Poor immunogenicity of BCG in helminth infected population is associated with increased in vitro TGF-beta production

Pre-vaccination Schistosoma mansoni and hookworm infections are associated with altered vaccine immune responses: a longitudinal analysis among adolescents living in helminth-endemic islands of Lake Victoria, Uganda

Background

Variations in vaccine responses have been observed between populations. A role for helminth infections has been proposed due to their immunomodulatory properties. In a secondary analysis of data from a randomised trial assessing effects of anthelminthic treatment on vaccine responses, we examined associations between helminth infections at baseline prior to vaccine administration, and vaccine responses among adolescents (9-17 years) in Koome Islands, Lake Victoria, Uganda.

Methods

Participants received BCG [week 0], yellow fever (YF-17D), oral typhoid (Ty21a), HPV-prime [week 4], and HPV-boost, tetanus/diphtheria [week 28]. Outcomes were BCG-specific interferon-γ ELISpot responses and antibody responses to yellow-fever-, typhoid-, HPV-, tetanus- and diphtheria-specific antigens measured at two time points post vaccination. S. mansoni infection was determined as positive if either the plasma Circulating Anodic Antigen (CAA) assay or stool PCR were positive. Hookworm and Strongyloides were determined by stool PCR. Linear mixed effects regression was used to assess associations.

Results

Among 478 adolescents, 70% were Schistosoma mansoni (Sm) infected and 23% hookworm infected at baseline. Sm was associated with lower Salmonella Typhi O:LPS-specific IgG responses (adjusted geometric mean ratio (aGMR) 0.69 (0.57-0.83)), and hookworm with higher diphtheria-specific IgG (aGMR 1.16 (1.02, 1.31)) and lower HPV-16-specific IgG (aGMR 0.70 (0.55, 0.90)) post-vaccination. High Sm intensity was associated with lower BCG-specific interferon-γ and S. Typhi O:LPS-specific IgG.

Conclusions

We found inverse associations between Sm and responses to two live vaccines, whereas hookworm was positively associated with diphtheria-specific IgG. These findings support the hypothesis that helminth infections can modulate vaccine responses, while also highlighting potential heterogeneity in the direction of these effects.

Intestinal helminth infection impairs vaccine-induced T cell responses and protection against SARS-CoV-2 in mice

Although vaccines have reduced the burden of COVID-19, their efficacy in helminth infection-endemic areas is not well characterized. We evaluated the impact of infection by Heligmosomoides polygyrus bakeri (Hpb), a murine intestinal roundworm, on the efficacy of an mRNA vaccine targeting the Wuhan-1 spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in mice. Although immunization generated similar B cell responses in Hpb-infected and uninfected mice, polyfunctional CD4+ and CD8+ T cell responses were markedly reduced in Hpb-infected mice. Hpb-infected and mRNA-vaccinated mice were protected against the ancestral SARS-CoV-2 strain WA1/2020, but control of lung infection was diminished against an Omicron variant compared with animals immunized without Hpb infection. Helminth-mediated suppression of spike protein-specific CD8+ T cell responses occurred independently of signal transducer and activator of transcription 6 (STAT6) signaling, whereas blockade of interleukin-10 (IL-10) rescued vaccine-induced CD8+ T cell responses. Together, these data show that, in mice, intestinal helminth infection impaired vaccine-induced T cell responses through an IL-10 pathway, which compromised protection against antigenically drifted SARS-CoV-2 variants.

Trichinella spiralis Infection Inhibits the Efficacy of RBD Protein of SARS-CoV-2 Vaccination via Regulating Humoral and Cellular Immunity

Vaccines are the most effective and feasible way to control pathogen infection. Helminths have been reported to jeopardize the protective immunity mounted by several vaccines. However, there are no experimental data about the effect of helminth infection on the effectiveness of COVID-19 vaccines. Here, a mouse model of trichinosis, a common zoonotic disease worldwide, was used to investigate effects of Trichinella spiralis infection on the RBD protein vaccine of SARS-CoV-2 and the related immunological mechanism, as well as the impact of albendazole (ALB) deworming on the inhibitory effect of the parasite on the vaccination. The results indicated that both the enteric and muscular stages of T. spiralis infection inhibited the vaccine efficacy, evidenced by decreased levels of IgG, IgM, sIgA, and reduced serum neutralizing antibodies, along with suppressed splenic germinal center (GC) B cells in the vaccinated mice. Pre-exposure to trichinosis promoted Th2 and/or Treg immune responses in the immunized mice. Furthermore, ALB treatment could partially reverse the inhibitory effect of T. spiralis infection on the efficiency of the vaccination, accompanied by a restored proportion of splenic GC B cells. Therefore, given the widespread prevalence of helminth infections worldwide, deworming therapy needs to be considered when implementing COVID-19 vaccination strategies.

Live Attenuated Vaccines against Tuberculosis: Targeting the Disruption of Genes Encoding the Secretory Proteins of Mycobacteria

Tuberculosis (TB), a chronic infectious disease affecting humans, causes over 1.3 million deaths per year throughout the world. The current preventive vaccine BCG provides protection against childhood TB, but it fails to protect against pulmonary TB. Multiple candidates have been evaluated to either replace or boost the efficacy of the BCG vaccine, including subunit protein, DNA, virus vector-based vaccines, etc., most of which provide only short-term immunity. Several live attenuated vaccines derived from Mycobacterium tuberculosis (Mtb) and BCG have also been developed to induce long-term immunity. Since Mtb mediates its virulence through multiple secreted proteins, these proteins have been targeted to produce attenuated but immunogenic vaccines. In this review, we discuss the characteristics and prospects of live attenuated vaccines generated by targeting the disruption of the genes encoding secretory mycobacterial proteins.

Immunological factors linked to geographical variation in vaccine responses

Vaccination is one of medicine's greatest achievements; however, its full potential is hampered by considerable variation in efficacy across populations and geographical regions. For example, attenuated malaria vaccines in high-income countries confer almost 100% protection, whereas in low-income regions these same vaccines achieve only 20-50% protection. This trend is also observed for other vaccines, such as bacillus Calmette-Guérin (BCG), rotavirus and yellow fever vaccines, in terms of either immunogenicity or efficacy. Multiple environmental factors affect vaccine responses, including pathogen exposure, microbiota composition and dietary nutrients. However, there has been variable success with interventions that target these individual factors, highlighting the need for a better understanding of their downstream immunological mechanisms to develop new ways of modulating vaccine responses. Here, we review the immunological factors that underlie geographical variation in vaccine responses. Through the identification of causal pathways that link environmental influences to vaccine responsiveness, it might become possible to devise modulatory compounds that can complement vaccines for better outcomes in regions where they are needed most.

Intestinal helminth infection impairs vaccine-induced T cell responses and protection against SARS-CoV-2

Although vaccines have reduced COVID-19 disease burden, their efficacy in helminth infection endemic areas is not well characterized. We evaluated the impact of infection by Heligmosomoides polygyrus bakeri (Hpb), a murine intestinal hookworm, on the efficacy of an mRNA vaccine targeting the Wuhan-1 spike protein of SARS-CoV-2. Although immunization generated similar B cell responses in Hpb-infected and uninfected mice, polyfunctional CD4+ and CD8+ T cell responses were markedly reduced in Hpb-infected mice. Hpb-infected and mRNA vaccinated mice were protected against the ancestral SARS-CoV-2 strain WA1/2020, but control of lung infection was diminished against an Omicron variant compared to animals immunized without Hpb infection. Helminth mediated suppression of spike-specific CD8+ T cell responses occurred independently of STAT6 signaling, whereas blockade of IL-10 rescued vaccine-induced CD8+ T cell responses. In mice, intestinal helminth infection impairs vaccine induced T cell responses via an IL-10 pathway and compromises protection against antigenically shifted SARS-CoV-2 variants.

