A novel mechanism for cancer cells to evade immune attack by NK cells: The interaction between NKp44 and proliferating cell nuclear antigen

Prospective Molecular Targets for Natural Killer Cell Immunotherapy against Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common type of primary malignant brain tumor and has a dismal overall survival rate. To date, no GBM therapy has yielded successful results in survival for patients beyond baseline surgical resection, radiation, and chemotherapy. Immunotherapy has taken the oncology world by storm in recent years and there has been movement from researchers to implement the immunotherapy revolution into GBM treatment. Natural killer (NK) cell-based immunotherapies are a rising candidate to treat GBM from multiple therapeutic vantage points: monoclonal antibody therapy targeting tumor-associated antigens (TAAs), immune checkpoint inhibitors, CAR-NK cell therapy, Bi-specific killer cell engagers (BiKEs), and more. NK therapies often focus on tumor antigens for targeting. Here, we reviewed some common targets analyzed in the fight for GBM immunotherapy relevant to NK cells: EGFR, HER2, CD155, and IL-13Rα2. We further propose investigating the Lectin-like Transcript 1 (LLT1) and cell surface proliferating cell nuclear antigen (csPCNA) as targets for NK cell-based immunotherapy.

Targeting proliferating cell nuclear antigen (PCNA) for cancer therapy

Proliferating cell nuclear antigen (PCNA) is an essential scaffold protein in many cellular processes. It is best known for its role as a DNA sliding clamp and processivity factor during DNA replication, which has been extensively reviewed by others. However, the importance of PCNA extends beyond its DNA-associated functions in DNA replication, chromatin remodelling, DNA repair and DNA damage tolerance (DDT), as new non-canonical roles of PCNA in the cytosol have recently been identified. These include roles in the regulation of immune evasion, apoptosis, metabolism, and cellular signalling. The diverse roles of PCNA are largely mediated by its myriad protein interactions, and its centrality to cellular processes makes PCNA a valid therapeutic anticancer target. PCNA is expressed in all cells and plays an essential role in normal cellular homeostasis; therefore, the main challenge in targeting PCNA is to selectively kill cancer cells while avoiding unacceptable toxicity to healthy cells. This chapter focuses on the stress-related roles of PCNA, and how targeting these PCNA roles can be exploited in cancer therapy.

mAb14, a Monoclonal Antibody against Cell Surface PCNA: A Potential Tool for Sezary Syndrome Diagnosis and Targeted Immunotherapy

Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common types of primary cutaneous T-cell lymphoma (CTCL). Proliferating cell nuclear antigen (PCNA) is expressed on the cell surface of cancer cells (csPCNA), but not on normal cells. It functions as an immune checkpoint ligand by interacting with natural killer (NK) cells through the NK inhibitory receptor NKp44, leading to the inhibition of NK cytotoxicity. A monoclonal antibody (mAb14) was established to detect csPCNA on cancer cells and block their interaction with NKp44. In this study, three CTCL cell lines and peripheral blood mononuclear cells (PBMCs) from patients with SS and healthy donors were analyzed for csPCNA using mAb14, compared to monoclonal antibody PC10, against nuclear PCNA (nPCNA). The following assays were used: immunostaining, imaging flow cytometry, flow cytometry, cell sorting, cell cycle analysis, ELISA, and the NK-cell cytotoxic assay. mAb14 successfully detected PCNA on the membrane and in the cytoplasm of viable CTCL cell lines associated with the G2/M phase. In the Sézary PBMCs, csPCNA was expressed on lymphoma cells that had an atypical morphology and not on normal cells. Furthermore, it was not expressed on PBMCs from healthy donors. In the co-culture of peripheral blood NK (pNK) cells with CTCL lines, mAb14 increased the secretion of IFN-γ, indicating the reactivation of pNK activity. However, mAb14 did not enhance the cytotoxic activity of pNK cells against CTCL cell lines. The unique expression of csPCNA detected by mAb14 suggests that csPCNA and mAb14 may serve as a potential biomarker and tool, respectively, for detecting malignant cells in SS and possibly other CTCL variants.

