Potential role of NKG2D/MHC class I-related chain A interaction in intrathymic maturation of single-positive CD8 T cells

NKG2D receptor signaling shapes T cell thymic education

The role of natural killer group 2D (NKG2D) in peripheral T cells as a costimulatory receptor is well established. However, its contribution to T cell thymic education and functional imprint is unknown. Here, we report significant changes in development, receptor signaling, transcriptional program, and function in T cells from mice lacking NKG2D signaling. In C57BL/6 (B6) and OT-I mice, we found that NKG2D deficiency results in Vβ chain usage changes and stagnation of the double-positive stage in thymic T cell development. We found that the expression of CD5 and CD45 in thymocytes from NKG2D deficient mice were reduced, indicating a direct influence of NKG2D on the strength of T cell receptor (TCR) signaling during the developmental stage of T cells. Depicting the functional consequences of NKG2D, peripheral OT-I NKG2D-deficient cells were unresponsive to ovalbumin peptide stimulation. Paradoxically, while αCD3/CD28 agonist antibodies led to phenotypic T cell activation, their ability to produce cytokines remained severely compromised. We found that OT-I NKG2D-deficient cells activate STAT5 in response to interleukin-15 but were unable to phosphorylate ERK or S6 upon TCR engagement, underpinning a defect in TCR signaling. Finally, we showed that NKG2D is expressed in mouse and human thymic T cells at the double-negative stage, suggesting an evolutionarily conserved function during T cell development. The data presented in this study indicate that NKG2D impacts thymic T cell development at a fundamental level by reducing the TCR threshold and affecting the functional imprint of the thymic progeny. In summary, understanding the impact of NKG2D on thymic T cell development and TCR signaling contributes to our knowledge of immune system regulation, immune dysregulation, and the design of immunotherapies.

A case of vitiligo after COVID-19 vaccination: a possible role of thymic dysfunction

During the coronavirus disease 2019 (COVID-19) pandemic, vaccines help control the spread of infection. To date, 47 vaccines have been approved, with another 227 candidates in various stages of development. In the short period of time since the beginning of their use, evidence has begun to emerge of complications following vaccination in the form of the development or exacerbation of a number of pathological conditions (Block et al., 2022; Haseeb et al., 2022). For example, a population-based study in France identified 1612 cases of myocarditis and 1613 cases of pericarditis requiring hospital treatment within five months of vaccination (le Vu et al., 2022).

Association of MICA and HLA-B alleles with leprosy in two endemic populations in Brazil

Leprosy is a prevalent disease in Brazil, which ranks as the country with the second highest number of cases in the world. The disease manifests in a spectrum of forms, and genetic differences in the host can help to elucidate the immunopathogenesis. For a better understanding of MICA association with leprosy, we performed a case-control and a family-based study in two endemic populations in Brazil. MICA and HLA-B alleles were evaluated in 409 leprosy patients and in 419 healthy contacts by PCR-SSOP-Luminex-based technology. In the familial study, analysis of 46 families was completed by direct sequencing of all exons and 3'/5'untranslated regions, using the Ilumina MiSeq platform. All data were collected between 2006 and 2009. Statistical analysis was performed using the Chi-square or Fisher's exact test together with a multivariate analysis. Family-based association was assessed by transmission disequilibrium test (TDT) software FBAT 2.0.4. We found associations between the haplotype MICA*002-HLA-B*35 with leprosy in both the per se and the multibacillary (MB) forms when compared to healthy contacts. The MICA allele *008 was associated with the clinical forms of paucibacillary (PB). Additionally, MICA*029 was associated with the clinical forms of MB. The association of MICA*029 allele (MICA-A4 variant) with the susceptibility to the MB form suggests this variant for the transmembrane domain of the MICA molecule may be a risk factor for leprosy. Two MICA and nine HLA-B variants were found associated with leprosy per se in the Colônia do Prata population. Linkage disequilibrium analysis revealed perfect linkage disequilibrium (LD) between HLA-B markers rs2596498 and rs2507992, and high LD (R²  = .92) between these and the marker rs2442718. This familial study demonstrates that MICA association signals are not independent from those observed for HLA-B. Our findings contribute the knowledge pool of the immunogenetics of Hansen's disease and reveals a new association of the MICA*029 allele.

PD-1 mediates functional exhaustion of activated NK cells in patients with Kaposi sarcoma

Programmed Death-1 (PD-1), an inhibitory receptor expressed by activated lymphocytes, is involved in regulating T- and B-cell responses. PD-1 and its ligands are exploited by a variety of cancers to facilitate tumor escape through PD-1-mediated functional exhaustion of effector T cells. Here, we report that PD-1 is upregulated on Natural Killer (NK) cells from patients with Kaposi sarcoma (KS). PD-1 was expressed in a sub-population of activated, mature CD56dimCD16pos NK cells with otherwise normal expression of NK surface receptors. PD-1pos NK cells from KS patients were hyporesponsive ex vivo following direct triggering of NKp30, NKp46 or CD16 activating receptors, or short stimulation with NK cell targets. PD-1pos NK cells failed to degranulate and release IFNγ, but exogenous IL-2 or IL-15 restored this defect. That PD-1 contributed to NK cell functional impairment and was not simply a marker of dysfunctional NK cells was confirmed in PD-1-transduced NKL cells. In vitro, PD-1 was induced at the surface of healthy control NK cells upon prolonged contact with cells expressing activating ligands, i.e. a condition mimicking persistent stimulation by tumor cells. Thus, PD-1 appears to plays a critical role in mediating NK cell exhaustion. The existence of this negative checkpoint fine-tuning NK activation highlights the possibility that manipulation of the PD-1 pathway may be a strategy for circumventing tumor escape not only from the T cell-, but also the NK-cell mediated immune surveillance.

