Cryo-EM reveals the conformational epitope of human monoclonal antibody PAM1.4 broadly reacting with polymorphic malarial protein VAR2CSA

Assembly and performance of a cholera RDT prototype that detects both Vibrio cholerae and associated bacteriophage as a proxy for pathogen detection

Cholera rapid diagnostic tests (RDTs) are vulnerable to virulent bacteriophage predation. We hypothesized that an enhanced cholera RDT that detects the common virulent bacteriophage ICP1 might serve as a proxy for pathogen detection. We previously developed a monoclonal antibody (mAb) to the ICP1 major capsid protein. Our objective was to design and assemble a first-of-its-kind RDT that detects both a bacterial pathogen (Vibrio cholerae) and associated virulent bacteriophage (ICP1). Candidate mAbs were expanded to increase design options and evaluated by immunological assays (ELISA; western blot). A subset of mAbs were selected for gold conjugation and printing on the RDT. The detection limit of the prototype RDTs was determined in diarrheal stools with the addition of ICP1. Three mAb candidates were developed and evaluated for the capsid decoration protein (ORF123) and tail fiber protein (ORF93), and the prior mAb for the major capsid protein (ORF122). A single mAb sandwich RDT prototype for ORF122 was able to detect ICP1; RDTs with mAbs to ORF123 and ORF93 failed to detect ICP1 in single- or dual-sandwich configurations. Biologically relevant concentrations for ICP1 were detected only after boiling the stool with ICP1; analysis by electron microscopy (EM) suggested increased epitope availability after boiling. In this study, we demonstrate a proof of concept for a functional RDT that can detect both the primary pathogen and a common virulent bacteriophage as a proxy for pathogen detection. Further optimization is required before scaled production and implementation.IMPORTANCEThis paper represents an important step forward to address the vulnerability of cholera RDTs to the effects of phage predation on the target Vibrio cholerae. The assembly and evaluation of an RDT that detects both the primary pathogen and a phage as a proxy for the primary pathogen is an innovative solution. When optimized and evaluated in clinical studies, this tool may become critical in the cholera response tool kit as well as represent a diagnostic proof-of-concept for other infectious agents.

New Strides in Prevention of Malaria during Pregnancy Present Multitudinous Opportunities

Pregnant women are at a higher risk of developing complications from malaria, a mosquito-borne disease caused by Plasmodium parasites, resulting in considerable maternal and infant morbidity and mortality. Malaria in pregnancy causes unfavorable and life-threatening outcomes for both the mother and fetus not limited to maternal anemia, hypoglycaemia, cerebral malaria, pulmonary edema, and puerperal sepsis. WHO recommends wide-ranging strategies for this detrimental but preventable disease; however, numerous challenges persist in ensuring high uptake of preventive therapies, effective usage of insecticide-treated bed nets, and early initiation and optimal antenatal care coverage for pregnant women. This work distils recent global advances in preventive strategies for malaria in pregnancy. We discuss three mainstay interventions by WHO, viz. intermittent preventive treatment of malaria in pregnancy (IPTp), utilization and outcomes of insecticide-treated bed nets (ITNs), and headways in malaria case management using therapeutic drugs. We cover multitudinous facets of antenatal care, WHO-advised community-based delivery of IPTp (c-IPTp), intermittent screening and treatment for malaria in pregnancy (ISTp), a malaria vaccine for pregnant women, and auxiliary factors that are crucial for improving prevention outcomes. Despite the reduction in malaria globally, malaria in pregnancy remains a prevalent issue in endemic areas, which warrants strengthening of preventative strategies. This work attempts to consolidate pivotal observations of the prevention of malaria during pregnancy by highlighting key advances, priority areas, new opportunities, research gaps, and challenges that need to be addressed to ensure improved outcomes in pregnant women infected with malaria.

Malaria in Pregnancy, Current Challenges, and Emerging Prevention Strategies in a Warming Climate

Malaria still presents a grave threat to the health of pregnancies worldwide with prevention currently stalling as traditional control and prevention strategies are limited by both insecticide and drug resistance. Furthermore, climate change is bringing malaria to locations where it was once eradicated and intensifying malaria in other areas. Even where malaria is not currently common, obstetricians will need to understand the pathogenesis of the disease, how it is transmitted, methods for prevention and treatment in pregnancy, and promising emerging strategies such as vaccines. A renewed global response is needed for this age-old disease in which pregnancy poses specific susceptibility.

PfEMP1 and var genes - Still of key importance in Plasmodium falciparum malaria pathogenesis and immunity

The most severe form of malaria, caused by infection with Plasmodium falciparum parasites, continues to be an important cause of human suffering and poverty. The P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of clonally variant antigens, which mediates the adhesion of infected erythrocytes to the vascular endothelium in various tissues and organs, is a central component of the pathogenesis of the disease and a key target of the acquired immune response to malaria. Much new knowledge has accumulated since we published a systematic overview of the PfEMP1 family almost ten years ago. In this chapter, we therefore aim to summarize research progress since 2015 on the structure, function, regulation etc. of this key protein family of arguably the most important human parasite. Recent insights regarding PfEMP1-specific immune responses and PfEMP1-specific vaccination against malaria, as well as an outlook for the coming years are also covered.

Structure-guided design of VAR2CSA-based immunogens and a cocktail strategy for a placental malaria vaccine

Placental accumulation of Plasmodium falciparum infected erythrocytes results in maternal anemia, low birth weight, and pregnancy loss. The parasite protein VAR2CSA facilitates the accumulation of infected erythrocytes in the placenta through interaction with the host receptor chondroitin sulfate A (CSA). Antibodies that prevent the VAR2CSA-CSA interaction correlate with protection from placental malaria, and VAR2CSA is a high-priority placental malaria vaccine antigen. Here, structure-guided design leveraging the full-length structures of VAR2CSA produced a stable immunogen that retains the critical conserved functional elements of VAR2CSA. The design expressed with a six-fold greater yield than the full-length protein and elicited antibodies that prevent adhesion of infected erythrocytes to CSA. The reduced size and adaptability of the designed immunogen enable efficient production of multiple variants of VAR2CSA for use in a cocktail vaccination strategy to increase the breadth of protection. These designs form strong foundations for the development of potent broadly protective placental malaria vaccines.

A conformational epitope in placental malaria vaccine antigen VAR2CSA: What does it teach us?

VAR2CSA is the Plasmodium falciparum variant surface antigen that mediates binding of infected erythrocytes to chondroitin sulfate A (CSA) and their sequestration in intervillous spaces of the placenta, leading to placental malaria (PM). Relatively high polymorphism in VAR2CSA sequences has hindered development of a vaccine that induces broadly neutralizing immunity. Recent research has highlighted that a broadly reactive human monoclonal antibody, called PAM1.4, binds to multiple conserved residues of different subfragments of VAR2CSA, forming a conformational epitope. In this short perspective, we describe evidence that residues located in the interdomain-1 fragment of VAR2CSA within the PAM1.4 binding epitope might be critical to broad reactivity of the antibody. Future investigation into broadly reactive anti-VAR2CSA antibodies may be important for the following: (1) identification of similar conformation epitopes targeted by broadly neutralizing antibodies; and (2) understanding different immune evasion mechanisms used by placenta-binding parasites through VAR2CSA polymorphism in critical epitopes.