Effect of NKG2D ligand expression on host immune responses

Impact of the MICA-129Met/Val Dimorphism on NKG2D-Mediated Biological Functions and Disease Risks

The major histocompatibility complex (MHC) class I chain-related A (MICA) is the most polymorphic non-classical MHC class I gene in humans. It encodes a ligand for NKG2D (NK group 2, member D), an activating natural killer (NK) receptor that is expressed mainly on NK cells and CD8⁺ T cells. The single-nucleotide polymorphism (SNP) rs1051792 causing a valine (Val) to methionine (Met) exchange at position 129 of the MICA protein is of specific interest. It separates MICA into isoforms that bind NKG2D with high (Met) and low affinities (Val). Therefore, this SNP has been investigated for associations with infections, autoimmune diseases, and cancer. Here, we systematically review these studies and analyze them in view of new data on the functional consequences of this polymorphism. It has been shown recently that the MICA-129Met variant elicits a stronger NKG2D signaling, resulting in more degranulation and IFN-γ production in NK cells and in a faster costimulation of CD8⁺ T cells than the MICA-129Val variant. However, the MICA-129Met isoform also downregulates NKG2D more efficiently than the MICA-129Val isoform. This downregulation impairs NKG2D-mediated functions at high expression intensities of the MICA-Met variant. These features of the MICA-129Met/Val dimorphism need to be considered when interpreting disease association studies. Particularly, in the field of hematopoietic stem cell transplantation, they help to explain the associations of the SNP with outcome including graft-versus-host disease and relapse of malignancy. Implications for future disease association studies of the MICA-129Met/Val dimorphism are discussed.

Inhibition of MMP activity can restore NKG2D ligand expression in gastric cancer, leading to improved NK cell susceptibility

BACKGROUND AND METHODS

Natural killer (NK) cells can react with tumor cells through the balance of inhibitory and stimulatory signals between NK cell surface receptors and their ligands, such as MHC class I chain-related A (MICA), MHC class I chain-related B (MICB), and several UL16-binding proteins (ULBPs). In the present study, we evaluated the relationship between NKG2D ligand expression and matrix metalloproteinase (MMP) activity in in vitro culture systems of a panel of gastric cancer cell lines (n = 10) and clinical samples (n = 102).

RESULTS

First, the surface expression of NK group 2 member D (NKG2D) ligands (MICA, MICB, ULBP-2, and ULBP-3) on tumor cells was markedly downregulated on in vitro culture, in parallel to the upregulation of MMPs analyzed by gelatin zymography and gene expression microarray, whereas the transcript levels of NKG2D ligands remained unchanged on in vitro culture. Second, MMP-specific inhibitors could restore the downregulated expression of NKG2D ligands and functionally improve susceptibilities to NK cells in vitro. Third, the production of soluble NKG2D ligands was increased on in vitro culture and was inhibited by MMP-specific inhibitors. Finally, there was a significant inverse correlation between MMP-9 expression and NKG2D ligand expression as analyzed by immunohistochemistry in clinical tumor samples.

CONCLUSION

The present study is a comprehensive study demonstrating that upregulation of MMP activity can induce a downregulation of expression of NKG2D ligands in gastric cancer cells, leading to lower-level susceptibility to NK cells.

A Herpesviral induction of RAE-1 NKG2D ligand expression occurs through release of HDAC mediated repression

Natural Killer (NK) cells are essential for control of viral infection and cancer. NK cells express NKG2D, an activating receptor that directly recognizes NKG2D ligands. These are expressed at low level on healthy cells, but are induced by stresses like infection and transformation. The physiological events that drive NKG2D ligand expression during infection are still poorly understood. We observed that the mouse cytomegalovirus encoded protein m18 is necessary and sufficient to drive expression of the RAE-1 family of NKG2D ligands. We demonstrate that RAE-1 is transcriptionally repressed by histone deacetylase inhibitor 3 (HDAC3) in healthy cells, and m18 relieves this repression by directly interacting with Casein Kinase II and preventing it from activating HDAC3. Accordingly, we found that HDAC inhibiting proteins from human herpesviruses induce human NKG2D ligand ULBP-1. Thus our findings indicate that virally mediated HDAC inhibition can act as a signal for the host to activate NK-cell recognition.

NKG2D ligand expression in pediatric brain tumors

Adult brain tumors establish an immunosuppressive tumor microenvironment as a modality of immune escape, with several immunotherapies designed to overcome this barrier. However, the relationship between tumor cells and immune cells in pediatric brain tumor patients is not as well-defined. In this study, we sought to determine whether the model of immune escape observed in adult brain tumors is reflected in patients with pediatric brain tumors by evaluating NKG2D ligand expression on tissue microarrays created from patients with a variety of childhood brain tumor diagnoses, and infiltration of Natural Killer and myeloid cells. We noted a disparity between mRNA and protein expression for the 8 known NKG2D ligands. Surprisingly, high-grade gliomas did not have increased NKG2D ligand expression compared to normal adjacent brain tissue, nor did they have significant myeloid or NK cell infiltration. These data suggest that pediatric brain tumors have reduced NK cell-mediated immune surveillance, and a less immunosuppressive tumor microenvironment as compared to their adult counterparts. These data indicate that therapies aimed to improve NK cell trafficking and functions in pediatric brain tumors may have a greater impact on anti-tumor immune responses and patient survival, with fewer obstacles to overcome.

Mesenchymal Stromal Cells Can Regulate the Immune Response in the Tumor Microenvironment

The tumor microenvironment is a good target for therapy in solid tumors and hematological malignancies. Indeed, solid tumor cells' growth and expansion can influence neighboring cells' behavior, leading to a modulation of mesenchymal stromal cell (MSC) activities and remodeling of extracellular matrix components. This leads to an altered microenvironment, where reparative mechanisms, in the presence of sub-acute inflammation, are not able to reconstitute healthy tissue. Carcinoma cells can undergo epithelial mesenchymal transition (EMT), a key step to generate metastasis; these mesenchymal-like cells display the functional behavior of MSC. Furthermore, MSC can support the survival and growth of leukemic cells within bone marrow participating in the leukemic cell niche. Notably, MSC can inhibit the anti-tumor immune response through either carcinoma-associated fibroblasts or bone marrow stromal cells. Experimental data have indicated their relevance in regulating cytolytic effector lymphocytes of the innate and adaptive arms of the immune system. Herein, we will discuss some of the evidence in hematological malignancies and solid tumors. In particular, we will focus our attention on the means by which it is conceivable to inhibit MSC-mediated immune suppression and trigger anti-tumor innate immunity.

DNA Damage: From Chronic Inflammation to Age-Related Deterioration

To lessen the "wear and tear" of existence, cells have evolved mechanisms that continuously sense DNA lesions, repair DNA damage and restore the compromised genome back to its native form. Besides genome maintenance pathways, multicellular organisms may also employ adaptive and innate immune mechanisms to guard themselves against bacteria or viruses. Recent evidence points to reciprocal interactions between DNA repair, DNA damage responses and aspects of immunity; both self-maintenance and defense responses share a battery of common players and signaling pathways aimed at safeguarding our bodily functions over time. In the short-term, this functional interplay would allow injured cells to restore damaged DNA templates or communicate their compromised state to the microenvironment. In the long-term, however, it may result in the (premature) onset of age-related degeneration, including cancer. Here, we discuss the beneficial and unrewarding outcomes of DNA damage-driven inflammation in the context of tissue-specific pathology and disease progression.