Importance of adjuvant selection in tuberculosis vaccine development: Exploring basic mechanisms and clinical implications

The global emergency of unexpected pathogens, exemplified by SARS-CoV-2, has emphasized the importance of vaccines in thwarting infection and curtailing the progression of severe disease. The scourge of tuberculosis (TB), emanating from the Mycobacterium tuberculosis (Mtb) complex, has inflicted a more profound toll in terms of mortality and morbidity than any other infectious agents prior to the SARS-CoV-2 pandemic. Despite the existence of Bacillus Calmette-Guérin (BCG), the only licensed vaccine developed a century ago, its efficacy against TB remains unsatisfactory, particularly in preventing pulmonary Mtb infections in adolescents and adults. However, collaborations between academic and industrial entities have led to a renewed impetus in the development of TB vaccines, with numerous candidates, particularly subunit vaccines with specialized adjuvants, exhibiting promising outcomes in recent clinical studies. Adjuvants are crucial in modulating optimal immunological responses, by endowing immune cells with sufficient antigen and immune signals. As exemplified by the COVID-19 vaccine landscape, the interplay between vaccine efficacy and adverse effects is of paramount importance, particularly for the elderly and individuals with underlying ailments such as diabetes and concurrent infections. In this regard, adjuvants hold the key to optimizing vaccine efficacy and safety. This review accentuates the pivotal roles of adjuvants and their underlying mechanisms in the development of TB vaccines. Furthermore, we expound on the prospects for the development of more efficacious adjuvants and their synergistic combinations for individuals in diverse states, such as aging, HIV co-infection, and diabetes, by examining the immunological alterations that arise with aging and comparing them with those observed in younger cohorts.

Bridging the gaps to overcome major hurdles in the development of next-generation tuberculosis vaccines

Although tuberculosis (TB) remains one of the leading causes of death from an infectious disease worldwide, the development of vaccines more effective than bacille Calmette-Guérin (BCG), the only licensed TB vaccine, has progressed slowly even in the context of the tremendous global impact of TB. Most vaccine candidates have been developed to strongly induce interferon-γ (IFN-γ)-producing T-helper type 1 (Th1) cell responses; however, accumulating evidence has suggested that other immune factors are required for optimal protection against Mycobacterium tuberculosis (Mtb) infection. In this review, we briefly describe the five hurdles that must be overcome to develop more effective TB vaccines, including those with various purposes and tested in recent promising clinical trials. In addition, we discuss the current knowledge gaps between preclinical experiments and clinical studies regarding peripheral versus tissue-specific immune responses, different underlying conditions of individuals, and newly emerging immune correlates of protection. Moreover, we propose how recently discovered TB risk or susceptibility factors can be better utilized as novel biomarkers for the evaluation of vaccine-induced protection to suggest more practical ways to develop advanced TB vaccines. Vaccines are the most effective tools for reducing mortality and morbidity from infectious diseases, and more advanced technologies and a greater understanding of host-pathogen interactions will provide feasibility and rationale for novel vaccine design and development.

Intestinal Helminth Infection Impairs Oral and Parenteral Vaccine Efficacy

The impact of endemic parasitic infection on vaccine efficacy is an important consideration for vaccine development and deployment. We have examined whether intestinal infection with the natural murine helminth Heligmosomoides polygyrus bakeri alters Ag-specific Ab and cellular immune responses to oral and parenteral vaccination in mice. Oral vaccination of mice with a clinically relevant, live, attenuated, recombinant Salmonella vaccine expressing chicken egg OVA (Salmonella-OVA) induced the accumulation of activated, OVA-specific T effector cells rather than OVA-specific regulatory T cells in the GALT. Intestinal helminth infection significantly reduced Th1-skewed Ab responses to oral vaccination with Salmonella-OVA. Activated, adoptively transferred, OVA-specific CD4+ T cells accumulated in draining mesenteric lymph nodes of vaccinated mice, regardless of their helminth infection status. However, helminth infection increased the frequencies of adoptively transferred OVA-specific CD4+ T cells producing IL-4 and IL-10 in the mesenteric lymph node. Ab responses to the oral Salmonella-OVA vaccine were reduced in helminth-free mice adoptively transferred with OVA-specific CD4+ T cells harvested from mice with intestinal helminth infection. Intestinal helminth infection also significantly reduced Th2-skewed Ab responses to parenteral vaccination with OVA adsorbed to alum. These findings suggest that vaccine-specific CD4+ T cells induced in the context of helminth infection retain durable immunomodulatory properties and may promote blunted Ab responses to vaccination. They also underscore the potential need to treat parasitic infection before mass vaccination campaigns in helminth-endemic areas.

Cytokine Responses during Mycobacterium tuberculosis H37Rv and Ascaris lumbricoides Costimulation Using Human THP-1 and Jurkat Cells, and a Pilot Human Tuberculosis and Helminth Coinfection Study

BACKGROUND

Helminth infections are widespread in tuberculosis-endemic areas and are associated with an increased risk of active tuberculosis. In contrast to the pro-inflammatory Th1 responses elicited by Mycobacterium tuberculosis (Mtb) infection, helminth infections induce anti-inflammatory Th2/Treg responses. A robust Th2 response has been linked to reduced tuberculosis protection. Several studies show the effect of helminth infection on BCG vaccination and TB, but the mechanisms remain unclear.

AIM

To determine the cytokine response profiles during tuberculosis and intestinal helminth coinfection.

METHODS

For the in vitro study, lymphocytic Jurkat and monocytic THP-1 cell lines were stimulated with Mtb H37Rv and Ascaris lumbricoides (A. lumbricoides) excretory-secretory protein extracts for 24 and 48 h. The pilot human ex vivo study consisted of participants infected with Mtb, helminths, or coinfected with both Mtb and helminths. Thereafter, the gene transcription levels of IFN-γ, TNF-α, granzyme B, perforin, IL-2, IL-17, NFATC2, Eomesodermin, IL-4, IL-5, IL-10, TGF-β and FoxP3 in the unstimulated/uninfected controls, singly stimulated/infected and costimulated/coinfected groups were determined using RT-qPCR.

RESULTS

TB-stimulated Jurkat cells had significantly higher levels of IFN-γ, TNF-α, granzyme B, and perforin compared to unstimulated controls, LPS- and A. lumbricoides-stimulated cells, and A. lumbricoides plus TB-costimulated cells (p < 0.0001). IL-2, IL-17, Eomes, and NFATC2 levels were also higher in TB-stimulated Jurkat cells (p < 0.0001). Jurkat and THP-1 cells singly stimulated with TB had lower IL-5 and IL-4 levels compared to those singly stimulated with A. lumbricoides and those costimulated with TB plus A. lumbricoides (p < 0.0001). A. lumbricoides-singly stimulated cells had higher IL-4 levels compared to TB plus A. lumbricoides-costimulated Jurkat and THP-1 cells (p < 0.0001). TGF-β levels were also lower in TB-singly stimulated cells compared to TB plus A. lumbricoides-costimulated cells (p < 0.0001). IL-10 levels were lower in TB-stimulated Jurkat and THP-1 cells compared to TB plus A. lumbricoides-costimulated cells (p < 0.0001). Similar results were noted for the human ex vivo study, albeit with a smaller sample size.

CONCLUSIONS

Data suggest that helminths induce a predominant Th2/Treg response which may downregulate critical Th1 responses that are crucial for tuberculosis protection.

Seroepidemiology of Strongyloides spp. Infection in Balimo, Western Province, Papua New Guinea

Strongyloidiasis in Papua New Guinea (PNG) is poorly understood. There have been limited surveys describing the levels of endemicity in some regions of PNG, but in the Western Province, its occurrence and level of burden are unknown. This study aimed to determine the seroepidemiology of Strongyloides spp. seropositivity within a community located in the Balimo region of the Western Province. Plasma samples were collected from 120 adult participants and were subjected to anti-IgG Strongyloides spp. serological testing. Logistical regression analyses were performed to identify relationships between strongyloidiasis and attributes of sociodemography. In this cross-sectional cohort study, 22.5% (27/120; 95% CI: 15.9-30.8%) of participants were seropositive for strongyloidiasis. Participants with higher body mass indices were less likely to be seropositive for Strongyloides spp. infection (odds ratio [OR] = 0.85, P value = 0.008), and in the multivariable analysis, increasing units of age (adjusted OR [aOR] = 0.93, P value = 0.048) and participants ≤ 40 years old were associated with a decreased likelihood of Strongyloides spp. seropositivity (aOR = 0.07, P value = 0.034). The results from this study indicate that the occurrence of strongyloidiasis is high in the Western Province, PNG, and age is a determining factor of seroreactivity. This study provides evidence of endemic strongyloidiasis in this community and raises questions as to the impact of this neglected disease and other intestinal parasites on disease burden and comorbidities.

