Influenza A Infection Stimulates RIG-I and Enhances Effector Function of Primary Human NK Cells.

Immune surveillance by natural killer (NK) cells and their recruitment to sites of inflammation renders them susceptible to viral infection, potentially modulating their effector function. Here, we analyzed innate RNA receptor signaling in NK cells downstream of direct Influenza A virus (IAV) infection and its impact on NK cell effector function. Infection of NK cells with IAV resulted in the activation of TBK1, NF-Ï°B and subsequent type-I IFN secretion. CRISPR-generated knockouts in primary human NK cells revealed that this effect depended on the antiviral cytosolic RNA receptor RIG-I. Transfection of NK cells with synthetic 3p-dsRNA, a strong RIG-I agonist that mimics viral RNA, resulted in a similar phenotype and rendered NK cells resistant to subsequent IAV infection. Strikingly, both IAV infection and 3p-dsRNA transfection enhanced degranulation and cytokine production by NK cells when exposed to target cells. Thus, RIG-I activation in NK cells both supports their cell intrinsic viral defense and enhances their cytotoxic effector function against target cells.

Raising the NKT cell family.

Natural killer T cells (NKT cells) are CD1d-restricted, lipid antigen-reactive, immunoregulatory T lymphocytes that can promote cell-mediated immunity to tumors and infectious organisms, including bacteria and viruses, yet paradoxically they can also suppress the cell-mediated immunity associated with autoimmune disease and allograft rejection. Furthermore, in some diseases, such as atherosclerosis and allergy, NKT cell activity can be deleterious to the host. Although the precise means by which these cells carry out such contrasting functions is unclear, recent studies have highlighted the existence of many functionally distinct NKT cell subsets. Because their frequency and number vary widely between individuals, it is important to understand the mechanisms that regulate the development and maintenance of NKT cells and subsets thereof, which is the subject of this review.

Classical Type 1 Dendritic Cells Dominate Priming of Th1 Responses to Herpes Simplex Virus Type 1 Skin Infection.

CD4+ T cell responses are crucial for the control of many intracellular pathogens, yet the requirements for their induction are not fully understood. To better understand the role that various dendritic cell (DC) subtypes play in CD4+ T cell priming, we compared in vivo T cell responses to skin inoculation of mice with infectious or UV-inactivated HSV type 1. Localized infection elicited a Th1 response that was primed in skin-draining lymph nodes involving Ag presentation by migratory dermal and lymph node-resident DC. However, expansion and Th1 differentiation was impaired in response to UV-inactivated virus (UV-HSV), and this defect correlated with a restriction of Ag presentation to migratory CD103- dermal DC. A similar differentiation defect was seen in infected mice lacking CD8α+ and CD103+ classical type 1 DC (cDC1). Finally, Th1 differentiation after UV-HSV inoculation was rescued by targeted Ag delivery to CD8α+ and CD103+ cDC1 using an anti-Clec9A Ab construct. This suggests that Ag presentation by cDC1 is crucial for optimal Th1 immunity to HSV type 1 infection and potentially other pathogens of the skin.

Limited Internodal Migration of T Follicular Helper Cells after Peripheral Infection with Herpes Simplex Virus-1.

The ability of CD4 T cells to give rise to specialized T follicular helper cells (TFH) critical to initiating appropriate Ab responses is regulated by environmental cues in lymphoid tissues draining the site of infection. In this study, we used a skin infection with HSV-1 characterized by the successive involvement of interconnected but distinct lymph nodes (LNs), to investigate the anatomical diversification of virus-specific CD4 T cell responses and the migratory capacity of TFH or their precursors. Whereas Th1 effector CD4 T cells expressing peripheral-targeting migration molecules readily migrated from primary to secondary reactive LNs, Bcl6(+) CXCR5(+) PD1(hi) TFH were largely retained at the site of initial activation with little spillover into the downstream LNs involved at later stages of infection. Consistent with this, TFH maintained high-level surface expression of CD69, indicative of impaired migratory capacity. Notably, the biased generation and retention of TFH in primary LNs correlated with a preferential generation of germinal centers at this site. Our results highlight a limited anatomical diversification of TFH responses and germinal center reactions that were imprinted within the first few cell divisions during TFH differentiation in LNs draining the site of initial infection.