Distinct Roles for Human Cytomegalovirus Immediate Early Proteins IE1 and IE2 in the Transcriptional Regulation of MICA and PVR/CD155 Expression

Elimination of virus-infected cells by cytotoxic lymphocytes is triggered by activating receptors, among which NKG2D and DNAM-1/CD226 play an important role. Their ligands, that is, MHC class I-related chain (MIC) A/B and UL16-binding proteins (ULBP)1-6 (NKG2D ligand), Nectin-2/CD112, and poliovirus receptor (PVR)/CD155 (DNAM-1 ligand), are often induced on virus-infected cells, although some viruses, including human CMV (HCMV), can block their expression. In this study, we report that infection of different cell types with laboratory or low-passage HCMV strains upregulated MICA, ULBP3, and PVR, with NKG2D and DNAM-1 playing a role in NK cell-mediated lysis of infected cells. Inhibition of viral DNA replication with phosphonoformic acid did not prevent ligand upregulation, thus indicating that early phases of HCMV infection are involved in ligand increase. Indeed, the major immediate early (IE) proteins IE1 and IE2 stimulated the expression of MICA and PVR, but not ULBP3. IE2 directly activated MICA promoter via its binding to an IE2-responsive element that we identified within the promoter and that is conserved among different alleles of MICA. Both IE proteins were instead required for PVR upregulation via a mechanism independent of IE DNA binding activity. Finally, inhibiting IE protein expression during HCMV infection confirmed their involvement in ligand increase. We also investigated the contribution of the DNA damage response, a pathway activated by HCMV and implicated in ligand regulation. However, silencing of ataxia telangiectasia mutated, ataxia telangiectasia and Rad3-related protein, and DNA-dependent protein kinase did not influence ligand expression. Overall, these data reveal that MICA and PVR are directly regulated by HCMV IE proteins, and this may be crucial for the onset of an early host antiviral response.

The NKG2D-IL-15 signaling pathway contributes to T-cell mediated pathology in inflammatory myopathies

NKG2D is an activating receptor on T cells, which has been implicated in the pathogenesis of autoimmune diseases. T cells are critically involved in idiopathic inflammatory myopathies (IIM) and have been proposed as specific therapeutic targets. However, the mechanisms underlying T cell-mediated progressive muscle destruction in IIM remain to be elucidated. We here determined the involvement of the NKG2D – IL-15 signaling pathway. Primary human myoblasts expressed NKG2D ligands, which were further upregulated upon inflammatory stimuli. In parallel, shedding of the soluble NKG2D ligand MICA (sMICA) decreased upon inflammation potentially diminishing inhibition of NKG2D signaling. Membrane-related expression of IL-15 by myoblasts induced differentiation of naïve CD8⁺ T cells into highly activated, cytotoxic CD8⁺NKG2D^high T cells demonstrating NKG2D-dependent lysis of myoblasts in vitro. CD8⁺NKG2D^high T cell frequencies were increased in the peripheral blood of polymyositis (PM) patients and correlated with serum creatinine kinase concentrations, while serum sMICA levels were not significantly changed. In muscle biopsy specimens from PM patients expression of the NKG2D ligand MICA/B was upregulated, IL-15 was expressed by muscle cells, CD68⁺ macrophages as well as CD4⁺ T cells, and CD8⁺NKG2D⁺ cells were frequently detected within inflammatory infiltrates arguing for a local signaling circuit in the inflammatory muscle milieu. In conclusion, the NKG2D – IL-15 signaling pathway contributes to progressive muscle destruction in IIM potentially opening new therapeutic avenues.

Peginterferon Alfa-2a/Ribavirin treatment efficacy in chronic hepatitis C patients is related to natural killer group 2D gene rs1049174 GC polymorphism

Natural killer group 2D (NKG2D), as an activating receptor, plays pivotal role in viral infectious diseases. Several single nucleotide polymorphisms (SNPs) in the NKG2D gene have characterized that the rs1049174G/C SNP of NKG2D is in the spotlight of notice because of its role in activating of human T cells. This study aimed to investigate rs1049174G/C genetic polymorphism in Chronic Hepatitis C (CHC) patients. The study compromised 107 CHC patients with genotype 1a and 1b. All recruited patients were under treatment with Peginterferon Alfa-2a/Ribavirin according to standard protocol. After completing treatment, 67 patients showed sustained virologic response (SVR) and the rest of patients did not respond to the treatment and considered as non-responder (NR). Genotyping of NKG2D rs1049174G/C SNP was performed using PCR-RFLP method in SVR and NR patients. The NKG2D rs1049174 genotypes frequency for GG, GC and CC were 45, 41 and 14 % respectively. Genotypes distribution were significantly different between SVR and NR groups (p = 0.005). So that the patients with the homozygous GG genotype demonstrated a higher response to Peginterferon Alfa-2a/Ribavirin therapy against HCV infection (OR = 6.0, 95 %CI 1.71-21.08, p = 0.005). In conclusion, the rs1049174 GG genotype of NKG2D receptor is an effective factor in successfully treatment of CHC patients by Peginterferon Alfa-2a/Ribavirin.

Regulation of NKG2D Expression and Signaling by Endocytosis

NKG2D is an activating receptor that can bind to a large number of stress-induced ligands that are expressed in the context of cancer or viral infection. This receptor is expressed on many cytotoxic lymphocytes, and plays a crucial role in antitumor and antiviral immune responses. However, exposure to NKG2D ligand-expressing target cells promotes receptor endocytosis, ultimately leading to lysosomal receptor degradation and impairment of NKG2D-mediated functions. Interestingly, before being degraded, internalized receptors can signal from the endosomal compartment, leading to the appropriate activation of cellular functional programs. This review summarizes recent findings on ligand-induced receptor internalization, with particular emphasis on the role of endocytosis in the control of both NKG2D-mediated intracellular signaling and receptor degradation.

Wogonin Inhibits Tumor-derived Regulatory Molecules by Suppressing STAT3 Signaling to Promote Tumor Immunity

Wogonin exerts effective antitumor activities through direct cytotoxicity against cancer cells and indirect immune modulation. However, the molecular mechanisms of these activities remain poorly understood and need further study. We found that wogonin could efficiently downregulate the expression of B7H1, retinoic acid early induced transcript-1ε (RAE-1ε), and vascular endothelial growth factor in gastric cancer cells. Wogonin also promoted the secretion of calreticulin and high-mobility group protein 1 by tumor cells. Apoptotic bodies from dying tumor cells treated with wogonin were susceptible for uptake by neighboring dendritic cells (DCs). With the xenograft tumor model, wogonin inhibited tumor growth and promoted the recruitment of DC, T, and NK cells into tumor tissues. Infiltrated frequencies of DC, T, and NK cells in tumors were inversely correlated with expression levels of vascular endothelial growth factor, B7H1, and RAE-1ε of tumor tissues. Wogonin directly inhibited the activation of STAT3 on tyrosine 705 in tumor cells. The dephosphorylation of STAT3 contributed to the decreased expression of B7H1 and MHC class I chain-related protein A, and the enhancement of calreticulin on the cell membrane. Our study confirmed the immune-enhancing function of wogonin, and indicated that wogonin could be used in collaboration with DC vaccine or activated lymphocytes for tumor therapy.

Altered Expression of Natural Cytotoxicity Receptors and NKG2D on Peripheral Blood NK Cell Subsets in Breast Cancer Patients

Human natural killer (NK) cells are considered professional cytotoxic cells that are integrated into the effector branch of innate immunity during antiviral and antitumoral responses. The purpose of this study was to examine the peripheral distribution and expression of NK cell activation receptors from the fresh peripheral blood mononuclear cells of 30 breast cancer patients prior to any form of treatment (including surgery, chemotherapy, and radiotherapy), 10 benign breast pathology patients, and 24 control individuals. CD3⁻CD56^dimCD16^bright NK cells (CD56^dim NK) and CD3⁻CD56^brightCD16^dim/− NK cells (CD56^bright NK) were identified using flow cytometry. The circulating counts of CD56^dim and CD56^bright NK cells were not significantly different between the groups evaluated, nor were the counts of other leukocyte subsets between the breast cancer patients and benign breast pathology patients. However, in CD56^dim NK cells, NKp44 expression was higher in breast cancer patients (P = .0302), whereas NKp30 (P = .0005), NKp46 (P = .0298), and NKG2D (P = .0005) expression was lower with respect to healthy donors. In CD56^bright NK cells, NKp30 (P = .0007), NKp46 (P = .0012), and NKG2D (P = .0069) expression was lower in breast cancer patients compared with control group. Only NKG2D in CD56^bright NK cells (P = .0208) and CD56^dim NK cells (P = .0439) showed difference between benign breast pathology and breast cancer patients. Collectively, the current study showed phenotypic alterations in activation receptors on CD56^dim and CD56^bright NK cells, suggesting that breast cancer patients have decreased NK cell cytotoxicity.

