DAP10 deficiency breaks the immune tolerance against transplantable syngeneic melanoma

A Protective Role for NKG2D-H60a Interaction via Homotypic T Cell Contact in Nonobese Diabetic Autoimmune Diabetes Pathogenesis

The NK group 2 member D (NKG2D) immune receptor is implicated in both human and mouse autoimmune diabetes. However, the significance of NKG2D in diabetes pathogenesis has been unclear due to conflicting reports as to the importance of this receptor in the NOD mouse model. In this study we demonstrate that NKG2D expression affects NOD diabetes development by at least two previously undescribed, and opposing, mechanisms. First, we demonstrate that the NKG2D ligand H60a is induced on activated NOD T cells, and that NKG2D-H60a interaction during CD8⁺ T cell differentiation into CTLs generally decreases the subsequent CTL effector cytokine response. This corresponds to an increase in diabetes development in NKG2D-deficient compared with wild-type NOD mice under microbiota-depleted conditions. Second, we demonstrate that NKG2D promotes NOD diabetes development through interaction with the microbiota. Together these findings reveal a previously undescribed role for NKG2D ligand expression by activated T cells in CTL development. Further, they demonstrate that NKG2D has both diabetogenic and antidiabetogenic roles in NOD diabetes development.

NKG2D: A versatile player in the immune system

NKG2D is known as a potent activating receptor of the immune system. It is expressed on a multitude of immune cells, including NK cells and different subsets of T cells. NKG2D recognizes various MHC I-like ligands that are induced on target cells exposed to stressors such as viral infection, DNA damage and oncological transformation. NKG2D drives or facilitates cytotoxic and cytokine responses towards cells expressing its ligands to eliminate the threat. Therefore, NKG2D is usually classified as a sensor that translates cellular stress into activation signals for immune cells. However, more recently it has become evident that NKG2D plays a role beyond direct killing of target cells. Lack of NKG2D affects development of NK cells in the bone marrow, resulting in hyperreactive NK cells. NKG2D deficiency on CD8 T cells affects the ability of effector cells to produce cytokines in response to T cell receptor engagement and reduces their capacity to establish immunological memory. Although NKG2D is not expressed on B cells subsets, lack of this receptor in hematopoietic precursors affects B cell development. Homing of mature B2 cells is altered in NKG2D-deficient mice and they have a strong reduction in peripheral B1a cell numbers, resulting in increased susceptibility to bacterial infections. The exact molecular mechanisms via which NKG2D mediates these versatile functions is still being explored, but appears to depend on the control of activation thresholds, either in hematopoietic precursors or mature immune cell subsets. In this review, we will elaborate on the underappreciated developmental and regulatory roles of NKG2D.

Basal-like breast cancer: molecular profiles, clinical features and survival outcomes

BACKGROUND

Basal-like constitutes an important molecular subtype of breast cancer characterised by an aggressive behaviour and a limited therapy response. The outcome of patients within this subtype is, however, divergent. Some individuals show an increased risk of dying in the first five years, and others a long-term survival of over ten years after the diagnosis. In this study, we aim at identifying markers associated with basal-like patients' survival and characterising subgroups with distinct disease outcome.

METHODS

We explored the genomic and transcriptomic profiles of 351 basal-like samples from the METABRIC and ROCK data sets. Two selection methods, labelled Differential and Survival filters, were employed to determine genes/probes that are differentially expressed in tumour and control samples, and are associated with overall survival. These probes were further used to define molecular subgroups, which vary at the microRNA level and in DNA copy number.

RESULTS

We identified the expression signature of 80 probes that distinguishes between two basal-like subgroups with distinct clinical features and survival outcomes. Genes included in this list have been mainly linked to cancer immune response, epithelial-mesenchymal transition and cell cycle. In particular, high levels of CXCR6, HCST, C3AR1 and FPR3 were found in Basal I; whereas HJURP, RRP12 and DNMT3B appeared over-expressed in Basal II. These genes exhibited the highest betweenness centrality and node degree values and play a key role in the basal-like breast cancer differentiation. Further molecular analysis revealed 17 miRNAs correlated to the subgroups, including hsa-miR-342-5p, -150, -155, -200c and -17. Additionally, increased percentages of gains/amplifications were detected on chromosomes 1q, 3q, 8q, 10p and 17q, and losses/deletions on 4q, 5q, 8p and X, associated with reduced survival.

CONCLUSIONS

The proposed signature supports the existence of at least two subgroups of basal-like breast cancers with distinct disease outcome. The identification of patients at a low risk may impact the clinical decisions-making by reducing the prescription of high-dose chemotherapy and, consequently, avoiding adverse effects. The recognition of other aggressive features within this subtype may be also critical for improving individual care and for delineating more effective therapies for patients at high risk.

