PRIMVAC vaccine adjuvanted with Alhydrogel or GLA-SE to prevent placental malaria: a first-in-human, randomised, double-blind, placebo-controlled study

Vaccine Adjuvants in the Immunocompromised Host: Science, Safety, and Efficacy

Vaccine adjuvants are essential for enhancing immune responses to vaccines, particularly in immunocompromised populations who typically demonstrate suboptimal responses to standard vaccination. This narrative review evaluates the safety and efficacy of approved and candidate adjuvants in immunocompromised hosts, with emphasis on solid organ and hematopoietic cell transplant recipients. We examine conventional aluminum-based adjuvants alongside modern adjuvant systems such as AS01B, MF59, and AS04, analyzing their mechanisms of action and clinical applications. The review synthesizes current evidence on the safety profiles of approved adjuvanted vaccines in immunocompromised individuals and explores emerging adjuvant candidates, including saponin complexes and toll-like receptor agonists. By examining factors that influence adjuvant immunogenicity and safety in these vulnerable populations, we identify critical knowledge gaps and future research priorities. This comprehensive analysis provides clinicians and researchers with an updated perspective on the rapidly evolving landscape of vaccine adjuvants and their specific applications in immunocompromised hosts.

A machine learning framework to identify complex physicochemical features of B cell epitopes

During infection with Plasmodium falciparum in pregnancy, parasites express a unique virulence factor, VAR2CSA, that mediates binding of infected red blood cells to the placenta. A major goal in designing vaccines to protect pregnant women from malaria is to elicit antibodies to VAR2CSA. The challenge is that VAR2CSA is highly polymorphic and identifying conserved epitopes is essential to elicit strain-transcending immunity. Unexpectedly, a mouse monoclonal antibody, 3D10, raised against the unrelated Duffy binding protein from P. vivax (DBPII) cross-reacts with diverse alleles of VAR2CSA in vitro. To identify these potentially conserved epitopes in VAR2CSA, we designed a machine learning framework to analyse 3D10 reactivity to peptides derived from two alleles of VAR2CSA, DBPII, and PvEBP2 (negative control). We used decision trees and a panel of 430 features to extract features correlated to 3D10 binding. We analysed patterns of these features in the dataset and designed mutant peptides to test complex sequence motifs. Features associated with 3D10 reactivity were mapped onto predicted 3D structures of Plasmodium proteins and validated based on 3D10 reactivity to the recombinant antigens. While the array data identified certain linear epitopes, the framework predicted other epitopes that are conformational. With this approach, peptide array data can be mined to extract physicochemical properties of epitopes recognized by polyreactive antibodies.

Evasive mechanisms of human VSG and PfEMP1 antigens with link to Vaccine scenario: a review

Recent fights on the control of trypanosomiasis and malaria focused on underscoring the concepts of antigen evasive mechanisms with the view to exploit the defensive mechanisms inherent in VSG and PfEMP1, although giant strides is being achieved towards beating the antigenic propensity of malaria parasites. Trypanosoma and Plasmodium falciparum adopt a common antigenic novelty through alternate expression of VSG and PfEMP1 respectively. These immunodominant antigens sterically shield other surface proteins from host antibodies and unvaryingly turn out to be the requisite elements with difficult underlining immunological concept for unmatched escape mechanisms of vaccine actions. Hence, the uncommon role of the pathogens to brazenly circumnavigate immunity through switching of variant antigens has not kept pace. Switching of variant surface in human trypanosomes occurs through programmed DNA rearrangements while in P. falciparum, switching occurs by purely transcriptional mechanism. The repertoire genes harmonize evasion of human immunity and also rekindle the outcome of infections. The extensive sequence divergence and genetic polymorphism of VSG and PfEMP1 are the requisite elements for the next generation breakthrough in vaccine discoveries. Thus, the springboard for the development of novel targets is lurking with the wit of unraveling the immunological concepts underlining the evasive aptitude of VSG and PfEMP1 with convincing biochemical techniques, hence offering a blueprint for enhanced vaccine targets. This review elucidates evasive mechanisms of VSG and PfEMP1 with link to pathologies, challenges of antigenic switches and prospects to current vaccine scenario.

Acquisition of Fc-afucosylation of PfEMP1-specific IgG is age-dependent and associated with clinical protection against malaria

Protective immunity to malaria depends on acquisition of parasite-specific antibodies, with Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) being one of the most important target antigens. The effector functions of PfEMP1-specific IgG include inhibition of infected erythrocyte (IE) sequestration and opsonization of IEs for cell-mediated destruction. IgG glycosylation modulates antibody functionality, with increased affinity to FcγRIIIa for IgG lacking fucose in the Fc region (Fc-afucosylation). We report here that selective Fc-afucosylation of PfEMP1-specific IgG1 increases with age in P. falciparum-exposed children and is associated with reduced risk of anemia, independent of the IgG levels. A similar association was found for children having PfEMP1-specific IgG1 inducing multiple effector functions against IEs, particularly those associated with antibody-dependent cellular cytotoxicity (ADCC) by NK cells. Our findings provide new insights regarding protective immunity to P. falciparum malaria and highlight the importance of cell-mediated destruction of IgG-opsonized IEs.

Malaria vaccines: a new era of prevention and control

Malaria killed over 600,000 people in 2022, a death toll that has not improved since 2015. Additionally, parasites and mosquitoes resistant to existing interventions are spreading across Africa and other regions. Vaccines offer hope to reduce the mortality burden: the first licensed malaria vaccines, RTS,S and R21, will be widely deployed in 2024 and should substantially reduce childhood deaths. In this Review, we provide an overview of the malaria problem and the Plasmodium parasite, then describe the RTS,S and R21 vaccines (the first vaccines for any human parasitic disease), summarizing their benefits and limitations. We explore next-generation vaccines designed using new knowledge of malaria pathogenesis and protective immunity, which incorporate antigens and platforms to elicit effective immune responses against different parasite stages in human or mosquito hosts. We describe a decision-making process that prioritizes malaria vaccine candidates for development in a resource-constrained environment. Future vaccines might improve upon the protective efficacy of RTS,S or R21 for children, or address the wider malaria scourge by preventing pregnancy malaria, reducing the burden of Plasmodium vivax or accelerating malaria elimination.

Safety and efficacy of PfSPZ Vaccine against malaria in healthy adults and women anticipating pregnancy in Mali: two randomised, double-blind, placebo-controlled, phase 1 and 2 trials

BACKGROUND

Plasmodium falciparum parasitaemia during pregnancy causes maternal, fetal, and infant mortality. Poor pregnancy outcomes are related to blood-stage parasite sequestration and the ensuing inflammatory response in the placenta, which decreases over successive pregnancies. A radiation-attenuated, non-replicating, whole-organism vaccine based on P falciparum sporozoites (PfSPZ Vaccine) has shown efficacy at preventing infection in African adults. Here, we aimed to examine vaccine safety and efficacy of the PfSPZ Vaccine in adults and women who anticipated conception.