The MICA-129 dimorphism affects NKG2D signaling and outcome of hematopoietic stem cell transplantation

The MHC class I chain-related molecule A (MICA) is a highly polymorphic ligand for the activating natural killer (NK)-cell receptor NKG2D. A single nucleotide polymorphism causes a valine to methionine exchange at position 129. Presence of a MICA-129Met allele in patients (n = 452) undergoing hematopoietic stem cell transplantation (HSCT) increased the chance of overall survival (hazard ratio [HR] = 0.77, P = 0.0445) and reduced the risk to die due to acute graft-versus-host disease (aGVHD) (odds ratio [OR] = 0.57, P = 0.0400) although homozygous carriers had an increased risk to experience this complication (OR = 1.92, P = 0.0371). Overall survival of MICA-129Val/Val genotype carriers was improved when treated with anti-thymocyte globulin (HR = 0.54, P = 0.0166). Functionally, the MICA-129Met isoform was characterized by stronger NKG2D signaling, triggering more NK-cell cytotoxicity and interferon-γ release, and faster co-stimulation of CD8⁺ T cells. The MICA-129Met variant also induced a faster and stronger down-regulation of NKG2D on NK and CD8⁺ T cells than the MICA-129Val isoform. The reduced cell surface expression of NKG2D in response to engagement by MICA-129Met variants appeared to reduce the severity of aGVHD.

DNA Damage Response and Immune Defense: Links and Mechanisms

DNA damage plays a causal role in numerous human pathologies including cancer, premature aging, and chronic inflammatory conditions. In response to genotoxic insults, the DNA damage response (DDR) orchestrates DNA damage checkpoint activation and facilitates the removal of DNA lesions. The DDR can also arouse the immune system by for example inducing the expression of antimicrobial peptides as well as ligands for receptors found on immune cells. The activation of immune signaling is triggered by different components of the DDR including DNA damage sensors, transducer kinases, and effectors. In this review, we describe recent advances on the understanding of the role of DDR in activating immune signaling. We highlight evidence gained into (i) which molecular and cellular pathways of DDR activate immune signaling, (ii) how DNA damage drives chronic inflammation, and (iii) how chronic inflammation causes DNA damage and pathology in humans.

Expanded and armed natural killer cells for cancer treatment

The capacity of natural killer (NK) cells to recognize and kill transformed cells suggests that their infusion could be used to treat cancer. It is difficult to obtain large numbers of NK cells ex vivo by exposure to cytokines alone but the addition of stimulatory cells to the cultures can induce NK cell proliferation and long-term expansion. Some of these methods have been validated for clinical-grade application and support clinical trials testing feasibility and safety of NK cell administration. Early data indicate that ex vivo expansion of NK cells from healthy donors or from patients with cancer is robust, allowing multiple infusions from a single apheresis. NK cells can transiently expand in vivo after infusion. Allogeneic NK cells are not direct effectors of graft-versus-host disease but this may occur if donor NK cells are infused after allogeneic hematopoietic stem cell transplant, which may activate T cell alloreactivity. NK cells can be directed with antibodies, or engineered using either transient modification by electroporation of mRNA or prolonged gene expression by viral transduction. Thus, expanded NK cells can be armed with activating receptors that enhance their natural anti-tumor capacity or with chimeric antigen receptors that can redirect them towards specific tumor targets. They can also be induced to express cytokines that promote their autonomous growth, further supporting their in vivo expansion. With the implementation of these approaches, expanded and armed NK cells should ultimately become a powerful component of immunotherapy of cancer.

CBP/p300 acetyltransferases regulate the expression of NKG2D ligands on tumor cells

Tumor surveillance of natural killer (NK) cells is mediated by the cytotoxicity receptor natural-killer group 2 member D (NKG2D). Ligands for NKG2D are generally not expressed on healthy cells, but induced on the surface of malignant cells. To date, NKG2D ligand (NKG2D-L) induction was mainly described to depend on the activation of the DNA damage response, although the molecular mechanisms that regulate NKG2D-L expression remain largely unknown. Here, we show that the acetyltransferases CBP (CREB-binding protein) and p300 play a crucial role in the regulation of NKG2D-L on tumor cells. Loss of CBP/p300 decreased the basal cell surface expression of human ligands and reduced the upregulation of MICA/B and ULBP2 in response to histone deacetylase inhibitors or DNA damage. Furthermore, CBP/P300 deficiency abrogated the sensitivity of stressed cells to NK cell-mediated killing. CBP/p300 were also identified as major regulators of mouse NKG2D ligand RAE-1 in vitro and in vivo using the Eμ-Myc lymphoma model. Mechanistically, we observed an enhanced activation of the CBP/p300 binding transcription factor CREB (cAMP response element-binding protein) correlating to the NKG2D-L upregulation. Moreover, increased binding of CREB and CBP/p300 to NKG2D-L promoters and elevated histone acetylation were detectable. This study provides strong evidence for a major role of CBP and p300 in orchestrating NKG2D-L induction and consequently immunosurveillance of tumors in mice and humans. These findings might help to develop novel immunotherapeutic approaches against cancer.

AID-expressing epithelium is protected from oncogenic transformation by an NKG2D surveillance pathway

Activation-induced deaminase (AID) initiates secondary antibody diversification in germinal center B cells, giving rise to higher affinity antibodies through somatic hypermutation (SHM) or to isotype-switched antibodies through class switch recombination (CSR). SHM and CSR are triggered by AID-mediated deamination of cytosines in immunoglobulin genes. Importantly, AID activity in B cells is not restricted to Ig loci and can promote mutations and pro-lymphomagenic translocations, establishing a direct oncogenic mechanism for germinal center-derived neoplasias. AID is also expressed in response to inflammatory cues in epithelial cells, raising the possibility that AID mutagenic activity might drive carcinoma development. We directly tested this hypothesis by generating conditional knock-in mouse models for AID overexpression in colon and pancreas epithelium. AID overexpression alone was not sufficient to promote epithelial cell neoplasia in these tissues, in spite of displaying mutagenic and genotoxic activity. Instead, we found that heterologous AID expression in pancreas promotes the expression of NKG2D ligands, the recruitment of CD8⁺ T cells, and the induction of epithelial cell death. Our results indicate that AID oncogenic potential in epithelial cells can be neutralized by immunosurveillance protective mechanisms.

Beyond Oncolytics: E1B55K-Deleted Adenovirus as a Vaccine Delivery Vector

Type 5 human adenoviruses (Ad5) deleted of genes encoding the early region 1B 55-kDa (E1B55K) protein including Onyx-015 (dl1520) and H101 are best known for their oncolytic potential. As a vaccine vector the E1B55K deletion may allow for the insertion of a transgene nearly 1,000 base pairs larger than now possible. This has the potential of extending the application for which the vectors are clinically known. However, the immune priming ability of E1B55K-deleted vectors is unknown, undermining our ability to gauge their usefulness in vaccine applications. For this reason, we created an E1B55K-deleted Ad5 vector expressing full-length single chain HIV_BaLgp120 attached to a flexible linker and the first two domains of rhesus CD4 (rhFLSC) in exchange for the E3 region. In cell-based experiments the E1B55K-deleted vector promoted higher levels of innate immune signals including chemokines, cytokines, and the NKG2D ligands MIC A/B compared to an E1B55K wild-type vector expressing the same immunogen. Based on these results we evaluated the immune priming ability of the E1B55K-deleted vector in mice. The E1B55K-deleted vector promoted similar levels of Ad5-, HIVgp120, and rhFLSC-specific cellular and humoral immune responses as the E1B55K wild-type vector. In pre-clinical HIV-vaccine studies the wild-type vector has been employed as part of a very effective prime-boost strategy. This study demonstrates that E1B55K-deleted adenoviruses may serve as effective vaccine delivery vectors.