DOCK8 is critical for the survival and function of NKT cells.

Patients with the dedicator of cytokinesis 8 (DOCK8) immunodeficiency syndrome suffer from recurrent viral and bacterial infections, hyper-immunoglobulin E levels, eczema, and greater susceptibility to cancer. Because natural killer T (NKT) cells have been implicated in these diseases, we asked if these cells were affected by DOCK8 deficiency. Using a mouse model, we found that DOCK8 deficiency resulted in impaired NKT cell development, principally affecting the formation and survival of long-lived, differentiated NKT cells. In the thymus, DOCK8-deficient mice lack a terminally differentiated subset of NK1.1(+) NKT cells expressing the integrin CD103, whereas in the liver, DOCK8-deficient NKT cells express reduced levels of the prosurvival factor B-cell lymphoma 2 and the integrin lymphocyte function-associated antigen 1. Although the initial NKT cell response to antigen is intact in the absence of DOCK8, their ongoing proliferative and cytokine responses are impaired. Importantly, a similar defect in NKT cell numbers was detected in DOCK8-deficient humans, highlighting the relevance of the mouse model. In conclusion, our data demonstrate that DOCK8 is required for the development and survival of mature NKT cells, consistent with the idea that DOCK8 mediates survival signals within a specialized niche. Accordingly, impaired NKT cell numbers and function are likely to contribute to the susceptibility of DOCK8-deficient patients to recurrent infections and malignant disease.

ZBTB7B (Th-POK) regulates the development of IL-17-producing CD1d-restricted mouse NKT cells.

CD1d-dependent NKT cells represent a heterogeneous family of effector T cells including CD4(+)CD8(-) and CD4(-)CD8(-) subsets that respond to glycolipid Ags with rapid and potent cytokine production. NKT cell development is regulated by a unique combination of factors, however very little is known about factors that control the development of NKT subsets. In this study, we analyze a novel mouse strain (helpless) with a mis-sense mutation in the BTB-POZ domain of ZBTB7B and demonstrate that this mutation has dramatic, intrinsic effects on development of NKT cell subsets. Although NKT cell numbers are similar in Zbtb7b mutant mice, these cells are hyperproliferative and most lack CD4 and instead express CD8. Moreover, the majority of ZBTB7B mutant NKT cells in the thymus are retinoic acid-related orphan receptor γt positive, and a high frequency produce IL-17 while very few produce IFN-γ or other cytokines, sharply contrasting the profile of normal NKT cells. Mice heterozygous for the helpless mutation also have reduced numbers of CD4(+) NKT cells and increased production of IL-17 without an increase in CD8(+) cells, suggesting that ZBTB7B acts at multiple stages of NKT cell development. These results reveal ZBTB7B as a critical factor genetically predetermining the balance of effector subsets within the NKT cell population.

Examining the impact of immunosuppressive drugs on antibody-dependent cellular cytotoxicity (ADCC) of human peripheral blood natural killer (NK) cells and gamma delta (γδ) T cells.