Protozoan co-infections and parasite influence on the efficacy of vaccines against bacterial and viral pathogens

A wide range of protozoan pathogens either transmitted by vectors (Plasmodium, Babesia, Leishmania and Trypanosoma), by contaminated food or water (Entamoeba and Giardia), or by sexual contact (Trichomonas) invade various organs in the body and cause prominent human diseases, such as malaria, babesiosis, leishmaniasis, trypanosomiasis, diarrhea, and trichomoniasis. Humans are frequently exposed to multiple pathogens simultaneously, or sequentially in the high-incidence regions to result in co-infections. Consequently, synergistic or antagonistic pathogenic effects could occur between microbes that also influences overall host responses and severity of diseases. The co-infecting organisms can also follow independent trajectory. In either case, co-infections change host and pathogen metabolic microenvironments, compromise the host immune status, and affect microbial pathogenicity to influence tissue colonization. Immunomodulation by protozoa often adversely affects cellular and humoral immune responses against co-infecting bacterial pathogens and promotes bacterial persistence, and result in more severe disease symptoms. Although co-infections by protozoa and viruses also occur in humans, extensive studies are not yet conducted probably because of limited animal model systems available that can be used for both groups of pathogens. Immunosuppressive effects of protozoan infections can also attenuate vaccines efficacy, weaken immunological memory development, and thus attenuate protection against co-infecting pathogens. Due to increasing occurrence of parasitic infections, roles of acute to chronic protozoan infection on immunological changes need extensive investigations to improve understanding of the mechanistic details of specific immune responses alteration. In fact, this phenomenon should be seriously considered as one cause of breakthrough infections after vaccination against both bacterial and viral pathogens, and for the emergence of drug-resistant bacterial strains. Such studies would facilitate development and implementation of effective vaccination and treatment regimens to prevent or significantly reduce breakthrough infections.

Immunological Interactions between Intestinal Helminth Infections and Tuberculosis

Helminth infections are among the neglected tropical diseases affecting billions of people globally, predominantly in developing countries. Helminths’ effects are augmented by coincident tuberculosis disease, which infects a third of the world’s population. The role of helminth infections on the pathogenesis and pathology of active tuberculosis (T.B.) remains controversial. Parasite-induced suppression of the efficacy of Bacille Calmette-Guerin (BCG) has been widely reported in helminth-endemic areas worldwide. T.B. immune response is predominantly proinflammatory T-helper type 1 (Th1)-dependent. On the other hand, helminth infections induce an opposing anti-inflammatory Th2 and Th3 immune-regulatory response. This review summarizes the literature focusing on host immune response profiles during single-helminth, T.B. and dual infections. It also aims to necessitate investigations into the complexity of immunity in helminth/T.B. coinfected patients since the research data are limited and contradictory. Helminths overlap geographically with T.B., particularly in Sub-Saharan Africa. Each disease elicits a response which may skew the immune responses. However, these effects are helminth species-dependent, where some parasites have no impact on the immune responses to concurrent T.B. The implications for the complex immunological interactions that occur during coinfection are highlighted to inform government treatment policies and encourage the development of high-efficacy T.B. vaccines in areas where helminths are prevalent.

A New Role for Old Friends: Effects of Helminth Infections on Vaccine Efficacy

Vaccines are one of the most successful medical inventions to enable the eradication or control of common and fatal diseases. Environmental exposure of hosts, including helminth infections, plays an important role in immune responses to vaccines. Given that helminth infections are among the most common infectious diseases in the world, evaluating vaccine efficiency in helminth-infected populations may provide critical information for selecting optimal vaccination programs. Here, we reviewed the effects of helminth infections on vaccination and its underlying immunological mechanisms, based on findings from human studies and animal models. Moreover, the potential influence of helminth infections on SARS-CoV-2 vaccine was also discussed. Based on these findings, there is an urgent need for anthelmintic treatments to eliminate helminth suppressive impacts on vaccination effectiveness during implementing mass vaccination in parasite endemic areas.

A century of BCG vaccination: Immune mechanisms, animal models, non-traditional routes and implications for COVID-19

Bacillus Calmette-Guerin (BCG) has been used as a vaccine against tuberculosis since 1921 and remains the only currently approved vaccine for this infection. The recent discovery that BCG protects against initial infection, and not just against progression from latent to active disease, has significant implications for ongoing research into the immune mechanisms that are relevant to generate a solid host defense against Mycobacterium tuberculosis (Mtb). In this review, we first explore the different components of immunity that are augmented after BCG vaccination. Next, we summarize current efforts to improve the efficacy of BCG through the development of recombinant strains, heterologous prime-boost approaches and the deployment of non-traditional routes. These efforts have included the development of new recombinant BCG strains, and various strategies for expression of important antigens such as those deleted during the M. bovis attenuation process or antigens that are present only in Mtb. BCG is typically administered via the intradermal route, raising questions about whether this could account for its apparent failure to generate long-lasting immunological memory in the lungs and the inconsistent level of protection against pulmonary tuberculosis in adults. Recent years have seen a resurgence of interest in the mucosal and intravenous delivery routes as they have been shown to induce a better immune response both in the systemic and mucosal compartments. Finally, we discuss the potential benefits of the ability of BCG to confer trained immunity in a non-specific manner by broadly stimulating a host immunity resulting in a generalized survival benefit in neonates and the elderly, while potentially offering benefits for the control of new and emerging infectious diseases such as COVID-19. Given that BCG will likely continue to be widely used well into the future, it remains of critical importance to better understand the immune responses driven by it and how to leverage these for the design of improved vaccination strategies against tuberculosis.

Helminth species dependent effects on Th1 and Th17 cytokines in active tuberculosis patients and healthy community controls

Despite that the impact of different helminth species is not well explored, the current dogma states that helminths affect the Th1/Th2 balance which in turn affects the risk of tuberculosis (TB) reactivation and severity of disease. We investigated the influence of helminth species on cytokine profiles including IL-17A in TB patients and healthy community controls (CCs). In total, 104 newly diagnosed pulmonary TB patients and 70 HIV negative and QuantiFERON negative CCs in Gondar, Ethiopia were included following helminth screening by stool microscopy. Plasma samples and ex vivo stimulation of peripheral blood mononuclear cells (PBMCs) with purified protein derivative (PPD) and Staphylococcus enterotoxin B (SEB) was used to determine cytokine profiles by cytometric bead array. In CCs, Ascaris lumbricoides or Schistosoma mansoni infections were associated with an impaired Th1-type response (IFN-gamma, IL-6 and TNF-alpha) in PBMCs mainly with SEB stimulations, whereas in TB patients only hookworm infection showed a similar pattern. Among CCs, the IL-17A response in PBMCs stimulated with SEB was higher only for S. mansoni, whereas in TB patients, the elevated systemic IL-17A plasma level was significantly suppressed in hookworm infected TB patients compared to patients without helminth coinfection. Following treatment of TB and helminth infection there was a general decrease in ex vivio IL-10 and TNF-alpha production in unstimulated, PPD or SEB stimulated PBMCs that was the most pronounced and significant in TB patients infected with S. mansoni, whereas the follow-up levels of IFN-gamma and IL-17A was significantly increased only in TB patients without helminth coinfection from PBMCs stimulated mainly with SEB. In summary, in addition to confirming helminth specific effects on the Th1/Th2 response before and after TB treatment, our novel finding is that IL-17A was impaired in helminth infected TB patients especially for hookworm, indicating a helminth species-specific immunoregulatory effect on IL-17A which needs to be further investigated.

Immunometabolism of Immune Cells in Mucosal Environment Drives Effector Responses against Mycobacterium tuberculosis

Tuberculosis remains a major threat to global public health, with more than 1.5 million deaths recorded in 2020. Improved interventions against tuberculosis are urgently needed, but there are still gaps in our knowledge of the host-pathogen interaction that need to be filled, especially at the site of infection. With a long history of infection in humans, Mycobacterium tuberculosis (Mtb) has evolved to be able to exploit the microenvironment of the infection site to survive and grow. The immune cells are not only reliant on immune signalling to mount an effective response to Mtb invasion but can also be orchestrated by their metabolic state. Cellular metabolism was often overlooked in the past but growing evidence of its importance in the functions of immune cells suggests that it can no longer be ignored. This review aims to gain a better understanding of mucosal immunometabolism of resident effector cells, such as alveolar macrophages and mucosal-associated invariant T cells (MAIT cells), in response to Mtb infection and how Mtb manipulates them for its survival and growth, which could address our knowledge gaps while opening up new questions, and potentially be applied for future vaccination and therapeutic strategies.

