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Review

The Role of Natural Killer Cells in the Tumor Immune Microenvironment of EBV-Associated Nasopharyngeal Carcinoma

by
Shuzhan Li
1,2,3,†,
Wei Dai
4,†,
Ngar-Woon Kam
4,5,
Jiali Zhang
1,2,3,
Victor H. F. Lee
4,6,
Xiubao Ren
1,2,3,* and
Dora Lai-Wan Kwong
4,6,*
1
Department of Biotherapy, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Tianjin 300060, China
2
Tianjin’s Clinical Research Center for Cancer, Tianjin 300060, China
3
Key Laboratory of Cancer Immunology and Biotherapy, Tianjin 300060, China
4
Department of Clinical Oncology, Centre of Cancer Medicine, School of Clinical Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong 999077, China
5
Laboratory for Synthetic Chemistry and Chemical Biology Limited, Hong Kong Science Park, New Territories, Hong Kong 999077, China
6
Clinical Oncology Center, The University of Hong Kong-Shenzhen Hospital, Shenzhen 518053, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Cancers 2024, 16(7), 1312; https://doi.org/10.3390/cancers16071312
Submission received: 23 February 2024 / Revised: 23 March 2024 / Accepted: 23 March 2024 / Published: 28 March 2024
(This article belongs to the Special Issue New Therapies and Immunological Findings in Nasopharyngeal Carcinoma)
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Abstract

:

Simple Summary

Nasopharyngeal carcinoma (NPC) is an epithelial cancer associated with Epstein–Barr virus (EBV) infection. EBV infection contributes to not only the tumorigenesis of NPC but also the formation of a complicated tumor immune microenvironment (TIME) in NPC. Natural killer (NK) cells are lymphoid members of the innate immune system exhibiting both anti-tumor and anti-virus abilities. The cytokine and cellular interaction features of NK cells are distinct from those of CD8+ cytotoxic T cells. This unique characteristic has not been fully described in EBV+ NPC. This review provides an overview of the complicated crosstalk between NK cells and the TIME of EBV+ NPC and potential therapeutic strategies. A new perspective is proposed to direct future exploration.

Abstract

Endemic nasopharyngeal carcinoma (NPC) is closely associated with the Epstein–Barr virus (EBV), which contributes to tumor development and influences the tumor immune microenvironment (TIME) in NPC. Natural killer (NK) cells, as part of the innate immune system, play a crucial role in responding to viral infections and malignant cell transformations. Notably, NK cells possess a unique ability to target tumor cells independent of major histocompatibility complex class I (MHC I) expression. This means that MHC I-deficient tumor cells, which can escape from effective T cell attack, are susceptible to NK-cell-mediated killing. The activation of NK cells is determined by the signals generated through inhibitory and activating receptors expressed on their surface. Understanding the role of NK cells in the complex TIME of EBV+ NPC is of utmost importance. In this review, we provide a comprehensive summary of the current understanding of NK cells in NPC, focusing on their subpopulations, interactions, and cytotoxicity within the TIME. Moreover, we discuss the potential translational therapeutic applications of NK cells in NPC. This review aims to enhance our knowledge of the role of NK cells in NPC and provide valuable insights for future investigations.

1. Introduction

Nasopharyngeal carcinoma (NPC) is caused by both environmental and genetic factors [1]. According to GLOBOCAN estimates, there were 133,354 newly diagnosed patients and 80,008 mortalities due to NPC in 2020 [2]. NPC is more common in Southern China and Southeast Asia [3]. The non-keratinizing and undifferentiated histologic type accounts for 95% of NPC cases in the endemic area [4]. This subtype is highly associated with a childhood Epstein–Barr virus (EBV) infection. Other susceptibility factors include Cantonese ethnicity, smoking, diet habits, and several human leukocyte antigen (HLA) class I alleles [5]. Chemoradiotherapy is the standard first-line treatment for NPC, but approximately 20–30% of patients experience recurrence and/or metastasis (R/M) [6]. Immune checkpoint inhibitors (ICIs)—for instance, anti-programmed death-1 (PD-1) antibodies—have been proven to be safe and effective for R/M NPC patients [7]. This highlights the events happening in the tumor immune microenvironment (TIME) that will impact the patients’ outcomes. Immune evasion induced by cancer cells is currently considered a hallmark of cancer [8]. The TIME is a complicated environment due to the presence of various types of cells, including immunostimulant cells like CD8+ cytotoxic T cells (CTL) and natural killer (NK) cells; immunosuppressive cells, like regulatory T cells (Tregs); myeloid-derived suppressor cells (MDSCs); pro-inflammatory cytokines such as interferon-γ (IFN-γ); interleukin-2 (IL-2); and anti-inflammatory cytokines like transforming growth factor-β (TGF-β) and indoleamine-pyrrole 2,3-dioxygenase (IDO) (Figure 1) [9]. The TIME in EBV-associated NPC (EBV+ NPC) has distinctive features since latent EBV infection participates in the premalignant stage and promotes tumor progression [10].
The downregulation of HLA class I, which is required for the priming and activation of CTLs, is a common tumor evasion mechanism observed in EBV NPC [11,12]. EBV has been shown to suppresses major histocompatibility complex class I (MHC I) expression on NPC tumor cells, impairing the antigen presentation toward CD8+ T cells and promoting immune escape [13]. However, the loss of MHC I expression in NPC serves as a “missing self” signal that can be recognized by NK cells [14]. This provides an opportunity for NK cells to eliminate cancer cells since NK-cell-mediated cytotoxicity is not HLA-dependent and therefore may confer great clinical benefit to NPC treatment. As a critical part of immune surveillance, NK cells are lymphoid non-T cells that can kill virally infected and tumor cells [15,16]. Furthermore, NK cells bridge the innate and adaptive immune responses [17,18].
Therefore, understanding the crosstalk between NK cells and the TIME in EBV+ NPC is needed. In the present review, we summarized the vital role of NK cells in EBV+ NPC, reviewing multiple lines of in vivo and in vitro evidence indicating that NK cells and their subpopulation significantly contribute to the anti-EBV immune defense during NPC tumorigenesis as well as the anticancer potential of these cells.

2. EBV-Associated NPC and NK Cells

2.1. EBV-Associated NPC

EBV was the first identified oncogenic virus with a permanently infectious capacity in humans [19]. It is a double-stranded DNA virus, also one of the members of the human herpesvirus family [20]. EBV infection is associated with various epithelial and lymphoid malignancies, represented by NPC and Burkitt lymphoma, respectively [21,22]. EBV infects both B cells and epithelial cells [21,23]. It has been shown that NPC cells develop from a clonal proliferation of a single EBV-infected epithelial cell [24]. The tumorigenesis of EBV+ NPC may be mediated by EBV infection, carcinogens, and HLA genotype, collectively. EBV infection of nasopharyngeal epithelium is mediated by the interactions between ephrin receptor tyrosine kinase A2 (EphA2) and viral proteins gH/gL and gB [25,26]. The establishment and persistence of latency are crucial for the pathogenesis and tumorigenesis of EBV+ NPC [19]. Preexisting genome alterations support the switch from the lytic to latent phase [27,28]. This genome instability is considered a consequence of contact with carcinogens such as nitrosamines in salty fish, which are common in the Cantonese diet [10]. Genetic susceptibility factors include the HLA-A*0207 genotype, common among Chinese people, which is associated with NPC [29,30]. This HLA allele may not be capable of inducing a sufficient immune response against EBV viral antigens. With epithelial cells, only type II latency occurs [31]. This is confirmed by the expression of viral proteins restricted to type II latency, including EBV nuclear antigen 1(EBNA1), latent membrane protein 1 (LMP1), LMP2, and EBV-encoded small RNAs (EBERs) [32]. Latent proteins stimulate the NF-κB, PI3K/AKT, and Wnt/β-catenin signal pathways in NPC tumor cells (Figure 1). Downstream signal transduction promotes tumor cell proliferation and immune evasion [33,34,35,36,37]. Furthermore, LMP1 promotes an immune suppressive microenvironment by inducing the sensitivity of lymphocytes to TGF-β, which is well known as an immunosuppressive factor [38]. A small subset of NPC cells is detected with lytic EBV gene expression [13,39]. These minority NPC cells may induce immune evasion [40,41]. It has been proven that heavy immune cell infiltration and abundant secreted cytokines in EBV+ NPC establishes an immunosuppressive TIME [42], with a large population of Tregs, exhausted T cells, and MDSCs (Figure 1) [43,44].

2.2. NK Cells in NPC

NK cell expansion acts as the first responder in acute EBV infection, including in the acute phase of symptomatic EBV-associated infectious mononucleosis (IM) [45]. Several studies have indicated that NK cells not only contribute to the innate immune response against viral infection but also serve as a significant component in anti-cancer immune elimination [46,47]. High NK cell percentage in the TIME is associated with a better prognosis in EBV+ NPC [48,49]. Activated NK cells kill targeted cells by releasing perforin and granzyme and inducing antibody-dependent cell-mediated cytotoxicity (ADCC), and apoptosis [50,51]. NK cells’ function is modulated by the interactions between activating/inhibitory receptors and their ligands. The cytotoxic status will occur if there are more stimulatory signals aroused by activating receptors than inhibitory receptors, and vice versa [50]. Figure 1 illustrates the role of effective T cells in the TIME of EBV+ NPC. However, how NK cells interact with cytokines and other components within the TIME remains unclear. Whether immune checkpoint molecules impact NK cell function also needs further discussion.

3. NK Subpopulations in NPC

3.1. Surface Markers of NK Cells

NK cells belong to innate lymphoid cells (ILCs) and exhibit anti-malignancy and anti-virus abilities. The typical biomarkers expressed on the NK cell surface are CD56+CD3−. The conventional categories of NK cells include CD56dimCD16+ (“mature” cytotoxic NK cells) and CD56brightCD16− (“immature” immunomodulatory NK cells). CD56dimCD16+ NK cells are the predominant component, producing abundant IFN-γ, tumor necrosis factor-α (TNF-α), and cytolytic mediators perforin and granzymes. CD56brightCD16− NK cells have poorer cytotoxic capability but can be activated within a pro-inflammatory microenvironment [52]. NKG2D and NKp30 are typical markers expressed on an activated NK cell’s surface, and the ligands are MHC Class-I-related Chain A (MICA) and MICB for the former and B7-H6 for the latter (Figure 2A) [53,54]. Meanwhile, NKG2A/CD94 heterodimers and killer immunoglobulin-like receptors (KIR) are inhibitory receptors that recognize the MHC I molecules expressed by host cells (Figure 2B). “Missing self recognition” will occur between activated NK cells and aberrant host cells with MHC I loss, then NK cells perform as innate immune defenders without antigen priming [55,56].

3.2. NK Cells in Peripheral Blood of NPC Patients

The percentage of NK cells out of all peripheral blood mononuclear cells ranges from 1% to 15% [57,58]. Regarding the subtypes of NK cells, it has been revealed that there is no difference between the percentage of NK cells in peripheral lymphocytes isolated from healthy individuals and NPC patients [59,60]. One study indicated that there was no difference between the percentage of NKG2D+ NK cells (activated) and KIR2DL2/DL3+NK2GA+ NK cells (inhibited) in peripheral blood samples of NPC patients and a healthy control. However, a lower NKp30+ NK cell percentage is noticed in NPC patients than in healthy controls [59]. A similar result has been discovered in another study, in which a lower NKG2D+ NK cell percentage was found when comparing NPC patients with healthy individuals [61]. These may indicate a poorer NK cell anti-cancerous function in NPC patients.