Viral inhibitors of NKG2D ligands for tumor surveillance

INTRODUCTION

Natural Killer cells (NK) are key for the innate immune response against tumors and viral infections. Several viral proteins evade host immune response and target the NK cell receptor NKG2D and its ligands. Areas covered: This review aimed to describe the viruses and their proteins that interfere with the NKG2D receptor and their ligands, and how these interactions lead to immune evasion, host protection, and tissue damage from acute and chronic viral infections. Expert opinion: The study of viral proteins has already impacted the field of oncology. A prime example is the HBV vaccine and the development of antiviral drugs for HIV, Hepatitis C, and the family of Herpesviridae viruses. The NKG2D system seems to be a rational therapeutic target. Nevertheless, an effective cytotoxic response by NK cells is mediated by a network of activating and inhibitory receptors, the integration of which determines if the NK cell becomes cytotoxic or permissive. Immunotherapeutic agents that increase the antitumor lytic activity of NK cells through modulating activation and inhibitory signaling of NK cells are being developed. Nevertheless, more research is needed to dissect the integrative mechanism of NK cells function to fully exploit their antitumor and antiviral effector mechanisms.

Alternative Splice Transcripts for MHC Class I-like MICA Encode Novel NKG2D Ligands with Agonist or Antagonist Functions

MHC class I chain-related proteins A and B (MICA and MICB) and UL16-binding proteins are ligands of the activating NKG2D receptor involved in cancer and immune surveillance of infection. Structurally, MICA/B proteins contain an α3 domain, whereas UL16-binding proteins do not. We identified novel alternative splice transcripts for MICA encoding five novel MICA isoforms: MICA-A, -B1, -B2, -C, and -D. Alternative splicing associates with MICA*015 and *017 and results from a point deletion (G) in the 5' splice donor site of MICA intron 4 leading to exon 3 and exon 4 skipping and/or deletions. These changes delete the α3 domain in all isoforms, and the α2 domain in the majority of isoforms (A, B1, C, and D). Endothelial and hematopoietic cells contained endogenous alternative splice transcripts and isoforms. MICA-B1, -B2, and -D bound NKG2D by surface plasmon resonance and were expressed at the cell surface. Functionally, MICA-B2 contains two extracellular domains (α1 and α2) and is a novel potent agonist ligand for NKG2D. We found that MICA-D is a new truncated form of MICA with weak affinity for NKG2D despite lacking α2 and α3 domains. MICA-D may functionally impair NKG2D activation by competing with full-length MICA or MICA-B2 for NKG2D engagement. Our study established NKG2D binding for recombinant MICA-B1 but found no function for this isoform. New truncated MICA isoforms exhibit a range of functions that may drive unexpected immune mechanisms and provide new tools for immunotherapy.

Comparative genomics of the NKG2D ligand gene family

NKG2D ligands (NKG2DLs) are a group of stress-inducible major histocompatibility complex (MHC) class I-like molecules that act as a danger signal alerting the immune system to the presence of abnormal cells. In mammals, two families of NKG2DL genes have been identified: the MIC gene family encoded in the MHC region and the ULBP gene family encoded outside the MHC region in most species. Some mammals have a third family of NKG2DL-like class I genes which we named MILL (MHC class I-like located near the leukocyte receptor complex). Despite the fact that MILL genes are more closely related to MIC genes than ULBP genes are to MIC genes, MILL molecules do not function as NKG2DLs, and their function remains unknown. With the progress of mammalian genome projects, information on the MIC, ULBP, and MILL gene families became available in many mammalian species. Here, we summarize such information and discuss the origin and evolution of the NKG2DL gene family from the viewpoint of host-pathogen coevolution.

Genetics, genomics, and evolutionary biology of NKG2D ligands

Human and mouse NKG2D ligands (NKG2DLs) are absent or only poorly expressed by most normal cells but are upregulated by cell stress, hence, alerting the immune system in case of malignancy or infection. Although these ligands are numerous and highly variable (at genetic, genomic, structural, and biochemical levels), they all belong to the major histocompatibility complex class I gene superfamily and bind to a single, invariant, receptor: NKG2D. NKG2D (CD314) is an activating receptor expressed on NK cells and subsets of T cells that have a key role in the recognition and lysis of infected and tumor cells. Here, we review the molecular diversity of NKG2DLs, discuss the increasing appreciation of their roles in a variety of medical conditions, and propose several explanations for the evolutionary force(s) that seem to drive the multiplicity and diversity of NKG2DLs while maintaining their interaction with a single invariant receptor.

Expanded and Activated Natural Killer Cells for Immunotherapy of Hepatocellular Carcinoma

Viral infection of the liver is a major risk factor for hepatocellular carcinoma (HCC). Natural killer (NK) cells recognize virally infected and oncogenically transformed cells, suggesting a therapeutic role for NK-cell infusions in HCC. Using the K562-mb15-41BBL cell line as a stimulus, we obtained large numbers of activated NK cells from the peripheral blood of healthy donors. Expanded NK cells exerted remarkably high cytotoxicity against HCC cell lines, which was generally much higher than that of unstimulated or IL2-activated NK cells. In immunodeficient NOD/scid IL2RGnull mice engrafted with Hep3B, treatment with expanded NK cells markedly reduced tumor growth and improved overall survival. HCC cells exposed for 48 hours to 5 μmol/L of sorafenib, a kinase inhibitor currently used for HCC treatment, remained highly sensitive to expanded NK cells. HCC cell reductions of 39.2% to 53.8% caused by sorafenib in three cell lines further increased to 80.5% to 87.6% after 4 hours of culture with NK cells at a 1:1 effector-to-target ratio. NK-cell cytotoxicity persisted even in the presence of sorafenib. We found that NKG2D, an NK-cell-activating receptor, was an important mediator of anti-HCC activity. We therefore enhanced its signaling capacity with a chimeric NKG2D-CD3ζ-DAP10 receptor. This considerably increased the anti-HCC cytotoxicity of expanded NK cells in vitro and in immunodeficient mice. The NK expansion and activation method applied in this study has been adapted to clinical-grade conditions. Hence, these results warrant clinical testing of expanded NK-cell infusions in patients with HCC, possibly after genetic modification with NKG2D-CD3ζ-DAP10. Cancer Immunol Res; 4(7); 574-81. ©2016 AACR.

NKG2D-NKG2D Ligand Interaction Inhibits the Outgrowth of Naturally Arising Low-Grade B Cell Lymphoma In Vivo

It is now clear that recognition of nascent tumors by the immune system is critical for survival of the host against cancer. During cancer immunoediting, the ability of the tumor to escape immune recognition is important for tumor development. The immune system recognizes tumors via the presence of classical Ags and also by conserved innate mechanisms. One of these mechanisms is the NKG2D receptor that recognizes ligands whose expression is induced by cell transformation. In this study, we show that in NKG2D receptor-deficient mice, increasing numbers of B cells begin to express NKG2D ligands as they age. Their absence in wild-type mice suggests that these cells are normally cleared by NKG2D-expressing cells. NKG2D-deficient mice and mice constitutively expressing NKG2D ligands had increased incidence of B cell tumors, confirming that the inability to clear NKG2D ligand-expressing cells was important in tumor suppression and that NKG2D ligand expression is a marker of nascent tumors. Supporting a role for NKG2D ligand expression in controlling the progression of early-stage B cell lymphomas in humans, we found higher expression of a microRNA that inhibits human NKG2D ligand expression in tumor cells from high-grade compared with low-grade follicular lymphoma patients.