The Road to Elimination: Current State of Schistosomiasis Research and Progress Towards the End Game

The new WHO Roadmap for Neglected Tropical Diseases targets the global elimination of schistosomiasis as a public health problem. To date, control strategies have focused on effective diagnostics, mass drug administration, complementary and integrative public health interventions. Non-mammalian intermediate hosts and other vertebrates promote transmission of schistosomiasis and have been utilized as experimental model systems. Experimental animal models that recapitulate schistosomiasis immunology, disease progression, and pathology observed in humans are important in testing and validation of control interventions. We discuss the pivotal value of these models in contributing to elimination of schistosomiasis. Treatment of schistosomiasis relies heavily on mass drug administration of praziquantel whose efficacy is comprised due to re-infections and experimental systems have revealed the inability to kill juvenile schistosomes. In terms of diagnosis, nonhuman primate models have demonstrated the low sensitivity of the gold standard Kato Katz smear technique. Antibody assays are valuable tools for evaluating efficacy of candidate vaccines, and sera from graded infection experiments are useful for evaluating diagnostic sensitivity of different targets. Lastly, the presence of Schistosomes can compromise the efficacy of vaccines to other infectious diseases and its elimination will benefit control programs of the other diseases. As the focus moves towards schistosomiasis elimination, it will be critical to integrate treatment, diagnostics, novel research tools such as sequencing, improved understanding of disease pathogenesis and utilization of experimental models to assist with evaluating performance of new approaches.

A Combination of Deworming and Prime-Boost Vaccination Regimen Restores Efficacy of Vaccination Against Influenza in Helminth-Infected Mice

Helminths still infect a quarter of the human population. They manage to establish chronic infections by downmodulating the immune system of their hosts. Consequently, the immune response of helminth-infected individuals to vaccinations may be impaired as well. Here we study the impact of helminth-induced immunomodulation on vaccination efficacy in the mouse system. We have previously shown that an underlying Litomosoides sigmodontis infection reduced the antibody (Ab) response to anti-influenza vaccination in the context of a systemic expansion of type 1 regulatory T cells (Tr1). Most important, vaccine-induced protection from a challenge infection with the 2009 pandemic H1N1 influenza A virus (2009 pH1N1) was impaired in vaccinated, L. sigmodontis-infected mice. Here, we aim at the restoration of vaccination efficacy by drug-induced deworming. Treatment of mice with Flubendazole (FBZ) resulted in elimination of viable L. sigmodontis parasites in the thoracic cavity after two weeks. Simultaneous FBZ-treatment and vaccination did not restore Ab responses or protection in L. sigmodontis-infected mice. Likewise, FBZ-treatment two weeks prior to vaccination did not significantly elevate the influenza-specific Ig response and did not protect mice from a challenge infection with 2009 pH1N1. Analysis of the regulatory T cell compartment revealed that L. sigmodontis-infected and FBZ-treated mice still displayed expanded Tr1 cell populations that may contribute to the sustained suppression of vaccination responses in successfully dewormed mice. To outcompete this sustained immunomodulation in formerly helminth-infected mice, we finally combined the drug-induced deworming with an improved vaccination regimen. Two injections with the non-adjuvanted anti-influenza vaccine Begripal conferred 60% protection while MF59-adjuvanted Fluad conferred 100% protection from a 2009 pH1N1 infection in FBZ-treated, formerly L. sigmodontis-infected mice. Of note, applying this improved prime-boost regimen did not restore protection in untreated L. sigmodontis-infected mice. In summary our findings highlight the risk of failed vaccinations due to helminth infection.

Tissue-specific immunity in helminth infections

A characteristic feature of host responses to helminth infections is the development of profound systemic and tissue-localised Type 2 immune responses that play critical roles in immunity, tissue repair and tolerance of the parasite at tissue sites. These same Type 2 responses are also seen in the tissue-associated immune-pathologies seen in asthma, atopic dermatitis and many forms of allergies. The recent identification of new subtypes of immune cells and cytokine pathways that influence both immune and non-immune cells and tissues creates the opportunity for reviewing helminth parasite-host responses in the context of tissue specific immunity. This review focuses on the new discoveries of the cells and cytokines involved in tissue specific immune responses to helminths and how these contribute to host immunity against helminth infection and allow the host to accommodate the presence of parasites when they cannot be eliminated.

Intestinal helminth infection transforms the CD4+ T cell composition of the skin

Intestinal helminth parasites can alter immune responses to vaccines, other infections, allergens and autoantigens, implying effects on host immune responses in distal barrier tissues. We herein show that the skin of C57BL/6 mice infected with the strictly intestinal nematode Heligmosomoides polygyrus contain higher numbers of CD4⁺ T cells compared to the skin of uninfected controls. Accumulated CD4⁺ T cells were H. polygyrus-specific T_H2 cells that skewed the skin CD4⁺ T cell composition towards a higher T_H2/T_H1 ratio which persisted after worm expulsion. Accumulation of T_H2 cells in the skin was associated with increased expression of the skin-homing chemokine receptors CCR4 and CCR10 on CD4⁺ T cells in the blood and mesenteric lymph nodes draining the infected intestine and was abolished by FTY720 treatment during infection, indicating gut-to-skin trafficking of cells. Remarkably, skin T_H2 accumulation was associated with impaired capacity to initiate IFN-γ recall responses and develop skin-resident memory cells to mycobacterial antigens, both during infection and months after deworming therapy. In conclusion, we show that infection by a strictly intestinal helminth has long-term effects on immune cell composition and local immune responses to unrelated antigens in the skin, revealing a novel process for T cell colonisation and worm-mediated immunosuppression in this organ.

Helminth infection is associated with dampened cytokine responses to viral and bacterial stimulations in Tsimane forager-horticulturalists

Background

Soil-transmitted helminths (STHs) and humans share long co-evolutionary histories over which STHs have evolved strategies to permit their persistence by downregulating host immunity. Understanding the interactions between STHs and other pathogens can inform our understanding of human evolution and contemporary disease patterns.

Methodology

We worked with Tsimane forager-horticulturalists in the Bolivian Amazon, where STHs are prevalent. We tested whether STHs and eosinophil levels—likely indicative of infection in this population—are associated with dampened immune responses to in vitro stimulation with H1N1 and lipopolysaccharide (LPS) antigens. Whole blood samples (n = 179) were treated with H1N1 vaccine and LPS and assayed for 13 cytokines (INF-γ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12p70, IL-13, GM-CSF and TNF-ɑ). We evaluated how STHs and eosinophil levels affected cytokine responses and T helper (Th) 1 and Th2-cytokine suite responses to stimulation.

Results

Infection with Ascaris lumbricoides was significantly (P ≤ 0.05) associated with lower response of some cytokines to H1N1 and LPS in women. Eosinophils were significantly negatively associated with some cytokine responses to H1N1 and LPS, with the strongest effects in women, and associated with a reduced Th1- and Th2-cytokine response to H1N1 and LPS in women and men.

Conclusions and implications

Consistent with the ‘old friends’ and hygiene hypotheses, we find that STHs were associated with dampened cytokine responses to certain viral and bacterial antigens. This suggests that STH infections may play an essential role in immune response regulation and that the lack of STH immune priming in industrialized populations may increase the risk of over-reactive immunity.

Lay Summary: Indicators of helminth infection were associated with dampened cytokine immune responses to in vitro stimulation with viral and bacterial antigens in Tsimane forager-horticulturalists in the Bolivian Amazon, consistent with the ‘old friends’ and hygiene hypotheses.

