Phosphoantigen-expanded human gammadelta T cells display potent cytotoxicity against monocyte-derived macrophages infected with human and avian influenza viruses

Porcine γδ T cells express cytotoxic cell-associated markers and display killing activity but are not selectively cytotoxic against PRRSV- or swIAV-infected macrophages

Background

Gamma-delta (γδ) T cells are a major immune cell subset in pigs. Approximately 50% of circulating T cells are γδ T cells in young pigs and up to 30% in adult sows. Despite this abundance, the functions of porcine γδ T cells are mostly unidentified. In humans and mice, activated γδ T cells exhibit broad innate cytotoxic activity against a wide variety of stressed, infected, and cancerous cells through death receptor/ligand-dependent and perforin/granzyme-dependent pathways. However, so far, it is unknown whether porcine γδ T cells have the ability to perform cytotoxic functions.

Methods

In this study, we conducted a comprehensive phenotypic characterization of porcine γδ T cells isolated from blood, lung, and nasal mucosa. To further analyze the cytolytic potential of γδ T cells, in vitro cytotoxicity assays were performed using purified γδ T cells as effector cells and virus-exposed or mock-treated primary porcine alveolar macrophages as target cells.

Results

Our results show that only CD2+ γδ T cells express cytotoxic markers (CD16, NKp46, perforin) with higher perforin and NKp46 expression in γδ T cells isolated from lung and nasal mucosa. Moreover, we found that γδ T cells can exhibit cytotoxic functions in a cell-cell contact and degranulation-dependent manner. However, porcine γδ T cells did not seem to specifically target Porcine Reproductive and Respiratory Syndrome Virus or swine Influenza A Virus-infected macrophages, which may be due to viral escape mechanisms.

Conclusion

Porcine γδ T cells express cytotoxic markers and can exhibit cytotoxic activity in vitro. The specific mechanisms by which porcine γδ T cells recognize target cells are not fully understood but may involve the detection of cellular stress signals.

Vγ9Vδ2 T-cells Are Potent Inhibitors of SARS-CoV-2 Replication and Represent Effector Phenotypes in Patients With COVID-19

Vγ9Vδ2 T cells play a key role in the innate immune response to viral infections through butyrophilin 3A (BTN3A). Here, we report blood Vγ9Vδ2 T cells decreased in clinically mild COVID-19 compared to healthy volunteers, and this was maintained up to 28 days and in the recovery period. Terminally differentiated Vγ9Vδ2 T cells tended to be enriched on the day of diagnosis, 28 days after, and during the recovery period. These cells showed cytotoxic and inflammatory activities following anti-BTN3A activation. BTN3A upregulation and Vγ9Vδ2 T-cell infiltration were observed in a lung biopsy from a fatal SARS-CoV-2 infection. In vitro, SARS-CoV-2 infection increased BTN3A expression in macrophages and lung cells that enhanced the anti-SARS-CoV-2 Vγ9Vδ2 T-cell cytotoxicity and interferon-γ and tumor necrosis factor-α. Increasing concentrations of anti-BTN3A lead to viral replication inhibition. Altogether, we report Vγ9Vδ2 T cells are important in the immune response against SARS-CoV-2 infection and activation by anti-BTN3A antibody may enhance their response. Clinical Trials Registration. NCT04816760.

Synthetic BSA-conjugated disaccharide related to the Streptococcus pneumoniae serotype 3 capsular polysaccharide increases IL-17A Levels, γδ T cells, and B1 cells in mice

The disaccharide (β-D-glucopyranosyluronic acid)-(1→4)-β-D-glucopyranoside represents a repeating unit of the capsular polysaccharide of Streptococcus pneumoniae serotype 3. A conjugate of the disaccharide with BSA (di-BSA conjugate) adjuvanted with aluminum hydroxide induced - in contrast to the non-adjuvanted conjugate - IgG1 antibody production and protected mice against S. pneumoniae serotype 3 infection after intraperitoneal prime-boost immunization. Adjuvanted and non-adjuvanted conjugates induced production of Th1 (IFNγ, TNFα); Th2 (IL-5, IL-13); Th17 (IL-17A), Th1/Th17 (IL-22), and Th2/Th17 cytokines (IL-21) after immunization. The concentration of cytokines in mice sera was higher in response to the adjuvanted conjugate, with the highest level of IL-17A production after the prime and boost immunizations. In contrast, the non-adjuvanted conjugate elicited only weak production of IL-17A, which gradually decreased after the second immunization. After boost immunization of mice with the adjuvanted di-BSA conjugate, there was a significant increase in the number of CD45+/CD19+ B cells, TCR+ γδ T cell, CD5+ В1 cells, and activated cells with MHC II+ expression in the spleens of the mice. IL-17A, TCR+ γδ T cells, and CD5+ В1 cells play a crucial role in preventing pneumococcal infection, but can also contribute to autoimmune diseases. Immunization with the adjuvanted and non-adjuvanted di-BSA conjugate did not elicit autoantibodies against double-stranded DNA targeting cell nuclei in mice. Thus, the molecular and cellular markers associated with antibody production and protective activity in response to immunization with the di-BSA conjugate adjuvanted with aluminum hydroxide are IL-17A, TCR+ γδ T cells, and CD5+ В1 cells against the background of increasing MHC II+ expression.

The role of γδT lymphocytes in atherosclerosis

Atherosclerosis poses a significant threat to human health, impacting overall well-being and imposing substantial financial burdens. Current treatment strategies mainly focus on managing low-density lipids (LDL) and optimizing liver functions. However, it's crucial to recognize that Atherosclerosis involves more than just lipid accumulation; it entails a complex interplay of immune responses. Research highlights the pivotal role of lipid-laden macrophages in the formation of atherosclerotic plaques. These macrophages attract lymphocytes like CD4 and CD8 to the inflamed site, potentially intensifying the inflammatory response. γδ T lymphocytes, with their diverse functions in innate and adaptive immune responses, pathogen defense, antigen presentation, and inflammation regulation, have been implicated in the early stages of Atherosclerosis. However, our understanding of the roles of γδ T cells in Atherosclerosis remains limited. This mini-review aims to shed light on the characteristics and functions of γδ T cells in Atherosclerosis. By gaining insights into the roles of γδ T cells, we may uncover a promising strategy to mitigate plaque buildup and dampen the inflammatory response, thereby opening new avenues for effectively managing this condition.

The immune system in neurological diseases: What innate-like T cells have to say

The immune system classically consists of 2 lines of defense, innate and adaptive, both of which interact with one another effectively to protect us against any pathogenic threats. Importantly, there is a diverse subset of cells known as innate-like T cells that act as a bridge between the innate and adaptive immune systems and are pivotal players in eliciting inflammatory immune responses. A growing body of evidence has demonstrated the regulatory impact of these innate-like T cells in central nervous system (CNS) diseases and that such immune cells can traffic into the brain in multiple pathological conditions, which can be typically attributed to the breakdown of the blood-brain barrier. However, until now, it has been poorly understood whether innate-like T cells have direct protective or causative properties, particularly in CNS diseases. Therefore, in this review, our attention is focused on discussing the critical roles of 3 unique subsets of unconventional T cells, namely, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells, in the context of CNS diseases, disorders, and injuries and how the interplay of these immune cells modulates CNS pathology, in an attempt to gain a better understanding of their complex functions.

Hyperactivation and enhanced cytotoxicity of reduced CD8+ gamma delta T cells in the intestine of patients with Crohn's disease correlates with disease activity

BACKGROUND AND AIMS

We aimed to investigate the immune characteristics of intestinal CD8+ gamma delta T (CD8+ γδ T) cells in Crohn's disease (CD) and their correlation with disease activity.

METHODS

The study cohorts included 21 CD patients and 21 healthy individuals. CD8+ γδ T cells were isolated from human ileal mucosa for detection by flow cytometry. The activation or inhibition status of cells was detected by detecting the expression of activation marker HLA-DR and the immunosuppressive molecule PD-1 on cells. The cytotoxicity of cells was assessed by detecting the expression of cytotoxic molecules (Perforin, Granzyme B, and TRAIL) in cells. Ratios of investigated cells were calculated as prediction factors by receiver operating characteristic curve (ROC) analysis.

