Gamma/Delta T Cells and Their Role in Protection Against Malaria

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.

The capability of heterogeneous γδ T cells in cancer treatment

γδ T cells, a specialized subset of T lymphocytes, have garnered significant attention within the realm of cancer immunotherapy. Operating at the nexus between adaptive and innate immunological paradigms, these cells showcase a profound tumor discernment repertoire, hinting at novel immunotherapeutic strategies. Significantly, these cells possess the capability to directly identify and eliminate tumor cells without reliance on HLA-antigen presentation. Furthermore, γδ T cells have the faculty to present tumor antigens to αβ T cells, amplifying their anti-tumoral efficacy.Within the diverse and heterogeneous subpopulations of γδ T cells, distinct immune functionalities emerge, manifesting either anti-tumor or pro-tumor roles within the tumor microenvironment. Grasping and strategically harnessing these heterogeneous γδ T cell cohorts is pivotal to their integration in tumor-specific immunotherapeutic modalities. The aim of this review is to describe the heterogeneity of the γδ T cell lineage and the functional plasticity it generates in the treatment of malignant tumors. This review endeavors to elucidate the intricate heterogeneity inherent to the γδ T cell lineage, the consequential functional dynamics in combating malignancies, the latest advancements from clinical trials, and the evolving landscape of γδ T cell-based oncological interventions, while addressing the challenges impeding the field.

Immunological characteristics of CD103+CD8+ Tc cells in the liver of C57BL/6 mouse infected with plasmodium NSM

CD103 is an important marker of tissue-resident memory T cells (TRM) which play important roles in fighting against infection. However, the immunological characteristics of CD103+ T cells are not thoroughly elucidated in the liver of mouse infected with Plasmodium. Six- to eight-week-old C57BL/6 mice were infected with Plasmodium yoelii nigeriensis NSM. Mice were sacrificed on 12-16 days after infection and the livers were picked out. Sections of the livers were stained, and serum aspartate aminotransferase (AST) and alanine transaminase (ALT) levels were measured. Moreover, lymphocytes in the liver were isolated, and the expression of CD103 was determined by using qPCR. The percentage of CD103 on different immune cell populations was dynamically observed by using flow cytometry (FCM). In addition, the phenotype and cytokine production characteristics of CD103+CD8+ Tc cell were analyzed by using flow cytometry, respectively. Erythrocyte stage plasmodium infection could result in severe hepatic damage, a widespread inflammatory response and the decrease of CD103 expression on hepatic immune cells. Only CD8+ Tc and γδT cells expressed higher levels of CD103 in the uninfected state.CD103 expression in CD8+ Tc cells significantly decreased after infection. Compared to that of CD103- CD8+ Tc cells, CD103+ CD8+ Tc cells from the infected mice expressed lower level of CD69, higher level of CD62L, and secreted more IL-4, IL-10, IL-17, and secreted less IFN-γ. CD103+CD8+ Tc cells might mediate the hepatic immune response by secreting IL-4, IL-10, and IL-17 except IFN-γ in the mice infected with the erythrocytic phase plasmodium, which could be involved in the pathogenesis of severe liver damage resulted from the erythrocytic phase plasmodium yoelii nigeriensis NSM infection.

Mouse Models for Unravelling Immunology of Blood Stage Malaria

Malaria comprises a spectrum of disease syndromes and the immune system is a major participant in malarial disease. This is particularly true in relation to the immune responses elicited against blood stages of Plasmodium-parasites that are responsible for the pathogenesis of infection. Mouse models of malaria are commonly used to dissect the immune mechanisms underlying disease. While no single mouse model of Plasmodium infection completely recapitulates all the features of malaria in humans, collectively the existing models are invaluable for defining the events that lead to the immunopathogenesis of malaria. Here we review the different mouse models of Plasmodium infection that are available, and highlight some of the main contributions these models have made with regards to identifying immune mechanisms of parasite control and the immunopathogenesis of malaria.