3.3. NK Cells in the TIME of EBV+ NPC

The distribution of NK cells in the TIME is a crucial it performing its role as an anti-cancer immune defender. In tumor tissue samples from an NPC biopsy, the NK cells account for 1–6.5% of all stromal cells regardless of their subtypes [12,44,48]. Chen and colleagues found that NK cells were enriched in the tumor stroma, with lower infiltration in the tumor epithelial nests [48]. Studies have also indicated that compared with nonmalignant nasopharyngeal biopsies, NK cells showed an increased trend in EBV+ NPC tissue [62,63]. Unfortunately, these studies have not indicated NK cell subtypes. On the contrary, when detected with immunohistochemical staining (IHC), CD56+ NK cells were reduced in non-keratinizing NPC tissue compared with normal nasopharyngeal mucosa [64]. Peng and colleagues demonstrated that CD56dimCD16+ NK cells, the cytotoxic subtype, accounted for the majority of NK cells in both treatment naïve and recurrent EBV+ NPC tissues. Significantly, CD56dimCD16+ NK cells exhibited more cytotoxicity and chemotaxis and a more exhausted status in recurrent than primary NPC samples [12]. This may suggest that the composition of NK cells can be modulated by both treatment methods and interactions between cancer cells and the immune system.
According to single-cell transcriptomic and proteomic analysis research, infiltrated NK cells within EBV+ NPC biopsies could be divided into three sub-groups, which showed cytotoxic, inhibited, and exhausted phenotypes, respectively. Notably, these exhausted NK cells showed an upregulation of both lymphocyte-activation gene 3 (LAG3) and T cell immunoreceptor with Ig and ITIM domain (TIGIT) expression, both known as immune checkpoint receptors [64]. Also, comparing the EBV+ NPC and EBV− NPC biopsies, the percentage of activated CD56+CD3− granzyme B+ NK cells was found to be lower for EBV+ NPC [65]. Overall, the subpopulations of NPC-infiltrated NK cells remain unclear. However, it seems that most NK cells within EBV+ NPC tissue express inhibitory or exhausted biomarkers, indicating a consequence of immune evasion.

4. The Crosstalk of NK Cells in the TIME

The functional status of NK cells is identified by the interaction between functional molecules expressed on the NK cell surface and their receptors/ligands. It can be divided into four types: where cell–cell interaction induces (1) an activating signal; (2) an inhibitory signal; (3) signals initiated by cytokines/chemokines; or (4) interaction turning on the apoptotic downstream signal or antibody-dependent cellular cytotoxicity (ADCC) in targeted cells [50]. Table 1 summarizes the relevant NK functional receptors and ligands that have been reported in NPC.

4.1. Activating and Inhibitory Signals of NK Cells

Tumor cells, other immune cells, and cytokines are capable of binding with the molecules expressed on NK cells, triggering activation or inhibition status. This complicated network needs further investigation. Figure 2 summarizes the activating and inhibitory signals affecting NK cells. Notably, EBV-derived latent protein LMP2 and microRNA suppress MICA/B expression, which are ligands binding to NKG2D (activating receptor) on NK cells [66,67,68]. Meanwhile, EBV performs as a “double-edged sword” in generating inhibitory signals affecting NK cells. EBV downregulates MHC I molecule expression to avoid effective CD8+ T cell attack but arouses “missing self” recognition by NK cells [13,76]. Persistent exposure to the EBV+ cell line promotes inhibitory KIR expression on NK cells ex vivo [77]. Therefore, the terminal NK functional status in the TIME of NPC may not be described precisely.

4.2. Cytokines/Chemokines and Immune Cells

Cytokines in the TIME show either stimulating or inhibitory patterns in the modulation of NK cell function (Figure 3). EBV+ NPC releases TGF-β, which inhibits NK cell function by promoting the differentiation of Tregs [77]. On the other hand, immune cells such as T cells express IFN-β in the TIME which promotes NK cell function via the TRAIL signaling pathway [83]. Chemokines like CCL5 and XCL1/2 are secreted by activated NK cells and recruit antigen-presenting dendritic cells (DCs) [18,44,48,93]. These molecules facilitate the interaction between NK cells and other components within the TIME. Tumor-associated macrophages (TAMs) and MDSCs have an inhibitory effect in the TIME of EBV+ NPC [91]. It has been reported that TAMs and MDSCs inhibit NK cell function to facilitate the immune escape of solid tumors [62,97]. The immune suppressive role of TAMs and MDSCs towards NK cells within EBV+ NPC needs further investigation.
It has been well defined that the pro-inflammatory cytokines IL-2 and IL-21 promote NK cell expansion [50,90,91]. The IL-12, IL-15, and IL-18 cytokine cocktail can convert the cells into long-lived, activated “memory-like NK cells” [90]. Based on this, therapeutic applications for NPC patients, such as adoptive NK cells combined with other immune stimulators, may trigger effective and steerable immune responses against NPC.

4.3. Immune Checkpoint Molecules

Notably, immune checkpoint receptors are involved in the modulation of NK cell function, of which the ligands expressed on NPC cells are also elevated to establish immune evasion (Figure 2C). Although EBV infection will induce high levels of the production of the pro-inflammatory cytokine IFN-γ by NK cells and cytotoxic T cells, persistent IFN-γ exposure in EBV+ NPC can promote the expression of exhausted biomarkers like PD-1 [62]. EBV increases PD-L1 expression in NPC cells via EBV-encoded miRNA [97]. Conventional chemotherapy and radiotherapy promote PD-L1 expression on NPC cells and PD-1 expression on NK cells [78,79]. Other novel immune checkpoint molecules like TIGIT, LAG3, and CD96 have been found expressed on exhausted NK cells in NPC [44,48,63]. The downstream effects of these exhausted markers on NK cells needs to be further investigated in EBV+ NPC.

5. NK Cell Cytotoxicity

NK cells are well known as a type of cytotoxic lymphocyte critical to the innate immune system. Normally, NK cell cytotoxicity involves several mechanisms including triggering apoptosis in targeted tumor cells, inducing ADCC, or the secretion of cytokines that recruit or stimulate other immune cell types (Figure 2D). Once NK cells are activated, the pore-forming protein perforin and the granzyme B contained in cytotoxic granules are released [98]. In the meantime, NK cells activate the death receptors FAS and TRAIL expressed on targeted tumor cells and induce apoptosis [99]. CD16 and CD32 are high-affinity Fc receptors expressed on the NK cell surface. Antibody-coated cells will be killed by NK cells once CD16/CD32 binds with the Fc region of the antibody [100]. IFN-γ and TNF-α are released by stimulated NK cells, which can induce tumor cell death [101]. Otherwise, NK cells participate in the stimulation of the adaptive immune system by recruiting other effective cells or activating antigen-presenting procedure (Figure 3) [17,18].

5.1. NK Cells against EBV Infection

Traditionally, the adaptive immune response is considered the primary defense against virus infections. However, it has been revealed that virus-specific T cells alone are not sufficient to eliminate EBV infection [102,103]. Patients with NK cell deficiency experience severe symptoms following EBV infection and are at a higher risk of developing EBV-related malignancies [103]. In summary, circulating CD56dimNKG2A+KIR− NK cell expansion may act as the first responder in acute EBV infection, as in the acute phase of symptomatic EBV-associated IM [45]. Several studies have indicated that NKG2A+ NK cells are significant effector cells against EBV-infected B cells [45,104]. Notably, it has been found that the latent phase of EBV infection is more resistant to NK-cell-mediated cytotoxicity compared to the lytic phase. This could be due to the downregulation of MHC I and upregulation of NK-activated ligands that occur during lytic EBV infection in B cells [105]. MHC I expression is regained after switching to the latent phase [45]. Additionally, the expression of lytic-phase genes carried by EBV makes EBV-infected B cells more susceptible to NK-cell-mediated killing [105,106]. The lifelong carrying of latent EBV infection in resting B cells may indicate a balance between the host cells and NK-cell-mediated killing processes.

5.2. NK Cells against EBV+ NPC

Since type II latent phase EBV infection is predominant in EBV+ NPC, it is more likely that the cytotoxic function of NK cells remains quiescent in the TIME. A stronger NK cell expansion and cytotoxicity could be induced in NPC-patient-derived NK cells in comparison with healthy controls and 5-year NPC survivors [60]. This could be explained by the higher production of pro-inflammatory cytokines (IL-12, IL-15, and TNF-α) but not the effector cytokine (IFN-γ) by cultured NPC-patient-derived NK cells ex vivo [60]. The activating signal for NK cells may not be sufficient to arouse an anti-tumor response. Gong and colleagues found that NK cells expressed a high level of cytotoxic genes in NPC [44]. However, a proteomic analysis revealed that the function of NK cells in NPC tissues was inhibited. This was confirmed by decreased CD56 and granzyme B IHC staining. Further investigation showed that NK cell downregulation is due to exhaustion induced by NPC tumor cells [64]. EBV infection may contribute to this downregulation of NK cell function. Decreased NK cell degranulation was exhibited in cocultured NK cells with EBV+ NPC cells when compared with their parental group, but not when cocultured with EBV− NPC cells ex vivo [65]. This indicated that NK cell cytolytic activity was inhibited by EBV+ NPC cells directly. This may be partially due to the upregulation of B7-H3, an immune checkpoint molecule that is also a member of B7 superfamily, mediated by EBV infection [65]. A lower expression of immune signatures in NK cells was found to be associated with EBV+ NPC when compared with EBV− NPC samples. Interestingly, in the same study, patients with a higher expression of immune signatures in NK cells had a better PFS [48]. Transcription factors (TFs) such as XBP1, EOMES, and RUNX3 were upregulated in NK cells. The same upregulated expression patterns were detected in the cytotoxic CD8+ T cell subtypes. To validate this result, NK cells and CD8+ T cells were isolated from NPC tissue samples. A higher percentage of cytotoxic granzyme B+ or perforin+ phenotype was verified in the XBP1+, EOMES+, and RUNX3+ NK cells and CD8+ T cells [48]. This study illustrated the significant effective role of NK cells and CD8+ T cells in the TIME for anti-tumor immune response. The “missing self” recognition of NK cells acts as a functional supplement to overcome the CD8+ T cell off-target tumor killing mediated by MHC I downregulation in EBV+ NPC. Meanwhile, activated immune cells secrete pro-inflammatory cytokines like IFN-β to enhance NK cell cytotoxicity (Figure 3).
To sum up, these inconsistent results suggests that NK cells within the NPC tumor site ensure an inhibitory, exhausted, and suboptimal status, more like a precursor for activated and cytotoxic NK cells. Overcoming this phenomenon could be used as a strategy to improve NPC-directed therapeutic methods.

6. NK Cells in Cancer Therapy

It is important to understand the initiating, expansion, recruiting, and activation/inhibition process, and the functional status of NK cells in NPC to further investigate treatment strategies. NK cells establish a relatively lower, more inhibitory, and exhausted subpopulation in the TIME of NPC. To overcome this, adoptive NK cell therapy with ex vivo expansion and pre-stimulation or with genetically engineering can be considered. Therapies that activate NK cells in vivo alone or combined with adoptive NK cells may also be effective. One advantage of adoptive NK cell therapy is that activated NK cells are not HLA-matching-dependent and do not mediate graft-versus-host disease (GVHD) [107]. Based on this, NK cell products can be used in allogeneic recipients, or designed to be commercially available.

6.1. Pre-Activated/Genetically Modified Adoptive NK Cells

In early investigations, the adoptive transfer of partially allogenic NK cells isolated from peripheral blood and co-cultured with IL-2 was proven to have anti-cancer capability with low toxicity in patients with acute myelocytic leukemia [108]. NK cells isolated from peripheral blood were pre-stimulated ex vivo with an IL-12, IL-15, and IL-18 cytokine cocktail to induce “memory-like” NK cells [109]. These “memory-like” NK cells exhibited higher IFN-γ production and expression of granzyme B and perforin. Several clinical trials based on these “memory-like” NK cells are ongoing [110,111,112]. However, these trials are focusing on hematologic tumors. Solid tumors like NPC treated by pre-stimulating NK cells with cytokines have limited efficacy. One approach to enhance the effective function of NK cells is to use NK cells armed with monoclonal antibodies to target molecules expressing on the surface of tumor cells, so-called “armed NK cells” [113]. It is reported that EGFR is highly expressed in most NPC and is a poor prognostic factor [114]. Cetuximab, a monoclonal antibody against EGFR, was added to the cultural system for autologous NK cells from NPC patients. CD16 expressed on NK cells recognized the Fc region of Cetuximab. This induced ADCC in NK cells against C666 NPC cells ex vivo [115]. Concurrent treatment of cetuximab plus autologous NK cells in EGFR-positive NPC was tolerable among R/M NPC patients. Durable stable disease was observed in three out of seven subjects (NCT02507154) [116]. In addition, the limited anti-cancer function of NK cells in solid tumors may partially be due to poor trafficking toward tumor nests. The genetically engineered transduction of chimeric antigen receptor (CAR) to NK cells increases the capability of recognition of NK cells to targeted tumor antigens. CD137, a costimulatory receptor expressed on T cells, was found to exhibit ectopic expression in 42 of 122 (34.4%) NPC cases, induced by EBV-related LMP1 expression. A negative feedback mechanism hijacked by NPC cells downregulated the expression of the ligand of CD137 (CD137L), causing immune evasion [117]. NK cells express CD137-specific CAR-induced death in CD137+ NPC cells, in vitro. CD137-specific CAR NK cells established an anti-tumor effect in a murine xenograft model [117]. Further investigation for safety and efficacy in CD137+ NPC patients is needed.