The role of microRNAs in the control of innate immune response in cancer

Ligands for receptors of natural killer (NK) cells and CD8(+) cytotoxic T lymphocytes (CTL), such as the inhibitory nonclassical HLA-G, the activating stress-induced major histocompatibility complex class I-related antigens MICA and MICB, and/or the UL16-binding proteins (ULBPs), are often aberrantly expressed upon viral infection and neoplastic transformation, thereby preventing virus-infected or malignant-transformed cells from elimination by immune effector cells. Recently, it has been shown that ligands of both NK and CD8(+) T cells are regulated by a number of cellular and/or viral microRNAs (miRs). These miRs are involved in shaping the antiviral and/or antitumoral immune responses as well as neoplastic growth properties. This review summarizes the expression pattern and function of miRs directed against selected NK and T cell receptor ligands, their putative role in shaping immune surveillance and tumorigenicity, and their clinical relevance. In addition, the potential role of RNA-binding proteins in the post-transcriptional gene regulation of these ligands will be discussed.

Enhanced prevalence of plasmatic soluble MHC class I chain-related molecule in vascular pregnancy diseases

The major histocompatibility complex class I related chain (MIC) is a stress-inducible protein modulating the function of immune natural killer (NK) cells, a major leukocyte subset involved in proper trophoblast invasion and spiral artery remodeling. Aim of the study was to evaluate whether upregulation of soluble MIC (sMIC) may reflect immune disorders associated to vascular pregnancy diseases (VPD). sMIC was more frequently detected in the plasma of women with a diagnostic of VPD (32%) than in normal term-matched pregnancies (1.6%, P < 0.0001), with highest prevalence in intrauterine fetal death (IUDF, 44%) and vascular intrauterine growth restriction (IUGR, 39%). sMIC levels were higher in preeclampsia (PE) than in IUFD (P < 0.01) and vascular IUGR (P < 0.05). sMIC detection was associated with bilateral early diastolic uterine notches (P = 0.037), thrombocytopenia (P = 0.03), and high proteinuria (P = 0.03) in PE and with the vascular etiology of IUGR (P = 0.0038). Incubation of sMIC-positive PE plasma resulted in downregulation of NKG2D expression and NK cell-mediated IFN-γ production in vitro. Our work thus suggests that detection of sMIC molecule in maternal plasma may constitute a hallmark of altered maternal immune functions that contributes to vascular disorders that complicate pregnancy, notably by impairing NK-cell mediated production of IFN-γ, an essential cytokine favoring vascular modeling.

Tissue-specific microvascular endothelial cells show distinct capacity to activate NK cells: implications for the pathophysiology of granulomatosis with polyangiitis

The relevance of tissue specificity of microvascular endothelial cells (MECs) in the response to inflammatory stimuli and sensitivity to immune cell-mediated injury is not well defined. We hypothesized that such MEC characteristics might shape their interaction with NK cells through the use of different adhesion molecules and NK cell receptor ligands or the release of different soluble factors and render them more or less vulnerable to NK cell injury during autoimmune vasculitis, such as granulomatosis with polyangiitis (GPA). To generate a comprehensive expression profile of human MECs of renal, lung, and dermal tissue origin, we characterized, in detail, their response to inflammatory cytokines and to proteinase 3, a major autoantigen in GPA, and analyzed the effects on NK cell activation. In this study, we show that renal MECs were more susceptible than lung and dermal MECs to the effect of inflammatory signals, showing upregulation of ICAM-1 and VCAM-1 on their surface, as well as release of CCL2, soluble fractalkine, and soluble VCAM-1. Proteinase 3-stimulated renal and lung MECs triggered CD107a degranulation in control NK cell. Notably, NK cells from GPA patients expressed markers of recent in vivo activation (CD69, CD107a), degranulated more efficiently than did control NK cells in the presence of renal MECs, and induced direct killing of renal MECs in vitro. These results suggest that, upon inflammatory conditions in GPA, renal MECs may contribute to the recruitment and activation of NK cells in the target vessel wall, which may participate in the necrotizing vasculitis of the kidney during this disease.

TLR and NKG2D signaling pathways mediate CS-induced pulmonary pathologies

Long-term exposure to cigarette smoke (CS) can have deleterious effects on lung epithelial cells including cell death and the initiation of inflammatory responses. CS-induced cell injury can elaborate cell surface signals and cellular byproducts that stimulate immune system surveillance. Our previous work has shown that the expression of ligands for the cytotoxic lymphocyte activating receptor NKG2D is enhanced in patients with COPD and that the induction of these ligands in a mouse model can replicate COPD pathologies. Here, we extend these findings to demonstrate a role for the NKG2D receptor in CS-induced pathophysiology and provide evidence linking nucleic acid-sensing endosomal toll-like receptor (TLR) signaling to COPD pathology through NKG2D activation. Specifically, we show that mice deficient in NKG2D exhibit attenuated pulmonary inflammation and airspace enlargement in a model of CS-induced emphysema. Additionally, we show that CS exposure induces the release of free nucleic acids in the bronchoalveolar lavage and that direct exposure of mouse lung epithelial cells to cigarette smoke extract similarly induces functional nucleic acids as assessed by TLR3, 7, and 9 reporter cell lines. We demonstrate that exposure of mouse lung epithelial cells to TLR ligands stimulates the surface expression of RAET1, a ligand for NKG2D, and that mice deficient in TLR3/7/9 receptor signaling do not exhibit CS-induced NK cell hyperresponsiveness and airspace enlargement. The findings indicate that CS-induced airway injury stimulates TLR signaling by endogenous nucleic acids leading to elevated NKG2D ligand expression. Activation of these pathways plays a major role in the altered NK cell function, pulmonary inflammation and remodeling related to long-term CS exposure.

Interleukin-15-dependent NKp46+ innate lymphoid cells control intestinal inflammation by recruiting inflammatory monocytes

With the goal in mind to define how interleukin-15 (IL-15) contributes to acute intestinal inflammation, we have used a mouse model of ileitis induced by oral infection with Toxoplasma gondii. We observed that a crosstalk between IL-15 and interleukin-18 (IL-18) promoted intestinal recruitment of inflammatory monocytes, where these cells participated in parasite control but also in tissue damage. A stromal source of IL-15 controlled the development of lamina propria NKp46(+)NK1.1(+) cells, whereas IL-18 produced during T. gondii infection stimulated their production of the chemokine CCL3. In turn, CCL3 attracted inflammatory monocytes via their chemokine receptor CCR1, which was indispensable for their recruitment into the inflamed gut. Collectively, these results identify the IL-15-dependent subset of intestinal NKp46(+) cells as an important source of CCL3, which can amplify intestinal inflammation via the recruitment of CCR1(+) inflammatory monocytes. Preliminary evidence suggests that this pathway might operate in Crohn's disease.