NKG2D-NKG2D Ligand Interaction Inhibits the Outgrowth of Naturally Arising Low-Grade B Cell Lymphoma In Vivo

It is now clear that recognition of nascent tumors by the immune system is critical for survival of the host against cancer. During cancer immunoediting, the ability of the tumor to escape immune recognition is important for tumor development. The immune system recognizes tumors via the presence of classical Ags and also by conserved innate mechanisms. One of these mechanisms is the NKG2D receptor that recognizes ligands whose expression is induced by cell transformation. In this study, we show that in NKG2D receptor-deficient mice, increasing numbers of B cells begin to express NKG2D ligands as they age. Their absence in wild-type mice suggests that these cells are normally cleared by NKG2D-expressing cells. NKG2D-deficient mice and mice constitutively expressing NKG2D ligands had increased incidence of B cell tumors, confirming that the inability to clear NKG2D ligand-expressing cells was important in tumor suppression and that NKG2D ligand expression is a marker of nascent tumors. Supporting a role for NKG2D ligand expression in controlling the progression of early-stage B cell lymphomas in humans, we found higher expression of a microRNA that inhibits human NKG2D ligand expression in tumor cells from high-grade compared with low-grade follicular lymphoma patients.

Interaction between natural killer cells and regulatory T cells: perspectives for immunotherapy

Regulatory T (Treg) cells and natural killer (NK) cells are key players in the immune system. The interaction between these two cell types has been reported to be beneficial in healthy conditions such as pregnancy. However, in the case of certain pathologies such as autoimmune diseases and cancer this interaction can become detrimental, as Treg cells have been described to suppress NK cells and in particular to impair NK cell effector functions. This review aims to discuss the recent information on the interaction between Treg cells and NK cells under healthy and pathologic conditions, to describe the specific conditions in which this interaction takes place, the effect of Treg cells on hematopoietic stem cell differentiation and the consequences of this interaction on the optimization of immunotherapeutic protocols.

Prevalence of the NKG2D Thr72Ala polymorphism in patients with cervical carcinoma

BACKGROUND

The natural killer group 2, member D (NKG2D) receptor is mainly situated on the surface of NK and CD8(+) αβ T cells that are involved in the defense against viral agents and in cancer immunosurveillance. The G>A transition (Thr72Ala) (rs2255336) located in the NKG2D region encoding the transmembrane part of this receptor has been associated with decreased functionality of NK and T cells.

METHODS

Using polymerase chain reaction-restriction fragment length polymorphisms, we examined the NKG2D Thr72Ala polymorphism in patients with cervical cancer (n=353) and controls (n=366) in a Polish population.

RESULTS

We observed an increased frequency of Thr/Thr or/and Thr/Ala genotypes in controls compared with all patients with cervical cancer; however, these differences were not significant. We found a significantly increased frequency of the NKG2D 72Thr allele in controls than in all patients (odds ratio [OR]=0.7410 [95% confidence intervals (CI)=0.5683-0.9662, p=0.0265]). Moreover, stratification of patients based on cancer stage showed a significant increase in the Thr/Thr genotype frequency (OR=0.3086 [95% CI=0.09097-1.047, p=0.0461]), as well as in the Thr/Thr and Thr/Ala genotype frequency (OR=0.4504 [95% CI=0.2891-0.7018, p=0.0003]), in controls compared with patients with cervical cancer in stages III and IV. The frequency of the NKG2D 72Thr allele was also significantly increased in controls as compared with patients in stage III and IV cancer (OR=0.4699 [95% CI=0.3170-0.6967, p=0.0001]).

CONCLUSION

Our studies may suggest that the women with cervical cancer bearing the NKG2D 72Thr gene variant might be protected against progression to advanced stages of this cancer.

RAE1ε ligand expressed on pancreatic islets recruits NKG2D receptor-expressing cytotoxic T cells independent of T cell receptor recognition

The mechanisms by which cytotoxic T lymphocytes (CTLs) enter and are retained in nonlymphoid tissue are not well characterized. With a transgenic mouse expressing the NKG2D ligand retinoic acid early transcript 1ε (RAE1ε) in β-islet cells of the pancreas, we found that RAE1 expression was sufficient to induce the recruitment of adoptively transferred CTLs to islets. This was dependent on NKG2D expression by the CTLs and independent of antigen recognition. Surprisingly, the recruitment of CTLs resulted in the subsequent recruitment of a large number of endogenous lymphocytes. Whereas transgenic mice did not develop diabetes, RAE1 expression was sufficient to induce insulitis in older, unmanipulated transgenic mice that was enhanced by viral infection and pancreatic inflammation. These results demonstrate that the expression of an NKG2D ligand in islets is sufficient to recruit CTLs regardless of their antigen specificity and to induce insulitis.

