NKG2D initiates caspase-mediated CD3zeta degradation and lymphocyte receptor impairments associated with human cancer and autoimmune disease

Interactions of NK Cells and Macrophages: From Infections to Cancer Therapeutics

The interaction between immune cells brings a consequence either on their role and functioning or the functioning of the other immune cells, modulating the whole mechanistic pathway. The interaction between natural killer (NK) cells and macrophages is one such interaction which is relatively less explored amongst diseased conditions. Their significance comes from their innate nature and secretion of large proportions of cytokines and chemokines which results in influencing adaptive immune responses. Their interplay can lead to several functional outcomes such as NK cell activation/inhibition, increased cytotoxicity and IFNγ release by NK cells, inhibition of macrophage function, etc. This paper delves into the interaction amongst NK cells and macrophages via different receptor-ligands and cytokines, particularly emphasising microbial infections and tumours. The review has the potential to uncover new insights and approaches that could lead to the development of innovative therapeutic tools and targets.

Immune evasion by proteolytic shedding of natural killer group 2, member D ligands in Helicobacter pylori infection

Background

Helicobacter pylori (H. pylori) uses various strategies that attenuate mucosal immunity to ensure its persistence in the stomach. We recently found evidence that H. pylori might modulate the natural killer group 2, member 2 (NKG2D) system. The NKG2D receptor and its ligands are a major activation system of natural killer and cytotoxic T cells, which are important for mucosal immunity and tumor immunosurveillance. The NKG2D system allows recognition and elimination of infected and transformed cells, however viruses and cancers often subvert its activation. Here we aimed to identify a potential evasion of the NKG2D system in H. pylori infection.

Methods

We analyzed expression of NKG2D system genes in gastric tissues of H. pylori gastritis and gastric cancer patients, and performed cell-culture based infection experiments using H. pylori isogenic mutants and epithelial and NK cell lines.

Results

In biopsies of H. pylori gastritis patients, NKG2D receptor expression was reduced while NKG2D ligands accumulated in the lamina propria, suggesting NKG2D evasion. In vitro, H. pylori induced the transcription and proteolytic shedding of NKG2D ligands in stomach epithelial cells, and these effects were associated with specific H. pylori virulence factors. The H. pylori-driven release of soluble NKG2D ligands reduced the immunogenic visibility of infected cells and attenuated the cytotoxic activity of effector immune cells, specifically the anti-tumor activity of NK cells.

Conclusion

H. pylori manipulates the NKG2D system. This so far unrecognized strategy of immune evasion by H. pylori could potentially facilitate chronic bacterial persistence and might also promote stomach cancer development by allowing transformed cells to escape immune recognition and grow unimpeded to overt malignancy.

The Human Soluble NKG2D Ligand Differentially Impacts Tumorigenicity and Progression in Temporal and Model-Dependent Modes

NKG2D is an activating receptor expressed by all human NK cells and CD8 T cells. Harnessing the NKG2D/NKG2D ligand axis has emerged as a viable avenue for cancer immunotherapy. However, there is a long-standing controversy over whether soluble NKG2D ligands are immunosuppressive or immunostimulatory, originating from conflicting data generated from different scopes of pre-clinical investigations. Using multiple pre-clinical tumor models, we demonstrated that the impact of the most characterized human solid tumor-associated soluble NKG2D ligand, the soluble MHC I chain-related molecule (sMIC), on tumorigenesis depended on the tumor model being studied and whether the tumor cells possessed stemness-like properties. We demonstrated that the potential of tumor formation or establishment depended upon tumor cell stem-like properties irrespective of tumor cells secreting the soluble NKG2D ligand sMIC. Specifically, tumor formation was delayed or failed if sMIC-expressing tumor cells expressed low stem-cell markers; tumor formation was rapid if sMIC-expressing tumor cells expressed high stem-like cell markers. However, once tumors were formed, overexpression of sMIC unequivocally suppressed tumoral NK and CD8 T cell immunity and facilitated tumor growth. Our study distinguished the differential impacts of soluble NKG2D ligands in tumor formation and tumor progression, cleared the outstanding controversy over soluble NKG2D ligands in modulating tumor immunity, and re-enforced the viability of targeting soluble NKG2D ligands for cancer immunotherapy for established tumors.

SUMOylation and related post-translational modifications in natural killer cell anti-cancer responses

SUMOylation is a reversible modification that involves the covalent attachment of small ubiquitin-like modifier (SUMO) to target proteins, leading to changes in their localization, function, stability, and interactor profile. SUMOylation and additional related post-translational modifications have emerged as important modulators of various biological processes, including regulation of genomic stability and immune responses. Natural killer (NK) cells are innate immune cells that play a critical role in host defense against viral infections and tumors. NK cells can recognize and kill infected or transformed cells without prior sensitization, and their activity is tightly regulated by a balance of activating and inhibitory receptors. Expression of NK cell receptors as well as of their specific ligands on target cells is finely regulated during malignant transformation through the integration of different mechanisms including ubiquitin- and ubiquitin-like post-translational modifications. Our review summarizes the role of SUMOylation and other related pathways in the biology of NK cells with a special emphasis on the regulation of their response against cancer. The development of novel selective inhibitors as useful tools to potentiate NK-cell mediated killing of tumor cells is also briefly discussed.

NKG2D engagement on human NK cells leads to DNAM-1 hypo-responsiveness through different converging mechanisms

Natural killer (NK) cell activation is regulated by activating and inhibitory receptors that facilitate diseased cell recognition. Among activating receptors, NKG2D and DNAM-1 play a pivotal role in anticancer immune responses since they bind ligands upregulated on transformed cells. During tumor progression, however, these receptors are frequently downmodulated and rendered functionally inactive. Of note, NKG2D internalization has been associated with the acquisition of a dysfunctional phenotype characterized by the cross-tolerization of unrelated activating receptors. However, our knowledge of the consequences of NKG2D engagement is still incomplete. Here, by cytotoxicity assays combined with confocal microscopy, we demonstrate that NKG2D engagement on human NK cells impairs DNAM-1-mediated killing through two different converging mechanisms: by the upregulation of the checkpoint inhibitory receptor TIGIT, that in turn suppresses DNAM-1-mediated cytotoxic function, and by direct inhibition of DNAM-1-promoted signaling. Our results highlight a novel interplay between NKG2D and DNAM-1/TIGIT receptors that may facilitate neoplastic cell evasion from NK cell-mediated clearance.

The imbalance between NKG2A and NKG2D expression is involved in NK cell immunosuppression and tumor progression of patients with hepatitis B virus-related hepatocellular carcinoma

BACKGROUND

Immunosuppression in a tumor microenvironment is associated with enhanced tumor progression. Natural killer group 2 (NKG2) family proteins, including inhibitory receptors and activators, can be used as attractive targets for immunotherapy of immune checkpoint inhibition. We further explore the expression level prognostic value of NKG2A and NKG2D in hepatitis B virus-related hepatocellular carcinoma (HBV-HCC).

