Upregulated expression of NKG2D and its ligands give potential therapeutic targets for patients with thymoma

The Role and Regulation of the NKG2D/NKG2D Ligand System in Cancer

The family of human NKG2D ligands (NKG2DL) consists of eight stress-induced molecules. Over 80% of human cancers express these ligands on the surface of tumour cells and/or associated stromal elements. In mice, NKG2D deficiency increases susceptibility to some types of cancer, implicating this system in immune surveillance for malignancy. However, NKG2DL can also be shed, released via exosomes and trapped intracellularly, leading to immunosuppressive effects. Moreover, NKG2D can enhance chronic inflammatory processes which themselves can increase cancer risk and progression. Indeed, tumours commonly deploy a range of countermeasures that can neutralise or even corrupt this surveillance system, tipping the balance away from immune control towards tumour progression. Consequently, the prognostic impact of NKG2DL expression in human cancer is variable. In this review, we consider the underlying biology and regulation of the NKG2D/NKG2DL system and its expression and role in a range of cancer types. We also consider the opportunities for pharmacological modulation of NKG2DL expression while cautioning that such interventions need to be carefully calibrated according to the biology of the specific cancer type.

Innate lymphoid cells in early tumor development

Innate and adaptive immune cells monitor, recognize, and eliminate transformed cells. Innate lymphoid cells (ILCs) are innate counterparts of T cells that play a key role in many facets of the immune response and have a profound impact on disease states, including cancer. ILCs regulate immune responses by responding and integrating a wide range of signals within the local microenvironment. As primarily tissue-resident cells, ILCs are ideally suited to sense malignant transformation and initiate anti-tumor immunity. However, as ILCs have been associated with anti-tumor and pro-tumor activities in established tumors, they could potentially have dual functions during carcinogenesis by promoting or suppressing the malignant outgrowth of premalignant lesions. Here we discuss emerging evidence that shows that ILCs can impact early tumor development by regulating immune responses against transformed cells, as well as the environmental cues that potentially induce ILC activation in premalignant lesions.

Clinical Impact of Natural Killer Group 2D Receptor Expression and That of Its Ligand in Ovarian Carcinomas: A Retrospective Study

PURPOSE

Natural killer (NK) cells are innate immune cells with antitumor activity. NKG2D is the most important activating receptor expressed on the NK cell surface; this receptor binds to the ligands MICA/B and ULBPs to activate NK cells. The current study aimed to evaluate the expression of NKG2D by NK cells, and to the evaluate expression of its ligands in ovarian carcinomas; it also examined the clinical relevance of NK receptor/ligand expression by analyzing the relationship between expression, clinicopathological parameters, and prognosis.

MATERIALS AND METHODS

Formalin-fixed paraffin-embedded archival ovarian high-grade serous carcinoma (HGSC, n=79) tissue samples were used for tissue microarray analysis. The expressions of NK cell markers (CD56 and NKG2D) and NKG2D ligands (MICA/B, ULBP1, ULBP3, and ULBP2/5/6) in carcinoma tissues were evaluated by immunohistochemical staining, and the association between these results and clinical prognostic parameters was analyzed statistically.

RESULTS

ULBP1 was highly expressed in 51 cases (64.6%), and ULBP2/5/6 was highly expressed in 56 cases (70.9%) of HGSC. High expression of ULBP1 and ULBP2/5/6 was significantly associated with lower recurrence of HGSC, whereas high expression of ULBP3 was significantly associated with higher recurrence. Multivariate Cox regression analysis revealed that high expression of ULBP1 was associated with increased overall survival and a decreased hazard ratio (0.150, p=0.044), suggesting that it is an independent predictor of better survival.

CONCLUSION

High expression of ULBP1 predicts a better prognosis for HGSC, suggesting that ULBP1 expression could be a novel prognostic indicator in this subset of carcinomas.

Ultrasound-guided radiofrequency ablation enhances natural killer-mediated antitumor immunity against liver cancer

For patients with liver cancer who are not sufficiently fit for surgical resection, radiofrequency ablation (RFA) is an effective and low risk treatment modality; however, the mechanism underlying this procedure is not fully understood. In the present study, a series of experiments were conducted, which demonstrated that RFA therapy stimulates innate antitumor immunity via directly enhancing natural killer (NK) cell cytotoxicity, thus achieving a favorable outcome for patients with liver tumors. It was determined that the percentage of NK cells within the peripheral blood of the rabbits in the RFA treatment groups were significantly higher, compared with the control groups. The levels of interferon-γ and tumor necrosis factor-α in NK cells were also significantly upregulated following thermal coagulation induced via RFA. In addition, RFA enhanced the NK cell receptor, NK group 2D (NKG2D), expression and NK cell antitumor cytotoxicity in hepatic cancer cells. The results indicated that the RFA treatment could effectively eliminate liver tumors via enhancing NK-mediated antitumor activity and NKG2D expression.