Human Herpesvirus 8 (HHV8) sequentially shapes the NK cell repertoire during the course of asymptomatic infection and Kaposi sarcoma

The contribution of innate immunity to immunosurveillance of the oncogenic Human Herpes Virus 8 (HHV8) has not been studied in depth. We investigated NK cell phenotype and function in 70 HHV8-infected subjects, either asymptomatic carriers or having developed Kaposi's sarcoma (KS). Our results revealed substantial alterations of the NK cell receptor repertoire in healthy HHV8 carriers, with reduced expression of NKp30, NKp46 and CD161 receptors. In addition, down-modulation of the activating NKG2D receptor, associated with impaired NK-cell lytic capacity, was observed in patients with active KS. Resolution of KS after treatment was accompanied with restoration of NKG2D levels and NK cell activity. HHV8-latently infected endothelial cells overexpressed ligands of several NK cell receptors, including NKG2D ligands. The strong expression of NKG2D ligands by tumor cells was confirmed in situ by immunohistochemical staining of KS biopsies. However, no tumor-infiltrating NK cells were detected, suggesting a defect in NK cell homing or survival in the KS microenvironment. Among the known KS-derived immunoregulatory factors, we identified prostaglandin E2 (PGE2) as a critical element responsible for the down-modulation of NKG2D expression on resting NK cells. Moreover, PGE2 prevented up-regulation of the NKG2D and NKp30 receptors on IL-15-activated NK cells, and inhibited the IL-15-induced proliferation and survival of NK cells. Altogether, our observations are consistent with distinct immunoevasion mechanisms that allow HHV8 to escape NK cell responses stepwise, first at early stages of infection to facilitate the maintenance of viral latency, and later to promote tumor cell growth through suppression of NKG2D-mediated functions. Importantly, our results provide additional support to the use of PGE2 inhibitors as an attractive approach to treat aggressive KS, as they could restore activation and survival of tumoricidal NK cells.

Natural Killer (NK) cells are part of the innate immune response against virus infections and tumors. Their activation is the net result of signals emanating from a panel of inhibitory and activating receptors recognizing specific ligands on target cells. Human Herpes Virus 8 (HHV8) is an oncogenic virus responsible of Kaposi Sarcoma (KS), a multifocal angiogenic tumor. How NK cells contribute to the control of infection by HHV8 infection and development of KS, is unclear. In this paper, we show different strategies used by HHV8 to escape NK cell response. Patients with asymptomatic infection or KS have down-modulated expression of NKp30, NKp46 and CD161 receptors. In addition, patients with active KS show additional down-modulation of the NKG2D activating receptor, associated with impaired NK-cell cytotoxicity against target cells. Resolution of KS correlates with regained NKG2D expression and cytotoxic function. We present evidence that down-modulation of NKG2D is mediated by inflammatory prostaglandin E2 (PGE2), known to be released by KS cells, and show that PGE2 acts by preventing IL-15-mediated activation of NK cells. These results strongly support the use of PGE2 inhibitors as an attractive approach to treat active KS.

NKG2D expression in CD4+ T lymphocytes as a marker of senescence in the aged immune system

Human aging is characterized by changes in the immune system which have a profound impact on the T-cell compartment. These changes are more frequently found in CD8+ T cells, and there are not well-defined markers of differentiation in the CD4+ subset. Typical features of cell immunosenescence are characteristics of pathologies in which the aberrant expression of NKG2D in CD4+ T cells has been described. To evaluate a possible age-related expression of NKG2D in CD4+ T cells, we compared their percentage in peripheral blood from 100 elderly and 50 young adults. The median percentage of CD4+ NKG2D+ in elders was 5.3% (interquartile range (IR): 8.74%) versus 1.4% (IR: 1.7%) in young subjects (p < 0.3 × 10(-10)). CD28 expression distinguished two subsets of CD4+ NKG2D+ cells with distinct functional properties and differentiation status. CD28+ cells showed an immature phenotype associated with high frequencies of CD45RA and CD31. However, most of the NKG2D+ cells belonged to the CD28(null) compartment and shared their phenotypical properties. NKG2D+ cells represented a more advanced stage of maturation and exhibited greater response to CMV (5.3 ± 3.1% versus 3.4 ± 2%, p = 0.037), higher production of IFN-γ (40.56 ± 13.7% versus 24 ± 8.8%, p = 0.015), lower activation threshold and reduced TREC content. Moreover, the frequency of the CD4+ NKG2D+ subset was clearly related to the status of the T cells. Higher frequencies of the NKG2D+ subset were accompanied with a gradual decrease of NAIVE and central memory cells, but also with a higher level of more differentiated subsets of CD4+ T cells. In conclusion, CD4+ NKG2D+ represent a subset of highly differentiated T cells which characterizes the senescence of the immune system.

Excessive interleukin-15 transpresentation endows NKG2D+CD4+ T cells with innate-like capacity to lyse vascular endothelium in granulomatosis with polyangiitis (Wegener's)

OBJECTIVE

Granulomatosis with polyangiitis (Wegener's) (GPA) is a rare systemic vasculitis of unknown etiology. Contribution of T cell-mediated immunity is suggested by the presence of granulomatous inflammation and T cell infiltrates in different tissues. We undertook this study to determine whether CD4+ T cells aberrantly expressing the NKG2D activating receptor might participate in the pathophysiology of the disease.

METHODS

We performed a detailed phenotype and functional analysis of CD4+ T cells in a cohort of 90 GPA patients (37 with localized GPA and 53 with generalized GPA) in comparison with 39 age-matched controls.