SARS-CoV-2 and helminth co-infections, and environmental pollution exposure: An epidemiological and immunological perspective

Soil-transmitted helminths infect billions of people globally, particularly those residing in low- and middle-income regions with poor environmental sanitation and high levels of air and water pollution. Helminths display potent immunomodulatory activity by activating T helper type 2 (Th2) anti-inflammatory and Th3 regulatory immune responses. The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus that causes Coronavirus disease 2019 (COVID-19), can exacerbate Th1/Th17 pro-inflammatory cytokine production in humans, leading to a cytokine storm. Air pollutants (particulate matter, oxygen radicals, hydrocarbons and volatile organic compounds) and water pollutants (metals and organic chemicals) can also intensify Th1/Th17 immune response and could exacerbate SARS-CoV-2 related respiratory distress and failure. The present review focused on the epidemiology of SARS-CoV-2, helminths and fine particulate matter 2.5 µm or less in diameter (PM2.5) air pollution exposure in helminth endemic regions, the possible immunomodulatory activity of helminths against SARS-CoV-2 hyper-inflammatory immune response, and whether air and water pollutants can further exacerbate SARS-CoV-2 related cytokine storm and in the process hinder helminths immunomodulatory functionality. Helminth Th2/Th3 immune response is associated with reductions in lung inflammation and damage, and decreased expression levels of angiotensin-converting enzyme 2 (ACE2) receptors (SARS-CoV-2 uses the ACE2 receptors to infect cells and associated with extensive lung damage). However, air pollutants are associated with overexpression of ACE2 receptors in the epithelial cell surface of the respiratory tract and exhaustion of Th2 immune response. Helminth-induced immunosuppression activity reduces vaccination efficacy, and diminishes vital Th1 cytokine production immune responses that are crucial for combating early stage infections. This could be reversed by continuous air pollution exposure which is known to intensify Th1 pro-inflammatory cytokine production to a point where the immunosuppressive activities of helminths could be hindered. Again, suppressed activities of helminths can also be disadvantageous against SARS-CoV-2 inflammatory response. This "yin and yang" approach seems complex and requires more understanding. Further studies are warranted in a cohort of SARS-CoV-2 infected individuals residing in helminths and air pollution endemic regions to offer more insights, and to impact mass periodic deworming programmes and environmental health policies.

Identifying novel candidates and configurations for human helminth vaccines

INTRODUCTION

: Human infections with helminth worm parasites are extraordinarily prevalent across tropical and subtropical parts of the world, and control relies primarily on drugs that offer short-term suppression of infection. There is an urgent need for new vaccines that would confer long-lived immunity, protecting children in particular and minimizing community transmission.

AREAS COVERED

: This article discusses the development of helminth vaccines, from the first successful veterinary vaccines that demonstrated the feasibility of inducing protective immunity to helminths, to more recent initiatives to test human helminth antigens. The field has focussed primarily on evaluating individual antigens that could constitute targets amenable to antibody attack to inhibit parasite establishment. In a new direction, vaccines employing extracellular vesicles released by helminths have also given exciting results.

EXPERT OPINION

: Taking into account the complex life cycles and sophisticated immune evasion strategies of many helminths, a combination of antigens and approaches designed to target essential functional pathways of the parasite will be required to achieve a high level of protection in future anti-helminth vaccines.

Investigating immunological interaction between lymphatic filariasis and COVID-19 infection: a preliminary evidence

The foremost concerns of COVID-19 vaccines are safety and efficacy, which becomes grave in countries with a high burden of Neglected Tropical Diseases. Studies proposed helminthic infections might alleviate the efficacy of COVID-19 vaccines. We share preliminary evidence on the association between filariasis and COVID-19 infection. We collated 2 ml of blood from 174 participants residing in filariasis endemic area. To determine filarial antigen, the Og4C3 test and for COVID-19 antibodies, tests through ELISA was performed. COVID-19 antibodies were present among 74/174 (42.5%), whereas filarial antigens were detected in 24/174 (13.8%) participants. An insignificant association [OR = 0.855 (0.36-2.034)] between two was observed. Hence, people in filarial endemic regions can continue taking vaccines without worrying about their efficacy due to the helminthic load in community.

The multi-faceted roles of TGF-β in regulation of immunity to infection

Transforming Growth Factor-β is a potent regulator of the immune system, acting at every stage from thymic differentiation, population of the periphery, control of responsiveness, tissue repair and generation of memory. It is therefore a central player in the immune response to infectious pathogens, but its contribution is often clouded by multiple roles acting on different cells in time and space. Hence, context is all-important in understanding when TGF-β is beneficial or detrimental to the outcome of infection. In this review, a full range of infectious agents from viruses to helminth parasites are explored within this framework, drawing contrasts and general conclusions about the importance of TGF-β in these diseases.

Activity of the Toll-like receptor ligands in children with high and low socioeconomic backgrounds

BACKGROUND

Adjuvants are essential in the induction of immunity by vaccines and interact with receptors, including the Toll-like receptors (TLRs). Responsiveness of these receptors differs between and within populations, which impacts vaccine effectiveness.

OBJECTIVE

Here we examine how the innate cytokine response towards TLR ligands differs between high and low socioeconomic status (SES) school-aged children from Makassar, Indonesia.

METHODS

We stimulated whole blood from children, of which 27 attended a high SES school and 27 children a low SES school, with ligands for TLR-2/1, -2/6, -3, -4, -5, -7, -9 and measured pro- (TNF) and anti-inflammatory (IL-10) cytokines released.

RESULTS

In the low SES there is an increased pro-inflammatory response after 24 h stimulation with TLR-2/1 ligand Pam3 and TLR-4 ligand LPS compared to the high SES. Comparison of the response to LPS after 24 h versus 72 h stimulation revealed that the pro-inflammatory response in the low SES after 24 h shifts to an anti-inflammatory response, whereas in the high SES the initial anti-inflammatory response shifts to a strong pro-inflammatory response after 72 h stimulation.

CONCLUSION

We observed differences in the TLR-mediated innate immune response between children attending low and high SES schools, which can have important implications for vaccine development.

Effect of Helicobacter pylori and Helminth Coinfection on the Immune Response to Mycobacterium tuberculosis

Tuberculosis remains one of the main causes of morbidity and mortality worldwide despite decades of efforts to eradicate the disease. Although the immune response controls the infection in most infected individuals (90%), the ability of the bacterium to persist throughout the host's life leads to a risk of reactivation. Underlying conditions including human immunodeficiency virus (HIV) infection, organ transplantation, and immunosuppressive therapies are considered risk factors for progression to active disease. However, many individuals infected with Mycobacterium tuberculosis may develop clinical disease in the absence of underlying immunosuppression. It is also possible that unknown conditions may drive the progression to disease. The human microbiota can be an important modulator of the immune system; it can not only trigger inflammatory disorders, but also drive the response to other infectious diseases. In developing countries, chronic mucosal infections with Helicobacter pylori and helminths may be particularly important, as these infections frequently coexist throughout the host's life. However, little is known about the interactions of these pathogens with the immune system and their effects on M. tuberculosis clinical disease, if any. In this review, we discuss the potential effects of H. pylori and helminth co-infections on the immune response to M. tuberculosis. This may contribute to our understanding of host-pathogen interactions and in designing new strategies for the prevention and control of tuberculosis.

Exploratory analysis of the effect of helminth infection on the immunogenicity and efficacy of the asexual blood-stage malaria vaccine candidate GMZ2

Background

Helminths can modulate the host immune response to Plasmodium falciparum and can therefore affect the risk of clinical malaria. We assessed here the effect of helminth infections on both the immunogenicity and efficacy of the GMZ2 malaria vaccine candidate, a recombinant protein consisting of conserved domains of GLURP and MSP3, two asexual blood-stage antigens of P. falciparum. Controlled human malaria infection (CHMI) was used to assess the efficacy of the vaccine.

Methodology

In a randomized, double-blind Phase I clinical trial, fifty, healthy, lifelong malaria-exposed adult volunteers received three doses of GMZ2 adjuvanted with either Cationic Adjuvant Formulation (CAF) 01 or Alhydrogel, or a control vaccine (Rabies) on days (D) 0, D28 and D56, followed by direct venous inoculation (DVI) of 3,200 P. falciparum sporozoites (PfSPZ Challenge) approximately 13 weeks after last vaccination to assess vaccine efficacy. Participants were followed-up on a daily basis with clinical examinations and thick blood smears to monitor P. falciparum parasitemia for 35 days. Malaria was defined as the presence of P. falciparum parasites in the blood associated with at least one symptom that can be associated to malaria over 35 days following DVI of PfSPZ Challenge. Soil-transmitted helminth (STH) infection was assessed by microscopy and by polymerase chain reaction (PCR) on stool, and Schistosoma infection was assessed by microscopy on urine. Participants were considered as infected if positive for any helminth either by PCR and/or microscopy at D0 and/or at D84 (Helm+) and were classified as mono-infection or co-infection. Total vaccine-specific IgG concentrations assessed on D84 were analysed as immunogenicity outcome.

Main findings

The helminth in mono-infection, particularly Schistosoma haematobium and STH were significantly associated with earlier malaria episodes following CHMI, while no association was found in case of coinfection. In further analyses, the anti-GMZ2 IgG concentration on D84 was significantly higher in the S. haematobium-infected and significantly lower in the Strongyloides stercoralis-infected groups, compared to helminth-negative volunteers. Interesting, in the absence of helminth infection, a high anti-GMZ2 IgG concentration on D84 was significantly associated with protection against malaria.

