Genetic Variant of DNAM-1 rs763361 C>T Is Associated with Ankylosing Spondylitis in a Mexican Population

DNAM-1 (CD226) is an activating receptor expressed in CD8+ T cells, NK cells, and monocytes. It has been reported that two SNPs in the DNAM-1 gene, rs763361 C>T and rs727088 G>A, have been associated with different autoimmune diseases; however, the role of DNAM-1 in ankylosing spondylitis has been less studied. For this reason, we focused on the study of these two SNPs in association with ankylosing spondylitis. For this, 34 patients and 70 controls were analyzed using endpoint PCR with allele-specific primers. Our results suggest that rs763361 C>T is involved as a possible protective factor under the CT co-dominant model (OR = 0.34, 95% CI = 0.13-0.88, p = 0.022) and the CT + TT dominant model (OR = 0.39, 95% CI = 0.17-0.90, p = 0.025), while rs727088 G>A did not show an association with the disease in any of the inheritance models. When analyzing the relationships of the haplotypes, we found that the T + A haplotype (OR = 0.31, 95% CI = 0.13-0.73, p = 0.0083) is a protective factor for developing the disease. In conclusion, the CT and CT + TT variants of rs763361 C>T and the T + A haplotype were considered as protective factors for developing ankylosing spondylitis.

Therapeutic application of human type 2 innate lymphoid cells via induction of granzyme B-mediated tumor cell death

The therapeutic potential for human type 2 innate lymphoid cells (ILC2s) has been underexplored. Although not observed in mouse ILC2s, we found that human ILC2s secrete granzyme B (GZMB) and directly lyse tumor cells by inducing pyroptosis and/or apoptosis, which is governed by a DNAM-1-CD112/CD155 interaction that inactivates the negative regulator FOXO1. Over time, the high surface density expression of CD155 in acute myeloid leukemia cells impairs the expression of DNAM-1 and GZMB, thus allowing for immune evasion. We describe a reliable platform capable of up to 2,000-fold expansion of human ILC2s within 4 weeks, whose molecular and cellular ILC2 profiles were validated by single-cell RNA sequencing. In both leukemia and solid tumor models, exogenously administered expanded human ILC2s show significant antitumor effects in vivo. Collectively, we demonstrate previously unreported properties of human ILC2s and identify this innate immune cell subset as a member of the cytolytic immune effector cell family.

NKG2A discriminates natural killer cells with a suppressed phenotype in pediatric acute leukemia

Natural killer (NK) cells are important for early tumor immune surveillance. In patients with hematological cancers, NK cells are generally functional deficient and display dysregulations in their receptor repertoires. Acute leukemia is the most common cancer in children, and we here performed a comparative phenotypic profiling of NK cells from B-cell precursor acute lymphoblastic leukemia (BCP-ALL) patients to identify aberrant NK cell phenotypes. NK cell phenotypes, maturation, and function were analyzed in matched bone marrow and blood NK cells from BCP-ALL patients at diagnosis, during treatment, and at end of treatment and compared with age-matched pediatric control subjects. Expression of several markers were skewed in patients, but with large interindividual variations. Undertaking a multiparameter approach, we found that high expression levels of NKG2A was the single predominant marker distinguishing NK cells in BCP-ALL patients compared with healthy control subjects. Moreover, naïve CD57-NKG2A NK cells dominated in BCP-ALL patients at diagnosis. Further, we found dysregulated expression of the activating receptor DNAM-1 in resident bone marrow CXCR6+ NK cells. CXCR6+ NK cells lacking DNAM-1 expressed NKG2A and had a tendency for lower degranulation activity. In conclusion, high expression of NKG2A dominates NK cell phenotypes from pediatric BCP-ALL patients, indicating that NKG2A could be targeted in therapies for this patient group.

DNAM-1 chimeric receptor-engineered NK cells: a new frontier for CAR-NK cell-based immunotherapy

DNAM-1 is a major NK cell activating receptor and, together with NKG2D and NCRs, by binding specific ligands, strongly contributes to mediating the killing of tumor or virus-infected cells. DNAM-1 specifically recognizes PVR and Nectin-2 ligands that are expressed on some virus-infected cells and on a broad spectrum of tumor cells of both hematological and solid malignancies. So far, while NK cells engineered for different antigen chimeric receptors (CARs) or chimeric NKG2D receptor have been extensively tested in preclinical and clinical studies, the use of DNAM-1 chimeric receptor-engineered NK cells has been proposed only in our recent proof-of-concept study and deserves further development. The aim of this perspective study is to describe the rationale for using this novel tool as a new anti-cancer immunotherapy.

MD Simulation Reveals Regulation of Mechanical Force and Extracellular Domain 2 on Binding of DNAM-1 to CD155

Two extracellular domains of the adhesive receptor DNAM-1 are involved in various cellular biological processes through binding to ligand CD155, usually under a mechano-microenvironment. The first extracellular domain (D1) plays a key role in recognition, but the function of the second extracellular domain (D2) and effects of force on the interaction of DNAM-1 with CD155 remain unclear. We herein studied the interaction of DNAM-1 with CD155 by performing steered molecular dynamics (MD) simulations, and observed the roles of tensile force and D2 on the affinity of DNAM-1 to CD155. The results showed that D2 improved DNAM-1 affinity to CD155; the DNAM-1/CD155 complex had a high mechanical strength and a better mechanical stability for its conformational conservation either at pulling with constant velocity or under constant tensile force (≤100 pN); the catch-slip bond transition governed CD155 dissociation from DNAM-1; and, together with the newly assigned key residues in the binding site, force-induced conformation changes should be responsible for the mechanical regulation of DNAM-1's affinity to CD155. This work provided a novel insight in understanding the mechanical regulation mechanism and D2 function in the interaction of DNAM-1 with CD155, as well as their molecular basis, relevant transmembrane signaling, and cellular immune responses under a mechano-microenvironment.

The co-inhibitory receptor TIGIT regulates NK cell function and is upregulated in human intrahepatic CD56bright NK cells

The crosstalk between NK cells and their surrounding environment is enabled through activating and inhibitory receptors, which tightly control NK cell activity. The co-inhibitory receptor TIGIT decreases NK cell cytotoxicity and is involved in NK cell exhaustion, but has also been associated with liver regeneration, highlighting that the contribution of human intrahepatic CD56bright NK cells in regulating tissue homeostasis remains incompletely understood. A targeted single-cell mRNA analysis revealed distinct transcriptional differences between matched human peripheral blood and intrahepatic CD56bright NK cells. Multiparameter flow cytometry identified a cluster of intrahepatic NK cells with overlapping high expression of CD56, CD69, CXCR6, TIGIT and CD96. Intrahepatic CD56bright NK cells also expressed significantly higher protein surface levels of TIGIT, and significantly lower levels of DNAM-1 compared to matched peripheral blood CD56bright NK cells. TIGIT+ CD56bright NK cells showed diminished degranulation and TNF-α production following stimulation. Co-incubation of peripheral blood CD56bright NK cells with human hepatoma cells or primary human hepatocyte organoids resulted in migration of NK cells into hepatocyte organoids and upregulation of TIGIT and downregulation of DNAM-1 expression, in line with the phenotype of intrahepatic CD56bright NK cells. Intrahepatic CD56bright NK cells represent a transcriptionally, phenotypically, and functionally distinct population of NK cells that expresses higher levels of TIGIT and lower levels of DNAM-1 than matched peripheral blood CD56bright NK cells. Increased expression of inhibitory receptors by NK cells within the liver environment can contribute to tissue homeostasis and reduction of liver inflammation.

NKG2D engagement on human NK cells leads to DNAM-1 hypo-responsiveness through different converging mechanisms

Natural killer (NK) cell activation is regulated by activating and inhibitory receptors that facilitate diseased cell recognition. Among activating receptors, NKG2D and DNAM-1 play a pivotal role in anticancer immune responses since they bind ligands upregulated on transformed cells. During tumor progression, however, these receptors are frequently downmodulated and rendered functionally inactive. Of note, NKG2D internalization has been associated with the acquisition of a dysfunctional phenotype characterized by the cross-tolerization of unrelated activating receptors. However, our knowledge of the consequences of NKG2D engagement is still incomplete. Here, by cytotoxicity assays combined with confocal microscopy, we demonstrate that NKG2D engagement on human NK cells impairs DNAM-1-mediated killing through two different converging mechanisms: by the upregulation of the checkpoint inhibitory receptor TIGIT, that in turn suppresses DNAM-1-mediated cytotoxic function, and by direct inhibition of DNAM-1-promoted signaling. Our results highlight a novel interplay between NKG2D and DNAM-1/TIGIT receptors that may facilitate neoplastic cell evasion from NK cell-mediated clearance.

