γδ T cells in malaria: a double-edged sword

Characteristics of splenic PD-1+ γδT cells in Plasmodium yoelii nigeriensis infection

Although the functions of programmed death-1 (PD-1) on αβ T cells have been extensively reported, a role for PD-1 in regulating γδT cell function is only beginning to emerge. Here, we investigated the phenotypic and functional characteristics of PD-1-expressing γδT cells, and the molecular mechanism was also explored in the Plasmodium yoelii nigeriensis (P. yoelii NSM)-infected mice. Flow cytometry and single-cell RNA sequencing (scRNA-seq) were performed. An inverse agonist of RORα, SR3335, was used to investigate the role of RORα in regulating PD-1+ γδT cells. The results indicated that γδT cells continuously upregulated PD-1 expression during the infection period. Higher levels of CD94, IL-10, CX3CR1, and CD107a; and lower levels of CD25, CD69, and CD127 were found in PD-1+ γδT cells from infected mice than in PD-1- γδT cells. Furthermore, GO enrichment analysis revealed that the marker genes in PD-1+ γδT cells were involved in autophagy and processes utilizing autophagic mechanisms. ScRNA-seq results showed that RORα was increased significantly in PD-1+ γδT cells. GSEA identified that RORα was mainly involved in the regulation of I-kappaB kinase/NF-κB signaling and the positive regulation of cytokine production. Consistent with this, PD-1-expressing γδT cells upregulated RORα following Plasmodium yoelii infection. Additionally, in vitro studies revealed that higher levels of p-p65 were found in PD-1+ γδT cells after treatment with a RORα selective synthetic inhibitor. Collectively, these data suggest that RORα-mediated attenuation of NF-κB signaling may be fundamental for PD-1-expressing γδT cells to modulate host immune responses in the spleen of Plasmodium yoelii nigeriensis-infected C57BL/6 mice, and it requires further investigation.

Phenotypic changes of γδ T cells in Plasmodium falciparum placental malaria and pregnancy outcomes in women at delivery in Cameroon

Introduction

Depending on the microenvironment, γδ T cells may assume characteristics similar to those of Th1, Th2, Th17, regulatory T cells or antigen presenting cells. Despite the wide documentation of the effect of Th1/Th2 balance on pregnancy associated malaria and outcomes, there are no reports on the relationship between γδ T cell phenotype change and Placental Malaria (PM) with pregnancy outcomes. This study sought to investigate the involvement of γδ T cells and its subsets in placental Plasmodium falciparum malaria.

Methods

In a case-control study conducted in Yaoundé, Cameroon from March 2022 to May 2023, peripheral, placental and cord blood samples were collected from 50 women at delivery (29 PM negative: PM- and 21 PM positive: PM+; as diagnosed by light microscopy). Hemoglobin levels were measured using hemoglobinometer. PBMCs, IVBMCs and CBMCs were isolated using histopaque-1077 and used to characterize total γδ T cell populations and subsets (Vδ1+, Vδ2+, Vδ1-Vδ2-) by flow cytometry.

Results

Placental Plasmodium falciparum infection was associated with significant increase in the frequency of total γδ T cells in IVBMC and of the Vδ1+ subset in PBMC and IVBMC, but decreased frequency of the Vδ2+ subset in PBMC and IVBMC. The expression of the activation marker: HLA-DR, and the exhaustion markers (PD1 and TIM3) within total γδ T cells and subsets were significantly up-regulated in PM+ compared to PM- group. The frequency of total γδ T cells in IVBMC, TIM-3 expression within total γδ T cells and subsets in IVBMC, as well as HLA-DR expression within total γδ T cells and Vδ2+ subset in IVBMC were negatively associated with maternal hemoglobin levels. Furthermore, the frequency of total γδ T cells in PBMC and PD1 expression within the Vδ2+ subset in CBMC were negatively associated with birth weight contrary to the frequency of Vδ1-Vδ2- subset in PBMC and HLA-DR expression within the Vδ2+ subset in IVBMC which positively associated with maternal hemoglobin level and birth weight, respectively.

Conclusion

The data indicate up-regulation of activated and exhausted γδ T cells in Plasmodium falciparum placental malaria, with effects on pregnancy outcomes including maternal hemoglobin level and birth weight.