Five decades of clinical assessment of whole-sporozoite malaria vaccines

In 1967, pioneering work by Ruth Nussenzweig demonstrated for the first time that irradiated sporozoites of the rodent malaria parasite Plasmodium berghei protected mice against a challenge with infectious parasites of the same species. This remarkable finding opened up entirely new prospects of effective vaccination against malaria using attenuated sporozoites as immunization agents. The potential for whole-sporozoite-based immunization in humans was established in a clinical study in 1973, when a volunteer exposed to X-irradiated P. falciparum sporozoites was found to be protected against malaria following challenge with a homologous strain of this parasite. Nearly five decades later, much has been achieved in the field of whole-sporozoite malaria vaccination, and multiple reports on the clinical evaluation of such candidates have emerged. However, this process has known different paces before and after the turn of the century. While only a few clinical studies were published in the 1970’s, 1980’s and 1990’s, remarkable progress was made in the 2000’s and beyond. This article reviews the history of the clinical assessment of whole-sporozoite malaria vaccines over the last forty-nine years, highlighting the impressive achievements made over the last few years, and discussing some of the challenges ahead.

A diversified role for γδT cells in vector-borne diseases

Vector-borne diseases have high morbidity and mortality and are major health threats worldwide. γδT cells represent a small but essential subpopulation of T cells. They reside in most human tissues and exert important functions in both natural and adaptive immune responses. Emerging evidence have shown that the activation and expansion of γδT cells invoked by pathogens play a diversified role in the regulation of host-pathogen interactions and disease progression. A better understanding of such a role for γδT cells may contribute significantly to developing novel preventative and therapeutic strategies. Herein, we summarize recent exciting findings in the field, with a focus on the role of γδT cells in the infection of vector-borne pathogens.

Immunological profiles associated with distinct parasitemic states in volunteers undergoing malaria challenge in Gabon

Controlled human malaria infection (CHMI) using cryopreserved non-attenuated Plasmodium falciparum sporozoites (PfSPZ) offers a unique opportunity to investigate naturally acquired immunity (NAI). By analyzing blood samples from 5 malaria-naïve European and 20 African adults with lifelong exposure to malaria, before, 5, and 11 days after direct venous inoculation (DVI) with Sanaria^R PfSPZ Challenge, we assessed the immunological patterns associated with control of microscopic and submicroscopic parasitemia. All (5/5) European individuals developed parasitemia as defined by thick blood smear (TBS), but 40% (8/20) of the African individuals controlled their parasitemia, and therefore remained thick blood smear-negative (TBS⁻ Africans). In the TBS⁻ Africans, we observed higher baseline frequencies of CD4⁺ T cells producing interferon-gamma (IFNγ) that significantly decreased 5 days after PfSPZ DVI. The TBS⁻ Africans, which represent individuals with either very strong and rapid blood-stage immunity or with immunity to liver stages, were stratified into subjects with sub-microscopic parasitemia (TBS^-PCR⁺) or those with possibly sterilizing immunity (TBS⁻PCR⁻). Higher frequencies of IFNγ⁺TNF⁺CD8⁺ γδ T cells at baseline, which later decreased within five days after PfSPZ DVI, were associated with those who remained TBS⁻PCR⁻. These findings suggest that naturally acquired immunity is characterized by different cell types that show varying strengths of malaria parasite control. While the high frequencies of antigen responsive IFNγ⁺CD4⁺ T cells in peripheral blood keep the blood-stage parasites to a sub-microscopic level, it is the IFNγ⁺TNF⁺CD8⁺ γδ T cells that are associated with either immunity to the liver-stage, or rapid elimination of blood-stage parasites.

Role of Vγ9vδ2 T lymphocytes in infectious diseases

The T cell receptor Vγ9Vδ2 T cells bridge innate and adaptive antimicrobial immunity in primates. These Vγ9Vδ2 T cells respond to phosphoantigens (pAgs) present in microbial or eukaryotic cells in a butyrophilin 3A1 (BTN3) and butyrophilin 2A1 (BTN2A1) dependent manner. In humans, the rapid expansion of circulating Vγ9Vδ2 T lymphocytes during several infections as well as their localization at the site of active disease demonstrates their important role in the immune response to infection. However, Vγ9Vδ2 T cell deficiencies have been observed in some infectious diseases such as active tuberculosis and chronic viral infections. In this review, we are providing an overview of the mechanisms of Vγ9Vδ2 T cell-mediated antimicrobial immunity. These cells kill infected cells mainly by releasing lytic mediators and pro-inflammatory cytokines and inducing target cell apoptosis. In addition, the release of chemokines and cytokines allows the recruitment and activation of immune cells, promoting the initiation of the adaptive immune response. Finaly, we also describe potential new therapeutic tools of Vγ9Vδ2 T cell-based immunotherapy that could be applied to emerging infections.