Advances in therapeutic targeting of immune checkpoints receptors within the CD96-TIGIT axis: clinical implications and future perspectives

INTRODUCTION

The development of therapeutic antibodies targeting immune checkpoint molecules (ICMs) that induce long-term remissions in cancer patients has revolutionized cancer immunotherapy. However, a major drawback is that relapse after an initial response may be attributed to innate and acquired resistance. Additionally, these treatments are not beneficial to all patients. Therefore, the discovery and targeting of novel ICMs and their combination with other immunotherapeutics are urgently needed.

AREAS COVERED

There has been increasing evidence of the CD96-TIGIT axis as ICMs in cancer immunotherapy in the last five years. This review will highlight and discuss the current knowledge about the role of CD96 and TIGIT in hematological and solid tumor immunotherapy in the context of empirical studies and clinical trials, and provide a comprehensive list of ongoing cancer clinical trials on the blockade of these ICMs, as well as the rationale behind combinational therapies with anti-PD-1/PD-L1 agents, chemotherapy drugs, and radiotherapy. Moreover, we share our perspectives on anti-CD96/TIGIT-related combination therapies.

EXPERT OPINION

CD96-TIGIT axis regulates anti-tumor immune responses. Thus, the receptors within this axis are the potential candidates for cancer immunotherapy. Combining the inhibition of CD96-TIGIT with anti-PD-1/PD-L1 mAbs and chemotherapy drugs has shown relatively effective results in the context of preclinical studies and tumor models.

Dynamic of Circulating DNAM-1+ Monocytes and NK Cells in Patients with STEMI Following Primary Percutaneous Coronary Intervention

Although the role of inflammation and adverse cardiac remodeling in myocardial infarction (MI) have been extensively explored, gaps in knowledge on the complex interaction between these processes still exist. Data suggest that DNAX accessory molecule-1 (DNAM-1), an activating receptor implicated in NK cell education, may be involved in cardiac remodeling following coronary artery occlusion. In the present study, we aimed to explore the dynamic of DNAM-1+ monocytes and NK cells in peripheral blood in the early phase following reperfusion in patients with ST-elevation MI (STEMI). The study enrolled 49 patients older than 18 years of age diagnosed with STEMI, referred to primary percutaneous coronary intervention (pPCI). Blood samples were obtained at three distinct points (at admission, 3 h, and 24 h after pPCI) and analyzed using flow cytometry. The number of circulating DNAM-1+ monocytes (CD16++ and CD14++) and CD56dimCD16++NK cells was significantly reduced 3 h after pPCI and subsequently returned to initial levels 24 h after procedure (p = 0.003, p < 0.001, and p = 0.002, respectively). Notably, such dynamic was dependent on age of patients. A positive correlation between high sensitivity troponin I levels and number of CD16++DNAM-1+ monocytes in peripheral blood 3 h after pPCI was observed (r = 0.431, p = 0.003). In conclusion, in the present study we delineated the post-reperfusion dynamic of DNAM-1-expresing leukocytes. Additionally, we demonstrated that the number of CD16++ DNAM-1+ monocytes correlate with the extent of myocardial injury.

[DNAM-1 regulates the proliferation and function of T regulatory type 1 cells via the IL-2/STAT5 pathway]

OBJECTIVE

To explore the role of DNAM-1 in the activation, proliferation and function of type Ⅰ regulatory T cells (Tr1 cells).

METHODS

Anti-CD3/CD28 antibodies were used to stimulate mouse T cells derived from the spleen of wild-type (WT) mice, and the expression level of DNAM-1 in resting and activated Tr1 cells was evaluated with flow cytometry. Na?ve CD4⁺ T cells isolated by magnetic cell sorting from the spleens of WT mice and DNAM-1 knockout (KO) mice were cultured in Tr1 polarizing conditions for 3 days, after which CD25 and CD69 expressions were measured using flow cytometry. The induced Tr1 cells were labelled with CFSE and cultured in the presence of anti-CD/CD28 antibodies for 3 days, and their proliferative activity was analyzed. The expressions of IL-10 and p-STAT5 in DNAM-1-deficient Tr1 cells were detected before and after IL-2 stimulation.

RESULTS

The expression level of DNAM-1 was significantly upregulated in CD4⁺ T cells and Tr1 cells after stimulation with anti-CD3/CD28 antibodies (P < 0.05). DNAM-1 knockout did not cause significant changes in the number or proportion of Tr1 cells, but but significantly increased the expression levels of the activation markers CD69 and CD25 (P < 0.05). Compared with WT Tr1 cells, DNAM-1-deficient Tr1 cells exhibited reduced proliferative activity in vitro (P < 0.05) with downregulated IL-10 production (P < 0.05) and decreased expressions of Il-10 and Gzmb mRNA (P < 0.05). In DNAM-1-deficient Tr1 cells, IL-2 stimulation significantly reduced IL-10 secretion level and the expression of p-STAT5 as compared with WT Tr1 cells.

CONCLUSION

DNAM-1 participate in the activation and proliferation of Tr1 cells and affect the biological functions of Tr1 cells through the IL-2/STAT5 pathway.

Defective DNAM-1 Dependent Cytotoxicity in Hepatocellular Carcinoma-Infiltrating NK Cells

Simple Summary

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer and the fourth leading cause of cancer-related deaths worldwide. Although therapeutic options have improved in the last few years, mortality remains disturbingly high. The key role of innate immunity, particularly of natural killer (NK) cells, in tumor surveillance and response is well established. The anti-tumor NK cell activity is modulated by interactions between NK cells activating or inhibiting receptors and their ligands, expressed or released by tumor cells. Alterations in these networks lead to inadequate NK cell responses and a lack of cancer control. In our study, we focus on NK cells activating receptor DNAM-1 and its ligand CD155, expressed in HCC cells. We provide evidence of impaired NK cytotoxic function as a result of altered receptor/ligand axis. We conclude that this may represent a tumor escape mechanism and a possible target for new immunotherapeutic approaches to HCC treatment.

Abstract

Background: Natural killer (NK) cells play a key role in immune surveillance and response to tumors, their function regulated by NK cell receptors and their ligands. The DNAM-1 activating receptor recognizes the CD155 molecule expressed in several tumor cells, such as hepatocellular carcinoma (HCC). This study aims to investigate the role of the DNAM-1/CD155 axis in mediating the NK cell response in patients with HCC. Methods: Soluble CD155 was measured by ELISA. CD155 expression was sought in HCC cells by immunohistochemistry, qPCR, and flow cytometry. DNAM-1 modulation in NK cells was evaluated in transwell experiments and by a siRNA-mediated knockdown. NK cell functions were examined by direct DNAM-1 triggering. Results: sCD155 was increased in sera from HCC patients and correlated with the parameters of an advanced disease. The expression of CD155 in HCC showed a positive trend toward better overall survival. DNAM-1 downmodulation was induced by CD155-expressing HCC cells, in agreement with lower DNAM-1 expressions in tumor-infiltrating NK (NK-TIL) cells. DNAM-1-mediated cytotoxicity was defective both in circulating NK cells and in NK-TIL of HCC patients. Conclusions: We provide evidence of alterations in the DNAM-1/CD155 axis in HCC, suggesting a possible mechanism of tumor resistance to innate immune surveillance.

CD155 mutation (Ala67Thr) increases the binding affinity for and the signaling via an inhibitory immunoreceptor TIGIT

CD155 is a shared ligand for activating and inhibitory immunoreceptors DNAX accessory molecule 1 (DNAM‐1), also called CD226, and T cell immunoglobulin and immunoreceptor tyrosine‐based inhibitory motif domain (TIGIT), which are expressed on natural killer (NK) cells and T cells, and positively and negatively regulates tumor immune responses, respectively. A recent study showed that the single nucleotide polymorphism rs1058402G>A causing a mutation to Thr from Ala at residue 67 of CD155 is associated with worse overall survival of patients with small cell lung cancer and suggested that this is caused by the decreased affinity of mutant CD155 for DNAM‐1 as a result of the 3D structural analysis. Unexpectedly, however, we found that the mutation increased the binding affinity for TIGIT rather than decreased the binding affinity for DNAM‐1 and induced a stronger signal than WT CD155. Our results suggest that the mutation suppresses tumor immune responses by generating a stronger inhibitory signal in immune cells in the tumor microenvironment.

Natural Killer Cell Responses during Human γ-Herpesvirus Infections

Herpesviruses are main sculptors of natural killer (NK) cell repertoires. While the β-herpesvirus human cytomegalovirus (CMV) drives the accumulation of adaptive NKG2C-positive NK cells, the human γ-herpesvirus Epstein–Barr virus (EBV) expands early differentiated NKG2A-positive NK cells. While adaptive NK cells support adaptive immunity by antibody-dependent cellular cytotoxicity, NKG2A-positive NK cells seem to preferentially target lytic EBV replicating B cells. The importance of this restriction of EBV replication during γ-herpesvirus pathogenesis will be discussed. Furthermore, the modification of EBV-driven NK cell expansion by coinfections, including by the other human γ-herpesvirus Kaposi sarcoma-associated herpesvirus (KSHV), will be summarized.