METHODS

This study was a prospective study involving 92 patients with HBV-HCC, 16 patients with HBV-related liver cirrhosis, 18 patients with CHB, and 38 healthy donors. We analyzed the expression and related functions of NKG2A, NKG2D, and the NKG2A/NKG2D ratio in the peripheral blood of patients with HBV-HCC and analyzed tumor progression. The tissue samples from patients with HBV-HCC were further used for multiple immunofluorescence and immunohistochemistry.

RESULTS

In patients with HBV-HCC with tumor progression, the ratio of NKG2A/NKG2D is higher in NK cells and T cells. The Kaplan-Meier survival curve showed that the NKG2A/NKG2D ratio on NK cells could predict tumor progression in patients with HBV-HCC, and that an increase in this ratio was associated with inhibition of NK cell function. The Cancer Genome Atlas (TCGA) database was further used to verify that the higher the NKG2A/NKG2D ratio, the shorter the progression-free survival of patients with HCC, and the more likely the immune function was suppressed.

CONCLUSIONS

The imbalance between NKG2A and NKG2D of NK cells is involved in NK cell immunosuppression, and the increase of the NKG2A/NKG2D ratio is related to the tumor progression of HBV-HCC.

An updated overview on celiac disease: from immuno-pathogenesis and immuno-genetics to therapeutic implications

INTRODUCTION

Celiac disease (CD) is an autoimmune enteropathy triggered by ingestion of gluten. While presenting many similarities with other autoimmune diseases, celiac disease is unique in that the external trigger, gluten, and the genetic background necessary for disease development (HLA DQ2/DQ8) are well described. The prevalence of celiac disease is dramatically increasing over the years and new epidemiologic data show changes regarding age of onset and symptoms. A better understanding of CD-pathogenesis is fundamental to highlight the reasons of this rise of celiac diagnoses.

AREAS COVERED

In this review we describe CD-pathogenesis by dissecting all the components necessary to lose tolerance to gluten (ingestion of gluten, genetic predisposition, loss of barrier function and immune response). Additionally, we also highlight the role that microbiome plays in celiac disease as well as new proposed therapies and experimental tools.

EXPERT OPINION

Prevalence of autoimmune diseases is increasing around the world. As a result, modern society is strongly impacted by a social and economic burden. Given the unique characteristics of celiac disease, a better understanding of its pathogenesis and the factors that contribute to it may shed light on other autoimmune diseases for which external trigger and genetic background are not known.

Defects at the Posttranscriptional Level Account for the Low TCRζ Chain Expression Detected in Gastric Cancer Independently of Caspase-3 Activity

BACKGROUND

Reduced TCRζ chain surface has been reported in T cells from patients with different inflammatory conditions and cancer. However, the causes of this diminished expression in cancer remain elusive.

METHODS

T cell-enriched populations of blood or tissue (tumoral and nontumoral) origin from 44 patients with gastric adenocarcinoma and 33 healthy subjects were obtained. Samples were subjected to cytofluorimetry, Western blot analysis, TCRζ cDNA sequencing experiments, measurement of TCRζ mRNA levels, and caspase-3 activity assays.

RESULTS

Cytofluorimetry revealed a decreased TCRζ expression in T cells of patients, assessed either as percentage of cells expressing this chain (blood: control subjects 99.8 ± 0.1%, patients 98.8 ± 1.1%P < 0.001; tissue: control subjects 96.7 ± 0.9%, patients tumoral tissue 67.9 ± 27.0%, patients nontumoral tissue 82.8 ± 12.6%, P = 0.019) or mean fluorescence intensity (MFI) value (blood: control subjects 102.2 ± 26.0; patients 58.0 ± 12.3, P = 0.001; tissue: control subjects 99.4 ± 21.4; patients tumoral tissue 41.6 ± 21.4; patients nontumoral tissue 62.3 ± 16.6, P = 0.001). Other chains pertaining to the TCR-CD3 complex (CD3ε) showed no significant differences (MFI values). Subsequent TCRζ cDNA sequencing experiments or measurements of TCRζ mRNA levels disclosed no differences between patients and control subjects. Evaluation of caspase-3 activity showed higher levels in T cell extracts of patients, and this activity could be decreased by 70% with the use of the inhibitor Ac-DEVD-FMK, although CD3ζ expression levels did not recover.

CONCLUSIONS

These results further place the defect responsible for the low TCRζ expression in cancer at the posttranscriptional level and suggests contrary to what has been proposed in other pathologies that elevated caspase-3 activity is not the causative agent.

Research Progress on NK Cell Receptors and Their Signaling Pathways

Natural killer cells (NK cells) play an important role in innate immunity. NK cells recognize self and nonself depending on the balance of activating receptors and inhibitory receptors. After binding to their ligands, NK cell receptors trigger subsequent signaling conduction and then determine whether NK is activated or inhibited. Furthermore, NK cell response includes cytotoxicity and cytokine release, which is tightly related to the activation of NK cell-activating receptors and the inhibition of inhibitory receptors on the surfaces of NK cells. The expression and function of NK cell surface receptors also alter in virus infection, tumor, and autoimmune diseases and influence the occurrence and development of diseases. So, it is important to understand the mechanism of recognition between NK receptors and their ligands in pathological conditions and the signaling pathways of NK cell receptors. This review mainly summarizes the research progress on NK cell surface receptors and their signal pathways.

Antibody targeting tumor-derived soluble NKG2D ligand sMIC reprograms NK cell homeostatic survival and function and enhances melanoma response to PDL1 blockade therapy

BACKGROUND

Melanoma patients who have detectable serum soluble NKG2D ligands either at the baseline or post-treatment of PD1/PDL1 blockade exhibit poor overall survival. Among families of soluble human NKG2D ligands, the soluble human MHC I chain-related molecule (sMIC) was found to be elevated in melanoma patients and mostly associated with poor response to PD1/PDL1 blockade therapy.

METHODS

In this study, we aim to investigate whether co-targeting tumor-released sMIC enhances the therapeutic outcome of PD1/PDL1 blockade therapy for melanoma. We implanted sMIC-expressing B16F10 melanoma tumors into syngeneic host and evaluated therapeutic efficacy of anti-sMIC antibody and anti-PDL1 antibody combination therapy in comparison with monotherapy. We analyzed associated effector mechanism. We also assessed sMIC/MIC prevalence in metastatic human melanoma tumors.