Immunological classification of hepatitis B virus-positive hepatocellular carcinoma by transcriptome analysis

BACKGROUND

Hepatitis B virus (HBV) infection is a major factor responsible for HBV+ hepatocellular carcinoma (HCC).

AIM

An immunological classification of HBV+ HCC may provide both biological insights and clinical implications for this disease.

METHODS

Based on the enrichment of 23 immune signatures, we identified two immune-specific subtypes (Imm-H and Imm-L) of HBV+ HCC by unsupervised clustering. We showed that this subtyping method was reproducible and predictable by analyzing three different datasets.

RESULTS

Compared to Imm-L, Imm-H displayed stronger immunity, more stromal components, lower tumor purity, lower stemness and intratumor heterogeneity, lower-level copy number alterations, higher global methylation level, and better overall and disease-free survival prognosis. Besides immune-related pathways, stromal pathways (ECM receptor interaction, focal adhesion, and regulation of actin cytoskeleton) and neuro-related pathways (neuroactive ligand-receptor interaction, and prion diseases) were more highly enriched in Imm-H than in Imm-L. We identified nine proteins differentially expressed between Imm-H and Imm-L, of which MYH11, PDCD4, Dvl3, and Syk were upregulated in Imm-H, while PCNA, Acetyl-a-Tubulin-Lys40, ER-α_pS118, Cyclin E2, and β-Catenin were upregulated in Imm-L.

CONCLUSION

Our data suggest that “hot” tumors have a better prognosis than “cold” tumors in HBV+ HCC and that “hot” tumors respond better to immunotherapy.

Cross-Talk Between Tumor Cells Undergoing Epithelial to Mesenchymal Transition and Natural Killer Cells in Tumor Microenvironment in Colorectal Cancer

Tumor cells undergoing epithelial to mesenchymal transition (EMT) and immune cells in tumor microenvironment (TME) reciprocally influence each other. Immune cells, by supplying TME with bioactive molecules including cytokines, chemokines, enzymes, metabolites, and by physical interactions with tumor cells via their receptors, represent an important factor that affects EMT. Chronical inflammation in TME favorizes tumor growth and invasiveness and stimulates synthesis of EMT promoting transcription factors. Natural killer (NK) cells, owing to their unique ability to exert cytotoxic function independent of major histocompatibility (MHC)-mediated antigen presentation, play a significant role in the control of metastasis in colorectal cancer (CRC). Although, the cross-talk between immune cells and tumor cells in general favors the induction of EMT and inhibition of antitumor immune responses, there are some changes in the immunogenicity of tumor cells during EMT of CRC cells that increase their susceptibility to NK cell cytotoxic lysis. However, suppressive TME downmodulates the expression of activating NK cell receptors, decreases the expression of activating and increases the expression of inhibitory NK cell ligands on tumor cells, and impairs NK cell metabolism that altogether negatively affects the overall NK cell function. Furthermore, process of EMT is often associated with increased expression of programmed cell death ligand (PD-L) and expression of immune checkpoint molecules PD-1, TIGIT, and TIM3 on functionally exhausted NK cells in TME in CRC. In this review we discuss modalities of cross-talk between tumor cells and NK cells, with regard of EMT-driven changes.

Expression of NK cell receptor ligands in primary colorectal cancer tissue in relation to the phenotype of circulating NK- and NKT cells, and clinical outcome

INTRODUCTION

Natural killer (NK) cells and natural killer T (NKT) cells are implicated in the development and progression of colorectal cancer (CRC). Tumor cells express NK cell receptor ligands that modulate their function. This study aimed to investigate the expression of such ligands in CRC in relation to the phenotype of circulating NK- and NKT cells, and clinical outcome.

METHODS

Primary tumor tissues were analyzed for protein expression of NK cell ligands using immunohistochemistry with automated image analysis in a cohort of 78 CRC patients. For 24 of the 78 patients, RNA expression of NK cell ligands was analyzed in primary tumor tissue using RNA sequencing. Receptor expression on circulating NK- and NKT cells was previously measured by us in 71 of the 78 patients using flow cytometry.

