Engagement of CD160 receptor by HLA-C is a triggering mechanism used by circulating natural killer (NK) cells to mediate cytotoxicity

Human decidual NK cells: unique and tightly regulated effector functions in healthy and pathogen-infected pregnancies

NK cells present in the peripheral blood (PB) respond rapidly to pathogens or pathogen-infected cells by various means including cytotoxicity and release of cytokines and chemokines. In addition they modulate adaptive immunity via the interaction with dendritic cells. Decidual NK cells (dNK) are poorly cytotoxic in healthy pregnancy, both in humans and rodents, when compared to their PB counterparts. We will discuss recent findings that may contribute to answer the following questions: (i) Do dNK possess functional killing machinery in normal healthy pregnancy? (ii) If so, what are the regulatory mechanisms that negatively control this effector function? (iii) Have dNK from early pregnant uterus the intrinsic ability to kill pathogen-infected autologous maternal uterine cells and/or produce soluble factors that stimulate the anti-pathogen adaptive immune response? (iv) Do dNK undergo a receptor repertoire profile shift when they are in contact with pathogen-infected uterine cells? (v) Which pathogen-mediated signal(s) and molecular interactions subvert the inhibition of dNK cytolytic activity?

CD160 activation by herpesvirus entry mediator augments inflammatory cytokine production and cytolytic function by NK cells

Lymphocyte activation is regulated by costimulatory and inhibitory receptors, of which both B and T lymphocyte attenuator (BTLA) and CD160 engage herpesvirus entry mediator (HVEM). Notably, it remains unclear how HVEM functions with each of its ligands during immune responses. In this study, we show that HVEM specifically activates CD160 on effector NK cells challenged with virus-infected cells. Human CD56(dim) NK cells were costimulated specifically by HVEM but not by other receptors that share the HVEM ligands LIGHT, Lymphotoxin-α, or BTLA. HVEM enhanced human NK cell activation by type I IFN and IL-2, resulting in increased IFN-γ and TNF-α secretion, and tumor cell-expressed HVEM activated CD160 in a human NK cell line, causing rapid hyperphosphorylation of serine kinases ERK1/2 and AKT and enhanced cytolysis of target cells. In contrast, HVEM activation of BTLA reduced cytolysis of target cells. Together, our results demonstrate that HVEM functions as a regulator of immune function that activates NK cells via CD160 and limits lymphocyte-induced inflammation via association with BTLA.

CD160Ig fusion protein targets a novel costimulatory pathway and prolongs allograft survival

CD160 is a cell surface molecule expressed by most NK cells and approximately 50% of CD8(+) cytotoxic T lymphocytes. Engagement of CD160 by MHC class-I directly triggers a costimulatory signal to TCR-induced proliferation, cytokine production and cytotoxic effector functions. The role of CD160 in alloimmunity is unknown. Using a newly generated CD160 fusion protein (CD160Ig) we examined the role of the novel costimulatory molecule CD160 in mediating CD4(+) or CD8(+) T cell driven allograft rejection. CD160Ig inhibits alloreactive CD8(+) T cell proliferation and IFN-γ production in vitro, in particular in the absence of CD28 costimulation. Consequently CD160Ig prolongs fully mismatched cardiac allograft survival in CD4(-/-), CD28(-/-) knockout and CTLA4Ig treated WT recipients, but not in WT or CD8(-/-) knockout recipients. The prolonged cardiac allograft survival is associated with reduced alloreactive CD8(+) T cell proliferation, effector/memory responses and alloreactive IFN-γ production. Thus, CD160 signaling is particularly important in CD28-independent effector/memory CD8(+) alloreactive T cell activation in vivo and therefore may serve as a novel target for prevention of allograft rejection.

Thiopurine treatment in patients with Crohn's disease leads to a selective reduction of an effector cytotoxic gene expression signature revealed by whole-genome expression profiling

Crohn's disease (CD) is characterized by chronic inflammation of the gastrointestinal tract, as a result of aberrant activation of the innate immune system through TLR stimulation by bacterial products. The conventional immunosuppressive thiopurine derivatives (azathioprine and mercaptopurine) are used to treat CD. The effects of thiopurines on circulating immune cells and TLR responsiveness are unknown. To obtain a global view of affected gene expression of the immune system in CD patients and the treatment effect of thiopurine derivatives, we performed genome-wide transcriptome analysis on whole blood samples from 20 CD patients in remission, of which 10 patients received thiopurine treatment, compared to 16 healthy controls, before and after TLR4 stimulation with LPS. Several immune abnormalities were observed, including increased baseline interferon activity, while baseline expression of ribosomal genes was reduced. After LPS stimulation, CD patients showed reduced cytokine and chemokine expression. None of these effects were related to treatment. Strikingly, only one highly correlated set of 69 genes was affected by treatment, not influenced by LPS stimulation and consisted of genes reminiscent of effector cytotoxic NK cells. The most reduced cytotoxicity-related gene in CD was the cell surface marker CD160. Concordantly, we could demonstrate an in vivo reduction of circulating CD160(+)CD3(-)CD8(-) cells in CD patients after treatment with thiopurine derivatives in an independent cohort. In conclusion, using genome-wide profiling, we identified a disturbed immune activation status in peripheral blood cells from CD patients and a clear treatment effect of thiopurine derivatives selectively affecting effector cytotoxic CD160-positive cells.