RESULTS

We found that the combination therapy of the anti-PDL1 antibody with an antibody targeting sMIC significantly improved animal survival as compared to monotherapies and that the effect of combination therapy depends significantly on NK cells. We show that combination therapy significantly increased IL-2Rα (CD25) on NK cells which sensitizes NK cells to low dose IL-2 for survival. We demonstrate that sMIC negatively reprograms gene expression related to NK cell homeostatic survival and proliferation and that antibody clearing sMIC reverses the effect of sMIC and reprograms NK cell for survival. We further show that sMIC/MIC is abundantly present in metastatic human melanoma tumors.

CONCLUSIONS

Our findings provide a pre-clinical proof-of-concept and a new mechanistic understanding to underscore the significance of antibody targeting sMIC to improve therapeutic efficacy of anti-PD1/PDL1 antibody for MIC/sMIC⁺ metastatic melanoma patients.

Boosting Natural Killer Cell-Mediated Targeting of Sarcoma Through DNAM-1 and NKG2D

Sarcomas are malignancies of mesenchymal origin that occur in bone and soft tissues. Many are chemo- and radiotherapy resistant, thus conventional treatments fail to increase overall survival. Natural Killer (NK) cells exert anti-tumor activity upon detection of a complex array of tumor ligands, but this has not been thoroughly explored in the context of sarcoma immunotherapy. In this study, we investigated the NK cell receptor/ligand immune profile of primary human sarcoma explants. Analysis of tumors from 32 sarcoma patients identified the proliferative marker PCNA and DNAM-1 ligands CD112 and/or CD155 as commonly expressed antigens that could be efficiently targeted by genetically modified (GM) NK cells. Despite the strong expression of CD112 and CD155 on sarcoma cells, characterization of freshly dissociated sarcomas revealed a general decrease in tumor-infiltrating NK cells compared to the periphery, suggesting a defect in the endogenous NK cell response. We also applied a functional screening approach to identify relevant NK cell receptor/ligand interactions that induce efficient anti-tumor responses using a panel NK-92 cell lines GM to over-express 12 different activating receptors. Using GM NK-92 cells against primary sarcoma explants (n = 12) revealed that DNAM-1 over-expression on NK-92 cells led to efficient degranulation against all tested explants (n = 12). Additionally, NKG2D over-expression showed enhanced responses against 10 out of 12 explants. These results show that DNAM-1⁺ or NKG2D⁺ GM NK-92 cells may be an efficient approach in targeting sarcomas. The degranulation capacity of GM NK-92 cell lines was also tested against various established tumor cell lines, including neuroblastoma, Schwannoma, melanoma, myeloma, leukemia, prostate, pancreatic, colon, and lung cancer. Enhanced degranulation of DNAM-1⁺ or NKG2D⁺ GM NK-92 cells was observed against the majority of tumor cell lines tested. In conclusion, DNAM-1 or NKG2D over-expression elicited a dynamic increase in NK cell degranulation against all sarcoma explants and cancer cell lines tested, including those that failed to induce a notable response in WT NK-92 cells. These results support the broad therapeutic potential of DNAM-1⁺ or NKG2D⁺ GM NK-92 cells and GM human NK cells for the treatment of sarcomas and other malignancies.

Antibody targeting tumor-derived soluble NKG2D ligand sMIC provides dual co-stimulation of CD8 T cells and enables sMIC+ tumors respond to PD1/PD-L1 blockade therapy

Background

Insufficient co-stimulation accounts for a great deal of the suboptimal activation of cytotoxic CD8 T cells (CTLs) and presumably unsatisfactory clinical expectation of PD1/PD-L1 therapy. Tumor-derived soluble NKG2D ligands are associated with poor clinical response to PD1/PD-L1 blockade therapy in cancer patients. One of the mostly occurring tumor-derived soluble NKG2D ligands, the soluble MHC I chain related molecule (sMIC) can impair co-stimulation to CD8 T cells. We investigated whether co-targeting sMIC can provide optimal co-stimulation to CTLs and enhance the therapeutic effect of PD1/PD-L1 blockades.

Methods

Single agent therapy of a PD1/PD-L1 blockade antibody or a sMIC-targeting non-blocking antibody or a combination therapy of the two antibodies were implied to well-characterized pre-clinical MIC/sMIC⁺ tumor models that closely resemble the NKG2D-mediated oncoimmune dynamics of MIC⁺ cancer patients. Therapeutic efficacy and associated effector mechanisms were evaluated.

Results

We show that antibody co-targeting sMIC enables or enhances the response of sMIC⁺ tumors to PD1/PD-L1 blockade therapy. The therapy response of the combination therapy was associated with enhanced antigen-specific CD8 T cell enrichment and function in tumors. We show that co-targeting sMIC with a nonblocking antibody provides antigen-specific CD8 T cells with NKG2D and CD28 dual co-stimulation, in addition to elimination of inhibitory signals, and thus amplifies antigen-specific CD8 T cell anti-tumor responses.

Conclusion

Our findings provide the proof-of-concept rationale and previously undiscovered mechanisms for co-targeting sMIC to enable and enhance the response to PD1/PD-L1 blockade therapy in sMIC⁺ cancer patients.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0693-y) contains supplementary material, which is available to authorized users.

NKG2D-ligands: Putting everything under the same umbrella can be misleading

NKG2D is a key receptor for the activation of immune effector cells, mainly Natural Killer cells and T lymphocytes, in infection, cancer and autoimmune diseases. Since the detection of ligands for NKG2D in sera of cancer patients is, in many human models, indicative of prognosis, a large number of studies have been undertaken to improve understanding of the biology regulating this receptor and its ligands, with the aim of translating this knowledge into clinical practice. Although it is becoming clear that the NKG2D system can be used as a tool for diagnosis and manipulated for therapy, some questions remain open due to the complexity associated with the existence of a large number of ligands, each one of them displaying distinct biological properties. In this review, we have highlighted some key aspects of this system that differ between humans and mice, including the properties of NKG2D, as well as the genetic and biochemical complexity of NKG2D-ligands. All of these features affect the characteristics of the immune response exerted by NKG2D-expressing cells and are likely to be important factors in the clearance of a tumour or the development of autoimmunity. Implementation of more global analyses, including information on genotype, transcription and protein properties (cellular vs released to the blood stream) of NKG2D-ligands expressed in patients will be necessary to fully understand the links between this system and disease progression.

B7-H6-mediated downregulation of NKp30 in natural killer cells contributes to HIV-2 immune escape

OBJECTIVE

HIV-1 and HIV-2 differ notably in their epidemiology, with worldwide HIV-1 spread and HIV-2 mainly confined to West Africa. Natural killer (NK) cells are critical antiviral effectors of the immune system; however, limited information is available about these innate effector cells during HIV-2 infection.

METHOD

In this study, 24 untreated HIV-2-infected patients were analyzed and compared with 21 long-term nonprogressor and 10 controller HIV-1 patients, and healthy donors. Extensive phenotype and functional NK-cell characteristics, as well as ligands of activating NK receptors involved in NK lysis were determined by flow cytometry.

