The role of different components of the immune system against Plasmodium falciparum malaria: Possible contribution towards malaria vaccine development

Current Developments in Malaria Vaccination: A Concise Review on Implementation, Challenges, and Future Directions

Introduction

Malaria remains a persistent challenge in global health, disproportionately affecting populations in endemic regions (eg, sub-Saharan Africa). Despite decades of international collaborative efforts, malaria continues to claim hundreds of thousands of lives each year, with young children and pregnant women enduring the heaviest burden. This concise review aimed to provide an up-to-date assessment of malaria vaccines progress, challenges, and future directions.

Methods

A PubMed/MEDLINE search (2015-2024) was conducted to identify studies on malaria vaccine development, implementation barriers, efficacy, and vaccination hesitancy. Clinical trials, reviews, and global health reports were included based on relevance to the review aims. No strict inclusion criteria were applied, and selection was guided by key review themes and policy relevance.

Results

The introduction of pre-erythrocytic malaria vaccines (RTS,S/AS01 and R21/Matrix-M), represents an important milestone in malaria control efforts with promising results from the erythrocytic vaccine RH5.1/Matrix-M in recent clinical trials. However, the approval of these vaccines is accompanied by significant challenges such as the limited efficacy, the complexity of multi-dose regimens, and numerous barriers to widespread implementation in resource-limited settings. The review identified the complex challenges to broad malaria vaccination coverage, including logistical barriers, healthcare infrastructure effect, financial limitations, malaria vaccine hesitancy, among other obstacles in malaria-endemic regions. Promising developments in malaria vaccination, such as next-generation candidates (eg, mRNA-based vaccines), hold the potential to offer improved efficacy, longer-lasting protection, and greater scalability. There is a critical need to integrate malaria vaccination efforts with established malaria control interventions (eg, insecticide-treated bed nets, vector control strategies, and anti-malarial drugs).

Conclusion

Achieving sustained control of malaria morbidity and mortality will require strong global collaboration, sufficient funding, and continuous efforts to address inequities in access and delivery of malaria control measures including the malaria vaccines.

Computational Development of Transmission-Blocking Vaccine Candidates Based on Fused Antigens of Pre- and Post-fertilization Gametocytes Against Plasmodium falciparum

Plasmodium falciparum is the most fatal species of malaria parasites in humans. Attempts at developing vaccines against the malaria parasites have not been very successful even after the approval of the RTS, S/AS01 vaccine. There is a continuous need for more effective vaccines including sexual-stage antigens that could block the transmission of malaria parasites between mosquitoes and humans. Low immunogenicity, expression, and stability are some of the challenges of transmission-blocking vaccine (TBV). This study was designed to computationally identify TBV candidates based on fused antigens by combining highly antigenic peptides from prefertilization (Pfs230, Pfs48/45) and postfertilization (Pfs25, Pfs28) gametocytes. The peptides were selected based on their antigenicity, nonallergenicity, and lack of similarity with the human proteome. Two fused antigens vaccine candidates (FAVCs) were constructed using Flagellin Salmonella enterica (FAVC-FSE) and Cholera toxin B (FAVC-CTB) as adjuvants. The constructs were evaluated for their physicochemical properties, structural stability, immunogenicity, and potential to elicit cross-protection across multiple Plasmodium species. The results yielded antigenic peptides, with antigenicity scores between 0.7589 and 1.1821. The structural analysis of FAVC-FSE and FAVC-CTB showed a Z-score of -6.70 and -4.79, a Ramachandran plot of 96.94% and 94.86% with overall quality of 94.20% and 89.85%, respectively. The FAVCs contained CD8+, CD4+, and linear B-cell epitopes with antigenicity scores between 1.2089 and 2.8623, 0.5663 and 2.4132, and 1.5196 and 2.2212, respectively. Each FAVC generated 6 conformational B-cells. High population coverage values were recorded for the FAVCs. The ability of the FAVCs to trigger immune response was evaluated through an in silico immune stimulation. The low-binding interaction energy that resulted from molecular docking and dynamics simulations showed a strong affinity of FAVCs to Toll-like receptor 5 (TLR5). The results indicate that the FAVC-FSE vaccine candidate is more promising to interrupt P falciparum transmission and provides a baseline for experimental validation.