RESULTS

The study revealed a reduction in intestinal CD8+ γδT cells among active CD patients, with a more pronounced reduction observed in moderately active patients compared to mildly active patients. Moreover, active CD patients exhibited heightened activation levels in their intestinal CD8+ γδT cells, whereas the activation was comparatively weakened in moderately active patients compared with mildly active patients. Additionally, the cytotoxicity of intestinal CD8+ γδT cells was enhanced solely in mildly active patients, while it was impaired in moderately active patients compared with mildly active patients. Furthermore, HLA-DR+ CD8+ γδT cell ratio, CD8+ γδT ratio, and CD8+ γδT count were identified as indicators in the diagnosis of active CD. Meanwhile, the ratios of Granzyme B+ CD8+ γδT cell and Perforin+ CD8+ γδT cell were identified as indicators that distinguish mildly moderately active CD cases.

CONCLUSIONS

Intestinal CD8+ γδT was reduced in active CD patients, but their activation and cytotoxicity were enhanced. However, with increased disease activity, intestinal CD8+ γδ T cells became dysfunctional. CD-specific perturbations observed in various phenotypic markers in CD8+ γδ T cells can be used as indicators to assist in diagnosing CD patients.

Interplay between Microbiota and γδ T Cells: Insights into Immune Homeostasis and Neuro-Immune Interactions

The gastrointestinal (GI) tract of multicellular organisms, especially mammals, harbors a symbiotic commensal microbiota with diverse microorganisms including bacteria, fungi, viruses, and other microbial and eukaryotic species. This microbiota exerts an important role on intestinal function and contributes to host health. The microbiota, while benefiting from a nourishing environment, is involved in the development, metabolism and immunity of the host, contributing to the maintenance of homeostasis in the GI tract. The immune system orchestrates the maintenance of key features of host-microbe symbiosis via a unique immunological network that populates the intestinal wall with different immune cell populations. Intestinal epithelium contains lymphocytes in the intraepithelial (IEL) space between the tight junctions and the basal membrane of the gut epithelium. IELs are mostly CD8+ T cells, with the great majority of them expressing the CD8αα homodimer, and the γδ T cell receptor (TCR) instead of the αβ TCR expressed on conventional T cells. γδ T cells play a significant role in immune surveillance and tissue maintenance. This review provides an overview of how the microbiota regulates γδ T cells and the influence of microbiota-derived metabolites on γδ T cell responses, highlighting their impact on immune homeostasis. It also discusses intestinal neuro-immune regulation and how γδ T cells possess the ability to interact with both the microbiota and brain.

Tumor vaccine based on extracellular vesicles derived from γδ-T cells exerts dual antitumor activities

γδ-T cells are innate-like T cells with dual antitumor activities. They can directly eradicate tumor cells and function as immunostimulatory cells to promote antitumor immunity. Previous studies have demonstrated that small extracellular vesicles (EVs) derived from γδ-T cells (γδ-T-EVs) inherited the dual antitumor activities from their parental cells. However, it remains unknown whether γδ-T-EVs can be designed as tumors vaccine to improve therapeutic efficacy. Here, we found that γδ-T-EVs had immune adjuvant effects on antigen-presenting cells, as revealed by enhanced expression of antigen-presenting and co-stimulatory molecules, secretion of pro-inflammatory cytokines and antigen-presenting ability of DCs after γδ-T-EVs treatment. The γδ-T-EVs-based vaccine was designed by loading tumor-associated antigens (TAAs) into γδ-T-EVs. Compared with γδ-T-EVs, the γδ-T-EVs-based vaccine effectively promoted more tumor-specific T-cell responses. In addition, the vaccine regimen preserved direct antitumor effects and induced tumor cell apoptosis. Interestingly, the allogeneic γδ-T-EVs-based vaccine showed comparable preventive and therapeutic antitumor effects to their autologous counterparts, indicating a better way of centralization and standardization in clinical practice. Furthermore, the allogeneic γδ-T-EVs-based vaccine displayed advantages over the DC-EVs-based vaccine through their dual antitumor activities. This study provides a proof-of-concept for using the allogeneic γδ-T-EVs-based vaccine in cancer control.

Aging unconventionally: γδ T cells, iNKT cells, and MAIT cells in aging

Unconventional T cells include γδ T cells, invariant Natural Killer T cells (iNKT) cells and Mucosal Associated Invariant T (MAIT) cells, which are distinguished from conventional T cells by their recognition of non-peptide ligands presented by non-polymorphic antigen presenting molecules and rapid effector functions that are pre-programmed during their development. Here we review current knowledge of the effect of age on unconventional T cells, from early life to old age, in both mice and humans. We then discuss the role of unconventional T cells in age-associated diseases and infections, highlighting the similarities between members of the unconventional T cell family in the context of aging.

Classification and function of γδT cells and its research progress in anti-glioblastoma

Human peripheral blood T lymphocytes are classified into alpha-beta T (αβΤ) cells and gamma-delta T (γδΤ) cells based on the difference in T cell receptors (TCRs). αβT cells are crucial for the acquired immune response, while γδΤ cells, though only a small subset, can recognize antigenic substances. These antigens do not need to be processed and presented and are not restricted by MHC. This distinguishes γδΤ cells from αβT cells and highlights their distinct role in innate immunity. Despite their small number, γδΤ cells hold significant significance in anti-tumor, anti-infection and immune regulation. Glioblastoma (GBM) represents one of the most prevalent malignant tumors within the central nervous system (CNS). Surgical resection alone proves to be an ineffective method for curing this type of cancer. Even with the combination of surgical resection, radiotherapy, and chemotherapy, the prognosis of some individuals with glioblastoma is still poor, and the recurrence rate is high. In this research, the classification, biological, and immunological functions of γδT cells and their research progress in anti-glioblastoma were reviewed.

Healthy adults supplemented with a nutraceutical formulation containing Aloe vera gel, rosemary and Poria cocos enhances the effect of influenza vaccination in a randomized, triple-blind, placebo-controlled trial

The study objective was to examine the role of a formulation, UP360, containing rosemary and Poria cocos extracts and Aloe vera gel powder, in healthy adults on supporting immune function with influenza vaccination. A 56-day randomized, triple-blind, placebo-controlled, parallel study consisted of a 28-day pre-vaccination period, an influenza vaccination on Day 28 and a 28-day post-vaccination period. Men and women ages 40-80 who had not yet been vaccinated for the flu were randomized to UP360 or Placebo (n = 25/group). At baseline, Days 28 and 56, blood lymphocyte populations, immunoglobulins (Ig), and cytokines were measured, and quality of life (QoL) questionnaires administered. The Wisconsin Upper Respiratory Symptom Survey (WURSS)-24 was completed daily by participants to measure incidence of upper respiratory tract infection (URTIs). In the post-vaccination period, TCR gamma-delta (γδ+) cells, known as γδ T cells, increased with UP360 supplementation compared to Placebo (p < 0.001). The UP360 group had a 15.6% increase in influenza B-specific IgG levels in the post-vaccination period (p = 0.0006). UP360 significantly increased the amount of circulating glutathione peroxidase (GSH-Px) from baseline at Day 28 (p = 0.0214), an enzyme that is important for neutralizing free radicals. While UP360 supplementation initially decreased levels of anti-inflammatory cytokine IL-1RA in the pre-vaccination period, IL-1RA levels were increased in the post-vaccination period (p ≤ 0.0482). Levels of IL-7 increased from baseline at Day 56 with UP360 supplementation (p = 0.0458). Despite these changes in immune markers, there were no differences in URTI symptoms or QoL between UP360 and Placebo. These results suggest UP360 supplementation was beneficial in eliciting a healthy, robust immune response in the context of vaccination. No changes in subjective measures of URTI illness or QoL demonstrated that participants' QoL was not negatively impacted by UP360 supplementation. There were no differences in clinical chemistry, vitals or adverse events confirming the good safety profile of UP360. The trial was registered on the International Clinical Trials Registry Platform (ISRCTN15838713).

