Schistosoma mansoni antigen Sm-p80: prophylactic efficacy using TLR4 agonist vaccine adjuvant glucopyranosyl lipid A-Alum in murine and non-human primate models

Transmission-Blocking Vaccines against Schistosomiasis Japonica

Control of schistosomiasis japonica, endemic in Asia, including the Philippines, China, and Indonesia, is extremely challenging. Schistosoma japonicum is a highly pathogenic helminth parasite, with disease arising predominantly from an immune reaction to entrapped parasite eggs in tissues. Females of this species can generate 1000-2200 eggs per day, which is about 3- to 15-fold greater than the egg output of other schistosome species. Bovines (water buffalo and cattle) are the predominant definitive hosts and are estimated to generate up to 90% of parasite eggs released into the environment in rural endemic areas where these hosts and humans are present. Here, we highlight the necessity of developing veterinary transmission-blocking vaccines for bovines to better control the disease and review potential vaccine candidates. We also point out that the approach to producing efficacious transmission-blocking animal-based vaccines before moving on to human vaccines is crucial. This will result in effective and feasible public health outcomes in agreement with the One Health concept to achieve optimum health for people, animals, and the environment. Indeed, incorporating a veterinary-based transmission vaccine, coupled with interventions such as human mass drug administration, improved sanitation and hygiene, health education, and snail control, would be invaluable to eliminating zoonotic schistosomiasis.

Anti-schistosomal immunity to core xylose/fucose in N-glycans

Schistosomiasis is a globally prevalent, debilitating disease that is poorly controlled by chemotherapy and for which no vaccine exists. While partial resistance in people may develop over time with repeated infections and treatments, some animals, including the brown rat (Rattus norvegicus), are only semi-permissive and have natural protection. To understand the basis of this protection, we explored the nature of the immune response in the brown rat to infection by Schistosoma mansoni. Infection leads to production of IgG to Infection leads to production of IgG to parasite glycoproteins parasite glycoproteins with complex-type N-glycans that contain a non-mammalian-type modification by core α2-Xylose and core α3-Fucose (core Xyl/Fuc). These epitopes are expressed on the surfaces of schistosomula and adult worms. Importantly, IgG to these epitopes can kill schistosomula by a complement-dependent process in vitro. Additionally, sera from both infected rhesus monkey and infected brown rat were capable of killing schistosomula in a manner inhibited by glycopeptides containing core Xyl/Fuc. These results demonstrate that protective antibodies to schistosome infections in brown rats and rhesus monkeys include IgG responses to the core Xyl/Fuc epitopes in surface-expressed N-glycans, and raise the potential of novel glyco-based vaccines that might be developed to combat this disease.

Human Schistosomiasis Vaccines as Next Generation Control Tools

Human schistosomiasis remains one of the most important yet neglected tropical diseases, with the latest estimates from the Global Burden of Disease Study indicating that over 140 million people are infected with schistosomes [...]

Pattern recognition receptor signaling and innate immune responses to schistosome infection

Schistosomiasis remains to be a significant public health problem in tropical and subtropical regions. Despite remarkable progress that has been made in the control of the disease over the past decades, its elimination remains a daunting challenge in many countries. This disease is an inflammatory response-driven, and the positive outcome after infection depends on the regulation of immune responses that efficiently clear worms and allow protective immunity to develop. The innate immune responses play a critical role in host defense against schistosome infection and pathogenesis. Initial pro-inflammatory responses are essential for clearing invading parasites by promoting appropriate cell-mediated and humoral immunity. However, elevated and prolonged inflammatory responses against the eggs trapped in the host tissues contribute to disease progression. A better understanding of the molecular mechanisms of innate immune responses is important for developing effective therapies and vaccines. Here, we update the recent advances in the definitive host innate immune response to schistosome infection, especially highlighting the critical roles of pattern recognition receptors and cytokines. The considerations for further research are also provided.

De Novo Design of Cathepsin B1 Inhibitors as Potential Anti-Schistosomal Agents Using Computational Studies

Background

Schistosomiasis is the world’s second most devastating disease after malaria and the leading cause of disease and mortality for more than 200 million people in developing countries. Cysteine proteases, in particular SmCB1, are the most well-researched biological targets for this disorder.