RESULTS

We observed circulating innate-like CD4+ T cells expressing an assortment of activating natural killer (NK) cell receptors (NKG2D, 2B4, DNAX-associated molecule 1, and some killer cell Ig-like receptors) and their signaling partners. Expansions of NKG2D+CD4+ T cells greater than a critical threshold of 3% yielded 100% specificity for generalized vasculitis versus localized granulomatosis, suggesting their participation in endothelium damage. Excessive interleukin-15 (IL-15) transpresentation through increased expression of IL-15 receptor α (IL-15Rα), together with abnormal expression of major histocompatibility complex (MHC) class I chain-related A protein on monocyte/macrophages, induced abnormal expansion of NKG2D+CD4+ T cells. These cells were primed in vivo to exert direct, MHC-independent cytotoxicity toward microvascular endothelial cells expressing the cognate ligands of NK cell receptors.

CONCLUSION

Our results suggest that NK cell-like CD4+ T cells might be the driving force of the vasculitis in GPA, and point to IL-15 as an important mediator in the progression of GPA toward generalized vasculitis. IL-15/IL-15Rα antagonists may thus become novel therapeutic tools to decrease the pool of NK cell receptor-positive CD4+ T cells in selected GPA patients.

Major histocompatibility complex class I-related chain A/B (MICA/B) expression in tumor tissue and serum of pancreatic cancer: role of uric acid accumulation in gemcitabine-induced MICA/B expression

Background

Major histocompatibility complex class I-related chain A and B (MICA/B) are two stress-inducible ligands that bind the immunoreceptor NKG2D and play an important role in mediating the cyotoxicity of NK and T cells. In this study, we sought to study MICA/B expression in pancreatic cancer and to determine whether and how genotoxic drugs such as gemcitabine can affect MICA/B expression and natural killer cytotoxity.

Methods

Seven pancreatic cancer cell lines were analyzed for MICA/B expression by flow cytometry and for their sensitivity to NK-92 cell killing by a ⁵¹Cr release assay. MICA/B expression in tumor tissues and sera of pancreatic cancer was analyzed by immunohistochemical staining (IHC) and ELISA, respectively.

Results

Two MICA/B-positive cell lines were sensitive to the cytotoxic activity of NK-92 cells. Other two MICA/B-positive cell lines and three MICA/B-negative cell lines were resistant to NK-92 cell killing. MICA/B expression was positive in 17 of 25 (68%) pancreatic ductal adenocarcinomas but not in normal pancreatic ductal epithelial cells. Serum MICA/B levels were significantly elevated in patients with pancreatic adenocarcinomas but did not correlate with the stage of pancreatic cancer and patient survival. Gemcitabine therapy led to increased serum MICA levels in 6 of 10 patients with detectable serum MICA. Allopurinol, an inhibitor of xanthine oxidoreductase that converts xanthine to uric acid, blocked uric acid production, MICA/B expression, and sensitivity to NK-92 cell killing toward a PANC-1 cancer cell line exposed to radiation and two genotoxic drugs, gemcitabine and 5-fluorouracil.

Conclusions

The levels of MICA/B expression in serum and tissue of pancreatic cancer are elevated. DNA damage-induced MICA/B expression is mediated through increased uric acid production.

Unique functional status of natural killer cells in metastatic stage IV melanoma patients and its modulation by chemotherapy

PURPOSE

Immunotherapy is an alternative for metastatic melanoma patients resistant to chemotherapy. Natural killer (NK) cells are powerful antileukemia effectors and their role in solid tumors is suspected. NK cell activation is regulated by a balance between activating receptors, which detect stress molecules on tumor cells, and HLA-I specific inhibitory receptors. Here, we studied the phenotype and function of NK cells in stage IV metastatic melanoma patients.

EXPERIMENTAL DESIGN

Circulating NK cells from 35 healthy donors and 51 patients were studied: 24 patients before chemotherapy (prechemotherapy), 17 patients 1 month after 1 to 4 lines of chemotherapy (postchemotherapy), and 10 patients analyzed pre- and postchemotherapy. NK functionality was carried out toward 2 primary metastatic melanoma cell lines, analyzed for the expression of NK receptor ligands.

RESULTS

NK cells from prechemotherapy patients exhibit an NKp46(dim)/NKG2A(dim) phenotype. In contrast, NK cells from postchemotherapy patients display high expression of NKp46 and NKG2A receptors. Purified NK cells from patients are efficiently activated in response to melanoma cells. Melanoma cells express different level of NKG2D ligands and HLA-I molecules. In agreements with their phenotype, NK cells from pre- and postchemotherapy patients present distinct functional status toward these primary melanoma cells. A dynamic label free assay was used to determine the pathways involved in the lysis of melanoma cells by IL-2-activated NK cells. NKG2D, NCR (natural cytotoxicity receptor), and DNAM-1 are involved in the NK-mediated lysis of melanoma cells.

CONCLUSIONS

These results provide new arguments and clues to design NK cell-based immunotherapeutic strategies for melanoma patients.

Hepatitis C virus (HCV) evades NKG2D-dependent NK cell responses through NS5A-mediated imbalance of inflammatory cytokines

Understanding how hepatitis C virus (HCV) induces and circumvents the host's natural killer (NK) cell-mediated immunity is of critical importance in efforts to design effective therapeutics. We report here the decreased expression of the NKG2D activating receptor as a novel strategy adopted by HCV to evade NK-cell mediated responses. We show that chronic HCV infection is associated with expression of ligands for NKG2D, the MHC class I-related Chain (MIC) molecules, on hepatocytes. However, NKG2D expression is downmodulated on circulating NK cells, and consequently NK cell-mediated cytotoxic capacity and interferon-γ production are impaired. Using an endotoxin-free recombinant NS5A protein, we show that NS5A stimulation of monocytes through Toll-like Receptor 4 (TLR4) promotes p38- and PI3 kinase-dependent IL-10 production, while inhibiting IL-12 production. In turn, IL-10 triggers secretion of TGFβ which downmodulates NKG2D expression on NK cells, leading to their impaired effector functions. Moreover, culture supernatants of HCV JFH1 replicating Huh-7.5.1 cells reproduce the effect of recombinant NS5A on NKG2D downmodulation. Exogenous IL-15 can antagonize the TGFβ effect and restore normal NKG2D expression on NK cells. We conclude that NKG2D-dependent NK cell functions are modulated during chronic HCV infection, and demonstrate that this alteration can be prevented by exogenous IL-15, which could represent a meaningful adjuvant for therapeutic intervention.