The dynamics of γδ T cell responses in nonhuman primates during SARS-CoV-2 infection

Although most SARS-CoV-2 infections are mild, some patients develop systemic inflammation and progress to acute respiratory distress syndrome (ARDS). However, the cellular mechanisms underlying this spectrum of disease remain unclear. γδT cells are T lymphocyte subsets that have key roles in systemic and mucosal immune responses during infection and inflammation. Here we show that peripheral γδT cells are rapidly activated following aerosol or intra-tracheal/intra-nasal (IT/IN) SARS-CoV-2 infection in nonhuman primates. Our results demonstrate a rapid expansion of Vδ1 γδT cells at day1 that correlate significantly with lung viral loads during the first week of infection. Furthermore, increase in levels of CCR6 and Granzyme B expression in Vδ1 T cells during viral clearance imply a role in innate-like epithelial barrier-protective and cytotoxic functions. Importantly, the early activation and mobilization of circulating HLA-DR+CXCR3+ γδT cells along with significant correlations of Vδ1 T cells with IL-1Ra and SCF levels in bronchoalveolar lavage suggest a novel role for Vδ1 T cells in regulating lung inflammation during aerosol SARS-CoV-2 infection. A deeper understanding of the immunoregulatory functions of MHC-unrestricted Vδ1 T cells in lungs during early SARS-CoV-2 infection is particularly important in the wake of emerging new variants with increased transmissibility and immune evasion potential.

(Not) Home alone: Antigen presenting cell - T Cell communication in barrier tissues

Priming of T cells by antigen presenting cells (APCs) is essential for T cell fate decisions, enabling T cells to migrate to specific tissues to exert their effector functions. Previously, these interactions were mainly explored using blood-derived cells or animal models. With great advances in single cell RNA-sequencing techniques enabling analysis of tissue-derived cells, it has become clear that subsets of APCs are responsible for priming and modulating heterogeneous T cell effector responses in different tissues. This composition of APCs and T cells in tissues is essential for maintaining homeostasis and is known to be skewed in infection and inflammation, leading to pathological T cell responses. This review highlights the commonalities and differences of T cell priming and subsequent effector function in multiple barrier tissues such as the skin, intestine and female reproductive tract. Further, we provide an overview of how this process is altered during tissue-specific infections which are known to cause chronic inflammation and how this knowledge could be harnessed to modify T cell responses in barrier tissue.

Host immunity to Plasmodium infection: Contribution of Plasmodium berghei to our understanding of T cell-related immune response to blood-stage malaria

Malaria is a life-threatening disease caused by infection with Plasmodium parasites. The goal of developing an effective malaria vaccine is yet to be reached despite decades of massive research efforts. CD4⁺ helper T cells, CD8⁺ cytotoxic T cells, and γδ T cells are associated with immune responses to both liver-stage and blood-stage Plasmodium infection. The immune responses of T cell-lineages to Plasmodium infection are associated with both protection and immunopathology. Studies with mouse model of malaria contribute to our understanding of host immune response. In this paper, we focus primarily on mouse malaria model with blood-stage Plasmodium berghei infection and review our knowledge of T cell immune responses against Plasmodium infection. Moreover, we also discuss findings of experimental human studies. Uncovering the precise mechanisms of T cell-mediated immunity to Plasmodium infection can be accomplished through further investigations using mouse models of malaria with rodent Plasmodium parasites. Those findings would be invaluable to advance the efforts for development of an effective malaria vaccine.

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.

SARS-CoV-2 spike and nucleocapsid proteins fail to activate human dendritic cells or γδ T cells

γδ T cells are thought to contribute to immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the mechanisms by which they are activated by the virus are unknown. Using flow cytometry, we investigated if the two most abundant viral structural proteins, spike and nucleocapsid, can activate human γδ T cell subsets, directly or in the presence of dendritic cells (DC). Both proteins failed to induce interferon-γ production by Vδ1 or Vδ2 T cells within fresh mononuclear cells or lines of expanded γδ T cells generated from healthy donors, but the same proteins stimulated CD3⁺ cells from COVID-19 patients. The nucleocapsid protein stimulated interleukin-12 production by DC and downstream interferon-γ production by co-cultured Vδ1 and Vδ2 T cells, but protease digestion and use of an alternative nucleocapsid preparation indicated that this activity was due to contaminating non-protein material. Thus, SARS-CoV-2 spike and nucleocapsid proteins do not have stimulatory activity for DC or γδ T cells. We propose that γδ T cell activation in COVID-19 patients is mediated by immune recognition of viral RNA or other structural proteins by γδ T cells, or by other immune cells, such as DC, that produce γδ T cell-stimulatory ligands or cytokines.

γδ T Cells in the Tumor Microenvironment-Interactions With Other Immune Cells

A growing number of studies have shown that γδ T cells play a pivotal role in mediating the clearance of tumors and pathogen-infected cells with their potent cytotoxic, cytolytic, and unique immune-modulating functions. Unlike the more abundant αβ T cells, γδ T cells can recognize a broad range of tumors and infected cells without the requirement of antigen presentation via major histocompatibility complex (MHC) molecules. Our group has recently demonstrated parts of the mechanisms of T-cell receptor (TCR)-dependent activation of Vγ9Vδ2+ T cells by tumors following the presentation of phosphoantigens, intermediates of the mevalonate pathway. This process is mediated through the B7 immunoglobulin family-like butyrophilin 2A1 (BTN2A1) and BTN3A1 complexes. Such recognition results in activation, a robust immunosurveillance process, and elicits rapid γδ T-cell immune responses. These include targeted cell killing, and the ability to produce copious quantities of cytokines and chemokines to exert immune-modulating properties and to interact with other immune cells. This immune cell network includes αβ T cells, B cells, dendritic cells, macrophages, monocytes, natural killer cells, and neutrophils, hence heavily influencing the outcome of immune responses. This key role in orchestrating immune cells and their natural tropism for tumor microenvironment makes γδ T cells an attractive target for cancer immunotherapy. Here, we review the current understanding of these important interactions and highlight the implications of the crosstalk between γδ T cells and other immune cells in the context of anti-tumor immunity.

Role of hormones in the pregnancy and sex-specific outcomes to infections with respiratory viruses

Pregnant women infected with pathogenic respiratory viruses, such as influenza A viruses (IAV) and coronaviruses, are at higher risk for mortality, hospitalization, preterm birth, and stillbirth. Several factors are likely to contribute to the susceptibility of pregnant individuals to severe lung disease including changes in pulmonary physiology, immune defenses, and effector functions of some immune cells. Pregnancy is also a physiologic state characterized by higher levels of multiple hormones that may impact the effector functions of immune cells, such as progesterone, estrogen, human chorionic gonadotropin, prolactin, and relaxin. Each of these hormones acts to support a tolerogenic immune state of pregnancy, which helps prevent fetal rejection, but may also contribute to an impaired antiviral response. In this review, we address the unique role of adaptive and innate immune cells in the control of pathogenic respiratory viruses and how pregnancy and specific hormones can impact their effector actions. We highlight viruses with sex-specific differences in infection outcomes and why pregnancy hormones may contribute to fetal protection but aid the virus at the expense of the mother's health.

CD137 Costimulation Enhances the Antitumor Activity of Vγ9Vδ2-T Cells in IL-10-Mediated Immunosuppressive Tumor Microenvironment

Although γδ-T cell-based tumor immunotherapy using phosphoantigens to boost γδ-T cell immunity has shown success in some cancer patients, the clinical application is limited due to the rapid exhaustion of Vγ9Vδ2-T cells caused by repetitive stimulation from phosphoantigens and the profoundly immunosuppressive tumor microenvironment (TME). In this study, using a cell culture medium containing human and viral interleukin-10 (hIL-10 and vIL-10) secreted from EBV-transformed lymphoblastoid B cell lines (EBV-LCL) to mimic the immunosuppressive TEM, we found that the antitumor activity of Vγ9Vδ2-T cells was highly suppressed by endogenous hIL-10 and vIL-10 within the TME. CD137 costimulation could provide an anti-exhaustion signal to mitigate the suppressive effects of IL-10 in TME by suppressing IL-10R1 expression on Vγ9Vδ2-T cells. CD137 costimulation also improved the compromised antitumor activity of Vγ9Vδ2-T cells in TME with high levels of IL-10 in Rag2^-/- γc^-/- mice. In humanized mice, CD137 costimulation boosted the therapeutic effects of aminobisphosphonate pamidronate against EBV-induced lymphoma. Our study offers a novel approach to overcoming the obstacle of the hIL-10 and vIL-10-mediated immunosuppressive microenvironment by costimulating CD137 and enhancing the efficacy of γδ-T cell-based tumor therapy.