6.2. Adoptive NK Cells Combined with Systemic/Conventional Therapies

Evidence is cumulating to confirm that NK cells upregulate PD-1 in certain cancers [118,119]. PD-1 blockades cause an anti-tumor NK cell response, which is essential to ensure the therapeutic effect of anti-PD-1 therapy [120]. The inhibition of PD-1 was proven to increase cytotoxicity towards NPC cells by activated NK cells [78]. The combination of IFN-β and anti-PD-1 augmented the cytolytic effect of NK cells against NPC cells [94]. TIGIT has been found to be overexpressed in the exhausted NK cell subset in the TIME of NPC [64]. The blockade of TIGIT with monoclonal antibodies reverted NK cell exhaustion to functional status in multiple tumor models [121]. A combination of PD-1 or TIGIT blockade with adoptive NK cell therapy may have an optimal therapeutic effect in NPC patients. These results need further investigation in vivo and in clinical trials.
Chemotherapies such as gemcitabine, cisplatin, and 5-fluorouracil can sensitize NPC cells to NK cell cytotoxicity. These chemotherapeutic agents also induce the expression of programmed death ligand-1 (PD-L1) on NPC cells [78]. Meanwhile, radiotherapy sensitizes NPC cells to NK cell killing. Radiation can induce PD-L1 expression in NPC cells and PD-1 expression in NK cells [79]. Conventional therapies such as chemotherapy and radiotherapy combined with ICIs and with/without adoptive NK cells may be a therapeutic choice for NPC patients after failing of systemic therapy.

6.3. NK Cell Agonists

NK cell activity can be strongly expanded by innate immune activators, such as the synthetic double-stranded RNA analog poly(I:C), a Toll-like receptor 3 (TLR3) agonist [122]. Poly(I:C) enhanced ADCC effect on NPC cells after overnight treatment of immature NK cells from NPC patients [115]. Additionally, poly(I:C)-treated NK cells established stronger degranulation and IFN-γ secretion after they were co-cultured with C666 and cetuximab [116]. The treatment of peripheral blood mononuclear cells (PBMC) with a selective TLR8 agonist VTX-2337 in vitro activated NK cells, enhanced cetuximab-mediated ADCC, and augmented tumor killing [123,124]. A phase I dose escalation open-label trial enrolled 13 patients with recurrent or metastatic squamous cell carcinoma of the head and neck (SCCHN), including NPC. The patients’ NK cells became more responsive to NKG2D stimulation following VTX-2337 treatment (NCT01334177) [125].
In addition, cytosolic DNA generated from viral DNA and chromosomal instability of cancer is thought to trigger the cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway [126]. The activation of the cGAS-STING pathway supports the initiation of NK cell response to viral infection and tumors [127]. Therefore, STING agonists mobilize powerful NK-cell-mediated antitumor response [128]. TAK-500, a novel STING agonist, is currently being evaluated as a single agent and in combination with pembrolizumab for tolerability and preliminary antitumor activity in adult patients with select locally advanced or metastatic solid tumors, including NPC (NCT05070247).
As described earlier in this review, NK cells express inhibitory receptors KIR and NKG2A. It has been reported that KIR and NKG2A are inhibitory receptors expressed by NK cells in EBV+ NPC [12]. Blocking KIR and NKG2A may have therapeutic potential in EBV+ NPC. Monoclonal antibodies against KIR and NKG2A have unleashed NK cell function in preclinical studies and multiple tumor models [129,130]. Anti-KIR antibodies and anti-NKG2A antibodies as monotherapy or combined with ICIs may arouse the persistent activation of NK cells [129,131]. The efficacy and safety need further investigation in clinical trials.

6.4. NK Cell Engager

Nowadays, an alternative approach, the NK cell engager, is being investigated to amplify NK cell function against tumors. The engager bridges NK-cell-activating receptors and molecules expressed on tumor cells. One arm of the engager binds the activating NKp46 receptor and the activating Fc receptor CD16 on NK cells. The other arm binds to tumor-associated antigens, including CD19, CD20 for hematologic tumors, and EGFR for solid tumors [50,132]. A bispecific engager with high affinity and specificity toward CD16 and human epidermal growth factor receptor 2 (HER2) was designed and tested. A higher ADCC effect was induced in HER2+ breast cancer cells in comparison to anti-HER2 monoclonal antibody trastuzumab [133]. This novel approach needs to be further tested in vivo and in clinical trials. Meanwhile, an optimal tumor antigen presented by NPC cells also needs to be determined for NK cell engager design.
The immunosuppressive and exhausted condition of NK cells in the TIME needs to be reversed to fully develop anti-cancer effectiveness. Table 2 summarizes the registered clinical trials relevant to NK cells in NPC treatment. Multiple investigations are necessary for the translational applications of NK cells in NPC in the future.

7. Conclusions and Future Directions

There has been impressive progress in the understanding of the TIME in EBV+ NPC. NK cells, as members of innate immune defenders, have been investigated deeply in recent years. In this review, we summarized the subpopulations, crosstalk with cytokines/chemokines and other components, and the functional status of NK cells in the TIME of EBV+ NPC. NK cell response is initiated after EBV infection. Then NK cell population expands and expresses several activating biomarkers like NKG2D and CD16 and inhibitory biomarkers like NKG2A/CD94 and KIR. Whether the cytotoxicity of NK cells is activated or inhibited is determined by the stronger signal generated by activated or inhibitory receptors. This procedure occurs in an early stage of EBV infection, even before premalignancy transformation. Finally, when the tumor is developed, NK cells present more insufficient and exhausted conditions in the TIME. Therapeutic methods such as exogenous NK cell infusion and agents stimulating endogenous NK cell function can be designed for further investigation to fully mobilize the anti-cancer function of the enriched immune cells infiltrated in the TIME of EBV+ NPC.

Author Contributions

Conceptualization, X.R. and D.L.-W.K.; writing—original draft preparation, S.L. and W.D.; writing—review and editing, N.-W.K. and J.Z.; supervision, V.H.F.L., X.R. and D.L.-W.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The author declares no conflicts of interest.