Autoimmune polyglandular syndromes

The autoimmune polyglandular syndromes-a group of syndromes comprising a combination of endocrine and nonendocrine autoimmune diseases-differ in their component diseases and in the immunologic features of their pathogenesis. One of the three main syndromes, type 1 autoimmune polyglandular syndrome (APS-1), has a unique pathogenic mechanism owing to mutations in the autoimmune regulator (AIRE) gene, which results in the loss of central tolerance-a process by which developing T cells with potential reactivity for self-antigens are eliminated during early differentiation in the thymus. Patients with IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked) syndrome harbor mutations in the forkhead box P3 (FOXP3) gene in regulatory T cells, which leads to severe autoimmunity and immune deficiency. Although both of these disorders are rare, their well-defined mechanisms of disease provide a basis for the understanding of the more common condition, APS-2. In this syndrome, alleles of human leukocyte antigens (HLAs) determine the targeting of specific tissues by autoreactive T cells, which leads to organ-specific autoimmunity as a result of this loss of tolerance. Non-HLA genes also contribute to autoimmunity in APS-2 and, depending on the polymorphism, potentially predispose to a loss of tolerance or influence which organ is specifically targeted. This Review discusses the genetic basis of APS-1, APS-2 and IPEX syndrome, with an emphasis on the mechanisms of autoimmunity and presents currently available therapies to treat their underlying autoimmune disorders.

Immunologic endocrine disorders

Autoimmunity affects multiple glands in the endocrine system. Animal models and human studies highlight the importance of alleles in HLA-like molecules determining tissue-specific targeting that, with the loss of tolerance, leads to organ-specific autoimmunity. Disorders such as type 1A diabetes, Graves disease, Hashimoto thyroiditis, Addison disease, and many others result from autoimmune-mediated tissue destruction. Each of these disorders can be divided into stages beginning with genetic susceptibility, environmental triggers, active autoimmunity, and finally metabolic derangements with overt symptoms of disease. With an increased understanding of the immunogenetics and immunopathogenesis of endocrine autoimmune disorders, immunotherapies are becoming prevalent, especially in patients with type 1A diabetes. Immunotherapies are being used more in multiple subspecialty fields to halt disease progression. Although therapies for autoimmune disorders stop the progress of an immune response, immunomodulatory therapies for cancer and chronic infections can also provoke an unwanted immune response. As a result, there are now iatrogenic autoimmune disorders arising from the treatment of chronic viral infections and malignancies.

Functionally mature CD4 and CD8 TCRalphabeta cells are generated in OP9-DL1 cultures from human CD34+ hematopoietic cells

Human CD34(+) hematopoietic precursor cells cultured on delta-like ligand 1 expressing OP9 (OP9-DL1) stromal cells differentiate to T lineage cells. The nature of the T cells generated in these cultures has not been studied in detail. Since these cultures do not contain thymic epithelial cells which are the main cell type mediating positive selection in vivo, generation of conventional helper CD4(+) and cytotoxic CD8(+) TCRalphabeta cells is not expected. Phenotypically mature CD27(+)CD1(-) TCRgammadelta as well as TCRalphabeta cells were generated in OP9-DL1 cultures. CD8 and few mature CD4 single-positive TCRalphabeta cells were observed. Mature CD8 single-positive cells consisted of two subpopulations: one expressing mainly CD8alphabeta and one expressing CD8alphaalpha dimers. TCRalphabeta CD8alphaalpha and TCRgammadelta cells both expressed the IL2Rbeta receptor constitutively and proliferated on IL-15, a characteristic of unconventional T cells. CD8alphabeta(+) and CD4(+) TCRalphabeta cells were unresponsive to IL-15, but could be expanded upon TCR stimulation as mature CD8alphabeta(+) and CD4(+) T cells. These T cells had the characteristics of conventional T cells: CD4(+) cells expressed ThPOK, CD40L, and high levels of IL-2 and IL-4; CD8(+) cells expressed Eomes, Runx3, and high levels of granzyme, perforin, and IFN-gamma. Induction of murine or human MHC class I expression on OP9-DL1 cells had no influence on the differentiation of mature CD8(+) cells. Similarly, the presence of dendritic cells was not required for the generation of mature CD4(+) or CD8(+) T cells. These data suggest that positive selection of these cells is induced by interaction between T precursor cells.

Homozygosity of the polymorphism MICA5.1 identifies extreme risk of progression to overt adrenal insufficiency among 21-hydroxylase antibody-positive patients with type 1 diabetes

CONTEXT

Autoimmunity associated with Addison's disease (AD) can be detected by measuring 21-hydroxylase (21OH) autoantibodies. Subjects with type 1 diabetes (T1D) are at increased risk for AD. Genetic factors including HLA-DRB1*0404 and MICA have been associated with AD in populations with and without T1D.

OBJECTIVE

The objective of the study was to examine the effect of the MICA5.1 allele in subjects with 21OH autoantibodies on progression to AD.

DESIGN

Two components were used: 1) a cross-sectional study with subjects with AD identified and enrolled from September 1993 to November 2008 and 2) a cohort study prospectively following up patients with T1D who screened positive for 21OH autoantibodies.

SETTING

Subjects were identified from the Barbara Davis Center and through the National Adrenal Diseases Foundation.

PATIENTS

Sixty-three subjects with AD were referred through the National Adrenal Diseases Foundation (AD referrals). Sixty-three subjects with positive 21OH antibodies from the Barbara Davis Center were followed up for progression to AD, and 11 were diagnosed with AD (progressors).

RESULTS

Seventy-three percent of progressors (eight of 11) and 57% of AD referrals (36 of 63) were MICA5.1 homozygous (P = ns). Overall, 59% of patients with AD (44 of 74) were MICA5.1/5.1 compared with 17% of nonprogressors (nine of 52) (P < 0.0001) and 19% of normal DR3/4-DQB1*0302 controls (64 of 336) (P < 0.0001).