Computational design, expression, and characterization of a Plasmodium falciparum multi-epitope, multi-stage vaccine candidate (PfCTMAG)

Malaria, a tropical disease, claims the lives of thousands of people annually and the development of resistance to insecticides and antimalarial drugs poses a great challenge to current prevention and control strategies. Current malaria vaccines are limited in efficacy, duration of protection, and safety, due to the high antigenic diversity and complex life cycle of the Plasmodium parasite. This study sought to design and assess a more effective multi-stage, multi-epitope vaccine candidate for the control of malaria. A multi-epitope malaria vaccine candidate was designed in silico using multiple antigens from both the pre-erythrocytic and erythrocytic stages, expressed in bacteria, and its sero-reactivity to antibodies in plasma from malaria-positive (cases) and negative individuals (controls) was assessed using enzyme-linked immunosorbent assay (ELISA). Immunization experiments were equally conducted with BALB/c mice. In-silico analysis revealed that the designed antigen, PfCTMAG (Plasmodium falciparum Circumsporozoite, Thrombospondin-related adhesion protein, Merozoite surface protein 2, Apical asparagine (Asn)-rich protein and Glutamate-Rich Protein), effectively bound to Toll-like receptor 4 (TLR-4) and triggered a strong immune response. In sero-reactivity studies, malaria-positives (cases) had higher anti-PfCTMAG IgG ( p  = 0.024) and IgM ( p < 0.001) levels compared to malaria negatives (controls). The mice immunized with PfCTMAG did not show adverse reactions and had higher levels of IgG antibodies (p = 0.002) compared to controls, thereby validating the safety and immunogenicity of PfCTMAG as a promising vaccine candidate.

Impact on parasitemia, survival time and pro-inflammatory immune response in mice infected with Plasmodium berghei treated with Eleutherine plicata

In vitro studies with Plasmodium falciparum have demonstrated the antiparasitic activity of E. plicata, attributed to its naphthoquinones. This study reports on pro-inflammatory changes in mice infected with P. berghei and correlates these changes with parasitemia and survival. The ethanol extract of Eleutherine plicata (EEEp) was fractionated under reflux to obtain the dichloromethane fraction (FDMEp) and isolated compounds from E. plicata, relating these to survival time and parasitemia. Antimalarial activity was evaluated using the Peters suppressive test, with mice infected with Plasmodium berghei and treated with E. plicata, assessing parasitemia and survival over 30 days. The pro-inflammatory profile was determined by measuring interleukin-10, interferon-γ (IFN-γ), and nitric oxide levels. EEEp, FDMEp, and eleutherol showed activity on the 5th day of infection, with only FDMEp being active on the 8th day. Treatment with EEEp and FDMEp extended animal survival, reduced IFN-γ and NO levels, and increased IL-10 levels. Eleutherol significantly altered the response, with eleutherol glucuronide seemingly active by binding to lactate dehydrogenase, inhibiting hemozoin metabolism, leading to parasite death. Pro-inflammatory changes did not appear to correlate with survival and reduced parasitemia. In summary, FDMEp and eleutherol reduced parasitemia, extended survival, and modulated the inflammatory response. FDMEp and eleutherol are promising candidates for developing new antimalarial drugs.

Plasmodium Falciparum and mosquito vector IgG patterns across suspected malaria cases in Ghana

INTRODUCTION

Malaria, a widespread tropical disease, remains a significant global health issue, resulting in numerous deaths each year. In Ghana, malaria is a leading cause of illness, contributing to a large proportion of hospital outpatient visits. The study assessed the pattern of malaria and vector IgG antibody levels among suspected malaria patients seeking healthcare at selected health facilities across Ghana.

METHODS

Samples from a total of 823 participants aged 1 to 85 years with clinical malaria from the ten regions of Ghana were recruited into the study. Archived plasma obtained from each participant was used to assess antibody responses against MSP1 (19 k), MSP2 (FC27 & 3D7), MSP3, gSG6-P1, and GLURP-RO using ELISA. The data were categorized according to study site, age group, gender, and diagnostic tests. Data were analyzed using Kruskal-Wallis's statistics. The statistical significance was assessed at 0.05.

