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

ULBP2 Promotes Tumor Progression by Suppressing NKG2D-Mediated Anti-Tumor Immunity

UL-16 binding protein 2 (ULBP2), a human NKG2D ligand, has been identified as a poor prognostic factor in several cancers based on recent comprehensive analyses of immune-related genes using the Cancer Genome Atlas datasets. Despite its clinical significance, the functional role of ULBP2 in vivo remains largely unknown. In this study, we investigated the role of ULBP2 in modulating anti-tumor immunity using murine melanoma cell lines engineered to stably express surface-expressed or soluble ULBP2. Subcutaneous transplantation of ULBP2-expressing melanoma cells into syngeneic mice resulted in accelerated tumor growth, mediated by surface-expressed ULBP2, through the suppression of NKG2D-dependent immune responses. In vitro experiments revealed that sustained exposure to tumor-expressed ULBP2 reduced NKG2D expression and cytotoxic activity of splenocytes. In contrast, soluble ULBP2 did not significantly affect tumor growth or immune responses. These findings suggest that surface-expressed ULBP2 plays a pivotal role in tumor immune evasion and highlight its potential as a therapeutic target to enhance anti-tumor immunity.

The emerging role of glycolysis and immune evasion in ovarian cancer

Ovarian cancer (OC) is one of the three most common malignant tumors of the female reproductive system, with the highest mortality rate among gynecologic malignancies. Like other tumors, OC cells undergo metabolic reprogramming phenomenon and convert glucose metabolism into "aerobic glycolysis" and generate a high concentration of lactate, i.e., the "Warburg effect", which provides a large amount of energy and corresponding intermediary metabolites for their survival, reproduction and metastasis. Numerous studies have shown that targeted inhibition of aerobic glycolysis and lactate metabolism is a promising strategy to enhance the sensitivity of cancer cells to immunotherapy. Therefore, this review summarizes the metabolic features of glycolysis in OC cells and highlights how abnormal lactate concentration affects the differentiation, metabolism, and function of infiltrating immune cells, which contributes to immunosuppression, and how targeted inhibition of this phenomenon may be a potential strategy to enhance the therapeutic efficacy of OC.

Ligands for Intestinal Intraepithelial T Lymphocytes in Health and Disease

The intestinal tract is constantly exposed to a diverse mixture of luminal antigens, such as those derived from commensals, dietary substances, and potential pathogens. It also serves as a primary route of entry for pathogens. At the forefront of this intestinal defense is a single layer of epithelial cells that forms a critical barrier between the gastrointestinal (GI) lumen and the underlying host tissue. The intestinal intraepithelial T lymphocytes (T-IELs), one of the most abundant lymphocyte populations in the body, play a crucial role in actively surveilling and maintaining the integrity of this barrier by tolerating non-harmful factors such as commensal microbiota and dietary components, promoting epithelial turnover and renewal while also defending against pathogens. This immune balance is maintained through interactions between ligands in the GI microenvironment and receptors on T-IELs. This review provides a detailed examination of the ligands present in the intestinal epithelia and the corresponding receptors expressed on T-IELs, including T cell receptors (TCRs) and non-TCRs, as well as how these ligand-receptor interactions influence T-IEL functions under both steady-state and pathological conditions. By understanding these engagements, we aim to shed light on the mechanisms that govern T-IEL activities within the GI microenvironment. This knowledge may help in developing strategies to target GI ligands and modulate T-IEL receptor expression, offering precise approaches for treating intestinal disorders.

The current state of knowledge on the role of NKG2D ligands in multiple sclerosis and other autoimmune diseases

Multiple sclerosis (MS) is a chronic central nervous system (CNS) disease with demyelinating inflammatory characteristics. It is the most common nontraumatic and disabling disease affecting young adults. The incidence and prevalence of MS have been increasing. However, its exact cause remains unclear. The main tests used to support the diagnosis are magnetic resonance imaging (MRI) examination and cerebrospinal fluid (CSF) analysis. Nonetheless, to date, no sensitive or specific marker has been identified for the detection of the disease at its initial stage. In recent years, researchers have focused on the fact that the number of natural killer cell group 2 member D (NKG2D) family of C-type lectin-like receptor + (NKG2D+) T cells in the peripheral blood, CSF, and brain tissue has been shown to be higher in patients with MS than in controls. The activating receptor belonging to the NKG2D is stimulated by specific ligands: in humans these are major histocompatibility complex (MHC) class I polypeptide-related sequence A (MICA) and MHC class I polypeptide-related sequence B (MICB) proteins and UL16 binding 1-6 proteins (ULBP1-6). Under physiological conditions, the aforementioned ligands are expressed at low or undetectable levels but can be induced in response to stress factors. NKG2D ligands (NKG2DLs) are involved in epigenetic regulation of their expression. To date, studies in cell cultures, animal models, and brain tissues have revealed elevated expression of MICA/B, ULPB4, and its mouse homolog murine UL16 binding protein-like transcript (MULT1), in oligodendrocytes and astrocytes from patients with MS. Furthermore, soluble forms of NKG2DLs were elevated in the plasma and CSF of patients with MS compared to controls. In this review, we aim to describe the role of NKG2D and NKG2DLs, and their interactions in the pathogenesis of MS, as well as in other autoimmune diseases such as rheumatoid arthritis (RA), inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE), and celiac disease (CeD). We also assess the potential of these proteins as diagnostic markers and consider future perspectives for targeting NKG2D ligands and their pathways as therapeutic targets in MS.