Conclusions

Our results suggest that helminth infection may reduce naturally acquired and vaccine-induced protection against malaria. Vaccine-specific antibody concentrations on D84 may be associated with protection in participants with no helminth infection. These results suggest that helminth infection affect malaria vaccine immunogenicity and efficacy in helminth endemic countries.

Helminths, mainly because of their immune regulatory effects, are able to impact the response induced by vaccines. In the context of clinical trial designs that measure accrual of natural infections during follow up or outcome of controlled human malaria infection (CHMI), their effect on vaccine efficacy can be measured. Indeed, most of such clinical trials on malaria vaccine candidates conducted in Africa, especially where the prevalence of helminths is high, have shown a certain limit in their efficacy and immunogenicity, as compared to results observed in European and U.S volunteers. The present analysis assessed the effect of helminths on GMZ2, a malaria vaccine candidate. We found a high level of anti-GMZ2 antibodies among volunteers not infected with helminths and protected against CHMI, indicating efficacy of the candidate vaccine in this population. We found a species-dependent effect of helminths on the level of post-immunization GMZ2-specific IgG concentration, and an association of helminths with an early onset of malaria in CHMI. Our findings reveal that helminths are associated with immunogenicity and may decrease the protective effect of antibodies induced by vaccination. Helminth infection status shall be determined when measuring the immunogenicity and efficacy of malaria vaccine candidates in helminth endemic countries.

A century of BCG: Impact on tuberculosis control and beyond

BCG turns 100 this year and while it might not be the perfect vaccine, it has certainly contributed significantly towards eradication and prevention of spread of tuberculosis (TB). The search for newer and better vaccines for TB is an ongoing endeavor and latest results from trials of candidate TB vaccines such as M72AS01 look promising. However, recent encouraging data from BCG revaccination trials in adults combined with studies on mucosal and intravenous routes of BCG vaccination in non-human primate models have renewed interest in BCG for TB prevention. In addition, several well-demonstrated non-specific effects of BCG, for example, prevention of viral and respiratory infections, give BCG an added advantage. Also, BCG vaccination is currently being widely tested in human clinical trials to determine whether it protects against SARS-CoV-2 infection and/or death with detailed analyses and outcomes from several ongoing trials across the world awaited. Through this review, we attempt to bring together information on various aspects of the BCG-induced immune response, its efficacy in TB control, comparison with other candidate TB vaccines and strategies to improve its efficiency including revaccination and alternate routes of administration. Finally, we discuss the future relevance of BCG use especially in light of its several heterologous benefits.

Genome-wide insights on gastrointestinal nematode resistance in autochthonous Tunisian sheep

Gastrointestinal nematode (GIN) infections have negative impacts on animal health, welfare and production. Information from molecular studies can highlight the underlying genetic mechanisms that enhance host resistance to GIN. However, such information often lacks for traditionally managed indigenous livestock. Here, we analysed 600 K single nucleotide polymorphism genotypes of GIN infected and non-infected traditionally managed autochthonous Tunisian sheep grazing communal natural pastures. Population structure analysis did not find genetic differentiation that is consistent with infection status. However, by contrasting the infected versus non-infected cohorts using ROH, LR-GWAS, F_ST and XP-EHH, we identified 35 candidate regions that overlapped between at least two methods. Nineteen regions harboured QTLs for parasite resistance, immune capacity and disease susceptibility and, ten regions harboured QTLs for production (growth) and meat and carcass (fatness and anatomy) traits. The analysis also revealed candidate regions spanning genes enhancing innate immune defence (SLC22A4, SLC22A5, IL-4, IL-13), intestinal wound healing/repair (IL-4, VIL1, CXCR1, CXCR2) and GIN expulsion (IL-4, IL-13). Our results suggest that traditionally managed indigenous sheep have evolved multiple strategies that evoke and enhance GIN resistance and developmental stability. They confirm the importance of obtaining information from indigenous sheep to investigate genomic regions of functional significance in understanding the architecture of GIN resistance.

Immunological underpinnings of Ascaris infection, reinfection and co-infection and their associated co-morbidities

Human ascariasis is the most common and prevalent neglected tropical disease and is estimated that ~819 million people are infected around the globe, accounting for 0.861 million years of disability-adjusted life years in 2017. Even with the existence of highly effective drugs, the constant presence of infective parasite eggs in the environment contribute to a high reinfection rate after treatment. Due to its high prevalence and broad geographic distribution Ascaris infection is associated with a variety of co-morbidities and co-infections. Here, we provide data from both experimental models and humans studies that illustrate how complex is the interaction of Ascaris with the host immune system, especially, in the context of reinfections, co-infections and associated co-morbidities.

Immunological Considerations for Schistosoma Vaccine Development: Transitioning to Endemic Settings

Despite mass drug administration programmes with praziquantel, the prevalence of schistosomiasis remains high. A vaccine is urgently needed to control transmission of this debilitating disease. As some promising schistosomiasis vaccine candidates are moving through pre-clinical and clinical testing, we review the immunological challenges that these vaccine candidates may encounter in transitioning through the clinical trial phases in endemic settings. Prior exposure of the target population to schistosomes and other infections may impact vaccine response and efficacy and therefore requires considerable attention. Schistosomes are known for their potential to induce T-reg/IL-10 mediated immune suppression in populations which are chronically infected. Moreover, endemicity of schistosomiasis is focal whereby target and trial populations may exhibit several degrees of prior exposure as well as in utero exposure which may increase heterogeneity of vaccine responses. The age dependent distribution of exposure and development of acquired immunity, and general differences in the baseline immunological profile, adds to the complexity of selecting suitable trial populations. Similarly, prior or concurrent infections with other parasitic helminths, viral and bacterial infections, may alter immunological responses. Consequently, treatment of co-infections may benefit the immunogenicity of vaccines and may be considered despite logistical challenges. On the other hand, viral infections leave a life-long immunological imprint on the human host. Screening for serostatus may be needed to facilitate interpretation of vaccine responses. Co-delivery of schistosome vaccines with PZQ is attractive from a perspective of implementation but may complicate the immunogenicity of schistosomiasis vaccines. Several studies have reported PZQ treatment to induce both transient and long-term immuno-modulatory effects as a result of tegument destruction, worm killing and subsequent exposure of worm antigens to the host immune system. These in turn may augment or antagonize vaccine immunogenicity. Understanding the complex immunological interactions between vaccine, co-infections or prior exposure is essential in early stages of clinical development to facilitate phase 3 clinical trial design and implementation policies. Besides well-designed studies in different target populations using schistosome candidate vaccines or other vaccines as models, controlled human infections could also help identify markers of immune protection in populations with different disease and immunological backgrounds.

Effect of intensive treatment for schistosomiasis on immune responses to vaccines among rural Ugandan island adolescents: randomised controlled trial protocol A for the 'POPulation differences in VACcine responses' (POPVAC) programme

INTRODUCTION

Several licensed and investigational vaccines have lower efficacy, and induce impaired immune responses, in low-income versus high-income countries and in rural, versus urban, settings. Understanding these population differences is essential to optimising vaccine effectiveness in the tropics. We suggest that repeated exposure to and immunomodulation by chronic helminth infections partly explains population differences in vaccine response.

METHODS AND ANALYSIS

We have designed an individually randomised, parallel group trial of intensive versus standard praziquantel (PZQ) intervention against schistosomiasis, to determine effects on vaccine response outcomes among school-going adolescents (9-17 years) from rural Schistosoma mansoni-endemic Ugandan islands. Vaccines to be studied comprise BCG on day 'zero'; yellow fever, oral typhoid and human papilloma virus (HPV) vaccines at week 4; and HPV and tetanus/diphtheria booster vaccine at week 28. The intensive arm will receive PZQ doses three times, each 2 weeks apart, before BCG immunisation, followed by a dose at week 8 and quarterly thereafter. The standard arm will receive PZQ at week 8 and 52. We expect to enrol 480 participants, with 80% infected with S. mansoni at the outset.Primary outcomes are BCG-specific interferon-γ ELISpot responses 8 weeks after BCG immunisation and for other vaccines, antibody responses to key vaccine antigens at 4 weeks after immunisation. Secondary analyses will determine the effects of intensive anthelminthic treatment on correlates of protective immunity, on waning of vaccine response, on priming versus boosting immunisations and on S. mansoni infection status and intensity. Exploratory immunology assays using archived samples will enable assessment of mechanistic links between helminths and vaccine responses.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from relevant ethics committes of Uganda and UK. Results will be shared with Uganda Ministry of Health, relevant district councils, community leaders and study participants. Further dissemination will be done through conference proceedings and publications.