Early Pregnancy Human Decidua Gamma/Delta T Cells Exhibit Tissue Resident and Specific Functional Characteristics

A successful pregnancy is a complicated process that builds upon two aspects of the maternal immune system that need to be balanced. As one of the indispensable groups of immune cell at the maternal-fetal interface, the decidual gamma/delta (γδ) T cells have attracted research attention in normal pregnancy and miscarriage. However, the role of γδ T cells in fetal growth remains poorly understood. Here we found that the γδ T cell population resident in decidua during early pregnancy was enriched and secreted growth factors including growth differentiation factor 15 (GDF15) and bone morphogenetic protein 1 (BMP1). A diminution in such growth factors may impair fetal development and result in fetal growth restriction. We also observed that early decidual γδ T cells exhibited stronger cytokine-secretion characteristics, but that their cytotoxic actions against A549 cells were weaker, compared with γδ T cells in peripheral blood mononuclear cells (PBMCs). In addition, the functional abilities of early decidual γδ T cells in promoting trophoblast cell proliferation, migration, invasion, and tube formation were also significantly more robust than in γδ T cells of PBMCs. These findings highlight the importance of γδ T cells in fetal growth and maternal immunotolerance during pregnancy, and show that they differ from γδ T cells in PBMCs. We thus recommend additional investigation in this research area to further elucidate a role for γδ T cells in pregnancy.

Systems analysis shows a role of cytophilic antibodies in shaping innate tolerance to malaria

Natural immunity to malaria develops over time with repeated malaria episodes, but protection against severe malaria and immune regulation limiting immunopathology, called tolerance, develops more rapidly. Here, we comprehensively profile the blood immune system in patients, with or without prior malaria exposure, over 1 year after acute symptomatic Plasmodium falciparum malaria. Using a data-driven analysis approach to describe the immune landscape over time, we show that a dampened inflammatory response is associated with reduced γδ T cell expansion, early expansion of CD16⁺ monocytes, and parasite-specific antibodies of IgG1 and IgG3 isotypes. This also coincided with reduced parasitemia and duration of hospitalization. Our data indicate that antibody-mediated phagocytosis during the blood stage infection leads to lower parasitemia and less inflammatory response with reduced γδ T cell expansion. This enhanced control and reduced inflammation points to a potential mechanism on how tolerance is established following repeated malaria exposure.

Emerging role of γδ T cells in protozoan infection and their potential clinical application

γδ T cells are thymus derived heterogeneous and unconventional T- lymphocyte expressing TCR γ (V γ9) and TCRδ (Vδ2) chain and play an important role in connecting innate and adaptive armaments of immune response. These cells can recognize wide ranges of antigens even without involvement of major histocompatibility complex and exert their biological functions by cytotoxicity or activating various types of immune cells. In recent past, γδ T cells have emerged as an important player during protozoa infection and rapidly expand after exposure with them. They have also been widely studied in vaccine induced immune response against many bacterial and protozoan infections with improved clinical outcome. In this review, we will discuss the various roles of γδ T cells in immunity against malaria and leishmaniasis, the two important protozoan diseases causing significant mortality and morbidity throughout the world.

Properties and Roles of γδT Cells in Plasmodium yoelii nigeriensis NSM Infected C57BL/6 Mice

Background

Many kinds of immune cells are involved in malaria infection. γδT cells represent a special type of immune cell between natural and adaptive immune cells that play critical roles in anti-parasite infection.

Methods

In this study, malaria infection model was constructed. Distribution of γδT cells in various immune organs and dynamic changes of γδT cells in the spleens of C57BL/6 mice after infection were detected by flow cytometry. And activation status of γδT cells was detected by flow cytometry. Then γδT cells in naive and infected mice were sorted and performed single-cell RNA sequencing (scRNA-seq). Finally, γδTCR KO mice model was constructed and the effect of γδT cell depletion on mouse T and B cell immunity against Plasmodium infection was explored.