DNAM-1 regulates Foxp3 expression in regulatory T cells by interfering with TIGIT under inflammatory conditions

Regulatory T (Treg) cells that express forkhead box P3 (Foxp3) are pivotal for immune tolerance. Although inflammatory mediators cause Foxp3 instability and Treg cell dysfunction, their regulatory mechanisms remain incompletely understood. Here, we show that the transfer of Treg cells deficient in the activating immunoreceptor DNAM-1 ameliorated the development of graft-versus-host disease better than did wild-type Treg cells. We found that DNAM-1 competes with T cell immunoreceptor with Ig and ITIM domains (TIGIT) in binding to their common ligand CD155 and therefore regulates TIGIT signaling to down-regulate Treg cell function without DNAM-1-mediated intracellular signaling. DNAM-1 deficiency augments TIGIT signaling; this subsequently inhibits activation of the protein kinase B-mammalian target of rapamycin complex 1 pathway, resulting in the maintenance of Foxp3 expression and Treg cell function under inflammatory conditions. These findings demonstrate that DNAM-1 regulates Treg cell function via TIGIT signaling and thus, it is a potential molecular target for augmenting Treg function in inflammatory diseases.

CD155 on Tumor Cells Drives Resistance to Immunotherapy by Inducing the Degradation of the Activating Receptor CD226 in CD8+ T Cells

The activating receptor CD226 is expressed on lymphocytes, monocytes, and platelets and promotes anti-tumor immunity in pre-clinical models. Here, we examined the role of CD226 in the function of tumor-infiltrating lymphocytes (TILs) and resistance to immunotherapy. In murine tumors, a large proportion of CD8⁺ TILs had decreased surface expression of CD226 and exhibited features of dysfunction, whereas CD226^hi TILs were highly functional. This correlation was seen also in TILs isolated from HNSCC patients. Mutation of CD226 at tyrosine 319 (Y319) led to increased CD226 surface expression, enhanced anti-tumor immunity and improved efficacy of immune checkpoint blockade (ICB). Mechanistically, tumor-derived CD155, the ligand for CD226, initiated phosphorylation of Y319 by Src kinases, thereby enabling ubiquitination of CD226 by CBL-B, internalization, and proteasomal degradation. In pre-treatment samples from melanoma patients, CD226⁺CD8⁺ T cells correlated with improved progression-free survival following ICB. Our findings argue for the development of therapies aimed at maintaining the expression of CD226.

Suppression of Th1 and Th17 Proinflammatory Cytokines and Upregulation of FOXP3 Expression by a Humanized Anti-DNAM-1 Monoclonal Antibody

DNAM-1 is an activating immunoreceptor expressed on hematopoietic cells, including both CD4⁺ and CD8⁺ T cells, natural killer cells, and platelets. Since DNAM-1 is involved in the pathogenesis of various inflammatory diseases and cancers in humans as well as mouse models, it is a potential target for immunotherapy for these diseases. In this study, we generated a humanized neutralizing antihuman DNAM-1 monoclonal antibody (mAb), named TNAX101A, which contains an engineered Fc portion of human IgG1 to reduce Fc-mediated effector functions. We show that TNAX101A efficiently interfered the binding of DNAM-1 to its ligand CD155 and showed unique functions; it decreased production of the inflammatory cytokines such as interferon-gamma, tumor necrosis factor alpha, interleukin (IL)-6, IL-17A, and IL-17F by anti-CD3 antibody-stimulated or alloantigen-stimulated T cells and increased FOXP3 expression in anti-CD3-stimulated regulatory T (Treg) cells. These dual functions of TNAX101A may be advantageous for the treatment of T cell-mediated inflammatory diseases through both downregulation of effector T cell function and upregulation of Treg cell function.

Activated Lymphocytes and Increased Risk of Dermatologic Adverse Events during Sorafenib Therapy for Hepatocellular Carcinoma

Simple Summary

Hepatocellular carcinoma is the second cause of cancer-related death worldwide. Of those advanced-stage patients who are treated with sorafenib, those who develop early dermatologic adverse events have a better prognosis. These events are possibly immune-related. Therefore, we analyzed the phenotype of 52 sorafenib-treated patients’ circulating lymphocytes throughout treatment. We found that different co-stimulatory and immune exhaustion markers, such as Programmed cell death protein 1 (PD-1) and DNAX accessory molecule 1 (DNAM-1) amongst others, correlate with the probability of developing these adverse events, both before and during the treatment. We also compared the phenotype of those lymphocytes expressing DNAM-1 with those that do not, and while NK DNAM-1-expressing cells have a co-stimulatory phenotype, T DNAM-1-expressing cells are immune-suppressors. Overall, we set a rationale for the combination of sorafenib and immune-targeted therapies; and for the use of immune markers (such as DNAM-1) for patients’ prognosis evaluation.

Abstract

Advanced hepatocellular carcinoma patients treated with sorafenib who develop early dermatologic adverse events (eDAEs) have a better prognosis. This may be linked to immune mechanisms, and thus, it is relevant to assess the association between peripheral immunity and the probability of developing eDAEs. Peripheral blood mononuclear cells of 52 HCC patients treated with sorafenib were analyzed at baseline and throughout the first eight weeks of therapy. T, B, Natural Killer cells, and their immune checkpoints expression data were characterized by flow cytometry. Cytokine release and immune-suppression assays were carried out ex vivo. Cox baseline and time-dependent regression models were applied to evaluate the probability of increased risk of eDAEs. DNAM-1, PD-1, CD69, and LAG-3 in T cells, plus CD16 and LAG-3 in NK cells, are significantly associated with the probability of developing eDAEs. While NK DNAM-1⁺ cells express activation markers, T DNAM-1⁺ cells induce immune suppression and show immune exhaustion. This is the first study to report an association between immune checkpoints expression in circulating immune cells and the increased incidence of eDAEs. Our results support the hypothesis for an off-target role of sorafenib in immune modulation. We also describe a novel association between DNAM-1 and immune exhaustion in T cells.

Alterations of NK Cell Phenotype in the Disease Course of Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is a deadly cancer localized in the bone marrow, where changes can support progression and therapy resistance. This study examined the expression of numerous biological markers on natural killer (NK) cells in blood and bone marrow of patients with MM. NK cells play key roles in the innate immunosurveillance of MM, so we sought to identify biomarkers on NK cells that may be prognostic for patient outcomes and identify new therapeutic targets in these patients. Biomarker expression was compared on NK cells between MM disease stages and healthy donors, between blood and bone marrow, and associations with disease progression. The study shows that loss of certain biomarkers on NK cells may limit their anti-tumor function in MM patients, that several drug-targetable biomarkers are upregulated on NK cells, and that high expression of the biomarker, SLAMF7, may have prognostic potential to identify patients more likely to show rapid disease progression.

Abstract

Accumulating evidence demonstrates important roles for natural killer (NK) cells in controlling multiple myeloma (MM). A prospective flow cytometry-based analysis of NK cells in the blood and bone marrow (BM) of MM patient subgroups was performed (smoldering (SMM), newly diagnosed (ND), relapsed/refractory, (RR) and post-stem cell transplantation (pSCT)). Assessments included the biomarker expression and function of NK cells, correlations between the expression of receptors on NK cells with their ligands on myeloma cells, and comparisons between MM patient subgroups and healthy controls. The most striking differences from healthy controls were found in RR and pSCT patients, in which NK cells were less mature and expressed reduced levels of the activating receptors DNAM-1, NKG2D, and CD16. These differences were more pronounced in the BM than in blood, including upregulation of the therapeutic targets TIM3, TIGIT, ICOS, and GITR. Their expression suggests NK cells became exhausted upon chronic encounters with the tumor. A high expression of SLAMF7 on blood NK cells correlated with shorter progression-free survival. This correlation was particularly evident in ND patients, including on mature CD56^dim NK cells in the BM. Thus, our NK cell analysis identified possible therapeutic targets in MM and a biomarker with prognostic potential for disease progression.

Role of the Main Non HLA-Specific Activating NK Receptors in Pancreatic, Colorectal and Gastric Tumors Surveillance

Human NK cells can control tumor growth and metastatic spread thanks to their powerful cytolytic activity which relies on the expression of an array of activating receptors. Natural cytotoxicity receptors (NCRs) NKG2D and DNAM-1 are those non-HLA-specific activating NK receptors that are mainly involved in sensing tumor transformation by the recognition of different ligands, often stress-induced molecules, on the surface of cancer cells. Tumors display several mechanisms aimed at dampening/evading NK-mediated responses, a relevant fraction of which is based on the downregulation of the expression of activating receptors and/or their ligands. In this review, we summarize the role of the main non-HLA-specific activating NK receptors, NCRs, NKG2D and DNAM-1, in controlling tumor growth and metastatic spread in solid malignancies affecting the gastrointestinal tract with high incidence in the world population, i.e., pancreatic ductal adenocarcinoma (PDAC), colorectal cancer (CRC), and gastric cancer (GC), also describing the phenotypic and functional alterations induced on NK cells by their tumor microenvironment.