RESULTS

The mean ± standard error of the mean (S.E) of MSP3 IgG concentration for the different age groups were 16, 847 ± 3, 031 ng/mL for 0-4 years, 18, 973 ± 4,357 ng/mL for 5-10 years, 25,961 ± 5,436 ng/mL for 11-15 years and 76, 244 ± 8, 209 ng/mL for ≥ 16 years. A significant (Kruskal-Wallis statistic = 122.6, p < 0.0001) increase in P. falciparum MSP 3 (p < 0.0001) and gSG6-P1(p < 0.0001) IgG concentration was observed with increasing age categories. There were significant differences in antibody responses against MSP2 (FC27) IgG (Kruskal-Wallis statistic = 29.63, p = 0.0005), MSP3 IgG (Kruskal-Wallis statistic = 32.53, p = 0.0002), GLURP-RO IgG (Kruskal-Wallis statistic = 52.8, p < 0.0001) and gSG6-P1 IgG (Kruskal-Wallis statistic = 152.8, p < 0.0001) across the study regions.

CONCLUSION

The study reveals that IgG against merozoite surface proteins MSP3, GLURP-RO, and gSG6-P1 but not MSP1 and MSP2 antibodies increase with age. The mean IgG antibody concentrations varied in the selected regions of Ghana. A longitudinal study where confounding factors are controlled for is recommended to provide insights into the development of immunity and antibody efficacy, and to enhance the effectiveness of malaria prevention efforts in Ghana. This will help improve the overall understanding of malaria transmission.

Identifying Plasmodium P36 and P52 antigens for co-administration with circumsporozoite protein to enhance vaccine efficacy

Vaccines targeting the complex pre-erythrocytic stage of Plasmodium parasites may benefit from inclusion of multiple antigens. However, discerning protective effects can be difficult because newer candidates may not be as protective as leading antigens like the circumsporozoite protein (CSP) in the conventional pre-clinical mouse model. We developed a modified mouse model challenge strategy that maximizes the contribution of T cells induced by novel candidate antigens at the sporozoite challenge time point and used this approach to test Plasmodium P36 and P52 vaccine candidates alone and in concert with non-protective doses of CSP. Co-administration of P36 and/or P52 with CSP achieved 80-100% sterile protection in mice, compared to only 7-30% protection for each individual antigen. P36 and P52 vaccination induced murine CD4+ and CD8+ T cell responses, but not antibody responses. This study adds P36 and P52 as promising vaccine antigens that may enhance protection achieved by CSP vaccination.

Adapting to the shifting landscape: Implications of climate change for malaria control: A review

Malaria, a global public health challenge, continues to affect millions of lives, particularly in regions where its transmission is endemic. The interplay between climate change and malaria dynamics has emerged as a critical concern, reshaping the landscape of this vector-borne disease. This review publication, titled "Adapting to the shifting landscape: Implications of climate change for malaria control," explores the multifaceted relationship between climate change and the control of malaria. The paper begins by dissecting the influence of climate change on malaria dynamics, including alterations in temperature, precipitation, and other climatic factors that impact the habitat and life cycle of malaria vectors. It delves into the evolving ecology and behavior of malaria vectors in response to changing climatic conditions, emphasizing the importance of understanding these adaptations. As a response to this shifting landscape, the review discusses adaptive strategies for malaria control, ranging from vector control measures to the utilization of climate data in early warning systems. Community engagement and education are highlighted as essential components of these strategies, recognizing the vital role of local communities in effective malaria control efforts. The paper also identifies future directions and research needs, underscoring the importance of staying ahead of the evolving climate-malaria relationship. This review underscores the urgency of adapting to the changing landscape of malaria transmission driven by climate change. It emphasizes the significance of proactively addressing climate-related challenges to enhance malaria control and protect the health and well-being of vulnerable populations.

