Human and murine memory γδ T cells: Evidence for acquired immune memory in bacterial and viral infections and autoimmunity

When inflammatory stressors dramatically change, disease phenotypes may transform between autoimmune hematopoietic failure and myeloid neoplasms

Aplastic anemia (AA) and hypoplastic myelodysplastic syndrome are paradigms of autoimmune hematopoietic failure (AHF). Myelodysplastic syndrome and acute myeloid leukemia are unequivocal myeloid neoplasms (MNs). Currently, AA is also known to be a clonal hematological disease. Genetic aberrations typically observed in MNs are detected in approximately one-third of AA patients. In AA patients harboring MN-related genetic aberrations, a poor response to immunosuppressive therapy (IST) and an increased risk of transformation to MNs occurring either naturally or after IST are predicted. Approximately 10%-15% of patients with severe AA transform the disease phenotype to MNs following IST, and in some patients, leukemic transformation emerges during or shortly after IST. Phenotypic transformations between AHF and MNs can occur reciprocally. A fraction of advanced MN patients experience an aplastic crisis during which leukemic blasts are repressed. The switch that shapes the disease phenotype is a change in the strength of extramedullary inflammation. Both AHF and MNs have an immune-active bone marrow (BM) environment (BME). In AHF patients, an inflamed BME can be evoked by infiltrated immune cells targeting neoplastic molecules, which contributes to the BM-specific autoimmune impairment. Autoimmune responses in AHF may represent an antileukemic mechanism, and inflammatory stressors strengthen antileukemic immunity, at least in a significant proportion of patients who have MN-related genetic aberrations. During active inflammatory episodes, normal and leukemic hematopoieses are suppressed, which leads to the occurrence of aplastic cytopenia and leukemic cell regression. The successful treatment of underlying infections mitigates inflammatory stress-related antileukemic activities and promotes the penetration of leukemic hematopoiesis. The effect of IST is similar to that of treating underlying infections. Investigating inflammatory stress-powered antileukemic immunity is highly important in theoretical studies and clinical practice, especially given the wide application of immune-activating agents and immune checkpoint inhibitors in the treatment of hematological neoplasms.

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.

γδ T cells respond directly and selectively to the skin commensal yeast Malassezia for IL-17-dependent fungal control

Stable microbial colonization of the skin depends on tight control by the host immune system. The lipid-dependent yeast Malassezia typically colonizes skin as a harmless commensal and is subject to host type 17 immunosurveillance, but this fungus has also been associated with diverse skin pathologies in both humans and animals. Using a murine model of Malassezia exposure, we show that Vγ4+ dermal γδ T cells expand rapidly and are the major source of IL-17A mediating fungal control in colonized skin. A pool of memory-like Malassezia-responsive Vγ4+ T cells persisted in the skin, were enriched in draining lymph nodes even after fungal clearance, and were protective upon fungal re-exposure up to several weeks later. Induction of γδT17 immunity depended on IL-23 and IL-1 family cytokine signalling, whereas Toll-like and C-type lectin receptors were dispensable. Furthermore, Vγ4+ T cells from Malassezia-exposed hosts were able to respond directly and selectively to Malassezia-derived ligands, independently of antigen-presenting host cells. The fungal moieties detected were shared across diverse species of the Malassezia genus, but not conserved in other Basidiomycota or Ascomycota. These data provide novel mechanistic insight into the induction and maintenance of type 17 immunosurveillance of skin commensal colonization that has significant implications for cutaneous health.

The role of γδ T cells in the immunopathogenesis of inflammatory diseases: from basic biology to therapeutic targeting

The γδ T cells are lymphocytes with an innate-like phenotype that can distribute to different tissues to reside and participate in homeostatic functions such as pathogen defense, tissue modeling, and response to stress. These cells originate during fetal development and migrate to the tissues in a TCR chain-dependent manner. Their unique manner to respond to danger signals facilitates the initiation of cytokine-mediated diseases such as spondyloarthritis and psoriasis, which are immune-mediated diseases with a very strong link with mucosal disturbances, either in the skin or the gut. In spondyloarthritis, γδ T cells are one of the main sources of IL-17 and, therefore, the main drivers of inflammation and probably new bone formation. Remarkably, this population can be the bridge between gut and joint inflammation.