TIGIT blockade enhances functionality of peritoneal NK cells with altered expression of DNAM-1/TIGIT/CD96 checkpoint molecules in ovarian cancer

Advanced ovarian cancer (OC) patients have a poor 5-year survival of only 28%, emphasizing the medical need for improved therapies. Adjuvant immunotherapy could be an attractive approach since OC is an immunogenic disease and the presence of tumor-infiltrating lymphocytes has shown to positively correlate with patient survival. Among these infiltrating lymphocytes are natural killer (NK) cells, key players involved in tumor targeting, initiated by signaling via activating and inhibitory receptors. Here, we investigated the role of the DNAM-1/TIGIT/CD96 axis in the anti-tumor response of NK cells toward OC. Ascites-derived NK cells from advanced OC patients showed lower expression of activating receptor DNAM-1 compared to healthy donor peripheral blood NK cells, while inhibitory receptor TIGIT and CD96 expression was equal or higher, respectively. This shift to a more inhibitory phenotype could also be induced in vitro by co-culturing healthy donor NK cells with OC tumor spheroids, and in vivo on intraperitoneally infused NK cells in SKOV-3 OC bearing NOD/SCID-IL2Rγnull (NSG) mice. Interestingly, TIGIT blockade enhanced degranulation and interferon gamma (IFNγ) production of healthy donor CD56^dim NK cells in response to OC tumor cells, especially when DNAM-1/CD155 interactions were in place. Importantly, TIGIT blockade boosted functional responsiveness of CD56^dim NK cells of OC patients with a baseline reactivity against SKOV-3 cells. Overall, our data show for the first time that checkpoint molecules TIGIT/DNAM-1/CD96 play an important role in NK cell responsiveness against OC, and provides rationale for incorporating TIGIT interference in NK cell-based immunotherapy in OC patients.

Characterization of the DNAM-1, TIGIT and TACTILE Axis on Circulating NK, NKT-Like and T Cell Subsets in Patients with Acute Myeloid Leukemia

Background: Acute myeloid leukemia (AML) remains a major clinical challenge due to poor overall survival, which is even more dramatic in elderly patients. TIGIT, an inhibitory receptor that interacts with CD155 and CD112 molecules, is considered as a checkpoint in T and NK cell activation. This receptor shares ligands with the co-stimulatory receptor DNAM-1 and with TACTILE. The aim of this work was to analyze the expression of DNAM-1, TIGIT and TACTILE in NK cells and T cell subsets in AML patients. Methods: We have studied 36 patients at the time of diagnosis of AML and 20 healthy volunteers. The expression of DNAM-1, TIGIT and TACTILE in NK cells and T cells, according to the expression of CD3 and CD56, was performed by flow cytometry. Results: NK cells, CD56− T cells and CD56+ T (NKT-like) cells from AML patients presented a reduced expression of DNAM-1 compared with healthy volunteers. An increased expression of TIGIT was observed in mainstream CD56− T cells. No differences were observed in the expression of TACTILE. Simplified presentation of incredibly complex evaluations (SPICE) analysis of the co-expression of DNAM-1, TIGIT and TACTILE showed an increase in NK and T cells lacking DNAM-1 and co-expressing TIGIT and TACTILE. Low percentages of DNAM-1−TIGIT+TACTILE+ NK cells and DNAM-1− TIGIT+TACTILE+ CD56− T cells were associated with a better survival of AML patients. Conclusions: The expression of DNAM-1 is reduced in NK cells and in CD4+ and CD8+ T cells from AML patients compared with those from healthy volunteers. An increased percentage of NK and T cells lacking DNAM-1 and co-expressing TIGIT and TACTILE is associated with patient survival, supporting the role of TIGIT as a novel candidate for checkpoint blockade.

Targeting the "PVR-TIGIT axis" with immune checkpoint therapies

Checkpoint inhibitors have become an efficient way to treat cancers. Indeed, anti-CTLA-4, anti-PD1, and anti-PDL-1 antibodies are now used as therapies for cancers. However, while these therapies are very efficient in certain tumors, they remain poorly efficient in others. This might be explained by the immune infiltrate, the expression of target molecules, and the influence of the tumor microenvironment. It is therefore critical to identify checkpoint antigens that represent alternative targets for immunotherapies. PVR-like molecules play regulatory roles in immune cell functions. These proteins are expressed by different cell types and have been shown to be upregulated in various malignancies. PVR and Nectin-2 are expressed by tumor cells as well as myeloid cells, while TIGIT, CD96, and DNAM-1 are expressed on effector lymphoid cells. PVR is able to bind DNAM-1, CD96, and TIGIT, which results in two distinct profiles of effector cell activation. Indeed, while binding to DNAM-1 induces the release of cytokines and cytotoxicity of cytotoxic effector cells, binding TIGIT induces an immunosuppressive and non-cytotoxic profile. PVR is also able to bind CD96, which induces an immunosuppressive response in murine models. Unfortunately, in humans, results remain contradictory, and this interaction might induce the activation or the suppression of the immune response. Similarly, Nectin-2 was shown to bind TIGIT and to induce regulatory profiles in effectors cells such as NK and T cells. Therefore, these data highlight the potential of each of the molecules of the “PVR–TIGIT axis” as a potential target for immune checkpoint therapy. However, many questions remain to be answered to fully understand the mechanisms of this synapse, in particular for human CD96 and Nectin-2, which are still understudied. Here, we review the recent advances in “PVR–TIGIT axis” research and discuss the potential of targeting this axis by checkpoint immunotherapies.

NK Cells Augment Oncolytic Adenovirus Cytotoxicity in Ovarian Cancer

Oncolytic viruses (OVs) can trigger profound innate and adaptive immune responses, which have the potential both to potentiate and reduce the activity of OVs. Natural killer (NK) cells can mediate potent anti-viral and anti-tumoral responses, but there are no data on the role of NK cells in oncolytic adenovirus activity. Here, we have used two different oncolytic adenoviruses-the Ad5 E1A CR2-deletion mutant dl922-947 (group C) and the chimeric Ad3/Ad11p mutant enadenotucirev (group B)-to investigate the effect of NK cells on overall anti-cancer efficacy in ovarian cancer. Because human adenoviruses do not replicate in murine cells, we utilized primary human NK cells from peripheral blood and ovarian cancer ascites. Our results show that dl922-947 and enadenotucirev do not infect NK cells, but induce contact-dependent activation and anti-cancer cytotoxicity against adenovirus-infected ovarian cancer cells. Moreover, manipulation of NK receptors DNAM-1 (DNAX accessory molecule-1) and TIGIT (T cell immunoreceptor with Ig and ITIM domains) significantly influences NK cytotoxicity against adenovirus-infected cells. Together, these results indicate that NK cells act to increase the activity of oncolytic adenovirus in ovarian cancer and suggest that strategies to augment NK activity further via the blockade of inhibitory NK receptor TIGIT could enhance therapeutic potential of OVs.

Type 1 Innate Lymphoid Cells Protect Mice from Acute Liver Injury via Interferon-γ Secretion for Upregulating Bcl-xL Expression in Hepatocytes

Although type 1 innate lymphoid cells (ILC1s) have been originally found as liver-resident ILCs, their pathophysiological role in the liver remains poorly investigated. Here, we demonstrated that carbon tetrachloride (CCl₄) injection into mice activated ILC1s, but not natural killer (NK) cells, in the liver. Activated ILC1s produced interferon-γ (IFN-γ) and protected mice from CCl₄-induced acute liver injury. IFN-γ released from activated ILC1s promoted the survival of hepatocytes through upregulation of Bcl-xL. An activating NK receptor, DNAM-1, was required for the optimal activation and IFN-γ production of liver ILC1s. Extracellular adenosine triphosphate accelerated interleukin-12-driven IFN-γ production by liver ILC1s. These findings suggest that ILC1s are critical for tissue protection during acute liver injury.