TNK cells (NKG2D+ CD8+ or CD4+ T lymphocytes) in the control of human tumors

Innate and adaptive immune responses have many interactions that are regulated by the balance of signals initiated by a variety of activatory and inhibitory receptors. Among these, the NKG2D molecule was identified as expressed by T lymphocytes, including most CD8+ cells and a minority of CD4+ cells, designated TNK cells in this paper. Tumor cells may overexpress the stress-inducible NKG2D ligands (NKG2DLs: MICA/B, ULBPs) and the NKG2D signaling has been shown to be involved in lymphocyte-mediated anti-tumor activity. Aberrant expression of NKG2DLs by cancer cells, such as the release of soluble form of NKG2DLs, can lead to the impairment of these immune responses. Here, we discuss the significance of NKG2D in TNK-mediated anti-tumor activity. Our studies demonstrate that NKG2D+ T cells (TNK) are commonly recruited at the tumor site in melanoma patients where they may exert anti-tumor activity by engaging both TCR and NKG2D. Moreover, NKG2D and TCR triggering was also observed by peripheral blood derived T lymphocyte- or T cell clone-mediated tumor recognition, both in melanoma and colorectal cancer (CRC) patients. Notably, heterogeneous expression of NKG2DLs was found in melanoma and CRC cells, with a decrease of these molecules along with tumor progression. Therefore, through the mechanisms that govern NKG2D engagement in anti-tumor activity and the expression of NKG2DLs by tumor cells that still need to be dissected, we showed that NKG2D expressing TNK cells are a relevant T cell subtype for immunosurveillance of tumors and we propose that new immunotherapeutic interventions for cancer patients should be aimed also at enhancing NKG2DLs expression by tumor cells.

Beyond Stressed Self: Evidence for NKG2D Ligand Expression on Healthy Cells

The activity of cytotoxic lymphocytes is regulated by the opposing function of stimulatory and inhibitory cell surface receptors. According to the now classical model of Natural Killer (NK) cell activity, the ligands for inhibitory receptors are constitutively expressed on healthy cells but can be lost on infection and on malignant cells. Loss of inhibitory checks will then allow activating signals to predominate, forming the basis of 'missing self recognition'. Natural Killer Group 2D (NKG2D) is an important member of the cohort of activating receptors expressed on Natural Killer (NK) cells and subsets of T cells. Ligands for the NKG2D receptor comprise a diverse array of self-proteins structurally related to MHC class I molecules. Expression of NKG2D ligands can be induced in cells during infection with pathogens, tumourigenesis, and by stimuli such as DNA damage, oxidative stress, and heat shock. Consequently NKG2D has been widely described as participating in 'stressed self' or 'damaged self' recognition. However, a body of evidence has recently emerged to suggest that this intuitive model of NKG2D function may be an oversimplification. NKG2D ligand expression has now widely been reported on cells that could not be described as stressed or damaged. For example activated T cells can express NKG2D ligands, and constitutive expression of NKG2D ligands has been reported on normal myelomonocytic cells, dendritic cells, and epithelial cells of the gut mucosa. In this article we will review the literature suggesting that NKG2D may function to recognise non-stressed cells and discuss the role NKG2D ligands could be playing in apparently healthy cells.

DAP10- and DAP12-associated receptors in innate immunity

The DAP10 and DAP12 signaling subunits are highly conserved in evolution and associate with a large family of receptors in hematopoietic cells, including dendritic cells, plasmacytoid dendritic cells, neutrophils, basophils, eosinophils, mast cells, monocytes, macrophages, natural killer cells, and some B and T cells. Some receptors are able to associate with either DAP10 or DAP12, which contribute unique intracellular signaling functions. Studies of humans and mice deficient in these signaling subunits have provided surprising insights into the physiological functions of DAP10 and DAP12, demonstrating that they can either activate or inhibit immune responses. DAP10- and DAP12-associated receptors have been shown to recognize both host-encoded ligands and ligands encoded by microbial pathogens, indicating that they play an important role in innate immune responses.

The extended human leukocyte receptor complex: diverse ways of modulating immune responses

The leukocyte receptor complex (LRC) and its extended region comprise a large set of genes encoding immunoglobulin superfamily (IgSF) receptors, interspersed with other loci. Although the external Ig-like domains of these molecules are related, they have evolved to bind a wide array of different ligands. Comparison of the organization and functions of the different receptors encoded in the LRC provides insight into their roles in immune recognition, their evolution, and their relevance to disease. In addition, these molecules provide classic examples of inhibitory receptors paired, side by side, with activating receptors that couple with adapter proteins, such as DAP12. Some of these activating receptors can be considered as bifunctional sensors that can perceive changes in the state of their ligands that favors an inhibitory rather than activating response, whereas other receptors have evolved different means, acting as transporters or even molecular chaperones to achieve immune repression. We briefly summarize the complement of receptors encoded in this region of chromosome 19 and discuss the many diverse and versatile mechanisms they have evolved to restrain immune responses.

The NKG2D receptor: sensing stressed cells

The activating killer cell lectin-like receptor NKG2D plays a key role in the natural killer (NK) cell-mediated lysis of tumours and infected cells. Unlike other receptors, the ligands recognised by NKG2D are 'induced-self' ligands on stressed cells. This system requires precise regulation because inappropriate expression of NKG2D ligands might compromise NK cell activation. For therapeutic purposes it is essential to understand the mechanisms that regulate the expression and function of the NKG2D system. This review focuses on the importance of the signalling pathways involved in the regulation of the NKG2D receptor and its ligand expression in arming the immune response against infected or tumour cells and for the identification of new molecular targets and therapeutic strategies.