Rhea J. Longley

Invasion of erythrocytes by members of the Plasmodium genus is an essential step of the parasite lifecycle, orchestrated by numerous host-parasite interactions. In P. falciparum Rh5, with PfCyRPA, PfRipr, PfCSS, and PfPTRAMP, forms the essential PCRCR complex which binds basigin on the erythrocyte surface. Rh5 is restricted to P. falciparum and its close relatives; however, PTRAMP, CSS and Ripr orthologs are present across the Plasmodium genus. We investigated PTRAMP, CSS and Ripr orthologs from three species to elucidate common features of the complex. Like P. falciparum, PTRAMP and CSS form a disulfide-linked heterodimer in both P. vivax and P. knowlesi with all three species forming a complex (PCR) with Ripr by binding its C-terminal region. Cross-reactive antibodies targeting the PCR complex differentially inhibit merozoite invasion. Cryo-EM visualization of the P. knowlesi PCR complex confirmed predicted models and revealed a core invasion scaffold in Plasmodium spp. with implications for vaccines targeting multiple species of malaria-causing parasites.

Invasion of erythrocytes by members of the Plasmodium genus is an essential step of the parasite lifecycle, orchestrated by numerous host-parasite interactions. In P. falciparum Rh5, with PfCyRPA, PfRipr, PfCSS, and PfPTRAMP, forms the essential PCRCR complex which binds basigin on the erythrocyte surface. Rh5 is restricted to P. falciparum and its close relatives; however, PTRAMP, CSS and Ripr orthologs are present across the Plasmodium genus. We investigated PTRAMP, CSS and Ripr orthologs from three species to elucidate common features of the complex. Like P. falciparum, PTRAMP and CSS form a disulfide-linked heterodimer in both P. vivax and P. knowlesi with all three species forming a complex (PCR) with Ripr by binding its C-terminal region. Cross-reactive antibodies targeting the PCR complex differentially inhibit merozoite invasion. Cryo-EM visualization of the P. knowlesi PCR complex confirmed predicted models and revealed a core invasion scaffold in Plasmodium spp. with implications for vaccines targeting multiple species of malaria-causing parasites.

In this article, we discuss our experiences and perspectives in forming a workplace Parents Group. We reflect on the need for these networks, what has worked well, and the challenges we've experienced. We also provide some practical advice for those with parenting-related career disruptions for addressing this topic in grant applications.

Background: After decades of progress towards malaria elimination, Plasmodium vivax is now the predominant source of infection and the major obstacle towards elimination in the Asia-Pacific region. In the Philippines, the situation is slightly different with P. falciparum still accounting for the largest burden. However, there has been a steady increase in the total number of reported P. vivax cases in the main transmission hotspot of Palawan, as well as two years of consecutive outbreaks of P. vivax in the near-elimination setting of Sultan Kudarat. Here, we describe the protocol for a new study in Sultan Kudarat that aims to identify whether an underlying, hidden, burden of P. vivax contributes to the ongoing risk of outbreaks. Methods: A challenge for surveillance of P. vivax is the presence of an additional hidden liver-stage, where parasites (hypnozoites) lie dormant for weeks to months before causing a relapse of infection. Hypnozoites cannot be detected with commercial diagnostic tests. We have designed novel serological exposure markers of recent P. vivax infection, which indirectly inform on hypnozoite carriage. In this study we will conduct a prospective 18-month survey in health facilities within Kalamansig, Sultan Kudarat, and compare epidemiology and serological data with that in archival samples from Palawan. We will enroll both care-seeking individuals and their companions, and utilise remote geolocation to uncover spatial trends. Conclusions: This study will generate important data for the malaria control program in the Philippines whilst also demonstrating utility of P. vivax serological exposure markers in near-elimination settings. We will utilise this data to build a decision-making framework to support novel, evidence-based elimination strategies relevant for the Philippines and the wider Asia-Pacific region.

Plasmodium vivax is emerging as the most prevalent species causing malaria outside Africa. Most P. vivax infections are relapses due to the reactivation of the dormant liver stage parasites (hypnozoites). Hypnozoites are a major reservoir for transmission but undetectable by commercial diagnostic tests. Antibodies against P. vivax reticulocyte-binding protein 2b (PvRBP2b) are among the most reliable serological biomarkers for recent P. vivax infections in the prior 9 months and act as indirect biomarkers for risk of relapse. We sought to design stabilized variants of PvRBP2b, under stringent conditions of minimally perturbing the solvent-accessible surfaces to maintain its antigenicity profile. Furthermore, for some of the designs, due to limited diversity of natural PvRBP2b homologs, we combined AI-based ProteinMPNN and PROSS atomistic design calculations. The best, bearing 19 core mutations relative to PvRBP2b, expressed 16-fold greater amounts (up to 11 mg/l), and had 14 °C higher thermal tolerance than the parental protein. Critically, the stabilized designs retained binding to naturally acquired human mAbs with nanomolar affinities, suggesting that the immunologically competent surfaces were retained as was confirmed by crystallographic analyses. Using longitudinal observational cohorts from malaria endemic regions of Thailand, Brazil, and the Solomon Islands, we show that antibody responses against the designs are highly correlated with those against the parental protein and can classify individuals as recently infected with P. vivax. This efficient computational stability design methodology can be used to enhance the biophysical properties of other recalcitrant proteins for use as diagnostics or vaccine immunogens.