Results

Here, splenic γδT cells were found to increase significantly on day 14 after Plasmodium yoelii nigeriensis NSM infection in C57BL/6 mice. Higher level of CD69, ICOS and PD-1, lower level of CD62L, and decreased IFN-γ producing after stimulation by PMA and ionomycin were found in γδT cells from infected mice, compared with naive mice. Moreover, 11 clusters were identified in γδT cells by scRNA-seq based t-SNE analysis. Cluster 4, 5, and 7 in γδT cells from infected mice were found the expression of numerous genes involved in immune response. In the same time, the GO enrichment analysis revealed that the marker genes in the infection group were involved in innate and adaptive immunity, pathway enrichment analysis identified the marker genes in the infected group shared many key signalling molecules with other cells or against pathogen infection. Furthermore, increased parasitaemia, decreased numbers of RBC and PLT, and increased numbers of WBC were found in the peripheral blood from γδTCR KO mice. Finally, lower IFN-γ and CD69 expressing CD4⁺ and CD8⁺ T cells, lower B cell percentage and numbers, and less CD69 expressing B cells were found in the spleen from γδTCR KO infected mice, and lower levels of IgG and IgM antibodies in the serum were also observed than WT mice.

Conclusions

Overall, this study demonstrates the diversity of γδT cells in the spleen of Plasmodium yoelii nigeriensis NSM infected C57BL/6 mice at both the protein and RNA levels, and suggests that the expansion of γδT cells in cluster 4, 5 and 7 could promote both cellular and humoral immune responses.

Repeated Plasmodium falciparum infection in humans drives the clonal expansion of an adaptive γδ T cell repertoire

[Figure: see text].

The Contribution of Human Herpes Viruses to γδ T Cell Mobilisation in Co-Infections

γδ T cells are activated in viral, bacterial and parasitic infections. Among viruses that promote γδ T cell mobilisation in humans, herpes viruses (HHVs) occupy a particular place since they infect the majority of the human population and persist indefinitely in the organism in a latent state. Thus, other infections should, in most instances, be considered co-infections, and the reactivation of HHV is a serious confounding factor in attributing γδ T cell alterations to a particular pathogen in human diseases. We review here the literature data on γδ T cell mobilisation in HHV infections and co-infections, and discuss the possible contribution of HHVs to γδ alterations observed in various infectious settings. As multiple infections seemingly mobilise overlapping γδ subsets, we also address the concept of possible cross-protection.

Recent Advances in Understanding the Inflammatory Response in Malaria: A Review of the Dual Role of Cytokines

Malaria is a serious and, in some unfortunate cases, fatal disease caused by a parasite of the Plasmodium genus. It predominantly occurs in tropical areas where it is transmitted through the bite of an infected Anopheles mosquito. The pathogenesis of malaria is complex and incompletely elucidated. During blood-stage infection, in response to the presence of the parasite, the host's immune system produces proinflammatory cytokines including IL-6, IL-8, IFN-γ, and TNF, cytokines which play a pivotal role in controlling the growth of the parasite and its elimination. Regulatory cytokines such as transforming growth factor- (TGF-) β and IL-10 maintain the balance between the proinflammatory and anti-inflammatory responses. However, in many cases, cytokines have a double role. On the one hand, they contribute to parasitic clearance, and on the other, they are responsible for pathological changes encountered in malaria. Cytokine-modulating strategies may represent a promising modern approach in disease management. In this review, we discuss the host immune response in malaria, analyzing the latest studies on the roles of pro- and anti-inflammatory cytokines.

Plasmodium falciparum Malaria Vaccines and Vaccine Adjuvants

Malaria-a parasite vector-borne disease-is a global health problem, and Plasmodium falciparum has proven to be the deadliest among Plasmodium spp., which causes malaria in humans. Symptoms of the disease range from mild fever and shivering to hemolytic anemia and neurological dysfunctions. The spread of drug resistance and the absence of effective vaccines has made malaria disease an ever-emerging problem. Although progress has been made in understanding the host response to the parasite, various aspects of its biology in its mammalian host are still unclear. In this context, there is a pressing demand for the development of effective preventive and therapeutic strategies, including new drugs and novel adjuvanted vaccines that elicit protective immunity. The present article provides an overview of the current knowledge of anti-malarial immunity against P. falciparum and different options of vaccine candidates in development. A special emphasis has been made on the mechanism of action of clinically used vaccine adjuvants.