RESULTS

High Proliferating Cell Nuclear Antigen (PCNA) protein expression in the primary tumor associated with shorter disease-free survival (DFS) of CRC patients (P = 0.026). A trend was observed towards shorter DFS in CRC patients with above-median galectin-3 protein expression in the primary tumor (P = 0.055). High protein expression of galectin-3, CD1d, and human leukocyte antigen (HLA) class I, and high RNA expression of UL16-binding protein (ULBP)-1, -2, and -5, and HLA-E in the tumor tissue correlated with low expression of the corresponding receptors on circulating NK- or NKT cells (P < 0.05).

CONCLUSIONS

Galectin-3 and PCNA expression in the primary tumor may be prognostic biomarkers in CRC patients. Furthermore, our results suggest that NK cell receptor ligands expressed by tumor cells may modulate the phenotype of circulating NK- and NKT cells, and facilitate immune escape of metastasizing cells.

Immunomodulation of the Natural Killer Cell Phenotype and Response during HCV Infection

Hepatitis C virus (HCV) infection develops into chronic hepatitis in over two-thirds of acute infections. While current treatments with direct-acting antivirals (DAAs) achieve HCV eradication in >95% of cases, no vaccine is available and re-infection can readily occur. Natural killer (NK) cells represent a key cellular component of the innate immune system, participating in early defence against infectious diseases, viruses, and cancers. When acute infection becomes chronic, however, NK cell function is altered. This has been well studied in the context of HCV, where changes in frequency and distribution of NK cell populations have been reported. While activating receptors are downregulated on NK cells in both acute and chronic infection, NK cell inhibiting receptors are upregulated in chronic HCV infection, leading to altered NK cell responsiveness. Furthermore, chronic activation of NK cells following HCV infection contributes to liver inflammation and disease progression through enhanced cytotoxicity. Consequently, the NK immune response is a double-edged sword that is a significant component of the innate immune antiviral response, but persistent activation can drive tissue damage during chronic infection. This review will summarise the role of NK cells in HCV infection, and the changes that occur during HCV therapy.

Dormant tumor cells interact with memory CD8+ T cells in RET transgenic mouse melanoma model

Melanoma is an aggressive form of skin-cancer. Melanoma cells are characterized by their plasticity, resulting in therapy resistance. Using RET transgenic mouse melanoma model, we characterized dormant tumor cells accumulated in the bone marrow (BM) and investigated their interaction with effector memory CD8⁺ T cells. We found that cells expressing melanoma-associated antigen tyrosinase related protein (TRP)-2 and stemness marker CD133 represented less than 1.5% of all melanoma cells in primary skin lesions and metastatic lymph nodes. The majority of these cells were negative for the proliferation marker Ki67. In the BM, CD133⁺TRP-2⁺ melanoma cells displayed an aberrant expression of p16, p27, Ki67 and PCNA proteins, suggesting their dormant phenotype. Moreover, these cells were characterized by an elevated expression of various molecules characterized stemness, metastatic, angiogenic and immunosuppressive properties such as CD271, CD34, HIF-1α, CXCR3, CXCR4, VEGR2, PD-L1, CTLA-4, CD39 and CCR4 as compared to their CD133^- counterparts. Disseminated BM dormant TRP-2⁺ tumor cells were found to be co-localized with memory CD8⁺ T cells. Our data suggest that these dormant melanoma cells in the BM could play an important role in the maintenance of memory T cells in the BM.