METHODS

Two randomised, double-blind, placebo-controlled trials (phase 1 MLSPZV3 and phase 2 MLSPZV4) were conducted at a clinical research centre in Mali. MLSPZV3 included adults aged 18-35 years and MLSPZV4 included non-pregnant women aged 18-38 years who anticipated conception within a year of enrolment. In MLSPZV3, participants were stratified by village and randomly assigned (2:1) using block randomisation to receive three doses of 9 × 105 PfSPZ Vaccine or saline placebo at weeks 0, 1, and 4 (4-week schedule) or at weeks 0, 8, and 16 (16-week schedule) and a booster dose around 1 year later. In MLSPZV4, women received presumptive artemether-lumefantrine twice per day for 3 days 2 weeks before dose one and were randomly assigned (1:1:1) using block randomisation to receive three doses of 9 × 105 or 1·8 × 106 PfSPZ Vaccine or saline placebo all administered at weeks 0, 1, and 4 (4-week schedule). Participants in both studies received artemether-lumefantrine 2 weeks before dose three and additionally 2 weeks before dose four (booster dose) in MLSPZV3. Investigators and participants were masked to group assignment. The primary outcome, assessed in the as-treated population, was PfSPZ Vaccine safety and tolerability within 7 days after each dose. The secondary outcome, assessed in the modified intention-to-treat population, was vaccine efficacy against P falciparum parasitaemia (defined as the time-to-first positive blood smear) from dose three until the end of transmission season. In exploratory analyses, MLSPZV4 evaluated incidence of maternal obstetric and neonatal outcomes as safety outcomes, and vaccine efficacy against P falciparum parasitaemia during pregnancy (defined as time-to-first positive blood smear post-conception). In MLSPZV4, women were followed at least once a month with human chorionic gonadotropin testing, and those who became pregnant received standard of care (including intermittent presumptive sulfadoxine-pyrimethamine antimalarial drugs after the first trimester) during routine antenatal visits. These studies are registered with ClinicalTrials.gov, NCT03510481 and NCT03989102.

FINDINGS

Participants were enrolled for vaccination during the onset of malaria seasons for two sequential studies conducted from 2018 to 2019 for MLSPZV3 and from 2019 to 2021 for MLSPZV4, with follow-up during malaria seasons across 2 years. In MLSPZV3, 478 adults were assessed for eligibility, of whom 220 were enrolled between May 30 and June 12, 2018, and then between Aug 13 and Aug 18, 2018, and 210 received dose one. 66 (96%) of 69 participants who received the 16-week schedule and 68 (97%) of 70 who received the 4-week schedule of the 9 × 105 PfSPZ Vaccine and 70 (99%) of 71 who received saline completed all three doses in year 1. In MLSPZV4, 407 women were assessed for eligibility, of whom 324 were enrolled from July 3 to July 27, 2019, and 320 received dose one of presumptive artemether-lumefantrine. 300 women were randomly assigned with 100 per group (PfSPZ Vaccine 9 × 105, 1·8 × 106, or saline) receiving dose one. First trimester miscarriages were the most commonly reported serious adverse event but occurred at a similar rate across study groups (eight [15%] of 54 with 9 × 105 PfSPZ Vaccine, 12 [21%] of 58 with 1·8 × 106 PfSPZ Vaccine, and five [12%] of 43 with saline). One unrelated maternal death occurred 425 days after the last vaccine dose in the 1·8 × 106 PfSPZ Vaccine group due to peritonitis shortly after childbirth. Most related adverse events reported in MLSPZV3 and MLSPZV4 were mild (grade 1) and frequency of adverse events in the PfSPZ Vaccine groups did not differ from that in the saline group. Two unrelated serious adverse events occurred in MLSPZV3 (one participant had appendicitis in the 9 × 105 PfSPZ Vaccine group and the other in the saline group died due to a road traffic accident). In MLSPZV3, the 9 × 105 PfSPZ Vaccine did not show vaccine efficacy against parasitaemia with the 4-week (27% [95% CI -18 to 55] in year 1 and 42% [-5 to 68] in year 2) and 16-week schedules (16% [-34 to 48] in year 1 and -14% [-95 to 33] in year 2); efficacies were similar or worse against clinical malaria compared with saline. In MLSPZV4, the PfSPZ Vaccine showed significant efficacy against parasitaemia at doses 9 × 105 (41% [15 to 59]; p=0·0069 in year 1 and 61% [36 to 77]; p=0·0011 in year 2) and 1·8 × 106 (54% [34 to 69]; p<0·0001 in year 1 and 45% [13 to 65]; p=0·029 in year 2); and against clinical malaria at doses 9 × 105 (47% [20 to 65]; p=0·0045 in year 1 and 56% [22 to 75]; p=0·0081 in year 2) and 1·8 × 106 (48% [22 to 65]; p=0·0013 in year 1 and 40% [2 to 64]; p=0·069 in year 2). Vaccine efficacy against post-conception P falciparum parasitaemia during first pregnancies that arose in the 2-year follow-up was 57% (14 to 78; p=0·017) in the 9 × 105 PfSPZ Vaccine group versus 49% (3 to 73; p=0·042) in the 1·8 × 106 PfSPZ Vaccine group. Among 55 women who became pregnant within 24 weeks after dose three, vaccine efficacy against parasitaemia was 65% (23 to 84; p=0·0088) with the 9 × 105 PfSPZ Vaccine and 86% (64 to 94; p<0·0001) with the 1·8 × 106 PfSPZ Vaccine. When combined in a post-hoc analysis, women in the PfSPZ Vaccine groups had a non-significantly reduced time-to-first pregnancy after dose one compared with those in the saline group (log-rank test p=0·056). Exploratory maternal obstetric and neonatal outcomes did not differ significantly between vaccine groups and saline.

INTERPRETATION

PfSPZ Vaccine was safe and well tolerated in adults in Mali. The 9 × 105 and 1·8 × 106 doses of PfSPZ Vaccine administered as per the 4-week schedule, which incorporated presumptive antimalarial treatment before the first vaccine dose, showed significant efficacy against P falciparum parasitaemia and clinical malaria for two malaria transmission seasons in women of childbearing age and against pregnancy malaria. PfSPZ Vaccine without presumptive antimalarial treatment before the first vaccine dose did not show efficacy.

FUNDING

National Institute of Allergy and Infectious Diseases, National Institutes of Health, and Sanaria.

Fc-Afucosylation of VAR2CSA-Specific Immunoglobulin G and Clinical Immunity to Placental Plasmodium falciparum Malaria

BACKGROUND

Acquired immunity to Plasmodium falciparum malaria is mainly mediated by immunoglobulin G (IgG) targeting erythrocyte membrane protein 1 (PfEMP1). These adhesins mediate infected erythrocyte (IE) sequestration, protecting IEs from splenic destruction. PfEMP1-specific IgG is therefore thought to protect mainly by inhibiting IE sequestration. VAR2CSA-type PfEMP1 mediates placental IE sequestration, putting pregnant women exposed to P falciparum parasites at risk of placental malaria (PM).

METHODS

Levels and Fc-afucosylation of VAR2CSA-specific plasma IgG were measured by a modified enzyme-linked immunosorbent assay (FEASI). We also measured the ability of the IgG to inhibit IE adhesion and to induce natural killer (NK) cell degranulation. The results were related to parity and clinical pregnancy outcomes.

RESULTS

Parity was positively correlated with levels and Fc-afucosylation of VAR2CSA-specific IgG, and with birth weight and plasma IgG inhibition of IE adhesion in vitro. Fc-afucosylation of VAR2CSA-specific IgG increased NK-cell degranulation. Women with Fc-afucosylated VAR2CSA-specific IgG had a reduced risk of delivering a low birth weight (LBW) baby, but not of PM or anemia.

