NK cells gain higher IFN-γ competence during terminal differentiation.

NK cells are the main cells of the innate immune system that produce IFN-γ, and they express this cytokine at early stages of maturation in response to cytokine stimulation. Conversely, acquisition of IFN-γ-competence in CD4(+) T helper cells requires a differentiation process from naïve toward type 1 (Th1) cells, which is associated with epigenetic remodeling at the IFNG locus. In the present study, we show that the ability of NK cells to produce IFN-γ in response to activating receptor (actR) engagement is gradually acquired during terminal differentiation and is accompanied by progressively higher NF-κB activation in response to actR triggering. Moreover, during the differentiation process NK cells gradually display increasing expression of IFNG and TBX21 (encoding T-bet) transcripts and demethylation at the IFNG promoter. This study provides new insights in the molecular mechanisms underlying NK-cell ability to express IFN-γ upon actR engagement. Thus, we propose that in order to efficiently produce IFN-γ in response to infected or transformed cells, NK cells gain Th1-like features, such as higher IFN-γ competence and epigenetic remodeling of the IFNG promoter, during their terminal differentiation.

Alternatively spliced NKp30 isoforms affect the prognosis of gastrointestinal stromal tumors.

The natural killer (NK) cell receptor NKp30 is involved in the recognition of tumor and dendritic cells (DCs). Here we describe the influence of three NKp30 splice variants on the prognosis of gastrointestinal sarcoma (GIST), a malignancy that expresses NKp30 ligands and that is treated with NK-stimulatory KIT tyrosine kinase inhibitors. Healthy individuals and those with GIST show distinct patterns of transcription of functionally different NKp30 isoforms. In a retrospective analysis of 80 individuals with GIST, predominant expression of the immunosuppressive NKp30c isoform (over the immunostimulatory NKp30a and NKp30b isoforms) was associated with reduced survival of subjects, decreased NKp30-dependent tumor necrosis factor-α (TNF-α) and CD107a release, and defective interferon-γ (IFN-γ) and interleukin-12 (IL-12) secretion in the NK-DC cross-talk that could be restored by blocking of IL-10. Preferential NKp30c expression resulted partly from a single-nucleotide polymorphism at position 3790 in the 3' untranslated region of the gene encoding NKp30. The genetically determined NKp30 status predicts the clinical outcomes of individuals with GIST independently from KIT mutation.

Distinct roles for the NK cell-activating receptors in mediating interactions with dendritic cells and tumor cells.

NK cells are innate immune cells that are important in tumor immunity, but also have the ability to modulate the adaptive immune system through cytokine production or direct cell-cell interactions. This study investigates the interaction of NK cells with dendritic cells (DCs) and tumor cells, and the role of specific NK cell-activating receptors in this process. Primary rat NK cells and an NK cell line produced IFN-γ when cocultured with either DCs or the rat hepatoma cell line McA-RH7777 (McA). This NK cell activation by DCs and McA required cell-cell contact and was dependent on distinct NK-activating receptors. Silencing NK cell expression of NKp46 and NKp30 significantly diminished DC- and McA-mediated NK cell IFN-γ production, respectively. NK cells killed immature and mature DCs independently of NKp46, NKp30, and NKG2D; however, cytotoxicity against McA cells was dependent on NKp30 and NKG2D. Thus, we have shown in this study that NKp30 plays dual activating roles in NK-McA tumor interactions by mediating cytokine production and cytotoxicity. More importantly, NK cells are activated by both DCs and hepatoma cells to produce IFN-γ, but require distinct NK cell-activating receptors, NKp46 and NKp30, respectively. Our data suggest that therapeutics could be developed specifically to target NK-DC interactions without compromising NK tumor immunity.

Analysis of NK cell/DC interaction in NK-type lymphoproliferative disease of granular lymphocytes (LDGL): role of DNAM-1 and NKp30.