Exosomes derived from γδ-T cells synergize with radiotherapy and preserve antitumor activities against nasopharyngeal carcinoma in immunosuppressive microenvironment

Background

Radiotherapy is the first-line treatment for patients nasopharyngeal carcinoma (NPC), but its therapeutic efficacy is poor in some patients due to radioresistance. Adoptive T cell-based immunotherapy has also shown promise to control NPC; however, its antitumor efficacy may be attenuated by an immunosuppressive tumor microenvironment. Exosomes derived from γδ-T cells (γδ-T-Exos) have potent antitumor potentials. However, it remains unknown whether γδ-T-Exos have synergistic effect with radiotherapy and preserve their antitumor activities against NPC in an immunosuppressive tumor microenvironment.

Methods

γδ-T-Exos were stained with fluorescent membrane dye, and their interactions with NPC were determined both in vitro and in vivo. NPC cell deaths were detected after treatment with γδ-T-Exos and/or irradiation. Moreover, effects of γδ-T-Exos on radioresistant cancer stem-like cells (CSCs) were determined. The therapeutic efficacy of combination therapy using γδ-T-Exos and irradiation on NPC tumor progression was also monitored in vivo. Finally, the tumor-killing and T cell-promoting activities of γδ-T-Exos were determined under the culture in immunosuppressive NPC supernatant.

Results

γδ-T-Exos effectively interacted with NPC tumor cells in vitro and in vivo. γδ-T-Exos not only killed NPC cells in vitro, which was mainly mediated by Fas/Fas ligand (FasL) and death receptor 5 (DR5)/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathways, but also controlled NPC tumor growth and prolonged tumor-bearing mice survival in vivo. Furthermore, γδ-T-Exos selectively targeted the radioresistant CD44^+/high CSCs and induced profound cell apoptosis. The combination of γδ-T-Exos with radiotherapy overcame the radioresistance of CD44^+/high NPC cells and significantly improved its therapeutic efficacy against NPC in vitro and in vivo. In addition, γδ-T-Exos promoted T-cell migration into NPC tumors by upregulating CCR5 on T cells that were chemoattracted by CCR5 ligands in the NPC tumor microenvironment. Although NPC tumor cells secreted abundant tumor growth factor beta to suppress T-cell responses, γδ-T-Exos preserved their direct antitumor activities and overcame the immunosuppressive NPC microenvironment to amplify T-cell antitumor immunity.

Conclusions

γδ-T-Exos synergized with radiotherapy to control NPC by overcoming the radioresistance of NPC CSCs. Moreover, γδ-T-Exos preserved their tumor-killing and T cell-promoting activities in the immunosuppressive NPC microenvironment. This study provides a proof of concept for a novel and potent strategy by combining γδ-T-Exos with radiotherapy in the control of NPC.

The Dual Role of CCR5 in the Course of Influenza Infection: Exploring Treatment Opportunities

Influenza is one of the most relevant respiratory viruses to human health causing annual epidemics, and recurrent pandemics. Influenza disease is principally associated with inappropriate activation of the immune response. Chemokine receptor 5 (CCR5) and its cognate chemokines CCL3, CCL4 and CCL5 are rapidly induced upon influenza infection, contributing to leukocyte recruitment into the airways and a consequent effective antiviral response. Here we discuss the existing evidence for CCR5 role in the host immune responses to influenza virus. Complete absence of CCR5 in mice revealed the receptor’s role in coping with influenza via the recruitment of early memory CD8+ T cells, B cell activation and later recruitment of activated CD4+ T cells. Moreover, CCR5 contributes to inflammatory resolution by enhancing alveolar macrophages survival and reprogramming macrophages to pro-resolving phenotypes. In contrast, CCR5 activation is associated with excessive recruitment of neutrophils, inflammatory monocytes, and NK cells in models of severe influenza pneumonia. The available data suggests that, while CCL5 can play a protective role in influenza infection, CCL3 may contribute to an overwhelming inflammatory process that can harm the lung tissue. In humans, the gene encoding CCR5 might contain a 32-base pair deletion, resulting in a truncated protein. While discordant data in literature regarding this CCR5 mutation and influenza severity, the association of CCR5delta32 and HIV resistance fostered the development of different CCR5 inhibitors, now being tested in lung inflammation therapy. The potential use of CCR5 inhibitors to modulate the inflammatory response in severe human influenza infections is to be addressed.

Imprint of unconventional T-cell response in acute hepatitis C persists despite successful early antiviral treatment

Unconventional T cells (UTCs) are a heterogeneous group of T cells that typically exhibit rapid responses toward specific antigens from pathogens. Chronic hepatitis C virus (HCV) infection causes dysfunction of several subsets of UTCs. This altered phenotype and function of UTCs can persist over time even after direct-acting antiviral (DAA)-mediated clearance of chronic HCV. However, it is less clear if and how UTCs respond in acute, symptomatic HCV infection, a rare clinical condition, and if rapid DAA treatment of such patients reverses the caused perturbations within UTCs. Here, we comprehensively analyzed the phenotype and reinvigoration capacity of three major UTC populations, mucosal-associated invariant T (MAIT) cells, γδ T cells, and CD4 and CD8 double-negative αβ T cells (DNT cells) before, during, and after DAA-mediated clearance of acute symptomatic HCV infection. Furthermore, MAIT cell functionality was systematically studied. We observed a reduced frequency of MAIT cells. However, remaining cells presented with a near-to-normal phenotype in acute infection, which contrasted with a significant dysfunction upon stimulation that was not restored after viral clearance. Notably, DNT and γδ T cells displayed a strong activation ex-vivo in acute HCV infection, which subsequently normalized during the treatment. In addition, DNT cell activation was specifically associated with liver inflammation and inflammatory cytokines. Altogether, these data provide evidence that UTCs respond in a cell type-specific manner during symptomatic HCV infection. However, even if early treatment is initiated, long-lasting imprints within UTCs remain over time.

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.

Decreased Frequencies of Gamma/Delta T Cells Expressing Th1/Th17 Cytokine, Cytotoxic, and Immune Markers in Latent Tuberculosis-Diabetes/Pre-Diabetes Comorbidity

Antigen-specific gamma-delta (γδ) T cells are important in exhibiting anti-mycobacterial immunity, but their role in latent tuberculosis (LTB) with diabetes mellitus (DM) or pre-DM (PDM) and non-DM comorbidities have not been studied. Thus, we have studied the baseline, mycobacterial (PPD, WCL), and positive control antigen-stimulated γδ T cells expressing Th1 (IFNγ, TNFα, IL-2) and Th17 (IL-17A, IL-17F, IL-22) cytokine as well as cytotoxic (perforin [PFN], granzyme [GZE B], granulysin [GNLSN]) and immune (GMCSF, PD-1, CD69) markers in LTB (DM, PDM, NDM) comorbidities by flow cytometry. In the unstimulated (UNS) condition, we did not observe any significant difference in the frequencies of γδ T cells expressing Th1 and Th17 cytokine, cytotoxic, and immune markers. In contrast, upon PPD antigen stimulation, the frequencies of γδ T cells expressing Th1 (IFNγ, TNFα) and Th17 (IL-17F, IL-22) cytokine, cytotoxic (PFN, GZE B, GNLSN), and immune (CD69) markers were significantly diminished in LTB DM and/or PDM individuals compared to LTB NDM individuals. Similarly, upon WCL antigen stimulation, the frequencies of γδ T cells expressing Th1 (TNFα) and Th17 (IL-17A, IL-22) cytokine, cytotoxic (PFN), and immune (PD-1, CD69) markers were significantly diminished in LTB DM and/or PDM individuals compared to LTB NDM individuals. Finally, upon P/I stimulation we did not observe any significant difference in the γδ T cell frequencies expressing cytokine, cytotoxic, and immune markers between the study populations. The culture supernatant levels of IFNγ, TNFα, and IL-17A cytokines were significantly increased in LTB DM and PDM after stimulation with Mtb antigens compared to LTB NDM individuals. Therefore, diminished γδ T cells expressing cytokine, cytotoxic, and other immune markers and elevated levels of cytokines in the supernatants is a characteristic feature of LTB PDM/DM co-morbidities.