ADAM10 new selective inhibitors reduce NKG2D ligand release sensitizing Hodgkin lymphoma cells to NKG2D-mediated killing

Hodgkin lymphoma (HL) resistant to conventional therapies is increasing, making of interest the search for new schemes of treatment. Members of the "A Disintegrin And Metalloproteases" (ADAMs) family, mainly ADAM10 or ADAM17, have been proposed as therapeutic targets in solid tumors and some ADAMs inhibitors have been shown to exert antitumor effects. We have previously described an overexpression of ADAM10 in HL, together with increased release of NKG2D ligands (NKG2D-L) and reduced activation of effector T lymphocytes with anti-lymphoma capacity. Aim of the present work was to verify whether inhibition of ADAM10 in HL cells could restore the triggering of NKG2D-dependent anti-lymphoma T cell response. As no selective ADAM10 blockers have been reported so far, we synthesized the two hydroxamate compounds LT4 and MN8 with selectivity for ADAM10 over metalloproteases (MMPs), LT4 showing higher specificity for ADAM10 over ADAM17. We show that (i) HL lymph nodes (LN) and cultured HL cells express high levels of the mature active membrane form of ADAM10; (ii) ADAM10 is the major sheddase for the NKG2D-L in HL cells; (iii) the new LT4 and MN8 compounds strongly reduce the shedding of NKG2D-L by HL cell lines and enhance the binding of NKG2D receptor; (iv) of note, these new ADAM10 inhibitors increase the sensitivity of HL cell lines to NKG2D-dependent cell killing exerted by natural killer and γδ T cells. Overall, the biologic activity of LT4 and MN8 appears to be more potent than that of the commercial inhibitor GI254023X.

Get It through Your Thick Head: Emerging Principles in Neuroimmunology and Neurovirology Redefine Central Nervous System "Immune Privilege"

The central nervous system (CNS) coordinates all aspects of life, autonomic and sentient, though how it has evolved to contend with pathogenic infections remains, to a great degree, a mystery. The skull and cerebrospinal fluid (CSF) provide protection from blunt force contacts, and it was once thought that the blood-brain barrier (BBB) was a fortress that restricted pathogen entry and limited inflammation. Recent studies, however, have caused a revision of this viewpoint: the CNS is monitored by blood-borne lymphocytes, but can use alternative strategies to prevent or resolve many pathogenic challenges. In this Review, we discuss emerging principles that indicate how the CNS is immunologically unique from peripheral tissues. We focus on developments that include glymphatics, recently characterized brain lymphatic vessels, distinctions in innate and adaptive immune strategies, novel points of entry for neurotropic viruses, and, finally, how the periphery can influence CNS homeostasis and immune responses within the brain. Collectively, these attributes demand a re-evaluation of immunity in the brain: not privileged, but distinct.

Scorpion venom activates natural killer cells in hepatocellular carcinoma via the NKG2D-MICA pathway

Previous studies have demonstrated that polypeptides extracted from scorpion venom (PESV) inhibited cell proliferation in several tumors, however, the effect on dysfunctional and exhausted natural killer cells which contribute to tumor escape from immune surveillance remain to be elucidated. In this study, we determined the effect of PESV on NK infiltration into H22 cells orthotopic transplantation tumors and on the expression of MHC class I chain-related proteins A (MICA) in HepG2 cells. We found that tumor growth in mice was significantly inhibited by PESV and the survival time of tumor-bearing mice treated with PESV was significantly prolonged. Moreover, levels of tumor-infiltrating NK cells, NKG2D protein, perforin and granzyme B mRNA were significantly increased in the group treated with PESV compared with the tumor-bearing control group. In addition, In addition, up-regulation of MICA by PESV enhances the susceptibility of HepG2 cells to NK lysis in vitro. These results indicate that the inhibitory effects of PESV on hepatic carcinoma are likely mediated by up-regulation of NK cell activity via the MICA-NKG2D pathway.

The influence of miR-34a expression on stemness and cytotoxic susceptibility of breast cancer stem cells

In this study, we investigate the effect of miR-34a expression and biological characteristics of breast cancer stem cells (BCSCs). The mammospheres were formed from murine breast cancer cell line 4T1 and regarded as murine BCSCs. Identification of stemness molecules and cloning experiments validate the biological characteristics of BCSCs we have established. We showed that miR-34a, as a tumor suppressor, could separately reduce the stemness of BCSCs and activate the cytotoxic susceptibility of BCSCs to natural killer (NK) cells in vitro via down regulating the expression of Notch1 signaling molecules. Moreover, miR-34a could completely restrain established mice breast tumor xenografts in vivo in the NOD/SCID mice that have functional NK cells at a normal level, whereas it was less effective in NOD/SCID/ CD122/IL-2Rβ mice that do not have functional NK cells. We conclude that miR-34a is a crucial, dual tumor suppressor and BCSCs-targeting immunotherapeutic agent and has shown efficacy in the treatment of murine breast cancer. The results also suggest that impaired NK cells could contribute to the resistance to therapies.

Viral Evasion of Natural Killer Cell Activation

Natural killer (NK) cells play a key role in antiviral innate defenses because of their abilities to kill infected cells and secrete regulatory cytokines. Additionally, NK cells exhibit adaptive memory-like antigen-specific responses, which represent a novel antiviral NK cell defense mechanism. Viruses have evolved various strategies to evade the recognition and destruction by NK cells through the downregulation of the NK cell activating receptors. Here, we review the recent findings on viral evasion of NK cells via the impairment of NK cell-activating receptors and ligands, which provide new insights on the relationship between NK cells and viral actions during persistent viral infections.

Regulation of Natural Killer Cell Function by STAT3

Natural killer (NK) cells, key members of a distinct hematopoietic lineage, innate lymphoid cells, are not only critical effectors that mediate cytotoxicity toward tumor and virally infected cells but also regulate inflammation, antigen presentation, and the adaptive immune response. It has been shown that NK cells can regulate the development and activation of many other components of the immune response, such as dendritic cells, which in turn, modulate the function of NK cells in multiple synergistic feed back loops driven by cell–cell contact, and the secretion of cytokines and chemokines that control effector function and migration of cells to sites of immune activation. The signal transducer and activator of transcription (STAT)-3 is involved in driving almost all of the pathways that control NK cytolytic activity as well as the reciprocal regulatory interactions between NK cells and other components of the immune system. In the context of tumor immunology, NK cells are a first line of defense that eliminates pre-cancerous and transformed cells early in the process of carcinogenesis, through a mechanism of “immune surveillance.” Even after tumors become established, NK cells are critical components of anticancer immunity: dysfunctional NK cells are often found in the peripheral blood of cancer patients, and the lack of NK cells in the tumor microenvironment often correlates to poor prognosis. The pathways and soluble factors activated in tumor-associated NK cells, cancer cells, and regulatory myeloid cells, which determine the outcome of cancer immunity, are all critically regulated by STAT3. Using the tumor microenvironment as a paradigm, we present here an overview of the research that has revealed fundamental mechanisms through which STAT3 regulates all aspects of NK cell biology, including NK development, activation, target cell killing, and fine tuning of the innate and adaptive immune responses.

Potential Cancer Prevention and Treatment by Silencing the Killer Cell Immunoglobulin-like Receptor Gene in Natural Killer Cells Derived from Induced Pluripotent Stem Cells

Cancer immunosurveillance is an important host protection process, monitoring the presence of irregular cells that could potentially transform into tumor cells, effectively clearing the body of transformed tumor cells at their earliest stages, and thus maintaining regular cellular homeostasis. Natural killer (NK) cells are effector lymphocytes of the innate immune system, playing a critical role in surveillance for tumor cells, while also eliminating virally infected cells. The significance of the anti-tumor role of NK cells was recently further verified by findings that immunosuppression in most cancer patients is not perceptible until late stages. NK cells express the low-affinity Fc-activating receptor, CD16, and the inhibitory receptor, killer cell immunoglobulin-like receptor (KIR). Consequently, activation of NK cells is determined by the balance of inhibitory and activating receptor stimulation. Here, we propose establishing an induced pluripotent stem cell (iPSC)-derived NK cell line with KIR gene knockout or knockdown as a possible regimen to treat and prevent cancer. We further postulate that an optimal mixture of NK iPSCs with and without KIR gene knockout, would reach a maximum antitumor activity, with minimal side effects. We also discuss the possible advantages of KIR-knockout NK iPSCs for adoptive immunotherapy in patients with cancer.