Cross-talk between immune cells and tumor cells in non-Hodgkin lymphomas arising in common variable immunodeficiency

INTRODUCTION

CVID is the commonest and most symptomatic primary immune deficiency of adulthood. NHLs are the most prevalent malignancies in CVID. The cross-talk between tumor cells and immune cells may be an important risk factor in lymphomagenesis.

AREAS COVERED

The present review highlights immune cell, genetic and histopathological alterations in the CVID-associated NHLs.

EXPERT OPINION

CVID patients exhibit some notable immune defects that may predispose to lymphomas. T/NK cell defects including reduced T cells, naïve CD4+T cells, T regs, and Th17 cells, increased CD8+T cells with reduced T cell proliferative and cytokine responses and reduced iNKT and NK cell count and cytotoxicity. B cell defects include increased transitional and CD21low B cells, clonal IgH gene rearrangements, and increased BCMA levels. Increase in IL-9, sCD30 levels, and upregulation of BAFF-BAFFR signaling are associated with lymphomas in CVID. Increased expression of PFTK1, duplication of ORC4L, germline defects in TACI, NFKB1, and PIK3CD, and somatic mutations in NOTCH2 and MYD88 are reported in CVID-associated lymphomas. Upregulation of PD-L1-PD-1 pathway may also promote lymphomagenesis in CVID. These abnormalities need to be explored as prognostic or predictive markers of CVID-associated NHLs by large multicentric studies.

Arachidonic acid impairs natural killer cell functions by disrupting signaling pathways driven by activating receptors and reactive oxygen species

BACKGROUND

High levels of the polyunsaturated fatty acid arachidonic acid (AA) within the ovarian carcinoma (OC) microenvironment correlate with reduced relapse-free survival. Furthermore, OC progression is tied to compromised immunosurveillance, partially attributed to the impairment of natural killer (NK) cells. However, potential connections between AA and NK cell dysfunction in OC have not been studied.

METHODS

We employed a combination of phosphoproteomics, transcriptional profiling and biological assays to investigate AA's impact on NK cell functions.

RESULTS

AA (i) disrupts interleukin-2/15-mediated expression of pro-inflammatory genes by inhibiting STAT1-dependent signaling, (ii) hampers signaling by cytotoxicity receptors through disruption of their surface expression, (iii) diminishes phosphorylation of NKG2D-induced protein kinases, including ERK1/2, LYN, MSK1/2 and STAT1, and (iv) alters reactive oxygen species production by transcriptionally upregulating detoxification. These modifications lead to a cessation of NK cell proliferation and a reduction in cytotoxicity.

CONCLUSION

Our findings highlight significant AA-induced alterations in the signaling network that regulates NK cell activity. As low expression of several NK cell receptors correlates with shorter OC patient survival, these findings suggest a functional linkage between AA, NK cell dysfunction and OC progression.

Solid tumor immunotherapy using NKG2D-based adaptor CAR T cells

NKG2D ligands (NKG2DLs) are broadly expressed in cancer. To target these, we describe an adaptor chimeric antigen receptor (CAR) termed NKG2D/Dap10-12. Herein, T cells are engineered to co-express NKG2D with a fusion protein that comprises Dap10 joined to a Dap12 endodomain. NKG2D/Dap10-12 T cells elicit compelling efficacy, eradicating or controlling NKG2DL-expressing tumors in several established xenograft models. Importantly, durable responses, long-term survival, and rejection of tumor re-challenge are reproducibly achieved. Efficacy is markedly superior to a clinical stage CAR analog, comprising an NKG2D-CD3ζ fusion. Structure-function analysis using an extended CAR panel demonstrates that potency is dependent on membrane proximity of signaling units, high NKG2D cell surface expression, adaptor structure, provision of exogenous Dap10, and inclusion of one rather than three immune tyrosine activation motifs per signaling unit. Potent therapeutic impact of NKG2D/Dap10-12 T cells is also underpinned by enhanced oxidative phosphorylation, reduced senescence, and transcriptomic re-programming for increased ribosomal biogenesis.

