Malaria vaccine research & innovation: the intersection of IA2030 and zero malaria

Innovative Multistage ML-QSAR Models for Malaria: From Data to Discovery

Malaria presents a significant challenge to global public health, with around 247 million cases estimated to occur annually worldwide. The growing resistance of Plasmodium parasites to existing therapies underscores the urgent need for new and innovative antimalarial drugs. This study leveraged artificial intelligence (AI) to tackle this complex challenge. We developed multistage Machine Learning Quantitative Structure-Activity Relationship (ML-QSAR) models to effectively analyze large datasets and predict the efficacy of chemical compounds against multiple life cycle stages of Plasmodium parasites. We then selected 16 compounds for experimental evaluation, six of which showed at least dual-stage inhibitory activity and one inhibited all life cycle stages tested. Moreover, explainable AI (XAI) analysis provided insights into critical molecular features influencing model predictions, thereby enhancing our understanding of compound interactions. This study not only empowers the development of advanced predictive AI models but also accelerates the identification and optimization of potential antiplasmodial compounds.

Detection of positive selection acting on protein surfaces at the whole-genome scale in the human malaria parasite Plasmodium falciparum

The host-parasite evolutionary arms race is a fundamental process with medical implications. During this process, the host develops parasite resistance, and the parasite develops host immune evasion strategies. Thus, this process accelerates relevant protein evolution. This study test hypothesizes that proteins subject to sequence evolution structural constraints play a crucial role and that these constraints hinder the modification of such proteins in this process. These hypotheses were tested using Plasmodium falciparum model and evaluated protein structures predicted for the entire proteome by the AlphaFold method. Based on dN/dS test results and P. falciparum and P. reichenowi comparisons, the presented approach identified proteins subject to purifying selection acting on the whole sequence and buried residues (dN < dS) and positive selection on nonburied residues. Of the 26 proteins, some known antigens (ring-exported protein 3, RAP protein, erythrocyte binding antigen-140, and protein P47) targeted by the host immune system are promising vaccine candidates. The set also contained 11 enzymes, including FIKK kinase, which modifies host proteins. This set was compared with genes for which the dN/dS test suggested that positive selection acts on the whole gene (i.e., dN > dS). The present study found that such genes encode enzymes and antigenic vaccine candidates less frequently than genes for which evolution is not subject to selection constraints and positive selection acts on only exposed residues. The analysis was repeated comparing P. falciparum with P. alderi, which is more distantly related. The study discusses the potential implications of the presented methodology for rational vaccine design and the parasitology and evolutionary biology fields.

Subcutaneous Immunization with Unaltered Axenic Malaria Parasite Liver Stages Induces Sterile Protection against Infectious Sporozoite Challenge

Host cell-free, axenic development of liver stages (LS) of the malaria parasite has been demonstrated. Here we explored axenic liver stages as a novel live whole parasite malaria vaccine platform, which is unaltered and not prone to human-error, compared to the immunization with live-attenuated sporozoites that must be done intravenously. We show that in contrast to live sporozoites, axenic LS are not infectious to the immunized host. Subcutaneous immunizations of mice with Plasmodium yoelii axenic LS, developed from wild-type (WT) sporozoites or WT sporozoites expressing enhanced-GFP, conferred sterile protection against P. yoelii infectious sporozoite challenge. Thus, axenic liver stages of P. falciparum and P. vivax might constitute an attractive alternative to live sporozoite immunization.

Genetic diversity and immunogenicity of the merozoite surface protein 1 C-terminal 19-kDa fragment of Plasmodium ovale imported from Africa into China

Background

Merozoite surface protein 1 (MSP1) plays an essential role in erythrocyte invasion by malaria parasites. The C-terminal 19-kDa region of MSP1 has long been considered one of the major candidate antigens for a malaria blood-stage vaccine against Plasmodium falciparum. However, there is limited information on the C-terminal 19-kDa region of Plasmodium ovale MSP1 (PoMSP1₁₉). This study aims to analyze the genetic diversity and immunogenicity of PoMSP1₁₉.