RESULTS

We report in HIV-2 patients a very significant reduced expression of the activating NKp30 receptor (P < 0.0001) on NK cells, much higher than observed in HIV-1 patients. The impaired expression of NKp30 is correlated negatively with HLA-DR (r = -0.5970; P = 0.0002), and positively with both NKG2A (r = 0.5324; P < 0.0001) and Siglec-7 (r = 0.5621; P = 0.0004). HIV-2 patients with NKp30 NK cells displayed overproduction of IFN-γ (P < 0.0001) associated with impaired cytolytic function when tested against target cells expressing surface B7-H6. This cellular ligand of NKp30 is strongly detectable as a surface molecule on CD4 T cells infected by HIV-2.

CONCLUSION

Altogether, our data suggested that the defective expression of NKp30 may be induced by the chronic engagement of this receptor by B7-H6 expressed on HIV-2-infected target cells. This represents a novel mechanism by which the chronic ligand exposure by the viral environment may subvert NK-cell-mediated function to establish persistent HIV-2 infection.

IL-17 production by NKG2D-expressing CD56+ T cells in type 2 diabetes

T cells expressing CD56 (identified as CD3+CD56+) play a potential role in activation or regulation of other immune cells by secreting various cytokines. We hypothesized that these cells expressing the natural group 2, member D (NKG2D) could produce high levels of interleukin (IL)-17 in type 2 diabetes (T2D). CD56 + T cells expressing NKG2D of T2D patients, particularly in poor glycemic control (PC) predominantly produced higher IL-17 compared to the NKG2D negative population. IL-17 production of CD56 + T cells with NKG2D + was positively correlated with the level of HbA1c (N = 22, R² = 0.120 and P =  0.044). Interestingly, CD56+ T cells with NKG2D^Hi of T2D patients had significantly higher IL-17 production than those of CD56 + T cells with NKG2D^Low (P =  0.027) and showed statistically significant with P-value < 0.001 compared to CD56 + T cells with NKG2D^Hi of non-diabetic individuals (ND). In summary, CD56 + T cells expressing NKG2D, especially in the NKG2D^Hi population may be involved in pathogenesis and severity of T2D via IL-17.

NKG2D Ligands-Critical Targets for Cancer Immune Escape and Therapy

DNA damage, oncogene activation and excessive proliferation, chromatin modulations or oxidative stress are all important hallmarks of cancer. Interestingly, all of these abnormalities also induce a cellular stress response. By upregulating “stress-induced ligands,” damaged or transformed cells can be recognized by immune cells and cleared. The human genome encodes eight functional “stress-induced ligands”: MICA, MICB, and ULBP1-6. All of them are recognized by a single receptor, NKG2D, which is expressed on natural killer (NK) cells, cytotoxic T cells and other T cell subsets. The NKG2D ligand/NKG2D-axis is well-recognized as an important mediator of anti-tumor activity; however, patient data about the role of NKG2D ligands in immune surveillance and escape appears conflicting. As these ligands are often actively transcribed, tumor cells are urged to manipulate the expression of these ligands on post-transcriptional or post-translational level. Although our knowledge on the regulation of NKG2D ligand expression remains fragmentary, research of the past years revealed multiple cellular mechanisms that are adopted by tumor cells to reduce the expression of “stress-induced ligands” and therefore escape immune recognition. Here, we review the post-transcriptional and post-translational mechanisms by which NKG2D ligands are modulated in cancer cells and their impact on patient prognosis.We discuss controversies and approaches to apply our understanding of the NKG2D ligand/NKG2D-axis for cancer therapy.

NKG2D and its ligands in cancer

NKG2D is an activating immune receptor expressed by NK and effector T cells. Induced expression of NKG2D ligand on tumor cell surface during oncogenic insults renders cancer cells susceptible to immune destruction. In advanced human cancers, tumor cells shed NKG2D ligand to produce an immune soluble form as a means of immune evasion. Soluble NKG2D ligands have been associated with poor clinical prognosis in cancer patients. Harnessing NKG2D pathway is considered a viable avenue in cancer immunotherapy over recent years. In this review, we will discuss the progress and perspectives.

Downregulation of CD3ζ in NK Cells from Systemic Lupus Erythematosus Patients Confers a Proinflammatory Phenotype

Cytotoxic function and cytokine profile of NK cells are compromised in patients with systemic lupus erythematosus (SLE). CD3ζ, an important molecule for NK cell activation, is downregulated in SLE T cells and contributes to their altered function. However, little is known about the role of CD3ζ in SLE NK cells. We studied CD3ζ levels and its contribution to cytotoxic, degranulation, and cytokine production capacity of NK cells from patients with SLE. Furthermore, we studied the human NK cell line, NKL, in which manipulation of CD3ζ levels was achieved using small interfering RNA and NK cells from Rag2 mice deficient in CD3ζ. We found reduced CD3ζ expression in NK cells from SLE patients independent of disease activity. Downregulation of CD3ζ expression in NK cells is mediated, at least in part, by Caspase 3, the activity of which is higher in NK cells from patients with SLE compared with NK cells from healthy donors. CD3ζ levels correlated inversely with natural cytotoxicity and the percentage of cells capable of producing the proinflammatory cytokines IFN-γ and TNF. In contrast, CD3ζ levels showed a direct correlation with levels of Ab-dependent cellular cytotoxicity. Experiments performed in CD3ζ-silenced NKL and CD3ζ-deficient NK cells from Rag2 mice confirmed the dependence of NK cell function on CD3ζ levels. Our results demonstrate a differential role for CD3ζ in natural cytotoxicity and Ab-dependent cellular cytotoxicity. We conclude that downregulated CD3ζ confers a proinflammatory phenotype to SLE NK cells and contributes to their altered function in patients with SLE.

NKG2D: A Master Regulator of Immune Cell Responsiveness

NKG2D is an activating receptor that is mostly expressed on cells of the cytotoxic arm of the immune system. Ligands of NKG2D are normally of low abundance, but can be induced in virtually any cell in response to stressors, such as infection and oncogenic transformation. Engagement of NKG2D stimulates the production of cytokines and cytotoxic molecules and traditionally this receptor is, therefore, viewed as a molecule that mediates direct responses against cellular threats. However, accumulating evidence indicates that this classical view is too narrow. During NK cell development, engagement of NKG2D has a long-term impact on the expression of NK cell receptors and their responsiveness to extracellular cues, suggesting a role in NK cell education. Upon chronic NKG2D engagement, both NK and T cells show reduced responsiveness of a number of activating receptors, demonstrating a role of NKG2D in induction of peripheral tolerance. The image that emerges is that NKG2D can mediate both inhibitory and activating signals, which depends on the intensity and duration of ligand engagement. In this review, we provide an overview of the impact of NKG2D stimulation during hematopoietic development and during acute and chronic stimulation in the periphery on responsiveness of other receptors than NKG2D. We propose that NKG2D interprets the context of the immunological environment through detection of cellular cues and in response sets the appropriate activation threshold for a large number of immune receptors. This perspective is of particular importance for future therapies that aim to exploit NKG2D signaling to fight tumors or infection.