CONCLUSIONS

Fc-afucosylated VAR2CSA-specific IgG effectively induced NK-cell degranulation and was associated with protection against LBW, independent of IgG levels. Our study has implications for the development of VAR2CSA-based subunit vaccines, which exclusively induce Fc-fucosylated IgG.

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.

Prokaryote- and Eukaryote-Based Expression Systems: Advances in Post-Pandemic Viral Antigen Production for Vaccines

This review addresses the ongoing global challenge posed by emerging and evolving viral diseases, underscoring the need for innovative vaccine development strategies. It focuses on the modern approaches to creating vaccines based on recombinant proteins produced in different expression systems, including bacteria, yeast, plants, insects, and mammals. This review analyses the advantages, limitations, and applications of these expression systems for producing vaccine antigens, as well as strategies for designing safer, more effective, and potentially 'universal' antigens. The review discusses the development of vaccines for a range of viral diseases, excluding SARS-CoV-2, which has already been extensively studied. The authors present these findings with the aim of contributing to ongoing research and advancing the development of antiviral vaccines.

Co-regulation of innate and adaptive immune responses induced by ID93+GLA-SE vaccination in humans

Introduction

Development of an effective vaccine against tuberculosis is a critical step towards reducing the global burden of disease. A therapeutic vaccine might also reduce the high rate of TB recurrence and help address the challenges of drug-resistant strains. ID93+GLA-SE is a candidate subunit vaccine that will soon be evaluated in a phase 2b efficacy trial for prevention of recurrent TB among patients undergoing TB treatment. ID93+GLA-SE vaccination was shown to elicit robust CD4+ T cell and IgG antibody responses among recently treated TB patients in the TBVPX-203 Phase 2a study (NCT02465216), but the mechanisms underlying these responses are not well understood.

Methods

In this study we used specimens from TBVPX-203 participants to describe the changes in peripheral blood gene expression that occur after ID93+GLA-SE vaccination.

Results

Analyses revealed several distinct modules of co-varying genes that were either up- or down-regulated after vaccination, including genes associated with innate immune pathways at 3 days post-vaccination and genes associated with lymphocyte expansion and B cell activation at 7 days post-vaccination. Notably, the regulation of these gene modules was affected by the dose schedule and by participant sex, and early innate gene signatures were correlated with the ID93-specific CD4+ T cell response.

Discussion

The results provide insight into the complex interplay of the innate and adaptive arms of the immune system in developing responses to vaccination with ID93+GLA-SE and demonstrate how dosing and schedule can affect vaccine responses.

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.

Cytokine profile of anti-spike CD4+T cells predicts humoral and CD8+T cell responses after anti-SARS-CoV-2 mRNA vaccination

Coordinating immune responses - humoral and cellular - is vital for protection against severe Covid-19. Our study evaluates a multicytokine CD4+T cell signature's predictive for post-vaccinal serological and CD8+T cell responses. A cytokine signature composed of four cytokines (IL-2, TNF-α, IP10, IL-9) excluding IFN-γ, and generated through machine learning, effectively predicted the CD8+T cell response following mRNA-1273 or BNT162b2 vaccine administration. Its applicability extends to murine vaccination models, encompassing diverse immunization routes (such as intranasal) and vaccine platforms (including adjuvanted proteins). Notably, we found correlation between CD4+T lymphocyte-produced IL-21 and the humoral response. Consequently, we propose a test that offers a rapid overview of integrated immune responses. This approach holds particular relevance for scenarios involving immunocompromised patients because they often have low cell counts (lymphopenia) or pandemics. This study also underscores the pivotal role of CD4+T cells during a vaccine response and highlights their value in vaccine immunomonitoring.

Vaccines and monoclonal antibodies: new tools for malaria control

SUMMARYMalaria remains one of the biggest health problems in the world. While significant reductions in malaria morbidity and mortality had been achieved from 2000 to 2015, the favorable trend has stalled, rather significant increases in malaria cases are seen in multiple areas. In 2022, there were 249 million estimated cases, and 608,000 malaria-related deaths, mostly in infants and children aged under 5 years, globally. Therefore, in addition to the expansion of existing anti-malarial control measures, it is critical to develop new tools, such as vaccines and monoclonal antibodies (mAbs), to fight malaria. In the last 2 years, the first and second malaria vaccines, both targeting Plasmodium falciparum circumsporozoite proteins (PfCSP), have been recommended by the World Health Organization to prevent P. falciparum malaria in children living in moderate to high transmission areas. While the approval of the two malaria vaccines is a considerable milestone in vaccine development, they have much room for improvement in efficacy and durability. In addition to the two approved vaccines, recent clinical trials with mAbs against PfCSP, blood-stage vaccines against P. falciparum or P. vivax, and transmission-blocking vaccine or mAb against P. falciparum have shown promising results. This review summarizes the development of the anti-PfCSP vaccines and mAbs, and recent topics in the blood- and transmission-blocking-stage vaccine candidates and mAbs. We further discuss issues of the current vaccines and the directions for the development of next-generation vaccines.

How to Accelerate Early Stage of Malaria Vaccine Development by Optimizing Functional Assays

While two Plasmodium falciparum circumsporozoite protein-based pre-erythrocytic vaccines (PEV), RTS,S and R21, have been approved by the WHO, no blood-stage vaccine (BSV) or transmission-blocking vaccine (TBV) has reached a phase 3 trial. One of the major obstacles that slows down malaria vaccine development is the shortage (or lack) of in vitro assays or animal models by which investigators can reasonably select the best vaccine formulation (e.g., antigen, adjuvant, or platform) and/or immunization strategy (e.g., interval of inoculation or route of immunization) before a human phase 2 trial. In the case of PEV, RTS,S and R21 have set a benchmark, and a new vaccine can be compared with (one of) the approved PEV directly in preclinical or early clinical studies. However, such an approach cannot be utilized for BSV or TBV development at this moment. The focus of this review is in vitro assays or in vivo models that can be used for P. falciparum BSV or TBV development, and I discuss important considerations during assay selection, standardization, qualification, validation, and interpretation of the assay results. Establishment of a robust assay/model with proper interpretation of the results is the one of key elements to accelerate future vaccine development.

Antibody response to malaria vaccine candidates in pregnant women with Plasmodium falciparum and Schistosoma haematobium infections

Malaria in pregnancy has severe consequences for the mother and foetus. Antibody response to specific malaria vaccine candidates (MVC) has been associated with a decreased risk of clinical malaria and its outcomes. We studied Plasmodium falciparum (Pf) and Schistosoma haematobium (Sh) infections and factors that could influence antibody responses to MVC in pregnant women. A total of 337 pregnant women receiving antenatal care (ANC) and 139 for delivery participated in this study. Pf infection was detected by qPCR and Sh infection using urine filtration method. Antibody levels against CSP, AMA-1, GLURP-R0, VAR2CSA and Pfs48/45 MVC were quantified by ELISA. Multivariable linear regression models identified factors associated with the modulation of antibody responses. The prevalence of Pf and Sh infections was 27% and 4% at ANC and 7% and 4% at delivery. Pf infection, residing in Adidome and multigravidae were positively associated with specific IgG response to CSP, AMA-1, GLURP-R0 and VAR2CSA. ITN use and IPTp were negatively associated with specific IgG response to GLURP-R0 and Pfs48/45. There was no association between Sh infection and antibody response to MVC at ANC or delivery. Pf infections in pregnant women were positively associated with antibody response to CSP, GLURP-R0 and AMA-1. Antibody response to GLURP-R0 and Pfs48/45 was low for IPTp and ITN users. This could indicate a lower exposure to Pf infection and low malaria prevalence observed at delivery.