Acute lung injury is prevented by monocyte locomotion inhibitory factor in an experimental severe malaria mouse model

Acute lung injury caused by severe malaria (SM) is triggered by a dysregulated immune response towards the infection with Plasmodium parasites. Postmortem analysis of human lungs shows diffuse alveolar damage (DAD), the presence of CD8 lymphocytes, neutrophils, and increased expression of Intercellular Adhesion Molecule 1 (ICAM-1). P. berghei ANKA (PbA) infection in C57BL/6 mice reproduces many SM features, including acute lung injury characterized by DAD, CD8+ T lymphocytes and neutrophils in the lung parenchyma, and tissular expression of proinflammatory cytokines and adhesion molecules, such as IFNγ, TNFα, ICAM, and VCAM. Since this is related to a dysregulated immune response, immunomodulatory agents are proposed to reduce the complications of SM. The monocyte locomotion inhibitory factor (MLIF) is an immunomodulatory pentapeptide isolated from axenic cultures of Entamoeba hystolitica. Thus, we evaluated if the MLIF intraperitoneal (i.p.) treatment prevented SM-induced acute lung injury. The peptide prevented SM without a parasiticidal effect, indicating that its protective effect was related to modifications in the immune response. Furthermore, peripheral CD8+ leukocytes and neutrophil proportions were higher in infected treated mice. However, the treatment prevented DAD, CD8+ cell infiltration into the pulmonary tissue and downregulated IFNγ. Moreover, VCAM-1 expression was abrogated. These results indicate that the MLIF treatment downregulated adhesion molecule expression, impeding cell migration and proinflammatory cytokine tissular production, preventing acute lung injury induced by SM. Our findings represent a potential novel strategy to avoid this complication in various events where a dysregulated immune response triggers lung injury.

Phenotype and function of IL-10 producing NK cells in individuals with malaria experience

Plasmodium falciparum infection can trigger high levels of inflammation that lead to fever and sometimes severe disease. People living in malaria-endemic areas gradually develop resistance to symptomatic malaria and control both parasite numbers and the inflammatory response. We previously found that adaptive natural killer (NK) cells correlate with reduced parasite load and protection from symptoms. We also previously found that murine NK cell production of IL-10 can protect mice from experimental cerebral malaria. Human NK cells can also secrete IL-10, but it was unknown what NK cell subsets produce IL-10 and if this is affected by malaria experience. We hypothesize that NK cell immunoregulation may lower inflammation and reduce fever induction. Here, we show that NK cells from subjects with malaria experience make significantly more IL-10 than subjects with no malaria experience. We then determined the proportions of NK cells that are cytotoxic and produce interferon gamma and/or IL-10 and identified a signature of adaptive and checkpoint molecules on IL-10-producing NK cells. Lastly, we find that co-culture with primary monocytes, Plasmodium -infected RBCs, and antibody induces IL-10 production by NK cells. These data suggest that NK cells may contribute to protection from malaria symptoms via IL-10 production.

Plasmodium falciparum alters the trophoblastic barrier and stroma villi organization of human placental villi explants

BACKGROUND

The sequestration of Plasmodium falciparum infected erythrocytes in the placenta, and the resulting inflammatory response affects maternal and child health. Despite existing information, little is known about the direct impact of P. falciparum on the placental barrier formed by trophoblast and villous stroma. This study aimed to assess placental tissue damage caused by P. falciparum in human placental explants (HPEs).

METHODS

HPEs from chorionic villi obtained of human term placentas (n = 9) from normal pregnancies were exposed to P. falciparum-infected erythrocytes (IE) for 24 h. HPEs were embedded in paraffin blocks and used to study tissue damage through histopathological and histochemical analysis and apoptosis using TUNEL staining. Culture supernatants were collected to measure cytokine and angiogenic factors and to determine LDH activity as a marker of cytotoxicity. A subset of archived human term placenta paraffin-embedded blocks from pregnant women with malaria were used to confirm ex vivo findings.

RESULTS

Plasmodium falciparum-IE significantly damages the trophoblast layer and the villous stroma of the chorionic villi. The increased LDH activity and pathological findings such as syncytial knots, fibrin deposits, infarction, trophoblast detachment, and collagen disorganization supported these findings. The specific damage to the trophoblast and the thickening of the subjacent basal lamina were more pronounced in the ex vivo infection. In contrast, apoptosis was higher in the in vivo infection. This disparity could be attributed to the duration of exposure to the infection, which significantly varied between individuals naturally exposed over time and the 24-h exposure in the ex vivo HPE model.