Concomitant deletion of SLAM-family receptors, NKG2D and DNAM-1 reveals gene redundancy of NK cell activating receptors in NK cell development and education

NK cells recognize "unwanted" cells using a variety of germline-encoded activating receptors, such as the seven members of signaling lymphocyte activating molecule (SLAM)-family receptors (SFRs), natural killer cell group 2D (NKG2D), and DNAX accessory molecule-1(DNAM-1). Whether these receptors redundantly or synergistically regulate NK cell development and effector function remains poorly understood. By generating mice lacking SFRs, NKG2D, and DNAM-1, separately or in combination, we found that SLAMF6, one of the SFR members, was associated with NK cell differentiation, but its absence had no severe effect on NK cell differentiation and function, likely due to SFR redundancy. Moreover, we revealed that SFRs might work with other NK cell activating receptors in regulating NK cell development and function. We found that SFR deficiency caused an increase in immature NK cell subsets (CD27⁺ CD11b^- ), and this effect was further augmented by the additional deficiency of NKG2D but not DNAM-1. However, SFR-deficient NK cells exhibited elevated responsiveness against "missing-self" hematopoietic targets, whereas the deletion of either NKG2D or DNAM-1 could partially abrogate the elevated effect of SFR deficiency on NK cell activation. Therefore, our results reveal the complexity of activating receptors in regulating NK cell differentiation and activation, extending our insights into the gene redundancy and compensatory effect of NK cell activating receptors.

NK Cell Precursors in Human Bone Marrow in Health and Inflammation

NK cells are generated from hematopoietic stem cells (HSC) residing in the bone marrow (BM), similar to other blood cells. Development toward mature NK cells occurs largely outside the BM through travel of CD34+ and other progenitor intermediates toward secondary lymphoid organs. The BM harbors multipotent CD34+ common lymphoid progenitors (CLPs) that generate T, B, NK, and Dendritic Cells and are devoid of erythroid, myeloid, and megakaryocytic potential. Over recent years, there has been a quest for single-lineage progenitors predominantly with the objective of manipulation and intervention in mind, which has led to the identification of unipotent NK cell progenitors devoid of other lymphoid lineage potential. Research efforts for the study of lymphopoiesis have almost exclusively concentrated on healthy donor tissues and on repopulation/transplant models. This has led to the widely accepted assumption that lymphopoiesis during disease states reflects the findings of these models. However, compelling evidences in animal models show that inflammation plays a fundamental role in the regulation of HSC maturation and release in the BM niches through several mechanisms including modulation of the CXCL12-CXCR4 expression. Indeed, recent findings during systemic inflammation in patients provide evidence that a so-far overlooked CLP exists in the BM (Lin⁻CD34⁺DNAM-1^brightCXCR4⁺) and that it overwhelmingly exits the BM during systemic inflammation. These “inflammatory” precursors have a developmental trajectory toward surprisingly functional NK and T cells as reviewed here and mirror the steady state maintenance of the NK cell pool by CD34⁺DNAM-1⁻CXCR4⁻ precursors. Our understanding of NK cell precursor development may benefit from including a distinct “inflammatory” progenitor modeling of lymphoid precursors, allowing rapid deployment of specialized Lin⁻CD34⁺DNAM-1^brightCXCR4⁺ -derived resources from the BM.

High expression of soluble CD155 in estrogen receptor-negative breast cancer

Background

The poliovirus receptor (CD155) is expressed ubiquitously at low levels on both hematopoietic and nonhematopoietic cells, but its expression is upregulated in various tumor cells. An activating receptor DNAM-1 expressed on cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells binds to CD155 and mediates the cytotoxic activity of CTLs and NK cells against tumors. Unlike mouse tissues, human tissues express a soluble form of CD155 (sCD155), which is a splicing isoform of CD155 lacking the transmembrane region. We previously reported that the serum levels of sCD155 were higher in lung, gastrointestinal, breast, and gynecologic cancer patients than in healthy donors. Here, we focus on breast cancer patients.

Methods

To analyze the association between serum level of sCD155 and clinicopathological parameters of breast cancer, we quantified sCD155 in the sera of 153 breast cancer patients by sandwich ELISA.

Results

sCD155 levels in the sera of breast cancer patients were positively correlated with patient age, disease stage, and invasive tumor size. Moreover, they were higher in patients with estrogen receptor (ER)-negative cancers than in those with ER-positive tumors, and higher in those with Ki-67-high cancers than in those with Ki-67-low cancers.

Conclusions

The serum level of sCD155 is correlated with high risk factors in breast cancer.

DNAM-1 Activating Receptor and Its Ligands: How Do Viruses Affect the NK Cell-Mediated Immune Surveillance during the Various Phases of Infection?

Natural Killer (NK) cells play a critical role in host defense against viral infections. The mechanisms of recognition and killing of virus-infected cells mediated by NK cells are still only partially defined. Several viruses induce, on the surface of target cells, the expression of molecules that are specifically recognized by NK cell-activating receptors. The main NK cell-activating receptors involved in the recognition and killing of virus-infected cells are NKG2D and DNAM-1. In particular, ligands for DNAM-1 are nectin/nectin-like molecules involved also in mechanisms allowing viral infection. Viruses adopt several immune evasion strategies, including those affecting NK cell-mediated immune surveillance, causing persistent viral infection and the development of virus-associated diseases. The virus's immune evasion efficacy depends on molecules differently expressed during the various phases of infection. In this review, we overview the molecular strategies adopted by viruses, specifically cytomegalovirus (CMV), human immunodeficiency virus (HIV-1), herpes virus (HSV), Epstein-Barr virus (EBV) and hepatitis C virus (HCV), aiming to evade NK cell-mediated surveillance, with a special focus on the modulation of DNAM-1 activating receptor and its ligands in various phases of the viral life cycle. The increasing understanding of mechanisms involved in the modulation of activating ligands, together with those mediating the viral immune evasion strategies, would provide critical tools leading to design novel NK cell-based immunotherapies aiming at viral infection control, thus improving cure strategies of virus-associated diseases.

DNAM-1 and the TIGIT/PVRIG/TACTILE Axis: Novel Immune Checkpoints for Natural Killer Cell-Based Cancer Immunotherapy

Natural killer (NK) cells are lymphocytes of the innate immune response characterized by their role in the destruction of tumor cells. Activation of NK cells depend on a fine balance between activating and inhibitory signals mediated by different receptors. In recent years, a family of paired receptors that interact with ligands of the Nectin/Nectin-like (Necl) family has attracted great interest. Two of these ligands, Necl-5 (usually termed CD155 or PVR) and Nectin-2 (CD112), frequently expressed on different types of tumor cells, are recognized by a group of receptors expressed on T and NK cells that exert opposite functions after interacting with their ligands. These receptors include DNAM-1 (CD226), TIGIT, TACTILE (CD96) and the recently described PVRIG. Whereas activation through DNAM-1 after recognition of CD155 or CD112 enhances NK cell-mediated cytotoxicity against a wide range of tumor cells, TIGIT recognition of these ligands exerts an inhibitory effect on NK cells by diminishing IFN-γ production, as well as NK cell-mediated cytotoxicity. PVRIG has also been identified as an inhibitory receptor that recognizes CD112 but not CD155. However, little is known about the role of TACTILE as modulator of immune responses in humans. TACTILE control of tumor growth and metastases has been reported in murine models, and it has been suggested that it negatively regulates the anti-tumor functions mediated by DNAM-1. In NK cells from patients with solid cancer and leukemia, it has been observed a decreased expression of DNAM-1 that may shift the balance in favor to the inhibitory receptors TIGIT or PVRIG, further contributing to the diminished NK cell-mediated cytotoxic capacity observed in these patients. Analysis of DNAM-1, TIGIT, TACTILE and PVRIG on human NK cells from solid cancer or leukemia patients will clarify the role of these receptors in cancer surveillance. Overall, it can be speculated that in cancer patients the TIGIT/PVRIG pathways are upregulated and represent novel targets for checkpoint blockade immunotherapy.

