Unlocking the potential of novel RTS, S/AS01, and R21/Matrix-M™ malaria vaccines in African nations

Development of an Activity-Based Ratiometric Electrochemical Switch for Direct, Real-Time Sensing of Pantetheinase in Live Cells, Blood, and Urine Samples

Pantetheinase is a key biomarker for the diagnosis of acute kidney injury and the monitoring of malaria progression. Currently, existing methods for sensing pantetheinase, also known as Vanin-1, show considerable potential but come with certain limitations, including their inability to directly sense analytes in turbid biofluid samples without tedious sample pretreatment. Here, we describe the first activity-based electrochemical probe, termed VaninLP, for convenient and specific direct targeting of pantetheinase activity in turbid liquid biopsy samples. The probe was designed such that cleavage of the pantetheinase amide linkage, triggered by a self-immolative reaction, simultaneously ejects an amino ferrocene reporter. Among the distinctive properties of the VaninLP probe for sensing pantetheinase are its high selectivity, sensitivity, and enzyme affinity, a wide linear concentration range (8-300 ng/mL), and low limit of detection (2.47 ng/mL). The designed probe precisely targeted pantetheinase and was free of interference by other electroactive biological species. We further successfully applied the VaninLP probe to monitor and quantify the activity of pantetheinase on the surfaces of HepG2 tumor cells, blood, and urine samples. Collectively, our findings indicate that VaninLP holds significant promise as a point-of-care tool for diagnosing early-stage kidney injury, as well as monitoring the progression of malaria.

A Plasmodium late liver stage arresting GAP provides superior protection in mice

Liver-stage genetically attenuated malaria parasites (GAPs) are powerful immunogens that provide protection against sporozoite challenge. We previously generated two late liver-stage-arresting GAPs by deleting the stearoyl-CoA desaturase (Scd) or sporozoite conserved orthologous transcript 1 (Scot1) genes in Plasmodium berghei. Immunization with Scd or Scot1 GAP conferred complete protection against a sporozoite challenge. In a safety study, we observed rare breakthrough blood-stage infections in mice inoculated with high doses of sporozoites, indicating that both GAPs were incompletely attenuated. In this study, we generated a Scd/Scot1 GAP by dual gene deletion. This resulted in complete attenuation of the parasites in the liver and did not transition to blood-stage infection despite a high-dose sporozoite challenge. The Scd/Scot1 KO and WT GFP parasites were indistinguishable during blood, mosquito and early liver stage development. Moreover, Scd/Scot1 KO liver-stage schizonts exhibited an abnormal apicoplast biogenesis and nuclear division phenotype, failed to form hepatic merozoites, and exhibited late liver-stage arrest. Compared with early-arresting Speld KO immunization, late-stage liver-arresting Scd/Scot1 KO induces greater and broader CD8+ T-cell responses and elicits stage-transcending immunity that provides superior protection in C57BL/6 mice. These data prove that multiple gene deletions lead to complete attenuation of the parasite and support the development of late liver stage-arresting P. falciparum GAP.

Chemoprevention of malaria with long-acting oral and injectable drugs: an updated target product profile

Malaria is preventable, but the burden of disease remains high with over 249 million cases and 608,000 deaths reported in 2022. Historically, the most important protective interventions have been vector control and chemopreventive medicines with over 50 million children receiving seasonal malaria chemoprevention in the year 2023. Two vaccines are approved and starting to be deployed, bringing additional protection for children up to 36 months. However, the impact of these currently available tools is somewhat limited on various fronts. Vaccines exhibit partial efficacy, are relatively costly, and not accessible in all settings. The challenges encountered with chemoprevention are barriers to acceptability and feasibility, including frequency of dosing, and the lack of options in the first trimester of pregnancy and for women living with HIV. Also, the emergence of resistance against chemopreventive medicines is concerning. To address these limitations, a target product profile (TPP) is proposed as a road map to guide innovation and to boost the quest for novel chemopreventive alternatives. This TPP describes the ideal product attributes, while acknowledging potential trade-offs that may be needed. Critically, it considers the target populations most at risk; primarily infants, children, and pregnant women. Malaria control and elimination requires appropriate chemoprevention, not only in areas of high endemicity and transmission, but also in lower transmission areas where immunity is declining, as well as for travellers from areas where malaria has been eliminated. New medicines should show acceptable safety and tolerability, with high and long protective efficacy. Formulations and costs need to support operational adherence, access, and effectiveness. Next generation long-acting oral and injectable drugs are likely to constitute the backbone of malaria prevention. Therefore, the perspectives of front-line experts in malaria prevention, researchers, and those involved in drug development are captured in the TPP. This inclusive approach aims at concentrating efforts and aligning responses across the community to develop new and transformative medicines.

A new malaria vaccination tool based on replication-competent Plasmodium falciparum parasites

D. Moita and M. Prudêncio discuss the study by Goswami et al, in this issue of EMBO Mol. Med ., on the generation and pre-clinical characterization of late liver stage-arresting genetically attenuated Plasmodium parasites as a potential vaccine against malaria.

Design and Evaluation of Chimeric Plasmodium falciparum Circumsporozoite Protein-Based Malaria Vaccines

Efficacy data on two malaria vaccines, RTS,S and R21, targeting Plasmodium falciparum circumsporozoite protein (PfCSP), are encouraging. Efficacy may be improved by induction of additional antibodies to neutralizing epitopes outside of the central immunodominant repeat domain of PfCSP. We designed four rPfCSP-based vaccines in an effort to improve the diversity of the antibody response. We also evaluated P. falciparum merozoite surface protein 8 (PfMSP8) as a malaria-specific carrier protein as an alternative to hepatitis B surface antigen. We measured the magnitude, specificity, subclass, avidity, durability, and efficacy of vaccine-induced antibodies in outbred CD1 mice. In comparison to N-terminal- or C-terminal-focused constructs, immunization with near full-length vaccines, rPfCSP (#1) or the chimeric rPfCSP/8 (#2), markedly increased the breadth of B cell epitopes recognized covering the N-terminal domain, junctional region, and central repeat. Both rPfCSP (#1) and rPfCSP/8 (#2) also elicited a high proportion of antibodies to conformation-dependent epitopes in the C-terminus of PfCSP. Fusion of PfCSP to PfMSP8 shifted the specificity of the T cell response away from PfCSP toward PfMSP8 epitopes. Challenge studies with transgenic Plasmodium yoelii sporozoites expressing PfCSP demonstrated high and consistent sterile protection following rPfCSP/8 (#2) immunization. Of note, antibodies to conformational C-terminal epitopes were not required for protection. These results indicate that inclusion of the N-terminal domain of PfCSP can drive responses to protective, repeat, and non-repeat B cell epitopes and that PfMSP8 is an effective carrier for induction of high-titer, durable anti-PfCSP antibodies.