CONCLUSIONS

Identifying extreme risk should facilitate monitoring of progression from 21OH antibody positivity to overt AD. The HLA-DR3/0404 genotype defines high-risk subjects for adrenal autoimmunity. MICA5.1/5.1 may define those at highest risk for progression to overt AD, a feature unique to AD and distinct from T1D.

NKG2D ligand expression in human colorectal cancer reveals associations with prognosis and evidence for immunoediting

PURPOSE

NKG2D (natural killer group 2, member D) binds to cellular ligands of the MIC and ULBP/RAET family. These ligands have restricted expression in normal tissue, but are frequently expressed on primary tumors. The role of NKG2D ligands is thought to be important in carcinogenesis but its prognostic effect has not been investigated in such a large cohort.

EXPERIMENTAL DESIGN

In our study, 462 primary colorectal tumors were screened for the expression of all MIC/ULBP/RAET proteins and NK cell infiltration. Tumor microarray technology was used for the purpose of this investigation.

RESULTS

NKG2D ligands were expressed by the majority of colorectal tumors; however, the level of expression varied considerably. High expression of MIC (68 versus 56 months) or RAET1G (74 versus 62 months) showed improved patient survival. Tumors expressing high levels of MIC and RAET1G showed improved survival of 77 months over tumors that expressed high levels of one ligand or low levels of both. High-level expression of all ligands was frequent in tumor-node-metastasis stage I tumors, but became progressively less frequent in stages II, III, and IV tumors. Expression of MIC was correlated with NK cellular infiltration.

CONCLUSION

The observations presented are consistent with an immunoediting mechanism that selects tumor cells that have lost or reduced their expression of NKG2D ligands. The combination of MIC and tumor-node-metastasis stage was found to be the strongest predictor of survival, splitting patients into eight groups and suggesting prognostic value in clinical assessment. Of particular interest were stage I patients with low expression of MIC who had a similar survival to stage III patients, and may be candidates for adjuvant therapy.

Cellular expression, trafficking, and function of two isoforms of human ULBP5/RAET1G

Background

The activating immunoreceptor NKG2D is expressed on Natural Killer (NK) cells and subsets of T cells. NKG2D contributes to anti-tumour and anti-viral immune responses in vitro and in vivo. The ligands for NKG2D in humans are diverse proteins of the MIC and ULBP/RAET families that are upregulated on the surface of virally infected cells and tumours. Two splicing variants of ULBP5/RAET1G have been cloned previously, but not extensively characterised.

Methodology/Principal Findings

We pursue a number of approaches to characterise the expression, trafficking, and function of the two isoforms of ULBP5/RAET1G. We show that both transcripts are frequently expressed in cell lines derived from epithelial cancers, and in primary breast cancers. The full-length transcript, RAET1G1, is predicted to encode a molecule with transmembrane and cytoplasmic domains that are unique amongst NKG2D ligands. Using specific anti-RAET1G1 antiserum to stain tissue microarrays we show that RAET1G1 expression is highly restricted in normal tissues. RAET1G1 was expressed at a low level in normal gastrointestinal epithelial cells in a similar pattern to MICA. Both RAET1G1 and MICA showed increased expression in the gut of patients with celiac disease. In contrast to healthy tissues the RAET1G1 antiserum stained a wide variety or different primary tumour sections. Both endogenously expressed and transfected RAET1G1 was mainly found inside the cell, with a minority of the protein reaching the cell surface. Conversely the truncated splicing variant of RAET1G2 was shown to encode a soluble molecule that could be secreted from cells. Secreted RAET1G2 was shown to downregulate NKG2D receptor expression on NK cells and hence may represent a novel tumour immune evasion strategy.

Conclusions/Significance

We demonstrate that the expression patterns of ULBP5RAET1G are very similar to the well-characterised NKG2D ligand, MICA. However the two isoforms of ULBP5/RAET1G have very different cellular localisations that are likely to reflect unique functionality.

Induction of NKG2D ligands by gamma radiation and tumor necrosis factor-alpha may participate in the tissue damage during acute graft-versus-host disease

Immunopathology of acute graft-versus-host disease (aGVHD) involves secretion of proinflammatory cytokines with subsequent expression of danger signals by injured host tissues. This explanation, however, does not explain the cluster of aGVHD target organs (skin, gut, and liver). NKG2D ligands (MICA/B and ULBP1-3 proteins) are stress-induced molecules that act as danger signals to alert NK and alphabeta or gammadelta CD8 T cells through engagement of the activating NKG2D receptor. We observed a strong and reversible induction of MICA/B expression in skin and liver sections during aGVHD. Tumor necrosis factor-alpha and gamma-radiation up-regulated expression of MICA/B and ULBP proteins in vitro on skin and intestine epithelial cell lines and ex vivo in normal skin explants. This NKG2D-ligand induction was regulated by a complex interplay between NFkB and JNK activation pathways. Our data suggest that NKG2D ligand induction might participate in the amplification loop that leads to tissue damage during aGVHD.

MICA gene polymorphism in the pathogenesis of type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a typical autoimmune disease and results from the destruction of insulin-producing beta cells of the pancreas. It develops in the presence of genetic susceptibility, even though more than 85% of patients with T1DM do not have a close relative with the disorder. The etiology of T1DM is complex, and both genetic and environmental factors play important roles. A permissive genetic background is required for the development of the islet autoimmune process. The strongest genetic association idengified is that with HLA class II genes located on the short arm of chromosome 6. It is well known that both HLA DRB1*04-DQA1*0301-DQB1*0302 (DR4-DQ8) and DRB1*03-DQA1*0501-DQB1*0201 (DR3-DQ2) are positively, and DRB1*15-DQA1*0102-DQB1*0602 is negatively, associated with T1DM. However, only a minority of the subjects carrying the high-risk haplotypes/genotypes develops the disease, which suggests that additional genes play a crucial role in conferring either protection or susceptibility to T1DM. Major histocompatibility complex (MHC) class I chain-related A (MICA) is located in a candidate susceptibility region and activates natural killer (NK) cells, T cells and gammadelta CD8 T cells by its receptor NKG2D. The polymorphism of the MICA gene is associated with T1DM in different populations as demonstrated in several papers published in the last 7 years.

