Checkpoint blockade enhances effector T cell function and has elicited long-term remission in a subset of patients with a broad spectrum of cancers. TIGIT is a checkpoint receptor thought to be involved in mediating T cell exhaustion in tumors; however, the relevance of TIGIT to the dysfunction of natural killer (NK) cells remains poorly understood. Here we found that TIGIT, but not the other checkpoint molecules CTLA-4 and PD-1, was associated with NK cell exhaustion in tumor-bearing mice and patients with colon cancer. Blockade of TIGIT prevented NK cell exhaustion and promoted NK cell-dependent tumor immunity in several tumor-bearing mouse models. Furthermore, blockade of TIGIT resulted in potent tumor-specific T cell immunity in an NK cell-dependent manner, enhanced therapy with antibody to the PD-1 ligand PD-L1 and sustained memory immunity in tumor re-challenge models. This work demonstrates that TIGIT constitutes a previously unappreciated checkpoint in NK cells and that targeting TIGIT alone or in combination with other checkpoint receptors is a promising anti-cancer therapeutic strategy.

Long non-coding RNAs (lncRNAs) have been shown to have important regulatory roles in cancer biology, and the lncRNA H19 is up-regulated in hypoxic stress and in some tumors. However, the contributions of H19 to gastric cancer remain largely unknown. In this study, we assayed the H19 expression level in gastric cancer tissues by real-time PCR, and defined the biological functions by flow cytometry and RNA immunoprecipitation. We demonstrated that H19 levels were markedly increased in gastric cancer cells and gastric cancer tissues compared with normal controls. Moreover, ectopic expression of H19 increased cell proliferation, whereas H19 siRNA treatment contributed to cell apoptosis in AGS cell line. We further verified that H19 was associated with p53, and that this association resulted in partial p53 inactivation. These data suggest an important role for H19 in the molecular etiology of gastric cancer and potential application of H19 in gastric cancer therapy.

Natural killer cells are important effector lymphocytes of the innate immune system, playing critical roles in antitumor and anti-infection host defense. Tumor progression or chronic infections, however, usually leads to exhaustion of NK cells, thus limiting the antitumor/infection potential of NK cells. In many tumors or chronic infections, multiple mechanisms might contribute to the exhaustion of NK cells, such as dysregulated NK cell receptors signaling, as well as suppressive effects by regulatory cells or soluble factors within the microenvironment. Better understanding of the characteristics, as well as the underlying mechanisms of NK cell exhaustion, not only should increase our understanding of the basic biology of NK cells but also could reveal novel NK cell-based antitumor/infection targets. Here, we provide an overview of our current knowledge on NK cell exhaustion in tumors, and in chronic infections.

These data suggest that c-Myc induction of CCAT1 holds an important role in gastric carcinoma and implicate the potential application of CCAT1 in the treatment of gastric carcinoma.

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Long non-coding RNAs (lncRNAs), a recently characterized class of noncoding RNAs, have been shown to have important regulatory roles and are de-regulated in a variety of tumors. However, the contributions of lncRNAs to gastric carcinoma and their functional mechanisms remain largely unknown. In this study, we found that lncRNA gastric carcinoma high expressed transcript 1 (lncRNA-GHET1) was up-regulated in gastric carcinoma. The over-expression of this lncRNA correlates with tumor size, tumor invasion and poor survival. Gain-of-function and loss-of-function analyses demonstrated that GHET1 over-expression promotes the proliferation of gastric carcinoma cells in vitro and in vivo. Knockdown of GHET1 inhibits the proliferation of gastric carcinoma cells. RNA pull-down and immunoprecipitation assays confirmed that GHET1 physically associates with insulin-like growth factor 2 mRNA binding protein 1 (IGF2BP1) and enhances the physical interaction between c-Myc mRNA and IGF2BP1, consequently increasing the stability of c-Myc mRNA and expression. The expression of GHET1 and c-Myc is strongly correlated in gastric carcinoma tissues. Depletion of c-Myc abolishes the effects of GHET1 on proliferation of gastric carcinoma cells. Taken together, these findings indicate that GHET1 plays a pivotal role in gastric carcinoma cell proliferation via increasing c-Myc mRNA stability and expression, which suggests potential use of GHET1 for the prognosis and treatment of gastric carcinoma.

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NK cells play important roles in the innate immune responses against tumors. The effector function of NK cells relies on the integration of activating and inhibitory signals. Emerging checkpoint receptors and molecules are being revealed to mediate NK cell dysfunction in the tumor microenvironment. Inhibition of some NK cell surface checkpoint receptors has displayed the potential to reverse NK cell dysfunction in tumors, and to boost anti-tumor immunity, both in clinical trials (anti-KIR and anti-NKG2A), and in preclinical studies (e.g., anti-TIGIT, and anti-CD96). To fully exploit the potential of NK–based checkpoint immunotherapy, more understanding of the regional features of NK cells in the tumor microenvironment is required. This will provide valuable information regarding the dynamic nature of NK cell immune response against tumors, as well as novel checkpoints or pathways to be targeted. In this Review, we discuss recent advances in the understanding of NK cell dysfunction in tumors, as well as emerging strategies of NK-based checkpoint immunotherapy for tumors.