Unlocking the potential of allogeneic Vδ2 T cells for ovarian cancer therapy through CD16 biomarker selection and CAR/IL-15 engineering

Allogeneic Vγ9Vδ2 (Vδ2) T cells have emerged as attractive candidates for developing cancer therapy due to their established safety in allogeneic contexts and inherent tumor-fighting capabilities. Nonetheless, the limited clinical success of Vδ2 T cell-based treatments may be attributed to donor variability, short-lived persistence, and tumor immune evasion. To address these constraints, we engineer Vδ2 T cells with enhanced attributes. By employing CD16 as a donor selection biomarker, we harness Vδ2 T cells characterized by heightened cytotoxicity and potent antibody-dependent cell-mediated cytotoxicity (ADCC) functionality. RNA sequencing analysis supports the augmented effector potential of Vδ2 T cells derived from CD16 high (CD16Hi) donors. Substantial enhancements are further achieved through CAR and IL-15 engineering methodologies. Preclinical investigations in two ovarian cancer models substantiate the effectiveness and safety of engineered CD16Hi Vδ2 T cells. These cells target tumors through multiple mechanisms, exhibit sustained in vivo persistence, and do not elicit graft-versus-host disease. These findings underscore the promise of engineered CD16Hi Vδ2 T cells as a viable therapeutic option for cancer treatment.

P2RX7 gene knockout or antagonism reduces angiotensin II-induced hypertension, vascular injury and immune cell activation

OBJECTIVE

Extracellular ATP is elevated in hypertensive mice and humans and may trigger immune activation through the purinergic receptor P2X7 (P2RX7) causing interleukin-1β production and T-cell activation and memory T-cell development. Furthermore, P2RX7 single nucleotide polymorphisms (SNP) are associated with hypertension. We hypothesized that P2RX7 activation contributes to hypertension and cardiovascular injury by promoting immune activation.

METHODS

Male wild-type and P2rx7-/- mice were infused or not with angiotensin II (AngII) for 14 days. A second group of AngII-infused wild-type mice were co-infused with the P2RX7 antagonist AZ10606120 or vehicle. BP was monitored by telemetry. Cardiac and mesenteric artery function and remodeling were assessed using ultrasound and pressure myography, respectively. T cells were profiled in thoracic aorta/perivascular adipose tissue by flow cytometry. Associations between SNPs within 50 kb of P2RX7 transcription, and BP or hypertension were modeled in 384 653 UK Biobank participants.

RESULTS

P2rx7 inactivation attenuated AngII-induced SBP elevation, and mesenteric artery dysfunction and remodeling. This was associated with decreased perivascular infiltration of activated and effector memory T-cell subsets. Surprisingly, P2rx7 knockout exaggerated AngII-induced cardiac dysfunction and remodeling. Treatment with a P2RX7 antagonist reduced BP elevation, preserved mesenteric artery function and reduced activated and effector memory T cell perivascular infiltration without adversely affecting cardiac function and remodeling in AngII-infused mice. Three P2RX7 SNPs were associated with increased odds of DBP elevation.

CONCLUSION

P2RX7 may represent a target for attenuating BP elevation and associated vascular damage by decreasing immune activation.

Angiotensin II-Induced Memory γδ T Cells Sensitize Mice to a Mild Hypertensive Stimulus

BACKGROUND

Memory T cells develop during an initial hypertensive episode, sensitizing mice to develop hypertension from further mild hypertensive challenges. We hypothesized that memory γδ T cells develop after a hypertensive challenge and sensitize mice to develop hypertension in response to a subsequent mild hypertensive challenge.