Single-Cell RNAseq Profiling of Human γδ T Lymphocytes in Virus-Related Cancers and COVID-19 Disease

The detailed characterization of human γδ T lymphocyte differentiation at the single-cell transcriptomic (scRNAseq) level in tumors and patients with coronavirus disease 2019 (COVID-19) requires both a reference differentiation trajectory of γδ T cells and a robust mapping method for additional γδ T lymphocytes. Here, we incepted such a method to characterize thousands of γδ T lymphocytes from (n = 95) patients with cancer or adult and pediatric COVID-19 disease. We found that cancer patients with human papillomavirus-positive head and neck squamous cell carcinoma and Epstein-Barr virus-positive Hodgkin's lymphoma have γδ tumor-infiltrating T lymphocytes that are more prone to recirculate from the tumor and avoid exhaustion. In COVID-19, both TCRVγ9 and TCRVγnon9 subsets of γδ T lymphocytes relocalize from peripheral blood mononuclear cells (PBMC) to the infected lung tissue, where their advanced differentiation, tissue residency, and exhaustion reflect T cell activation. Although severe COVID-19 disease increases both recruitment and exhaustion of γδ T lymphocytes in infected lung lesions but not blood, the anti-IL6R therapy with Tocilizumab promotes γδ T lymphocyte differentiation in patients with COVID-19. PBMC from pediatric patients with acute COVID-19 disease display similar γδ T cell lymphopenia to that seen in adult patients. However, blood γδ T cells from children with the COVID-19-related multisystem inflammatory syndrome are not lymphodepleted, but they are differentiated as in healthy PBMC. These findings suggest that some virus-induced memory γδ T lymphocytes durably persist in the blood of adults and could subsequently infiltrate and recirculate in tumors.

Gamma Delta T Cells and Their Involvement in COVID-19 Virus Infections

The global outbreak of the SARS-Cov-2 virus in 2020 has killed millions of people worldwide and forced large parts of the world into lockdowns. While multiple vaccine programs are starting to immunize the global population, there is no direct cure for COVID-19, the disease caused by the SARS-Cov-2 infection. A common symptom in patients is a decrease in T cells, called lymphopenia. It is as of yet unclear what the exact role of T cells are in the immune response to COVID-19. The research so far has mainly focused on the involvement of classical αβ T cells. However, another subset of T cells called γδ T cells could have an important role to play. As part of the innate immune system, γδ T cells respond to inflammation and stressed or infected cells. The γδ T cell subset appears to be particularly affected by lymphopenia in COVID-19 patients and commonly express activation and exhaustion markers. Particularly in children, this subset of T cells seems to be most affected. This is interesting and relevant because γδ T cells are more prominent and active in early life. Their specific involvement in this group of patients could indicate a significant role for γδ T cells in this disease. Furthermore, they seem to be involved in other viral infections and were able to kill SARS infected cells in vitro. γδ T cells can take up, process and present antigens from microbes and human cells. As e.g. tumour-associated antigens are presented by MHC on γδ T cells to classical T-cells, we argue here that it stands to reason that also viral antigens, such as SARS-Cov-2-derived peptides, can be presented in the same way. γδ T cells are already used for medical purposes in oncology and have potential in cancer therapy. As γδ T cells are not necessarily able to distinguish between a transformed and a virally infected cell it could therefore be of great interest to investigate further the relationship between COVID-19 and γδ T cells.

Cheap and Commonplace: Making the Case for BCG and γδ T Cells in COVID-19

Antigen-specific vaccines developed for the COVID-19 pandemic demonstrate a remarkable achievement and are currently being used in high income countries with much success. However, new SARS-CoV-2 variants are threatening this success via mutations that lessen the efficacy of antigen-specific antibodies. One simple approach to assisting with this issue is focusing on strategies that build on the non-specific protection afforded by the innate immune response. The BCG vaccine has been shown to provide broad protection beyond tuberculosis disease, including against respiratory viruses, and ongoing studies are investigating its efficacy as a tool against SARS-CoV-2. Gamma delta (γδ) T cells, particularly the Vδ2 subtype, undergo rapid expansion after BCG vaccination due to MHC-independent mechanisms. Consequently, γδ T cells can produce diverse defenses against virally infected cells, including direct cytotoxicity, death receptor ligands, and pro-inflammatory cytokines. They can also assist in stimulating the adaptive immune system. BCG is affordable, commonplace and non-specific, and therefore could be a useful tool to initiate innate protection against new SARS-CoV-2 variants. However, considerations must also be made to BCG vaccine supply and the prioritization of countries where it is most needed to combat tuberculosis first and foremost.

Exosomes derived from Vδ2-T cells control Epstein-Barr virus-associated tumors and induce T cell antitumor immunity

Treatment of life-threatening Epstein-Barr virus (EBV)-associated tumors remains a great challenge, especially for patients with relapsed or refractory disease. Here, we found that exosomes derived from phosphoantigen-expanded Vδ2-T cells (Vδ2-T-Exos) contained death-inducing ligands (FasL and TRAIL), an activating receptor for natural killer (NK) cells (NKG2D), immunostimulatory ligands (CD80 and CD86), and antigen-presenting molecules (MHC class I and II). Vδ2-T-Exos targeted and efficiently killed EBV-associated tumor cells through FasL and TRAIL pathways and promoted EBV antigen-specific CD4 and CD8 T cell expansion. Administration of Vδ2-T-Exos effectively controlled EBV-associated tumors in Rag2^-/-γc^-/- and humanized mice. Because expanding Vδ2-T cells and preparing autologous Vδ2-T-Exos from cancer patients ex vivo in large scale is challenging, we explored the antitumor activity of allogeneic Vδ2-T-Exos in humanized mouse cancer models. Here, we found that allogeneic Vδ2-T-Exos had more effective antitumor activity than autologous Vδ2-T-Exos in humanized mice; the allogeneic Vδ2-T-Exos increased the infiltration of T cells into tumor tissues and induced more robust CD4 and CD8 T cell-mediated antitumor immunity. Compared with exosomes derived from NK cells (NK-Exos) with direct cytotoxic antitumor activity or dendritic cells (DC-Exos) that induced T cell antitumor responses, Vδ2-T-Exos directly killed tumor cells and induced T cell-mediated antitumor response, thus resulting in more effective control of EBV-associated tumors. This study provided proof of concept for the strategy of using Vδ2-T-Exos, especially allogeneic Vδ2-T-Exos, to treat EBV-associated tumors.

How to Train Your Dragon: Harnessing Gamma Delta T Cells Antiviral Functions and Trained Immunity in a Pandemic Era

The emergence of viruses with pandemic potential such as the SARS-CoV-2 coronavirus causing COVID-19 poses a global health challenge. There is remarkable progress in vaccine technology in response to this threat, but their design often overlooks the innate arm of immunity. Gamma Delta (γδ) T cells are a subset of T cells with unique features that gives them a key role in the innate immune response to a variety of homeostatic alterations, from cancer to microbial infections. In the context of viral infection, a growing body of evidence shows that γδ T cells are particularly equipped for early virus detection, which triggers their subsequent activation, expansion and the fast deployment of antiviral functions such as direct cytotoxic pathways, secretion of cytokines, recruitment and activation of other immune cells and mobilization of a trained immunity memory program. As such, γδ T cells represent an attractive target to stimulate for a rapid and effective resolution of viral infections. Here, we review the known aspects of γδ T cells that make them crucial component of the immune response to viruses, and the ways that their antiviral potential can be harnessed to prevent or treat viral infection.

NKG2D as a Cell Surface Marker on γδ-T Cells for Predicting Pregnancy Outcomes in Patients With Unexplained Repeated Implantation Failure

Maternal immune tolerance to semi-allogeneic fetus is essential for a successful implantation and pregnancy. Growing evidence indicated that low cytotoxic activity of γδ-T cells, which is mediated by activation and inhibitory receptors, is important for establishment of maternal immune tolerant microenvironment. However, the correlation between receptors on peripheral blood γδ-T cells, such as NKG2D, CD158a, and CD158b, and pregnancy outcome in patients with unexplained repeated implantation failure (uRIF) remains unclear. In this study, the association between the expression level of these receptors and pregnancy outcome in patients with uRIF was investigated. Thirty-eight women with uRIF were enrolled and divided into two groups: successful group and failed group, according to the pregnancy outcome on different gestational periods. The percentage of NKG2D⁺ γδ-T cells in lymphocytes was significantly higher in uRIF patients who had failed clinical pregnancy in subsequent cycle, compared with those who had successful clinical pregnancy. However, there were no differences about the frequencies of CD158a⁺ and CD158b⁺ γδ-T cells between the successful and failed groups. The receiver operating characteristic curve exhibited that the optimal cut-off value of NKG2D⁺ γδ-T cells was 3.24%, with 92.3% sensitivity and 66.7% specificity in predicting clinical pregnancy failure in uRIF patients. The patients with uRIF were further divided into two groups, group 1 (NKG2D⁺ γδ-T cells <3.24%) and group 2 (NKG2D⁺ γδ-T cells ≥3.24%), based on the cut-off value. The live birth rate of patients in the group 1 and group 2 were 61.5 and 28.0%, respectively. Kaplan-Meier survival curve further suggested that the frequency of NKG2D⁺ γδ-T cells in lymphocytes negatively correlated with live birth rate in patients with uRIF. In conclusion, our study demonstrated that the frequency of peripheral blood NKG2D⁺ γδ-T cells among lymphocytes is a potential predictor for pregnancy outcome in uRIF patients.