Human ApoE2 protects mice against Plasmodium berghei ANKA experimental cerebral malaria

IMPORTANCE

Cerebral malaria (CM) is the deadliest complication of malaria infection with an estimated 15%-25% mortality. Even with timely and effective treatment with antimalarial drugs such as quinine and artemisinin derivatives, survivors of CM may suffer long-term cognitive and neurological impairment. Here, we show that human apolipoprotein E variant 2 (hApoE2) protects mice from experimental CM (ECM) via suppression of CD8+ T cell activation and infiltration to the brain, enhanced cholesterol metabolism, and increased IFN-γ production, leading to reduced endothelial cell apoptosis, BBB disruption, and ECM symptoms. Our results suggest that hApoE can be an important factor for risk assessment and treatment of CM in humans.

Liver-stage Plasmodium infection tunes clinical outcomes

Chora and colleagues show that infection of the liver by Plasmodium modulates severity of disease in the experimental cerebral malaria (ECM) model by generating gamma delta (ɣδ) T cells that produce IL-17. This work calls into question the long-standing assumption that liver infection does not modulate severity of malaria.

The Complexity of Interferon Signaling in Host Defense against Protozoan Parasite Infection

Protozoan parasites, such as Plasmodium, Leishmania, Toxoplasma, Cryptosporidium, and Trypanosoma, are causative agents of health-threatening diseases in both humans and animals, leading to significant health risks and socioeconomic losses globally. The development of effective therapeutic and prevention strategies for protozoan-caused diseases requires a full understanding of the pathogenesis and protective events occurring in infected hosts. Interferons (IFNs) are a family of cytokines with diverse biological effects in host antimicrobial defense and disease pathogenesis, including protozoan parasite infection. Type II IFN (IFN-γ) has been widely recognized as the essential defense cytokine in intracellular protozoan parasite infection, whereas recent studies also revealed the production and distinct function of type I and III IFNs in host defense against these parasites. Decoding the complex network of the IFN family in host-parasite interaction is critical for exploring potential new therapeutic strategies against intracellular protozoan parasite infection. Here, we review the complex effects of IFNs on the host defense against intracellular protozoan parasites and the crosstalk between distinct types of IFN signaling during infections.

CAR γδ T cells for cancer immunotherapy. Is the field more yellow than green?

Engineered immune cell therapy to treat malignancies refractory to conventional therapies is modernizing oncology. Although αβ T cells are time-tested chassis for CAR, potential graft versus host disease (GvHD) apart from cytokine toxicity and antigen escape pose limitations to this approach. αβ T cell malignancy challenges isolation and expansion of therapeutic T cells. Moreover, αβ T cells may pose toxicity risk to inflammation sensitive vital tissues bearing the tumor. The HLA independent, multivalent, versatile and systemic anti-tumor immunity increases the desirability of γδ T cells as an alternate chassis for CAR. Indeed, CD19 γδ CAR T cell therapy to treat advanced lymphoma reached a milestone with the fast track status by FDA. However, reduced tumor-toxicity, homing, in vivo persistence and heterogeneity limits the translation of this therapy. The field is gaining momentum in recent years with optimization of gene delivery approaches and mechanistic insights into co-signaling requirements in γδ T cells. There is a renewed interest in customizing design of CAR guided by the biology of the host immune cells. Progress has been made in the current good manufacturing practice compatible expansion and engineering protocols for the δ1 and δ2 T cells. γδ CAR T cells may find its niche in the clinical situations wherein conventional CAR therapy is less suitable due to propensity for cytokine toxicity or off-tumor effect. As the therapy is moving towards clinical trials, this review chronicles the hitherto progress in the therapeutic engineering of γδ T cells for cancer immunotherapy.

Longitudinal immune profiling after radiation-attenuated sporozoite vaccination reveals coordinated immune processes correlated with malaria protection

Background

Identifying immune processes required for liver-stage sterilizing immunity to malaria remains an open problem. The IMRAS trial comprised 5x immunizations with radiation-attenuated sporozoites resulting in 55% protection from subsequent challenge.

Methods

To identify correlates of vaccination and protection, we performed detailed systems immunology longitudinal profiling of the entire trial time course including whole blood transcriptomics, detailed PBMC cell phenotyping and serum antigen array profiling of 11 IMRAS radiation-attenuated sporozoite (RAS) vaccinees at up to 21 timepoints each.

Results

RAS vaccination induced serum antibody responses to CSP, TRAP, and AMA1 in all vaccinees. We observed large numbers of differentially expressed genes associated with vaccination response and protection, with distinctly differing transcriptome responses elicited after each immunization. These included inflammatory and proliferative responses, as well as increased abundance of monocyte and DC subsets after each immunization. Increases in Vδ2 γδ; T cells and MAIT cells were observed in response to immunization over the course of study, and CD1c+ CD40+ DC abundance was significantly associated with protection. Interferon responses strongly differed between protected and non-protected individuals with high interferon responses after the 1^st immunization, but not the 2^nd-5^th. Blood transcriptional interferon responses were correlated with abundances of different circulating classical and non-classical monocyte populations.