BACKGROUND: Human natural killer (NK) cells and gamma delta (γδ) T cells may impact outcomes of solid organ transplantation (SOT) such as lung transplantation (LTx) following the differential engagement of an array of activating and inhibitory receptors. Amongst these, CD16 may be particularly important due to its capacity to bind IgG to trigger antibody-dependent cellular cytotoxicity (ADCC) and the production of proinflammatory cytokines. While the use of immunosuppressive drugs (ISDs) is an integral component of SOT practice, their relative impact on various immune cells, especially γδT cells and CD16-induced functional responses, is still unclear. METHODS: The ADCC responses of peripheral blood NK cells and γδT cells from both healthy blood donors and adult lung transplant recipients (LTRs) were assessed by flow cytometry. Specifically, the degranulation response, as reflected in the expression of CD107a, and the capacity of both NK cells and γδT cells to produce IFN-γ and TNF-α was assessed following rituximab (RTX)-induced activation. Additionally, the effect of cyclosporine A (CsA), tacrolimus (TAC), prednisolone (Prdl) and azathioprine (AZA) at the concentration of 1 ng/ml, 10 ng/ml, 100 ng/ml, and 1000 ng/ml on these responses was also compared in both cell types. RESULTS: Flow cytometric analyses of CD16 expresion showed that its expression on γδT cells was both at lower levels and more variable than that on peripheral blood NK cells. Nevertheless functional analyses showed that despite these differences, γδT cells like NK cells can be readily activated by engagement with RTX to degranulate and produce cytokines such as IFNg and TNF-a. RTX-induced degranulation by either NK cells or γδT cells from healthy donors was not impacted by co-culture with individual ISDs. However, CsA and TAC but not Prdl and AZA did inhibit the production of IFN-γ and TNF-α by both cell types. Flow cytometric analyses of RTX-induced activation of NK cells and γδT cells from LTRs suggested their capacity to degranulate was not markedly impacted by transplantation with similar levels of cells expressing CD107 pre- and post-LTx. However an impairment in the ability of NK cells to produce cytokines was observed in samples obtained post LTx whereas γδT cell cytokine responses were not significantly impacted. CONCLUSIONS: In conclusion, the findings show that despite differences in the expression levels of CD16, γδT cells like NK cells can be readily activated by engagement with RTX and that in vitro exposure to CsA and TAC (calcineurin inhibitors) had a measurable effect on cytokine production but not degranulation by both NK cells and gdT cells from healthy donors. Finally the observation that in PBMC obtained from LTx recipients, NK cells but not γδT cells exhibited impaired cytokine reponses suggests that transplantation or chronic exposure to ISDs differentially impacts their potential to respond to the introduction of an allograft and/or transplant-associated infections.

Cytomegalovirus Immunity Assays Predict Viremia but not Replication Within the Lung Allograft.

Cytomegalovirus (CMV) infection causes significant morbidity and mortality in lung transplant recipients. Current guidelines use pretransplant donor and recipient CMV serostatus to predict the risk of subsequent CMV replication and length of antiviral prophylaxis. Immunological monitoring may better inform the risk of CMV infection in patients, thereby allowing for improved tailoring of antiviral prophylaxis. In this study, we compared 2 commercially available assays, the QuantiFERON-CMV (QFN-CMV) and T-Track-CMV (enzyme-linked immunosorbent spot assay), to predict the risk of CMV disease in lung transplant recipients. Methods: We performed CMV immunity assays on 32 lung transplant recipients at risk of CMV disease as defined by serostatus (CMV-seropositive recipients, n = 26; or CMV-seronegative lung transplant recipient receiving a CMV-seropositive donor organ, n = 6). QFN-CMV and T-Track were performed on peripheral blood mononuclear cells, and episodes of CMV replication in both serum and bronchoalveolar lavage were found to be correlated to the CMV immune assays. The predictive ability of the assays was determined using Kaplan-Meier curves. Results: There was a degree of concordance between tests, with 44% of recipients positive for both tests and 28% negative for both tests; however, test results were discordant in 28% of cases. A negative result in either the QFN-CMV (P < 0.01) or T-Track (P < 0.05) assays was obtained in a significantly higher number of recipients who experienced CMV replication in the blood. Using these assays together gave higher predictability of CMV replication, with only 1 recipient experiencing CMV replication in the blood who obtained a positive test result for both assays. Neither assay was able to predict recipients who experienced CMV replication in the lung allograft. Conclusions: Our study demonstrates that CMV immunity assays can predict viremia; however, the lack of association with allograft infection suggests that CMV-specific T-cell immunity in the circulation is not associated with the control of CMV replication within the transplanted lung allograft.