Upregulation of BST-2 by Type I Interferons Reduces the Capacity of Vpu To Protect HIV-1-Infected Cells from NK Cell Responses

The HIV-1 accessory protein Vpu enhances viral release by counteracting the restriction factor BST-2. Furthermore, Vpu promotes NK cell evasion by downmodulating cell surface NTB-A and PVR, known ligands of the NK cell receptors NTB-A and DNAM-1, respectively. While it has been established that Vpu's transmembrane domain (TMD) is required for the interaction and intracellular sequestration of BST-2, NTB-A, and PVR, it remains unclear how Vpu manages to target these proteins simultaneously. In this study, we show that upon upregulation, BST-2 is preferentially downregulated by Vpu over its other TMD substrates. We found that type I interferon (IFN)-mediated BST-2 upregulation greatly impairs the ability of Vpu to downregulate NTB-A and PVR. Our results suggest that occupation of Vpu by BST-2 affects its ability to downregulate other TMD substrates. Accordingly, knockdown of BST-2 increases Vpu's potency to downmodulate NTB-A and PVR in the presence of type I IFN treatment. Moreover, we show that expression of human BST-2, but not that of the macaque orthologue, decreases Vpu's capacity to downregulate NTB-A. Importantly, we show that type I IFNs efficiently sensitize HIV-1-infected cells to NTB-A- and DNAM-1-mediated direct and antibody-dependent NK cell responses. Altogether, our results reveal that type I IFNs decrease Vpu's polyfunctionality, thus reducing its capacity to protect HIV-1-infected cells from NK cell responses.IMPORTANCE The restriction factor BST-2 and the NK cell ligands NTB-A and PVR are among a growing list of membrane proteins found to be downregulated by HIV-1 Vpu. BST-2 antagonism enhances viral release, while NTB-A and PVR downmodulation contributes to NK cell evasion. However, it remains unclear how Vpu can target multiple cellular factors simultaneously. Here we provide evidence that under physiological conditions, BST-2 is preferentially targeted by Vpu over NTB-A and PVR. Specifically, we show that type I IFNs decrease Vpu's polyfunctionality by upregulating BST-2, thus reducing its capacity to protect HIV-1-infected cells from NK cell responses. This indicates that there is a hierarchy of Vpu substrates upon IFN treatment, revealing that for the virus, targeting BST-2 as part of its resistance to IFN takes precedence over evading NK cell responses. This reveals a potential weakness in HIV-1's immunoevasion mechanisms that may be exploited therapeutically to harness NK cell responses against HIV-1.

Diminished cytolytic activity of γδ T cells with reduced DNAM-1 expression in neuroblastoma patients

Neuroblastoma is one of the children's malignant tumors with poor prognosis, as well as high recurrence and metastasis rates after surgical removal and chemotherapy. γδ T-cell based immunotherapy receives increasing attention thanks to the strong cytolytic activity to tumor cells. Our previous data revealed a significant increase in circulating γδ T-cell frequency in NB patients. In the present study, we found that beside a reduction of IFN-γ in serum of NB patients, DNAM-1 expression decreased in both circulating and PAM-expanded NB γδ T cells. Upon PAM stimulation, NB γδ T cells showed a reduced level of cell proliferation. In addition, the cytolytic activity of NB γδ T cells to NB cell lines was proved to be attenuated in a co-culture system. The fact that DNAM-1 neutralizing antibody abolished the tumor cell killing accentuates the indispensable role of DNAM-1 molecule in γδ T-cell cytolytic function.

Monitoring TIGIT/DNAM-1 and PVR/PVRL2 Immune Checkpoint Expression Levels in Allogeneic Stem Cell Transplantation for Acute Myeloid Leukemia

After allogeneic stem cell transplantation (alloSCT), several immune checkpoints play an important role in the antileukemic immune response in the bone marrow (BM) microenvironment. However, immune checkpoint expression levels in the BM have not been reported after alloSCT in patients with acute myeloid leukemia (AML). We investigated the clinical impact of immune checkpoint expression in BM samples after alloSCT for AML. Higher expression of T cell immunoreceptor with Ig and ITIM domains (TIGIT) was associated with a decreased incidence of acute graft-versus-host disease (P = .048) and poor overall (P = .046) and progression-free survival (P = 0.024). In addition, higher expression of TIGIT at engraftment after alloSCT was correlated with a decreased number of natural killer cells in BM (P = .019). Monitoring TIGIT expression in the BM could be useful for predicting outcome after alloSCT for AML. Our findings raise the possibility that blockade of TIGIT would improve survival.

Binding mode of the side-by-side two-IgV molecule CD226/DNAM-1 to its ligand CD155/Necl-5

Natural killer (NK) cells are important component of innate immunity and also contribute to activating and reshaping the adaptive immune responses. The functions of NK cells are modulated by multiple inhibitory and stimulatory receptors. Among these receptors, the activating receptor CD226 (DNAM-1) mediates NK cell activation via binding to its nectin-like (Necl) family ligand, CD155 (Necl-5). Here, we present a unique side-by-side arrangement pattern of two tandem immunoglobulin V-set (IgV) domains deriving from the ectodomains of both human CD226 (hCD226-ecto) and mouse CD226 (mCD226-ecto), which is substantially different from the conventional head-to-tail arrangement of other multiple Ig-like domain molecules. The hybrid complex structure of mCD226-ecto binding to the first domain of human CD155 (hCD155-D1) reveals a conserved binding interface with the first domain of CD226 (D1), whereas the second domain of CD226 (D2) both provides structural supports for the unique architecture of CD226 and forms direct interactions with CD155. In the absence of the D2 domain, CD226-D1 exhibited substantially reduced binding efficacy to CD155. Collectively, these findings would broaden our knowledge of the interaction between NK cell receptors and the nectin/Necl family ligands, as well as provide molecular basis for the development of CD226-targeted antitumor immunotherapeutics.

CD226 gene polymorphism (rs763361 C>T) is associated with susceptibility to type 1 diabetes mellitus among Egyptian children

OBJECTIVE

Genetic factors contribute significantly to type 1 diabetes (T1D) etiology. A single nucleotide polymorphism in the CD226 gene (rs763361 C>T) has been associated with T1D susceptibility in European patients, but data from other populations is limited. Our aim was to study the contribution of this polymorphism to T1D susceptibility among Egyptian children.

METHODS

A case-control study including 74 children with T1D and 82 healthy children as a control group. Genotyping of CD226 gene polymorphism was performed for all participants by DNA extraction followed by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

The frequency of T allele was 78.4% in patients and 68.3% in controls (OR, 1.68; 95% CI, 1.01-2.8; P=0.046). TT, TC, and CC genotypes were found in 62.2%, 32.4%, and 5.4% of the patients, respectively, and in 41.5%, 53.7%, and 4.9% of controls, respectively. Under the recessive model, TT genotype was significantly associated with T1D risk (OR, 2.32; 95% CI, 1.21-4.41; P=0.010). The mean age at diabetes onset was significantly lower in patients carrying T allele compared with C allele (8.03±3.8 year vs. 10.5±2.54 year; P<0.001) and among those with TT genotype compared with the pooled TC+CC genotypes (7.5±2.6 year vs. 10.6±2.6 year; P<0.001). No significant difference was found between genotypes or alleles regarding the HbA1c level.

CONCLUSION

T allele and TT genotype of the CD226 rs763361 polymorphism is associated with susceptibility to T1D and with a lower age of disease onset among Egyptian children.

The paired receptors TIGIT and DNAM-1 as targets for therapeutic antibodies

One of the most exciting fields in modern medicine is immunotherapy, treatment which looks to harness the power of the immune system to fight disease. A particularly effective strategy uses antibodies designed to influence the activity levels of the immune system. Here we look at two receptors - TIGIT and DNAM-1 - which bind the same ligands but have opposite effects on immune cells, earning them the label `paired receptors'. Importantly, natural killer cells and cytotoxic T cells express both of these receptors, and in certain cases their effector functions are dictated by TIGIT or DNAM-1 signaling. Agonist and antagonist antibodies targeting either TIGIT or DNAM-1 present many therapeutic options for diseases spanning from cancer to auto-immunity. In this review we present cases in which the modulation of these receptors holds potential for the development of novel therapies.

Epstein-Barr Virus Induces Adhesion Receptor CD226 (DNAM-1) Expression during Primary B-Cell Transformation into Lymphoblastoid Cell Lines

Epstein-Barr virus (EBV), an oncogenic herpesvirus, infects and transforms primary B cells into immortal lymphoblastoid cell lines (LCLs), providing a model for EBV-mediated tumorigenesis. EBV transformation stimulates robust homotypic aggregation, indicating that EBV induces molecules that mediate cell-cell adhesion. We report that EBV potently induced expression of the adhesion molecule CD226, which is not normally expressed on B cells. We found that early after infection of primary B cells, EBV promoted an increase in CD226 mRNA and protein expression. CD226 levels increased further from early proliferating EBV-positive B cells to LCLs. We found that CD226 expression on B cells was independent of B-cell activation as CpG DNA failed to induce CD226 to the extent of EBV infection. CD226 expression was high in EBV-infected B cells expressing the latency III growth program, but low in EBV-negative and EBV latency I-infected B-lymphoma cell lines. We validated this correlation by demonstrating that the latency III characteristic EBV NF-κB activator, latent membrane protein 1 (LMP1), was sufficient for CD226 upregulation and that CD226 was more highly expressed in lymphomas with increased NF-κB activity. Finally, we found that CD226 was not important for LCL steady-state growth, survival in response to apoptotic stress, homotypic aggregation, or adhesion to activated endothelial cells. These findings collectively suggest that EBV induces expression of a cell adhesion molecule on primary B cells that may play a role in the tumor microenvironment of EBV-associated B-cell malignancies or facilitate adhesion in the establishment of latency in vivo. IMPORTANCE Epstein-Barr virus (EBV) is a common human herpesvirus that establishes latency in B cells. While EBV infection is asymptomatic for most individuals, immune-suppressed individuals are at significantly higher risk of a form of EBV latent infection in which infected B cells are reactivated, grow unchecked, and generate lymphomas. This form of latency is modeled in the laboratory by infecting B cells from the blood of normal human donors in vitro. In this model, we identified a protein called CD226 that is induced by EBV but is not normally expressed on B cells. Rather, it is known to play a role in aggregation and survival signaling of non-B cells in the immune system. Cultures of EBV-infected cells adhere to one another in "clumps," and while the proteins that are responsible for this cellular aggregation are not fully understood, we hypothesized that this form of cellular aggregation may provide a survival advantage. In this article, we characterize the mechanism by which EBV induces this protein and its expression on lymphoma tissue and cell lines and characterize EBV-infected cell lines in which CD226 has been knocked out.