Generation and first characterization of TRDC-knockout pigs lacking γδ T cells

The TRDC-locus encodes the T cell receptor delta constant region, one component of the γδ T cell receptor which is essential for development of γδ T cells. In contrast to peptide recognition by αβ T cells, antigens activating γδ T cells are mostly MHC independent and not well characterized. Therefore, the function of γδ T cells and their contribution to protection against infections is still unclear. Higher numbers of circulating γδ T cells compared to mice, render the pig a suitable animal model to study γδ T cells. Knocking-out the porcine TRDC-locus by intracytoplasmic microinjection and somatic cell nuclear transfer resulted in healthy living γδ T cell deficient offspring. Flow cytometric analysis revealed that TRDC-KO pigs lack γδ T cells in peripheral blood mononuclear cells (PBMC) and spleen cells. The composition of the remaining leucocyte subpopulations was not affected by the depletion of γδ T cells. Genome-wide transcriptome analyses in PBMC revealed a pattern of changes reflecting the impairment of known or expected γδ T cell dependent pathways. Histopathology did not reveal developmental abnormalities of secondary lymphoid tissues. However, in a vaccination experiment the KO pigs stayed healthy but had a significantly lower neutralizing antibody titer as the syngenic controls.

Characterization of γδT cells in lung of Plasmodium yoelii-infected C57BL/6 mice

Background

Malaria has high morbidity and mortality rates in some parts of tropical and subtropical countries. Besides respiratory and metabolic function, lung plays a role in immune system. γδT cells have multiple functions in producing cytokines and chemokines, regulating the immune response by interacting with other cells. It remains unclear about the role of γδT cells in the lung of mice infected by malaria parasites.

Methods

Flow cytometry (FCM) was used to evaluate the frequency of γδT cells and the effects of γδT cells on the phenotype and function of B and T cells in Plasmodium yoelii-infected wild-type (WT) or γδTCR knockout (γδT KO) mice. Haematoxylin-eosin (HE) staining was used to observe the pathological changes in the lungs.

Results

The percentage and absolute number of γδT cells in the lung increased after Plasmodium infection (p < 0.01). More γδT cells were expressing CD80, CD11b, or PD-1 post-infection (p < 0.05), while less γδT cells were expressing CD34, CD62L, and CD127 post-infection (p < 0.05). The percentages of IL-4⁺, IL-5⁺, IL-6⁺, IL-21⁺, IL-1α⁺, and IL-17⁺ γδT cells were increased (p < 0.05), but the percentage of IFN-γ-expressing γδT cells decreased (p < 0.05) post-infection. The pathological changes in the lungs of the infected γδT KO mice were not obvious compared with the infected WT mice. The proportion of CD3⁺ cells and absolute numbers of CD3⁺ cells, CD3⁺ CD4⁺ cells, CD3⁺ CD8⁺ cells decreased in γδT KO infected mice (p < 0.05). γδT KO infected mice exhibited no significant difference in the surface molecular expression of T cells compared with the WT infected mice (p > 0.05). While, the percentage of IFN-γ-expressing CD3⁺ and CD3⁺ CD8⁺ cells increased in γδT KO infected mice (p < 0.05). There was no significant difference in the absolute numbers of the total, CD69⁺, ICOS⁺, and CD80⁺ B cells between the WT infected and γδT KO infected mice (p > 0.05).

Conclusions

The content, phenotype, and function of γδT cells in the lung of C57BL/6 mice were changed after Plasmodium infection. γδT cells contribute to T cell immune response in the progress of Plasmodium infection.

A Cell for the Ages: Human γδ T Cells across the Lifespan

The complexity of the human immune system is exacerbated by age-related changes to immune cell functionality. Many of these age-related effects remain undescribed or driven by mechanisms that are poorly understood. γδ T cells, while considered an adaptive subset based on immunological ontogeny, retain both innate-like and adaptive-like characteristics. This T cell population is small but mighty, and has been implicated in both homeostatic and disease-induced immunity within tissues and throughout the periphery. In this review, we outline what is known about the effect of age on human peripheral γδ T cells, and call attention to areas of the field where further research is needed.

