Vaccination Against Whipworm: Identification of Potential Immunogenic Proteins in Trichuris muris Excretory/Secretory Material

Another decade of Trichuris muris research: An update and application of key discoveries

The mouse whipworm, Trichuris muris, has been used for over 60 years as a tractable model for human trichuriasis, caused by the related whipworm species, T. trichiura. The history of T. muris research, from the discovery of the parasite in 1761 to understanding the lifecycle and outcome of infection with different doses (high versus low dose infection), as well as the immune mechanisms associated with parasite expulsion and chronic infection have been detailed in an earlier review published in 2013. Here, we review recent advances in our understanding of whipworm biology, host-parasite interactions and basic immunology brought about using the T. muris mouse model, focussing on developments from the last decade. In addition to the traditional high/low dose infection models that have formed the mainstay of T. muris research to date, novel models involving trickle (repeated low dose) infection in laboratory mice or infection in wild or semi-wild mice have led to important insights into how immunity develops in situ in a multivariate environment, while the use of novel techniques such as the development of caecal organoids (enabling the study of larval development ex vivo) promise to deliver important insights into host-parasite interactions. In addition, the genome and transcriptome analyses of T. muris and T. trichiura have proven to be invaluable tools, particularly in the context of vaccine development and identification of secreted products including proteins, extracellular vesicles and micro-RNAs, shedding further light on how these parasites communicate with their host and modulate the immune response to promote their own survival.

Soil-transmitted helminthic vaccines: Where are we now?

It has been tested and proven that vaccination is still the best strategy to combat infectious diseases. However, to date, there are still no vaccines against human soil-transmitted helminthic diseases, despite their high prevalence globally, particularly in developing countries and rural areas with tropical climates and poor sanitation. The development of vaccines against helminths is riddled with obstacles. Helminths have a complex life cycle, multiple stages within the same host with stage-specific antigen expression, and the ability to regulate host immune reactions to evade the immune response. These elements contribute to the main challenge of helminthic vaccines: the identification of effective vaccine candidates. Therefore, this article reviews the current progress and potential future direction of soil-transmitted helminthic vaccines, particularly against Trichuris trichiura, Ascaris lumbricoides, Strongyloides stercoralis, Necator americanus and Ancylostoma duodenale. The study design employed was a systematic review, using qualitative meta-summary synthesis. Preclinical studies and clinical trials on the development of protein subunit vaccines against the five soil-transmitted helminths were searched on PubMed and Scopus. Effectiveness was indicated by a reduction in worm burden or larval output, an increase in specific IgG levels, or an increase in cytokine production. Our findings show that only the hookworm vaccine against N. americanus is in the clinical trial phase, while the rest is still in exploratory research and pre-clinical development phase.

Trichuris WAP and CAP proteins: Potential whipworm vaccine candidates?

Trichuris trichiura and T. suis are gastrointestinal dwelling roundworms that infect humans and pigs, respectively. Heavy infections cause gastrointestinal symptoms and impaired growth and development. Vaccination has the potential to reduce the disease burden of whipworm infection; however, there are currently no commercially available vaccines against these parasites and very few against other gastrointestinal-dwelling nematodes of medical and agricultural importance. The naturally occurring mouse whipworm, T. muris, has been used for decades to model human trichuriasis, and the immunogenic potential of the excretory/secretory material (E/S, which can be collected following ex vivo culture of worms) has been studied in the context of vaccine candidate identification. Despite this, researchers are yet to progress an effective vaccine candidate to clinical trials. The T. muris, T. trichiura, and T. suis genomes each encode between 10 and 27 whey acidic protein (WAP) domain-containing proteins and 15 to 34 cysteine-rich secretory protein/antigen 5/pathogenesis related-1 (CAP) family members. WAP and CAP proteins have been postulated to play key roles in host-parasite interactions and may possess immunomodulatory functions. In addition, both protein families have been explored in the context of helminth vaccines. Here, we use phylogenetic and functional analysis to investigate the evolutionary relationship between WAP and CAP proteins encoded by T. muris, T. trichiura, and T. suis. We highlight several WAP and CAP proteins that warrant further study to understand their biological function and as possible vaccine candidates against T. trichiura and/or T. suis, based on the close evolutionary relationship with WAP or CAP proteins identified within T. muris E/S products.