Increase of Vδ2+ T Cells That Robustly Produce IL-17A in Advanced Abdominal Aortic Aneurysm Tissues

Abdominal aortic aneurysm (AAA) is a chronic dilation of the aorta with a tendency to enlarge and eventually rupture, which constitutes a major cause of cardiovascular mortality. Although T-cell infiltrates have been observed in AAA, the cellular, phenotypic, and functional characteristics of these tissue-infiltrating T cells are not fully understood. Here, we investigated the proportional changes of T-cell subsets-including CD4⁺ T cells, CD8⁺ T cells, and γδ T cells-and their effector functions in AAAs. We found that Vδ2⁺ T cells were presented at a higher frequency in aortic aneurysmal tissue compared to normal aortic tissue and PBMCs from patients with AAA. In contrast, no differences were observed in the frequencies of CD4⁺, CD8⁺, and Vδ1⁺ T cells. Moreover, we observed that the Vδ2⁺ T cells from AAA tissue displayed immunophenotypes indicative of CCR5⁺ non-exhausted effector memory cells, with a decreased proportion of CD16⁺ cells. Finally, we found that these Vδ2⁺ T cells were the main source of IL-17A in abdominal aortic aneurysmal tissue. In conclusion, our results suggest that increased Vδ2⁺ T cells that robustly produce IL-17A in aortic aneurysmal tissue may contribute to AAA pathogenesis and progression.

Granzyme B-expressing γδ-T and NK cells as a predictor of clinical pregnancy failure in patients with unexplained repeated implantation failure

The limited cytotoxicity of immune cells facilitates a successful establishment of pregnancy. However, the association between cytotoxic granules and unexplained repeated implantation failure (uRIF) remains unkown. Twenty-one fertile controls and 54 patients with uRIF were included in this study. The pregnancy outcomes were monitored at different gestational periods. The peripheral blood lymphocytes were detected using specific monoclonal antibodies by flow cytometry. The percentage of perforin⁺ (Pfr⁺), granzyme B⁺ (GrB⁺), or granulysin⁺ (Gnly⁺) lymphocytes was not significantly different among fertile controls, uRIF patients with successful pregnancy outcomes, and uRIF patients with pregnancy failure. The percentage of GrB⁺ γδ-T cells in lymphocytes was markedly higher in uRIF patients with implantation failure and clinical pregnancy failure than that in uRIF patients with a corresponding successful pregnancy outcome. A four-tier risk model showed that the risk of suffering clinical pregnancy failure in uRIF patients among high risk tier (83.3 %), normal risk tier (65.0 %) and low risk tier (39.1 %) was elevated by 2-4 fold compared with uRIF patients among lowest risk tier (20.0 %). In addition, the percentage of GrB⁺ NK cells in lymphocytes tended to decrease in uRIF patients with pregnancy failure. The AUC of the combined indicator with GrB⁺ γδ-T cells and GrB⁺ NK cells was increased than that of GrB⁺ γδ-T cells and GrB⁺ NK cells for predicting clinical pregnancy failure. In conclusion, the frequency of GrB-expressing γδ-T and NK cells in peripheral blood could serve as a predictor of clinical pregnancy failure in patients with uRIF.

The BTLA and PD-1 signaling pathways independently regulate the proliferation and cytotoxicity of human peripheral blood γδ T cells

Background

B‐ and T‐lymphocyte attenuator (BTLA) and programmed cell death‐1 (PD‐1) inhibit γδ T cell homeostasis and activation. This study aimed to determine whether BTLA and PD‐1 signaling pathways were convergent or independent in human peripheral blood γδ T cells. Herein we demonstrate that the signalings of BTLA and PD‐1 regulated proliferation and cytotoxicity of human γδ T cells, respectively.

Methods

Human peripheral blood γδ T cells were cultured with inactivated Jurkat cells in the presence of interleukin‐2 and zoledronate (Zol) for 14 days. Flow cytometry was performed to evaluate the phenotypes and functions of γδ T cells.

Results

The proliferation of the γδ T cells was increased when PBMCs were cocultured with inactivated herpes virus entry mediator (HVEM)^low Jurkat cells. The cytotoxicity of the expanded γδ T cells was not affected by coculture with inactivated HVEM^low Jurkat cells and was further increased in the presence of anti‐PD‐L1 mAb. These results suggest that the inactivation of the BTLA signaling pathway during expansion could help produce more γδ T cells without compromising γδ T cell function. The inhibition of BTLA or PD‐1 signaling repressed phosphorylation of the src homology region 2‐containing protein tyrosine phosphatase 2 and increased the phosphorylation of protein kinase B in γδ T cells. However, there were no synergistic or additive effects by a combination of BTLA and PD‐1 blockade.

Conclusion

These results suggest that BTLA signaling is crucial in regulating γδ T cell proliferation and function and that the BTLA and PD‐1 signaling pathways act independently on the proliferation and cytotoxicity of human peripheral γδ T cells.

The Unknown Unknowns: Recovering Gamma-Delta T Cells for Control of Human Immunodeficiency Virus (HIV)

Recent advances in γδ T cell biology have focused on the unique attributes of these cells and their role in regulating innate and adaptive immunity, promoting tissue homeostasis, and providing resistance to various disorders. Numerous bacterial and viral pathogens, including human immunodeficiency virus-1 (HIV), greatly alter the composition of γδ T cells in vivo. Despite the effectiveness of antiretroviral therapy (ART) in controlling HIV and restoring health in those affected, γδ T cells are dramatically impacted during HIV infection and fail to reconstitute to normal levels in HIV-infected individuals during ART for reasons that are not clearly understood. Importantly, their role in controlling HIV infection, and the implications of their failure to rebound during ART are also largely unknown and understudied. Here, we review important aspects of human γδ T cell biology, the effector and immunomodulatory properties of these cells, their prevalence and function in HIV, and their immunotherapeutic potential.

Establishing a Multicolor Flow Cytometry to Characterize Cellular Immune Response in Chickens Following H7N9 Avian Influenza Virus Infection

Avian influenza virus (AIV) emerged and has continued to re-emerge, continuously posing great threats to animal and human health. The detection of hemagglutination inhibition (HI) or virus neutralization antibodies (NA) is essential for assessing immune protection against AIV. However, the HI/NA-independent immune protection is constantly observed in vaccines’ development against H7N9 subtype AIV and other subtypes in chickens and mammals, necessitating the analysis of the cellular immune response. Here, we established a multi-parameter flow cytometry to examine the innate and adaptive cellular immune responses in chickens after intranasal infection with low pathogenicity H7N9 AIV. This assay allowed us to comprehensively define chicken macrophages, dendritic cells, and their MHC-II expression, NK cells, γδ T cells, B cells, and distinct T cell subsets in steady state and during infection. We found that NK cells and KUL01⁺ cells significantly increased after H7N9 infection, especially in the lung, and the KUL01⁺ cells upregulated MHC-II and CD11c expression. Additionally, the percentages and numbers of γδ T cells and CD8 T cells significantly increased and exhibited an activated phenotype with significant upregulation of CD25 expression in the lung but not in the spleen and blood. Furthermore, B cells showed increased in the lung but decreased in the blood and spleen in terms of the percentages or/and numbers, suggesting these cells may be recruited from the periphery after H7N9 infection. Our study firstly disclosed that H7N9 infection induced local and systemic cellular immune responses in chickens, the natural host of AIV, and that the flow cytometric assay developed in this study is useful for analyzing the cellular immune responses to AIVs and other avian infectious diseases and defining the correlates of immune protection.

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.