γδ T cells in malaria: a double-edged sword

Malaria remains a devastating global health problem, resulting in many annual deaths due to the complications of severe malaria. However, in endemic regions, individuals can acquire ‘clinical immunity’ to malaria, characterized by a decrease in severe malaria episodes and an increase of asymptomatic Plasmodium falciparum infections. Recently, it has been reported that tolerance to ‘clinical malaria’ and reduced disease severity correlates with a decrease in the numbers of circulating Vγ9Vδ2 T cells, the major subset of γδ T cells in the human peripheral blood. This is particularly interesting as this population typically undergoes dramatic expansions during acute Plasmodium infections and was previously shown to play antiparasitic functions. Thus, regulated γδ T‐cell responses may be critical to balance immune protection with severe pathology, particularly as both seem to rely on the same pro‐inflammatory cytokines, most notably TNF and IFN‐γ. This has been clearly demonstrated in mouse models of experimental cerebral malaria (ECM) based on Plasmodium berghei ANKA infection. Furthermore, our recent studies suggest that the natural course of Plasmodium infection, mimicked in mice through mosquito bite or sporozoite inoculation, includes a major pathogenic component in ECM that depends on γδ T cells and IFN‐γ production in the asymptomatic liver stage, where parasite virulence is seemingly set and determines pathology in the subsequent blood stage. Here, we discuss these and other recent advances in our understanding of the complex—protective versus pathogenic—functions of γδ T cells in malaria.

Human γδ TCR Repertoires in Health and Disease

The T cell receptor (TCR) repertoires of γδ T cells are very different to those of αβ T cells. While the theoretical TCR repertoire diversity of γδ T cells is estimated to exceed the diversity of αβ T cells by far, γδ T cells are still understood as more invariant T cells that only use a limited set of γδ TCRs. Most of our current knowledge of human γδ T cell receptor diversity builds on specific monoclonal antibodies that discriminate between the two major subsets, namely Vδ2⁺ and Vδ1⁺ T cells. Of those two subsets, Vδ2⁺ T cells seem to better fit into a role of innate T cells with semi-invariant TCR usage, as compared to an adaptive-like biology of some Vδ1⁺ subsets. Yet, this distinction into innate-like Vδ2⁺ and adaptive-like Vδ1⁺ γδ T cells does not quite recapitulate the full diversity of γδ T cell subsets, ligands and interaction modes. Here, we review how the recent introduction of high-throughput TCR repertoire sequencing has boosted our knowledge of γδ T cell repertoire diversity beyond Vδ2⁺ and Vδ1⁺ T cells. We discuss the current understanding of clonal composition and the dynamics of human γδ TCR repertoires in health and disease.

Schistosoma haematobium infection modulates Plasmodium falciparum parasite density and antimalarial antibody responses

AIMS

Schistosomiasis and malaria are endemic in sub-Saharan Africa where Schistosoma haematobium (Sh) and Plasmodium falciparum (Pf) coinfections are thus frequent. We explored the effect of Sh infection on antibody responses directed to Pf merozoite antigens and on malaria susceptibility in Beninese children.

METHODS AND RESULTS

A total of 268 children were followed during a malaria transmission season. Detection of Pf infection was performed by microscopy and rapid diagnostic tests. Sh infection was determined in urine by microscopy. Antimalarial antibody, cytokine and HLA-G concentrations were quantified by ELISA. The expression of HLA-G receptors by immune cells was assessed by flow cytometry. Children infected by Sh had higher concentrations of IgG1 directed to MSP3 and GLURP_R0 , IgG2 directed to GLURP_R0 and IgG3 directed to MSP3, GLURP_R0 and GLURP_R2 and have lower Pf densities than those uninfected by Sh. No difference in cytokine and HLA-G concentrations was observed between Sh egg carriers and non-carriers.

CONCLUSION

Schistosoma haematobium modulates host immune responses directed to Pf antigens. The absence of immune downregulation usually observed during helminth infections is surprising in our study. We hypothesize that the stage of Sh development could partly explain the immune pathways leading to increased antibody levels that favour better control of Pf parasitemia.