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.

Mechanical forces control the valency of the malaria adhesin VAR2CSA by exposing cryptic glycan binding sites

Plasmodium falciparum (Pf) is responsible for the most lethal form of malaria. VAR2CSA is an adhesin protein expressed by this parasite at the membrane of infected erythrocytes for attachment to the placenta, leading to pregnancy-associated malaria. VAR2CSA is a large 355 kDa multidomain protein composed of nine extracellular domains, a transmembrane helix, and an intracellular domain. VAR2CSA binds to Chondroitin Sulphate A (CSA) of the proteoglycan matrix of the placenta. Shear flow, as the one occurring in blood, has been shown to enhance the (VAR2CSA-mediated) adhesion of Pf-infected erythrocytes on the CSA-matrix. However, the underlying molecular mechanism governing this enhancement has remained elusive. Here, we address this question by using equilibrium, force-probe, and docking-based molecular dynamics simulations. We subjected the VAR2CSA protein-CSA sugar complex to a force mimicking the tensile force exerted on this system due to the shear of the flowing blood. We show that upon this force exertion, VAR2CSA undergoes a large opening conformational transition before the CSA sugar chain dissociates from its main binding site. This preferential order of events is caused by the orientation of the molecule during elongation, as well as the strong electrostatic attraction of the sugar to the main protein binding site. Upon opening, two additional cryptic CSA binding sites get exposed and a functional dodecameric CSA molecule can be stably accommodated at these force-exposed positions. Thus, our results suggest that mechanical forces increase the avidity of VAR2CSA by turning it from a monovalent to a multivalent state. We propose this to be the molecular cause of the observed shear-enhanced adherence. Mechanical control of the valency of VAR2CSA is an intriguing hypothesis that can be tested experimentally and which is of relevance for the understanding of the malaria infection and for the development of anti placental-malaria vaccines targeting VAR2CSA.

Aotus nancymaae model predicts human immune response to the placental malaria vaccine candidate VAR2CSA

Placental malaria vaccines (PMVs) are being developed to prevent severe sequelae of placental malaria (PM) in pregnant women and their offspring. The leading candidate vaccine antigen VAR2CSA mediates parasite binding to placental receptor chondroitin sulfate A (CSA). Despite promising results in small animal studies, recent human trials of the first two PMV candidates (PAMVAC and PRIMVAC) generated limited cross-reactivity and cross-inhibitory activity to heterologous parasites. Here we immunized Aotus nancymaae monkeys with three PMV candidates (PAMVAC, PRIMVAC and ID1-ID2a_M1010) adjuvanted with Alhydrogel, and exploited the model to investigate boosting of functional vaccine responses during PM episodes as well as with nanoparticle antigens. PMV candidates induced high levels of antigen-specific IgG with significant cross-reactivity across PMV antigens by enzyme-linked immunosorbent assay. Conversely, PMV antibodies recognized native VAR2CSA and blocked CSA adhesion of only homologous parasites and not of heterologous parasites. PM episodes did not significantly boost VAR2CSA antibody levels or serum functional activity; nanoparticle and monomer antigens alike boosted serum reactivity but not functional activities. Overall, PMV candidates induced functional antibodies with limited heterologous activity in Aotus monkeys, similar to responses reported in humans. The Aotus model appears suitable for preclinical downselection of PMV candidates and assessment of antibody boosting by PM episodes.

Pathogenicity and virulence of malaria: Sticky problems and tricky solutions

Infections with Plasmodium falciparum and Plasmodium vivax cause over 600,000 deaths each year, concentrated in Africa and in young children, but much of the world's population remain at risk of infection. In this article, we review the latest developments in the immunogenicity and pathogenesis of malaria, with a particular focus on P. falciparum, the leading malaria killer. Pathogenic factors include parasite-derived toxins and variant surface antigens on infected erythrocytes that mediate sequestration in the deep vasculature. Host response to parasite toxins and to variant antigens is an important determinant of disease severity. Understanding how parasites sequester, and how antibody to variant antigens could prevent sequestration, may lead to new approaches to treat and prevent disease. Difficulties in malaria diagnosis, drug resistance, and specific challenges of treating P. vivax pose challenges to malaria elimination, but vaccines and other preventive strategies may offer improved disease control.

Hiding in plain sight: an epitope-based strategy for a subunit malaria vaccine

Recent data suggest that approaches to developing a subunit blood-stage malaria vaccine may be misdirected. While antigenic polymorphism is recognized as a challenge, efforts to counter this have primarily involved enhancing the quantity and quality of antibody with potent adjuvants, identifying conserved target proteins, or combining multiple antigens to broaden the immune response. However, paradoxically, evidence has emerged that narrowing, rather than broadening, the immune response may be required to obtain an immune response protective against multiple Plasmodium strains. Non-immunodominant, conserved epitopes are crucial. The evidence comes from studying the immune response to red cell surface-expressed antigens but should also be applicable to merozoite surface antigens. Strategies to define the targets of these highly focused immune responses are provided.

Malaria Vaccines: Progress to Date

Malaria is a mosquito-borne disease caused by protozoan parasites of the genus Plasmodium. Despite significant declines in malaria-attributable morbidity and mortality over the last two decades, it remains a major public health burden in many countries. This underscores the critical need for improved strategies to prevent, treat and control malaria if we are to ultimately progress towards the eradication of this disease. Ideally, this will include the development and deployment of a highly effective malaria vaccine that is able to induce long-lasting protective immunity. There are many malaria vaccine candidates in development, with more than a dozen of these in clinical development. RTS,S/AS01 (also known as Mosquirix) is the most advanced malaria vaccine and was shown to have modest efficacy against clinical malaria in phase III trials in 5- to 17-month-old infants. Following pilot implementation trials, the World Health Organisation has recommended it for use in Africa in young children who are most at risk of infection with P. falciparum, the deadliest of the human malaria parasites. It is well recognised that more effective malaria vaccines are needed. In this review, we discuss malaria vaccine candidates that have progressed into clinical evaluation and highlight the most advanced candidates: Sanaria's irradiated sporozoite vaccine (PfSPZ Vaccine), the chemoattenuated sporozoite vaccine (PfSPZ-CVac), RTS,S/AS01 and the novel malaria vaccine candidate, R21, which displayed promising, high-level efficacy in a recent small phase IIb trial in Africa.