TRIAL REGISTRATION NUMBER

ISRCTN60517191.

Pathogenesis and Host Immune Response in Leprosy

Leprosy is an ancient insidious disease caused by Mycobacterium leprae, where the skin and peripheral nerves undergo chronic granulomatous infections, leading to sensory and motor impairment with characteristic deformities. Susceptibility to leprosy and its disease state are determined by the manifestation of innate immune resistance mediated by cells of monocyte lineage. Due to insufficient innate resistance, granulomatous infection is established, influencing the specific cellular immunity. The clinical presentation of leprosy ranges between two stable polar forms (tuberculoid to lepromatous) and three unstable borderline forms. The tuberculoid form involves Th1 response, characterized by a well demarcated granuloma, infiltrated by CD4⁺ T lymphocytes, containing epitheloid and multinucleated giant cells. In the lepromatous leprosy, there is no characteristic granuloma but only unstructured accumulation of ineffective macrophages containing engulfed pathogens. Th1 response, characterised by IFN-γ and IL-2 production, activates macrophages in order to kill intracellular pathogens. Conversely, a Th2 response, characterized by the production of IL-4, IL-5 and IL-10, helps in antibody production and consequently downregulates the cell-mediated immunity induced by the Th1 response. M. lepare has a long generation time and its inability to grow in culture under laboratory conditions makes its study challenging. The nine-banded armadillo still remains the best clinical and immunological model to study host-pathogen interaction in leprosy. In this chapter, we present cellular morphology and the genomic uniqueness of M. leprae, and how the pathogen shows tropism for Schwann cells, macrophages and dendritic cells.

Immunotherapeutic Activities of a DNA Plasmid Carrying the Mycobacterial hsp65 Gene (DNAhsp65)

DNA vaccines have become relevant subject matter, and efforts for their development have been increasing due to their potential as technology platforms applicable for prophylactic and therapeutic approaches for infectious diseases and for cancer treatment, allergies, and autoimmune diseases. This review aimed to summarize current knowledge about the plasmid DNA vaccine carrying the mycobacterial hsp65 gene (DNAhsp65), which demonstrates immunomodulatory and immunoregulatory properties of both the innate and adaptive immune systems. The possible mechanisms associated with the modulation and regulatory role of DNAhsp65 in the control of various conditions is also discussed.

Long-term efficacy of BCG vaccination in goat herds with a high prevalence of tuberculosis

Vaccination of goats against tuberculosis (TB) has been promoted as an ancillary tool for controlling the disease in infected livestock herds. A three-year trial to assess the efficacy of BCG vaccine was carried out in five goat herds. At the beginning of the trial (month 0), all animals were tested for TB using thee different diagnostic tests. Animals negative to all tests were vaccinated with BCG and all replacement goat kids were also systematically vaccinated throughout the trial. All animals were tested by Interferon-gamma release assay (IGRA) using vaccine compatible reagents at months 6, 12, 24, and 36. The risk factors for TB infection were also evaluated. At the end of the study, four out of five farms showed variable reductions of the initial prevalence (93.5%, 28.5%, 23.2%, and 14.3% respectively), and an overall incidence reduction of 50% was observed in BCG vaccinated goats, although adult vaccinated goats showed higher incidences than vaccinated goat kids. The unvaccinated positive animals remaining in herds and adult BCG vaccinated goats significantly enhanced the risk of infection in vaccinated animals. A systematic vaccination of goats with BCG, together with the removal of positive unvaccinated animals, may contribute to reducing the TB prevalence in goat herds.

The early life education of the immune system: Moms, microbes and (missed) opportunities

The early life immune system is characterized by unique developmental milestones. Functionally diverse immune cells arise from distinct waves of hematopoietic stem cells, a phenomenon referred to as 'layered' immunity. This stratified development of immune cells extends to lineages of both innate and adaptive cells. The defined time window for the development of these immune cells lends itself to the influence of specific exposures typical of the early life period. The perinatal immune system develops in a relatively sterile fetal environment but emerges into one filled with a multitude of antigenic encounters. A major burden of this comes in the form of the microbiota that is being newly established at mucosal surfaces of the newborn. Accumulating evidence suggests that early life microbial exposures, including those arising in utero, can imprint long-lasting changes in the offspring's immune system and determine disease risk throughout life. In this review, I highlight unique features of early life immunity and explore the role of intestinal bacteria in educating the developing immune system.

Helminths and COVID-19 Co-Infections: A Neglected Critical Challenge

Helminth infections are among the most common infectious diseases in underdeveloped countries. Helminths suppress the host immune responses and consequently mitigate vaccine efficacy and increase severity of other infectious diseases. Helminth co-infections might suppress the efficient immune response against SARS-CoV-2 at the early stage of the infection and may increase morbidity and mortality of COVID-19.

Women's socioeconomic position in ontogeny is associated with improved immune function and lower stress, but not with height

Immune function, height and resource accumulation comprise important life history traits in humans. Resource availability models arising from life history theory suggest that socioeconomic conditions influence immune function, growth and health status. In this study, we tested whether there are associations between family income during ontogeny, adult height, cortisol level and immune response in women. A hepatitis B vaccine was administered to 66 young Latvian women from different socioeconomic backgrounds, and blood samples were then collected to measure the level of antibodies that the women produced in response to the vaccination. Cortisol levels were measured from plasma samples pre- and post-vaccination. Women from wealthier families had lower cortisol levels, and women from the highest family income group had the highest levels of antibody titers against hepatitis B vaccine. No significant relationships were observed between cortisol level and immune function, nor between family income and height. The results show that income level during ontogeny is associated with the strength of immune response and with psychoneuroendocrine pathways underlying stress perception in early adulthood. The findings indicate that the quality of the developmental niche is associated with the condition-dependent expression of immune function and stress response.

Interactions between helminths and tuberculosis infections: Implications for tuberculosis diagnosis and vaccination in Africa

Africa is the second most populous continent and has perennial health challenges. Of the estimated 181 million school aged children in sub-Saharan Africa (SSA), nearly half suffer from ascariasis, trichuriasis, or a combination of these infections. Coupled with these is the problem of tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection, which is a leading cause of death in the region. Compared to the effect of the human immunodeficiency virus on the development of TB, the effect of chronic helminth infections is a neglected area of research, yet helminth infections are as ubiquitous as they are varied and may potentially have profound effects upon host immunity, particularly as it relates to TB infection, diagnosis, and vaccination. Protection against active TB is known to require a clearly delineated T-helper type 1 (Th1) response, while helminths induce a strong opposing Th2 and immune-regulatory host response. This Review highlights the potential challenges of helminth-TB co-infection in Africa and the need for further research.

Urban-rural differences in immune responses to mycobacterial and tetanus vaccine antigens in a tropical setting: A role for helminths?

Several vaccines elicit lower efficacy or impaired immune responses in rural compared to urban settings, and in tropical low-income countries compared to high-income countries. An unresolved hypothesis is that immunomodulation by parasitic infections such as helminths (prevalent in rural tropical settings) contributes to suppression of vaccine responses. Among 1–17-year-old Ugandan residents of rural Schistosoma mansoni (Sm)-endemic islands and proximate urban communities with lower helminth exposure, we assessed plasma antibody and whole blood assay cytokine responses to tetanus toxoid (TT) and purified protein derivative of Mycobacterium tuberculosis (PPD). These were taken to represent recall responses to tetanus and BCG vaccination in infancy. PPD-specific responses are additionally induced by tuberculous and non-tuberculous mycobacterial exposure. Urban-rural comparisons showed that PPD-specific IFN-γ and IL-13 and TT-specific IL-13 and IgG concentrations were lower in the rural setting, but that PPD-specific IgE concentrations were higher. Among rural participants, Sm infection was inversely associated with PPD-specific IFN-γ, while nematode infection was positively associated with PPD-specific IgG. Among urban participants, Sm infection was positively associated with PPD-specific responses but inversely associated with TT-specific responses, while nematode infection was inversely associated with TT-specific IgG and IgG4, but no associations were observed with PPD-specific responses. Despite these associations, for the urban-rural comparisons there were no notable changes in test statistics after adjusting for current helminth infections, suggesting that helminths were not the sole explanation for the urban-rural differences observed. Helminths likely work in concert with other environmental exposures and operational factors to influence vaccine response.