Inhibition of NKG2D receptor function by antibody therapy attenuates transfer-induced colitis in SCID mice

A role for the activating NK-receptor NKG2D has been indicated in several autoimmune diseases in humans and in animal models of type 1 diabetes and multiple sclerosis, and treatment with monoclonal antibodies to NKG2D attenuated disease severity in these models. In an adoptive transfer-induced model of colitis, we found a significantly higher frequency of CD4(+)NKG2D(+) cells in blood, mesenteric lymph nodes, colon, and spleen from colitic mice compared to BALB/c donor-mice. We, therefore, wanted to study the effect of anti-NKG2D antibody (CX5) treatment initiated either before onset of colitis, when the colitis was mild, or when severe colitis was established. CX5 treatment decreased the detectable levels of cell-surface NKG2D and prophylactic administration of CX5 attenuated the development of colitis significantly, whereas a more moderate reduction in the severity of disease was observed after CX5 administration to mildly colitic animals. CX5 did not attenuate severe colitis. We conclude that the frequency of CD4(+)NKG2D(+) cells increase during development of experimental colitis. NKG2D may play a role in the early stages of colitis in this model, since early administration of CX5 attenuated disease severity.

Cytokine-driven regulation of NK cell functions in tumor immunity: role of the MICA-NKG2D system

Natural killer (NK) cells are critical players during tumor growth control in immunocompetent hosts. These cells also establish a cross-talk with dendritic cells (DCs) and promote a Th1-mediated immunity. NKG2D is a pivotal receptor that directs the tumoricidal activity of NK cells through the recognition of a group of ligands such as MICA widely expressed on different tumors. Here we will review the most important tumor immune escape mechanisms that compromise the functionality of NKG2D and its cognate ligands, including TGF-beta secretion, tumor shedding of soluble MICA, and additional mechanisms that compromise the tumoricidal activity of NKG2D-expressing cells. Such mechanisms may also dampen the cross-talk between NK cells and DCs during the anti-tumor immune responses. Recent knowledge may lead to innovative approaches to promote efficient NK cell-mediated anti-tumor immune responses.

MICA A8: a new allele within MHC class I chain-related A transmembrane region with eight GCT repeats

Analysis of the MICA gene revealed a trinucleotide repeat (GCT) microsatellite polymorphism within the transmembrane region. So far, seven alleles of the exon 5 of the MICA gene, which consist of 4, 5, 6, 7, 9, and 10 repetitions of GCT or five repetitions of GCT with an additional nucleotide insertion (GGCT), have been identified. These alleles have been accordingly named A4, A5, A6, A7, A9, A10, and A5.1, and the sizes are, respectively, 179 bp, 182 bp, 186 bp, 189 bp, 194 bp, 197 bp, and 185 bp. We analyzed 1100 Italian subjects for MICA exon 5 microsatellite polymorphism. A new peak corresponding to 191-bp size was observed in one individual, and we confirmed the presence of new polymorphism in exon 5 by sequencing, which consisted of eight GCT repeats. We named this allele, as a current nomenclature, MICA8.

Killer Ig-like receptor (KIR) genotype and HLA ligand combinations in ulcerative colitis susceptibility

Killer immunoglobulin-like receptors (KIRs) are expressed on natural killer cells and some T-cell subsets and produce either activation or inhibitory signals upon binding with the appropriate human leucocyte antigen (HLA) ligand on target cells. Recent genetic association studies have implicated KIR genotype in the development of several inflammatory conditions. Ulcerative colitis (UC) is an inflammatory disorder of the colonic mucosa that results from an inappropriate activation of the immune system driven by host bacterial flora. We developed a polymerase chain reaction-sequence specific primer (SSP)-based assay to genotype 194 UC patients and 216 control individuals for 14 KIR genes, the HLA-Cw ligand epitopes of the KIR2D receptors and a polymorphism of the lectin-like-activating receptor NKG2D. Initial analysis found the phenotype frequency of KIR2DL2 and -2DS2 to be significantly increased in the UC cohort (P=0.030 and 0.038, respectively). Logistic regression analysis revealed a protective effect conferred by KIR2DL3 in the presence of its ligand HLA-Cw group 1 (P=0.019). These results suggest that KIR genotype and HLA ligand interaction may contribute to the genetic susceptibility of UC.

Release of MICB molecules by tumor cells: mechanism and soluble MICB in sera of cancer patients

MICA, a ligand of the activating immunoreceptor NKG2D, is released by tumor cells in a soluble form and can be detected in sera of tumor patients at significant levels. Soluble MICA has been proposed to counteract NKG2D-mediated immunosurveillance of tumors. Here, we report that MICB, the second member of the human MIC protein family, is likewise shed by metalloproteases from tumor cells and is present in sera of patients with gastrointestinal tumors. While cell-bound MICB causes downregulation of surface NKG2D, soluble MICB did not alter NKG2D expression on NK cells in vitro. Thus, proteolytic shedding of MICB by tumor cells may impair immunogenicity of tumors primarily by reducing NKG2D-ligand densities on malignant cells.

Diversity of MICA and linkage disequilibrium with HLA-B in two North American populations

The MICA gene has a high degree of polymorphism. Allelic variation of MICA may influence binding of these ligands to the NK cell receptor NKG2D and may affect organ transplantation and/or disease pathogenesis. Knowledge of the population distribution of MICA alleles and their linkage disequilibrium (LD) with class I human leukocyte antigen (HLA) will enhance our understanding of the potential functional significance of the MICA polymorphism. In the present study, we characterized the MICA and HLA-B polymorphisms in two North American populations: European and African. The individual racial groups showed rather limited variation at the MICA locus, where the same set of three most common alleles, MICA*00201, *004, and *00801, account for 64 and 71% of the allele frequency in European-Americans and African-Americans, respectively. Other common alleles (allele frequency >5% in a population) include MICA*00901 and *010. MICA alleles showed strong linkage disequilibrium with HLA-B. Typically, a common MICA allele has strong LD with several HLA-B alleles, whereas most HLA-B alleles and their related serological groups are associated with a single MICA allele. The lack of evidence for an active diversification of the MICA gene after racial separation indicates an evolutionary history distinct from that of the classical HLA genes.