References

  1. Torre, L.A.; Bray, F.; Siegel, R.L.; Ferlay, J.; Lortet-Tieulent, J.; Jemal, A. Global cancer statistics, 2012. CA Cancer J. Clin. 2015, 65, 87–108. [Google Scholar] [CrossRef] [PubMed]
  2. Sung, H.; Ferlay, J.; Siegel, R.L.; Laversanne, M.; Soerjomataram, I.; Jemal, A.; Bray, F. Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries. CA Cancer J. Clin. 2021, 71, 209–249. [Google Scholar] [CrossRef]
  3. Xia, C.; Yu, X.Q.; Zheng, R.; Zhang, S.; Zeng, H.; Wang, J.; Liao, Y.; Zou, X.; Zuo, T.; Yang, Z.; et al. Spatial and temporal patterns of nasopharyngeal carcinoma mortality in China, 1973–2005. Cancer Lett. 2017, 401, 33–38. [Google Scholar] [CrossRef]
  4. Chua, M.L.K.; Wee, J.T.S.; Hui, E.P.; Chan, A.T.C. Nasopharyngeal carcinoma. Lancet 2016, 387, 1012–1024. [Google Scholar] [CrossRef]
  5. Lo, K.W.; To, K.F.; Huang, D.P. Focus on nasopharyngeal carcinoma. Cancer Cell 2004, 5, 423–428. [Google Scholar] [CrossRef] [PubMed]
  6. Chen, L.; Zhang, Y.; Lai, S.Z.; Li, W.F.; Hu, W.H.; Sun, R.; Liu, L.Z.; Zhang, F.; Peng, H.; Du, X.J.; et al. 10-Year Results of Therapeutic Ratio by Intensity-Modulated Radiotherapy versus Two-Dimensional Radiotherapy in Patients with Nasopharyngeal Carcinoma. Oncologist 2019, 24, e38–e45. [Google Scholar] [CrossRef] [PubMed]
  7. Huang, H.; Yao, Y.; Deng, X.; Huang, Z.; Chen, Y.; Wang, Z.; Hong, H.; Huang, H.; Lin, T. Immunotherapy for nasopharyngeal carcinoma: Current status and prospects (Review). Int. J. Oncol. 2023, 63, 97. [Google Scholar] [CrossRef]
  8. Hanahan, D. Hallmarks of Cancer: New Dimensions. Cancer Discov. 2022, 12, 31–46. [Google Scholar] [CrossRef]
  9. de Visser, K.E.; Joyce, J.A. The evolving tumor microenvironment: From cancer initiation to metastatic outgrowth. Cancer Cell 2023, 41, 374–403. [Google Scholar] [CrossRef]
  10. Tsao, S.W.; Tsang, C.M.; Lo, K.W. Epstein-Barr virus infection and nasopharyngeal carcinoma. Philos. Trans. R. Soc. Lond. Ser. B Biol. Sci. 2017, 372, 20160270. [Google Scholar] [CrossRef]
  11. Shi, W.; Fijardo, M.; Bruce, J.P.; Su, J.; Xu, W.; Bell, R.; Bissey, P.A.; Hui, A.B.Y.; Waldron, J.; Pugh, T.J.; et al. CD8+ Tumor-Infiltrating Lymphocyte Abundance Is a Positive Prognostic Indicator in Nasopharyngeal Cancer. Clin. Cancer Res. 2022, 28, 5202–5210. [Google Scholar] [CrossRef]
  12. Peng, W.S.; Zhou, X.; Yan, W.B.; Li, Y.J.; Du, C.R.; Wang, X.S.; Shen, C.Y.; Wang, Q.F.; Ying, H.M.; Lu, X.G.; et al. Dissecting the heterogeneity of the microenvironment in primary and recurrent nasopharyngeal carcinomas using single-cell RNA sequencing. Oncoimmunology 2022, 11, 2026583. [Google Scholar] [CrossRef] [PubMed]
  13. Sengupta, S.; den Boon, J.A.; Chen, I.H.; Newton, M.A.; Dahl, D.B.; Chen, M.; Cheng, Y.J.; Westra, W.H.; Chen, C.J.; Hildesheim, A.; et al. Genome-wide expression profiling reveals EBV-associated inhibition of MHC class I expression in nasopharyngeal carcinoma. Cancer Res. 2006, 66, 7999–8006. [Google Scholar] [CrossRef]
  14. Raulet, D.H.; Marcus, A.; Coscoy, L. Dysregulated cellular functions and cell stress pathways provide critical cues for activating and targeting natural killer cells to transformed and infected cells. Immunol. Rev. 2017, 280, 93–101. [Google Scholar] [CrossRef]
  15. Cerwenka, A.; Lanier, L.L. Natural killer cells, viruses and cancer. Nat. Rev. Immunol. 2001, 1, 41–49. [Google Scholar] [CrossRef]
  16. Orange, J.S. Human natural killer cell deficiencies. Curr. Opin. Allergy Clin. Immunol. 2006, 6, 399–409. [Google Scholar] [CrossRef]
  17. Barry, K.C.; Hsu, J.; Broz, M.L.; Cueto, F.J.; Binnewies, M.; Combes, A.J.; Nelson, A.E.; Loo, K.; Kumar, R.; Rosenblum, M.D.; et al. A natural killer-dendritic cell axis defines checkpoint therapy-responsive tumor microenvironments. Nat. Med. 2018, 24, 1178–1191. [Google Scholar] [CrossRef]
  18. Böttcher, J.P.; Bonavita, E.; Chakravarty, P.; Blees, H.; Cabeza-Cabrerizo, M.; Sammicheli, S.; Rogers, N.C.; Sahai, E.; Zelenay, S.; Reis e Sousa, C. NK Cells Stimulate Recruitment of cDC1 into the Tumor Microenvironment Promoting Cancer Immune Control. Cell 2018, 172, 1022–1037.e1014. [Google Scholar] [CrossRef] [PubMed]
  19. Jha, H.C.; Pei, Y.; Robertson, E.S. Epstein-Barr Virus: Diseases Linked to Infection and Transformation. Front. Microbiol. 2016, 7, 1602. [Google Scholar] [CrossRef] [PubMed]
  20. Zanella, M.C.; Cordey, S.; Kaiser, L. Beyond Cytomegalovirus and Epstein-Barr Virus: A Review of Viruses Composing the Blood Virome of Solid Organ Transplant and Hematopoietic Stem Cell Transplant Recipients. Clin. Microbiol. Rev. 2020, 33, 10-1128. [Google Scholar] [CrossRef]
  21. Tsao, S.W.; Tsang, C.M.; To, K.F.; Lo, K.W. The role of Epstein-Barr virus in epithelial malignancies. J. Pathol. 2015, 235, 323–333. [Google Scholar] [CrossRef] [PubMed]
  22. Young, L.S.; Yap, L.F.; Murray, P.G. Epstein-Barr virus: More than 50 years old and still providing surprises. Nat. Rev. Cancer 2016, 16, 789–802. [Google Scholar] [CrossRef] [PubMed]
  23. Young, L.S.; Rickinson, A.B. Epstein-Barr virus: 40 years on. Nat. Rev. Cancer 2004, 4, 757–768. [Google Scholar] [CrossRef] [PubMed]
  24. Pathmanathan, R.; Prasad, U.; Sadler, R.; Flynn, K.; Raab-Traub, N. Clonal proliferations of cells infected with Epstein-Barr virus in preinvasive lesions related to nasopharyngeal carcinoma. N. Engl. J. Med. 1995, 333, 693–698. [Google Scholar] [CrossRef]
  25. Chen, J.; Sathiyamoorthy, K.; Zhang, X.; Schaller, S.; Perez White, B.E.; Jardetzky, T.S.; Longnecker, R. Ephrin receptor A2 is a functional entry receptor for Epstein-Barr virus. Nat. Microbiol. 2018, 3, 172–180. [Google Scholar] [CrossRef] [PubMed]
  26. Zhang, H.; Li, Y.; Wang, H.B.; Zhang, A.; Chen, M.L.; Fang, Z.X.; Dong, X.D.; Li, S.B.; Du, Y.; Xiong, D.; et al. Ephrin receptor A2 is an epithelial cell receptor for Epstein-Barr virus entry. Nat. Microbiol. 2018, 3, 1–8. [Google Scholar] [CrossRef] [PubMed]
  27. Chan, A.S.; To, K.F.; Lo, K.W.; Ding, M.; Li, X.; Johnson, P.; Huang, D.P. Frequent chromosome 9p losses in histologically normal nasopharyngeal epithelia from southern Chinese. Int. J. Cancer 2002, 102, 300–303. [Google Scholar] [CrossRef] [PubMed]
  28. Chan, A.S.; To, K.F.; Lo, K.W.; Mak, K.F.; Pak, W.; Chiu, B.; Tse, G.M.; Ding, M.; Li, X.; Lee, J.C.; et al. High frequency of chromosome 3p deletion in histologically normal nasopharyngeal epithelia from southern Chinese. Cancer Res. 2000, 60, 5365–5370. [Google Scholar] [PubMed]
  29. Ning, L.; Ko, J.M.; Yu, V.Z.; Ng, H.Y.; Chan, C.K.; Tao, L.; Lam, S.Y.; Leong, M.M.; Ngan, R.K.; Kwong, D.L.; et al. Nasopharyngeal carcinoma MHC region deep sequencing identifies HLA and novel non-HLA TRIM31 and TRIM39 loci. Commun. Biol. 2020, 3, 759. [Google Scholar] [CrossRef]
  30. Hildesheim, A.; Apple, R.J.; Chen, C.J.; Wang, S.S.; Cheng, Y.J.; Klitz, W.; Mack, S.J.; Chen, I.H.; Hsu, M.M.; Yang, C.S.; et al. Association of HLA class I and II alleles and extended haplotypes with nasopharyngeal carcinoma in Taiwan. J. Natl. Cancer Inst. 2002, 94, 1780–1789. [Google Scholar] [CrossRef]
  31. Ansari, M.A.; Singh, V.V.; Dutta, S.; Veettil, M.V.; Dutta, D.; Chikoti, L.; Lu, J.; Everly, D.; Chandran, B. Constitutive interferon-inducible protein 16-inflammasome activation during Epstein-Barr virus latency I, II, and III in B and epithelial cells. J. Virol. 2013, 87, 8606–8623. [Google Scholar] [CrossRef] [PubMed]
  32. Perri, F.; Della Vittoria Scarpati, G.; Giuliano, M.; D’Aniello, C.; Gnoni, A.; Cavaliere, C.; Licchetta, A.; Pisconti, S. Epstein-Barr virus infection and nasopharyngeal carcinoma: The other side of the coin. Anti-Cancer Drugs 2015, 26, 1017–1025. [Google Scholar] [CrossRef]
  33. Li, H.P.; Chang, Y.S. Epstein-Barr virus latent membrane protein 1: Structure and functions. J. Biomed. Sci. 2003, 10, 490–504. [Google Scholar] [CrossRef]
  34. Fukuda, M.; Longnecker, R. Epstein-Barr virus latent membrane protein 2A mediates transformation through constitutive activation of the Ras/PI3-K/Akt Pathway. J. Virol. 2007, 81, 9299–9306. [Google Scholar] [CrossRef]
  35. Scholle, F.; Bendt, K.M.; Raab-Traub, N. Epstein-Barr virus LMP2A transforms epithelial cells, inhibits cell differentiation, and activates Akt. J. Virol. 2000, 74, 10681–10689. [Google Scholar] [CrossRef]
  36. Morris, M.A.; Dawson, C.W.; Young, L.S. Role of the Epstein-Barr virus-encoded latent membrane protein-1, LMP1, in the pathogenesis of nasopharyngeal carcinoma. Future Oncol. 2009, 5, 811–825. [Google Scholar] [CrossRef] [PubMed]
  37. Tsao, S.W.; Tramoutanis, G.; Dawson, C.W.; Lo, A.K.; Huang, D.P. The significance of LMP1 expression in nasopharyngeal carcinoma. Semin. Cancer Biol. 2002, 12, 473–487. [Google Scholar] [CrossRef] [PubMed]
  38. Ye, D.; Zhu, J.; Zhao, Q.; Ma, W.; Xiao, Y.; Xu, G.; Zhang, Z. LMP1 Up-regulates Calreticulin to Induce Epithelial-mesenchymal Transition via TGF-β/Smad3/NRP1 Pathway in Nasopharyngeal Carcinoma Cells. J. Cancer 2020, 11, 1257–1269. [Google Scholar] [CrossRef]
  39. Martel-Renoir, D.; Grunewald, V.; Touitou, R.; Schwaab, G.; Joab, I. Qualitative analysis of the expression of Epstein-Barr virus lytic genes in nasopharyngeal carcinoma biopsies. J. Gen. Virol. 1995, 76 Pt 6, 1401–1408. [Google Scholar] [CrossRef]
  40. Shen, Y.; Zhang, S.; Sun, R.; Wu, T.; Qian, J. Understanding the interplay between host immunity and Epstein-Barr virus in NPC patients. Emerg. Microbes Infect. 2015, 4, e20. [Google Scholar] [CrossRef]
  41. Ning, S. Innate immune modulation in EBV infection. Herpesviridae 2011, 2, 1. [Google Scholar] [CrossRef] [PubMed]
  42. Forder, A.; Stewart, G.L.; Telkar, N.; Lam, W.L.; Garnis, C. New insights into the tumour immune microenvironment of nasopharyngeal carcinoma. Curr. Res. Immunol. 2022, 3, 222–227. [Google Scholar] [CrossRef] [PubMed]
  43. Ooft, M.L.; Ipenburg, J.A.v.; Sanders, M.E.; Kranendonk, M.; Hofland, I.; Bree, R.d.; Koljenović, S.; Willems, S.M. Prognostic role of tumour-associated macrophages and regulatory T cells in EBV-positive and EBV-negative nasopharyngeal carcinoma. J. Clin. Pathol. 2018, 71, 267–274. [Google Scholar] [CrossRef] [PubMed]
  44. Gong, L.; Kwong, D.L.; Dai, W.; Wu, P.; Li, S.; Yan, Q.; Zhang, Y.; Zhang, B.; Fang, X.; Liu, L.; et al. Comprehensive single-cell sequencing reveals the stromal dynamics and tumor-specific characteristics in the microenvironment of nasopharyngeal carcinoma. Nat. Commun. 2021, 12, 1540. [Google Scholar] [CrossRef] [PubMed]