Control of Metastasis by NK Cells

The metastatic spread of malignant cells to distant anatomical locations is a prominent cause of cancer-related death. Metastasis is governed by cancer-cell-intrinsic mechanisms that enable neoplastic cells to invade the local microenvironment, reach the circulation, and colonize distant sites, including the so-called epithelial-to-mesenchymal transition. Moreover, metastasis is regulated by microenvironmental and systemic processes, such as immunosurveillance. Here, we outline the cancer-cell-intrinsic and -extrinsic factors that regulate metastasis, discuss the key role of natural killer (NK) cells in the control of metastatic dissemination, and present potential therapeutic approaches to prevent or target metastatic disease by harnessing NK cells.

Natural Killer Cell Development and Maturation Revisited: Possible Implications of a Novel Distinct Lin-CD34+DNAM-1brightCXCR4+ Cell Progenitor

Since the first description of natural killer (NK) cells, the view on their role in innate immunity has evolved considerably. In addition to first-line defense against transformed and pathogen-infected autologous cells, NK cells contribute to modulate adaptive immune responses and in some cases acquire specialized functions, including exhausted, adaptive, and decidual NK cells. NK cells derive from CD34⁺ progenitors, in vivo and in vitro; however, it is unclear whether the high phenotype diversity in vivo may be generated from these precursors alone. The recent characterization of a novel CD34⁺DNAM-1^brightCXCR4⁺ precursor giving rise to apparently licensed and functional maturing NK cells may suggest the possibility for a higher than expected common lymphocyte precursor diversity and a consequently higher peripheral NK cell phenotype variability. Here, we review the evidences on NK cell central and peripheral development from CD34⁺ precursors and propose a possible updated reading frame based on the characterization of CD34⁺DNAM-1^brightCXCR4⁺ cell progenies, which favors the possibility of concurrent NK cell maturation from different CD34⁺ precursors.

IL-12, IL-15, and IL-18 pre-activated NK cells target resistant T cell acute lymphoblastic leukemia and delay leukemia development in vivo

NK cells have shown promise in therapy of hematological cancers, in particular against acute myeloid leukemia. In contrast, the more NK cell-resistant acute lymphoblastic leukemia (ALL) is difficult to treat with NK-cell-based therapies, and we hypothesized that pre-activation of NK cells could overcome this resistance. We show in pediatric and adult patients with T-cell ALL (T-ALL) perturbed NK cell effector functions at diagnosis. Using an in vivo rat model for T-ALL, Roser leukemia (RL), suppressed NK cell effector functions were observed. NK cells from T-ALL patients had reduced expression of the activating receptors NKp46 and DNAM-1, but not NKG2D. In contrast to T-ALL patients, NKG2D but not NKp46 was downregulated on NK cells during rat RL. Decreased frequencies of terminally differentiated NKG2A⁺CD57^-CD56^dim NK cells in human T-ALL was paralleled in the rat by reduced frequencies of bone marrow NK cells expressing the maturation marker CD11b, possibly indicating impairment of differentiation during leukemia. RL was highly resistant to autologous NK cells, but this resistance was overcome upon pre-activation of NK cells with IL-12, IL-15, and IL-18, with concomitant upregulation of activation markers and activating receptors. Importantly, adoptive transfers of IL-12, IL-15, and IL-18 pre-activated NK cells significantly slowed progression of RL in vivo. The data thus shows that T-ALL blasts normally resistant to NK cells may be targeted by cytokine pre-activated autologous NK cells, and this approach could have potential implications for immunotherapeutic protocols using NK cells to more efficiently target leukemia.

NK Cell Influence on the Outcome of Primary Epstein-Barr Virus Infection

The herpesvirus Epstein–Barr virus (EBV) was discovered as the first human candidate tumor virus in Burkitt’s lymphoma more than 50 years ago. Despite its strong growth transforming capacity, more than 90% of the human adult population carries this virus asymptomatically under near perfect immune control. The mode of primary EBV infection is in part responsible for EBV-associated diseases, including Hodgkin’s lymphoma. It is, therefore, important to understand which circumstances lead to symptomatic primary EBV infection, called infectious mononucleosis (IM). Innate immune control of lytic viral replication by early-differentiated natural killer (NK) cells was found to attenuate IM symptoms and continuous loss of the respective NK cell subset during the first decade of life might predispose for IM during adolescence. In this review, we discuss the evidence that NK cells are involved in the immune control of EBV, mechanisms by which they might detect and control lytic EBV replication, and compare NK cell subpopulations that expand during different human herpesvirus infections.

Natural killer cell recognition of in vivo drug-induced senescent multiple myeloma cells

Recognition of tumor cells by the immune system is a key step in cancer eradication. Melphalan is an alkylating agent routinely used in the treatment of patients with multiple myeloma (MM), but at therapeutic doses it leads to an immunosuppressive state due to lymphopenia. Here, we used a mouse model of MM to investigate the ability of in vivo treatment with low doses of melphalan to modulate natural killer (NK) cell activity, which have been shown to play a major role in the control of MM growth. Melphalan treatment was able to enhance the surface expression of the stress-induced NKG2D ligands RAE-1 and MULT-1, and of the DNAM-1 ligand PVR (CD155) on MM cells, leading to better tumor cell recognition and killing by NK cells, as highlighted by NK cell increased degranulation triggered by melphalan-treated tumor cells. Remarkably, NK cell population was not affected by the melphalan dose used, but rather displayed activation features as indicated by CD107a and CD69 expression. Furthermore, we showed that low doses of melphalan fail to induce tumor cell apoptosis, but promote the in vivo establishment of a senescent tumor cell population, harboring high levels of the stress-induced ligands RAE-1 and PVR. Taken together our data support the concept of using chemotherapy in order to boost antitumor innate immune responses and report the possibility to induce cellular senescence of tumor cells in vivo.

Loss of DNAM-1 ligand expression by acute myeloid leukemia cells renders them resistant to NK cell killing

Acute myeloid leukemia (AML) is associated with poor natural killer (NK) cell function through aberrant expression of NK-cell-activating receptors and their ligands on tumor cells. These alterations are thought to promote formation of inhibitory NK-target cell synapses, in which killer cell degranulation is attenuated. Allogeneic stem cell transplantation can be effective in treating AML, through restoration of NK cell lytic activity. Similarly, agents that augment NK-cell-activating signals within the immunological synapse may provide some therapeutic benefit. However, the receptor-ligand interactions that critically dictate NK cell function in AML remain undefined. Here, we demonstrate that CD112/CD155 expression is required for DNAM-1-dependent killing of AML cells. Indeed, the low, or absent, expression of CD112/CD155 on multiple AML cell lines resulted in failure to stimulate optimal NK cell function. Importantly, isolated clones with low CD112/155 expression were resistant to NK cell killing while those expressing abundant levels of CD112/155 were highly susceptible. Attenuated NK cell killing in the absence of CD112/CD155 originated from decreased NK-target cell conjugation. Furthermore, we reveal by time-lapse microscopy, a significant increase in NK cell 'failed killing' in the absence of DNAM-1 ligands. Consequently, NK cells preferentially lysed ligand-expressing cells within heterogeneous populations, driving clonal selection of CD112/CD155-negative blasts upon NK cell attack. Taken together, we identify reduced CD155 expression as a major NK cell escape mechanism in AML and an opportunity for targeted immunotherapy.