Role of γδ T cells in controlling viral infections with a focus on influenza virus: implications for designing novel therapeutic approaches

BACKGROUND

Influenza virus infection is among the most detrimental threats to the health of humans and some animals, infecting millions of people annually all around the world and in many thousands of cases giving rise to pneumonia and death. All those health crises happen despite previous and recent developments in anti-influenza vaccination, suggesting the need for employing more sophisticated methods to control this malign infection. Main body The innate immunity modules are at the forefront of combating against influenza infection in the respiratory tract, among which, innate T cells, particularly gamma-delta (γδ) T cells, play a critical role in filling the gap needed for adaptive immune cells maturation, linking the innate and adaptive immunity together. Upon infection with influenza virus, production of cytokines and chemokines including CCL3, CCL4, and CCL5 from respiratory epithelium recruits γδ T cells at the site of infection in a CCR5 receptor-dependent fashion. Next, γδ T cells become activated in response to influenza virus infection and produce large amounts of proinflammatory cytokines, especially IL-17A. Regardless of γδ T cells' roles in triggering the adaptive arm of the immune system, they also protect the respiratory epithelium by cytolytic and non-cytolytic antiviral mechanisms, as well as by enhancing neutrophils and natural killer cells recruitment to the infection site.

CONCLUSION

In this review, we explored varied strategies of γδ T cells in defense to influenza virus infection and how they can potentially provide balanced protective immune responses against infected cells. The results may provide a potential window for the incorporation of intact or engineered γδ T cells for developing novel antiviral approaches or for immunotherapeutic purposes.

Making a case for using γδ T cells against SARS-CoV-2

Intensive worldwide efforts are underway to determine both the pathogenesis of SARS-CoV-2 infection and the immune responses in COVID-19 patients in order to develop effective therapeutics and vaccines. One type of cell that may contribute to these immune responses is the γδ T lymphocyte, which plays a key role in immunosurveillance of the mucosal and epithelial barriers by rapidly responding to pathogens. Although found in low numbers in blood, γδ T cells consist the majority of tissue-resident T cells and participate in the front line of the host immune defense. Previous studies have demonstrated the critical protective role of γδ T cells in immune responses to other respiratory viruses, including SARS-CoV-1. However, no studies have profoundly investigated these cells in COVID-19 patients to date. γδ T cells can be safely expanded in vivo using existing inexpensive FDA-approved drugs such as bisphosphonate, in order to test its protective immune response to SARS-CoV-2. To support this line of research, we review insights gained from previous coronavirus research, along with recent findings, discussing the potential role of γδ T cells in controlling SARS-CoV-2. We conclude by proposing several strategies to enhance γδ T cell's antiviral function, which may be used in developing therapies for COVID-19.

γδ T cell frequencies are altered in HIV positive pregnant South African women and are associated with preterm birth

Background

Preterm birth is the leading cause of neonatal and child mortality worldwide. Maternal HIV infection and antiretroviral treatment (ART) increase the rate of preterm birth, but the underlying mechanisms remain unknown, limiting progress in prediction, prevention and treatment. While overall γδ T cell levels remain constant, acute HIV infection is associated with a depletion of the Vδ2 subset and an increase in the Vδ1 subset, which do not return to baseline with ART. γδ T cells have also been implicated in adverse pregnancy outcomes and we therefore investigated the potential association between maternal HIV infection, peripheral γδ T cell frequencies and preterm birth.

Methods

Study participants were HIV positive (n = 47) and HIV negative (n = 45) women enrolled in a prospective pregnancy cohort study at Chris Hani Baragwanath Academic Hospital in Soweto, South Africa. Women were enrolled in early pregnancy and gestational age was accurately determined by first trimester ultrasound scan. Peripheral blood samples were collected in each trimester and peripheral blood mononuclear cells isolated. Frequencies of γδ T cells, Vδ1+ and Vδ2+ γδ T cell subsets, and CCR6 chemokine receptor expression were determined by flow cytometry.

Results

Total γδ T cell levels were similar between HIV positive and HIV negative women throughout pregnancy. However, in each trimester maternal HIV infection was associated with reduced levels of the Vδ2+ subset and increased levels of the Vδ1+ subset, leading to a reversal of the Vδ1/Vδ2 ratio. Timing of ART initiation among HIV positive women did not affect levels of γδ T cells, the Vδ1+ and Vδ2+ subsets, or the Vδ1/Vδ2 ratio. Importantly, preterm birth was associated with lower total γδ T cell levels in early pregnancy and γδ T cell frequencies were lowest in HIV positive women who delivered preterm. Moreover, in the first trimester the proportion of Vδ1+ T cells that were CCR6+ was significantly reduced in HIV+ women and women who delivered preterm, resulting in the lowest proportion of CCR6+ Vδ1 T cells in HIV positive women who delivered preterm.

Conclusions

Our findings suggest that altered γδ T cell frequencies may link maternal HIV infection and preterm birth. γδ T cell frequencies in early pregnancy may serve as predictive biomarkers to identify women at risk of delivering preterm.

CD137 costimulation enhances the antiviral activity of Vγ9Vδ2-T cells against influenza virus

Influenza epidemics and pandemics are constant threats to global public health. Although strategies including vaccines and antiviral drugs have achieved great advances in controlling influenza virus infection, the efficacy of these strategies is limited by the highly frequent mutations in the viral genome and the emergence of drug-resistant strains. Our previous study indicated that boosting the immunity of human Vγ9Vδ2-T cells with the phosphoantigen pamidronate could be a therapeutic strategy to treat seasonal and avian influenza virus infections. However, one notable drawback of γδ-T cell-based immunotherapy is the rapid exhaustion of proliferation and effector responses due to repeated treatments with phosphoantigens. Here, we found that the expression of CD137 was inducible in Vγ9Vδ2-T cells following antigenic stimulation. CD137⁺ Vγ9Vδ2-T cells displayed more potent antiviral activity against influenza virus than their CD137⁻ counterparts in vitro and in Rag2^-/- γc^-/- mice. We further demonstrated that CD137 costimulation was essential for Vγ9Vδ2-T cell activation, proliferation, survival and effector functions. In humanized mice reconstituted with human peripheral blood mononuclear cells, CD137 costimulation with a recombinant human CD137L protein boosted the therapeutic effects of pamidronate against influenza virus. Our study provides a novel strategy of targeting CD137 to improve the efficacy of Vγ9Vδ2-T cell-based immunotherapy.

B7-H3 inhibits the IFN-γ-dependent cytotoxicity of Vγ9Vδ2 T cells against colon cancer cells

The immunoregulatory protein B7-H3, a member of the B7 family, has been confirmed to be highly expressed in colon cancer. However, the exact influence of B7-H3 on the features and antitumor ability of γδT cells in colon cancer remains unknown. In the present study, we investigated that the proportions of B7-H3⁺ γδT cells were distinctly increased in the peripheral blood and tumor tissues of colon cancer patients. B7-H3 blockade or knockdown promoted proliferation, inhibited cell apoptosis and induced the expression of activation markers (CD25 and CD69) on Vδ2 T cells. In contrast, treatment with the B7-H3 agonist 4H7 had the opposite effect. Furthermore, B7-H3 suppressed IFN-γ expression by inhibiting T-bet in Vδ2 T cells. Moreover, B7-H3 mediated the inhibition of Vδ2 T cell cytotoxicity via the downregulation of IFN-γ and perforin/granzyme B expression. More importantly, blocking the B7-H3 function significantly enhanced the cytotoxicity of Vδ2 T cells against colon cancer cells in vivo. Therefore, the inhibition or blockade of B7-H3 is a potential immunotherapeutic approach for colon cancer.

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.

Human γδ T-cell receptor repertoire is shaped by influenza viruses, age and tissue compartmentalisation

Background

Although γδ T cells comprise up to 10% of human peripheral blood T cells, questions remain regarding their role in disease states and T‐cell receptor (TCR) clonal expansions. We dissected anti‐viral functions of human γδ T cells towards influenza viruses and defined influenza‐reactive γδ TCRs in the context of γδ‐TCRs across the human lifespan.

Methods

We performed ⁵¹Cr‐killing assay and single‐cell time‐lapse live video microscopy to define mechanisms underlying γδ T‐cell‐mediated killing of influenza‐infected targets. We assessed cytotoxic profiles of γδ T cells in influenza‐infected patients and IFN‐γ production towards influenza‐infected lung epithelial cells. Using single‐cell RT‐PCR, we characterised paired TCRγδ clonotypes for influenza‐reactive γδ T cells in comparison with TCRs from healthy neonates, adults, elderly donors and tissues.