  45. Azzi, T.; Lünemann, A.; Murer, A.; Ueda, S.; Béziat, V.; Malmberg, K.J.; Staubli, G.; Gysin, C.; Berger, C.; Münz, C.; et al. Role for early-differentiated natural killer cells in infectious mononucleosis. Blood 2014, 124, 2533–2543. [Google Scholar] [CrossRef] [PubMed]
  46. Rosenberg, J.; Huang, J. CD8+ T Cells and NK Cells: Parallel and Complementary Soldiers of Immunotherapy. Curr. Opin. Chem. Eng. 2018, 19, 9–20. [Google Scholar] [CrossRef] [PubMed]
  47. Li, Y.; Dong, H.; Dong, Y.; Wu, Q.; Jiang, N.; Luo, Q.; Chen, F. Distribution of CD8 T Cells and NK Cells in the Stroma in Relation to Recurrence or Metastasis of Nasopharyngeal Carcinoma. Cancer Manag. Res. 2022, 14, 2913–2926. [Google Scholar] [CrossRef] [PubMed]
  48. Chen, Y.P.; Yin, J.H.; Li, W.F.; Li, H.J.; Chen, D.P.; Zhang, C.J.; Lv, J.W.; Wang, Y.Q.; Li, X.M.; Li, J.Y.; et al. Single-cell transcriptomics reveals regulators underlying immune cell diversity and immune subtypes associated with prognosis in nasopharyngeal carcinoma. Cell Res. 2020, 30, 1024–1042. [Google Scholar] [CrossRef]
  49. Lu, J.; Chen, X.M.; Huang, H.R.; Zhao, F.P.; Wang, F.; Liu, X.; Li, X.P. Detailed analysis of inflammatory cell infiltration and the prognostic impact on nasopharyngeal carcinoma. Head Neck 2018, 40, 1245–1253. [Google Scholar] [CrossRef]
  50. Wolf, N.K.; Kissiov, D.U.; Raulet, D.H. Roles of natural killer cells in immunity to cancer, and applications to immunotherapy. Nat. Rev. Immunol. 2023, 23, 90–105. [Google Scholar] [CrossRef]
  51. Dianat-Moghadam, H.; Rokni, M.; Marofi, F.; Panahi, Y.; Yousefi, M. Natural killer cell-based immunotherapy: From transplantation toward targeting cancer stem cells. J. Cell. Physiol. 2018, 234, 259–273. [Google Scholar] [CrossRef] [PubMed]
  52. Dogra, P.; Rancan, C.; Ma, W.; Toth, M.; Senda, T.; Carpenter, D.J.; Kubota, M.; Matsumoto, R.; Thapa, P.; Szabo, P.A.; et al. Tissue Determinants of Human NK Cell Development, Function, and Residence. Cell 2020, 180, 749–763.e713. [Google Scholar] [CrossRef]
  53. Raulet, D.H.; Gasser, S.; Gowen, B.G.; Deng, W.; Jung, H. Regulation of ligands for the NKG2D activating receptor. Annu. Rev. Immunol. 2013, 31, 413–441. [Google Scholar] [CrossRef] [PubMed]
  54. Obiedat, A.; Charpak-Amikam, Y.; Tai-Schmiedel, J.; Seidel, E.; Mahameed, M.; Avril, T.; Stern-Ginossar, N.; Springuel, L.; Bolsée, J.; Gilham, D.E.; et al. The integrated stress response promotes B7H6 expression. J. Mol. Med. 2020, 98, 135–148. [Google Scholar] [CrossRef] [PubMed]
  55. Liao, N.S.; Bix, M.; Zijlstra, M.; Jaenisch, R.; Raulet, D. MHC class I deficiency: Susceptibility to natural killer (NK) cells and impaired NK activity. Science 1991, 253, 199–202. [Google Scholar] [CrossRef]
  56. Ljunggren, H.G.; Kärre, K. In search of the ‘missing self’: MHC molecules and NK cell recognition. Immunol. Today 1990, 11, 237–244. [Google Scholar] [CrossRef] [PubMed]
  57. Freud, A.G.; Mundy-Bosse, B.L.; Yu, J.; Caligiuri, M.A. The Broad Spectrum of Human Natural Killer Cell Diversity. Immunity 2017, 47, 820–833. [Google Scholar] [CrossRef]
  58. Angelo, L.S.; Banerjee, P.P.; Monaco-Shawver, L.; Rosen, J.B.; Makedonas, G.; Forbes, L.R.; Mace, E.M.; Orange, J.S. Practical NK cell phenotyping and variability in healthy adults. Immunol. Res. 2015, 62, 341–356. [Google Scholar] [CrossRef]
  59. Xu, Y.; Zhou, R.; Huang, C.; Zhang, M.; Li, J.; Zong, J.; Qiu, S.; Lin, S.; Chen, H.; Ye, Y.; et al. Analysis of the Expression of Surface Receptors on NK Cells and NKG2D on Immunocytes in Peripheral Blood of Patients with Nasopharyngeal Carcinoma. Asian Pac. J. Cancer Prev. 2018, 19, 661–665. [Google Scholar] [CrossRef]
  60. Zheng, Y.; Cao, K.Y.; Ng, S.P.; Chua, D.T.; Sham, J.S.; Kwong, D.L.; Ng, M.H.; Lu, L.; Zheng, B.J. Complementary activation of peripheral natural killer cell immunity in nasopharyngeal carcinoma. Cancer Sci. 2006, 97, 912–919. [Google Scholar] [CrossRef]
  61. Zhao, C.; Liu, Y.; Liang, Z.; Feng, H.; Xu, S.E. MACC1 facilitates the escape of nasopharyngeal carcinoma cells from killing by natural killer cells. Biotechnol. Biotechnol. Equip. 2019, 33, 579–588. [Google Scholar] [CrossRef]
  62. Jin, S.; Li, R.; Chen, M.Y.; Yu, C.; Tang, L.Q.; Liu, Y.M.; Li, J.P.; Liu, Y.N.; Luo, Y.L.; Zhao, Y.; et al. Single-cell transcriptomic analysis defines the interplay between tumor cells, viral infection, and the microenvironment in nasopharyngeal carcinoma. Cell Res. 2020, 30, 950–965. [Google Scholar] [CrossRef] [PubMed]
  63. Gao, P.; Lu, W.; Hu, S.; Zhao, K. Differentially Infiltrated Identification of Novel Diagnostic Biomarkers Associated with Immune Infiltration in Nasopharyngeal Carcinoma. Dis. Markers 2022, 2022, 3934704. [Google Scholar] [CrossRef] [PubMed]
  64. Chen, C.; Wang, C.; Pang, R.; Liu, H.; Yin, W.; Chen, J.; Tao, L. Comprehensive single-cell transcriptomic and proteomic analysis reveals NK cell exhaustion and unique tumor cell evolutionary trajectory in non-keratinizing nasopharyngeal carcinoma. J. Transl. Med. 2023, 21, 278. [Google Scholar] [CrossRef] [PubMed]
  65. Chen, H.; Duan, X.; Deng, X.; Huang, Y.; Zhou, X.; Zhang, S.; Zhang, X.; Liu, P.; Yang, C.; Liu, G.; et al. EBV-Upregulated B7-H3 Inhibits NK cell-Mediated Antitumor Function and Contributes to Nasopharyngeal Carcinoma Progression. Cancer Immunol. Res. 2023, 11, 830–846. [Google Scholar] [CrossRef] [PubMed]
  66. Singh, S.; Banerjee, S. Downregulation of HLA-ABC expression through promoter hypermethylation and downmodulation of MIC-A/B surface expression in LMP2A-positive epithelial carcinoma cell lines. Sci. Rep. 2020, 10, 5415. [Google Scholar] [CrossRef] [PubMed]
  67. Fan, C.; Tang, Y.; Wang, J.; Xiong, F.; Guo, C.; Wang, Y.; Xiang, B.; Zhou, M.; Li, X.; Wu, X.; et al. The emerging role of Epstein-Barr virus encoded microRNAs in nasopharyngeal carcinoma. J. Cancer 2018, 9, 2852–2864. [Google Scholar] [CrossRef] [PubMed]
  68. Wong, T.S.; Chen, S.; Zhang, M.J.; Chan, J.Y.; Gao, W. Epstein-Barr virus-encoded microRNA BART7 downregulates major histocompatibility complex class I chain-related peptide A and reduces the cytotoxicity of natural killer cells to nasopharyngeal carcinoma. Oncol. Lett. 2018, 16, 2887–2892. [Google Scholar] [CrossRef]
  69. Wang, W.; Tian, W.; Zhu, F.; Li, L.; Cai, J.; Wang, F.; Liu, K.; Jin, H.; Wang, J. MICA Gene Deletion in 3411 DNA Samples from Five Distinct Populations in Mainland China and Lack of Association with Nasopharyngeal Carcinoma (NPC) in a Southern Chinese Han population. Ann. Hum. Genet. 2016, 80, 319–326. [Google Scholar] [CrossRef]
  70. Tse, K.P.; Su, W.H.; Yang, M.L.; Cheng, H.Y.; Tsang, N.M.; Chang, K.P.; Hao, S.P.; Yao Shugart, Y.; Chang, Y.S. A gender-specific association of CNV at 6p21.3 with NPC susceptibility. Hum. Mol. Genet. 2011, 20, 2889–2896. [Google Scholar] [CrossRef]
  71. Cao, W.; Xi, X.; Hao, Z.; Li, W.; Kong, Y.; Cui, L.; Ma, C.; Ba, D.; He, W. RAET1E2, a soluble isoform of the UL16-binding protein RAET1E produced by tumor cells, inhibits NKG2D-mediated NK cytotoxicity. J. Biol. Chem. 2007, 282, 18922–18928. [Google Scholar] [CrossRef] [PubMed]
  72. Li, L.; Tian, W.; Wang, W.; Liu, K.; Wang, J.; Jin, H.; Cai, J.; Wang, J. NKG2C copy number variations in five distinct populations in mainland China and susceptibility to nasopharyngeal carcinoma (NPC). Hum. Immunol. 2015, 76, 90–94. [Google Scholar] [CrossRef] [PubMed]
  73. Butsch Kovacic, M.; Martin, M.; Gao, X.; Fuksenko, T.; Chen, C.J.; Cheng, Y.J.; Chen, J.Y.; Apple, R.; Hildesheim, A.; Carrington, M. Variation of the killer cell immunoglobulin-like receptors and HLA-C genes in nasopharyngeal carcinoma. Cancer Epidemiol. Biomark. Prev. 2005, 14, 2673–2677. [Google Scholar] [CrossRef] [PubMed]
  74. Cai, M.B.; Han, H.Q.; Bei, J.X.; Liu, C.C.; Lei, J.J.; Cui, Q.; Feng, Q.S.; Wang, H.Y.; Zhang, J.X.; Liang, Y.; et al. Expression of human leukocyte antigen G is associated with prognosis in nasopharyngeal carcinoma. Int. J. Biol. Sci. 2012, 8, 891–900. [Google Scholar] [CrossRef] [PubMed]
  75. Wu, B.; Yang, H.; Ying, S.; Lu, H.; Wang, W.; Lv, J.; Xiong, H.; Hu, W. High HLA-F Expression Is a Poor Prognosis Factor in Patients with Nasopharyngeal Carcinoma. Anal. Cell. Pathol. 2018, 2018, 7691704. [Google Scholar] [CrossRef] [PubMed]
  76. Li, J.; Lin, T.Y.; Chen, L.; Liu, Y.; Dian, M.J.; Hao, W.C.; Lin, X.L.; Li, X.Y.; Li, Y.L.; Lian, M.; et al. miR-19 regulates the expression of interferon-induced genes and MHC class I genes in human cancer cells. Int. J. Med. Sci. 2020, 17, 953–964. [Google Scholar] [CrossRef] [PubMed]
  77. Guo, K.Y.; Mei, J.Z.; Yao, K.T. Immunoediting of natural killer cells by human nasopharyngeal carcinoma cell line: Altered expression of KIRs and NKG2D receptors leads to reduction of natural killer cell-mediated cytolysis. Nan Fang Yi Ke Da Xue Xue Bao J. South. Med. Univ. 2007, 27, 247–249. [Google Scholar]
  78. Makowska, A.; Meier, S.; Shen, L.; Busson, P.; Baloche, V.; Kontny, U. Anti-PD-1 antibody increases NK cell cytotoxicity towards nasopharyngeal carcinoma cells in the context of chemotherapy-induced upregulation of PD-1 and PD-L1. Cancer Immunol. Immunother. CII 2021, 70, 323–336. [Google Scholar] [CrossRef]
  79. Makowska, A.; Lelabi, N.; Nothbaum, C.; Shen, L.; Busson, P.; Tran, T.T.B.; Eble, M.; Kontny, U. Radiotherapy Combined with PD-1 Inhibition Increases NK Cell Cytotoxicity towards Nasopharyngeal Carcinoma Cells. Cells 2021, 10, 2458. [Google Scholar] [CrossRef]
  80. Liou, A.K.; Soon, G.; Tan, L.; Peng, Y.; Cher, B.M.; Goh, B.C.; Wang, S.; Lim, C.M. Elevated IL18 levels in Nasopharyngeal carcinoma induced PD-1 expression on NK cells in TILS leading to poor prognosis. Oral Oncol. 2020, 104, 104616. [Google Scholar] [CrossRef]
  81. Yang, J.; Hu, M.; Bai, X.; Ding, X.; Xie, L.; Ma, J.; Fan, B.; Yu, J. Plasma levels of soluble programmed death ligand 1 (sPD-L1) in WHO II/III nasopharyngeal carcinoma (NPC): A preliminary study. Medicine 2019, 98, e17231. [Google Scholar] [CrossRef] [PubMed]
  82. Nanbo, A.; Ohashi, M.; Yoshiyama, H.; Ohba, Y. The Role of Transforming Growth Factor β in Cell-to-Cell Contact-Mediated Epstein-Barr Virus Transmission. Front. Microbiol. 2018, 9, 984. [Google Scholar] [CrossRef] [PubMed]
  83. Makowska, A.; Wahab, L.; Braunschweig, T.; Kapetanakis, N.I.; Vokuhl, C.; Denecke, B.; Shen, L.; Busson, P.; Kontny, U. Interferon beta induces apoptosis in nasopharyngeal carcinoma cells via the TRAIL-signaling pathway. Oncotarget 2018, 9, 14228–14250. [Google Scholar] [CrossRef] [PubMed]