γδ T Cells Kill Plasmodium falciparum in a Granzyme- and Granulysin-Dependent Mechanism during the Late Blood Stage

Plasmodium spp., the causative agent of malaria, have a complex life cycle. The exponential growth of the parasites during the blood stage is responsible for almost all malaria-associated morbidity and mortality. Therefore, tight immune control of the intraerythrocytic replication of the parasite is essential to prevent clinical malaria. Despite evidence that the particular lymphocyte subset of γδ T cells contributes to protective immunity during the blood stage in naive hosts, their precise inhibitory mechanisms remain unclear. Using human PBMCs, we confirmed in this study that γδ T cells specifically and massively expanded upon activation with Plasmodium falciparum culture supernatant. We also demonstrate that these activated cells gain cytolytic potential by upregulating cytotoxic effector proteins and IFN-γ. The killer cells bound to infected RBCs and killed intracellular P. falciparum via the transfer of the granzymes, which was mediated by granulysin in a stage-specific manner. Several vital plasmodial proteins were efficiently destroyed by granzyme B, suggesting proteolytic degradation of these proteins as essential in the lymphocyte-mediated death pathway. Overall, these data establish a granzyme- and granulysin-mediated innate immune mechanism exerted by γδ T cells to kill late-stage blood-residing P. falciparum.

Activation of TCR Vδ1+ and Vδ1-Vδ2- γδ T Cells upon Controlled Infection with Plasmodium falciparum in Tanzanian Volunteers

Our understanding of the human immune response to malaria remains incomplete. Clinical trials using whole-sporozoite-based vaccination approaches such as the Sanaria PfSPZ Vaccine, followed by controlled human malaria infection (CHMI) to assess vaccine efficacy offer a unique opportunity to study the immune response during Plasmodium falciparum infection. Diverse populations of T cells that are not restricted to classical HLA (unconventional T cells) participate in the host response during Plasmodium infection. Although several populations of unconventional T cells exist, the majority of studies focused on TCR Vγ9Vδ2 cells, the most abundant TCR γδ cell population in peripheral blood. In this study, we dissected the response of three TCR γδ cell subsets and mucosal-associated invariant T cells in healthy volunteers immunized with PfSPZ Vaccine and challenged by CHMI using Sanaria PfSPZ Challenge. Using a flow cytometry-based unbiased analysis followed by T cell cloning, several findings were made. Whereas major ex vivo alterations were not detectable after immunization with PfSPZ Vaccine, TCR Vδ2, and mucosal-associated invariant T cells expanded after asexual blood-stage parasitemia induced by CHMI. CHMI, but not vaccination, also induced the activation of TCR Vδ1 and Vδ1^-Vδ2^- γδ T cells. The activated TCR Vδ1 cells were oligoclonal, suggesting clonal expansion, and upon repeated CHMI, showed diminished response, indicating long-term alterations induced by blood-stage parasitemia. Some TCR Vδ1 clones recognized target cells in the absence of parasite-derived Ags, thus suggesting recognition of self-molecules. These findings reveal the articulate participation of different populations of unconventional T cells to P. falciparum infection.

Malawian children with uncomplicated and cerebral malaria have decreased activated Vγ9Vδ2 γδ T cells which increase in convalescence

Malaria is responsible for almost half a million deaths annually. The role of Vγ9Vδ2 γδ T cells in malaria is still unclear. Studies have reported an association between this cell subset and malaria symptoms and severity. Profiles of Vγ9Vδ2 γδ T cells in bigger cohorts with different levels of clinical severity have not been described. Proportion, numbers, and activation status of Vγ9Vδ2 γδ T cells were measured by flow cytometry in 59 healthy controls (HCs), 58 children with uncomplicated malaria (UM) and 67 with cerebral malaria (CM,) during acute malaria and in convalescence 28 days later. Vγ9Vδ2 γδ T cell were lower in children presenting with UM and CM than in HCs. Cell counts did not vary with malaria severity (CM median counts 40 x 10³ cells/μL, IQR [23–103]; UM median counts 30 x 10³ cells/μL [10–90], P = 0.224). Vγ9Vδ2 γδ T cell counts increased during convalescence for UM (70 [40–60] x 10³ cells/μL and CM (90 [60–140] x 10³ cells/μL), to levels similar to those in HCs (70 [50–140] x 10³ cells/μL), p = 0.70 and p = 0.40 respectively. Expression of the activation markers CD69 and HLA-DR on Vγ9Vδ2 γδ T cells was higher in malaria cases than in controls (HCs vs UM or CM, p < 0.0001) but was similar between UM and CM. HLA-DR expression remained elevated at 28 days, suggesting sustained activation of Vγ9Vδ2 γδ T cells during recovery. Vγ9Vδ2 γδ T cell proportions and cells counts were suppressed in acute disease and normalized in convalescence, a phenomenon previously hypothesized to be due to transient migration of the cells to secondary lymphoid tissue. The presence of highly activated Vγ9Vδ2 γδ T cells suggests that this T cell subset plays a specific role in response to malaria infection.