CONCLUSION

Exposure to P. falciparum-IE induces a detachment of the syncytiotrophoblast, disorganization of the stroma villi, and an increase in apoptosis, alterations that may be associated with adverse results such as intrauterine growth restriction and low birth weight.

The interleukin-10 family: Major regulators of the immune response against Plasmodium falciparum infections

Malaria caused by the Plasmodium falciparum strain is more severe because of this protozoan's ability to disrupt the physiology of host cells during the blood stages of development by initiating the production of the interleukin-10 (IL-10) family of cytokines. P. falciparum feeds on hemoglobin and causes host cells to adhere to the walls of blood vessels by remodeling their composition. IL-10 is produced by CD4+ T cells that inhibits antigen-presenting cells' activity to prevent inflammation. This cytokine and its family members are crucial in promoting malarial infection by inhibiting the host's protective immune response, thus initiating Plasmodium parasitemia. IL-10 is also responsible for preventing severe pathology during Plasmodium infection and initiates several signaling pathways to alter the physiology of host cells during malarial infection. This review summarizes the critical aspects of P. falciparum infection, including its role in signaling pathways for cytokine exudation, its effect on microRNA, the human immune response in malaria, and the role played by the liver hormone hepcidin. Moreover, future aspects of vaccine development and therapeutic strategies to combat P. falciparum infections are also discussed in detail.

Malaria Vaccines: From the Past towards the mRNA Vaccine Era

Plasmodium spp. is the etiological agent of malaria, a life-threatening parasitic disease transmitted by infected mosquitoes. Malaria remains a major global health challenge, particularly in endemic regions. Over the years, various vaccine candidates targeting different stages of Plasmodium parasite life-cycle have been explored, including subunit vaccines, vectored vaccines, and whole organism vaccines with Mosquirix, a vaccine based on a recombinant protein, as the only currently approved vaccine for Plasmodium falciparum malaria. Despite the aforementioned notable progress, challenges such as antigenic diversity, limited efficacy, resistant parasites escaping protective immunity and the need for multiple doses have hindered the development of a highly efficacious malaria vaccine. The recent success of mRNA-based vaccines against SARS-CoV-2 has sparked renewed interest in mRNA vaccine platforms. The unique mRNA vaccine features, including their potential for rapid development, scalability, and flexibility in antigen design, make them a promising avenue for malaria vaccine development. This review provides an overview of the malaria vaccines' evolution from the past towards the mRNA vaccine era and highlights their advantages in overcoming the limitations of previous malaria vaccine candidates.

Escaping the enemy's bullets: an update on how malaria parasites evade host immune response

Malaria continues to cause untold hardship to inhabitants of malaria-endemic regions, causing significant morbidity and mortality that severely impact global health and the economy. Considering the complex life cycle of malaria parasites (MPs) and malaria biology, continued research efforts are ongoing to improve our understanding of the pathogenesis of the diseases. Female Anopheles mosquito injects MPs into its hosts during a blood meal, and MPs invade the host skin and the hepatocytes without causing any serious symptoms. Symptomatic infections occur only during the erythrocytic stage. In most cases, the host's innate immunity (for malaria-naïve individuals) and adaptive immunity (for pre-exposed individuals) mount severe attacks and destroy most MPs. It is increasingly understood that MPs have developed several mechanisms to escape from the host's immune destruction. This review presents recent knowledge on how the host's immune system destroys invading MPs as well as MPs survival or host immune evasion mechanisms. On the invasion of host cells, MPs release molecules that bind to cell surface receptors to reprogram the host in a way to lose the capacity to destroy them. MPs also hide from the host immune cells by inducing the clustering of both infected and uninfected erythrocytes (rosettes), as well as inducing endothelial activation. We hope this review will inspire more research to provide a complete understanding of malaria biology and promote interventions to eradicate the notorious disease.