Overexpression of natural killer group 2 member D ligands predicts favorable prognosis in cholangiocarcinoma

The natural killer group 2 member D (NKG2D) receptor and its ligands are important mediators of immune responses to tumors. NKG2D ligands are overexpressed in several malignant tumor types; however, the prognostic value of these ligands is unclear. Here, we aimed to elucidate the role of NKG2D ligands in extrahepatic cholangiocarcinoma (EHCC). We therefore investigated the expression of the NKG2D receptor and its ligands MHC class I chain-related proteins A and B (MICA/B), unique long 16 binding protein (ULBP) 1, and ULBP2/5/6 in resected specimens from 82 patients with EHCC. All NKG2D ligands were highly expressed in EHCC. High expression of MICA/B or ULBP2/5/6 correlated with overall and disease-free survival. In contrast, high expression of ULBP1 was significantly associated with improved overall survival, but not disease-free survival. Concurrent high expression of multiple NKG2D ligands revealed significantly better overall and disease-free survival than that observed with the overexpression of any one NKG2D ligand. Co-expression of multiple NKG2D ligands was an independent prognostic indicator of improved survival. Furthermore, co-overexpression of multiple NKG2D ligands was significantly correlated with high expression of the NKG2D receptor. Inhibiting interactions between multiple NKG2D ligands and the NKG2D receptor might be a promising approach for controlling cancer progression and improving patient prognosis in EHCC.

Natural killer group 2D and CD28 receptors differentially activate mammalian/mechanistic target of rapamycin to alter murine effector CD8+ T-cell differentiation

Memory CD8+ T cells are an essential component of anti-tumour and anti-viral immunity. Activation of the mammalian/mechanistic target of rapamycin (mTOR) pathway has been implicated in regulating the differentiation of effector and memory T cells. However, the mechanisms that control mTOR activity during immunity to tumours and infections are not well known. Activation of co-stimulatory receptors, including CD28 and natural killer group 2D (NKG2D), activate phosphatidylinositol-3 kinase and subsequently may activate the mTOR pathway in CD8+ T cells. This study compared the activation of the mTOR signalling pathway after co-stimulation through CD28 or NKG2D receptors in murine effector CD8+ T cells. Compared with CD28 co-stimulation, activation through CD3 and NKG2D receptors had weaker activation of mTORc1, as shown by decreased phosphorylation of mTORc1 targets S6K1, ribosomal protein S6 and eukaryotic initiation factor 4E binding protein 1. NKG2D co-stimulation also showed increased gene expression of tuberous sclerosis protein 2, a negative regulator of mTORc1, whereas CD28 co-stimulation increased gene expression of Ras homologue enriched in brain, an activator of mTORc1, and hypoxia-inducible factor-1α and vascular endothelial growth factor-α, pro-angiogenic factors downstream of mTORc1. Strong mTORc1 activation in CD28-co-stimulated cells also increased expression of transcription factors that support effector cell differentiation, namely T-bet, B lymphocyte-induced maturation protein (BLIMP-1), interferon regulatory factor 4, and inhibitor of DNA binding 2, whereas low levels of mTORc1 activation allowed for the expression of Eomes, B-cell lymphoma 6 (BCL6), and inhibitor of DNA binding 3 during NKG2D stimulation, and increased expression of memory markers CD62 ligand and CD127. These data show that compared with CD28, co-stimulation through the NKG2D receptor leads to the differential activation of the mTOR signalling pathway and potentially supports memory CD8+ T-cell differentiation.

Immunological mechanisms of the antitumor effects of supplemental oxygenation

Antitumor T cells either avoid or are inhibited in hypoxic and extracellular adenosine-rich tumor microenvironments (TMEs) by A2A adenosine receptors. This may limit further advances in cancer immunotherapy. There is a need for readily available and safe treatments that weaken the hypoxia-A2-adenosinergic immunosuppression in the TME. Recently, we reported that respiratory hyperoxia decreases intratumoral hypoxia and concentrations of extracellular adenosine. We show that it also reverses the hypoxia-adenosinergic immunosuppression in the TME. This, in turn, stimulates (i) enhanced intratumoral infiltration and reduced inhibition of endogenously developed or adoptively transfered tumor-reactive CD8 T cells, (ii) increased proinflammatory cytokines and decreased immunosuppressive molecules, such as transforming growth factor-β (TGF-β), (iii) weakened immunosuppression by regulatory T cells, and (iv) improved lung tumor regression and long-term survival in mice. Respiratory hyperoxia also promoted the regression of spontaneous metastasis from orthotopically grown breast tumors. These effects are entirely T cell- and natural killer cell-dependent, thereby justifying the testing of supplemental oxygen as an immunological coadjuvant to combine with existing immunotherapies for cancer.

NK cells and cancer: you can teach innate cells new tricks

Natural killer (NK) cells are the prototype innate lymphoid cells endowed with potent cytolytic function that provide host defence against microbial infection and tumours. Here, we review evidence for the role of NK cells in immune surveillance against cancer and highlight new therapeutic approaches for targeting NK cells in the treatment of cancer.

Clinical significance of tumor expression of major histocompatibility complex class I-related chains A and B (MICA/B) in gastric cancer patients

Gastric cancer (GC) is the third most common cause of cancer death worldwide. Natural killer cells play an important role in the immune defense against transformed cells. They express the activating receptor NKG2D, whose ligands belong to the MIC and ULBP/RAET family. Although it is well established that these ligands are generally expressed in tumors, the association between their expression in the tumor and gastric mucosa and clinical parameters and prognosis of GC remains to be addressed. In the present study, MICA and MICB expression was analyzed, by flow cytometry, in 23 and 20 pairs of gastric tumor and adjacent non-neoplasic gastric mucosa, respectively. Additionally, ligands expression in 13 tumors and 7 gastric mucosa samples from GC patients were evaluated by immunohistochemistry. The mRNA levels of MICA in 9 pairs of tumor and mucosa were determined by quantitative PCR. Data were associated with the clinicopathological characteristics and the patient outcome. MICA expression was observed in 57% of tumors (13/23) and 44% of mucosal samples (10/23), while MICB was detected in 50% of tumors (10/20) and 45% of mucosal tissues (9/20). At the protein level, ligand expression was significantly higher in the tumor than in the gastric mucosa. MICA mRNA levels were also increased in the tumor as compared to the mucosa. However, clinicopathological analysis indicated that, in patients with tumors >5 cm, the expression of MICA and MICB in the tumor did not differ from that of the mucosa, and tumors >5 cm showed significantly higher MICA and MICB expression than tumors ≤5 cm. Patients presenting tumors >5 cm that expressed MICA and MICB had substantially shorter survival than those with large tumors that did not express these ligands. Our results suggest that locally sustained expression of MICA and MICB in the tumor may contribute to the malignant progression of GC and that expression of these ligands predicts an unfavorable prognosis in GC patients presenting large tumors.