Chronic NKG2D Engagement In Vivo Differentially Impacts NK Cell Responsiveness by Activating NK Receptors

Immunosuppression is a typical hallmark of cancer and frequently includes perturbations of the NKG2D tumor recognition system as well as impaired signaling by other activating NK cell receptors. Several in vitro studies suggested that sustained engagement of the NKG2D receptor, as it is occurring in the tumor microenvironment, not only impairs expression and function of NKG2D but also impacts signaling by other activating NK receptors. Here, we made use of a transgenic mouse model of ubiquitous NKG2D ligand expression (H2-K^b-MICA mice) to investigate consequences of chronic NKG2D engagement in vivo for functional responsiveness by other activating NK receptors such as NKp46 and Ly49D. Unexpectedly, we found no evidence for an impairment of NKp46 expression and function in H2-K^b-MICA mice, as anticipated from previous in vitro experiments. However, we observed a marked downregulation and dysfunction of the activating receptor Ly49D in activated NK cells from H2-K^b-MICA mice. Ly49D shares the adaptor proteins DAP10 and DAP12 with NKG2D possibly explaining the collateral impairment of Ly49D function in situations of chronic NKG2D engagement. Altogether, our results demonstrate that persistent engagement of NKG2D in vivo, as often observed in tumors, can selectively impair functions of unrelated NK receptors and thereby compromise NK responsiveness to third-party antigens.

Regulation of NKG2D-Dependent NK Cell Functions: The Yin and the Yang of Receptor Endocytosis

Natural-killer receptor group 2, member D (NKG2D) is a well characterized natural killer (NK) cell activating receptor that recognizes several ligands poorly expressed on healthy cells but up-regulated upon stressing stimuli in the context of cancer or viral infection. Although NKG2D ligands represent danger signals that render target cells more susceptible to NK cell lysis, accumulating evidence demonstrates that persistent exposure to ligand-expressing cells causes the decrease of NKG2D surface expression leading to a functional impairment of NKG2D-dependent NK cell functions. Upon ligand binding, NKG2D is internalized from the plasma membrane and sorted to lysosomes for degradation. However, receptor endocytosis is not only a mechanism of receptor clearance from the cell surface, but is also required for the proper activation of signalling events leading to the functional program of NK cells. This review is aimed at providing a summary of current literature relevant to the molecular mechanisms leading to NKG2D down-modulation with particular emphasis given to the role of NKG2D endocytosis in both receptor degradation and signal propagation. Examples of chronic ligand-induced down-regulation of NK cell activating receptors other than NKG2D, including natural cytotoxicity receptors (NCRs), DNAX accessory molecule-1 (DNAM1) and CD16, will be also discussed.

Control of Tumor Initiation by NKG2D Naturally Expressed on Ovarian Cancer Cells

Cancer cells may co-opt the NKG2D lymphocyte receptor to complement the presence of its ligands for autonomous stimulation of oncogenic signaling. Previous studies raise the possibility that cancer cell NKG2D may induce high malignancy traits, but its full oncogenic impact is unknown. Using epithelial ovarian cancer as model setting, we show here that ex vivo NKG2D⁺ cancer cells have stem-like capacities, and provide formal in vivo evidence linking NKG2D stimulation with the development and maintenance of these functional states. NKG2D⁺ ovarian cancer cell populations harbor substantially greater capacities for self-renewing in vitro sphere formation and in vivo tumor initiation in immunodeficient (NOD scid gamma) mice than NKG2D⁻ controls. Sphere formation and tumor initiation are impaired by NKG2D silencing or ligand blockade using antibodies or a newly designed pan ligand-masking NKG2D multimer. In further support of pathophysiological significance, a prospective study of 47 high-grade serous ovarian cancer cases revealed that the odds of disease recurrence were significantly greater and median progression-free survival rates higher among patients with above and below median NKG2D⁺ cancer cell frequencies, respectively. Collectively, our results define cancer cell NKG2D as an important regulator of tumor initiation in ovarian cancer and presumably other malignancies and thus challenge current efforts in immunotherapy aimed at enhancing NKG2D function.

Antibody-mediated neutralization of soluble MIC significantly enhances CTLA4 blockade therapy

Antibody therapy targeting cytotoxic T lymphocyte-associated antigen 4 (CTLA4) elicited survival benefits in cancer patients; however, the overall response rate is limited. In addition, anti-CTLA4 antibody therapy induces a high rate of immune-related adverse events. The underlying factors that may influence anti-CTLA4 antibody therapy are not well defined. We report the impact of a cancer-derived immune modulator, the human-soluble natural killer group 2D (NKG2D) ligand sMIC (soluble major histocompatibility complex I chain-related molecule), on the therapeutic outcome of anti-CTLA4 antibody using an MIC transgenic spontaneous TRAMP (transgenic adenocarcinoma of the mouse prostate)/MIC tumor model. Unexpectedly, animals with elevated serum sMIC (sMIC^hi) responded poorly to anti-CTLA4 antibody therapy, with significantly shortened survival due to increased lung metastasis. These sMIC^hi animals also developed colitis in response to anti-CTLA4 antibody therapy. Coadministration of an sMIC-neutralizing monoclonal antibody with the anti-CTLA4 antibody alleviated treatment-induced colitis in sMIC^hi animals and generated a cooperative antitumor therapeutic effect by synergistically augmenting innate and adoptive antitumor immune responses. Our findings imply that a new combination therapy could improve the clinical response to anti-CTLA4 antibody therapy. Our findings also suggest that prescreening cancer patients for serum sMIC may help in selecting candidates who will elicit a better response to anti-CTLA4 antibody therapy.

MHC class I chain-related protein A and B (MICA and MICB) are predominantly expressed intracellularly in tumour and normal tissue

BACKGROUND

Major histocompatibility complex (MHC) class I chain-related protein A (MICA) and MHC class I chain-related protein B (MICB) are polymorphic proteins that are induced upon stress, damage or transformation of cells which act as a 'kill me' signal through the natural-killer group 2, member D receptor expressed on cytotoxic lymphocytes. MICA/B are not thought to be constitutively expressed by healthy normal cells but expression has been reported for most tumour types. However, it is not clear how much of this protein is expressed on the cell surface.

METHODS

Using a novel, well-characterised antibody and both standard and confocal microscopy, we systematically profiled MICA/B expression in multiple human tumour and normal tissue.

RESULTS

High expression of MICA/B was detected in the majority of tumour tissues from multiple indications. Importantly, MICA/B proteins were predominantly localised intracellularly with only occasional evidence of cell membrane localisation. MICA/B expression was also demonstrated in most normal tissue epithelia and predominantly localised intracellularly. Crucially, we did not observe qualitative differences in cell surface expression between tumour and MICA/B expressing normal epithelia.