OBJECTIVE: Natural killer (NK) cells and dendritic cells (DC) can give rise to reciprocal functional interactions resulting in promotion of DC maturation, killing of immature DC (iDC), and proliferation of NK cells. In this study, we analyze whether, in NK-lymphoproliferative disease of granular lymphocytes (LDGL) patients, this function could be altered and contribute to the persistence of the disease. MATERIALS AND METHODS: Freshly isolated peripheral blood NK granular lymphocytes (GL) and NK cell lines derived from 13 different NK-LDGL patients were analyzed in coculture experiments to evaluate their ability to interact with monocyte-derived DCs (Mo-DC). RESULTS: As compared to NK cells isolated from healthy donors, NK-GLs displayed, in most cases, a reduced capability of promoting Mo-DC maturation and of killing iDC. These findings could be explained, at least in part, by the low expression levels of NKp30: an activating receptor involved in the molecular interactions occurring between NK cells and DC. We also show that, in the presence of DC-derived cytokines such as interleukin-12, in both patients and healthy individuals, DNAM-1 can cooperate with NKp30 to induce NK cells to kill DC, release tumor necrosis factor-alpha, and promote DC maturation. This contribution, however, is not sufficient to compensate for the defect in patients' NK cells. CONCLUSION: Besides expanding knowledge of the molecular basis of the NK/DC cross-talk, our study demonstrates that NK cells from NK-LDGL patients are impaired in their ability to interact with Mo-DC. The possible relationship between such abnormal NK cell/DC interactions and chronic NK cell proliferation are discussed.

Myeloid derived suppressor cells inhibit natural killer cells in patients with hepatocellular carcinoma via the NKp30 receptor.

UNLABELLED: Several immune suppressive mechanisms that evade the host immune response have been described in patients with hepatocellular carcinoma (HCC); one of these mechanisms is expansion of myeloid-derived suppressor cells (MDSCs). MDSCs have been shown to inhibit T cell responses in tumor-bearing mice, but little is known about these cells in humans. Here, we have analyzed and characterized the effect of MDSCs on the innate immune system, in particular, their interaction with natural killer (NK) cells in patients with HCC. MDSCs from patients with HCC inhibited autologous NK cell cytotoxicity and cytokine secretion when cultured together in vitro. This suppression was dependent on cell contact, but did not rely on the arginase activity of MDSCs, which is a hallmark function of these cells. However, MDSC-mediated inhibition of NK cell function was dependent mainly on the NKp30 on NK cells. CONCLUSION: Our study suggests a new role for MDSCs in patients with HCC in disarming the innate immune system and further contributing to the immune suppressor network in these patients. These findings have important implications when designing immunotherapy protocols.

Umbilical cord blood T cells express multiple natural cytotoxicity receptors after IL-15 stimulation, but only NKp30 is functional.

The natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46 are thought to be NK lineage restricted. Herein we show that IL-15 induces NCR expression on umbilical cord blood (UCB) T cells. NCRs were mainly on CD8(+) and CD56(+) UCB T cells. Only NKp30 was functional as demonstrated by degranulation, IFN-gamma release, redirected killing, and apoptosis. Since NCRs require adaptor proteins for function, the expressions of these adaptors were determined. The adaptors used by NKp30 and NKp46, FcepsilonR1gamma and CD3zeta, were detected in UCB T cells. There was a near absence of DAP12, the adaptor for NKp44, consistent with a hypofunctional state. NKp46 was on significantly fewer UCB T cells, possibly accounting for its lack of function. Adult peripheral blood (PB) T cells showed minimal NCR acquisition after culture with IL-15. Since UCB contains a high frequency of naive T cells, purified naive T cells from adult PB were tested. Although NKp30 was expressed on a small fraction of naive PB T cells, it was nonfunctional. In contrast to UCB, PB T cells lacked FcepsilonR1gamma expression. These results demonstrate differences between UCB and PB T cells regarding NCR expression and function. Such findings challenge the concept that NCRs are NK cell specific.