Three-Dimensional Model Analysis Revealed Differential Cytotoxic Effects of the NK-92 Cell Line and Primary NK Cells on Breast and Ovarian Carcinoma Cell Lines Mediated by Variations in Receptor-Ligand Interactions and Soluble Factor Profiles

Background/objectives: The functional activity of a certain tumor determines the effectiveness of primary NK cells and NK-92 cell line-based cancer therapy; their therapeutic effectiveness against different tumors can vary. This work provides a direct simultaneous comparison of the cytotoxic effects of in vitro-activated peripheral NK (pNK) cells and NK-92 cells in spheroid models of BT-474, MCF7 and SKOV-3 carcinomas and uncovers the reasons for the differential effectiveness of NK cells against tumors. Methods: Tumor spheroids of similar size and shape, obtained from agarose molds, were incubated with NK-92 or pNK cells for 24 h. Tumor cell death was detected using flow cytometry or confocal microscopy. Cytokine production, granzyme B levels and NK cell degranulation analyses were performed, along with pNK and target-cell phenotypic characterization. Results: While NK-92 and pNK cells lysed BT-474 spheroids with comparably low efficiency, pNK cells were more capable of eliminating MCF7 and SKOV-3 spheroids than NK-92 cells were. The results of the functional and phenotypic analyses strongly support the participation of the NKG2D-NKG2DL pathway in pNK cell activation induced by the most sensitive cytotoxic attack on SKOV-3 spheroids, whereas the CX3CR1-CX3CL1 axis appears to be involved in the pNK reaction against MCF-7 spheroids. Conclusions: We provide a new approach for the preliminary identification of the most promising NK cell receptors that can alter the effectiveness of cancer therapy depending on the specific tumor type. Using this approach, NK-92 cells or pNK subsets can be selected for further accumulation and/or genetic modification to improve specificity and reactivity.

A potential mechanism of tumor immune escape: Regulation and application of soluble natural killer group 2 member D ligands (Review)

The immune system is integral to the surveillance and eradication of tumor cells. Interactions between the natural killer group 2 member D (NKG2D) receptor and its ligands (NKG2DLs) are vital for activating NKG2D receptor‑positive immune cells, such as natural killer cells. This activation enables these cells to identify and destroy tumor cells presenting with NKG2DLs, which is an essential aspect of tumor immunity. However, tumor immune escape is facilitated by soluble NKG2DL (sNKG2DL) shed from the surface of tumor cells. The production of sNKG2DL is predominantly regulated by metalloproteinases [a disintegrin and metalloproteinases (ADAM) and matrix metalloproteinase (MMP) families] and exosomes. sNKG2DL not only diminish immune recognition on the tumor cell surface but also suppress the function of immune cells, such as NK cells, and reduce the expression of the NKG2D receptor. This process promotes immune evasion, progression, and metastasis of tumors. In this review, an in‑depth summary of the mechanisms and factors that influence sNKG2DL production and their contribution to immune suppression within the tumor microenvironment are provided. Furthermore, due to the significant link between sNKG2DLs and tumor progression and metastasis, they have great potential as novel biomarkers. Detectable via liquid biopsies, sNKG2DLs could assess tumor malignancy and prognosis, and act as pivotal targets for immunotherapy. This could lead to the discovery of new drugs or the enhancement of existing treatments. Thus, the application of sNKG2DLs in clinical oncology was explored, offering substantial theoretical support for the development of innovative immunotherapeutic strategies for sNKG2DLs.

The use of organoids in creating immune microenvironments and treating gynecological tumors

Owing to patient-derived tumor tissues and cells, significant advances have been made in personalized cancer treatment and precision medicine, with cancer stem cell-derived three-dimensional tumor organoids serving as crucial in vitro models that accurately replicate the structural, phenotypic, and genetic characteristics of tumors. However, despite their extensive use in drug testing, genome editing, and transplantation for facilitating personalized treatment approaches in clinical practice, the inadequate capacity of these organoids to effectively model immune cells and stromal components within the tumor microenvironment limits their potential. Additionally, effective clinical immunotherapy has led the tumor immune microenvironment to garner considerable attention, increasing the demand for simulating patient-specific tumor-immune interactions. Consequently, co-culture techniques integrating tumor organoids with immune cells and tumor microenvironment constituents have been developed to expand the possibilities for personalized drug response investigations, with recent advancements enhancing the understanding of the strengths, limitations, and applicability of the co-culture approach. Herein, the recent advancements in the field of tumor organoids have been comprehensively reviewed, specifically highlighting the tumor organoid co-culture-related developments with various immune cell models and their implications for clinical research. Furthermore, this review delineates the current state of research and application of organoid models regarding the therapeutic approaches and related challenges for gynecological tumors. This study may provide a theoretical basis for further research on the use of patient-derived organoids in tumor immunity, drug development, and precision medicine.