CONCLUSIONS

This demonstrates for the first time that MICA/B is more broadly expressed in normal tissue and that expression is mainly intracellular with only a small fraction appearing on the cell surface of some epithelia and tumour cells.

Functionally Diverse NK-Like T Cells Are Effectors and Predictors of Successful Aging

The fundamental challenge of aging and long-term survivorship is maintenance of functional independence and compression of morbidity despite a life history of disease. Inasmuch as immunity is a determinant of individual health and fitness, unraveling novel mechanisms of immune homeostasis in late life is of paramount interest. Comparative studies of young and old persons have documented age-related atrophy of the thymus, the contraction of diversity of the T cell receptor (TCR) repertoire, and the intrinsic inefficiency of classical TCR signaling in aged T cells. However, the elderly have highly heterogeneous health phenotypes. Studies of defined populations of persons aged 75 and older have led to the recognition of successful aging, a distinct physiologic construct characterized by high physical and cognitive functioning without measurable disability. Significantly, successful agers have a unique T cell repertoire; namely, the dominance of highly oligoclonal αβT cells expressing a diverse array of receptors normally expressed by NK cells. Despite their properties of cell senescence, these unusual NK-like T cells are functionally active effectors that do not require engagement of their clonotypic TCR. Thus, NK-like T cells represent a beneficial remodeling of the immune repertoire with advancing age, consistent with the concept of immune plasticity. Significantly, certain subsets are predictors of physical/cognitive performance among older adults. Further understanding of the roles of these NK-like T cells to host defense, and how they integrate with other physiologic domains of function are new frontiers for investigation in Aging Biology. Such pursuits will require a research paradigm shift from the usual young-versus-old comparison to the analysis of defined elderly populations. These endeavors may also pave way to age-appropriate, group-targeted immune interventions for the growing elderly population.

Neuropeptide Levels as well as Neprilysin Activity Decrease in Renal Cell Carcinoma

Calcitonin Gene-related Peptide (CGRP), Vasoactive Intestinal Peptide (VIP) and Substance P (SP) are sensory neuropeptides which may alter cancer growth through modulation of chronic inflammation. We recently reported that SP suppresses breast cancer growth and metastasis through neuroimmune modulation. These neuropeptides are hydrolyzed by Neprilysin (NEP) to bioactive fragments. Decreased activity of NEP was reported in clear cell and chromophobe type renal cell carcinoma (RCC). It is however not known how the levels of neuropeptides hydrolyzed with NEP changes in RCC. Decrease activity of SP and CGRP containing sensory nerve endings was previously reported to increase cancer metastasis in animal models. It is however not known how peptidergic nerve endings are altered in RCC. Hence we here evaluated the levels of neuronal and non-neuronal neuropeptides and NEP activity in RCC including papillary type as well as neighboring uninvolved kidney. A cross-sectional study was conducted in 57 patients undergoing radical nephrectomy and diagnosed with RCC. NEP activity, levels and expression were determined using flourogenic substrate, western blot and qPCR respectively in freshly-frozen tissues. Immunohistochemical analyses were also performed. Neuronal and non-neuronal levels of CGRP, SP and VIP levels were determined using two-step acetic acid extraction. Levels and activity of NEP were markedly decreased in RCC regardless of subtype. Similar levels of VIP were detected in first and second extractions. VIP levels were higher in clear cell and papillary RCC compared to nearby kidney tissue. VIP levels of neighboring kidney tissue of papillary type RCC was significantly lower compared to kidney samples from clear cell RCC. CGRP levels were higher in second extraction. Similar to VIP levels, CGRP levels of neighboring kidney tissue from clear cell and chromophobe type RCC was significantly lower compared to corresponding tumor samples, an effect observed in the second extraction. VIP and CGRP levels of nearby kidney tissue varied subtype dependently demonstrating that different subtypes of RCC alter their local environment differently. Furthermore NEP-induce hydrolysis of VIP creates selective VPAC-1 receptor agonist which has anti-proliferative and anti-inflammatory effects. Hence loss of NEP activity may prevent anti-tumoral effects of VIP on RCC.

Regulation of NKG2D Expression and Signaling by Endocytosis

NKG2D is an activating receptor that can bind to a large number of stress-induced ligands that are expressed in the context of cancer or viral infection. This receptor is expressed on many cytotoxic lymphocytes, and plays a crucial role in antitumor and antiviral immune responses. However, exposure to NKG2D ligand-expressing target cells promotes receptor endocytosis, ultimately leading to lysosomal receptor degradation and impairment of NKG2D-mediated functions. Interestingly, before being degraded, internalized receptors can signal from the endosomal compartment, leading to the appropriate activation of cellular functional programs. This review summarizes recent findings on ligand-induced receptor internalization, with particular emphasis on the role of endocytosis in the control of both NKG2D-mediated intracellular signaling and receptor degradation.

Progressive natural killer cell dysfunction associated with alterations in subset proportions and receptor expression in soft-tissue sarcoma patients

Immunotherapy is currently investigated as treatment option in many types of cancer. So far, results from clinical trials have demonstrated that significant benefit from immunomodulatory therapies is restricted to patients with select histologies. To broaden the potential use of these therapies, a deeper understanding for mechanisms of immunosuppression in patients with cancer is needed. Soft-tissue sarcoma (STS) presents a medical challenge with significant mortality even after multimodal treatment. We investigated function and immunophenotype of peripheral natural killer (NK) cells from chemotherapy-naive STS patients (1st line) and STS patients with progression or relapse after previous chemotherapeutic treatment (2nd line). We found NK cells from peripheral blood of both STS patient cohorts to be dysfunctional, being unable to lyse K562 target cells while NK cells from renal cell cancer (RCC) patients did not display attenuated lytic activity. Ex vivo stimulation of NK cells from STS patients with interleukin-2 plus TKD restored cytotoxic function. Furthermore, altered NK cell subset composition with reduced proportions of CD56(dim) cells could be demonstrated, increasing from 1st- to 2nd-line patients. 2nd-line patients additionally displayed significantly reduced expression of receptors (NKG2D), mediators (CD3ζ), and effectors (perforin) of NK cell activation. In these patients, we also detected fewer NK cells with CD57 expression, a marker for terminally differentiated cytotoxic NK cells. Our results elucidate mechanisms of NK cell dysfunction in STS patients with advanced disease. Markers like NKG2D, CD3ζ, and perforin are candidates to characterize NK cells with effective antitumor function for immunotherapeutic interventions.