METHODS

The first aim was to profile memory γδ T cells after a 14-day pressor dose angiotensin II (AngII) infusion (490 ng/kg/min, subcutaneously) in male mice. The second aim was to deplete γδ T cells during a second 14-day subpressor dose AngII challenge (140 ng/kg/min, subcutaneously) in mice pre-exposed to an initial pressor dose AngII challenge. The third aim was to transfer 2.5 × 105 live pre-activated or not γδ T cells from mice that had received a 14-day pressor dose AngII infusion or sham treatment, to naive recipient mice stimulated with a subpressor dose AngII infusion.

RESULTS

Effector memory γδ T cells increased 5.2-fold in mesenteric vessels and perivascular adipose tissue, and 1.8-fold in mesenteric lymph nodes in pressor dose AngII-infused mice compared with sham-treated mice. Mice depleted of γδ T cells had 14 mm Hg lower systolic blood pressure (SBP) elevation than control mice from day 7 to 14 of subpressor dose AngII infusion. Adoptive transfer of γδ T cells from hypertensive mice induced an 18 mm Hg higher SBP elevation compared with a subpressor dose AngII infusion vs. γδ T cells transferred from sham-treated mice.

CONCLUSIONS

Memory γδ T cells develop in response to hypertensive stimuli, and contribute to the pathogenesis of hypertension.

Cytometry profiling of ex vivo recall responses to Coxiella burnetii in previously naturally exposed individuals reveals long-term changes in both adaptive and innate immune cellular compartments

Introduction

Q fever, caused by the intracellular bacterium Coxiella burnetii, is considered an occupational and biodefense hazard and can result in debilitating long-term complications. While natural infection and vaccination induce humoral and cellular immune responses, the exact nature of cellular immune responses to C. burnetii is incompletely understood. The current study seeks to investigate more deeply the nature of long-term cellular recall responses in naturally exposed individuals by both cytokine release assessment and cytometry profiling.

Methods

Individuals exposed during the 2007-2010 Dutch Q fever outbreak were grouped in 2015, based on a C. burnetii-specific IFNγ release assay (IGRA), serological status, and self-reported clinical symptoms during initial infection, into asymptomatic IGRA-negative/seronegative controls, and three IGRA-positive groups (seronegative/asymptomatic; seropositive/asymptomatic and seropositive/symptomatic). Recall responses following in vitro re-stimulation with heat-inactivated C. burnetii in whole blood, were assessed in 2016/2017 by cytokine release assays (n=55) and flow cytometry (n=36), and in blood mononuclear cells by mass cytometry (n=36).

Results

Cytokine release analysis showed significantly elevated IL-2 responses in all seropositive individuals and elevated IL-1β responses in those recovered from symptomatic infection. Comparative flow cytometry analysis revealed significantly increased IFNγ, TNFα and IL-2 recall responses by CD4 T cells and higher IL-6 production by monocytes from symptomatic, IGRA-positive/seropositive individuals compared to controls. Mass cytometry profiling and unsupervised clustering analysis confirmed recall responses in seropositive individuals by two activated CD4 T cell subsets, one characterized by a strong Th1 cytokine profile (IFNγ+IL-2+TNFα+), and identified C. burnetii-specific activation of CD8 T cells in all IGRA-positive groups. Remarkably, increased C. burnetii-specific responses in IGRA-positive individuals were also observed in three innate cell subpopulations: one characterized by an IFNγ+IL-2+TNFα+ Th1 cytokine profile and lack of canonical marker expression, and two IL-1β-, IL-6- and IL-8-producing CD14+ monocyte subsets that could be the drivers of elevated secretion of innate cytokines in pre-exposed individuals.

Discussion

These data highlight that there are long-term increased responses to C. burnetii in both adaptive and innate cellular compartments, the latter being indicative of trained immunity. These findings warrant future studies into the protective role of these innate responses and may inform future Q fever vaccine design.