Distinct roles in NKT cell maturation and function for the different transcription factors in the classical NF-κB pathway.

The nuclear factor (NF)-κB signalling pathway is known to be critical for natural killer T (NKT) cell differentiation; however, the role of individual NF-κB transcription factors and the precise developmental stages that they control remain unclear. We have investigated the influence of the classical NF-κB transcription factors NF-κB1, c-Rel and RelA on NKT cell development and function, using gene-deleted mice. Individually, none of these factors were essential for the requirement of NF-κB signalling in early NKT cell development before NK1.1 expression, in contrast to earlier reports in which the classical NF-κB pathway was globally disrupted. Instead, we found that each factor played a non-redundant role in later stages of NKT cell maturation and function. Although NF-κB1 deficiency resulted in a moderate reduction in mature NK1.1+ NKT cells, this was found to be more subtle than previously reported. RelA deficiency had a more profound effect on the NK1.1+ stage of NKT cell development, whereas c-Rel-deficient mice had normal NKT cell numbers. All three factors (NF-κB1, RelA and c-Rel) were necessary for normal NKT cell cytokine production. Notably, IL-17, which is produced by a specific subset of NKT cells (NKT-17 cells), defined as NK1.1(-)CD4(-), was not impaired by a lack of these individual NF-κB transcription factors, nor was this subset depleted, suggesting that NKT-17 cells are regulated independently of the NF-κB pathway. Thus, individual NF-κB family members have a largely redundant role in early NKT cell development, but each of them has an important and distinct role in NKT cell maturation and/or function.

Structural plasticity of KIR2DL2 and KIR2DL3 enables altered docking geometries atop HLA-C.

The closely related inhibitory killer-cell immunoglobulin-like receptors (KIR), KIR2DL2 and KIR2DL3, regulate the activation of natural killer cells (NK) by interacting with the human leukocyte antigen-C1 (HLA-C1) group of molecules. KIR2DL2, KIR2DL3 and HLA-C1 are highly polymorphic, with this variation being associated with differences in the onset and progression of some human diseases. However, the molecular bases underlying these associations remain unresolved. Here, we determined the crystal structures of KIR2DL2 and KIR2DL3 in complex with HLA-C*07:02 presenting a self-epitope. KIR2DL2 differed from KIR2DL3 in docking modality over HLA-C*07:02 that correlates with variabilty of recognition of HLA-C1 allotypes. Mutagenesis assays indicated differences in the mechanism of HLA-C1 allotype recognition by KIR2DL2 and KIR2DL3. Similarly, HLA-C1 allotypes differed markedly in their capacity to inhibit activation of primary NK cells. These functional differences derive, in part, from KIR2DS2 suggesting KIR2DL2 and KIR2DL3 binding geometries combine with other factors to distinguish HLA-C1 functional recognition.

Natural killer cell receptors regulate responses of HLA-E-restricted T cells.

Human cytomegalovirus (CMV) infection can stimulate robust human leukocyte antigen (HLA)-E-restricted CD8+ T cell responses. These T cells recognize a peptide from UL40, which differs by as little as a single methyl group from self-peptides that also bind HLA-E, challenging their capacity to avoid self-reactivity. Unexpectedly, we showed that the UL40/HLA-E T cell receptor (TCR) repertoire included TCRs that had high affinities for HLA-E/self-peptide. However, paradoxically, lower cytokine responses were observed from UL40/HLA-E T cells bearing TCRs with high affinity for HLA-E. RNA sequencing and flow cytometric analysis revealed that these T cells were marked by the expression of inhibitory natural killer cell receptors (NKRs) KIR2DL1 and KIR2DL2/L3. On the other hand, UL40/HLA-E T cells bearing lower-affinity TCRs expressed the activating receptor NKG2C. Activation of T cells bearing higher-affinity TCRs was regulated by the interaction between KIR2D receptors and HLA-C. These findings identify a role for NKR signaling in regulating self/non-self discrimination by HLA-E-restricted T cells, allowing for antiviral responses while avoiding contemporaneous self-reactivity.