  84. Makowska, A.; Franzen, S.; Braunschweig, T.; Denecke, B.; Shen, L.; Baloche, V.; Busson, P.; Kontny, U. Interferon beta increases NK cell cytotoxicity against tumor cells in patients with nasopharyngeal carcinoma via tumor necrosis factor apoptosis-inducing ligand. Cancer Immunol. Immunother. 2019, 68, 1317–1329. [Google Scholar] [CrossRef] [PubMed]
  85. Robinson, D.; Shibuya, K.; Mui, A.; Zonin, F.; Murphy, E.; Sana, T.; Hartley, S.B.; Menon, S.; Kastelein, R.; Bazan, F.; et al. IGIF does not drive Th1 development but synergizes with IL-12 for interferon-gamma production and activates IRAK and NFkappaB. Immunity 1997, 7, 571–581. [Google Scholar] [CrossRef] [PubMed]
  86. Strowig, T.; Brilot, F.; Arrey, F.; Bougras, G.; Thomas, D.; Muller, W.A.; Münz, C. Tonsilar NK cells restrict B cell transformation by the Epstein-Barr virus via IFN-gamma. PLoS Pathog. 2008, 4, e27. [Google Scholar] [CrossRef] [PubMed]
  87. Jud, A.; Kotur, M.; Berger, C.; Gysin, C.; Nadal, D.; Lünemann, A. Tonsillar CD56brightNKG2A+ NK cells restrict primary Epstein-Barr virus infection in B cells via IFN-γ. Oncotarget 2017, 8, 6130–6141. [Google Scholar] [CrossRef] [PubMed]
  88. Zhang, M.; Wen, B.; Anton, O.M.; Yao, Z.; Dubois, S.; Ju, W.; Sato, N.; DiLillo, D.J.; Bamford, R.N.; Ravetch, J.V.; et al. IL-15 enhanced antibody-dependent cellular cytotoxicity mediated by NK cells and macrophages. Proc. Natl. Acad. Sci. USA 2018, 115, E10915–E10924. [Google Scholar] [CrossRef] [PubMed]
  89. Wagner, J.A.; Rosario, M.; Romee, R.; Berrien-Elliott, M.M.; Schneider, S.E.; Leong, J.W.; Sullivan, R.P.; Jewell, B.A.; Becker-Hapak, M.; Schappe, T.; et al. CD56bright NK cells exhibit potent antitumor responses following IL-15 priming. J. Clin. Investig. 2017, 127, 4042–4058. [Google Scholar] [CrossRef]
  90. Romee, R.; Schneider, S.E.; Leong, J.W.; Chase, J.M.; Keppel, C.R.; Sullivan, R.P.; Cooper, M.A.; Fehniger, T.A. Cytokine activation induces human memory-like NK cells. Blood 2012, 120, 4751–4760. [Google Scholar] [CrossRef]
  91. Parrish-Novak, J.; Dillon, S.R.; Nelson, A.; Hammond, A.; Sprecher, C.; Gross, J.A.; Johnston, J.; Madden, K.; Xu, W.; West, J.; et al. Interleukin 21 and its receptor are involved in NK cell expansion and regulation of lymphocyte function. Nature 2000, 408, 57–63. [Google Scholar] [CrossRef] [PubMed]
  92. Li, J.P.; Wu, C.Y.; Chen, M.Y.; Liu, S.X.; Yan, S.M.; Kang, Y.F.; Sun, C.; Grandis, J.R.; Zeng, M.S.; Zhong, Q. PD-1+CXCR5−CD4+ Th-CXCL13 cell subset drives B cells into tertiary lymphoid structures of nasopharyngeal carcinoma. J. Immunother. Cancer 2021, 9, e002101. [Google Scholar] [CrossRef] [PubMed]
  93. Ma, W.; Feng, L.; Zhang, S.; Zhang, H.; Zhang, X.; Qi, X.; Zhang, Y.; Feng, Q.; Xiang, T.; Zeng, Y.X. Induction of chemokine (C-C motif) ligand 5 by Epstein-Barr virus infection enhances tumor angiogenesis in nasopharyngeal carcinoma. Cancer Sci. 2018, 109, 1710–1722. [Google Scholar] [CrossRef]
  94. Makowska, A.; Braunschweig, T.; Denecke, B.; Shen, L.; Baloche, V.; Busson, P.; Kontny, U. Interferon β and Anti-PD-1/PD-L1 Checkpoint Blockade Cooperate in NK Cell-Mediated Killing of Nasopharyngeal Carcinoma Cells. Transl. Oncol. 2019, 12, 1237–1256. [Google Scholar] [CrossRef] [PubMed]
  95. Malarkannan, S. Molecular mechanisms of FasL-mediated ‘reverse-signaling’. Mol. Immunol. 2020, 127, 31–37. [Google Scholar] [CrossRef] [PubMed]
  96. López-Montañés, M.; Alari-Pahissa, E.; Sintes, J.; Martínez-Rodríguez, J.E.; Muntasell, A.; López-Botet, M. Antibody-Dependent NK Cell Activation Differentially Targets EBV-Infected Cells in Lytic Cycle and Bystander B Lymphocytes Bound to Viral Antigen-Containing Particles. J. Immunol. 2017, 199, 656–665. [Google Scholar] [CrossRef]
  97. Wang, J.; Ge, J.; Wang, Y.; Xiong, F.; Guo, J.; Jiang, X.; Zhang, L.; Deng, X.; Gong, Z.; Zhang, S.; et al. EBV miRNAs BART11 and BART17-3p promote immune escape through the enhancer-mediated transcription of PD-L1. Nat. Commun. 2022, 13, 866. [Google Scholar] [CrossRef] [PubMed]
  98. Voskoboinik, I.; Whisstock, J.C.; Trapani, J.A. Perforin and granzymes: Function, dysfunction and human pathology. Nat. Rev. Immunol. 2015, 15, 388–400. [Google Scholar] [CrossRef] [PubMed]
  99. Zamai, L.; Ahmad, M.; Bennett, I.M.; Azzoni, L.; Alnemri, E.S.; Perussia, B. Natural killer (NK) cell-mediated cytotoxicity: Differential use of TRAIL and Fas ligand by immature and mature primary human NK cells. J. Exp. Med. 1998, 188, 2375–2380. [Google Scholar] [CrossRef]
  100. Bhatnagar, N.; Ahmad, F.; Hong, H.S.; Eberhard, J.; Lu, I.N.; Ballmaier, M.; Schmidt, R.E.; Jacobs, R.; Meyer-Olson, D. FcγRIII (CD16)-mediated ADCC by NK cells is regulated by monocytes and FcγRII (CD32). Eur. J. Immunol. 2014, 44, 3368–3379. [Google Scholar] [CrossRef]
  101. Wang, R.; Jaw, J.J.; Stutzman, N.C.; Zou, Z.; Sun, P.D. Natural killer cell-produced IFN-γ and TNF-α induce target cell cytolysis through up-regulation of ICAM-1. J. Leukoc. Biol. 2012, 91, 299–309. [Google Scholar] [CrossRef] [PubMed]
  102. Chijioke, O.; Müller, A.; Feederle, R.; Barros, M.H.; Krieg, C.; Emmel, V.; Marcenaro, E.; Leung, C.S.; Antsiferova, O.; Landtwing, V.; et al. Human natural killer cells prevent infectious mononucleosis features by targeting lytic Epstein-Barr virus infection. Cell Rep. 2013, 5, 1489–1498. [Google Scholar] [CrossRef]
  103. Orange, J.S. Natural killer cell deficiency. J. Allergy Clin. Immunol. 2013, 132, 515–525. [Google Scholar] [CrossRef] [PubMed]
  104. Hatton, O.; Strauss-Albee, D.M.; Zhao, N.Q.; Haggadone, M.D.; Pelpola, J.S.; Krams, S.M.; Martinez, O.M.; Blish, C.A. NKG2A-Expressing Natural Killer Cells Dominate the Response to Autologous Lymphoblastoid Cells Infected with Epstein-Barr Virus. Front. Immunol. 2016, 7, 607. [Google Scholar] [CrossRef] [PubMed]
  105. Williams, L.R.; Quinn, L.L.; Rowe, M.; Zuo, J. Induction of the Lytic Cycle Sensitizes Epstein-Barr Virus-Infected B Cells to NK Cell Killing That Is Counteracted by Virus-Mediated NK Cell Evasion Mechanisms in the Late Lytic Cycle. J. Virol. 2016, 90, 947–958. [Google Scholar] [CrossRef] [PubMed]
  106. Jochum, S.; Moosmann, A.; Lang, S.; Hammerschmidt, W.; Zeidler, R. The EBV immunoevasins vIL-10 and BNLF2a protect newly infected B cells from immune recognition and elimination. PLoS Pathog. 2012, 8, e1002704. [Google Scholar] [CrossRef] [PubMed]
  107. Mancusi, A.; Ruggeri, L.; Velardi, A. Haploidentical hematopoietic transplantation for the cure of leukemia: From its biology to clinical translation. Blood 2016, 128, 2616–2623. [Google Scholar] [CrossRef] [PubMed]
  108. Miller, J.S.; Soignier, Y.; Panoskaltsis-Mortari, A.; McNearney, S.A.; Yun, G.H.; Fautsch, S.K.; McKenna, D.; Le, C.; Defor, T.E.; Burns, L.J.; et al. Successful adoptive transfer and in vivo expansion of human haploidentical NK cells in patients with cancer. Blood 2005, 105, 3051–3057. [Google Scholar] [CrossRef] [PubMed]
  109. Romee, R.; Rosario, M.; Berrien-Elliott, M.M.; Wagner, J.A.; Jewell, B.A.; Schappe, T.; Leong, J.W.; Abdel-Latif, S.; Schneider, S.E.; Willey, S.; et al. Cytokine-induced memory-like natural killer cells exhibit enhanced responses against myeloid leukemia. Sci. Transl. Med. 2016, 8, 357ra123. [Google Scholar] [CrossRef]
  110. Berrien-Elliott, M.M.; Foltz, J.A.; Russler-Germain, D.A.; Neal, C.C.; Tran, J.; Gang, M.; Wong, P.; Fisk, B.; Cubitt, C.C.; Marin, N.D.; et al. Hematopoietic cell transplantation donor-derived memory-like NK cells functionally persist after transfer into patients with leukemia. Sci. Transl. Med. 2022, 14, eabm1375. [Google Scholar] [CrossRef]
  111. Bednarski, J.J.; Zimmerman, C.; Berrien-Elliott, M.M.; Foltz, J.A.; Becker-Hapak, M.; Neal, C.C.; Foster, M.; Schappe, T.; McClain, E.; Pence, P.P.; et al. Donor memory-like NK cells persist and induce remissions in pediatric patients with relapsed AML after transplant. Blood 2022, 139, 1670–1683. [Google Scholar] [CrossRef] [PubMed]
  112. Berrien-Elliott, M.M.; Becker-Hapak, M.; Cashen, A.F.; Jacobs, M.; Wong, P.; Foster, M.; McClain, E.; Desai, S.; Pence, P.; Cooley, S.; et al. Systemic IL-15 promotes allogeneic cell rejection in patients treated with natural killer cell adoptive therapy. Blood 2022, 139, 1177–1183. [Google Scholar] [CrossRef] [PubMed]
  113. Shimasaki, N.; Coustan-Smith, E.; Kamiya, T.; Campana, D. Expanded and armed natural killer cells for cancer treatment. Cytotherapy 2016, 18, 1422–1434. [Google Scholar] [CrossRef]
  114. Chen, X.; Liang, R.; Zhu, X. Anti-EGFR therapies in nasopharyngeal carcinoma. Biomed. Pharmacother. Biomed. Pharmacother. 2020, 131, 110649. [Google Scholar] [CrossRef]
  115. Tan, L.S.Y.; Wong, B.; Gangodu, N.R.; Lee, A.Z.E.; Kian Fong Liou, A.; Loh, K.S.; Li, H.; Yann Lim, M.; Salazar, A.M.; Lim, C.M. Enhancing the immune stimulatory effects of cetuximab therapy through TLR3 signalling in Epstein-Barr virus (EBV) positive nasopharyngeal carcinoma. Oncoimmunology 2018, 7, e1500109. [Google Scholar] [CrossRef] [PubMed]
  116. Lim, C.M.; Liou, A.; Poon, M.; Koh, L.P.; Tan, L.K.; Loh, K.S.; Petersson, B.F.; Ting, E.; Campana, D.; Goh, B.C.; et al. Phase I study of expanded natural killer cells in combination with cetuximab for recurrent/metastatic nasopharyngeal carcinoma. Cancer Immunol. Immunother. CII 2022, 71, 2277–2286. [Google Scholar] [CrossRef]
  117. Prasad, M.; Ponnalagu, S.; Zeng, Q.; Luu, K.; Lang, S.M.; Wong, H.Y.; Cheng, M.S.; Wu, M.; Mallilankaraman, K.; Sobota, R.M.; et al. Epstein-Barr virus-induced ectopic CD137 expression helps nasopharyngeal carcinoma to escape immune surveillance and enables targeting by chimeric antigen receptors. Cancer Immunol. Immunother. 2022, 71, 2583–2596. [Google Scholar] [CrossRef]
  118. Liu, Y.; Cheng, Y.; Xu, Y.; Wang, Z.; Du, X.; Li, C.; Peng, J.; Gao, L.; Liang, X.; Ma, C. Increased expression of programmed cell death protein 1 on NK cells inhibits NK-cell-mediated anti-tumor function and indicates poor prognosis in digestive cancers. Oncogene 2017, 36, 6143–6153. [Google Scholar] [CrossRef] [PubMed]
  119. Beldi-Ferchiou, A.; Lambert, M.; Dogniaux, S.; Vély, F.; Vivier, E.; Olive, D.; Dupuy, S.; Levasseur, F.; Zucman, D.; Lebbé, C.; et al. PD-1 mediates functional exhaustion of activated NK cells in patients with Kaposi sarcoma. Oncotarget 2016, 7, 72961–72977. [Google Scholar] [CrossRef]
  120. Hsu, J.; Hodgins, J.J.; Marathe, M.; Nicolai, C.J.; Bourgeois-Daigneault, M.C.; Trevino, T.N.; Azimi, C.S.; Scheer, A.K.; Randolph, H.E.; Thompson, T.W.; et al. Contribution of NK cells to immunotherapy mediated by PD-1/PD-L1 blockade. J. Clin. Investig. 2018, 128, 4654–4668. [Google Scholar] [CrossRef]