Objective

To apply computational techniques to design new antischistosomal agents against SmCB1 protein with favorable pharmacokinetic properties.

Methods

The smCB1 receptor-based pharmacophore model was created and used to screen 567,000 fragments from the Enamine library. The best scoring fragments have been linked to build novel compounds that were subjected to molecular docking, MM-GBSA free energy estimation, ADME prediction, and molecular dynamics.

Results

A seven-point pharmacophore hypothesis ADDDRRR was created. The developed hypothesis was used to screen 1.3 M fragment conformations. Among them, 23,732 fragments matched the hypothesis and screened against the protein. The top 50 fragments were used to design new 7745 compounds using the Breed ligand panel which were subjected to docking and MMGBSA binding energy. This led to the identification of 10 compounds with better docking scores (−8.033– −7.483 kcal/mol) and lower-bound free energies (−58.49 – −40.02 kcal/mol) compared to the reference bound ligand. Most of the designed compounds demonstrated good drug-like properties. Concerning Molecular dynamics (MD) simulation results, a low root mean square deviation (RMSD) range (0.25–1.2 Å) was found for the top 3 complexes which indicated their stability.

Conclusion

We identified compounds that could be potential candidates in the search for novel Schistosoma mansoni inhibitors by targeting SmCB1 utilizing various computational tools. Three newly designed compounds namely breed 1, 2, and 3 showed promising affinity to the target as well as favorable drug-like properties which might be considered potential anti-schistosomal agents.

Vaccines for Human Schistosomiasis: Recent Progress, New Developments and Future Prospects

Schistosomiasis, caused by human trematode blood flukes (schistosomes), remains one of the most prevalent and serious of the neglected tropical parasitic diseases. Currently, treatment of schistosomiasis relies solely on a single drug, the anthelmintic praziquantel, and with increased usage in mass drug administration control programs for the disease, the specter of drug resistance developing is a constant threat. Vaccination is recognized as one of the most sustainable options for the control of any pathogen, but despite the discovery and reporting of numerous potentially promising schistosome vaccine antigens, to date, no schistosomiasis vaccine for human or animal deployment is available. This is despite the fact that Science ranked such an intervention as one of the top 10 vaccines that need to be urgently developed to improve public health globally. This review summarizes current progress of schistosomiasis vaccines under clinical development and advocates the urgent need for the establishment of a revolutionary and effective anti-schistosome vaccine pipeline utilizing cutting-edge technologies (including developing mRNA vaccines and exploiting CRISPR-based technologies) to provide novel insight into future vaccine discovery, design, manufacture and deployment.

A comprehensive and critical overview of schistosomiasis vaccine candidates

A digenetic platyhelminth Schistosoma is the causative agent of schistosomiasis, one of the neglected tropical diseases that affect humans and animals in numerous countries in the Middle East, sub-Saharan Africa, South America and China. Several control methods were used for prevention of infection or treatment of acute and chronic disease. Mass drug administration led to reduction in heavy-intensity infections and morbidity, but failed to decrease schistosomiasis prevalence and eliminate transmission, indicating the need to develop anti-schistosome vaccine to prevent infection and parasite transmission. This review summarizes the efficacy and protective capacity of available schistosomiasis vaccine candidates with some insights and future prospects.

Testing of Schistosoma mansoni Vaccine Targets

Vaccination has greatly reduced the burden of human diseases caused by infectious pathogens. Systematic development of vaccine targets requires established protocols to assess immunogenicity and efficacy of such vaccine candidates. Using a leading schistosomiasis vaccine candidate, Sm-p80, as an example, we describe standardized approaches for testing the immunogenicity and efficacy of Schistosoma mansoni vaccine targets. Unlike other parasite systems in which sterile immunity is required, the goal of S. mansoni vaccine targets is overall reduction in morbidity. Methods related to the parasitological parameters described in this chapter allow for the testing of the prophylactic (reduction in adult worm burden), anti-pathology (liver and intestine egg retention), and transmission blocking (fecal egg expulsion and egg hatching rates) efficacies for the vaccine target. The RNA sequencing approaches provide basis for identification of molecular signatures predictive of desirable outcomes for schistosomiasis vaccines.