Reassessment of HLA-G isoform specificity of MEM-G/9 and 4H84 monoclonal antibodies

Human leukocyte antigen (HLA)-G is a non-classical HLA class I molecule thought to play a key role in maternal-fetal tolerance. Although initial studies suggested that HLA-G expression is restricted to extravillous cytotrophoblasts, expression was subsequently reported in a wide variety of other human tissues and tumor cells. However, consensus as to the validity of these collective findings has proven difficult because the antibodies used to define the temporal and spatial expression patterns of HLA-G remain incompletely characterized. The aim of our study was to reassess two of the most widely used HLA-G antibodies (MEM-G/9 and 4H84) in HLA-G-positive (JEG-3 and HLA-G transduced) and -negative (dermal fibroblast, mesenchymal stem cell, K562, and Jurkat) lines using flow cytometry, immunofluorescence, and western blotting. We found that MEM-G/9 recognized HLA-G3 by flow cytometry, indicating that its epitope is present on the α1 domain of HLA-G. Although 4H84 preferably recognized unfolded HLA-G-free chains, it showed strong non-specificity under certain methodological conditions.

Membrane-bound IL-21 promotes sustained ex vivo proliferation of human natural killer cells

NK cells have therapeutic potential for a wide variety of human malignancies. However, because NK cells expand poorly in vitro, have limited life spans in vivo, and represent a small fraction of peripheral white blood cells, obtaining sufficient cell numbers is the major obstacle for NK-cell immunotherapy. Genetically-engineered artificial antigen-presenting cells (aAPCs) expressing membrane-bound IL-15 (mbIL15) have been used to propagate clinical-grade NK cells for human trials of adoptive immunotherapy, but ex vivo proliferation has been limited by telomere shortening. We developed K562-based aAPCs with membrane-bound IL-21 (mbIL21) and assessed their ability to support human NK-cell proliferation. In contrast to mbIL15, mbIL21-expressing aAPCs promoted log-phase NK cell expansion without evidence of senescence for up to 6 weeks of culture. By day 21, parallel expansion of NK cells from 22 donors demonstrated a mean 47,967-fold expansion (median 31,747) when co-cultured with aAPCs expressing mbIL21 compared to 825-fold expansion (median 325) with mbIL15. Despite the significant increase in proliferation, mbIL21-expanded NK cells also showed a significant increase in telomere length compared to freshly obtained NK cells, suggesting a possible mechanism for their sustained proliferation. NK cells expanded with mbIL21 were similar in phenotype and cytotoxicity to those expanded with mbIL15, with retained donor KIR repertoires and high expression of NCRs, CD16, and NKG2D, but had superior cytokine secretion. The mbIL21-expanded NK cells showed increased transcription of the activating receptor CD160, but otherwise had remarkably similar mRNA expression profiles of the 96 genes assessed. mbIL21-expanded NK cells had significant cytotoxicity against all tumor cell lines tested, retained responsiveness to inhibitory KIR ligands, and demonstrated enhanced killing via antibody-dependent cell cytotoxicity. Thus, aAPCs expressing mbIL21 promote improved proliferation of human NK cells with longer telomeres and less senescence, supporting their clinical use in propagating NK cells for adoptive immunotherapy.

The signaling networks of the herpesvirus entry mediator (TNFRSF14) in immune regulation

The tumor necrosis factor (TNF) receptor superfamily member herpesvirus entry mediator (HVEM) (TNFRSF14) regulates T-cell immune responses by activating both inflammatory and inhibitory signaling pathways. HVEM acts as both a receptor for the canonical TNF-related ligands, LIGHT [lymphotoxin-like, exhibits inducible expression, and competes with herpes simplex virus glycoprotein D for HVEM, a receptor expressed on T lymphocytes] and lymphotoxin-α, and as a ligand for the immunoglobulin superfamily proteins BTLA (B and T lymphocyte attenuator) and CD160, a feature distinguishing HVEM from other immune regulatory molecules. The ability of HVEM to interact with multiple ligands in distinct configurations creates a functionally diverse set of intrinsic and bidirectional signaling pathways that control both inflammatory and inhibitory responses. The HVEM system is integrated into the larger LTβR and TNFR network through extensive shared ligand and receptor usage. Experimental mouse models and human diseases indicate that dysregulation of HVEM network may contribute to autoimmune pathogenesis, making it an attractive target for drug intervention.

Molecular basis for herpesvirus entry mediator recognition by the human immune inhibitory receptor CD160 and its relationship to the cosignaling molecules BTLA and LIGHT

CD160 was recently identified as a T cell coinhibitory molecule that interacts with the herpesvirus entry mediator (HVEM) on antigen-presenting cells to deliver a potent inhibitory signal to CD4(+) T cells. HVEM also binds to the coinhibitory receptor BTLA (B- and T-lymphocyte attenuator) and the costimulatory receptor LIGHT (which is homologous to lymphotoxins, exhibits inducible expression, and competes with the herpes simplex virus glycoprotein D for HVEM, a receptor expressed by T lymphocytes, or TNFSF14), thus regulating the CD160/BTLA/LIGHT/HVEM signaling pathway. To date, the detailed properties of the formation of these complexes, especially HVEM binding to the newly identified receptor CD160, and the relationship of CD160 with BTLA and LIGHT are still unclear. We performed N-terminal sequencing and a mass spectrometric analysis, which revealed that the extracellular domain of CD160 exists primarily in the monomeric form. The surface plasmon resonance analysis revealed that CD160 binds directly to the cysteine-rich domain 1-3 of HVEM with a similar affinity to, but slower dissociation rate than, that of BTLA. Notably, CD160 competed with BTLA for binding to HVEM; in contrast, LIGHT did not affect HVEM binding to either CD160 or BTLA. The results of a mutagenesis study of HVEM also suggest that the CD160 binding region on HVEM was slightly different from, but overlapped with, the BTLA binding site. Interestingly, an anti-CD160 antibody exhibiting antiangiogenic properties blocked CD160/HVEM binding. These results provide insight into the molecular architecture of the CD160/BTLA/LIGHT/HVEM signaling complex that regulates immune function.