  121. Zhang, Q.; Bi, J.; Zheng, X.; Chen, Y.; Wang, H.; Wu, W.; Wang, Z.; Wu, Q.; Peng, H.; Wei, H.; et al. Blockade of the checkpoint receptor TIGIT prevents NK cell exhaustion and elicits potent anti-tumor immunity. Nat. Immunol. 2018, 19, 723–732. [Google Scholar] [CrossRef] [PubMed]
  122. Miyake, T.; Kumagai, Y.; Kato, H.; Guo, Z.; Matsushita, K.; Satoh, T.; Kawagoe, T.; Kumar, H.; Jang, M.H.; Kawai, T.; et al. Poly I:C-induced activation of NK cells by CD8 alpha+ dendritic cells via the IPS-1 and TRIF-dependent pathways. J. Immunol. 2009, 183, 2522–2528. [Google Scholar] [CrossRef] [PubMed]
  123. López-Albaitero, A.; Lee, S.C.; Morgan, S.; Grandis, J.R.; Gooding, W.E.; Ferrone, S.; Ferris, R.L. Role of polymorphic Fc gamma receptor IIIa and EGFR expression level in cetuximab mediated, NK cell dependent in vitro cytotoxicity of head and neck squamous cell carcinoma cells. Cancer Immunol. Immunother. 2009, 58, 1853–1864. [Google Scholar] [CrossRef] [PubMed]
  124. Chen, X.; Trivedi, P.P.; Ge, B.; Krzewski, K.; Strominger, J.L. Many NK cell receptors activate ERK2 and JNK1 to trigger microtubule organizing center and granule polarization and cytotoxicity. Proc. Natl. Acad. Sci. USA 2007, 104, 6329–6334. [Google Scholar] [CrossRef] [PubMed]
  125. Dietsch, G.N.; Lu, H.; Yang, Y.; Morishima, C.; Chow, L.Q.; Disis, M.L.; Hershberg, R.M. Coordinated Activation of Toll-Like Receptor8 (TLR8) and NLRP3 by the TLR8 Agonist, VTX-2337, Ignites Tumoricidal Natural Killer Cell Activity. PLoS ONE 2016, 11, e0148764. [Google Scholar] [CrossRef] [PubMed]
  126. Ho, S.S.; Zhang, W.Y.; Tan, N.Y.; Khatoo, M.; Suter, M.A.; Tripathi, S.; Cheung, F.S.; Lim, W.K.; Tan, P.H.; Ngeow, J.; et al. The DNA Structure-Specific Endonuclease MUS81 Mediates DNA Sensor STING-Dependent Host Rejection of Prostate Cancer Cells. Immunity 2016, 44, 1177–1189. [Google Scholar] [CrossRef] [PubMed]
  127. Schadt, L.; Sparano, C.; Schweiger, N.A.; Silina, K.; Cecconi, V.; Lucchiari, G.; Yagita, H.; Guggisberg, E.; Saba, S.; Nascakova, Z.; et al. Cancer-Cell-Intrinsic cGAS Expression Mediates Tumor Immunogenicity. Cell Rep. 2019, 29, 1236–1248.e1237. [Google Scholar] [CrossRef] [PubMed]
  128. Nicolai, C.J.; Wolf, N.; Chang, I.C.; Kirn, G.; Marcus, A.; Ndubaku, C.O.; McWhirter, S.M.; Raulet, D.H. NK cells mediate clearance of CD8+ T cell-resistant tumors in response to STING agonists. Sci. Immunol. 2020, 5, eaaz2738. [Google Scholar] [CrossRef] [PubMed]
  129. André, P.; Denis, C.; Soulas, C.; Bourbon-Caillet, C.; Lopez, J.; Arnoux, T.; Bléry, M.; Bonnafous, C.; Gauthier, L.; Morel, A.; et al. Anti-NKG2A mAb Is a Checkpoint Inhibitor that Promotes Anti-tumor Immunity by Unleashing Both T and NK Cells. Cell 2018, 175, 1731–1743.e1713. [Google Scholar] [CrossRef]
  130. Vey, N.; Karlin, L.; Sadot-Lebouvier, S.; Broussais, F.; Berton-Rigaud, D.; Rey, J.; Charbonnier, A.; Marie, D.; André, P.; Paturel, C.; et al. A phase 1 study of lirilumab (antibody against killer immunoglobulin-like receptor antibody KIR2D; IPH2102) in patients with solid tumors and hematologic malignancies. Oncotarget 2018, 9, 17675–17688. [Google Scholar] [CrossRef]
  131. Carlsten, M.; Korde, N.; Kotecha, R.; Reger, R.; Bor, S.; Kazandjian, D.; Landgren, O.; Childs, R.W. Checkpoint Inhibition of KIR2D with the Monoclonal Antibody IPH2101 Induces Contraction and Hyporesponsiveness of NK Cells in Patients with Myeloma. Clin. Cancer Res. 2016, 22, 5211–5222. [Google Scholar] [CrossRef] [PubMed]
  132. Gauthier, L.; Morel, A.; Anceriz, N.; Rossi, B.; Blanchard-Alvarez, A.; Grondin, G.; Trichard, S.; Cesari, C.; Sapet, M.; Bosco, F.; et al. Multifunctional Natural Killer Cell Engagers Targeting NKp46 Trigger Protective Tumor Immunity. Cell 2019, 177, 1701–1713.e1716. [Google Scholar] [CrossRef] [PubMed]
  133. Nikkhoi, S.K.; Li, G.; Eleya, S.; Yang, G.; Vandavasi, V.G.; Hatefi, A. Bispecific killer cell engager with high affinity and specificity toward CD16a on NK cells for cancer immunotherapy. Front. Immunol. 2022, 13, 1039969. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Tumor immune microenvironment of EBV+ NPC. EBV-associated LMP1/2 and EBERs activate NF-κB, PI3K/AKT, and Wnt/β-catenin pathways to induce the proliferation and immune evasion of NPC cells. TGF-β released by EBV+ NPC recruits immune-suppressive Tregs and LAMP3+ DCs. LAMP3+ DCs release IDO to promote Treg proliferation. TGF-β induces the M2 polarization of TAMs. MDSC promotes M2 proliferation. The effective T cell is inhibited by Treg and MDSC. T cell cytotoxicity is negatively regulated by the binding immune checkpoint receptors and their ligands. The NPC cell escapes the CD8+ T cell’s killing effect by diminishing MHC I expression. IL-2 activates the CD8+ T cell and NK cell, which are the major immune effectors. The B cell is a component within the TIME of EBV+ NPC. How NK cells interact with cytokines and other components and whether immune checkpoint molecules impact NK cell function need further discussion. Abbreviations: TIME, tumor immune microenvironment; EBV, Epstein–Barr virus; NPC, nasopharyngeal carcinoma; LMP1/2, latent membrane protein 1/2; EBERs, EBV-encoded small RNAs; TGF-β, transforming growth factor-β; Treg, regulatory T cell; LAMP3, lysosome-associated membrane glycoprotein 3; DC, dendritic cell; IDO, indoleamine-pyrrole 2,3-dioxygenase; TAM, tumor-associated macrophage; M2, M2-polarized TAM; MDSC, myeloid-derived suppressor cell; MHC I, major histocompatibility complex class I; IL-2, interleukin-2; NK, natural killer; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; MICA/B, major histocompatibility complex class-I-related chain A/B; IFN-γ, interferon-γ; Gal-9, galectin-9; TIM-3, T cell immunoglobulin domain and mucin domain-3; PD-1, programmed death-1; PD-L1, programmed death ligand-1; CTLA-4, cytotoxic T-lymphocyte antigen 4.
Figure 1. Tumor immune microenvironment of EBV+ NPC. EBV-associated LMP1/2 and EBERs activate NF-κB, PI3K/AKT, and Wnt/β-catenin pathways to induce the proliferation and immune evasion of NPC cells. TGF-β released by EBV+ NPC recruits immune-suppressive Tregs and LAMP3+ DCs. LAMP3+ DCs release IDO to promote Treg proliferation. TGF-β induces the M2 polarization of TAMs. MDSC promotes M2 proliferation. The effective T cell is inhibited by Treg and MDSC. T cell cytotoxicity is negatively regulated by the binding immune checkpoint receptors and their ligands. The NPC cell escapes the CD8+ T cell’s killing effect by diminishing MHC I expression. IL-2 activates the CD8+ T cell and NK cell, which are the major immune effectors. The B cell is a component within the TIME of EBV+ NPC. How NK cells interact with cytokines and other components and whether immune checkpoint molecules impact NK cell function need further discussion. Abbreviations: TIME, tumor immune microenvironment; EBV, Epstein–Barr virus; NPC, nasopharyngeal carcinoma; LMP1/2, latent membrane protein 1/2; EBERs, EBV-encoded small RNAs; TGF-β, transforming growth factor-β; Treg, regulatory T cell; LAMP3, lysosome-associated membrane glycoprotein 3; DC, dendritic cell; IDO, indoleamine-pyrrole 2,3-dioxygenase; TAM, tumor-associated macrophage; M2, M2-polarized TAM; MDSC, myeloid-derived suppressor cell; MHC I, major histocompatibility complex class I; IL-2, interleukin-2; NK, natural killer; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; MICA/B, major histocompatibility complex class-I-related chain A/B; IFN-γ, interferon-γ; Gal-9, galectin-9; TIM-3, T cell immunoglobulin domain and mucin domain-3; PD-1, programmed death-1; PD-L1, programmed death ligand-1; CTLA-4, cytotoxic T-lymphocyte antigen 4.
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Figure 2. Profile of NK cells within the TIME of EBV+ NPC. (A) EBV+ NPC impairs NK cell activation; (B) EBV+ NPC promotes NK cell inhibition; (C) exhausted markers on NK cell; (D) cytotoxic function of NK cell is suboptimal. Abbreviations: EBV, Epstein–Barr virus; NPC, nasopharyngeal carcinoma; NK, natural killer; LMP2, latent membrane protein 2; miR, microRNA, a small non-coding RNA molecule; MACC1, metastasis-associated colon cancer 1; B7-H6, B7 homolog 6; HLA, human leukocyte antigen; ULBP, UL16 binding protein; MICA/B, major histocompatibility complex class-I-related chain A/B; CD94, killer cell lectin-like receptor subfamily D, member 1 (KLRD1), pairs with the NKG2 molecule as a heterodimer; NKp30, natural cytotoxicity triggering receptor 3; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; TFs, transcription factors; KIR, killer immunoglobulin-like receptor; MHC, major histocompatibility complex; TRAIL, TNF-related apoptosis-inducing ligand; TRAILR, receptor of TRAIL; FASL, Fas ligand; FAS, Fas receptor, apoptosis antigen 1; CD16, Fc receptors FcγRIII; ADCC, antibody-dependent cell-mediated cytotoxicity; PD-1, programmed death-1; PD-L1, programmed death ligand-1; TIGIT, T cell immunoreceptor with Ig and ITIM domains; PVR, polio virus receptor; CD96, T cell activation, increased late expression (TACTILE); LAG3, lymphocyte-activation gene 3; GAL3, galectin 3; B7-H3, B7 homolog 3, CD276; B7-H3R, receptor of B7-H3, not identified yet.
Figure 2. Profile of NK cells within the TIME of EBV+ NPC. (A) EBV+ NPC impairs NK cell activation; (B) EBV+ NPC promotes NK cell inhibition; (C) exhausted markers on NK cell; (D) cytotoxic function of NK cell is suboptimal. Abbreviations: EBV, Epstein–Barr virus; NPC, nasopharyngeal carcinoma; NK, natural killer; LMP2, latent membrane protein 2; miR, microRNA, a small non-coding RNA molecule; MACC1, metastasis-associated colon cancer 1; B7-H6, B7 homolog 6; HLA, human leukocyte antigen; ULBP, UL16 binding protein; MICA/B, major histocompatibility complex class-I-related chain A/B; CD94, killer cell lectin-like receptor subfamily D, member 1 (KLRD1), pairs with the NKG2 molecule as a heterodimer; NKp30, natural cytotoxicity triggering receptor 3; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; TFs, transcription factors; KIR, killer immunoglobulin-like receptor; MHC, major histocompatibility complex; TRAIL, TNF-related apoptosis-inducing ligand; TRAILR, receptor of TRAIL; FASL, Fas ligand; FAS, Fas receptor, apoptosis antigen 1; CD16, Fc receptors FcγRIII; ADCC, antibody-dependent cell-mediated cytotoxicity; PD-1, programmed death-1; PD-L1, programmed death ligand-1; TIGIT, T cell immunoreceptor with Ig and ITIM domains; PVR, polio virus receptor; CD96, T cell activation, increased late expression (TACTILE); LAG3, lymphocyte-activation gene 3; GAL3, galectin 3; B7-H3, B7 homolog 3, CD276; B7-H3R, receptor of B7-H3, not identified yet.
