Lack of NKG2D in MAGT1-deficient patients is caused by hypoglycosylation.

Mutations in the X-linked gene MAGT1 cause a Congenital Disorder of Glycosylation (CDG), with two distinct clinical phenotypes: a primary immunodeficiency (XMEN disorder) versus intellectual and developmental disability. It was previously established that MAGT1 deficiency abolishes steady-state expression of the immune response protein NKG2D (encoded by KLRK1) in lymphocytes. Here, we show that the reduced steady-state levels of NKG2D are caused by hypoglycosylation of the protein and we pinpoint the exact site that is underglycosylated in MAGT1-deficient patients. Furthermore, we challenge the possibility that supplementation with magnesium restores NKG2D levels and show that the addition of this ion does not significantly improve NKG2D steady-state expression nor does it rescue the hypoglycosylation defect in CRISPR-engineered human cell lines. Moreover, magnesium supplementation of an XMEN patient did not result in restoration of NKG2D expression on the cell surface of lymphocytes. In summary, we demonstrate that in MAGT1-deficient patients, the lack of NKG2D is caused by hypoglycosylation, further elucidating the pathophysiology of XMEN/MAGT1-CDG.

Exploiting natural killer group 2D receptors for CAR T-cell therapy.

Chimeric antigen receptors (CARs) are genetically engineered proteins that combine an extracellular antigen-specific recognition domain with one or several intracellular T-cell signaling domains. When expressed in T cells, these CARs specifically trigger T-cell activation upon antigen recognition. While the clinical proof of principle of CAR T-cell therapy has been established in hematological cancers, CAR T cells are only at the early stages of being explored to tackle solid cancers. This special report discusses the concept of exploiting natural killer cell receptors as an approach that could broaden the specificity of CAR T cells and potentially enhance the efficacy of this therapy against solid tumors. New data demonstrating feasibility of this approach in humans and supporting the ongoing clinical trial are also presented.

Tetramethypyrazine inhibits renal cell carcinoma cells through inhibition of NKG2D signaling pathways.

Tetramethypyrazine (TMP), one of the active compounds extracted from the traditional Chinese medicinal herb (Chuanxiong), has been verified as an anticancer compound against several types of cancer. However, understanding of the molecular mechanisms have not been fully elucidated. In the present study, the anticancer efficacy of TMP was investigated in human clear cell renal cell carcinoma (ccRCC) cells. We showed that TMP significantly inhibited ccRCC cell viability, proliferation, apoptosis, invasion and migration through the methods of MTT, flow cytometry, wound healing and transwell assays. Furthermore, reverse transcription polymerase chain reaction (RT-PCR), western blotting and immunofluorescence results demonstrated TMP upregulation of the expression of NKG2D ligands (NKG2DLs) MHC class I chain-related molecules A and B (MICA/B) and epithelial cell expression marker of E-cadherin, and downregulation of mesenchymal cell expression markers of vimentin and fibronectin. Taken together, the inhibition of TMP on ccRCC cells might be mediated via inhibition of NKG2D related signaling pathway to further suppress epithelial-mesenchymal transition (EMT) progression. The binding of NKG2D to its ligands activates NK cells, giving the rationale for studies on the utilization of TMP as a potential cancer therapeutic compound to increase NK cells-mediated cytotoxicity against high MICA/B expression in cancer cells.

Mg2+ regulates cytotoxic functions of NK and CD8 T cells in chronic EBV infection through NKG2D.

The magnesium transporter 1 (MAGT1) is a critical regulator of basal intracellular free magnesium (Mg(2+)) concentrations. Individuals with genetic deficiencies in MAGT1 have high levels of Epstein-Barr virus (EBV) and a predisposition to lymphoma. We show that decreased intracellular free Mg(2+) causes defective expression of the natural killer activating receptor NKG2D in natural killer (NK) and CD8(+) T cells and impairs cytolytic responses against EBV. Notably, magnesium supplementation in MAGT1-deficient patients restores intracellular free Mg(2+) and NKG2D while concurrently reducing EBV-infected cells in vivo, demonstrating a link between NKG2D cytolytic activity and EBV antiviral immunity in humans. Moreover, these findings reveal a specific molecular function of free basal intracellular Mg(2+) in eukaryotic cells.

Hyperthermia increases natural killer cell cytotoxicity against SW-872 liposarcoma cell line.

BACKGROUND: Although there is convincing data in support of the effectiveness of hyperthermia in tumor therapy, the molecular mechanisms underlying the clinical effects of hyperthermia are still poorly understood. OBJECTIVE: To investigate natural killer (NK) cell cytotoxicity against heat-treated SW-872 and HeLa tumor cell lines. METHODS: NKG2D ligands and HLA class I transcription were examined using quantitative real-time PCR in treated tumor cell lines at 0, 2, 4, 6 and 12 h following thermal treatment at 39C and 42C for 1 h. The expression of MICA/B, ULBP1 and ULBP2 were also determined by flow cytometry. NK92-MI cytotoxic activity against heat-treated target cell lines was assessed by LDH release as well as annexin-V and 7-AAD assays. RESULTS: Our results showed that heat treatment at 39C improved the cytolytic activity of NK cells against SW-872 cells without increasing NKG2D ligand concentration or decreasing HLA class I levels. CONCLUSION: The observed increase in the cytotoxicity of NK cells against SW-872 cells after hyperthermia does not coincide with changes in MICA/B, ULBP1 and ULBP2 ligands of NKG2, however, the expression of other ligands in target cells may have made the cells susceptible to the cytotoxic effect of NK cells.