Whipworm secretions and their roles in host-parasite interactions

Whipworm (Trichuris) is a genus of roundworms that causes gastrointestinal infections in humans and animals. Of particular interest are T. trichiura, the causative agent of human trichuriasis, a neglected tropical disease that affects 477 million people worldwide, and T. suis, the pig whipworm species, responsible for growth stunting and economic losses within the agricultural industry. The naturally occurring mouse whipworm, T. muris, has been used for decades as a model for trichuriasis, yielding knowledge on the biology of these parasites and the host response to infection. Ex vivo culture of T. muris (and to some extent, T. suis) has provided insight into the composition of the excretory/secretory (E/S) products released by worms, which include a myriad of proteins, RNAs, lipids, glycans, metabolites and extracellular vesicles. T. muris E/S has formed the basis of the search for whipworm vaccine candidates, while the immunomodulatory potential of T. suis and T. muris secretions has been investigated with the aim of improving our understanding of how these parasites modulate host immunity, as well as identifying immunomodulatory candidates with therapeutic potential in the context of inflammatory diseases. This article will review the various components found within Trichuris E/S, their potential as vaccine candidates and their immunomodulatory properties.

Immunoregulatory molecules secreted by Trichuris muris

Trichuris, whipworm nematode infections are prevalent in humans, domestic livestock and mammals. All share an epithelial dwelling niche and similar life cycle with the chronic infections that follow implying that immune evasion mechanisms are operating. Nematode excretory secretory (ES) products have been shown to be a rich source of immunomodulatory molecules for many species. The Trichuris muris model is a natural parasite of mice and has been used extensively to study host–parasite interactions and provides a tractable platform for investigation of the immunoregulatory capacity of whipworm ES. The present review details progress in identification of the composition of T. muris ES, immunomodulatory components and their potential mechanisms of action. The adult T. muris secretome is dominated by one protein with modulatory capacity although remains to be completely characterized. In addition, the secretome contains multiple other proteins and small molecules that have immunomodulatory potential, certainly by comparison to other Trichuris species. Moreover, T. muris-derived exosomes/exosome-like vesicles contain both protein and multiple miRNAs providing an alternate delivery process for molecules with the potential to modulate host immunity.

Rodent Models for the Study of Soil-Transmitted Helminths: A Proteomics Approach

Soil-transmitted helminths (STH) affect hundreds of millions worldwide and are some of the most important neglected tropical diseases in terms of morbidity. Due to the difficulty in studying STH human infections, rodent models have become increasingly used, mainly because of their similarities in life cycle. Ascaris suum and Trichuris muris have been proven appropriate and low maintenance models for the study of ascariasis and trichuriasis. In the case of hookworms, despite most of the murine models do not fully reproduce the life cycle of Necator americanus, their proteomic similarity makes them highly suitable for the development of novel vaccine candidates and for the study of hookworm biological features. Furthermore, these models have been helpful in elucidating some basic aspects of our immune system, and are currently being used by numerous researchers to develop novel molecules with immunomodulatory proteins. Herein we review the similarities in the proteomic composition between Nippostrongylus brasiliensis, Heligmosomoides polygyrus bakeri and Trichuris muris and their respective human counterpart with a focus on the vaccine candidates and immunomodulatory proteins being currently studied.

Intestinal helminth co-infection is an unrecognised risk factor for increased pneumococcal carriage density and invasive disease

Infection with Streptococcus pneumoniae is the leading cause of death in children and burden of disease is greatest where helminth infections are also common. We investigated the impact of intestinal helminth co-infection on pneumococcal carriage; a risk factor for invasive disease. We used a mouse co-infection model and clinical data to assess the impact of co-infection on carriage density. Co-infection in mice was associated with increased pneumococcal carriage density and dissemination into lungs. Helminth-infected children also exhibited increased carriage density as compared to uninfected children. Anthelmintic treatment may be a cost-effective method of reducing pneumococcal disease burden in lower-income countries.