Conclusions

This study has revealed multiple coordinated immunological processes induced by vaccination and associated with protection. Our work represents the most detailed immunological profiling of a RAS vaccine trial performed to date and will guide the design and interpretation of future malaria vaccine trials.

Gamma/Delta (γδ) T Cells: The Role of the T-Cell Receptor in Diagnosis and Prognosis of Hematologic Malignancies

ABSTRACT

There are 2 types of T cells: αβ and γδ T cells, named based on the composition of the T-cell receptor. γδ T cells are rare, making up 0.5%-10% of T cells. Although most leukemias, lymphomas, and immune-mediated conditions derive from αβ T cells, a handful of rare but important diseases are generally derived from γδ T cells, particularly primary cutaneous γδ T-cell lymphoma, hepatosplenic T-cell lymphoma, and monomorphic epitheliotropic intestinal T-cell lymphoma. There are also malignancies that may evince a γδ TCR phenotype, including large granulocytic lymphocyte leukemia, T-cell acute lymphobplastic leukemia (T-ALL), and mycosis fungoides, although such cases are rare. In this article, we will review the genesis of the T-cell receptor, the role of γδ T cells, and the importance of TCR type and methods of detection and outline the evidence for prognostic significance (or lack thereof) in lymphomas of γδ T cells. We will also highlight conditions that rarely may present with a γδ TCR phenotype and assess the utility of testing for TCR type in these diseases.

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.

Activation of chicken gamma-delta T lymphocytes by a purified ulvan extract

Chicken γδ T lymphocytes are present in a variety of tissues such as blood, spleen and intestine. They constitute a major cytotoxic population. In chicken, Salmonella immunization as well as vaccination against Newcastle disease virus are accompanied by an increase of γδ T lymphocytes in peripheral blood, which may be activated, and thus represent a protective immune response. It has been published that activation of avian γδ T cells can occur in a MHC non-restricted manner. Ulvans are complex sulfated polysaccharides composed of disaccharide repetitions found in the cell walls of green algae belonging to the genus Ulva. We recently demonstrated that a purified ulvan extract activates chicken heterophils and monocytes in vivo through TLR2 and TLR4 receptors when given in drinking water. We demonstrate here, that the same extract given once in drinking water at 25 and 50 mg/l, results in increased membrane expression of Major Histocompatibility Complex class 2 as soon as day 2, as detected using flow cytometry. We conclude chicken γδ T lymphocytes to be activated, or at least primed, in vivo, with the extract. Further experiments are required to fully understand whether their activation or priming is the result of direct and/or indirect mechanisms.

Innate and adaptive γδ T cells: How, when, and why

γδ T cells comprise the third cell lineage of lymphocytes that use, like αβ T cells and B cells, V(D)J gene rearrangement with the potential to generate a highly diverse T cell receptor (TCR) repertoire. There is no obvious conservation of γδ T cell subsets (based on TCR repertoire and/or function) between mice and human, leading to the notion that human and mouse γδ T cells are highly different. In this review, we focus on human γδ T cells, building on recent studies using high-throughput sequencing to analyze the TCR repertoire in various settings. We make then the comparison with mouse γδ T cell subsets highlighting the similarities and differences and describe the remarkable changes during lifespan of innate and adaptive γδ T cells. Finally, we propose mechanisms contributing to the generation of innate versus adaptive γδ T cells. We conclude that key elements related to the generation of the γδ TCR repertoire and γδ T cell activation/development are conserved between human and mice, highlighting the similarities between these two species.

γδ T cells in tissue physiology and surveillance

γδ T cells are a unique T cell subpopulation that are rare in secondary lymphoid organs but enriched in many peripheral tissues, such as the skin, intestines and lungs. By rapidly producing large amounts of cytokines, γδ T cells make key contributions to immune responses in these tissues. In addition to their immune surveillance activities, recent reports have unravelled exciting new roles for γδ T cells in steady-state tissue physiology, with functions ranging from the regulation of thermogenesis in adipose tissue to the control of neuronal synaptic plasticity in the central nervous system. Here, we review the roles of γδ T cells in tissue homeostasis and in surveillance of infection, aiming to illustrate their major impact on tissue integrity, tissue repair and immune protection.