Targeting the non-canonical roles of PCNA modifies and increases the response to targeted anti-cancer therapy

Receptor tyrosine kinases (RTKs), such as HER2 and/or EGFR are important therapeutic targets in multiple cancer cells. Low and/or short response to targeted therapies are often due to activation of compensatory signaling pathways, and therefore a combination of kinase inhibitors with other anti-cancer therapies have been proposed as promising strategies. PCNA is recently shown to have non-canonical cytosolic roles, and targeting PCNA with a cell-penetrating peptide containing the PCNA-interacting motif APIM is shown to mediate changes in central signaling pathways such as PI3K/Akt and MAPK, acting downstream of multiple RTKs. In this study, we show how targeting PCNA increased the anti-cancer activity of EGFR/HER2/VEGFR inhibition in vitro as well as in vivo. The combination treatment resulted in reduced tumor load and increased the survival compared to either single agent treatments. The combination treatment affected multiple cellular signaling responses not seen by EGFR/HER2/VEGFR inhibition alone, and changes were seen in pathways determining protein degradation, ER-stress, apoptosis and autophagy. Our results suggest that targeting the non-canonical roles of PCNA in cellular signaling have the potential to improve targeted therapies.

NKp44-NKp44 Ligand Interactions in the Regulation of Natural Killer Cells and Other Innate Lymphoid Cells in Humans

Natural Killer (NK) cells are potent cytotoxic cells belonging to the family of Innate Lymphoid Cells (ILCs). Their most characterized effector functions are directed to the control of aberrant cells in the body, including both transformed and virus-infected cells. NK cell-mediated recognition of abnormal cells primarily occurs through receptor-ligand interactions, involving an array of inhibitory and activating NK receptors and different types of ligands expressed on target cells. While most of the receptors have become known over many years, their respective ligands were only defined later and their impressive complexity has only recently become evident. NKp44, a member of Natural Cytotoxicity Receptors (NCRs), is an activating receptor playing a crucial role in most functions exerted by activated NK cells and also by other NKp44⁺ immune cells. The large and heterogeneous panel of NKp44 ligands (NKp44L) now includes surface expressed glycoproteins and proteoglycans, nuclear proteins that can be exposed outside the cell, and molecules that can be either released in the extracellular space or carried in extracellular vesicles. Recent findings have extended our knowledge on the nature of NKp44L to soluble plasma glycoproteins, such as secreted growth factors or extracellular matrix (ECM)-derived glycoproteins. NKp44L are induced upon tumor transformation or viral infection but may also be expressed in normal cells and tissues. In addition, NKp44-NKp44L interactions are involved in the crosstalk between NK cells and different innate and adaptive immune cell types. NKp44 expression in different ILCs located in tissues further extends the potential role of NKp44-NKp44L interactions.

T-cells "à la CAR-T(e)" - Genetically engineering T-cell response against cancer

The last decade will be remembered as the dawn of the immunotherapy era during which we have witnessed the approval by regulatory agencies of genetically engineered CAR T-cells and of checkpoint inhibitors for cancer treatment. Understandably, T-lymphocytes represent the essential player in these approaches. These cells can mediate impressive tumor regression in terminally-ill cancer patients. Moreover, they are amenable to genetic engineering to improve their function and specificity. In the present review, we will give an overview of the most recent developments in the field of T-cell genetic engineering including TCR-gene transfer and CAR T-cells strategies. We will also elaborate on the development of other types of genetic modifications to enhance their anti-tumor immune response such as the use of co-stimulatory chimeric receptors (CCRs) and unconventional CARs built on non-antibody molecules. Finally, we will discuss recent advances in genome editing and synthetic biology applied to T-cell engineering and comment on the next challenges ahead.

Molecular characterization and function analysis of a nucleotide excision repair gene Rad23 from Litopenaeus vannamei after Vibrio alginolyticus challenge