Trichuris spp. in Animals, with Specific Reference to Neo-Tropical Rodents

Trichuriasis is the clinical disease of animals infected with the parasite of the genus Trichuris. This review attempts to present information on Trichuris spp. infestation in neo-tropical rodents that are utilized for meat consumption by humans. Neo-tropical rodents utilized for meat production can be divided into two categories: those that have been domesticated, which include the guinea pig (Cavia porcellus), and those that are on the verge of domestication, such as the capybara (Hydrochoerus hydrochaeris), lappe (Cuniculus paca/Agouti paca), and agouti (Dasyprocta leporina). This document reviews the literature on the species of Trichuris that affects the rodents mentioned above, as well as the clinical signs observed. The literature obtained spans over sixty years, from 1951 to 2020. Trichuris spp. was found in these neo-tropical rodents mentioned. However, there is a dearth of information on the species of Trichuris that parasitize these animals. The capybara was the only rodent where some molecular techniques were used to identify a new species named T. cutillasae. In most cases, Trichuris spp. was found in combination with other endoparasites, and was found at a low prevalence in the lappe and guinea pig. The presence of Trichuris spp. ranged from 4.62-53.85% in the agouti, 4.21-10.00% in the lappe, 50% in the capybaras, and 1-31% in guinea pigs. Further work must be done towards molecular identification of various Trichuris spp. present in these rodents, as well as the clinical effect of infection on the performance of agouti, lappe, capybara, and guinea pigs.

Human intestinal parasitic infection: a narrative review on global prevalence and epidemiological insights on preventive, therapeutic and diagnostic strategies for future perspectives

INTRODUCTION

Intestinal parasitic infection (IPI) is a global health concern among socioeconomically deprived communities in many developing countries. Many preventative strategies have been deployed to control IPI, however, there is a lack in standards on the techniques used to diagnose and monitor the prevalence of IPI.

AREAS COVERED

The present article will review the diseases associated with IPI and discuss the current IPI control strategies such as the water, sanitation, and hygiene (WASH) interventions, community-led total sanitation (CLTS) approach, and regular anthelminthic treatments. For the first time, this review will also evaluate all currently practised diagnostic techniques for the detection of intestinal parasites and provide insights on future IPI control strategies.

EXPERT OPINION

Advanced and improved diagnostic methods such as qPCR coupled with a high-resolution melting curve, aptamers, biosensors, and detection of extracellular vesicles can be used for detection of IPI. Vaccination against intestinal parasites can be made available to increase antibodies to interfere with the blood-feeding process by the parasites, which subsequently reduces the reproductive rates of the parasites. These methods collectively can serve as future management strategies for intestinal parasitic infections.

Proteomic Insights into the Biology of the Most Important Foodborne Parasites in Europe

Foodborne parasitoses compared with bacterial and viral-caused diseases seem to be neglected, and their unrecognition is a serious issue. Parasitic diseases transmitted by food are currently becoming more common. Constantly changing eating habits, new culinary trends, and easier access to food make foodborne parasites' transmission effortless, and the increase in the diagnosis of foodborne parasitic diseases in noted worldwide. This work presents the applications of numerous proteomic methods into the studies on foodborne parasites and their possible use in targeted diagnostics. Potential directions for the future are also provided.

Soil-Transmitted Helminth Vaccines: Are We Getting Closer?

Parasitic helminths infect over one-fourth of the human population resulting in significant morbidity, and in some cases, death in endemic countries. Despite mass drug administration (MDA) to school-aged children and other control measures, helminth infections are spreading into new areas. Thus, there is a strong rationale for developing anthelminthic vaccines as cost-effective, long-term immunological control strategies, which, unlike MDA, are not haunted by the threat of emerging drug-resistant helminths nor limited by reinfection risk. Advances in vaccinology, immunology, and immunomics include the development of new tools that improve the safety, immunogenicity, and efficacy of vaccines; and some of these tools have been used in the development of helminth vaccines. The development of anthelminthic vaccines is fraught with difficulty. Multiple lifecycle stages exist each presenting stage-specific antigens. Further, helminth parasites are notorious for their ability to dampen down and regulate host immunity. One of the first significant challenges in developing any vaccine is identifying suitable candidate protective antigens. This review explores our current knowledge in lead antigen identification and reports on recent pre-clinical and clinical trials in the context of the soil-transmitted helminths Trichuris, the hookworms and Ascaris. Ultimately, a multivalent anthelminthic vaccine could become an essential tool for achieving the medium-to long-term goal of controlling, or even eliminating helminth infections.

Development of caecaloids to study host-pathogen interactions: new insights into immunoregulatory functions of Trichuris muris extracellular vesicles in the caecum

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Development of new methods to generate, culture and characterise mouse caecaloids is described.

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Caecaloids recapitulate the caecal epithelium composition and spatial organisation.

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Caecaloids can be used to study host–caecal pathogen interactions in vitro.