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Vaccine (BCG, tetanus)-specific immune responses differ by urban/rural setting.

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Associations between helminths and vaccine-specific response also differ by setting.

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Urban-rural differences are not fully explained by helminth infection prevalence.

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Helminths likely work in concert with other factors to influence vaccine response.

Regulatory T-cells in helminth infection: induction, function and therapeutic potential

Helminth parasites infect an alarmingly large proportion of the world's population, primarily within tropical regions, and their ability to down‐modulate host immunity is key to their persistence. Helminths have developed multiple mechanisms that induce a state of hyporesponsiveness or immune suppression within the host; of particular interest are mechanisms that drive the induction of regulatory T‐cells (Tregs). Helminths actively induce Tregs either directly by secreting factors, such as the TGF‐β mimic Hp‐TGM, or indirectly by interacting with bystander cell types such as dendritic cells and macrophages that then induce Tregs. Expansion of Tregs not only enhances parasite survival but, in cases such as filarial infection, Tregs also play a role in preventing parasite‐associated pathologies. Furthermore, Tregs generated during helminth infection have been associated with suppression of bystander immunopathologies in a range of inflammatory conditions such as allergy and autoimmune disease. In this review, we discuss evidence from natural and experimental infections that point to the pathways and molecules involved in helminth Treg induction, and postulate how parasite‐derived molecules and/or Tregs might be applied as anti‐inflammatory therapies in the future.

Training the Fetal Immune System Through Maternal Inflammation-A Layered Hygiene Hypothesis

Over the last century, the alarming surge in allergy and autoimmune disease has led to the hypothesis that decreasing exposure to microbes, which has accompanied industrialization and modern life in the Western world, has fundamentally altered the immune response. In its current iteration, the “hygiene hypothesis” suggests that reduced microbial exposures during early life restricts the production and differentiation of immune cells suited for immune regulation. Although it is now well-appreciated that the increase in hypersensitivity disorders represents a “perfect storm” of many contributing factors, we argue here that two important considerations have rarely been explored. First, the window of microbial exposure that impacts immune development is not limited to early childhood, but likely extends into the womb. Second, restricted microbial interactions by an expectant mother will bias the fetal immune system toward hypersensitivity. Here, we extend this discussion to hypothesize that the cell types sensing microbial exposures include fetal hematopoietic stem cells, which drive long-lasting changes to immunity.

Helminth infections and immunosenescence: The friend of my enemy

Age-associated alterations of the immune system, which known as "immunosenescence", is characterized by a decline in innate and adaptive immunity, which leading to increased susceptibility to age-associated diseases, such as infectious diseases, rheumatic disease and malignancies. On the other hand, helminth infections are among the most prevalent infections in older individuals, especially in the nursing homes. Most of helminth infections have minor clinical symptoms and usually causing chronic infections without treatment. Nevertheless, chronic helminthiasis alters immune responses somewhat similar to the immunosenescence. Some similarities also exist between helminth infections and immunosenescence: 1) both of them led to declining the immune responses; 2) undernutrition is a consequence of immunosenescence and helminthiasis; 3) vaccine efficacy declines in aging and individuals with helminth infections; 4) increase incidence and prevalence of infectious diseases in the elder individuals and patients with helminth infections; and 5) both of them promote tumorigenesis. Hence, it is probable that helminth infections in the elderly population can intensify the immunosenescence outcomes due to the synergistic immunoregulatory effects of each of them. It would be suggested that, diagnosis, treatment and prevention of helminth infections should be more considered in older individuals. Also, it would be suggested that helminths or their antigens can be used for investigation of immunosenescence because both of them possess some similarities in immune alterations. Taken together, this review offers new insights into the immunology of aging and helminth infections.

Mucosal delivery of tuberculosis vaccines: a review of current approaches and challenges

Introduction: Tuberculosis (TB) remains a major health threat and it is now clear that the current vaccine, BCG, is unable to arrest the global TB epidemic. A new vaccine is needed to either replace or boost BCG so that a better level of protection could be achieved. The route of entry of Mycobacterium tuberculosis, the causative organism, is via inhalation making TB primarily a respiratory disease. There is therefore good reason to hypothesize that a mucosally delivered vaccine against TB could be more effective than one delivered via the systemic route.

Areas covered: This review summarizes the progress that has been made in the area of TB mucosal vaccines in the last few years. It highlights some of the strengths and shortcomings of the published evidence and aims to discuss immunological and practical considerations in the development of mucosal vaccines.

Expert opinion: There is a growing body of evidence that the mucosal approach to vaccination against TB is feasible and should be pursued. However, further key studies are necessary to both improve our understanding of the protective immune mechanisms operating in the mucosa and the technical aspects of aerosolized delivery, before such a vaccine could become a feasible, deployable strategy.

Bacille Calmette-Guérin Vaccine Strain Modulates the Ontogeny of Both Mycobacterial-Specific and Heterologous T Cell Immunity to Vaccination in Infants

Differences in Bacille Calmette-Guérin (BCG) immunogenicity and efficacy have been reported, but various strains of BCG are administered worldwide. Since BCG immunization may also provide protection against off-target antigens, we sought to identify the impact of different BCG strains on the ontogeny of vaccine-specific and heterologous vaccine immunogenicity in the first 9 months of life, utilizing two African birth cohorts. A total of 270 infants were studied: 84 from Jos, Nigeria (vaccinated with BCG-Bulgaria) and 187 from Cape Town, South Africa (154 vaccinated with BCG-Denmark and 33 with BCG-Russia). Infant whole blood was taken at birth, 7, 15, and 36 weeks and short-term stimulated (12 h) in vitro with BCG, Tetanus and Pertussis antigens. Using multiparameter flow cytometry, CD4+ T cell memory subset polyfunctionality was measured by analyzing permutations of TNF-α, IL-2, and IFN-γ expression at each time point. Data was analyzed using FlowJo, SPICE, R, and COMPASS. We found that infants vaccinated with BCG-Denmark mounted significantly higher frequencies of BCG-stimulated CD4+ T cell responses, peaking at week 7 after immunization, and possessed durable polyfunctional CD4+ T cells that were in a more early differentiated memory stage when compared with either BCG-Bulgaria and BCG-Russia strains. The latter responses had lower polyfunctional scores and tended to accumulate in a CD4+ T cell naïve-like state (CD45RA+CD27+). Notably, BCG-Denmark immunization resulted in higher magnitudes and polyfunctional cytokine responses to heterologous vaccine antigens (Tetanus and Pertussis). Collectively, our data show that BCG strain was the strongest determinant of both BCG-stimulated and heterologous vaccine stimulated T cell magnitude and polyfunctionality. These findings have implications for vaccine policy makers, manufacturers and programs worldwide and also suggest that BCG-Denmark, the first vaccine received in many African infants, has both specific and off-target effects in the first few months of life, which may provide an immune priming benefit to other EPI vaccines.

Parasitic infections in Malaysian aborigines with pulmonary tuberculosis: a comparative cross-sectional study

The geographical distribution of tuberculosis (TB) overlaps with various parasitic infections. Uncovering the characteristics of coinfecting parasites that potentially affect the host susceptibility to TB is pertinent as it may provide input to current TB therapeutic and prophylactic measures. The present study was aimed at examining the types of parasitic infections in TB patients and healthy TB contacts (HC) in Orang Asli, Malaysian aborigines, who dwelled in the co-endemic areas. Stool and serum samples were collected from Orang Asli who fulfilled the selection criteria and provided written informed consents. Selected parasitic infections in the two study groups were determined by stool examination and commercial serum antibody immunoassays. The prevalence of parasitic infections in TB and HC participants were 100% (n = 82) and 94.6% (n = 55) respectively. The parasitic infections comprised toxocariasis, trichuriasis, amoebiasis, toxoplasmosis, hookworm infection, ascariasis, strongyloidiasis, and brugian filariasis, in decreasing order of prevalence. Overall, helminth or protozoa infection did not show any significant association with the study groups. However, when the species of the parasite was considered, individuals exposed to trichuriasis and toxoplasmosis showed significant odds reduction (odds ratio (OR) 0.338; 95% confidence interval (CI) 0.166, 0.688) and odds increment (OR 2.193; 95% CI 1.051, 4.576) to have active pulmonary TB, respectively. In conclusion, trichuriasis and toxoplasmosis may have distinct negative and positive associations respectively with the increase of host susceptibility to TB.