AF region, an enclosure area with deficient transmission levels of P. vivax zoonotic malaria. In both Brazilian regions, pvmsp-1₁₉, pvmsp-7E, and pvmsp-7F are conserved, most likely due to their roles in parasite survival, and could be considered potential targets for a "blood-stage vaccine".