Associations between prenatal malaria exposure, maternal antibodies at birth, and malaria susceptibility during the first year of life in Burkina Faso

In this study, we investigated how different categories of prenatal malaria exposure (PME) influence levels of maternal antibodies in cord blood samples and the subsequent risk of malaria in early childhood in a birth cohort study (N = 661) nested within the COSMIC clinical trial (NCT01941264) in Burkina Faso. Plasmodium falciparum infections during pregnancy and infants' clinical malaria episodes detected during the first year of life were recorded. The levels of maternal IgG and IgG1-4 to 15 P. falciparum antigens were measured in cord blood by quantitative suspension array technology. Results showed a significant variation in the magnitude of maternal antibody levels in cord blood, depending on the PME category, with past placental malaria (PM) more frequently associated with significant increases of IgG and/or subclass levels across three groups of antigens defined as pre-erythrocytic, erythrocytic, and markers of PM, as compared to those from the cord of non-exposed control infants. High levels of antibodies to certain erythrocytic antigens (i.e., IgG to EBA140 and EBA175, IgG1 to EBA175 and MSP142, and IgG3 to EBA140 and MSP5) were independent predictors of protection from clinical malaria during the first year of life. By contrast, high levels of IgG, IgG1, and IgG2 to the VAR2CSA DBL1-2 and IgG4 to DBL3-4 were significantly associated with an increased risk of clinical malaria. These findings indicate that PME categories have different effects on the levels of maternal-derived antibodies to malaria antigens in children at birth, and this might drive heterogeneity to clinical malaria susceptibility in early childhood.

Advancements and Challenges in Developing Malaria Vaccines: Targeting Multiple Stages of the Parasite Life Cycle

Malaria, caused by Plasmodium species, remains a major global health concern, causing millions of deaths annually. While the introduction of the RTS,S vaccine has shown promise, there is a pressing need for more effective vaccines due to the emergence of drug-resistant parasites and insecticide-resistant vectors. However, the complex life cycle and genetic diversity of the parasite, technical obstacles, limited funding, and the impact of the 2019 pandemic have hindered progress in malaria vaccine development. This review focuses on advancements in malaria vaccine development, particularly the ongoing clinical trials targeting antigens from different stages of the Plasmodium life cycle. Additionally, we discuss the rationale, strategies, and challenges associated with vaccine design, aiming to enhance the immune response and protective efficacy of vaccine candidates. A cost-effective and multistage vaccine could hold the key to controlling and eradicating malaria.

Malaria-specific Type 1 regulatory T cells are more abundant in first pregnancies and associated with placental malaria

BACKGROUND

Malaria in pregnancy (MIP) causes higher morbidity in primigravid compared to multigravid women; however, the correlates and mechanisms underlying this gravidity-dependent protection remain incompletely understood. We aimed to compare the cellular immune response between primigravid and multigravid women living in a malaria-endemic region and assess for correlates of protection against MIP.

METHODS

We characterised the second trimester cellular immune response among 203 primigravid and multigravid pregnant women enrolled in two clinical trials of chemoprevention in eastern Uganda, utilizing RNA sequencing, flow cytometry, and functional assays. We compared responses across gravidity and determined associations with parasitaemia during pregnancy and placental malaria.

FINDINGS

Using whole blood RNA sequencing, no significant differentially expressed genes were identified between primigravid (n = 12) and multigravid (n = 11) women overall (log 2(FC) > 2, FDR < 0.1). However, primigravid (n = 49) women had higher percentages of malaria-specific, non-naïve CD4+ T cells that co-expressed IL-10 and IFNγ compared with multigravid (n = 85) women (p = 0.000023), and higher percentages of these CD4+ T cells were associated with greater risks of parasitaemia in pregnancy (Rs = 0.49, p = 0.001) and placental malaria (p = 0.0073). These IL-10 and IFNγ co-producing CD4+ T cells had a genomic signature of Tr1 cells, including expression of transcription factors cMAF and BATF and cell surface makers CTLA4 and LAG-3.

INTERPRETATION

Malaria-specific Tr1 cells were highly prevalent in primigravid Ugandan women, and their presence correlated with a higher risk of malaria in pregnancy. Understanding whether suppression of Tr1 cells plays a role in naturally acquired gravidity-dependent immunity may aid the development of new vaccines or treatments for MIP.

FUNDING

This work was funded by NIH (PO1 HD059454, U01 AI141308, U19 AI089674, U01 AI155325, U01 AI150741), the March of Dimes (Basil O'Connor award), and the Bill and Melinda Gates Foundation (OPP 1113682).

A conserved epitope in VAR2CSA is targeted by a cross-reactive antibody originating from Plasmodium vivax Duffy binding protein

During Plasmodium falciparum infection in pregnancy, VAR2CSA is expressed on the surface of infected erythrocytes (IEs) and mediates their sequestration in the placenta. As a result, antibodies to VAR2CSA are largely restricted to women who were infected during pregnancy. However, we discovered that VAR2CSA antibodies can also be elicited by P. vivax Duffy binding protein (PvDBP). We proposed that infection with P. vivax in non-pregnant individuals can generate antibodies that cross-react with VAR2CSA. To better understand the specificity of these antibodies, we took advantage of a mouse monoclonal antibody (3D10) raised against PvDBP that cross-reacts with VAR2CSA and identified the epitopes targeted by this antibody. We screened two peptide arrays that span the ectodomain of VAR2CSA from the FCR3 and NF54 alleles. Based on the top epitope recognized by 3D10, we designed a 34-amino acid synthetic peptide, which we call CRP1, that maps to a highly conserved region in DBL3X. Specific lysine residues are critical for 3D10 recognition, and these same amino acids are within a previously defined chondroitin sulfate A (CSA) binding site in DBL3X. We showed by isothermal titration calorimetry that the CRP1 peptide can bind directly to CSA, and antibodies to CRP1 raised in rats significantly blocked the binding of IEs to CSA in vitro. In our Colombian cohorts of pregnant and non-pregnant individuals, at least 45% were seroreactive to CRP1. Antibody reactivities to CRP1 and the 3D10 natural epitope in PvDBP region II, subdomain 1 (SD1), were strongly correlated in both cohorts. These findings suggest that antibodies arising from PvDBP may cross-react with VAR2CSA through the epitope in CRP1 and that CRP1 could be a potential vaccine candidate to target a distinct CSA binding site in VAR2CSA.

The glycobiology of plasmodium falciparum: New approaches and recent advances

Like any other microorganism, pathogenic protozoan parasites rely heavily on glycoconjugates and glycan binding proteins to protect themselves from the environment and to interact with their diverse hosts. A thorough comprehension of how glycobiology contributes to the survival and virulence of these organisms may reveal unknown aspects of their biology and may open much needed avenues for the design of new strategies against them. In the case of Plasmodium falciparum, which causes the vast majority of malaria cases and deaths, the restricted variety and the simplicity of its glycans seemed to confer limited significance to the role played by glycoconjugates in the parasite. Nonetheless, the last 10 to 15 years of research are revealing a clearer and more defined picture. Thus, the use of new experimental techniques and the results obtained provide new avenues for understanding the biology of the parasite, as well as opportunities for the development of much required new tools against malaria.

Safety and Immunogenicity of the ID93 + GLA-SE Tuberculosis Vaccine in BCG-Vaccinated Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Phase 2 Trial

INTRODUCTION

This randomized, double-blind, placebo-controlled, phase 2a trial was conducted to evaluate the safety and immunogenicity of the ID93 + glucopyranosyl lipid adjuvant (GLA)-stable emulsion (SE) vaccine in human immunodeficiency virus (HIV)-negative, previously Bacillus Calmette-Guérin (BCG)-vaccinated, and QuantiFERON-TB-negative healthy adults in South Korea.