NKG2D- and T-cell receptor-dependent lysis of malignant glioma cell lines by human γδ T cells: Modulation by temozolomide and A disintegrin and metalloproteases 10 and 17 inhibitors

The interaction of the MHC class I-related chain molecules A and B (MICA and MICB) and UL-16 binding protein (ULBP) family members expressed on tumor cells with the corresponding NKG2D receptor triggers cytotoxic effector functions in NK cells and γδ T cells. However, as a mechanism of tumor immune escape, NKG2D ligands (NKG2DLs) can be released from the cell surface. In this study, we investigated the NKG2DL system in different human glioblastoma (GBM) cell lines, the most lethal brain tumor in adults. Flow cytometric analysis and ELISA revealed that despite the expression of various NKG2DLs only ULBP2 is released as a soluble protein via the proteolytic activity of "a disintegrin and metalloproteases" (ADAM) 10 and 17. Moreover, we report that temozolomide (TMZ), a chemotherapeutic agent in clinical use for the treatment of GBM, increases the cell surface expression of NKG2DLs and sensitizes GBM cells to γδ T cell-mediated lysis. Both NKG2D and the T-cell receptor (TCR) are involved. The cytotoxic activity of γδ T cells toward GBM cells is strongly enhanced in a TCR-dependent manner by stimulation with pyrophosphate antigens. These data clearly demonstrate the complexity of mechanisms regulating NKG2DL expression in GBM cells and further show that treatment with TMZ can increase the immunogenicity of GBM. Thus, TMZ might enhance the potential of the adoptive transfer of ex vivo expanded γδ T cells for the treatment of malignant glioblastoma.

Immunological landscape and immunotherapy of hepatocellular carcinoma

Advanced hepatocellular carcinoma (HCC) is a serious therapeutic challenge and targeted therapies only provide a modest benefit in terms of overall survival. Novel approaches are urgently needed for the treatment of this prevalent malignancy. Evidence demonstrating the antigenicity of tumour cells, the discovery that immune checkpoint molecules have an essential role in immune evasion of tumour cells, and the impressive clinical results achieved by blocking these inhibitory receptors, are revolutionizing cancer immunotherapy. Here, we review the data on HCC immunogenicity, the mechanisms for HCC immune subversion and the different immunotherapies that have been tested to treat HCC. Taking into account the multiplicity of hyperadditive immunosuppressive forces acting within the HCC microenvironment, a combinatorial approach is advised. Strategies include combinations of systemic immunomodulation and gene therapy, cell therapy or virotherapy.

The MICA-129Met/Val dimorphism affects plasma membrane expression and shedding of the NKG2D ligand MICA

The MHC class I chain-related molecule A (MICA) is a ligand for the activating natural killer (NK) cell receptor NKG2D. A polymorphism causing a valine to methionine exchange at position 129 affects binding to NKG2D, cytotoxicity, interferon-γ release by NK cells and activation of CD8⁺ T cells. It is known that tumors can escape NKG2D-mediated immune surveillance by proteolytic shedding of MICA. Therefore, we investigated whether this polymorphism affects plasma membrane expression (pmMICA) and shedding of MICA. Expression of pmMICA was higher in a panel of tumor (n = 16, P = 0.0699) and melanoma cell lines (n = 13, P = 0.0429) carrying the MICA-129Val/Val genotype. MICA-129Val homozygous melanoma cell lines released more soluble MICA (sMICA) by shedding (P = 0.0015). MICA-129Met or MICA-129Val isoforms differing only in this amino acid were expressed in the MICA-negative melanoma cell line Malme, and clones with similar pmMICA expression intensity were selected. The MICA-129Met clones released more sMICA (P = 0.0006), and a higher proportion of the MICA-129Met than the MICA-129Val variant was retained in intracellular compartments (P = 0.0199). The MICA-129Met clones also expressed more MICA messenger RNA (P = 0.0047). The latter phenotype was also observed in mouse L cells transfected with the MICA expression constructs (P = 0.0212). In conclusion, the MICA-129Met/Val dimorphism affects the expression density of MICA on the plasma membrane. More of the MICA-129Met variants were retained intracellularly. If expressed at the cell surface, the MICA-129Met isoform was more susceptible to shedding. Both processes appear to limit the cell surface expression of MICA-129Met variants that have a high binding avidity to NKG2D.

MHC Class I Expression by Donor Hematopoietic Stem Cells Is Required to Prevent NK Cell Attack in Allogeneic, but Not Syngeneic Recipient Mice

NK cells resist engraftment of syngeneic and allogeneic bone marrow (BM) cells lacking major histocompatibility (MHC) class I molecules, suggesting a critical role for donor MHC class I molecules in preventing NK cell attack against donor hematopoietic stem and progenitor cells (HSPCs), and their derivatives. However, using high-resolution in vivo imaging, we demonstrated here that syngeneic MHC class I knockout (KO) donor HSPCs persist with the same survival frequencies as wild-type donor HSPCs. In contrast, syngeneic MHC class I KO differentiated hematopoietic cells and allogeneic MHC class I KO HSPCs were rejected in a manner that was significantly inhibited by NK cell depletion. In vivo time-lapse imaging demonstrated that mice receiving allogeneic MHC class I KO HSPCs showed a significant increase in NK cell motility and proliferation as well as frequencies of NK cell contact with and killing of HSPCs as compared to mice receiving wild-type HSPCs. The data indicate that donor MHC class I molecules are required to prevent NK cell-mediated rejection of syngeneic differentiated cells and allogeneic HSPCs, but not of syngeneic HSPCs.

Ubiquitin-dependent endocytosis of NKG2D-DAP10 receptor complexes activates signaling and functions in human NK cells

Cytotoxic lymphocytes share the presence of the activating receptor NK receptor group 2, member D (NKG2D) and the signaling-competent adaptor DNAX-activating protein 10 (DAP10), which together play an important role in antitumor immune surveillance. Ligand stimulation induces the internalization of NKG2D-DAP10 complexes and their delivery to lysosomes for degradation. In experiments with human NK cells and cell lines, we found that the ligand-induced endocytosis of NKG2D-DAP10 depended on the ubiquitylation of DAP10, which was also required for degradation of the internalized complexes. Moreover, through combined biochemical and microscopic analyses, we showed that ubiquitin-dependent receptor endocytosis was required for the activation of extracellular signal-regulated kinase (ERK) and NK cell functions, such as the secretion of cytotoxic granules and the inflammatory cytokine interferon-γ. These results suggest that NKG2D-DAP10 endocytosis represents a means to decrease cell surface receptor abundance, as well as to control signaling outcome in cytotoxic lymphocytes.

Effects of radiation on T regulatory cells in normal states and cancer: mechanisms and clinical implications

Radiation remains an important component of cancer treatment. In addition to inducing tumor cell death through direct cytotoxic effects, radiation can also promote the regression of tumor via augment of immune response. Regulatory T cells (Tregs) are a unique subpopulation of CD4 positive cells, which are characterized by expression of the forkhead box P3 (Foxp3) transcription factor and high levels of CD25. Mounting evidence has shown that Tregs are implicated in the development and progression of various types of cancer, which makes Tregs an important target in cancer therapeutics. Generally, lymphocytes are regarded as radiosensitive. However, Tregs have been demonstrated to be relatively resistant to radiotherapy, which is partly mediated by downregulation of pro-apoptotic proteins and upregulation of anti-apoptotic proteins. Moreover, radiotherapy can increase the production of Tregs and the recruitment of Tregs to local tumor microenvironment. Tregs can attenuate radiation-induced tumor death, which cause the resistance of tumor to radiotherapy. Recent experimental studies and clinical trails have demonstrated that the combination of radiation with medications that target Tregs is promising in the treatment of several types of neoplasms. In this review, we discussed the effect of radiation on Tregs in physiological states and cancer. Further, we presented an overview of therapies that target Tregs to enhance the efficacy of radiation in cancer therapeutics.

Matrine increases NKG2D ligand ULBP2 in K562 cells via inhibiting JAK/STAT3 pathway: a potential mechanism underlying the immunotherapy of matrine in leukemia

PURPOSE

The study aimed to investigate the role of the JAK/STAT3 pathway in the matrine induced ULBP2 expression on the human chronic myelogenous leukemia K562 cells.