Leukemic transformation during anti-tuberculosis treatment in aplastic anemia-paroxysmal nocturnal hemoglobinuria syndrome: A case report and review of literature

BACKGROUND

Accumulating evidence demonstrates that autoimmune hematopoietic failure and myeloid neoplasms have an intrinsic relationship with regard to clonal hematopoiesis and disease evolution. In approximately 10%-15% of patients with severe aplastic anemia (SAA), the disease phenotype is transformed into myeloid neoplasms following antithymocyte globulin plus cyclosporine-based immunosuppressive therapy. In some of these patients, myeloid neoplasms appear during or shortly after immunosuppressive therapy. Leukemic transformation in SAA patients during anti-tuberculosis treatment has not been reported.

CASE SUMMARY

A middle-aged Chinese female had a 6-year history of non-SAA and a 2-year history of paroxysmal nocturnal hemoglobinuria (PNH). With aggravation of systemic inflammatory symptoms, severe pancytopenia developed, and her hemoglobinuria disappeared. Laboratory findings in cytological, immunological and cytogenetic analyses of bone marrow samples met the diagnostic criteria for "SAA." Definitive diagnosis of disseminated tuberculosis was made in the search for infectious niches. Remarkable improvement in hematological parameters was achieved within 1 mo of anti-tuberculosis treatment, and complete hematological remission was achieved within 4 mo of treatment. Frustratingly, the hematological response lasted for only 3 mo, and pancytopenia reemerged. At this time, cytological findings (increased bone marrow cellularity and an increased percentage of myeloblasts that accounted for 16.0% of all nucleated hematopoietic cells), immunological findings (increased percentage of cluster of differentiation 34+ cells that accounted for 12.28% of all nucleated hematopoietic cells) and molecular biological findings (identification of somatic mutations in nucleophosmin-1 and casitas B-lineage lymphoma genes) revealed that "SAA" had transformed into acute myeloid leukemia with mutated nucleophosmin-1. The transformation process suggested that the leukemic clones were preexistent but were suppressed in the PNH and SAA stages, as development of symptomatic myeloid neoplasm through acquisition and accumulation of novel oncogenic mutations is unlikely in an interval of only 7 mo. Aggravation of inflammatory stressors due to disseminated tuberculosis likely contributed to the repression of normal and leukemic hematopoiesis, and the relief of inflammatory stressors due to anti-tuberculosis treatment contributed to penetration of neoplastic hematopoiesis. The concealed leukemic clones in the SAA and PNH stages raise the possibility of an inflammatory stress-fueled antileukemic mechanism.

CONCLUSION

Aggravated inflammatory stressors can repress normal and leukemic hematopoiesis, and relieved inflammatory stressors can facilitate penetration of neoplastic hematopoiesis.

Biology of GD2 ganglioside: implications for cancer immunotherapy

Part of the broader glycosphingolipid family, gangliosides are composed of a ceramide bound to a sialic acid-containing glycan chain, and locate at the plasma membrane. Gangliosides are produced through sequential steps of glycosylation and sialylation. This diversity of composition is reflected in differences in expression patterns and functions of the various gangliosides. Ganglioside GD2 designates different subspecies following a basic structure containing three carbohydrate residues and two sialic acids. GD2 expression, usually restrained to limited tissues, is frequently altered in various neuroectoderm-derived cancers. While GD2 is of evident interest, its glycolipid nature has rendered research challenging. Physiological GD2 expression has been linked to developmental processes. Passing this stage, varying levels of GD2, physiologically expressed mainly in the central nervous system, affect composition and formation of membrane microdomains involved in surface receptor signaling. Overexpressed in cancer, GD2 has been shown to enhance cell survival and invasion. Furthermore, binding of antibodies leads to immune-independent cell death mechanisms. In addition, GD2 contributes to T-cell dysfunction, and functions as an immune checkpoint. Given the cancer-associated functions, GD2 has been a source of interest for immunotherapy. As a potential biomarker, methods are being developed to quantify GD2 from patients' samples. In addition, various therapeutic strategies are tested. Based on initial success with antibodies, derivates such as bispecific antibodies and immunocytokines have been developed, engaging patient immune system. Cytotoxic effectors or payloads may be redirected based on anti-GD2 antibodies. Finally, vaccines can be used to mount an immune response in patients. We review here the pertinent biological information on GD2 which may be of use for optimizing current immunotherapeutic strategies.