Differential and tumor-specific expression of CD160 in B-cell malignancies

CD160 is a human natural killer (NK)-cell-activating receptor that is also expressed on T-cell subsets. In the present study, we examined 811 consecutive cases of B-cell lymphoproliferative disorders (B-LPDs), and demonstrated CD160 expression in 98% (590 of 600) of chronic lymphocytic leukemia (CLL) cases, 100% (32 of 32) of hairy cell leukemia (HCL) cases, 15% (5 of 34) of mantle cell lymphoma (MCL) in the leukemic phase, and 16% (23 of 145) of other B-LPD cases. CD160 transcript and protein were absent in the normal B-cell hierarchy, from stem cells, B-cell precursors, maturing B cells in the germinal center, and circulating B cells, including CD5(+)CD19(+) B1 cells in umbilical cord. CD160 positivity was significantly higher in CLL and HCL in terms of percentage (65.9% and 67.8%, respectively, P < .0001) and median fluorescence intensity (552 and 857, respectively, P < .0001) compared with all other B-LPD cases. Lymph node CLL samples were also CD160(+). Using the disease-specific expression of CD5, CD23, and CD160, a score of 3 characterized CLL (diagnostic odds ratio, 1430); a score of 0 excluded CLL, MCL, and HCL; and the CD23/CD5 ratio differentiated CLL from leukemic CD23(+) MCL. In the B-cell lineage, CD160 is a tumor-specific antigen known to mediate cellular activation signals in CLL, and is a novel target for therapeutic manipulation and monitoring of minimal residual disease.

A novel antiangiogenic and vascular normalization therapy targeted against human CD160 receptor

A monoclonal anti-CD160 antibody inhibits the growth of new vessels in pathological ocular and tumor neoangiogenesis but not in healthy tissues.

Angiogenesis plays an essential role in several diseases of the eye and in the growth of solid tumors, but existing antiangiogenic therapies have limited benefits in several cases. We report the antiangiogenic effects of a monoclonal antibody, CL1-R2, in several animal models of neovascularization. CL1-R2 recognizes human CD160, a membrane receptor which is conserved in various mammal species. We show that CD160 is expressed on the endothelial cells of newly formed blood vessels in human colon carcinoma and mouse B16 melanoma but not in vessels of healthy tissues. CL1-R2 reduced fibroblast growth factor 2–induced neovascularization in the rabbit cornea, in a mouse model of oxygen-induced retinopathy, and in a mouse Matrigel plug assay. Treatment of B16 melanoma-bearing mice with CL1-R2 combined with cyclophosphamide chemotherapy caused regression of the tumor vasculature and normalization of the remaining vessels as shown by Doppler ultrasonography, intravital microscopy, and histology. These studies validate CD160 as a potential new target in cases of human pathological ocular and tumor neoangiogenesis that do not respond or become resistant to existing antiangiogenic drugs.

CD160: a unique activating NK cell receptor

Here we discuss CD160 an essential NK cell activating receptor that remains poorly understood. CD160 receptor exhibits a number of unique structural and functional characteristics that are not common to other killer immunoglobulin-like receptors that recognize major histocompatibility complex (MHC) class I molecules: (1) In addition to humans and mice, the cd160 gene is conserved in several other mammal species; (2) cd160 is located outside the NK gene complex and the Leukocyte Receptor Complex in humans; (3) CD160 expression is associated to the CD56(dim) CD16+ cytotoxic NK cell phenotype; (4) both human and mouse CD160 recognize MHC class Ia and Ib molecules; (5) unlike the other MHC class I-dependent activating NK receptors, CD160 is a glycosylphosphatidylinositol-anchored molecule with a single immunoglobulin-like domain, and does not bear immunoreceptor tyrosine-based activation motifs. Consequently, CD160 cannot signal by itself, requiring the recruitment of adaptor proteins. CD160 recruits phosphoinositide-3 kinase to trigger cytotoxicity and cytokine secretion; (6) specific engagement of NK CD160 receptor expressed by circulating NK cells produces proinflammatory cytokines IFN-γ, TNF-α, and, most notably, IL-6 and IL-8 as well as MIP1-β chemokine. The level of CD160-mediated IFN-γ production is always higher than the one observed after engagement of the CD16 receptor.

Expression profiles of peripheral CD160+ lymphocytes during the course of healthy human pregnancy

PROBLEM

CD160 receptor is expressed by natural killer (NK) and T-cell subsets, and after activation, it could enhance cytotoxicity or pro-inflammatory cytokine production on NK cells. Here, we investigated the phenotype of peripheral CD160+ cells during healthy pregnancy.

METHOD OF STUDY

We analyzed the expression of CD69 activation marker, gamma/delta TCR, and NKG2A or NKG2D NK cell receptors on CD160+ lymphocytes of non-pregnant and healthy pregnant women at four different stages of pregnancy by flow cytometry.

RESULTS

In our hands, CD160 receptor-positive lymphocytes were present during pregnancy; however, they had different characteristics depending on gestational age. During implantation, CD160+ cells showed low activation rate, decreased NK receptor expression while 40% of Vδ2 + T cells expressed CD160 receptor. In turn, all the above parameters increased as pregnancy proceeds.

CONCLUSION

Our results indicate that CD160+ lymphocytes could be able to play a role in the maintenance of healthy pregnancy.

The human decidual NK-cell response to virus infection: what can we learn from circulating NK lymphocytes?