Methods

A total of 37 clinical Plasmodium ovale isolates including Plasmodium ovale curtisi and Plasmodium ovale wallikeri imported from Africa into China and collected during the period 2012–2016 were used. Genomic DNA was used to amplify P. ovale curtisi (poc) msp1₁₉ (pocmsp1₁₉) and P. ovale wallikeri (pow) msp1₁₉ (powmsp1₁₉) genes by polymerase chain reaction. The genetic diversity of pomsp1₁₉ was analyzed using the GeneDoc version 6 programs. Recombinant PoMSP1₁₉ (rPoMSP1₁₉)-glutathione S-transferase (GST) proteins were expressed in an Escherichia coli expression system and analyzed by western blot. Immune responses in BALB/c mice immunized with rPoMSP1₁₉-GST were determined using enzyme-linked immunosorbent assay. In addition, antigen-specific T cell responses were assessed by lymphocyte proliferation assays. A total of 49 serum samples from healthy individuals and individuals infected with P. ovale were used for the evaluation of natural immune responses by using protein microarrays.

Results

Sequences of pomsp1₁₉ were found to be thoroughly conserved in all the clinical isolates. rPoMSP1₁₉ proteins were efficiently expressed and purified as ~ 37-kDa proteins. High antibody responses in mice immunized with rPoMSP1₁₉-GST were observed. rPoMSP1₁₉-GST induced high avidity indexes, with an average of 92.57% and 85.32% for rPocMSP1₁₉ and rPowMSP1₁₉, respectively. Cross-reactivity between rPocMSP1₁₉ and rPowMSP1₁₉ was observed. Cellular immune responses to rPocMSP1₁₉ (69.51%) and rPowMSP1₁₉ (52.17%) induced in rPocMSP1₁₉- and rPowMSP1₁₉-immunized mice were found in the splenocyte proliferation assays. The sensitivity and specificity of rPoMSP1₁₉-GST proteins for the detection of natural immune responses in patients infected with P. ovale were 89.96% and 75%, respectively.

Conclusions

This study revealed highly conserved gene sequences of pomsp1₁₉. In addition, naturally acquired humoral immune responses against rPoMSP1 were observed in P. ovale infections, and high immunogenicity of rPoMSP1₁₉ in mice was also identified. These instructive findings should encourage further testing of PoMSP1₁₉ for rational vaccine design.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05086-6.

Towards Eradication of Malaria: Is the WHO's RTS,S/AS01 Vaccination Effective Enough?

BACKGROUND

Recent advances in mosquito eradication and antimalarial treatments have reduced the malaria burden only modestly. An effective malaria vaccine remains a high priority, but its development has several challenges. Among many potential candidates, the RTS,S/AS01 vaccine (MosquirixTM) remains the leading candidate.

OBJECTIVE AND METHOD

This review aims to understand the advances in the RTS,S/AS01 vaccine, and future comments regarding the vaccine's effectiveness in malaria eradication. Literature review for the past five decades was performed searching PubMed, EMBASE Ovid, and Cochrane Library, with using the following search items: ("malaria" OR "WHO's malaria" OR "Plasmodium falciparum" OR "RTS,S" OR "RTS,S/AS01" OR "RTS,S/AS02" OR "pre-erythrocytic malaria" OR "circumsporozoite" OR "Mosquirix") AND ("vaccine" OR "vaccination").

RESULTS

RTS,S/AS01, a recombinant pre-erythrocytic vaccine containing Plasmodium falciparum surface-protein (circumsporozoite) antigen, is safe, well-tolerated, and immunogenic in children. Three doses, along with a booster, have a modest efficacy of about 36% in children (age 5-17 months) and about 26% in infants (age 6-12 weeks) against clinical malaria during a 48-month follow-up. However, the efficacy varies among population subgroups and with the parasite strain, it reduces without a booster and offers protection for a limited duration. Because of its potential cost-effectiveness and positive public health effect, the vaccine is being investigated in a pilot program for mortality benefits and broader deployment.

CONCLUSION

The RTS,S/AS01 vaccine prevents malaria; however, it should be considered another addition to the malaria-control program and not as an eradication tool because of its relatively low to modest efficacy.