Nucleotide excision repair (NER) removes many different types of DNA lesions, and NER related host factors are reported to aid recovery steps during viral integration. Here, we report the identification and characterization of a DNA repair gene Rad23 from Litopenaeus vannamei and explore its role in innate immunity of crustaceans. LvRad23 contains a1149 bp open reading frame (ORF) which encodes a 382 amino acids protein with predicted theoretical isoelectric point of 4.21. LvRad23 was ubiquitously expressed in the muscle, eyestalk, gill, stomach, heart, legs, intestine, and hepatopancreas in order from high to low and LvRad23 protein was showed to be located in the cytoplasm of Drosophila S2 cells. The homology analysis showed that it has a high sequence homology with Rad23 protein from Marsupenaeus japonicus. Vibrio alginolyticus challenge induced a remarkable up-regulation of LvRad23 mRNA in hepatopancreas. Knocking down LvRad23can interfere the NER pathway by down regulating the expression of replication protein A (RPA) and proliferating cell nuclear antigen (PCNA). However it didn't cause any significant difference on total hemocyte count (THC) between LvRad23-silenced and non-silenced group.LvRad23-silenced then challenge with V. alginolyticus inducing high level of reactive oxygen species (ROS) and DNA damage in hemolymph. As well as decreased THC, which seriously diminished the innate immune system of L. vannamei. Meanwhile, the NER pathway was reactived by enhancing the expression of LvRad23 and promoting the production of LvPCNA to resist apoptosis and maintain proliferation of hemolymph cells in the later stage. Our results suggest that LvRad23 plays a vital role in shrimp specific immune response to V. alginolytcus through its participation in NER pathway.

Prostaglandin E2 Secreted by Thyroid Cancer Cells Contributes to Immune Escape Through the Suppression of Natural Killer (NK) Cell Cytotoxicity and NK Cell Differentiation

Natural killer (NK) cells play important roles in immune surveillance. However, the tumor microenvironment suppresses NK cell function and allows cancer cells to evade immune detection. In this study, we investigated whether the thyroid cancer cell microenvironment has this effect on NK cells. We found that prostaglandin (PG) E2 produced by thyroid cancer cells suppressed the cytolytic activity of NK cells by inhibiting the expression of the natural cytotoxicity receptors NKp44 and NKp30 and the death receptor tumor necrosis factor-related apoptosis-inducing ligand. PGE2 and cyclooxygenase-2 were highly expressed in thyroid cancer cells; moreover, anaplastic thyroid cancer cells released higher amounts of PGE2 than the papillary subtype, which was associated with suppression of NK cell-inducing nuclear factor-κB and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways via PGE2 receptor (EP) 2 and EP4 expressed on the NK cell surface. In addition, PGE2 inhibited the functional maturation of NK cells and reduced their cytotoxicity against target cells. These results indicate that PGE2 promotes thyroid cancer progression by inhibiting NK cell maturation and cytotoxicity. Thus, therapeutic strategies that target PGE2 in thyroid cancer could potentiate the immune response and improve patient prognosis.

NKp44-Derived Peptide Binds Proliferating Cell Nuclear Antigen and Mediates Tumor Cell Death

Proliferating cell nuclear antigen (PCNA) is considered as a hub protein and is a key regulator of DNA replication, repair, cell cycle control, and apoptosis. PCNA is overexpressed in many cancer types, and PCNA overexpression is correlated with cancer virulence. Membrane-associated PCNA is a ligand for the NKp44 (NCR2) innate immune receptor. The purpose of this study was to characterize the PCNA-binding site within NKp44. We have identified NKp44-derived linear peptide (pep8), which can specifically interact with PCNA and partly block the NKp44–PCNA interaction. We then tested whether NKp44-derived pep8 (NKp44-pep8) fused to cell-penetrating peptides (CPPs) can be employed for targeting the intracellular PCNA for the purpose of anticancer therapy. Treatment of tumor cells with NKp44-pep8, fused to R11-NLS cell-penetrating peptide (R11-NLS-pep8), reduced cell viability and promoted cell death, in various murine and human cancer cell lines. Administration of R11-NLS-pep8 to tumor-bearing mice suppressed tumor growth in the 4T1 breast cancer and the B16 melanoma in vivo models. We therefore identified the NKp44 binding site to PCNA and further developed an NKp44-peptide-based agent that can inhibit tumor growth through interfering with the function of intracellular PCNA in the tumor cell.