Comparative studies on mannan and imiquimod induced experimental plaque psoriasis inflammation in inbred mice

Psoriasis is a genetically determined, environmentally triggered, immune system-mediated autoimmune disease. Different animal models are needed to investigate the complex pathological mechanisms underlying this disease. Therefore, we established mannan-induced psoriasis model and compared with the most commonly used imiquimod-induced psoriasis in terms of disease, induction of innate immune cells, expression of cytokines, and the effect of dexamethasone treatment. Mannan significantly induced more severe psoriasis with better disease relapsing feature than imiquimod (IMQ). As determined by immunohistochemistry, IMQ induced significantly more infiltration of CD11c+ and F4/80+ cells than mannan in the skin. However, cytometric analysis showed a significant increase in the percentage of Gr-1+ neutrophils in the spleen and lymph nodes as well as F4/80+ macrophages in the spleen after mannan exposure. Variation in the percentage of significantly increased Vγ4 T cells was also found to be dependent on the lymphoid organs tested. However, there is a clear difference between these models in terms of expression of certain cytokine genes: IL-22, IL-23, IL-17E, and IL-17F were expressed more predominantly in mannan-induced inflammation, while IL-6 and IL-17A expressions were significantly higher in IMQ model. Interestingly, dexamethasone treatment strongly reduced epidermal thickness and histological scores induced by mannan than IMQ. Despite inducing psoriasis-like inflammation, certain differences and similarities were observed in the immune responses induced by mannan and IMQ. However, mannan-induced psoriasis model is relatively more simple, economical and less harmful to mice with an increased possibility to develop a chronic psoriasis model by exposing mice to mannan.

Surfing on the waves of the human γδ T cell ontogenic sea

While γδ T cells are present virtually in all vertebrates, there is a remarkable lack of conservation of the TRG and TRD loci underlying the generation of the γδ T cell receptor (TCR), which is associated with the generation of species-specific γδ T cells. A prominent example is the human phosphoantigen-reactive Vγ9Vδ2 T cell subset that is absent in mice. Murine γδ thymocyte cells were among the first immune cells identified to follow a wave-based layered development during embryonic and early life, and since this initial observation, in-depth insight has been obtained in their thymic ontogeny. By contrast, less is known about the development of human γδ T cells, especially regarding the generation of γδ thymocyte waves. Here, after providing an overview of thymic γδ wave generation in several vertebrate classes, we review the evidence for γδ waves in the human fetal thymus, where single-cell technologies have allowed the breakdown of human γδ thymocytes into functional waves with important TCR associations. Finally, we discuss the possible mechanisms contributing to the generation of waves of γδ thymocytes and their possible significance in the periphery.

Are CD45RO+ and CD45RA- genuine markers for bovine memory T cells?

Effective vaccination induces memory T cells, which protect the host against pathogen re-infections. Therefore, detection of memory T cells is essential for evaluating vaccine efficacy, which was originally dependent on cytokine induction assays. Currently, two isoforms of CD45 tyrosine phosphatase, CD45RO expression and CD45RA exclusion (CD45RO+/ CD45RA-) are used extensively for detecting memory T cells in cattle. The CD45RO+/CD45RA- markers were first established in humans around three decades ago, and were adopted in cattle soon after. However, in the last two decades, some published data in humans have challenged the initial paradigm, and required multiple markers for identifying memory T cells. On the contrary, memory T cell detection in cattle still mostly relies on CD45RO+/CD45RA- despite some controversial evidence. In this review, we summarized the current literature to examine if CD45RO+/CD45RA- are valid markers for detecting memory T cells in cattle. It seems CD45RA and CD45RO (CD45RA/RO) as markers for identifying bovine memory T cells are questionable.