Extracellular 2'5'-oligoadenylate synthetase 2 mediates T-cell receptor CD3-ζ chain down-regulation via caspase-3 activation in oral cancer

Decreased expression of CD3-ζ chain, an adaptor protein associated with T-cell signalling, is well documented in patients with oral cancer, but the mechanistic justifications are fragmentary. Previous studies in patients with oral cancer have shown that decreased expression of CD3-ζ chain was associated with decreased responsiveness of T cells. Tumours are known to induce localized as well as systemic immune suppression. This study provides evidence that oral tumour-derived factors promote immune suppression by down-regulating CD3-ζ chain expression. 2'5'-Oligoadenylate synthetase 2 (OAS2) was identified by the proteomic approach and our results established a causative link between CD3-ζ chain down-regulation and OAS2 stimulation. The surrogate situation was established by over-expressing OAS2 in a HEK293 cell line and cell-free supernatant was collected. These supernatants when incubated with T cells resulted in down-regulation of CD3-ζ chain, which shows that the secreted OAS2 is capable of regulating CD3-ζ chain expression. Incubation of T cells with cell-free supernatants of oral tumours or recombinant human OAS2 (rh-OAS2) induced caspase-3 activation, which resulted in CD3-ζ chain down-regulation. Caspase-3 inhibition/down-regulation using pharmacological inhibitor or small interfering RNA restored down-regulated CD3-ζ chain expression in T cells induced by cell-free tumour supernatant or rh-OAS2. Collectively these results show that OAS2 leads to impairment in CD3-ζ chain expression, so offering an explanation that might be applicable to the CD3-ζ chain deficiency observed in cancer and diverse disease conditions.

Natural killer (NK) cell profiles in blood and tumour in women with large and locally advanced breast cancer (LLABC) and their contribution to a pathological complete response (PCR) in the tumour following neoadjuvant chemotherapy (NAC): differential restoration of blood profiles by NAC and surgery

Background

NK cells contribute to tumour surveillance, inhibition of growth and dissemination by cytotoxicity, secretion of cytokines and interaction with immune cells. Their precise role in human breast cancer is unclear and the effect of therapy poorly studied. The purpose of our study was to characterise NK cells in women with large (≥3 cm) and locally advanced (T3–4, N1–2, M0) breast cancers (LLABCs) undergoing neoadjuvant chemotherapy (NAC) and surgery, and to ascertain their possible contribution to a pathological complete response (pCR).

Methods

Women with LLABCs (n = 25) and healthy female donors [HFDs (n = 10)] were studied. Pathological responses in the breast were assessed using established criteria. Blood samples were collected pre and post NAC and surgery. Flow cytometry and labelled monoclonal antibodies established absolute numbers (AbNs) and percentages (%) of NK cells, and expressing granzyme B/perforin and NKG2D. In vitro NK cytotoxicity was assessed and NK cells and cytokines (IL-2, INF-γ, TGF-β) documented in tumours using immunohistochemical techniques. Data was analysed by SPSS.

Results

Women with LLABCs had significantly reduced AbNs (160.00 ± 40.00 cells/µl) but not % of NK cells, compared with HFDs (NK: 266.78 ± 55.00 cells/µl; p = 0.020). NAC enhanced the AbN (p = 0.001) and % (p = 0.006) of NK cells in patients with good pathological responses. Granzyme B⁺/perforin⁺ cells were significantly reduced (43.41 ± 4.00%), compared with HFDs (60.26 ± 7.00%; p = 0.003). NAC increased the % in good (p = 0.006) and poor (p = 0.005) pathological responders. Pretreatment NK cytotoxicity was significantly reduced in good (37.80 ± 8.05%) and poor (22.80 ± 7.97%) responders (p = 0.001) but remained unchanged following NAC. NK-NKG2D⁺ cells were unaltered and unaffected by NAC; NKG2D expression was increased in patients with a pCR (p = 0.001). Surgery following NAC was not beneficial, except in those with a pCR. Tumour-infiltrating NK cells were infrequent but increased peritumourally (p = 0.005) showing a significant correlation (p = 0.004) between CD56⁺ cells and grade of response. Tumour cytokines had no effect.

Conclusion

Women with LLABCs have inhibited blood innate immunity, variably reversed by NAC (especially with tumour pCRs), which returned to pretreatment levels following surgery. These and in situ tumour findings suggest a role for NK cells in NAC-induced breast pCR.

NKG2D Ligands in Tumor Immunity: Two Sides of a Coin

The activating/co-stimulatory receptor NKG2D (natural-killer group 2, member D) is expressed on the surface of all human NK, NKT, CD8(+) T, and subsets of γδ(+) T cells. The significance of NKG2D function in tumor immunity has been well demonstrated in experimental animal models. However, the role of human NKG2D ligands in regulating tumor immunity and cancer prognosis had been controversial in the literature. In this review, we summarize the latest advancement, discuss the controversies, and present evidence that membrane-bound and soluble NKG2D ligands oppositely regulate tumor immunity. We also discuss new perspectives of targeting NKG2D ligands for cancer immunotherapy.

Acute myeloid leukemia impairs natural killer cells through the formation of a deficient cytotoxic immunological synapse

Acute myeloid leukemia (AML) cells are killed by allogeneic NK cells. However, autologous NK cells from AML patients express decreased levels of activating receptors, and show reduced cytotoxicity. Here, we investigated how interactions between NK and AML cells might cause loss of NK-cell activity in patients. Our results show that AML cell lines and primary blasts alter the NK-cell phenotype, reducing their cytotoxic potential upon prolonged contact. Downregulation of NK-cell-activating receptors was contact-dependent and correlated with conjugate formation. Time-lapse imaging of HL60 AML cell line and NK-cell interactions showed a high proportion of noncytolytic contacts. Studies of NK-cell immunological synapses revealed a defect in lytic synapse formation. Namely, despite correct F-actin and LFA-1 recruitment, polarization of lytic granules toward primary blasts or AML cell lines was reduced. The NK-AML cell line synapses showed impairment of CD3ζ recruitment. Attempts to correct these synapse defects by cytokine stimulation of NK cells improved conjugate formation, but not granule polarization. Pretreatment of AML cell lines with the immunomodulating molecule lenalidomide significantly enhanced granule polarization. We speculate that combining immunomodulatory drugs and cytokines could increase AML cell sensitivity to autologous NK cells and reinforce the activity of allogeneic NK cells in adoptive immunotherapy.

c-Cbl regulates MICA- but not ULBP2-induced NKG2D down-modulation in human NK cells

The NKG2D activating receptor on human NK cells mediates "altered self" recognition, as its ligands (NKG2DLs) are upregulated on target cells in a variety of stress conditions. Evidence collected in the past years shows that, even though expression of NKG2DLs acts as a danger signal that renders tumor cells susceptible to cytotoxicity, chronic exposure to soluble or membrane-bound NKG2DLs can lead to down-modulation of receptor expression and impairment of NKG2D-mediated cell functions. Here, we evaluated whether different cell-bound NKG2DLs, namely MICA and ULBP2, are equivalently able to induce NKG2D down-modulation on human NK cells. We found that although both ligands reduce NKG2D surface expression, MICA promotes a stronger receptor down-modulation than ULBP2, leading to a severe impairment of NKG2D-dependent NK-cell cytotoxicity. We also provide evidence that the ubiquitin pathway and c-Cbl direct MICA-induced but not ULBP2-induced NKG2D internalization and degradation, thus identifying a molecular mechanism to explain the differential effects of MICA and ULBP2 on NKG2D expression. A better understanding of the molecular mechanisms employed by the different NKG2DLs to control NKG2D surface expression could be useful for the development of anti-tumor strategies to restore a normal level of NKG2D receptors on human NK cells.