Targeting Multiple Tumors Using T-Cells Engineered to Express a Natural Cytotoxicity Receptor 2-Based Chimeric Receptor

Recent developments in cancer treatment are demonstrating the increasing and powerful potential of immunotherapeutic strategies. In this regard, the adoptive transfer of tumor-specific T-lymphocytes approaches can lead to tumor regression in cancer patients. More recently, the use of T-cells genetically engineered to express cancer-specific receptors such as the anti-CD19 chimeric antigen receptor (CAR) continues to show promise for the treatment of hematological malignancies. Still, there is a crucial need to develop efficient CAR-T cell approaches for the treatment of solid tumors. It has been shown that other lymphocytes such as natural killer (NK) cells can demonstrate potent antitumor function—nonetheless, their use in immunotherapy is rather limited due to difficulties in expanding these cells to therapeutically relevant numbers and to suppression by endogenous inhibitory mechanisms. Cancer recognition by NK cells is partly mediated by molecules termed natural cytotoxicity receptors (NCRs). In the present study, we hypothesize that it is possible to endow T-cells with an NK recognition pattern, providing them with a mean to recognize tumor cells, in a non-MHC restricted way. To test this, we genetically modified human T-cells with different chimeric receptors based on the human NCR2 molecule and then assessed their antitumor activity in vitro and in vivo. Our results show that expression in primary lymphocytes of an NCR2-derived CAR, termed s4428z, confers T-cells with the ability to specifically recognize heterogeneous tumors and to mediate tumor cytotoxicity in a mouse model. This study demonstrates the benefit of combining tumor recognition capability of NK cells with T cell effectiveness to improve cancer immunotherapy.

NKp44 and NKp30 splice variant profiles in decidua and tumor tissues: a comparative viewpoint

NKp44 and NKp30 splice variant profiles have been shown to promote diverse cellular functions. Moreover, microenvironment factors such as TGF-β, IL-15 and IL-18 are able to influence both NKp44 and NKp30 splice variant profiles, leading to cytokine-associated profiles. Placenta and cancerous tissues have many similarities; both are immunologically privileged sites and both share immune tolerance mechanisms to support tissue development. Therefore, we studied the profiles of NKp44 and NKp30 splice variants in these states by comparing (i) decidua from pregnancy disorder and healthy gestation and (ii) matched normal and cancer tissue. Decidua samples had high incidence of both NKp44 and NKp30. In cancerous state it was different; while NKp30 expression was evident in most cancerous and matched normal tissues, NKp44 incidence was lower and was mostly associated with the cancerous tissues. A NKp44-1dominant inhibitory profile predominated in healthy pregnancy gestation. Interestingly, the NKp44-2/3 activation profile becomes the leading profile in spontaneous abortions, whereas balanced NKp44 profiles were observed in preeclampsia. In contrast, a clear preference for the NKp30a/b profile was evident in the 1st trimester decidua, yet no significant differences were observed for NKp30 profiles between healthy gestation and spontaneous abortions/preeclampsia. Both cancerous and matched normal tissues manifested balanced NKp30c inhibitory and NKp30a/b activation profiles with a NKp44-1dominant profile. However, a shift in NKp30 profiles between matched normal and cancer tissue was observed in half of the cases. To summarize, NKp44 and NKp30 splice variants profiles are tissue/condition specific and demonstrate similarity between placenta and cancerous tissues.

Survival in acute myeloid leukemia is associated with NKp44 splice variants

NKp44 is a receptor encoded by the NCR2 gene, which is expressed by cytokine-activated natural killer (NK) cells that are involved in anti-AML immunity. NKp44 has three splice variants corresponding to NKp44ITIM+ (NKp44-1) and NKp44ITIM- (NKp44-2, and NKp44-3) isoforms. RNAseq data of AML patients revealed similar survival of NKp46+NKp44+ and NKp46+NKp44- patients. However, if grouped according to the NKp44 splice variant profile, NKp44-1 expression was significantly associated with poor survival of AML patients. Moreover, activation of PBMC from healthy controls showed co-dominant expression of NKp44-1 and NKp44-3, while primary NK clones show more diverse NKp44 splice variant profiles. Cultured primary NK cells resulted in NKp44-1 dominance and impaired function associated with PCNA over-expression by target cells. This impaired functional phenotype could be rescued by blocking of NKp44 receptor. Human NK cell lines revealed co-dominant expression of NKp44-1 and NKp44-3 and showed a functional phenotype that was not inhibited by PCNA over-expression. Furthermore, transfection-based overexpression of NKp44-1, but not NKp44-2/NKp44-3, reversed the endogenous resistance of NK-92 cells to PCNA-mediated inhibition, and resulted in poor formation of stable lytic immune synapses. This research contributes to the understanding of AML prognosis by shedding new light on the functional implications of differential splicing of NKp44.