Process Development of Sj-p80: A Low-Cost Transmission-Blocking Veterinary Vaccine for Asiatic Schistosomiasis

Asiatic schistosomiasis caused by Schistosoma japonicum is a neglected tropical disease resulting in significant morbidity to both humans and animals - particularly bovines - in endemic areas. Infection with this parasite leads to less healthy herds, causing problems in communities which rely on bovines for farming, milk and meat production. Additionally, excretion of parasite eggs in feces perpetuates the life cycle and can lead to human infection. We endeavored to develop a minimally purified, inexpensive, and effective vaccine based on the 80 kDa large subunit of the calcium activated neutral protease (calpain) from S. japonicum (Sj-p80). Here we describe the production of veterinary vaccine-grade Sj-p80 at four levels of purity and demonstrate in a pilot study that minimally purified antigen provides protection against infection in mice when paired with a low-cost veterinary adjuvant, Montanide™ ISA61 VG. Preliminary data demonstrate that the vaccine is immunogenic with robust antibody titers following immunization, and vaccination resulted in a reduction of parasite eggs being deposited in the liver (23.4-51.4%) and intestines (1.9-55.1%) depending on antigen purity as well as reducing the ability of these eggs to hatch into miracidia by up to 31.6%. We therefore present Sj-p80 as a candidate vaccine antigen for Asiatic schistosomiasis which is now primed for continued development and testing in bovines in endemic areas. A successful bovine vaccine could play a major role in reducing pathogen transmission to humans by interrupting the parasitic life cycle and improving quality of life for people living in endemic countries.

Current status and future prospects of protein vaccine candidates against Schistosoma mansoni infection

Schistosomiasis is an acute and chronic tropical parasitic disease caused by blood dwelling worm of the genus Schistosoma. It is the most destructive disease globally and is a major cause of morbidity and mortality for developing countries. Three main species of schistosomes infect human beings from which S. mansoni is the most common and widespread. Over the last several decades, chemotherapy using praziquantel has been a commonly used strategy for the treatment and control of schistosomiasis. However, control programs focused exclusively on chemotherapy have been challenging because of the frequency and rapidity of reinfection and these programs were expensive. Thus, new schistosomiasis control strategies will be needed. Vaccination strategy would be an ideal tool for a significant and sustainable reduction in the transmission and disease burden of schistosomiasis. An effective anti schistosome vaccine would greatly contribute to decreasing schistosomiasis-associated morbidity via protective immune responses leading to reduced worm burdens and decreased egg production. Vaccine development is a long process that can take decades. There have been three candidate vaccines that have been produced by Good Manufacturing Procedure and entered human clinical trials for S. mansoni are Sm14, SmTSP-2, and Sm-p80. Other candidates that are in pre-clinical trials at various stages include paramyosin, Sm29, SmKI-1, and Sm23. Since the growth of several new technologies, including genomics, transcriptomics, microarrays, immunomic profiling, and proteomics, have helped in the identification of promising new target schistosome antigens. Therefore, this review considers the present status of protein vaccine candidates against Schistosoma mansoni and provides some insight on prospects vaccine design and discovery.

Fifteen Years of Sm-p80-Based Vaccine Trials in Nonhuman Primates: Antibodies From Vaccinated Baboons Confer Protection in vivo and in vitro From Schistosoma mansoni and Identification of Putative Correlative Markers of Protection

Recent advances in systems biology have shifted vaccine development from a largely trial-and-error approach to an approach that promote rational design through the search for immune signatures and predictive correlates of protection. These advances will doubtlessly accelerate the development of a vaccine for schistosomiasis, a neglected tropical disease that currently affects over 250 million people. For over 15 years and with contributions of over 120 people, we have endeavored to test and optimize Sm-p80-based vaccines in the non-human primate model of schistosomiasis. Using RNA-sequencing on eight different Sm-p80-based vaccine strategies, we sought to elucidate immune signatures correlated with experimental protective efficacy. Furthermore, we aimed to explore the role of antibodies through in vivo passive transfer of IgG obtained from immunized baboons and in vitro killing of schistosomula using Sm-p80-specific antibodies. We report that passive transfer of IgG from Sm-p80-immunized baboons led to significant worm burden reduction, egg reduction in liver, and reduced egg hatching percentages from tissues in mice compared to controls. In addition, we observed that sera from Sm-p80-immunized baboons were able to kill a significant percent of schistosomula and that this effect was complement-dependent. While we did not find a universal signature of immunity, the large datasets generated by this study will serve as a substantial resource for further efforts to develop vaccine or therapeutics for schistosomiasis.