NK cells present in the peripheral blood respond rapidly to pathogens or pathogen-infected cells by various means including cytotoxicity and production of cytokines. Whether decidual NK (dNK) cells are able to play a similar role when the pregnant uterus is infected by viruses is still largely unknown. Decidual NK cells are generally considered as poorly cytotoxic when compared to their peripheral blood counterparts. However, we have recently demonstrated that freshly isolated dNK cells from healthy early pregnant uterus do have a cytotoxic potential mediated by the specific engagement of NKp46 activating receptor. We further found that the co-engagement of CD94/NKG2A inhibiting receptor drastically inhibits the cytolytic function of dNK. This latter observation suggests that in situ the CD94/NKG2A receptor interaction with its HLA-E specific ligand is a dominant negative regulatory mechanism that prevents unwanted dNK cell cytotoxicity in non-infected pregnant uterus. How do dNK cells behave when they are activated by virus-infected cells present at the maternal-fetal interface? Largely based on data obtained from circulating NK cells, this review briefly discusses the following questions: Does uterine viral infection promote decidual NK cell proliferative capacity in situ? Are dNK cells able to kill virus-infected autologous decidual target cells and thus limit the virus spreading to the fetus? Which viral-mediated signal(s) and molecular interactions may subvert inhibition of dNK cytotoxic potential? Does uterine viral infection promote decidual NK cell secretion of cytokines and chemokines that boost the anti-viral immune response?

Human and mouse mast cells express and secrete the GPI-anchored isoform of CD160

CD160 is expressed by human and mouse natural killer (NK) cells and other cytotoxic lymphocyte subpopulations. CD160 is mostly expressed as a trimeric 83 kDa glycosylphosphatidylinositol (GPI)-anchored activating NK receptor, cleaved upon IL-15 stimulation in a secreted trimeric soluble form (sCD160) that binds to major histocompatibility complex (MHC) class I molecules, while a transmembrane isoform appears. sCD160 exhibits immunoregulatory function as it inhibits CD8(+) T-lymphocyte cytotoxic activity. We show that human mast cells (MCs) express CD160. In human and mouse skin, resident MCs expressed CD160, whereas in C57BL/6-Kit(W-sh/W-sh) mice, CD160(+) cells were only identified at the site of reconstitution with syngeneic cultured MCs. In the human mast cell line, HMC-1, we only identified the transcripts of the GPI-anchored CD160 isoform. Furthermore, CD160 was identified in HMC-1 and mouse MC supernatants, suggesting that MCs release sCD160. Supporting this hypothesis, HMC-1 express the GPI-specific phospholipase D variant 2 involved in the NK lymphocyte membrane cleavage of CD160, and morphological studies highlighted a relative loss of CD160 expression in inflammatory skin sites, where MC degranulation is expected to occur. We also demonstrated an inhibition of T-cell cytotoxicity by HMC-1 supernatant that was partially reversed by anti-CD160 mAb. In conclusion, sCD160, produced by MCs, may have a role in T-cell-MC interactions in vivo.

CD160 signaling mediates PI3K-dependent survival and growth signals in chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) expresses CD160, a glycosylphosphatidylinositol-linked receptor found on normal natural killer (NK) and T cells, but not B cells. CD160 is a multifunctional molecule in normal lymphocytes, but its role in CLL biology is unknown. In vitro, CLL cells undergo rapid spontaneous apoptosis, which CD160 activation protected against-mean cell viability increased from 67% to 79% (P < .001). This was associated with up-regulation of Bcl-2, Bcl-xL, and Mcl-1, but not Bax. As expected from these changes in Bcl-2/Bax and Bcl-xL/Bax ratios, CD160 triggering reduced mitochondrial membrane potential collapse and cytochrome c release. CD160 stimulation also induced DNA synthesis, cell cycle progression, and proliferation. B-cell antigen receptor (BCR)-induced CLL proliferation was generally greater than with CD160, but marked variation was seen. Both BCR and CD160 signaling led to CLL secretion of interleukin-6 (IL-6) and IL-8, although CD160 induced greater increases of IL-6 (51-fold) and IL-8 (15-fold). Survival and activation signals mediated by CD160 showed dose-dependent suppression by phosphoinositide-3 kinase (PI3K) inhibitors. Thus, in vitro, CLL cells can use the CD160 pathway for survival and activation, mimicking CD160 signaling in normal NK and CD8(+) T cells. Establishing the pathophysiologic relevance of these findings may reveal new therapeutic targets.

CD2AP is indispensable to multistep cytotoxic process by NK cells

CD2-associated protein (CD2AP) is a cytoplasmic protein which localizes to membrane ruffles, lipid rafts and the leading edges of cells. It is implicated in podocyte homeostasis, signal transduction, dynamic actin remodeling and also membrane trafficking during endocytosis and cytokinesis. CD2AP was reported to orchestrate receptor patterning and cytoskeletal polarity in T cell contacts and it could also modulate TCR signaling. However, whether it plays a role in NK cell killing remains unknown. In this study, we discovered that interfering with CD2AP expression strongly reduced cytotoxicity of human NK92 cell line and this effect was independent of FasL sensitivity of target cells. Conjugate formation and degranulation were impeded in NK92 cells after CD2AP knockdown. Upon encountering target cells, CD2AP in NK92 is enriched near contact site and colocalizes with FasL-bearing granules. In contrast, FasL-bearing granules were found rarely polarized toward cell contact site after CD2AP knockdown. Furthermore, by immunoprecipitation from NK92 cell lysates and transient expression studies in 293T and Hela cells, we demonstrated that CD2AP associates with FasL. Thus, CD2AP, through facilitating conjugate formation and directed transport of lytic granules, plays an important role in NK cells killing.

2B4 (CD244) signaling by recombinant antigen-specific chimeric receptors costimulates natural killer cell activation to leukemia and neuroblastoma cells

PURPOSE

Novel natural killer (NK) cell-directed strategies in cancer immunotherapy aim at specifically modulating the balance between NK cell receptor signals toward tumor-specific activation. The signaling lymphocyte activation molecule-related receptor 2B4 (CD244) is an important regulator of NK cell activation. We investigated whether 2B4-enhanced activation signals can redirect the cytolytic function of human NK cells to NK cell-resistant and autologous leukemia and tumor targets.