Cytomegalovirus replication is associated with enrichment of distinct γδ T cell subsets following lung transplantation: A novel therapeutic approach?

BACKGROUND: Anti-viral treatments to control cytomegalovirus (CMV) after lung transplantation (LTx) are associated with toxicity and anti-viral resistance. Cellular immunotherapy with virus-specific cytotoxic T cells has yielded promising results but requires donor/recipient matching. γδ T cells are involved in anti-viral immunity and can recognize antigens independently of major histocompatibility complex molecules and may not require the same level of matching. We assessed the phenotype of circulating γδ T cells after LTx to identify the candidate populations for CMV immunotherapy. METHODS: Peripheral blood mononuclear cells were isolated from lung transplant recipients before transplantation and at routine bronchoscopies after LTx. Patients were stratified by risk of CMV disease into moderate risk (recipient CMV seropositive, n = 15) or high risk (HR) (recipient CMV seronegative/donor CMV seropositive, n = 10). CMV replication was classified as polymerase chain reaction positive (>150 copies/ml) in blood and/or bronchoalveolar lavage within the first 18 months. The phenotype of γδ T cells was assessed by multicolor flow cytometry, and T-cell receptor (TCR) sequences were determined by deep sequencing. RESULTS: In HR lung transplant recipients with CMV replication, we observed striking phenotypic changes in γδ T cells, marked by an increase in the proportion of effector Vδ1+ γδ T cells expressing the activating natural killer cell receptor NKG2C. Moreover, we observed a remarkable increase in TCR diversity. CONCLUSIONS: NKG2C+ Vδ1+ γδ T cells were associated with CMV replication and may indicate their potential to control infection. As such, we propose that they could be a potential target for cellular therapy against CMV.

The complex existence of γδ T cells following transplantation: the good, the bad and the simply confusing.

Gamma delta (γδ) T cells are a highly heterogeneous population of lymphocytes that exhibit innate and adaptive immune properties. Despite comprising the majority of residing lymphocytes in many organs, the role of γδ T cells in transplantation outcomes is under-researched. γδ T cells can recognise a diverse array of ligands and exert disparate effector functions. As such, they may potentially contribute to both allograft acceptance and rejection, as well as impacting on infection and post-transplant malignancy. Here, we review the current literature on the role and function of γδ T cells following solid organ and hematopoietic stem cell transplantation.

Enrichment of Cytomegalovirus-induced NKG2C+ Natural Killer Cells in the Lung Allograft.

BACKGROUND: In lung transplant recipients, immunosuppressive medications result in impaired antiviral immunity and a propensity for cytomegalovirus (CMV) reactivation within the lung allograft. Natural killer (NK) cells play a key role in immunity to CMV, with an increase in the proportion of NK cells expressing activating CD94-NKG2C receptors in the blood being a strong correlate of CMV infection. Whether a similar increase in NKG2C NK cells occurs in lung transplant recipients following CMV reactivation in the allograft and if such cells contribute to viral control remains unclear. METHODS: In this pilot study, we longitudinally assessed the frequency and phenotype of NKG2C NK cells in the blood and bronchoalveolar lavage (BAL) of lung transplant recipients and stratified recipients based on their risk of developing CMV disease. RESULTS: We observed an increase in the proportion of NKG2C NK cells in the blood and BAL of CMV high-risk patients, coincident with both the cessation of antiviral prophylaxis and subsequent detection of actively replicating CMV in the blood and lung allograft. Additionally, these NKG2C NK cells expressed killer-cell immunoglobulin-like receptors distinct from those of other NK subsets and BAL NKG2C NK cells possessed an activated phenotype. Finally, the frequency of NKG2C NK cells in the BAL may be inversely correlated with CMV blood titers. CONCLUSIONS: Monitoring the phenotype of NK cells postlung transplant may be a useful biomarker for monitoring patient levels of CMV immunity.