NK cell receptor imbalance and NK cell dysfunction in HBV infection and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is currently the third leading cause of cancer mortality and a common poor-prognosis malignancy due to postoperative recurrence and metastasis. There is a significant correlation between chronic hepatitis B virus (HBV) infection and hepatocarcinogenesis. As the first line of host defense against viral infections and tumors, natural killer (NK) cells express a large number of immune recognition receptors (NK receptors (NKRs)) to recognize ligands on hepatocytes, liver sinusoidal endothelial cells, stellate cells and Kupffer cells, which maintain the balance between immune response and immune tolerance of NK cells. Unfortunately, the percentage and absolute number of liver NK cells decrease significantly during the development and progression of HCC. The abnormal expression of NK cell receptors and dysfunction of liver NK cells contribute to the progression of chronic HBV infection and HCC and are significantly associated with poor prognosis for liver cancer. In this review, we focus on the role of NK cell receptors in anti-tumor immune responses in HCC, particularly HBV-related HCC. We discuss specifically how tumor cells evade attack from NK cells and how emerging understanding of NKRs may aid the development of novel treatments for HCC. Novel mono- and combination therapeutic strategies that target the NK cell receptor-ligand system may potentially lead to successful and effective immunotherapy in HCC.Cellular & Molecular Immunology advance online publication, 6 October 2014; doi:10.1038/cmi.2014.91.

Differential expression of proteins in naïve and IL-2 stimulated primary human NK cells identified by global proteomic analysis

Natural killer (NK) cells efficiently cytolyse tumors and virally infected cells. Despite the important role that interleukin (IL)-2 plays in stimulating the proliferation of NK cells and increasing NK cell activity, little is known about the alterations in the global NK cell proteome following IL-2 activation. To compare the proteomes of naïve and IL-2-activated primary NK cells and identify key cellular pathways involved in IL-2 signaling, we isolated proteins from naïve and IL-2-activated NK cells from healthy donors, the proteins were trypsinized and the resulting peptides were analyzed by 2D LC ESI-MS/MS followed by label-free quantification. In total, more than 2000 proteins were identified from naïve and IL-2-activated NK cells where 383 proteins were found to be differentially expressed following IL-2 activation. Functional annotation of IL-2 regulated proteins revealed potential targets for future investigation of IL-2 signaling in human primary NK cells. A pathway analysis was performed and revealed several pathways that were not previously known to be involved in IL-2 response, including ubiquitin proteasome pathway, integrin signaling pathway, platelet derived growth factor (PDGF) signaling pathway, epidermal growth factor receptor (EGFR) signaling pathway and Wnt signaling pathway.

BIOLOGICAL SIGNIFICANCE

The development and functional activity of natural killer (NK) cells is regulated by interleukin (IL)-2 which stimulates the proliferation of NK cells and increases NK cell activity. With the development of IL-2-based immunotherapeutic strategies that rely on the IL-2-mediated activation of NK cells to target human cancers, it is important to understand the global molecular events triggered by IL-2 in human NK cells. The differentially expressed proteins in human primary NK cells following IL-2 activation identified in this study confirmed the activation of JAK-STAT signaling pathway and cell proliferation by IL-2 as expected, but also led to the discovery and identification of other factors that are potentially important in IL-2 signaling. These new factors warrant further investigation on their potential roles in modulating NK cell biology. The results from this study suggest that the activation of NK cells by IL-2 is a dynamic process through which proteins with various functions are regulated. Such findings will be important for the elucidation of molecular pathways involved in IL-2 signaling in NK cells and provide new targets for future studies in NK cell biology.