EXPERIMENTAL DESIGN

In vitro-stimulated NK cells from healthy donors and pediatric leukemia patients were gene modified with CD19 or G(D2)-specific chimeric receptors containing either the T-cell receptor zeta or 2B4 endodomain alone or combined.

RESULTS

Chimeric 2B4 signaling alone failed to induce interleukin-2 receptor up-regulation and cytokine secretion but triggered a specific degranulation response. Integration of the 2B4 endodomain into T-cell receptor zeta chimeric receptors significantly enhanced all aspects of the NK cell activation response to antigen-expressing leukemia or neuroblastoma cells, including CD25 up-regulation, secretion of IFN-gamma and tumor necrosis factor-alpha, release of cytolytic granules, and growth inhibition, and overcame NK cell resistance of autologous leukemia cells while maintaining antigen specificity.

CONCLUSION

These data indicate that the 2B4 receptor has a potent costimulatory effect in NK cells. Antigen-specific 2B4zeta-expressing NK cells may be a powerful new tool for adoptive immunotherapy of leukemia and other malignancies.

Identification and characterization of a transmembrane isoform of CD160 (CD160-TM), a unique activating receptor selectively expressed upon human NK cell activation

CD160 has been initially identified as a GPI-anchored MHC-class I activating receptor mainly expressed on peripheral blood NK cells. Herein, we report the identification of three additional CD160-related mRNAs generated through alternative splicings of the CD160 gene, among which one encoded a putative CD160 transmembrane isoform (CD160-TM). We first establish that CD160-TM surface expression is highly restricted to NK cells and is activation-dependent. Additionally, we provide evidence that CD160-TM represents a novel activating receptor, as assessed by the increased CD107a NK cell surface mobilization observed upon its engagement. Finally, we demonstrate that the CD160-TM cytoplasmic tail is by itself sufficient to mediate the recruitment of Erk1/2 signaling pathway, and that the initiation of this activation process is dependent on the Src-family kinase p56(lck). The identification of CD160-TM therefore provides new possibilities regarding the role of CD160 isoforms in the regulation of NK cell functions.

NK cells in HIV-1 infection: evidence for their role in the control of HIV-1 infection

Increasing evidence supports the notion that the innate immune response, and in particular, natural killer cells play a central role in determining the quality of the host immune response to infection. In this review we highlight recent evidence that suggests that NK cells influence the clinical fate of HIV-infected individuals.

Dengue virus replicon expressing the nonstructural proteins suffices to enhance membrane expression of HLA class I and inhibit lysis by human NK cells

Many viruses escape the cellular immune response by downregulating cell surface expression of major histocompatibility complex (MHC) class I molecules. However, infection of cells with flaviviruses can upregulate the expression of these molecules. In this study we analyzed the expression of MHC class I in K562 and THP-1 human cell lines that were stably transfected with self-replicating subgenomic dengue virus RNA (replicons) and express all the dengue virus nonstructural proteins together. We show that MHC class I expression is upregulated in the dengue virus replicon-expressing cells and that the binding of natural killer (NK) inhibitory receptors to these cells is augmented. This upregulation results in reduced susceptibility of the dengue virus replicon-expressing cells to NK lysis, indicating a possible mechanism for evasion of the dengue virus from NK cell recognition. Visualizing MHC class I expression in replicon-containing K562 and THP-1 cells by confocal microscopy demonstrated aggregation of MHC class I molecules on the cell surface. Finally, replicon-expressing K562 cells manifested increased TAP (transporter associated with antigen processing) and LMP (low-molecular-mass protein) gene transcription, while replicon-expressing THP-1 cells manifested increased NF-kappaB activity and MHC class I transcription. We suggest that expression of dengue virus nonstructural proteins is sufficient to induce MHC class I upregulation through both TAP-dependent and -independent mechanisms. Additionally, aggregation of MHC class I molecules on the cell membrane also contributes to significantly higher binding of low-affinity NK inhibitory receptors, resulting in lower sensitivity to lysis by NK cells.

CD160 inhibits activation of human CD4+ T cells through interaction with herpesvirus entry mediator

CD160, a glycosylphosphatidylinositol-anchored member of the immunoglobulin superfamily, is expressed on both cytolytic lymphocytes and some unstimulated CD4+ T cells. Here we show that CD160 expression was increased after activation of human CD4+ T cells and that crosslinking CD160 with monoclonal antibody strongly inhibited CD3- and CD28-mediated activation. We found that herpesvirus entry mediator (HVEM) was a ligand of CD160 that acted as a 'bidirectional switch' for T cell activation, producing a positive or negative outcome depending on the engagement of HVEM by CD160 and known HVEM ligands such as B and T lymphocyte attenuator (BTLA) and the T lymphocyte receptor LIGHT. Inhibition of CD4+ T cell activation by HVEM-transfected cells was dependent on CD160 and BTLA; when the cysteine-rich domain 1 of HVEM was deleted, this inhibition was lost, resulting in strong T cell activation. CD160 thus serves as a negative regulator of CD4+ T cell activation through its interaction with HVEM.