The nuclear factor-κB pathway down-regulates expression of the NKG2D ligand H60a in vitro: implications for use of nuclear factor-κB inhibitors in cancer therapy.

NKG2D ligands are cell surface proteins that activate NKG2D, a receptor used by natural killer (NK) cells to detect virus-infected and transformed cells. When tumour cells express high levels of NKG2D ligands, they are rejected by the immune system. Hence, reagents that increase NKG2D ligand expression on tumour cells can be important for tumour immunotherapy. To identify genes that regulate the NKG2D ligand H60a, we performed a microarray analysis of 3'-methylcholanthrene-induced sarcoma cell lines expressing high versus low H60a levels. A20, an inhibitor of nuclear factor-κB (NF-κB) activation, was differentially expressed in H60a-hi sarcoma cells. Correspondingly, treatment of tumour cells with inhibitors of NF-κB activation, such as sulfasalazine (slz), BAY-11-7085, or a non-phosphorylatable IκB, led to increased levels of H60a protein, whereas transduction of cells with an active form of IκB kinase-ß (IKKß) led to decreased levels of H60a. The regulation probably occurred at the transcriptional level, because NF-κB pathway inhibition led to increased H60a transcripts and promoter activity. Moreover, treatment of tumour cells with slz enhanced their killing by NK cells in vitro, suggesting that NF-κB inhibition can lead to tumour cell rejection. Indeed, when we blocked the NF-κB pathway specifically in tumour cells, there was decreased tumour growth in wild-type but not immune-deficient mice. Our results suggest that reagents that can block NF-κB activity specifically in the tumour and not the host immune cells would be efficacious for tumour therapy.

5-Fluorouracil and interferon-α immunochemotherapy enhances immunogenicity of murine pancreatic cancer through upregulation of NKG2D ligands and MHC class I.

Pancreatic cancer has the poorest prognosis of all gastrointestinal cancers, driving the need for new therapeutic approaches. Adjuvant 5-fluorouacil (5-FU) chemotherapy proved effective in increasing the survival of patients with resected tumors. Furthermore, the addition of interferon alpha (IFN-α) immunotherapy to 5-FU has shown encouraging clinical results. The aim of this study was to determine the relevance of different immune cell populations, namely natural killer (NK) cells, CD8 T cells, and dendritic cells, in the anticancer immune response mediated by the combination therapy using an orthotopic mouse model of pancreatic carcinoma and to get more insight into the underlying mechanisms of action. Depleting CD8 T cells, NK cells, or dendritic cells significantly reduced the anticancer effects mediated by the combination therapy. Tumors of mice treated with 5-FU+IFN-α harbored higher numbers of infiltrating NK cells in comparison with control mice. In addition, NK cells isolated from these mice showed enhanced cytotoxicity against Panc02 pancreatic cancer cells. Furthermore, 5-FU+IFN-α treatment increased the expression of major histocompatibility complex class I and NKG2D ligands on Panc02 cells that could be a potential key for enhancing the immunogenicity of tumors. Understanding how this combination therapy enhances the immunogenicity of pancreatic tumors in our model may provide potential predictive biomarkers. This will allow to evaluate the efficacy of this immunochemotherapy more effectively in future clinical trials and to identify patients who will benefit most from it.

Enhancement of natural killer cell activity in healthy subjects by Immulina®, a Spirulina extract enriched for Braun-type lipoproteins.

Immulina®, a commercial extract of Arthrospira (Spirulina) platensis is a potent activator of THP-1 monocytes and CD4+ T cells IN VITRO and enhances several immunological functions in mice. We further characterized Immulina® by determining that Braun-type lipoproteins are responsible for a major portion of the IN VITRO monocyte activation exhibited by this material. In order to understand the effect of Immulina® on NK cell activity, a pilot study was conducted on ten healthy North American individuals who supplemented their diet with Immulina® (400 mg/day) for seven days. We observed a 40% average increase in the killing of K562 tumor cells by NK cells (p < 0.01) after Immulina® supplementation. In a separate placebo-controlled, crossover study involving 11 healthy Danish subjects, we observed increased mRNA expression of the NK cell marker NKG2D by 37% (p = 0.02) and by 55% (p = 0.0003) after administration of Immulina® (200 mg and 400 mg per day, respectively) for seven days. The mRNA expression of the NK- and T-cell marker perforin increased by 75% (p = 0.008) after administration of 400 mg Immulina® per day. Both markers displayed significant dose-dependent effects (p = 0.0003 and p = 0.02, respectively). The ratio between CD56 (bright) and CD56 (dim) NK cells was not affected by Immulina® administration. In summary, two independent studies showed enhancement of NK cell activity following administration of Immulina® for seven days.