Cordycepin for Health and Wellbeing: A Potent Bioactive Metabolite of an Entomopathogenic Cordyceps Medicinal Fungus and Its Nutraceutical and Therapeutic Potential

Cordyceps is a rare naturally occurring entomopathogenic fungus usually found at high altitudes on the Himalayan plateau and a well-known medicinal mushroom in traditional Chinese medicine. Cordyceps contains various bioactive components, out of which, cordycepin is considered most vital, due to its utmost therapeutic as well as nutraceutical potential. Moreover, the structure similarity of cordycepin with adenosine makes it an important bioactive component, with difference of only hydroxyl group, lacking in the 3′ position of its ribose moiety. Cordycepin is known for various nutraceutical and therapeutic potential, such as anti-diabetic, anti-hyperlipidemia, anti-fungal, anti-inflammatory, immunomodulatory, antioxidant, anti-aging, anticancer, antiviral, hepato-protective, hypo-sexuality, cardiovascular diseases, antimalarial, anti-osteoporotic, anti-arthritic, cosmeceutical etc. which makes it a most valuable medicinal mushroom for helping in maintaining good health. In this review, effort has been made to bring altogether the possible wide range of cordycepin’s nutraceutical potential along with its pharmacological actions and possible mechanism. Additionally, it also summarizes the details of cordycepin based nutraceuticals predominantly available in the market with expected global value. Moreover, this review will attract the attention of food scientists, nutritionists, pharmaceutical and food industries to improve the use of bioactive molecule cordycepin for nutraceutical purposes with commercialization to aid and promote healthy lifestyle, wellness and wellbeing.

Immune responses in liver and spleen against Plasmodium yoelii pre-erythrocytic stages in Swiss mice model

Though the immunity to malaria has been associated with cellular immune responses, the exact function of the phenotypic cell population is still unclear. This study investigated the host immune responses elicited during the pre-erythrocytic stage, post-Plasmodium yoelii sporozoite infection in Swiss mice model. For this purpose, we analyzed the dynamics of different subsets of immune cells population and cytokine levels in the hepatic mononuclear and splenic cells population during pre-erythrocytic liver-stage infection. We observed a significant reduction in the effectors immune cells population including CD8⁺ T cell, F4/80⁺ macrophage and in plasmacytoid dendritic cells (CD11c⁺ B220⁺). Interestingly, substantial down-regulation was also noted in pro-inflammatory cytokines (i.e. IFN-γ, TNF-α, IL-12, IL-2, IL-17 and iNOS), while, up-regulation of anti-inflammatory cytokines (i.e. IL-10, IL-4 and TGF-β) during asymptomatic pre-erythrocytic liver-stage infection. Collectively, this study demonstrated that during pre-erythrocytic development, Plasmodium yoelii sporozoite impaired the host activators of innate and adaptive immune responses by regulating the immune effector cells, gene expression and cytokines levels for the establishment of infection and subsequent development in the liver and spleen. The results in this study provided a better understanding of the events leading to malarial infection and will be helpful in supportive treatment and vaccine development strategy.