METHODS

K562 cells were cultured, and the relevant mRNA expressions were detected.

RESULTS

Matrine induced the expression of four NKG2D ligands on K562 cells, of which ULBP2 had the highest increase. After treatment with 0.8 mg/mL matrine for 24 h, the mean fluorescence intensity (MFI) of ULBP2 increased. After matrine treatment, the sensitivity of K562 cells to NK cell-mediated killing increased significantly. After treatment with 0.2, 0.5 and 0.8 mg/ mL matrine, the percentage of K562 cells killed by NK cells was significantly higher than that of untreated cells (29.2%) (P<0.05). Matrine significantly inhibit the protein expression of phosphorylated STAT 3 and JAK2. Matrine markedly inhibited the IL-6 expression of K562 cells, and antagonized the IL-6 mediated STAT3 and JAK2 phosphorylation. In addition, matrine enhanced the inhibitory effect of STAT 3 inhibitor on STAT 3 activity. The silencing of STAT expression and inhibition of STAT3 activity significantly up-regulated the ULPB2 expression. Matrine had no effect on the expression of IL-6R and gp130 on K562 cells, the mRNA expression of IL-6R and gp130 increased slightly and the sgp 130 in cell supernatant significantly increased.

CONCLUSIONS

Our findings reveal IL-6 and IL-6 receptor-mediated JAK/STAT3 pathway is involved in the matrine induced up-regulation of NKG2D ligands ULBP2 on K562 cells. Matrine might inhibit IL-6 expression and then suppress the activation of IL-6 receptor-mediated JAK/STAT3 pathway.

Tissue-Resident NK Cells Mediate Ischemic Kidney Injury and Are Not Depleted by Anti-Asialo-GM1 Antibody

NK cells are innate lymphoid cells important for immune surveillance, identifying and responding to stress, infection, and/or transformation. Whereas conventional NK (cNK) cells circulate systemically, many NK cells reside in tissues where they appear to be poised to locally regulate tissue function. In the present study, we tested the contribution of tissue-resident NK (trNK) cells to tissue homeostasis by studying ischemic injury in the mouse kidney. Parabiosis experiments demonstrate that the kidney contains a significant fraction of trNK cells under homeostatic conditions. Kidney trNK cells developed independent of NFIL3 and T-bet, and they expressed a distinct cell surface phenotype as compared with cNK cells. Among these, trNK cells had reduced asialo-GM1 (AsGM1) expression relative to cNK cells, a phenotype observed in trNK cells across multiple organs and mouse strains. Strikingly, anti-AsGM1 Ab treatment, commonly used as an NK cell-depleting regimen, resulted in a robust and selective depletion of cNKs, leaving trNKs largely intact. Using this differential depletion, we tested the relative contribution of cNK and trNK cells in ischemic kidney injury. Whereas anti-NK1.1 Ab effectively depleted both trNK and cNK cells and protected against ischemic/reperfusion injury, anti-AsGM1 Ab preferentially depleted cNK cells and failed to protect against injury. These data demonstrate unanticipated specificity of anti-AsGM1 Ab depletion on NK cell subsets and reveal a new approach to study the contributions of cNK and trNK cells in vivo. In total, these data demonstrate that trNK cells play a key role in modulating local responses to ischemic tissue injury in the kidney and potentially other organs.

Comparative study of various subpopulations of cytotoxic cells in blood and ascites from patients with ovarian carcinoma

AIM OF THE STUDY

A number of observations have indicated that the immune system plays a significant role in patients with epithelial ovarian cancer (EOC). In cases of EOC, the prognostic significance of tumour infiltrating lymphocytes has not been clearly explained yet. The aim is to determine the phenotype and activation molecules of cytotoxic T cell and NK cell subpopulations and to compare their representation in malignant ascites and peripheral blood in patients with ovarian cancer.

MATERIAL AND METHODS

Cytotoxic cells taken from blood samples of the cubital vein and malignant ascites were obtained from 53 patients with EOC. Their surface and activation characteristics were determined by means of a flow cytometer. Immunophenotype multiparametric analysis of peripheral blood lymphocytes (PBLs) and tumour infiltrating lymphocytes (TILs) was carried out.

RESULTS

CD3(+) T lymphocytes were the main population of TILs (75.9%) and PBLs (70.9%). The number of activating T cells was significantly higher in TILs: CD3(+)/69(+) 6.7% vs. 0.8% (p < 0.001). The representation of (CD3(-)/16(+)56(+)) NK cells in TILs was significantly higher: 11.0% vs. 5.6% (p = 0.041); likewise CD56(bright) and CD-56(bright) from CD56(+) cells were higher in TILs (both p < 0.001). The activation receptor NKG2D was present in 45.1% of TILs vs. 32.3% of PBLs (p = 0.034), but we did not find a significant difference in the numbers of CD56(+)/NKG2D(+) in TILs and PBLs.

CONCLUSIONS

These results prove that the characteristics and intensity of anti-tumour responses are different in compared compartments (ascites/PBLs). The knowledge of phenotype and functions of effector cells is the basic precondition for understanding the anti-tumour immune response.

Failure recovery of circulating NKG2D+CD56dimNK cells in HBV-associated hepatocellular carcinoma after hepatectomy predicts early recurrence

Dysfunction of natural killer (NK) cells has been implicated in the failure of antitumor immune responses in hepatocellular carcinoma (HCC) patients. However, the changes of NK profile in peripheral blood after surgery and tumor tissues of HCC patients, as well as the underlying reason and the significance are vague. Here, we observed that the frequencies of circulating NKG2D⁺CD56^dimNK cells decreased significantly in HBV-related HCC and were negatively correlated with the levels of serum TGF-β and soluble MICA (sMICA). In vitro experiments confirmed that the TGF-β and sMICA in tumor tissue homogenates, as well as sMICA in HCC cells culture supernatants could reduce the frequency of NKG2D⁺CD56^dimNK cells. In addition, in HCC patients the lower frequency of circulating NKG2D⁺CD56^dimNK cells was associated with larger tumor size and/or higher serum GGT. Noticeably, the frequency of NKG2D⁺CD56^dimNK cells at one month after surgery usually failed to restore in early recurrent patients, and that frequency was negatively associated with early recurrence and shorter overall survival. These results suggest that declined frequency of NKG2D⁺CD56^dimNK cells in HCC was associated with higher TGF-β and sMICA production, and low frequency of circulating NKG2D⁺CD56^dimNK cells at one month after surgery may predict poor prognosis of HBV-related HCC patients accepting hepatectomy.

T Cells Engineered With Chimeric Antigen Receptors Targeting NKG2D Ligands Display Lethal Toxicity in Mice

Ligands for the NKG2D receptor are overexpressed on tumors, making them interesting immunotherapy targets. To assess the tumoricidal properties of T cells directed to attack NKG2D ligands, we engineered murine T cells with two distinct NKG2D-based chimeric antigen receptors (CARs): (i) a fusion between the NKG2D receptor and the CD3ζ chain and (ii) a conventional second-generation CAR, where the extracellular domain of NKG2D was fused to CD28 and CD3ζ. To enhance the CAR surface expression, we also engineered T cells to coexpress DAP10. In vitro functionality and surface expression levels of all three CARs was greater in BALB/c T cells than C57BL/6 T cells, indicating strain-specific differences. Upon adoptive transfer of NKG2D-CAR-T cells into syngeneic animals, we observed significant clinical toxicity resulting in morbidity and mortality. The severity of these toxicities varied between the CAR configurations and paralleled their in vitro NKG2D surface expression. BALB/c mice were more sensitive to these toxicities than C57BL/6 mice, consistent with the higher in vitro functionality of BALB/c T cells. Treatment with cyclophosphamide prior to adoptive transfer exacerbated the toxicity. We conclude that while NKG2D ligands may be useful targets for immunotherapy, the pursuit of NKG2D-based CAR-T cell therapies should be undertaken with caution.