Analysis of HLA class I?II haplotype frequency and segregation in a cohort of patients with advanced stage ovarian cancer

In solid tumors, human leucocyte antigen (HLA)-A2 has been suggested to be a risk factor and a negative prognostic factor. The HLA-A2 allele in Scandinavia has a high prevalence; it decreases with latitude and also with ovarian cancer mortality in Europe. Furthermore, an association of the HLA-A2 allele with severe prognosis in serous adenocarcinoma of the ovary in stages III-IV was found. Thirty-two unrelated Swedish women with relapsing or progressive ovarian cancer were analysed for the genotypes at the HLA-A, HLA-B, HLA-Cw, and HLA-DRB1 loci by the polymerase chain reaction/sequence-specific primer method. The frequencies of HLA alleles of healthy Swedish bone marrow donors provided by the coordinating centre of the Bone Marrow Donors Worldwide Registries, Leiden, the Netherlands were used as controls. When this cohort of epithelial ovarian cancer patients was compared with healthy Swedish donors, the frequency of HLA-A1 and HLA-A2 gene/phenotype appears, although not statistically significant, to be increased in patients with ovarian carcinoma, while HLA-A3 was decreased. HLA-A2 homozygotes were twofold higher in patients. The A2-B8 haplotype was significantly increased (corrected P value). A2-B5, A2-B15, A2-DRB1*03, A2-DRB1*04, A2-B15-Cw3, and A2-B8-DRB1*03 had odds ratio as well as the level of the lower confidence interval above 1 and significant P value only when considered as single, non-corrected analysis. HLA-B15 and HLA-Cw3 were only present in HLA-A2-positive patients showing that the HLA-A2-HLA-Cw3 and HLA-B15 haplotypes were segregated. In this selected cohort with advanced disease, there are indications of an unusual overrepresentation of HLA class I and II genes/haplotypes as well as segregation for the HLA-A2-HLA-Cw3 and HLA-B15 haplotypes. These findings are presented as a descriptive analysis and need further investigations on a larger series of ovarian cancer patients to establish prognostic associations.

Prospects for the use of NK cells in immunotherapy of human cancer

Current insights into the molecular specificities that regulate natural killer (NK)-cell function suggest that it might be possible to design NK-cell-based immunotherapeutic strategies against human cancer. Here, we describe evidence for NK-cell targeting of human tumours and address crucial questions that, in our opinion, require consideration for the development of successful NK-cell-based therapies. Appropriately used, we predict that NK cells will have a role, both directly and in combination with other treatment modalities, in future treatment of cancer.

Soluble HLA-G and control of angiogenesis

In this review, we summarize the results of a number of our recent in vitro and in vivo experiments demonstrating that, in addition to the immunoregulatory functions, soluble HLA-G molecules also affect endothelial cell activity. We have found that soluble HLA-G1 (also designated HLA-G5) inhibits endothelial cell proliferation, migration and tubule formation, and this occurred through binding to the CD160 receptor and via an apoptotic pathway. Moreover, we have demonstrated that soluble HLA-G1 blocks in vivo rabbit corneal neoangiogenesis. Although it cannot be excluded that other soluble HLA class I molecules may have similar effects, as soluble forms of HLA-G are being produced by trophoblast cells at the maternal-fetal interface during early gestation, we discuss how such anti-angiogenic properties of soluble HLA-G1 may locally influence uterine vascular remodeling.

A soluble form of the MHC class I-specific CD160 receptor is released from human activated NK lymphocytes and inhibits cell-mediated cytotoxicity

CD160 is a GPI-anchored lymphocyte surface receptor in which expression is mostly restricted to the highly cytotoxic CD56(dim)CD16(+) peripheral blood NK subset. We previously reported that MHC class I (MHC-I) molecules bind to CD160 receptors on circulating NK lymphocytes and that this interaction triggers their cytotoxic activity and cytokine production. We also observed that CD160 surface expression on NK cells is down-modulated upon activation with PMA or IL-2. In this study, we further report that short-time incubation of NK lymphocytes with IL-15 converts the membrane-bound CD160 to a soluble form through a proteolytic cleavage involving a metalloprotease. Thus, CD160 is no longer detected at the cell surface, but can be immunoprecipitated from the NK cell culture medium. Interestingly, CD160 transcript remains highly expressed during the process of protein shedding. In addition, we demonstrate that CD160 mRNA synthesis can be induced in CD56(bright) separated lymphocytes following exposure to IL-15. By producing a Flag-tagged soluble CD160 protein, we establish that its binding to MHC-I molecules results in the inhibition of the cytotoxic CD8(+) T lymphocyte activity and of the CD160-mediated NK cell cytotoxicity. Thus, we show that activated NK lymphocytes release a soluble form of CD160 that functionally impairs the MHC-I-specific cytotoxic CD8(+) T lymphocyte responsiveness.

Identification of a novel CD160+ CD4+ T-lymphocyte subset in the skin: a possible role for CD160 in skin inflammation

CD160 is a glycosylphosphatidylinositol-anchored cell surface molecule expressed by human circulating cytotoxic lymphocytes that correspond to the majority of natural killer cell (NK) expressing CD56(dim), TCRgammadelta lymphocytes, and to a minor CD8 T-cell subset. CD160 engagement by major histocompatibility complex class I molecules triggers by itself both cytotoxic function and cytokine production in NK lymphocytes, whereas it provides co-activating signals to TCR-induced proliferation in T CD8+ lymphocytes. In this study, we analyzed by immunohistochemistry the phenotype of lymphocytes infiltrating normal skin and inflammatory skin lesions of atopic dermatitis, contact dermatitis, and psoriasis. We identified a minor original subset of CD4+ CD160+ T cells infiltrating inflammatory lesions. We found that this lymphocyte subset localization is not restricted to the skin, as we demonstrated that CD160 transcripts could be induced in IL-2 or IL-15-activated CD4+ peripheral blood lymphocytes. Finally, we report that CD160 acts as a co-activator receptor for CD3-induced proliferation of CD4+ CD160+ T cells isolated from inflammatory skin lesions. Thus, we hypothesize that the unique CD4+ CD160+ lymphocyte subset plays a role in the pathogenesis of skin inflammation.