Schistosomiasis and hookworm infection in humans: Disease burden, pathobiology and anthelmintic vaccines

Helminth diseases are the ancient scourges of humans and their damages are 'silent and insidious'. Of the helminth infections, schistosomiasis and hookworm infection have a great impact. This review covers information regarding vaccine candidates against schistosomiasis and hookworms that reached at least up to the phase-1 trial and literatures regarding other vaccine candidates have been excluded. For clinical manifestations, all available literatures were included, and for epidemiology and global burden of the diseases (GBD), literatures only within 2000-2019 were included. Literatures were searched surfing various databases including PubMED, Google Scholar, and Science Direct and overall over 150 literatures were identified. Globally ~250 million people are suffering from schistosomiasis, resulting 1430 thousand DALY (disability adjusted life year) per year. On the other hand, about 1.3 billion people are infected with hookworm (HW), and according to WHO, ~878 million school-age children (SAC) are at risk. HW is estimated to cause 65,000 deaths annually, accounts for 845 thousand DALYs as well as to cause 6-35.3% loss in productivity. Despite tremendous efforts, very few anthelmintic vaccine candidates such as Na-GST-1, Na-APR-1 and Na-ASP-2 against HW, and Sm28GST/Sh28GST, Sm-p80, Sm14 and Sm-TSP-1/SmTSP-2 against schistosomiasis reached up to the clinical trials. More efforts are needed to achieve the WHO targets taken against the maladies.

Interleukin (IL)-21 in Inflammation and Immunity During Parasitic Diseases

Parasitic diseases cause significant morbidity and mortality in the developing and underdeveloped countries. No efficacious vaccines are available against most parasitic diseases and there is a critical need for developing novel vaccine strategies for care. IL-21 is a pleiotropic cytokine whose functions in protection and immunopathology during parasitic diseases have been explored in limited ways. IL-21 and its cognate receptor, IL-21R, are highly expressed in parasitized organs of infected humans as well in murine models of the human parasitic diseases. Prior studies have indicated the ability of the IL-21/IL-21R signaling axis to regulate the effector functions (e.g., cytokine production) of T cell subsets by enhancing the expression of T-bet and STAT4 in human T cells, resulting in an augmented production of IFN-γ. Mice deficient for either IL-21 (Il21^−/−) or IL-21R (Il21r^−/−) showed significantly reduced inflammatory responses following parasitic infections as compared with their WT counterparts. Targeting the IL-21/IL-21R signaling axis may provide a novel approach for the development of new therapeutic agents for the prevention of parasite-induced immunopathology and tissue destruction.

Cordyceps militaris Improves Chronic Kidney Disease by Affecting TLR4/NF-κB Redox Signaling Pathway

Cordyceps militaris may show good promise in protecting against chronic kidney disease (CKD) but the molecular mechanism remains unclear. CKD risk is associated with the Toll-like receptor 4/nuclear factor-kappa B (TLR4/NF-κB) signaling pathway. Cordycepin is the main component of Cordyceps militaris and may affect the TLR4/NF-κB pathway. Cordycepin was prepared by preparative HPLC. CKD patients were assigned into Cordyceps militaris (COG, 100 mg daily) and placebo (CG) groups. Cordycepin activity was measured using human embryo kidney cells (HEK293T). Biochemical indices, the levels of TLR4, NF-κB, cyclooxygenase-2 (COX2), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β), were measured by real-time qRT-PCR, or ELISA kits and or Western blot. After 3-month treatment, cordycepin reduced the levels of urinal protein, blood urea nitrogen (BUN), and creatinine by 36.7%±8.6%, 12.5%±3.2%, and 18.3%±6.6%, respectively (P < 0.05). Cordyceps militaris improved lipid profile and redox capacity of CKD patients by reducing the serum levels of TG, TC, and LDL-C by 12.8%±3.6%, 15.7%±4.1%, and 16.5%±4.4% and increasing the HDL-C level by 10.1%±1.4% in the COG group when compared with the CG group, respectively (P < 0.05). The serum levels of cystatin-C (Cys-C), myeloperoxidase (MPO), and malondialdehyde (MDA) were reduced by 14.0%±3.8%, 26.9%±12.3%, and 19.7%±7.9% while nitric oxide (NO) and superoxide dismutase (SOD) were increased by 12.5%±2.9% and 25.3%±13.4% in the COG group when compared with the CG group, respectively (P < 0.05). Cordycepin reduced the levels of TLR4, NF-κB, COX2, TNF-α, and IL-1β in HEK293T cells too (P < 0.05). However, cordycepin could not affect the levels anymore if TLR4 was silenced. Cordyceps militaris protected against CKD progression by affecting the TLR4/NF-κB lipid and redox signaling pathway via cordycepin.