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.

Isolation and expansion of murine γδ T cells from mouse splenocytes

Elucidation of the function of gamma delta T cells (γδ T cells) requires robust models that show how γδ T cells are commonly involved in inflammation, since very little is known about the factors that promote and control their development and function. There are few studies of murine γδ T cells primarily because these cells have proven difficult to isolate, expand and characterize. Here, we describe a simple method that utilizes key expansion elements to isolate and expand murine CD4^-CD8^-CD3⁺ γδ T cells typically found in secondary lymphoid tissues. Expansion of γδ T cells reached 150-fold by day 8 of culture, depended on exogenous IL-2, αCD3, and αCD28, and supported efficient and reproducible in vitro differentiation. These studies showed high production of cytokines IFNγ and Granzyme B, with the novel finding of IL-24 upregulation as well. Expression analysis of expanded γδ T cells, after treatment with IL-2, revealed high levels of Granzyme B, Granzyme D, and IFNγ. Lactate dehydrogenase (LDH) cytotoxicity assays showed that expanded γδ T cells were effective at inducing >90% cytolysis of murine MC38 colon cancer, E0771 breast cancer, and B16 melanoma cells at 10:1 effector to target ratios. These findings indicated that murine γδ T cells can be successfully isolated, expanded, and used to perform preclinical therapy studies.

Japanese Encephalitis Virus Persistence in Porcine Tonsils Is Associated With a Weak Induction of the Innate Immune Response, an Absence of IFNγ mRNA Expression, and a Decreased Frequency of CD4+CD8+ Double-Positive T Cells

In humans, Japanese encephalitis virus (JEV) causes a devastating neurotropic disease with high mortality, whereas in pigs, the virus only causes mild symptoms. Besides tropism to the central nervous system, JEV seems to harbor a particular tropism for the tonsils in pigs. This secondary lymphoid organ appears to act as a reservoir for the virus, and we show that it is found up to 21 days post infection at high viral titers. The immune response in the tonsils was studied over time upon intradermal inoculation of pigs. Entry of the virus in the tonsils was accompanied by a significant increase in anti-viral OAS1 and IFNβ mRNA expression. This limited antiviral response was, however, not sufficient to stop JEV replication, and importantly, no IFNγ or innate inflammatory cytokine mRNA expression could be observed. Strikingly, the persistence of JEV in tonsils was also associated with a significant decreased frequency of CD4⁺CD8⁺ double-positive T lymphocytes. Furthermore, it is important to note that JEV persistence in tonsils occurred despite a strong induction of the adaptive immune response. JEV-specific antibodies were found after 6 days post infection in serum, and cell-mediated immune responses upon NS3 restimulation of PBMCs from experimentally infected pigs showed that CD4⁺CD8⁺ double-positive T cells were found to display the most prominent proliferation and IFNγ production among lymphocyte subtypes. Taken together, these results suggest that an inadequate induction of the innate immune response and the absence of an IFNγ antiviral response contribute to the persistence of JEV in the tonsils and is associated with a decrease in the frequency of CD4⁺CD8⁺ double-positive T cells.

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.