Engagement of the CD160 activating NK cell receptor leads to its association with CD2 in circulating human NK cells

CD160 activating NK cell receptor is a glycosylphosphatidylinositol-anchored molecule. Upon specific engagement by its HLA class I physiological ligand, CD160 NK cell receptor triggers cytotoxicity and release of different cytokines, including IL-6. How CD160 intracellular signaling is mediated following its specific ligation is unknown. One key element of this signaling may be through the co-activation of other receptors associated to CD160. Using confocal microscopy and freshly isolated human peripheral blood NK cells, we observed a co-polarization of CD160 and CD2 after their respective specific engagement. These results demonstrate that CD160 activating NK cell receptor, upon its specific engagement, physically associates to the CD2 co-activating receptor present in the lipid raft that might play a role as signaling molecule.

Inhibition of term decidual NK cell cytotoxicity by soluble HLA-G1

OBJECTIVES

Soluble (s)HLA-G1 is produced by trophoblast cells. Aim was to analyze the capacities and mechanisms of sHLA-G1 to regulate interleukin (IL)-2-induced cytotoxicity of natural killer (NK) cells from human deciduas.

METHODS

Natural killer cells were isolated from decidual layers of term placentae, stimulated or not with IL-2 and supplemented with various concentrations of recombinant soluble HLA-G1 (sHLA-G1). For NK cell cytotoxicity assays, K562 cells were used as targets. Expression of signal transducer and activator of transcription 3 (STAT3) and perforin was analyzed by Western blotting. Apoptosis was examined by assessment of poly(ADP-ribose) polymerase cleavage. NK cells were analyzed by flow cytometry for IL-2receptor-alpha (IL-2R alpha; CD25) and transferrin receptor CD71 expression.

RESULTS

Interleukin-2 increases CD71, STAT3, perforin expression and cytotoxic potential of NK cells. Expression of CD71, STAT3 and perforin decreased simultaneously with cytotoxicity and dose-dependently when sHLA-G1 (1.6 micro g/mL-1.6 ng/mL) was added to IL-2 stimulated cultures. sHLA-G1 did not induce apoptosis and CD25 expression was not affected.

CONCLUSION

Interleukin-2R alpha expression is not controlled by sHLA-G1, but its signal transducer STAT3 as well as several downstream effects, such as perforin expression, proliferation and cytotoxicity. The control of STAT3 bioavailability through sHLA-G1 may be a key regulator of the mentioned effects.

The co-expression of 2B4 (CD244) and CD160 delineates a subpopulation of human CD8+ T cells with a potent CD160-mediated cytolytic effector function

Within human CD8+ T lymphocytes, the CD27-CD45RAhigh or CD56+ phenotypes contribute to precisely define the cells with CTL effector function. Novel markers were demonstrated to correlate with CTL properties, such as the 2B4 (CD244) receptor, a member of the CD2 subset of the immunoglobulin superfamily or the glycosylphosphatidylinositol-anchored CD160 receptor. We performed a study of these markers to further define the population of effectors with CTL functions. Here we show that cytotoxic subpopulations defined by surface markers CD160, CD56 and CD57 are mostly contained in the 2B4+CD8+ T cell population. Expression of CD160 identifies two populations in the 2B4+ population. The 2B4+CD160+ subset expresses a bona fide CTL phenotype. The co-expression of 2B4 and CD160 defines T cells containing high amounts of perforin and granzyme B. During CTL ontogeny, an up-regulation of 2B4 and CD160 is observed from a naive to a terminally differentiated phenotype. Finally, we demonstrated that CD160 triggering failed to induce cytotoxicity per se, but costimulated CD3-redirected killing. We conclude that the co-expression of 2B4 and CD160 defines a CD8+ T lymphocyte subpopulation with high CTL activity.

Immunologie de la grossesse : faits nouveaux

The long-standing question of pregnancy immunological paradox has been generating renewed interest. Recent insights have emerged from studies in pregnant mice and humans demonstrating a number of mechanisms that prevent potentially harmful effects of maternal anti-paternal allo-antibodies (complement inhibition, partial deletion of maternal B cells specific of paternal antigens), cytotoxic CD8+ T cells (lack of HLA-A and HLA-B expression on trophoblast, local immunosuppressive molecules, transient tolerance of paternal allo-antigens specific T cells) and uterine NK cells directed against fetal-derived trophoblast cells (limited NK cytotoxic potential, trophoblast resistance to NK killing). Interestingly, it appears that not only decidual NK cell/trophoblast interactions are not harmful for the fetus but are beneficial for the placental vascularization and its subsequent development. A recent report has indeed demonstrated that during pregnancy most of the combinations of uterine KIR (killer cell immunoglobulin-like receptor) NK cell receptors and fetal HLA-C molecules expressed by trophoblast led to normal pregnancies, whereas mothers lacking activating KIR of the AA genotype when the fetus possessed HLA-C of the C2 group were at a greatly increased risk of severe preeclampsia pathology.

Protocadherin 15 (PCDH15): a new secreted isoform and a potential marker for NK/T cell lymphomas

Natural killer cells are well known to play an important role in immune defense against tumor development and viral infections. To further characterize new functionally relevant structures in these cells, we studied a series of monoclonal antibodies that we have raised against the NK cell line YT. One of these antibodies previously described as AY19, recognizes a 85 kD surface glycoprotein. Here we report the identification of a new secreted isoform of protocadherin 15, PCDH15C, which represents a potential associated protein for p85. Importantly, whereas protocadherins are absent from the surface of normal hematopoietic cells, we describe, for the first time, that PCDH15 is expressed in cytotoxic tumor-derived T- and NK-cell lines as well as in biopsies of nasal NK/T-cell lymphomas.