Polymorphisms in MICA, but not in DEPDC5, HCP5 or PNPLA3, are associated with chronic hepatitis C-related hepatocellular carcinoma

Recently, the MICA rs2596542 and DEPDC5 rs1012068 variants in Japanese individuals as well as the HCP5 rs2244546 and PNPLA3 rs738409 variants in European individuals have been found associated with hepatocellular carcinoma (HCC). The present study determined which single nucleotide polymorphism (SNP) is the most predictive for developing hepatitis C virus (HCV)-related HCC in a Japanese cohort. Of the 4 SNPs analysed, only the MICA genotypes were significantly associated with development of HCC (p = 0.0185). The major (MA), hetero (HE), and minor (MI) genotypes occurred in 40%, 41%, and 19% of HCC patients and in 43%, 47%, and 10% of non-HCC patients, respectively. Interestingly, the MICA genotype was significantly correlated with MICA mRNA and soluble protein levels. In patients older than 70 years, the MI genotype was significantly associated with HCC development. In addition, the MI genotype was related to HCC development when the platelet count range was 10-15 × 104/μL, corresponding with the fibrosis stage; but not when the range was less than 10, indicating advanced fibrosis; or greater than 15 × 104/μL, as mild fibrosis. Thus, polymorphisms in MICA, but not in DEPDC5, HCP5 or PNPLA3, are associated with HCC development in Japanese patients with chronic HCV infection.

NK cell activating receptor ligand expression in lymphangioleiomyomatosis is associated with lung function decline

Lymphangioleiomyomatosis (LAM) is a rare lung disease of women that leads to progressive cyst formation and accelerated loss of pulmonary function. Neoplastic smooth muscle cells from an unknown source metastasize to the lung and drive destructive remodeling. Given the role of NK cells in immune surveillance, we postulated that NK cell activating receptors and their cognate ligands are involved in LAM pathogenesis. We found that ligands for the NKG2D activating receptor UL-16 binding protein 2 (ULBP2) and ULBP3 are localized in cystic LAM lesions and pulmonary nodules. We found elevated soluble serum ULBP2 (mean = 575 pg/ml ± 142) in 50 of 100 subjects and ULBP3 in 30 of 100 (mean = 8,300 pg/ml ± 1,515) subjects. LAM patients had fewer circulating NKG2D⁺ NK cells and decreased NKG2D surface expression. Lung function decline was associated with soluble NKG2D ligand (sNKG2DL) detection. The greatest rate of decline forced expiratory volume in 1 second (FEV₁, -124 ± 30 ml/year) in the 48 months after enrollment (NHLBI LAM Registry) occurred in patients expressing both ULBP2 and ULBP3, whereas patients with undetectable sNKG2DL levels had the lowest rate of FEV₁ decline (-32.7 ± 10 ml/year). These data suggest a role for NK cells, sNKG2DL, and the innate immune system in LAM pathogenesis.

Abnormal expression levels of sMICA and NKG2D are correlated with poor prognosis in pancreatic cancer

Soluble major histocompatibility complex class I-related chain A molecules (sMICA) and natural-killer group 2 member D (NKG2D) not only correlate with tumorigenesis and progression, but also with tumor invasion and metastasis. In this study, we used immunohistochemistry to investigate the correlation and prognostic significance of the differential expression of sMICA and NKG2D in pancreatic carcinoma and paracarcinoma tissues from 70 patients with pancreatic carcinomas. The results showed that sMICA expression was significantly (P<0.05) higher in tumor tissues (67.1%) than that in adjacent nontumor tissues (31.4%), whereas NKG2D expression was significantly (P<0.001) lower in tumor tissues (32.9%) than that in adjacent nontumor tissues (60.0%). Spearman’s rank correlation test showed a negative correlation between the expression of sMICA and that of NKG2D (r=−0.676, P<0.001). Kaplan–Meier survival analysis showed that a high sMICA expression was significantly correlated with decreased disease-free survival (DFS) (P<0.001) and overall survival (OS) (P<0.001), while a high NKG2D expression was significantly associated with increased DFS (P=0.001) and OS (P=0.001) of the patients. Multivariate analysis showed that a high sMICA expression was an independent predictive factor for poor DFS (P<0.001) and OS (P=0.012); but low NKG2D expression was not an independent prognostic factor for poor DFS (P=0.238) and OS (P=0.574). In conclusion, our findings suggest that the expression levels of sMICA and NKG2D are abnormal and negatively correlated with one another in pancreatic carcinoma tissues; they may be considered as valuable biomarkers for the prognosis of pancreatic carcinoma.