NKG2D (Natural Killer Group 2, Member D) ligand expression and ameloblastoma recurrence: a retrospective immunohistological pilot study

BACKGROUND/PURPOSE

This retrospective immunohistological pilot study aimed to investigate the influence of natural killer group 2, member D (NKG2D) ligand expression on ameloblastoma recurrence after surgical resection. It also aimed to elucidate additional clinical factors that could serve as predictors of ameloblastoma recurrence.

MATERIALS AND METHODS

This study included 96 patients who were histologically diagnosed with ameloblastoma after surgical resection. The expression of NKG2D ligands, including UL16-binding proteins (ULBPs) 1-3 and major histocompatibility complex class I chain-related molecule (MIC) A/B, was evaluated in formalin-fixed paraffin-embedded tumor tissues via immunohistochemistry assays. Furthermore, the patients' electronic medical records were reviewed. Multivariate Cox regression analysis was conducted, and data were expressed as adjusted hazard ratios [HRs] with 95% confidence intervals [95% CIs].

RESULTS

Multivariate analysis revealed that recurrent tumors (ref.: primary; adjusted HR [95% CI]: 2.780 [1.136, 6.803], p = 0.025) and positive MICA/B expression (ref.: negative; adjusted HR [95% CI]: 0.223 [0.050, 0.989], p = 0.048) independently affected recurrence-free survival in ameloblastoma.

CONCLUSION

This study identified recurrent cases and loss of MICA/B expression as independent predictors of early ameloblastoma recurrence following surgical resection. The findings suggest that decreased MICA/B expression might undermine NKG2D-mediated tumor immunosurveillance, thereby influencing early recurrence.

Dual Targeting of Glioblastoma Cells with Bispecific Killer Cell Engagers Directed to EGFR and ErbB2 (HER2) Facilitates Effective Elimination by NKG2D-CAR-Engineered NK Cells

NKG2D is an activating receptor of natural killer cells that recognizes stress-induced ligands (NKG2DL) expressed by many tumor cells. Nevertheless, NKG2DL downregulation or shedding can still allow cancer cells to evade immune surveillance. Here, we used lentiviral gene transfer to engineer clinically usable NK-92 cells with a chimeric antigen receptor (NKAR) which contains the extracellular domain of NKG2D for target recognition, or an NKAR, together with the IL-15 superagonist RD-IL15, and combined these effector cells with recombinant NKG2D-interacting bispecific engagers that simultaneously recognize the tumor-associated antigens epidermal growth factor receptor (EGFR) or ErbB2 (HER2). Applied individually, in in vitro cell-killing assays, these NKAB-EGFR and NKAB-ErbB2 antibodies specifically redirected NKAR-NK-92 and NKAR_RD-IL15-NK-92 cells to glioblastoma and other cancer cells with elevated EGFR or ErbB2 levels. However, in mixed glioblastoma cell cultures, used as a model for heterogeneous target antigen expression, NKAR-NK cells only lysed the EGFR- or ErbB2-expressing subpopulations in the presence of one of the NKAB molecules. This was circumvented by applying NKAB-EGFR and NKAB-ErbB2 together, resulting in effective antitumor activity similar to that against glioblastoma cells expressing both target antigens. Our results demonstrate that combining NK cells carrying an activating NKAR receptor with bispecific NKAB antibodies allows for flexible targeting, which can enhance tumor-antigen-specific cytotoxicity and prevent immune escape.

The Role of NKG2D and Its Ligands in Autoimmune Diseases: New Targets for Immunotherapy

Natural killer (NK) cells and CD8+ T cells can clear infected and transformed cells and generate tolerance to themselves, which also prevents autoimmune diseases. Natural killer group 2 member D (NKG2D) is an important activating immune receptor that is expressed on NK cells, CD8+ T cells, γδ T cells, and a very small percentage of CD4+ T cells. In contrast, the NKG2D ligand (NKG2D-L) is generally not expressed on normal cells but is overexpressed under stress. Thus, the inappropriate expression of NKG2D-L leads to the activation of self-reactive effector cells, which can trigger or exacerbate autoimmunity. In this review, we discuss the role of NKG2D and NKG2D-L in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), type I diabetes (T1DM), inflammatory bowel disease (IBD), and celiac disease (CeD). The data suggest that NKG2D and NKG2D-L play a pathogenic role in some autoimmune diseases. Therefore, the development of strategies to block the interaction of NKG2D and NKG2D-L may have therapeutic effects in some autoimmune diseases.