METHODS

Adults (n = 107) with no signs or symptoms of tuberculosis were randomly assigned to receive three intramuscular injections of 2 μg ID93 + 5 μg GLA-SE, 10 μg ID93 + 5 μg GLA-SE, or 0.9% normal saline placebo on days 0, 28, and 56. For safety assessment, data on solicited adverse events (AEs), unsolicited AEs, serious AEs (SAEs), and special interest AEs were collected. Antigen-specific antibody responses were measured using serum enzyme-linked immunosorbent assay. T-cell immune responses were measured using enzyme-linked immunospot and intracellular cytokine staining.

RESULTS

No SAEs, deaths, or AEs leading to treatment discontinuation were found. The solicited local and systemic AEs observed were consistent with those previously reported. Compared with adults administered with the placebo, those administered with three intramuscular vaccine injections exhibited significantly higher antigen-specific antibody levels and Type 1 T-helper cellular immune responses.

CONCLUSION

The ID93 + GLA-SE vaccine induced antigen-specific cellular and humoral immune responses, with an acceptable safety profile in previously healthy, BCG-vaccinated, Mycobacterium tuberculosis-uninfected adult healthcare workers.

TRIAL REGISTRATION

This clinical trial was retrospectively registered on 16 January 2019 at Clinicaltrials.gov (NCT03806686).

Diverging maternal and infant cord antibody functions from SARS-CoV-2 infection and vaccination in pregnancy

Immunization in pregnancy is a critical tool that can be leveraged to protect the infant with an immature immune system but how vaccine-induced antibodies transfer to the placenta and protect the maternal-fetal dyad remains unclear. Here, we compare matched maternal-infant cord blood from individuals who in pregnancy received mRNA COVID-19 vaccine, were infected by SARS-CoV-2, or had the combination of these two immune exposures. We find that some but not all antibody neutralizing activities and Fc effector functions are enriched with vaccination compared to infection. Preferential transport to the fetus of Fc functions and not neutralization is observed. Immunization compared to infection enriches IgG1-mediated antibody functions with changes in antibody post-translational sialylation and fucosylation that impact fetal more than maternal antibody functional potency. Thus, vaccine enhanced antibody functional magnitude, potency and breadth in the fetus are driven more by antibody glycosylation and Fc effector functions compared to maternal responses, highlighting prenatal opportunities to safeguard newborns as SARS-CoV-2 becomes endemic.

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.

Disulfide bond and crosslinking analyses reveal inter-domain interactions that contribute to the rigidity of placental malaria VAR2CSA structure and formation of CSA binding channel

VAR2CSA, a multidomain Plasmodium falciparum protein, mediates the adherence of parasite-infected red blood cells to chondroitin 4-sulfate (C4S) in the placenta, contributing to placental malaria. Therefore, detailed understanding of VAR2CSA structure likely help developing strategies to treat placental malaria. The VAR2CSA ectodomain consists of an N-terminal segment (NTS), six Duffy binding-like (DBL) domains, and three interdomains (IDs) present in sequence NTS-DBL1x-ID1-DBL2x-ID2-DBL3x-DBL4ε-ID3-DBL5ε-DBL6ε. Recent electron microscopy studies showed that VAR2CSA is compactly organized into a globular structure containing C4S-binding channel, and that DBL5ε-DBL6ε arm is attached to the NTS-ID3 core structure. However, the structural elements involved in inter-domain interactions that stabilize the VAR2CSA structure remain largely not understood. Here, limited proteolysis and peptide mapping by mass spectrometry showed that VAR2CSA contains several inter-domain disulfide bonds that stabilize its compact structure. Chemical crosslinking-mass spectrometry showed that all IDs interact with DBL4ε; additionally, IDs interact with other DBL domains, demonstrating that IDs are the key structural scaffolds that shape the functional NTS-ID3 core. Ligand binding analysis suggested that NTS considerably restricts the C4S binding. Overall, our study revealed that inter-domain disulfide bonds and interactions between IDs and DBL domains contribute to the stability of VAR2CSA structural architecture and formation of C4S-binding channel.

Pregnancy outcomes in a malaria-exposed Malian cohort of women of child-bearing age

In Sub-Saharan Africa, malaria continues to be associated with adverse pregnancy outcomes including stillbirth, early neonatal death, preterm delivery, and low birth weight. Current preventive measures are insufficient and new interventions are urgently needed. However, before such interventions can be tested in pregnant women, background information on pregnancy outcomes in this target population must be collected. We conducted an observational study in Ouélessébougou, Mali, a malaria-endemic area where first antenatal visit commonly occurs during the second trimester of pregnancy, hindering calculation of miscarriage rate in the population. To accurately determine the rate of miscarriage, 799 non-pregnant women of child-bearing age were enrolled and surveyed via monthly follow up visits that included pregnancy tests. Out of 505 women that completed the study, 364 became pregnant and 358 pregnancies were analyzed: 43 (12%) resulted in miscarriage, 28 (65.1%) occurred during the first trimester of pregnancy. We also determined rates of stillbirth, neonatal death, preterm delivery, and small for gestational age. The results showed high rate of miscarriage during the first trimester and established a basis to evaluate new interventions to prevent pregnancy malaria. This survey design enabled identification of first trimester miscarriages that are often missed by studies conducted in antenatal clinics.

Clinical trial registration

[https://clinicaltrials.gov/], identifier [NCT0297 4608].

Current approaches to malaria vaccines

The complex Plasmodium life cycle offers different vaccine approaches with distinct parasitological and clinical effects. The approaches and their rationales were established decades ago: vaccines targeting pre-erythrocytic (sporozoite and liver-stage) parasites prevent infection, those to blood-stage parasites reduce disease, and those to sexual-stage parasites or mosquito vector reduce transmission and eliminate malaria through herd immunity. The pre-erythrocytic RTS,S vaccine (Mosquirix, GlaskoSmithKline (GSK)), recommended by WHO in 2021, reduces clinical malaria in children. Knowledge of parasite biology, host-parasite interactions, and immune mechanisms is informing new concepts to improve on RTS,S and to target other parasite stages. This review emphasizes vaccine approaches and candidates currently in the clinic or likely to enter clinical testing soon.

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

Malaria during pregnancy is a major global health problem caused by infection with Plasmodium falciparum parasites. Severe effects arise from the accumulation of infected erythrocytes in the placenta. Here, erythrocytes infected by late blood-stage parasites adhere to placental chondroitin sulphate A (CS) via VAR2CSA-type P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion proteins. Immunity to placental malaria is acquired through exposure and mediated through antibodies to VAR2CSA. Through evolution, the VAR2CSA proteins have diversified in sequence to escape immune recognition but retained their overall macromolecular structure to maintain CS binding affinity. This structural conservation may also have allowed development of broadly reactive antibodies to VAR2CSA in immune women. Here we show the negative stain and cryo-EM structure of the only known broadly reactive human monoclonal antibody, PAM1.4, in complex with VAR2CSA. The data shows how PAM1.4’s broad VAR2CSA reactivity is achieved through interactions with multiple conserved residues of different sub-domains forming conformational epitope distant from the CS binding site on the VAR2CSA core structure. Thus, while PAM1.4 may represent a class of antibodies mediating placental malaria immunity by inducing phagocytosis or NK cell-mediated cytotoxicity, it is likely that broadly CS binding-inhibitory antibodies target other epitopes at the CS binding site. Insights on both types of broadly reactive monoclonal antibodies may aid the development of a vaccine against placental malaria.