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Trichuris muris EVs exert novel immunoregulatory effects on intestinal epithelial cells.

The caecum, an intestinal appendage in the junction of the small and large intestines, displays a unique epithelium that serves as an exclusive niche for a range of pathogens including whipworms (Trichuris spp.). While protocols to grow organoids from small intestine (enteroids) and colon (colonoids) exist, the conditions to culture organoids from the caecum have yet to be described. Here, we report methods to grow, differentiate and characterise mouse adult stem cell-derived caecal organoids, termed caecaloids. We compare the cellular composition of caecaloids with that of enteroids, identifying differences in intestinal epithelial cell populations that mimic those found in the caecum and small intestine. The remarkable similarity in the intestinal epithelial cell composition and spatial conformation of caecaloids and their tissue of origin enables their use as an in vitro model to study host interactions with important caecal pathogens. Thus, exploiting this system, we investigated the responses of caecal intestinal epithelial cells to extracellular vesicles secreted/excreted by the intracellular helminth Trichuris muris. Our findings reveal novel immunoregulatory effects of whipworm extracellular vesicles on the caecal epithelium, including the downregulation of responses to nucleic acid recognition and type-I interferon signalling.

In silico design of a T-cell epitope vaccine candidate for parasitic helminth infection

Trichuris trichiura is a parasite that infects 500 million people worldwide, leading to colitis, growth retardation and Trichuris dysentery syndrome. There are no licensed vaccines available to prevent Trichuris infection and current treatments are of limited efficacy. Trichuris infections are linked to poverty, reducing children's educational performance and the economic productivity of adults. We employed a systematic, multi-stage process to identify a candidate vaccine against trichuriasis based on the incorporation of selected T-cell epitopes into virus-like particles. We conducted a systematic review to identify the most appropriate in silico prediction tools to predict histocompatibility complex class II (MHC-II) molecule T-cell epitopes. These tools were used to identify candidate MHC-II epitopes from predicted ORFs in the Trichuris genome, selected using inclusion and exclusion criteria. Selected epitopes were incorporated into Hepatitis B core antigen virus-like particles (VLPs). Bone marrow-derived dendritic cells and bone marrow-derived macrophages responded in vitro to VLPs irrespective of whether the VLP also included T-cell epitopes. The VLPs were internalized and co-localized in the antigen presenting cell lysosomes. Upon challenge infection, mice vaccinated with the VLPs+T-cell epitopes showed a significantly reduced worm burden, and mounted Trichuris-specific IgM and IgG2c antibody responses. The protection of mice by VLPs+T-cell epitopes was characterised by the production of mesenteric lymph node (MLN)-derived Th2 cytokines and goblet cell hyperplasia. Collectively our data establishes that a combination of in silico genome-based CD4+ T-cell epitope prediction, combined with VLP delivery, offers a promising pipeline for the development of an effective, safe and affordable helminth vaccine.

Secretome of the carcinogenic helminth Spirocerca lupi reveals specific parasite proteins associated with its different life stages

Spirocerca lupi is a parasitic and carcinogenic nematode of canids distributed in tropical and subtropical regions around the world. The excretion-secretion proteins (PES) of S. lupi have been suggested to play a role in the pathogenesis of its infection. We aimed to identify the PES of different stages of S. lupi and search for proteins that would be useful for diagnostic, therapeutic and vaccination purposes as well as understand their functions. A nano-UPLC mass spectrometry de novo analysis was performed on proteins collected from cultures of S. lupi L3 larvae, L4 females, adult females and adult males from naturally infected hosts. A total of 211 proteins were identified in all cultures. Accordingly, 117, 130, 99 and 116 proteins were detected in L3 larva, L4 females, adult females and adult males, respectively, with a strong correlation in the biological replicates (Pearson coefficients > 0.73). Fourty-four proteins were detected in all developmental stages, 64 were stage-specific and 49 were exclusively identified in L4 females. Cell compartment enrichment analysis revealed that proteins common to all stages were cytoplasmatic (p < 9.x10^-6), whereas L4 unique proteins were in collagen trimers, and macromolecular complexes (p < 0.00001). Functional enrichment analysis of proteins showed significant enrichment in lipid metabolism in L3-unique proteins (p<0.00005), in mannose metabolism and protein de-glycosylation for L4-unique proteins (p < 0.00004), and in phosphorus metabolism in proteins shared by all stages (p <  2.1 x10^-9). Interestingly, annexin 6, associated with cancer in humans, was detected in all life stages, but in a larger abundance in L4 females and adults. These findings indicate that S. lupi establishes complex interactions with its hosts by an arsenal of proteins expressed in different patterns in each life stage which influence the pathogenesis and oncogenesis of S. lupi and may be used as potential targets for diagnostic assays, drug targets or vaccine candidates.