Erysipelothrix rhusiopathiae-specific T-cell responses after experimental infection of chickens selectively bred for high and low serum levels of mannose-binding lectin

Erysipelas, caused by infection with Erysipelothrix rhusiopathiae (ER) is an important emerging disease in laying hens. We have earlier observed prominent mannose-binding lectin (MBL) acute phase responses in experimentally ER infected chickens. The present study aimed to further examine immune responses to ER by using chickens selectively bred for high (L10H) and low (L10L) serum MBL levels. Chickens were infected with ER at 3 weeks of age and immune parameters and bacterial load were monitored in blood until day 18 after infection. Blood and spleen leukocytes collected on day 18 were stimulated in vitro with ER antigens and blast transformation of different T-cell populations was assessed. The ER infection gave a very varied outcome and no clear differences were observed between L10H and L10L chickens with respect to leukocyte counts, bacterial load or clinical outcome. Nonetheless, rapid innate responses, e.g., heterophilia and increased serum MBL levels were noted in bacteraemic chickens. All ER infected chickens also showed transient increased expression of mannose receptor MRC1L-B and decreased expression of major histocompatibility complex II on monocytes day 1 after infection indicating monocyte activation or relocation. In vitro ER stimulation showed antigen specific blast transformation of CD4+, TCRγ/δ-CD8αβ+ and TCRγ/δ+CD8αβ+ spleen cells from all infected chickens. For CD4+ and TCRγ/δ-CD8αβ+ cells the proportions of blast transformed cells were significantly higher for samples from L10L chickens than those for samples from L10H chickens. This is the first observation of ER-specific T-cells in chickens and interestingly a Th1-type response comprising cytotoxic T-cells was indicated.

Inhibiting the Unconventionals: Importance of Immune Checkpoint Receptors in γδ T, MAIT, and NKT Cells

Simple Summary

All conventional major histocompatibility complex (MHC)-restricted T cells transiently express immune checkpoint/inhibitory receptors (ICRs) following activation as a means to counter-regulate overactivation. However, tumors promote chronic ICR expression rendering T cells chronically unresponsive or “exhausted”. Checkpoint inhibitor (CPI) therapy targets and blocks ICRs, restoring T cell activation and anti-tumor immunity. However, CPI therapy often fails, partly because of the tumor’s many abilities to inhibit MHC-driven T cell responses. In this regard, our immune system contains an arsenal of unconventional non-MHC-restricted T cells, whose importance in anti-tumor immunity is rapidly gaining momentum. There is currently little knowledge as to whether unconventional T cells can get exhausted and how CPI therapy affects them. In this article we review the current understanding of the role of ICRs in unconventional T cell biology and discuss the importance of targeting these unique immune cell populations for CPI therapy.

Abstract

In recent years, checkpoint inhibitor (CPI) therapy has shown promising clinical responses across a broad range of cancers. However, many patients remain unresponsive and there is need for improvement. CPI therapy relies on antibody-mediated neutralization of immune inhibitory or checkpoint receptors (ICRs) that constitutively suppress leukocytes. In this regard, the clinical outcome of CPI therapy has primarily been attributed to modulating classical MHC-restricted αβ T cell responses, yet, it will inevitably target most lymphoid (and many myeloid) populations. As such, unconventional non-MHC-restricted gamma delta (γδ) T, mucosal associated invariant T (MAIT) and natural killer T (NKT) cells express ICRs at steady-state and after activation and may thus be affected by CPI therapies. To which extent, however, remains unclear. These unconventional T cells are polyfunctional innate-like lymphocytes that play a key role in tumor immune surveillance and have a plethora of protective and pathogenic immune responses. The robust anti-tumor potential of γδ T, MAIT, and NKT cells has been established in a variety of preclinical cancer models and in clinical reports. In contrast, recent studies have documented a pro-tumor effect of innate-like T cell subsets that secrete pro-inflammatory cytokines. Consequently, understanding the mechanisms that regulate such T cells and their response to CPI is critical in designing effective cancer immunotherapies that favor anti-tumor immunity. In this Review, we will discuss the current understanding regarding the role of immune checkpoint regulation in γδ T, MAIT, and NKT cells and its importance in anti-cancer immunity.