Homeostatic proliferation of intestinal intraepithelial lymphocytes precedes their migration to extra-intestinal sites.

Cells with the phenotype of intraepithelial lymphocytes (IEL) are present systemically and have been implicated in immune regulation. To determine whether IEL undergo homeostatic proliferation and migrate from the small intestine, we analysed the fate of congenic IEL transferred into lymphopenic mice. Donor IEL homed to the small intestinal epithelium, where they expanded in an IL-15-dependent manner and expressed CD69, CD44 and CD103; proliferation did not occur in the spleen, the main other site of IEL detection early after transfer. By 12 days after transfer, a small proportion of intestinal IEL had up-regulated the trafficking molecule CD62L. Four weeks after transfer, donor IEL with a CD69-CD44hiCD103- phenotype similar to memory T cells were present in spleen and other extra-intestinal sites. Treatment of mice with blocking antibody to CD62L reduced appearance of cells in mesenteric lymph nodes; treatment with FTY720, a sphingosine 1-phosphate receptor agonist that blocks egress of T cells from lymph nodes, reduced appearance of cells in spleen. The distribution of TCR alphabeta and gammadelta IEL varied between organs, alphabeta IEL being predominant. IEL proliferation and emigration under lymphopenic conditions suggests similar IEL turnover, albeit at a lower level, under physiological conditions.

TCR gamma delta intraepithelial lymphocytes are required for self-tolerance.

Neonatal thymectomy (NTX) impairs T cell regulation and leads to organ-specific autoimmune disease in susceptible mouse strains. In the NOD mouse model of spontaneous type 1 diabetes, we observed that NTX dramatically accelerated autoimmune pancreatic beta cell destruction and diabetes. NTX had only a minor effect in NOD mice protected from diabetes by transgenic expression of the beta cell autoantigen proinsulin in APCs, inferring that accelerated diabetes after NTX is largely due to failure to regulate proinsulin-specific T cells. NTX markedly impaired the development of intraepithelial lymphocytes (IEL), the number of which was already reduced in euthymic NOD mice compared with control strains. IEL purified from euthymic NOD mice, specifically CD8alphaalpha TCRgammadelta IEL, when transferred into NTX-NOD mice, trafficked to the small intestinal epithelium and prevented diabetes. Transfer of prototypic CD4+CD25+ regulatory T cells also prevented diabetes in NTX-NOD mice; however, the induction of these cells by oral insulin in euthymic mice depended on the integrity of TCRgammadelta IEL. We conclude that TCRgammadelta IEL at the mucosal interface between self and nonself play a key role in maintaining peripheral tolerance both physiologically and during oral tolerance induction.

Persistence of recipient lymphocytes in NOD mice after irradiation and bone marrow transplantation.

The non-obese diabetic (NOD) mouse is a unique and invaluable model of autoimmune disease, in particular type 1 diabetes. Bone marrow transplantation as a therapy for type 1 diabetes has been explored in NOD mice. NOD mice require higher doses of conditioning irradiation for successful allogeneic bone marrow transplantation, suggesting that NOD hematopoietic cells are radioresistant compared to those of other mouse strains. However, studies of hematopoietic reconstitution in NOD mice are hampered by the lack of mice bearing a suitable cell-surface marker that would allow transferred cells or their progeny to be distinguished. In order to monitor hematopoietic reconstitution in NOD mice we generated congenic NOD mice that carry the alternative allelic form of the pan-leukocyte alloantigen CD45. Following irradiation and congenic bone marrow transplantation, we found that the myeloid lineage was rapidly reconstituted by cells of donor origin but substantial numbers of recipient T lymphocytes persisted even after supra-lethal irradiation. This indicates that radiation resistance in the NOD hematopoietic compartment is a property primarily of mature T lymphocytes.