Results

We provide the first visual evidence of γδ T‐cell‐mediated killing of influenza‐infected targets and show distinct features to those reported for CD8⁺ T cells. γδ T cells displayed poly‐cytotoxic profiles in influenza‐infected patients and produced IFN‐γ towards influenza‐infected cells. These IFN‐γ‐producing γδ T cells were skewed towards the γ9δ2 TCRs, particularly expressing the public GV9‐TCRγ, capable of pairing with numerous TCR‐δ chains, suggesting their significant role in γδ T‐cell immunity. Neonatal γδ T cells displayed extensive non‐overlapping TCRγδ repertoires, while adults had enriched γ9δ2‐pairings with diverse CDR3γδ regions. Conversely, the elderly showed distinct γδ‐pairings characterised by large clonal expansions, a profile also prominent in adult tissues.

Conclusion

Human TCRγδ repertoire is shaped by age, tissue compartmentalisation and the individual's history of infection, suggesting that these somewhat enigmatic γδ T cells indeed respond to antigen challenge.

Experimental H1N1pdm09 infection in pigs mimics human seasonal influenza infections

Pigs are anatomically, genetically and physiologically comparable to humans and represent a natural host for influenza A virus (IAV) infections. Thus, pigs may represent a relevant biomedical model for human IAV infections. We set out to investigate the systemic as well as the local immune response in pigs upon two subsequent intranasal infections with IAV H1N1pdm09. We detected decreasing numbers of peripheral blood lymphocytes after the first infection. The simultaneous increase in the frequencies of proliferating cells correlated with an increase in infiltrating leukocytes in the lung. Enhanced perforin expression in αβ and γδ T cells in the respiratory tract indicated a cytotoxic T cell response restricted to the route of virus entry such as the nose, the lung and the bronchoalveolar lavage. Simultaneously, increasing frequencies of CD8αα expressing αβ T cells were observed rapidly after the first infection, which may have inhibited uncontrolled inflammation in the respiratory tract. Taking together, the results of this study demonstrate that experimental IAV infection in pigs mimics major characteristics of human seasonal IAV infections.

The Role of Innate Leukocytes during Influenza Virus Infection

Influenza virus infection is a serious threat to humans and animals, with the potential to cause severe pneumonia and death. Annual vaccination strategies are a mainstay to prevent complications related to influenza. However, protection from the emerging subtypes of influenza A viruses (IAV) even in vaccinated individuals is challenging. Innate immune cells are the first cells to respond to IAV infection in the respiratory tract. Virus replication-induced production of cytokines from airway epithelium recruits innate immune cells to the site of infection. These leukocytes, namely, neutrophils, monocytes, macrophages, dendritic cells, eosinophils, natural killer cells, innate lymphoid cells, and γδ T cells, become activated in response to IAV, to contain the virus and protect the airway epithelium while triggering the adaptive arm of the immune system. This review addresses different anti-influenza virus schemes of innate immune cells and how these cells fine-tune the balance between immunoprotection and immunopathology during IAV infection. Detailed understanding on how these innate responders execute anti-influenza activity will help to identify novel therapeutic targets to halt IAV replication and associated immunopathology.

Emerging role of γδ T cells in vaccine-mediated protection from infectious diseases

γδ T cells are fascinating cells that bridge the innate and adaptive immune systems. They have long been known to proliferate rapidly following infection; however, the identity of the specific γδ T cell subsets proliferating and the role of this expansion in protection from disease have only been explored more recently. Several recent studies have investigated γδ T‐cell responses to vaccines targeting infections such as Mycobacterium, Plasmodium and influenza, and studies in animal models have provided further insight into the association of these responses with improved clinical outcomes. In this review, we examine the evidence for a role for γδ T cells in vaccine‐induced protection against various bacterial, protozoan and viral infections. We further discuss results suggesting potential mechanisms for protection, including cytokine‐mediated direct and indirect killing of infected cells, and highlight remaining open questions in the field. Finally, building on current efforts to integrate strategies targeting γδ T cells into immunotherapies for cancer, we discuss potential approaches to improve vaccines for infectious diseases by inducing γδ T‐cell activation and cytotoxicity.

Diminished cytolytic activity of γδ T cells with reduced DNAM-1 expression in neuroblastoma patients

Neuroblastoma is one of the children's malignant tumors with poor prognosis, as well as high recurrence and metastasis rates after surgical removal and chemotherapy. γδ T-cell based immunotherapy receives increasing attention thanks to the strong cytolytic activity to tumor cells. Our previous data revealed a significant increase in circulating γδ T-cell frequency in NB patients. In the present study, we found that beside a reduction of IFN-γ in serum of NB patients, DNAM-1 expression decreased in both circulating and PAM-expanded NB γδ T cells. Upon PAM stimulation, NB γδ T cells showed a reduced level of cell proliferation. In addition, the cytolytic activity of NB γδ T cells to NB cell lines was proved to be attenuated in a co-culture system. The fact that DNAM-1 neutralizing antibody abolished the tumor cell killing accentuates the indispensable role of DNAM-1 molecule in γδ T-cell cytolytic function.

Multivariate Computational Analysis of Gamma Delta T Cell Inhibitory Receptor Signatures Reveals the Divergence of Healthy and ART-Suppressed HIV+ Aging

Even with effective viral control, HIV-infected individuals are at a higher risk for morbidities associated with older age than the general population, and these serious non-AIDS events (SNAEs) track with plasma inflammatory and coagulation markers. The cell subsets driving inflammation in aviremic HIV infection are not yet elucidated. Also, whether ART-suppressed HIV infection causes premature induction of the inflammatory events found in uninfected elderly or if a novel inflammatory network ensues when HIV and older age co-exist is unclear. In this study we measured combinational expression of five inhibitory receptors (IRs) on seven immune cell subsets and 16 plasma markers from peripheral blood mononuclear cells (PBMC) and plasma samples, respectively, from a HIV and Aging cohort comprised of ART-suppressed HIV-infected and uninfected controls stratified by age (≤35 or ≥50 years old). For data analysis, multiple multivariate computational algorithms [cluster identification, characterization, and regression (CITRUS), partial least squares regression (PLSR), and partial least squares-discriminant analysis (PLS-DA)] were used to determine if immune parameter disparities can distinguish the subject groups and to investigate if there is a cross-impact of aviremic HIV and age on immune signatures. IR expression on gamma delta (γδ) T cells exclusively separated HIV+ subjects from controls in CITRUS analyses and secretion of inflammatory cytokines and cytotoxic mediators from γδ T cells tracked with TIGIT expression among HIV+ subjects. Also, plasma markers predicted the percentages of TIGIT+ γδ T cells in subjects with and without HIV in PSLR models, and a PLS-DA model of γδ T cell IR signatures and plasma markers significantly stratified all four of the subject groups (uninfected younger, uninfected older, HIV+ younger, and HIV+ older). These data implicate γδ T cells as an inflammatory driver in ART-suppressed HIV infection and provide evidence of distinct “inflamm-aging” processes with and without ART-suppressed HIV infection.

γδ T Cells Provide Protective Function in Highly Pathogenic Avian H5N1 Influenza A Virus Infection

Given the high mortality rate (>50%) and potential danger of intrapersonal transmission, highly pathogenic avian influenza (HPAI) H5N1 epidemics still pose a significant threat to humans. γδ T cells, which participate on the front line of the host immune defense, demonstrate both innate, and adaptive characteristics in their immune response and have potent antiviral activity against various viruses. However, the roles of γδ T cells in HPAI H5N1 viral infection remain unclear. In this study, we found that γδ T cells provided a crucial protective function in the defense against HPAI H5N1 viral infection. HPAI H5N1 viruses could directly activate γδ T cells, leading to enhanced CD69 expression and IFN-γ secretion. Importantly, we found that the trimer but not the monomer of HPAI H5N1 virus hemagglutinin (HA) proteins could directly activate γδ T cells. HA-induced γδ T cell activation was dependent on both sialic acid receptors and HA glycosylation, and this activation could be inhibited by the phosphatase calcineurin inhibitor cyclosporin A but not by the phosphatidylinositol 3-kinase (PI3-K) inhibitors wortmannin and LY294002. Our findings provide a further understanding the mechanism underlying γδ T cell-mediated innate and adoptive immune responses against HPAI H5N1 viral infection, which helps to develop novel therapeutic strategies for the treatment of H5N1 infection in the future.