A novel asexual blood-stage malaria vaccine candidate: PfRipr5 formulated with human-use adjuvants induces potent growth inhibitory antibodies

PfRipr is a highly conserved asexual-blood stage malaria vaccine candidate against Plasmodium falciparum. PfRipr5, a protein fragment of PfRipr inducing the most potent inhibitory antibodies, is a promising candidate for the development of next-generation malaria vaccines, requiring validation of its potential when formulated with adjuvants already approved for human use. In this study, PfRipr5 antigen was efficiently produced in a tank bioreactor using insect High Five cells and the baculovirus expression vector system; purified PfRipr5 was thermally stable in its monomeric form, had high purity and binding capacity to functional monoclonal anti-PfRipr antibody. The formulation of purified PfRipr5 with Alhydrogel®, GLA-SE or CAF®01 adjuvants accepted for human use showed acceptable compatibility. Rabbits immunized with these formulations induced comparable levels of anti-PfRipr5 antibodies, and significantly higher than the control group immunized with PfRipr5 alone. To investigate the efficacy of the antibodies, we used an in vitro parasite growth inhibition assay (GIA). The highest average GIA activity amongst all groups was attained with antibodies induced by immunization with PfRipr5 formulated with CAF®01. Overall, this study validates the potential of adjuvanted PfRipr5 as an asexual blood-stage malaria vaccine candidate, with PfRipr5/CAF®01 being a promising formulation for subsequent pre-clinical and clinical development.

Pregnancy and malaria: the perfect storm

PURPOSE OF REVIEW

Malaria in pregnancy continues to exert a toll on pregnant women and their offspring.

RECENT FINDINGS

The burden of Plasmodium falciparum infection is especially large in Africa, and new data show lasting effects of maternal infection on the infant's neurocognitive development. Elsewhere, P. vivax infection causes relapsing infections that are challenging to prevent. Infection in first trimester of pregnancy is an area of increasing focus, and its adverse effects on pregnancy outcome are increasingly recognised. First-trimester infection is common and frequently acquired prior to conception. Although newer rapid diagnostic tests still have limited sensitivity, they may be useful in detection of early pregnancy malaria for treatment. Artemisinin-based combination therapies are efficacious in later pregnancy but have yet to be recommended in first trimester because of limited safety data. In Africa, intermittent preventive treatment in pregnancy (IPTp) with monthly sulfadoxine-pyrimethamine improves pregnancy outcomes, but sulfadoxine-pyrimethamine resistance is worsening. The alternative, IPTp with dihydroartemisinin-piperaquine, has greater antimalarial efficacy, but does not appear to improve pregnancy outcomes, because sulfadoxine-pyrimethamine has poorly understood nonmalarial benefits on birthweight.

SUMMARY

Novel IPTp regimens must be combined with interventions to strengthen protection from malaria infection acquired before and in early pregnancy.

Towards identification and development of alternative vaccines against pregnancy-associated malaria based on naturally acquired immunity

Pregnant women are particularly susceptible to Plasmodium falciparum malaria, leading to substantial maternal and infant morbidity and mortality. While highly effective malaria vaccines are considered an essential component towards malaria elimination, strides towards development of vaccines for pregnant women have been minimal. The leading malaria vaccine, RTS,S/AS01, has modest efficacy in children suggesting that it needs to be strengthened and optimized if it is to be beneficial for pregnant women. Clinical trials against pregnancy-associated malaria (PAM) focused on the classical VAR2CSA antigen are ongoing. However, additional antigens have not been identified to supplement these initiatives despite the new evidence that VAR2CSA is not the only molecule involved in pregnancy-associated naturally acquired immunity. This is mainly due to a lack of understanding of the immune complexities in pregnancy coupled with difficulties associated with expression of malaria recombinant proteins, low antigen immunogenicity in humans, and the anticipated complications in conducting and implementing a vaccine to protect pregnant women. With the accelerated evolution of molecular technologies catapulted by the global pandemic, identification of novel alternative vaccine antigens is timely and feasible. In this review, we discuss approaches towards novel antigen discovery to support PAM vaccine studies.

Drugs for Intermittent Preventive Treatment of Malaria in Pregnancy: Current Knowledge and Way Forward

Malaria infection during pregnancy is an important driver of maternal and neonatal health in endemic countries. Intermittent preventive treatment in pregnancy (IPTp) with sulfadoxine-pyrimethamine (SP) is recommended for malaria prevention at each scheduled antenatal care visit, starting at the second trimester, in areas of high and moderate transmission. However, the increased resistance to SP in some endemic areas challenges its effectiveness. Furthermore, SP is contraindicated in the first trimester of pregnancy and in HIV-infected women on co-trimoxazole prophylaxis due to potential drug–drug interactions. Thus, in recent last decades, several studies evaluated alternative drugs that could be used for IPTp. A comprehensive literature review was conducted to summarize the evidence on the efficacy and safety of antimalarial drugs being evaluated for IPTp. Chloroquine, amodiaquine, mefloquine and azithromycin as IPTp have proven to be worse tolerated than SP. Mefloquine was found to increase the risk of mother-to-child transmission of HIV. Dihydroartemisin-piperaquine currently constitutes the most promising IPTp drug alternative; it reduced the prevalence of malaria infection, and placental and clinical malaria in studies among HIV-uninfected women, and it is currently being tested in HIV-infected women. Research on effective antimalarial drugs that can be safely administered for prevention to pregnant women should be prioritized. Malaria prevention in the first trimester of gestation and tailored interventions for HIV-infected women remain key research gaps to be addressed.

Analysis of allelic cross-reactivity of monoclonal IgG antibodies by a multiplexed reverse FluoroSpot assay

The issue of antibody cross-reactivity is of central importance in immunology, and not least in protective immunity to Plasmodium falciparum malaria, where key antigens show substantial allelic variation (polymorphism). However, serological analysis often does not allow the distinction between true cross-reactivity (one antibody recognizing multiple antigen variants) and apparent cross-reactivity (presence of multiple variant-specific antibodies), as it requires analysis at the single B-cell/monoclonal antibody level. ELISpot is an assay that enables that, and a recently developed multiplexed variant of ELISpot (FluoroSpot) facilitates simultaneous assessment of B-cell/antibody reactivity to several different antigens. In this study, we present a further enhancement of this assay that makes direct analysis of monoclonal antibody-level cross-reactivity with allelic variants feasible. Using VAR2CSA-type PfEMP1-a notoriously polymorphic antigen involved in the pathogenesis of placental malaria-as a model, we demonstrate the robustness of the assay and its applicability to analysis of true cross-reactivity of monoclonal VAR2CSA-specific antibodies in naturally exposed individuals. The assay is adaptable to the analysis of other polymorphic antigens, rendering it a powerful tool in studies of immunity to malaria and many other diseases.