Mechanism of Immune Evasion in Mosquito-Borne Diseases

In recent decades, mosquito-borne illnesses have emerged as a major health burden in many tropical regions. These diseases, such as malaria, dengue fever, chikungunya, yellow fever, Zika virus infection, Rift Valley fever, Japanese encephalitis, and West Nile virus infection, are transmitted through the bite of infected mosquitoes. These pathogens have been shown to interfere with the host's immune system through adaptive and innate immune mechanisms, as well as the human circulatory system. Crucial immune checkpoints such as antigen presentation, T cell activation, differentiation, and proinflammatory response play a vital role in the host cell's response to pathogenic infection. Furthermore, these immune evasions have the potential to stimulate the human immune system, resulting in other associated non-communicable diseases. This review aims to advance our understanding of mosquito-borne diseases and the immune evasion mechanisms by associated pathogens. Moreover, it highlights the adverse outcomes of mosquito-borne disease.

Exploring the potential of antimalarial nanocarriers as a novel therapeutic approach

Malaria is a life-threatening parasitic disease that affects millions of people worldwide, especially in developing countries. Despite advances in conventional therapies, drug resistance in malaria parasites has become a significant concern. Hence, there is a need for a new therapeutic approach. To combat the disease effectively means eliminating vectors and discovering potent treatments. The nanotechnology research efforts in nanomedicine show promise by exploring the potential use of nanomaterials that can surmount these limitations occurring with antimalarial drugs, which include multidrug resistance or lack of specificity when targeting parasites directly. Utilizing nanomaterials would possess unique advantages over conventional chemotherapy systems by increasing the efficacy levels while reducing side effects significantly by delivering medications precisely within the diseased area. It also provides cheap yet safe measures against Malaria infections worldwide-ultimately improving treatment efficiency holistically without reinventing new methods therapeutically. This review is an effort to provide an overview of the various stages of malaria parasites, pathogenesis, and conventional therapies, as well as the treatment gap existing with available formulations. It explores different types of nanocarriers, such as liposomes, ethosomal cataplasm, solid lipid nanoparticles, nanostructured lipid carriers, polymeric nanocarriers, and metallic nanoparticles, which are frequently employed to boost the efficiency of antimalarial drugs to overcome the challenges and develop effective and safe therapies. The study also highlights the improved pharmacokinetics, enhanced drug bioavailability, and reduced toxicity associated with nanocarriers, making them a promising therapeutic approach for treating malaria.

Potential Epha2 Receptor Blockers Involved in Cerebral Malaria from Taraxacum officinale, Tinospora cordifolia, Rosmarinus officinalis and Ocimum basilicum: A Computational Approach

Cerebral malaria (CM) is a severe manifestation of parasite infection caused by Plasmodium species. In 2018, there were approximately 228 million malaria cases worldwide, resulting in about 405,000 deaths. Survivors of CM may live with lifelong post-CM consequences apart from an increased risk of childhood neurodisability. EphA2 receptors have been linked to several neurological disorders and have a vital role in the CM-associated breakdown of the blood-brain barrier. Molecular docking (MD) studies of phytochemicals from Taraxacum officinale, Tinospora cordifolia, Rosmarinus officinalis, Ocimum basilicum, and the native ligand ephrin-A were conducted to identify the potential blockers of the EphA2 receptor. The software program Autodock Vina 1.1.2 in PyRx-Virtual Screening Tool and BIOVIA Discovery Studio visualizer was used for this MD study. The present work showed that blocking the EphA2 receptor by these phytochemicals prevents endothelial cell apoptosis by averting ephrin-A ligand-expressing CD8+ T cell bioadhesion. These phytochemicals showed excellent docking scores and binding affinity, demonstrating hydrogen bond, electrostatic, Pi-sigma, and pi alkyl hydrophobic binding interactions when compared with native ligands at the EphA2 receptor. The comparative MD study using two PDB IDs showed that isocolumbin, carnosol, luteolin, and taraxasterol have better binding affinities (viz. -9.3, -9.0, -9.5, and -9.2 kcal/mol, respectively). Ocimum basilicum phytochemicals showed a lower docking score but more binding interactions than native ligands at the EphA2 receptor for both PDB IDs. This suggests that these phytochemicals may serve as potential drug candidates in the management of CM. We consider that the present MD study provides leads in drug development by targeting the EphA2 receptor in managing CM. The approach is innovative because a role for EphA2 receptors in CM has never been highlighted.