Impaired NK-mediated regulation of T-cell activity in multiple sclerosis is reconstituted by IL-2 receptor modulation

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system (CNS) resulting from a breakdown in peripheral immune tolerance. Although a beneficial role of natural killer (NK)-cell immune-regulatory function has been proposed, it still needs to be elucidated whether NK cells are functionally impaired as part of the disease. We observed NK cells in active MS lesions in close proximity to T cells. In accordance with a higher migratory capacity across the blood-brain barrier, CD56(bright) NK cells represent the major intrathecal NK-cell subset in both MS patients and healthy individuals. Investigating the peripheral blood and cerebrospinal fluid of MS patients treated with natalizumab revealed that transmigration of this subset depends on the α4β1 integrin very late antigen (VLA)-4. Although no MS-related changes in the migratory capacity of NK cells were observed, NK cells derived from patients with MS exhibit a reduced cytolytic activity in response to antigen-activated CD4(+) T cells. Defective NK-mediated immune regulation in MS is mainly attributable to a CD4(+) T-cell evasion caused by an impaired DNAX accessory molecule (DNAM)-1/CD155 interaction. Both the expression of the activating NK-cell receptor DNAM-1, a genetic alteration consistently found in MS-association studies, and up-regulation of the receptor's ligand CD155 on CD4(+) T cells are reduced in MS. Therapeutic immune modulation of IL-2 receptor restores impaired immune regulation in MS by increasing the proportion of CD155-expressing CD4(+) T cells and the cytolytic activity of NK cells.

Natural killer cell immunosenescence in acute myeloid leukaemia patients: new targets for immunotherapeutic strategies?

Several age-associated changes in natural killer (NK) cell phenotype have been reported that contribute to the defective NK cell response observed in elderly patients. A remodelling of the NK cell compartment occurs in the elderly with a reduction in the output of immature CD56(bright) cells and an accumulation of highly differentiated CD56(dim) NK cells. Acute myeloid leukaemia (AML) is generally a disease of older adults. NK cells in AML patients show diminished expression of several activating receptors that contribute to impaired NK cell function and, in consequence, to AML blast escape from NK cell immunosurveillance. In AML patients, phenotypic changes in NK cells have been correlated with disease progression and survival. NK cell-based immunotherapy has emerged as a possibility for the treatment of AML patients. The understanding of age-associated alterations in NK cells is therefore necessary to define adequate therapeutic strategies in older AML patients.

Immunoreceptor TIGIT inhibits the cytotoxicity of human cytokine-induced killer cells by interacting with CD155

T cell Ig and ITIM domain (TIGIT) is a newly identified inhibitory receptor expressed on T and natural killer (NK) cells. Cytokine-induced killer (CIK) cells express CD3 and CD56 molecules, and share functional properties with both NK and T cells. However, it remains unknown whether TIGIT is expressed in CIK cells. Here, we show that TIGIT is expressed by CIK cells and interacts with CD155. By blocking TIGIT using an anti-TIGIT functional antibody, we demonstrate that CIK cells display increased proliferation; higher cytotoxic targeting of tumor cells expressing CD155; and higher expression of interferon-γ (IFN-γ), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Furthermore, increases in IFN-γ and cytotoxicity by blockade of TIGIT were reduced by blocking DNAX accessory molecule-1 (DNAM-1) signaling, implying that TIGIT exerts immunosuppressive effects by competing with DNAM-1 for the same ligand, CD155. Our results provide evidence that blockade of TIGIT may be a novel strategy to improve the cytotoxic activity of CIK cells.

Critical roles of co-activation receptor DNAX accessory molecule-1 in natural killer cell immunity

Natural killer (NK) cells, which can exert early and powerful anti-tumour and anti-viral responses, are important components of the innate immune system. DNAX accessory molecule-1 (DNAM-1) is an activating receptor molecule expressed on the surface of NK cells. Recent findings suggest that DNAM-1 is a critical regulator of NK cell biology. DNAM-1 is involved in NK cell education and differentiation, and also plays a pivotal role in the development of cancer, viral infections and immune-related diseases. However, tumours and viruses have developed multiple mechanisms to evade the immune system. They are able to impair DNAM-1 activity by targeting the DNAM-1 receptor-ligand system. We have reviewed the roles of DNAM-1, and its biological functions, with respect to NK cell biology and DNAM-1 chimeric antigen receptor-based immunotherapy.

Drug-induced hyperploidy stimulates an antitumor NK cell response mediated by NKG2D and DNAM-1 receptors

Formation of polyploid or aneuploid cells is a pathological hallmark of malignant tumors. Cell cycle checkpoint mechanisms play a crucial role in ensuring genomic integrity during mitosis, avoiding the generation of aneuploid cells. Additionally, cancer cell DNA ploidy is subjected to extrinsic controls operated by activation of adaptive immune responses mediated by T cells. NK cells exert a central role in the innate anticancer immunity; however, the mechanisms involved in the recognition of tumor cells by NK cells have not been fully elucidated. Herein, we report that drug-induced polyploidy in cancer cells activates antitumor responses mediated by NK cells. Thus, hyperploidy-inducing chemotherapeutic agents strongly upregulate the tumor expression of ligands for the NK cell activating receptors NKG2D and DNAM-1. Drug-induced hyperploidy modulated the repertoire of activating receptors and the cytokine profile of NK cells, rendering tumor cells more susceptible to NK cell-mediated lysis through the activation of NKG2D and DNAM-1 receptors. In addition, hyperploidization stimulated the production of IL-2 by CD4 T cells, which induced NK cell proliferation and activity. The stimulation of MICA, a key NKG2D ligand, in hyperploid cells was mainly mediated by ATM protein kinase. Likewise, pharmacological inhibition of key regulators of endoplasmic reticulum stress in certain cell models supports a role for this pathway in NKG2D ligand upregulation. Overall, our findings indicate that, besides the cytotoxic effect on tumor cells, the therapeutic activity of anti-mitotic drugs may be mediated by the induction of a coordinated antitumor immune response involving NK and T cells.

Modulation of CD112 by the alphaherpesvirus gD protein suppresses DNAM-1-dependent NK cell-mediated lysis of infected cells

Natural killer (NK) cells are key players in the innate response to viruses, including herpesviruses. In particular, the variety of viral strategies to modulate the recognition of certain herpesviruses witnesses the importance of NK cells in the control of this group of viruses. Still, NK evasion strategies have remained largely elusive for the largest herpesvirus subfamily, the alphaherpesviruses. Here, we report that the gD glycoprotein of the alphaherpesviruses pseudorabies virus (PRV) and herpes simplex virus 2 (HSV-2) displays previously uncharacterized immune evasion properties toward NK cells. Expression of gD during infection or transfection led to degradation and consequent down-regulation of CD112, a ligand for the activating NK receptor DNAX accessory molecule 1 (DNAM-1). CD112 downregulation resulted in a reduced ability of DNAM-1 to bind to the surface of both virus-infected and gD-transfected cells. Consequently, expression of gD suppressed NK cell degranulation and NK cell-mediated lysis of PRV- or HSV-2-infected cells. These data identify an alphaherpesvirus evasion strategy from NK cells and point out that interactions between viral envelope proteins and host cell receptors can have biological consequences that stretch beyond virus entry.

Development of NK cell expansion methods using feeder cells from human myelogenous leukemia cell line

Background

Natural killer (NK) cells constantly survey surrounding tissues and remove newly generated cancer cells, independent of cancer antigen recognition. Although there have been a number of attempts to apply NK cells for cancer therapy, clinical application has been somewhat limited because of the difficulty in preparing a sufficient number of NK cells. Therefore, ex vivo NK cell expansion is one of the important steps for developing NK cell therapeutics.

Methods

CD3⁺ depleted lymphocytes were cocultured with IL-2 and with feeder cells (peripheral blood mononuclear cells [PBMCs], K562, and Jurkat) for 15 days. Expanded NK cells were tested for cytotoxicity against cancer cell lines.

Results

We compared feeder activities of three different cells-PBMC, K562, and Jurkat. K562 expanded NK cells by almost 20 fold and also showed powerful cytotoxic activity against cancer cells. K562-NK cells remarkably expressed the NK cell activation receptors, NKG2D, and DNAM-1. K562-NK cells exhibited more than two-fold production of cytotoxic granules compared with Jurkat-NK cells, producing more perforin and granzyme B than naïve NK cells.

Conclusion

Our findings suggest that K562 are more efficient feeder cells than Jurkat or PBMCs. K562 feeder cells expanded NK cells by almost 20 fold and showed powerful cytotoxic activity against cancer cells. We herein propose an intriguing approach for a design of NK cell expansion.

Recognition of tumors by the innate immune system and natural killer cells

In recent years, roles of the immune system in immune surveillance of cancer have been explored using a variety of approaches. The roles of the adaptive immune system have been a major emphasis, but increasing evidence supports a role for innate immune effector cells such as natural killer (NK) cells in tumor surveillance. Here, we discuss some of the evidence for roles in tumor surveillance of innate immune cells. In particular, we focus on NK cells and other immune cells that express germline-encoded receptors, often labeled NK receptors. The impact of these receptors and the cells that express them on tumor suppression is summarized. We discuss in detail some of the pathways and events in tumor cells that induce or upregulate cell-surface expression of the ligands for these receptors, and the logic of how those pathways serve to identify malignant, or potentially malignant cells. How tumors often evade tumor suppression mediated by innate killer cells is another major subject of the review. We end with a discussion on some of the implications of the various findings with respect to possible therapeutic approaches.