Expanding the Malaria Antibody Toolkit: Development and Characterisation of Plasmodium falciparum RH5, CyRPA, and CSP Recombinant Human Monoclonal Antibodies

Malaria, an infection caused by apicomplexan parasites of the genus Plasmodium, continues to exact a significant toll on public health with over 200 million cases world-wide, and annual deaths in excess of 600,000. Considerable progress has been made to reduce malaria burden in endemic countries in the last two decades. However, parasite and mosquito resistance to frontline chemotherapies and insecticides, respectively, highlights the continuing need for the development of safe and effective vaccines. Here we describe the development of recombinant human antibodies to three target proteins from Plasmodium falciparum: reticulocyte binding protein homologue 5 (PfRH5), cysteine-rich protective antigen (PfCyRPA), and circumsporozoite protein (PfCSP). All three proteins are key targets in the development of vaccines for blood-stage or pre-erythrocytic stage infections. We have developed potent anti-PfRH5, PfCyRPA and PfCSP monoclonal antibodies that will prove useful tools for the standardisation of assays in preclinical research and the assessment of these antigens in clinical trials. We have generated some very potent anti-PfRH5 and anti-PfCyRPA antibodies with some clones >200 times more potent than the polyclonal anti-AMA-1 antibodies used for the evaluation of blood stage antigens. While the monoclonal and polyclonal antibodies are not directly comparable, the data provide evidence that these new antibodies are very good at blocking invasion. These antibodies will therefore provide a valuable resource and have potential as biological standards to help harmonise pre-clinical malaria research.

Polymorphic Molecular Signatures in Variable Regions of the Plasmodium falciparum var2csa DBL3x Domain Are Associated with Virulence in Placental Malaria

The Plasmodium falciparum protein VAR2CSA allows infected erythrocytes to accumulate within the placenta, inducing pathology and poor birth outcomes. Multiple exposures to placental malaria (PM) induce partial immunity against VAR2CSA, making it a promising vaccine candidate. However, the extent to which VAR2CSA genetic diversity contributes to immune evasion and virulence remains poorly understood. The deep sequencing of the var2csa DBL3X domain in placental blood from forty-nine primigravid and multigravid women living in malaria-endemic western Kenya revealed numerous unique sequences within individuals in association with chronic PM but not gravidity. Additional analysis unveiled four distinct sequence types that were variably present in mixed proportions amongst the study population. An analysis of the abundance of each of these sequence types revealed that one was inversely related to infant gestational age, another was inversely related to placental parasitemia, and a third was associated with chronic PM. The categorization of women according to the type to which their dominant sequence belonged resulted in the segregation of types as a function of gravidity: two types predominated in multigravidae whereas the other two predominated in primigravidae. The univariate logistic regression analysis of sequence type dominance further revealed that gravidity, maternal age, placental parasitemia, and hemozoin burden (within maternal leukocytes), reported a lack of antimalarial drug use, and infant gestational age and birth weight influenced the odds of membership in one or more of these sequence predominance groups. Cumulatively, these results show that unique var2csa sequences differentially appear in women with different PM exposure histories and segregate to types independently associated with maternal factors, infection parameters, and birth outcomes. The association of some var2csa sequence types with indicators of pathogenesis should motivate vaccine efforts to further identify and target VAR2CSA epitopes associated with maternal morbidity and poor birth outcomes.

Tackling variants with antibodies

Antibodies targeting the protein that causes placental malaria can recognise multiple variants of the protein, which may help guide the development of new vaccines to protect pregnant women from malaria.

Recent Advances in the Development of Toll-like Receptor Agonist-Based Vaccine Adjuvants for Infectious Diseases

Vaccines are powerful tools for controlling microbial infections and preventing epidemic diseases. Efficient inactive, subunit, or viral-like particle vaccines usually rely on a safe and potent adjuvant to boost the immune response to the antigen. After a slow start, over the last decade there has been increased developments on adjuvants for human vaccines. The development of adjuvants has paralleled our increased understanding of the molecular mechanisms for the pattern recognition receptor (PRR)-mediated activation of immune responses. Toll-like receptors (TLRs) are a group of PRRs that recognize microbial pathogens to initiate a host’s response to infection. Activation of TLRs triggers potent and immediate innate immune responses, which leads to subsequent adaptive immune responses. Therefore, these TLRs are ideal targets for the development of effective adjuvants. To date, TLR agonists such as monophosphoryl lipid A (MPL) and CpG-1018 have been formulated in licensed vaccines for their adjuvant activity, and other TLR agonists are being developed for this purpose. The COVID-19 pandemic has also accelerated clinical research of vaccines containing TLR agonist-based adjuvants. In this paper, we reviewed the agonists for TLR activation and the molecular mechanisms associated with the adjuvants’ effects on TLR activation, emphasizing recent advances in the development of TLR agonist-based vaccine adjuvants for infectious diseases.

Tropical Infections Induced Fulminant Hepatitis in Peripartum Managed Successfully: Tales of Fate

Tropical diseases such as malaria, dengue, intestinal helminths, schistosomiasis, leishmaniasis, and filariasis have an essential influence on the reproductive health of patients.

Various cases of pregnancy loss in unexplained circumstances are a result of underdiagnosed tropical diseases. Term pregnancy complicated by tropical diseases is a challenge for the treating clinicians as these infections tend to mimic HELLP (Hemolysis, Elevated Liver enzymes, and Low Platelets) syndrome and increase the chances of perinatal complications and maternal mortality. Except for tropical diseases, ever since the conception of the COVID-19 pandemic, the differentials for fever pregnancy have become extensive, and the treating clinicians need to solve the puzzle of the etiology behind these symptoms that are non-specific and might be due to both COVID-19 and tropical Infections. Prophylactic treatment for malaria is pivotal in pregnancy as immunity is decreased during pregnancy, making the patient susceptible to developing malaria-related complications. Dengue is one of the most common mosquito-borne infections found around the globe. Complications of dengue during pregnancy include pregnancy loss as well as vertical transmission of infection to the fetus. Leptospirosis, even though rare, has a wide range of complications in pregnancy ranging from fetal loss to congenital infection and oligohydramnios, thereby requiring close monitoring and prompt management during pregnancy.

We report a case series of three cases where patients presented during the period of pregnancy with fulminant hepatic failure, which turned out to be a consequence of tropical diseases. All the cases were treated successfully and discharged in stable condition.

BMFPs, a versatile therapeutic tool for redirecting a preexisting Epstein-Barr virus antibody response toward defined target cells

Industrial production of therapeutic monoclonal antibodies is mostly performed in eukaryotic-based systems, allowing posttranslational modifications mandatory for their functional activity. The resulting elevated product cost limits therapy access to some patients. To address this limitation, we conceptualized a novel immunotherapeutic approach to redirect a preexisting polyclonal antibody response against Epstein-Barr virus (EBV) toward defined target cells. We engineered and expressed in bacteria bimodular fusion proteins (BMFPs) comprising an Fc-deficient binding moiety targeting an antigen expressed at the surface of a target cell, fused to the EBV-P18 antigen, which recruits circulating endogenous anti-P18 IgG in EBV⁺ individuals. Opsonization of BMFP-coated targets efficiently triggered antibody-mediated clearing effector mechanisms. When assessed in a P18-primed mouse tumor model, therapy performed with an anti-huCD20 BMFP significantly led to increased survival and total cancer remission in some animals. These results indicate that BMFPs could represent potent and useful therapeutic molecules to treat a number of diseases.