MHC Class I Chain-Related Gene A Diversity in Head and Neck Squamous Cell Carcinoma

Many immune-related genes are located within the human leukocyte antigen (HLA) region on chromosome 6. The MHC class I chain-related gene A (MICA), located centromeric of HLA-B, is involved in the innate and adaptive immune response through activation of NK and T cells. Differences of MICA transmembrane repeat lengths have been associated with diseases and expression is observed on epithelial tumors. Head and neck squamous cell carcinoma (HNSCC) is an epithelial tumor. In the present study we evaluated the MICA repeat length diversity in relation to MICA expression in Dutch HNSCC patients. MICA short tandem repeat analysis indicated a significant decrease in the frequency for the MICA-A9 repeat in patients diagnosed with oral cavity squamous cell carcinoma (SCC) but not in patients with SCC in the hypoharynx, larynx, or oropharynx. Interestingly, the majority of patients expressed MICA as observed with immunohistochemical staining whereas no soluble MICA was detected in patients' sera by enzyme-linked immunosorbent assay. In conclusion, the length of the MICA transmembrane repeats in Dutch HNSCC patients does not influence the MICA expression on tumor cells.

Vdelta1 T cell receptor binds specifically to MHC I chain related A: molecular and biochemical evidences

Human MHC class I chain-related A (MICA) is a tumor-associated antigen that can be recognized by Vdelta1 subset of tumor-infiltrating gammadelta T cells. We previously reported that immobilized recombinant MICA protein could induce the proliferation of tumor-infiltrating Vdelta1 gammadelta T cells in vitro. But there has been no direct evidence showing the engagement of gammadelta T cell receptors (TCR) of the induced cells with MICA. In the current investigation, we show that MICA induces specific cytolytic activity of the expanded gammadelta T cells. We expressed the coupled V domains from the MICA-induced T cells as a single polypeptide chain Vdelta Vgamma TCR (gammadelta scTCR). Such scTCR can specifically bind MICA of HeLa cells. Direct interaction of gammadelta scTCRs with in vitro expressed MICA was monitored using an IAsys biosensor. We found that the Vdelta1 scTCR can specifically bind to immobilized MICA molecule and MICA alpha1alpha2 domains are responsible for the binding reaction.

Systemic NKG2D down-regulation impairs NK and CD8 T cell responses in vivo

The immunoreceptor NKG2D stimulates activation of cytotoxic lymphocytes upon engagement with MHC class I-related NKG2D ligands of which at least some are expressed inducibly upon exposure to carcinogens, cell stress, or viruses. In this study, we investigated consequences of a persistent NKG2D ligand expression in vivo by using transgenic mice expressing MHC class I chain-related protein A (MICA) under control of the H2-K(b) promoter. Although MICA functions as a potent activating ligand of mouse NKG2D, H2-K(b)-MICA mice appear healthy without aberrations in lymphocyte subsets. However, NKG2D-mediated cytotoxicity of H2-K(b)-MICA NK cells is severely impaired in vitro and in vivo. This deficiency concurs with a pronounced down-regulation of surface NKG2D that is also seen on activated CD8 T cells. As a consequence, H2-K(b)-MICA mice fail to reject MICA-expressing tumors and to mount normal CD8 T cell responses upon Listeria infection emphasizing the importance of NKG2D in immunity against tumors and intracellular infectious agents.

Non-classical MHC class I molecules on intestinal epithelial cells: mediators of mucosal crosstalk

The mucosal immune environment consists of a complex combination of lymphoid cells, non-lymphoid cells, and lumenal bacteria. Signals from lumenal bacteria are constantly transmitted to the underlying tissues across the intestinal epithelial barrier. Intestinal epithelial cells (IECs) can sense these signals, integrate them, and interpret them for lamina propria lymphoid populations. One mechanism by which these signals are communicated is by the expression of non-classical major histocompatibility complex (MHC) class I molecules by IECs. Epithelial cells can express a surprising variety of non-classical MHC class I molecules. In some cases, IECs can act as non-professional antigen-presenting cells utilizing the expression of such non-classical MHC class I molecules to directly present bacterial antigens. In other cases, the expression of non-classical MHC class I molecules may act as a co-stimulatory molecule or adhesion molecule that can modify the mucosal immune response. Finally, the expression of these molecules on IECs can lead to a broad array of responses ranging from tolerance to inflammation. Overall, the IEC, via the expression of non-classical MHC class I molecules, is a central mediator of the constant crosstalk between the intestinal lumen and the mucosal immune system.

Polyendocrine autoimmunity

Autoimmune polyendocrine disorders are characterized by the presence of more than one autoimmune endocrine disease. Study of such disorders has provided unique insight into the pathogenesis of autoimmunity and the development of tolerance in the normal individual. Autoimmune polyendocrine syndromes I and II have distinctive inheritance patterns, genetic causes, component diseases, and implications for follow-up. Care for individuals with these diseases requires monitoring for additional autoimmune disorders and aggressive treatment of identified diseases to prevent morbidity and mortality in affected individuals.

A Direct Role for NKG2D/MICA Interaction in Villous Atrophy during Celiac Disease

MICA molecules interact with the NKG2D-activating receptor on human NK and CD8 T cells. We investigated the participation of the MICA/NKG2D pathway in the destruction of intestinal epithelium by intraepithelial T lymphocytes (IEL) in Celiac disease and its premalignant complication, refractory sprue. We show that MICA is strongly expressed at epithelial cell surface in patients with active disease and is induced by gliadin or its p31-49 derived peptide upon in vitro challenge, an effect relayed by IL-15. This triggers direct activation and costimulation of IEL through engagement of NKG2D, leading to an innate-like cytotoxicity toward epithelial targets and enhanced TCR-dependent CD8 T cell-mediated adaptive response. Villous atrophy in Celiac disease might thus be ascribed to an IEL-mediated damage to enterocytes involving NKG2D/MICA interaction after gliadin-induced expression of MICA on gut epithelium. This supports a key role for MIC/NKG2D in the activation of intraepithelial immunity in response to danger.