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Figure 3. Interaction between NK cells and cytokines, chemokines, and other immune cells. NK-cell-derived CCL5 and XCL1/2 play a vital role in recruiting DCs; IFN-γ released by NK cells induces the apoptosis of NPC cells. IL-12, IL-15, and IL-18 cocktail cytokines convert NK cells into “memory-like” NK cells. IL-2 and IL-21 promote strong NK cell expansion and cytotoxicity. “×” The cytotoxicity of CD8+ T cells is inhibited through MHC I downregulation in EBV+ NPC. “√” The NK cell is activated via “missing self” recognition of downregulated MHC I expression on EBV+ NPC. Effective T cells release pro-inflammatory cytokine IFN-β to enhance NK cell cytotoxicity. Abbreviations: NPC, nasopharyngeal carcinoma; TGF-β, transforming growth factor-β; MDSC, myeloid-derived suppressor cell; Treg, regulatory T cell; NK, natural killer; IFN, interferon; TCR, T-cell receptor; MHC I, major histocompatibility complex class I; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; KIR, killer immunoglobulin-like receptor; CCL5, chemokine (C–C motif) ligand 5; XCL1/2, chemokine C motif ligand 1/2; DC, dendritic cell; TAM, tumor-associated macrophage.
Figure 3. Interaction between NK cells and cytokines, chemokines, and other immune cells. NK-cell-derived CCL5 and XCL1/2 play a vital role in recruiting DCs; IFN-γ released by NK cells induces the apoptosis of NPC cells. IL-12, IL-15, and IL-18 cocktail cytokines convert NK cells into “memory-like” NK cells. IL-2 and IL-21 promote strong NK cell expansion and cytotoxicity. “×” The cytotoxicity of CD8+ T cells is inhibited through MHC I downregulation in EBV+ NPC. “√” The NK cell is activated via “missing self” recognition of downregulated MHC I expression on EBV+ NPC. Effective T cells release pro-inflammatory cytokine IFN-β to enhance NK cell cytotoxicity. Abbreviations: NPC, nasopharyngeal carcinoma; TGF-β, transforming growth factor-β; MDSC, myeloid-derived suppressor cell; Treg, regulatory T cell; NK, natural killer; IFN, interferon; TCR, T-cell receptor; MHC I, major histocompatibility complex class I; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; KIR, killer immunoglobulin-like receptor; CCL5, chemokine (C–C motif) ligand 5; XCL1/2, chemokine C motif ligand 1/2; DC, dendritic cell; TAM, tumor-associated macrophage.
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Table 1. Receptors and ligands relevant to NK cells in NPC.
Table 1. Receptors and ligands relevant to NK cells in NPC.
Molecules on NK CellsCorresponding Receptors/LigandsFunctional Signal Reported in NPCReferences
(1) Activating signaling
NKG2DMICA/B
ULBP		LMP2 induced MICA/B downregulation in NPC.[66]
EBV-encoded mircoRNAs promoted MICA/B downregulation in NPC.[67,68]
MICA gene deletion was found in NPC.[69,70]
Free soluble ULBP protein secreted by NPC cells impaired NK function.[71]
Over-expression of MACC1 on NPC cells reduced NKG2D expression on NK cells.[61]
NKp30B7-H6A low percentage of NKp30+NK cells was found in NPC tissues.[59]
NKG2C/CD94HLA-ECD94 expression on NK cells was increased in NPC; NKG2C-HLA-E signaling pathway was not relevant to genetic susceptibility in NPC.[44,72]
(2) Inhibitory signaling
KIRMHC IHLA-C (tumor cell) and KIR2DL4 (NK cell) interaction was reported in NPC.[62,73]
Higher HLA-G expression was found in NPC when compared with normal tissue.[74]
Higher soluble HLA-F was found in NPC plasma than normal controls.[75]
miR-19 reduced MHC I molecule expression on NPC cell line.[76]
Persistent exposure to CNE2 cell line increased KIR expression on NK.[77]
NKG2A/CD94NKG2A expression of NK cells was not upregulated in NPC; HLA-E (tumor cell) and CD94 (NK cell) interaction was found in NPC.[44,62]
PD-1PD-L1B7-H3 knockdown in EBV+ NPC cell line increased PD-1 expression on cocultured NK cells.[65]
Chemotherapy upregulated PD-1 on NK cells and PD-L1 on NPC cells via NF-κB pathway.[78]
Radiotherapy for NPC increased PD-1 expression on NK cells and PD-L1 expression on tumor cells.[79]
PD-1 expression on NK cells in NPC could be induced by IL-18.[80]
Soluble PD-L1 was detected in NPC plasma, indicating poor prognosis.[81]
TIGITPVRTIGIT-PVR interaction was detected between NK and tumor cells and between NK and macrophages/dendritic cells in NPC; TIGIT expression was upregulated on exhausted NK cells in NPC.[48,64]
CD96-PVR interaction was detected between NK and tumor cells in NPC
CD96TIGIT and CD96 were positively correlated with FCER2 and KHDRBS2 and negatively correlated with IGSF9 in NPC *.[63]
LAG3Gal-3LAG3 expression was upregulated on exhausted NK cells in NPC.[64]
LAG3 was positively correlated with FCER2 and KHDRBS2 and negatively correlated with IGSF9 in NPC *.[63]
(3) NK-cell-related cytokines/chemokines
TGF-βTGF-β inhibited NK cell function by promoting Tregs differentiation; TGF-β promoted the transmission of EBV infection in NPC.[82]
Type I InterferonType I Interferon induced granzyme B directly in NK cells; IFN-β induced NK-cell-mediated cytotoxicity against NPC targets in vitro.[83,84]
IL-2IL-2 promoted strong NK cytotoxicity.[50]
IL-12IL-12 and IL-18 stimulated IFN-γ production by NK cells synergistically; IL-12 secretion was related to EBV viral stimuli; the anti-EBV NK subset could be activated by IL-12.[85,86,87]
IL-15IL-15 promoted strong NK cytotoxicity and ADCC and induced the expression of NKp30.[88,89]
IL-18A negative correlation between IL-18 and NK cytotoxicity in NPC was reported; IL-18 level increased during EBV infection.
IL-12, IL-15, and IL-18 cocktail cytokines converted NK cells into long-lived, activated NK cells called “memory-like” NK cells.		[80,90]
IL-21IL-21 promoted the expansion of NK cells in vitro; IL-21 expression elevated on follicular TLSs in NPC.[91,92]
XCL1/2Interaction between XCR1 and XCL1/2 was involved in DCs recruited by NK cells; XCL1/2 were overexpressed by NK cells in NPC.[18,44,48]
CCL5NK-cell-derived CCL5 played a vital role in recruiting DCs; CCL5 was identified as an EBV-regulated molecule driver promoting NPC angiogenesis.[93]
(4) Functional signal inducing apoptosis in target cells
TRAILTRAILRBinding of TRAIL and TRAILR activated downstream death signal; TRAIL sensitivity was redox-dependent in NPC cells; NK-cell-dependent NPC cell killing was predominately mediated via TRAIL pathway.[94]
FASLFASFAS/FASL signal triggered apoptosis in target cells; FAS expression was suppressed in radioresistant NPC patients.[95]
CD16Fc regionCD16 was considered as an activated biomarker for NK cells; CD16/CD32 binding with Fc region of IgG antibody triggered ADCC effect; ADCC participated in anti-EBV infection in lytic phase.[96]
* FCER2, KHDRBS2, and IGSF9 were found to be associated with NPC [63]. Abbreviations: NK, natural killer; NPC, nasopharyngeal carcinoma; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; MICA/B, major histocompatibility complex class-I-related chain A/B; ULBP, UL16 binding protein; LMP2, latent membrane protein 2; EBV, Epstein–Barr virus; MACC1, metastasis-associated colon cancer 1; NKp30, natural cytotoxicity triggering receptor 3, CD337; B7-H6, B7 homolog 6; HLA, human leukocyte antigen; KIR, killer immunoglobulin-like receptor; MHC, major histocompatibility complex; miR, microRNA, a small non-coding RNA molecule; CD94, killer cell lectin-like receptor subfamily D, member 1 (KLRD1), pairs with the NKG2 molecule as a heterodimer; PD-1, programmed death-1; PD-L1, programmed death ligand-1; B7-H3, B7 homolog 3, CD276; IL, interleukin; TIGIT, T cell immunoreceptor with Ig and ITIM domains; PVR, polio virus receptor; CD96, T cell activation, increased late expression (TACTILE); LAG3, lymphocyte-activation gene 3; Gal-3, galectin 3; TGF-β, transforming growth factor-β; IFN-β, interferon-β; TLSs, tertiary lymphoid structures; DCs, dendritic cells; XCL1/2, chemokine C motif ligand 1/2; XCR1, the receptor for XCL1/2; CCL5, chemokine (C–C motif) ligand 5; TRAIL, TNF-related apoptosis-inducing ligand; TRAILR, receptor of TRAIL; FASL, Fas ligand; FAS, Fas receptor, apoptosis antigen 1; CD16, Fc receptors FcγRIII; CD32, Fc receptors FcγRII.
Table 2. Registered clinical trials associated with NK cells.
Table 2. Registered clinical trials associated with NK cells.
PhaseTreatmentConditionEstimated EnrollmentCompletion DateStatusNCT No.
Phase IIL-2 and NK cellsMetastatic NPCNot mentionedNot mentionedCompletedNCT00717184
Phase I/IICetuximab with NK cellsNPC311 August 2019UnknownNCT02507154 [116]
Phase I/IIHigh-activity natural killer immunotherapiesSmall metastatic NPC201 June 2019CompletedNCT03007836
Phase IHaplo/Allogeneic NKG2DL-targeting CAR-grafted γδ T CellsRelapsed or refractory solid tumors including NPC101 March 2021UnknownNCT04107142
Phase IVTX-2337 with cetuximabLocally advanced, recurrent, or metastatic SCCHN including NPC13Not mentionedCompletedNCT01334177 [125]
Phase I/IITAK-500 with or without pembrolizumabLocally advanced or metastatic solid tumors including NPC31311 August 2026RecruitingNCT05070247
Abbreviations: NK, natural killer; NPC, nasopharyngeal carcinoma; IL, interleukin; NKG2, members of C-type lectin-like receptor superfamily, receptors of NK cells; CAR, chimeric antigen receptor; SCCHN, squamous cell carcinoma of the head and neck.
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Li, S.; Dai, W.; Kam, N.-W.; Zhang, J.; Lee, V.H.F.; Ren, X.; Kwong, D.L.-W. The Role of Natural Killer Cells in the Tumor Immune Microenvironment of EBV-Associated Nasopharyngeal Carcinoma. Cancers 2024, 16, 1312. https://doi.org/10.3390/cancers16071312

AMA Style

Li S, Dai W, Kam N-W, Zhang J, Lee VHF, Ren X, Kwong DL-W. The Role of Natural Killer Cells in the Tumor Immune Microenvironment of EBV-Associated Nasopharyngeal Carcinoma. Cancers. 2024; 16(7):1312. https://doi.org/10.3390/cancers16071312

Chicago/Turabian Style

Li, Shuzhan, Wei Dai, Ngar-Woon Kam, Jiali Zhang, Victor H. F. Lee, Xiubao Ren, and Dora Lai-Wan Kwong. 2024. "The Role of Natural Killer Cells in the Tumor Immune Microenvironment of EBV-Associated Nasopharyngeal Carcinoma" Cancers 16, no. 7: 1312. https://doi.org/10.3390/cancers16071312

APA Style

Li, S., Dai, W., Kam, N. -W., Zhang, J., Lee, V. H. F., Ren, X., & Kwong, D. L. -W. (2024). The Role of Natural Killer Cells in the Tumor Immune Microenvironment of EBV-Associated Nasopharyngeal Carcinoma. Cancers, 16(7), 1312. https://doi.org/10.3390/cancers16071312

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