Immunobiology and conflicting roles of the human NKG2D lymphocyte receptor and its ligands in cancer

Cancers adopt diverse strategies to safeguard their survival, which often involve blinding or incapacitating the immune response, thereby gaining battleground advantage against the host. In immune responses against cancer, an important stimulatory lymphocyte receptor is NKG2D because the tumor-associated expression of its ligands promotes destruction of malignant cells. However, with advanced human cancers profound changes unfold wherein NKG2D and its ligands are targeted or exploited for immune evasion and suppression. This negative imprinting on the immune system may be accompanied by another functional state wherein cancer cells coopt expression of NKG2D to complement the presence of its ligands for self-stimulation of tumor growth and presumably malignant progression. This review emphasizes these conflicting functional dynamics at the immunity-cancer biology interface in humans, within an overview of the immunobiology of NKG2D and mechanisms underlying the regulation of its ligands in cancer, with reference to instructive clinical observations and translational approaches.

Generation of soluble NKG2D ligands: proteolytic cleavage, exosome secretion and functional implications

The activating natural killer group 2 member D (NKG2D) receptor is expressed on NK cells, cytotoxic T cells and additional T cell subsets. Ligands for human NKG2D comprise two groups of MHC class I-related molecules, the MHC class I chain-related proteins A and B (MICA/B) and 6 UL16-binding proteins (ULBP1-6). While NKG2D ligands are absent from most normal cells, expression is induced upon stress and malignant transformation. In fact, most solid tumours and leukaemia/lymphomas constitutively express at least one NKG2D ligand and thereby are susceptible to NKG2D-dependent immunosurveillance. However, soluble NKG2D ligands are released from tumour cells and can down-modulate NKG2D activation as a means of tumour immune escape. In some tumour entities, levels of soluble NKG2D ligands in the serum correlate with tumour progression. NKG2D ligands can be proteolytically shed from the cell surface or liberated from the membrane by phospholipase C in the case of glycosylphosphatidylinositol (GPI)-anchored molecules. Moreover, NKG2D ligands can be secreted in exosomal microvesicles together with other tumour-derived molecules. Depending on the specific tumour/immune cell setting, these various forms of soluble and/or exosome-bound NKG2D ligands can exert multiple effects on NKG2D/NKG2D ligand interactions. In this review, we focus on the role of various proteases in the shedding of human NKG2D ligands from tumour cells and discuss the not completely unanimous reported functional implications of soluble and exosome-secreted NKG2D ligands for immunosurveillance.

IL-17 producing T cells in celiac disease: angels or devils?

Celiac disease (CD) is a very common chronic condition in human beings, affecting approximately one in 100 individuals. It is an autoimmune disease with a defined environmental trigger, the gluten contained in dietary cereals, occurring in genetically susceptible individuals. The disease has a very strong HLA association. More than 90% of CD patients have HLA-DQ2, and almost all of the remaining celiac population possesses HLA-DQ8 molecules. Th17 cells seem to participate in the disease pathogenesis producing and secreting either proinflammatory or anti-inflammatory cytokines.

Antibody-dependent cell lysis by NK cells is preserved after sarcoma-induced inhibition of NK cell cytotoxicity

Osteosarcoma and Ewing's sarcoma tumor cells are susceptible to IL15-induced or antibody-mediated cytolytic activity of NK cells in short-term cytotoxicity assays. When encountering the tumor environment in vivo, NK cells may be in contact with tumor cells for a prolonged time period. We explored whether a prolonged interaction with sarcoma cells can modulate the activation and cytotoxic activity of NK cells. The 40 h coculture of NK cells with sarcoma cells reversibly interfered with the IL15-induced expression of NKG2D, DNAM-1 and NKp30 and inhibited the cytolytic activity of NK cells. The inhibitory effects on receptor expression required physical contact between NK cells and sarcoma cells and were independent of TGF-β. Five days pre-incubation of NK cells with IL15 prevented the down-regulation of NKG2D and cytolytic activity in subsequent cocultures with sarcoma cells. NK cell FcγRIIIa/CD16 receptor expression and antibody-mediated cytotoxicity were not affected after the coculture. Inhibition of NK cell cytotoxicity was directly linked to the down-regulation of the respective NK cell-activating receptors. Our data demonstrate that the inhibitory effects of sarcoma cells on the cytolytic activity of NK cells do not affect the antibody-dependent cytotoxicity and can be prevented by pre-activation of NK cells with IL15. Thus, the combination of cytokine-activated NK cells and monoclonal antibody therapy may be required to improve tumor targeting and NK cell functionality in the tumor environment.

New insights into chronic inflammation-induced immunosuppression

Chronic inflammation is a common factor linking various pathologies that differ in their etiology and physiology such as cancer, autoimmune diseases, and infections. At a certain stage of each of these diseases, while the chronic inflammation proceeds, some key players of the immune system become immunosuppressed as natural killer (NK) cells and T cells. The suppressive environment induced during chronic inflammation is governed by a complex processes characterized by the accumulation and activation of immune suppressor cells, pro-inflammatory cytokines, chemokines, growth and angiogenic factors, and by the activation of several inflammatory signaling pathways mediated predominantly by NFκB and STAT3 transcription factors. A substantial body of evidence supports the notion that the development of a suppressive environment during chronic inflammation limits the success of immune-based and conventional therapies, skewing the balance in favor of a developing pathology. Thus, appropriate, well-designed and fine tuned immune interventions that could resolve inflammatory responses and associated immunosuppression could enhance disease regression and reinforce successful responses to a given therapy. This review describes the interrelationship between chronic inflammation and induced immunosuppression, and explains the current evidence linking inflammation and pathological processes, as found in cancer. We further highlight potential strategies, harnessing the immunosuppressive environment in treating autoimmune diseases and facilitating transplantation. In parallel, we emphasize the use of modalities to combat chronic inflammation-induced immunosuppression in cancer, to enhance the success of immune-based therapies leading to tumor regression. In both cases, the urgent necessity of identifying biomarkers for the evaluation of host immune status is discussed, with the goal of developing optimal personalized treatments.