γδ T-cell responses during HIV infection and antiretroviral therapy

HIV infection is associated with a rapid and sustained inversion of the Vδ1:Vδ2 T‐cell ratio in peripheral blood. Studies of antiretroviral therapy (ART)‐treated cohorts suggest that ART is insufficient to reconstitute either the frequency or function of the γδ T‐cell subset. Recent advances are now beginning to shed light on the relationship between microbial translocation, chronic inflammation, immune ageing and γδ T‐cell immunology. Here, we review the impact of acute, chronic untreated and treated HIV infection on circulating and mucosal γδ T‐cell subsets and highlight novel approaches to harness γδ T cells as components of anti‐HIV immunotherapy.

Babesiosis Vaccines: Lessons Learned, Challenges Ahead, and Future Glimpses

The incidence and prevalence of babesiosis in animals and humans is increasing, yet prevention, control, or treatment measures remain limited and ineffective. Despite a growing body of new knowledge of the biology, pathogenicity, and virulence of Babesia parasites, there is still no well-defined, adequately effective and easily deployable vaccine. While numerous published studies suggest that the development of such anti-Babesia vaccines should be feasible, many others identify significant challenges that need to be overcome in order to succeed. Here, we review historic and recent attempts in babesiosis vaccine discovery to avoid past pitfalls, learn new lessons, and provide a roadmap to guide the development of next-generation babesiosis vaccines.

Human Vδ1+ T Cells in the Immune Response to Plasmodium falciparum Infection

Naturally acquired protective immunity to Plasmodium falciparum malaria is mainly antibody-mediated. However, other cells of the innate and adaptive immune system also play important roles. These include so-called unconventional T cells, which express a γδ T-cell receptor (TCR) rather than the αβ TCR expressed by the majority of T cells—the conventional T cells. The γδ T-cell compartment can be divided into distinct subsets. One expresses a TCR involving Vγ9 and Vδ2, while another major subset uses instead a TCR composed of Vδ1 paired with one of several types of γ chains. The former of these subsets uses a largely semi-invariant TCR repertoire and responds in an innate-like fashion to pyrophosphate antigens generated by various stressed host cells and infectious pathogens, including P. falciparum. In this short review, we focus instead on the Vδ1 subset, which appears to have a more adaptive immunobiology, but which has been much less studied in general and in malaria in particular. We discuss the evidence that Vδ1⁺ cells do indeed play a role in malaria and speculate on the function and specificity of this cell type, which is increasingly attracting the attention of immunologists.

The Role of IL-10 in Malaria: A Double Edged Sword

IL-10 produced by CD4⁺ T cells suppresses inflammation by inhibiting T cell functions and the upstream activities of antigen presenting cells (APCs). IL-10 was first identified in Th2 cells, but has since been described in IFNγ-producing Tbet⁺ Th1, FoxP3⁺ CD4⁺ regulatory T (Treg) and IL-17-producing CD4⁺ T (Th17) cells, as well as many innate and innate-like immune cell populations. IL-10 production by Th1 cells has emerged as an important mechanism to dampen inflammation in the face of intractable infection, including in African children with malaria. However, although these type I regulatory T (Tr1) cells protect tissue from inflammation, they may also promote disease by suppressing Th1 cell-mediated immunity, thereby allowing infection to persist. IL-10 produced by other immune cells during malaria can also influence disease outcome, but the full impact of this IL-10 production is still unclear. Together, the actions of this potent anti-inflammatory cytokine along with other immunoregulatory mechanisms that emerge following Plasmodium infection represent a potential hurdle for the development of immunity against malaria, whether naturally acquired or vaccine-induced. Recent advances in understanding how IL-10 production is initiated and regulated have revealed new opportunities for manipulating IL-10 for therapeutic advantage. In this review, we will summarize our current knowledge about IL-10 production during malaria and discuss its impact on disease outcome. We will highlight recent advances in our understanding about how IL-10 production by specific immune cell subsets is regulated and consider how this knowledge may be used in drug delivery and vaccination strategies to help eliminate malaria.