A new level of complexity in parasite-host interaction: The role of extracellular vesicles

Humans and animals have co-existed with parasites in a battle of constant adaptation to one another. It is becoming increasingly clear that extracellular vesicles (EVs) play important roles in this co-existence and pathology. This chapter reviews the current research on EVs released by protozoa, nematodes, trematodes, and cestodes with a special focus on EVs in parasite life cycles. The environmental changes experienced by the parasite during its life cycle is associated with distinct changes in EV release and content. The function of these EV seems to have a significant influence on parasite pathology and survival in the host by concomitantly modulating host immune responses and triggering parasite differentiation. The role of EVs in communication between the parasites and the host adds a new level of complexity in our understanding of parasite biology, which may be a key to further understand the complexity behind host-parasite interactions and communication. This increased understanding can, in turn, open up new avenues for vaccine, diagnostic, and therapeutic development for a wide variety of diseases such as parasite infection, cancers, and immunological disorders.

Trichuris muris whey acidic protein induces type 2 protective immunity against whipworm

Human whipworm (Trichuris trichiura) infects approximately 1 in 15 people worldwide, representing the leading infectious cause of colitis and subsequent, inflammatory bowel disease (IBD). Current control measures focused on mass deworming have had limited success due to low drug efficacies. Vaccination would be an ideal, cost-effective strategy to induce protective immunity, leading to control of infection and transmission. Here we report the identification of whey acidic protein, a whipworm secretory protein, as a strong immunogen for inducing protective efficacy in a surrogate mouse T. muris infection model. The recombinant WAP protein (rTm-WAP49), as well as a single, highly conserved repeat within WAP (fragment 8) expressed as an Na-GST-1 fusion protein (rTm-WAP-F8+Na-GST-1), generate a strong T helper type 2 (Th2) immune response when delivered as subcutaneous vaccines formulated with Montanide ISA 720. Oral challenge with T. muris infective eggs following vaccination led to a significant reduction in worm burden of 48% by rTm-WAP49 and 33% by rTm-WAP-F8+Na-GST-1. The cellular immune correlates of protection included significant antigen-specific production of Th2 cytokines IL-4, IL-9, and IL-13 by cells isolated from the vaccine-draining inguinal lymph nodes, parasite-draining mesenteric lymph nodes, and spleen in mice vaccinated with either rTm-WAP49 or rTm-WAP-F8+Na-GST-1. The humoral immune correlates included a high antigen-specific ratio of IgG1 to IgG2a, without eliciting an IgE-mediated allergic response. Immunofluorescent staining of adult T. muris with WAP antisera identified the worm's pathogenic stichosome organ as the site of secretion of native Tm-WAP protein into the colonic mucosa. Given the high sequence conservation for the WAP proteins from T. muris and T. trichiura, the results presented here support the WAP protein to be further evaluated as a potential human whipworm vaccine candidate.

Extracellular vesicles induce protective immunity against Trichuris muris

Gastrointestinal nematodes, such as Trichuris trichiura (human whipworm), are a major source of morbidity in humans and their livestock. There is a paucity of commercially available vaccines against these parasites, and vaccine development for T. trichiura has been impeded by a lack of known host protective antigens. Experimental vaccinations with T. muris (murine whipworm) soluble Excretory/Secretory (ES) material have demonstrated that it is possible to induce protective immunity in mice; however, the potential for extracellular vesicles (EVs) as a source of antigenic material has remained relatively unexplored. Here, we demonstrate that EVs isolated from T. muris ES can induce protective immunity in mice when administered as a vaccine without adjuvant and show that the protective properties of these EVs are dependent on intact vesicles. We also identified several proteins within EV preparations that are targeted by the host antibodies following vaccination and subsequent infection with T. muris. Many of these proteins, including VWD and vitellogenin N and DUF1943-domain-containing protein, vacuolar protein sorting-associated protein 52 and TSP-1 domain-containing protein, were detected in both soluble ES and EV samples and have homologues in other parasites of medical and veterinary importance, and as such are possible protective antigens.