Characterization of murine CD160+ CD8+ T lymphocytes

CD160 is an Ig-like glycoprotein expressed on NK, NKT and TCRgammadelta T cells, as well as intestinal intraepithelial T lymphocytes. In addition, a minor subset of CD8(+) but not CD4(+) T cells in the periphery is also known to express CD160, but the subset has not been fully characterized. In this study, we prepared anti-murine CD160 mAbs and investigated the expression profile of CD160 on various subsets of CD8(+) T cells. The amount of CD160 on almost all CD8(+) T cells was increased upon CD3-mediated stimulation in vitro, and soluble CD160 was found to be released. Flow cytometric analysis revealed most CD8(+) T cells expressing CD160 to show a CD44(high) phenotype in vivo. On further analysis, both CD44(high)CD62L(low) effector memory T cells (T(EM)) and CD44(high)CD62L(high) central memory T cells (T(CM)) expressed CD160 at an intermediate level. High levels were evident with recently activated CD8(+) T(EM). Naïve CD8(+) T cells presumably immediately after stimulation (CD44(low)CD62L(low)CD69(+)) also expressed CD160, but only at a low level. Purified CD160(+) CD8(+) T cells from OT-1 transgenic mice expressing TCR against OVA residues 257-264 presented by H-2K(b) produced IFN-gamma more rapidly than CD160(-) CD8(+) T cells upon antigen stimulation. These results together show that CD160 is expressed on the majority of CD8(+) memory T cells as well as recently activated CD8(+) T cells.

Subtle sequence variation among MHC class I locus products greatly influences sensitivity to HCMV US2- and US11-mediated degradation

Human cytomegalovirus (HCMV) interferes with cellular immune responses by modulating surface expression of MHC class I molecules. Here, we focused on HCMV-encoded unique short (US) 2 and US11, which bind newly synthesized MHC class I heavy chains (HCs) and support their dislocation into the cytosol for subsequent degradation by proteasomes. Not all MHC class I locus products are equally sensitive to this down-modulation. The aim of this study was to identify which domains, and ultimately which residues, are responsible for the resistance or sensitivity of MHC class I molecules to US2- and US11-mediated down-regulation. We show that, besides endoplasmic reticulum-lumenal regions, the C-terminus of class I molecules represents an important determinant for allele specificity in US11-mediated degradation. HLA-E becomes sensitive to US11-mediated down-regulation when its cytoplasmic tail is extended. Interestingly, this only requires two additional residues, lysine and valine, at its C-terminus. For US2, the MHC class I allele specificity is largely determined by a small region at the junction of the alpha2/alpha3 domain of the HC. It is quite remarkable that minor changes, in only four residues, can completely revert the sensitivity of naturally US2-resistant HLA-E molecules. With this study we provide better insights into the features underlying the selectivity in MHC class I down-regulation by US2 and US11.

Circulating Natural Killer Lymphocytes Are Potential Cytotoxic Effectors Against Autologous Malignant Cells in Sezary Syndrome Patients

Patients with advanced cutaneous T cell lymphoma (CTCL) exhibit profound defects in cell-mediated immunity. Although it has been suggested that Sezary syndrome (SS) patients have a decreased natural killer (NK) lymphocyte activity, nothing has been reported concerning the sensitivity of Sezary cells to NK lymphocyte-mediated cytotoxicity. Peripheral blood NK cells from healthy donors were tested against Sezary tumoral cell lines as well as against freshly isolated Sezary cells. Further, we studied their ability to exhibit antibody -dependent cell-mediated cytotoxicity using either the murine anti-CD158k/KIR3DL2 monoclonal antibody (moAb) AZ158 that specifically recognizes Sezary cells, or the anti-CD52 monoclonal antibody alemtuzumab. The results show that Sezary cell lines are susceptible to NK lymphocyte lysis. More importantly, we found that freshly isolated malignant cells are killed either by IL-2 activated allogeneic NK lymphocytes or when the tumor lymphocyte targets are incubated with an anti-MHC class I F(ab)'2 antibody. Further, anti-KIR3DL2 and anti-CD52 moAb can enhance the NK lysis. Finally, we report that NK lymphocytes isolated from SS patients are potentially cytotoxic lymphocytes against autologous malignant Sezary cells. These findings indicate that antitumor-mediated NK lymphocyte cytotoxic activity can be triggered in patients with CTCL and raise the possibility of developing novel therapeutic strategies by stimulating their innate immunity.

Murine CD160, Ig-Like Receptor on NK Cells and NKT Cells, Recognizes Classical and Nonclassical MHC Class I and Regulates NK Cell Activation

Human and mouse NK cells use different families of receptors to recognize MHC class I (MHC I) on target cells. Although human NK cells express both Ig-like receptors and lectin-like receptors specific for MHC I, all the MHC I-specific receptors identified on mouse NK cells to date are lectin-like receptors, and no Ig-like receptors recognizing MHC I have been identified on mouse NK cells. In this study we report the first MHC I-specific Ig-like receptor on mouse NK cells, namely, murine CD160 (mCD160). The expression of mCD160 is restricted to a subset of NK cells, NK1.1+ T cells, and activated CD8+ T cells. The mCD160-Ig fusion protein binds to rat cell lines transfected with classical and nonclassical mouse MHC I, including CD1d. Furthermore, the level of mCD160 on NK1.1+ T cells is modulated by MHC I of the host. Overexpression of mCD160 in the mouse NK cell line KY-2 inhibits IFN-gamma production induced by phorbol ester plus ionomycin, whereas it enhances IFN-gamma production induced by NK1.1 cross-linking or incubation with dendritic cells. Cross-linking of mCD160 also inhibits anti-NK1.1-mediated stimulation of KY-2 cells. Anti-mCD160 mAb alone has no effect. Thus, mCD160, the first MHC I-specific Ig-like receptor on mouse NK cells, regulates NK cell activation both positively and negatively, depending on the stimulus.

The HLA-G*0105N null allele induces cell surface expression of HLA-E molecule and promotes CD94/NKG2A-mediated recognition in JAR choriocarcinoma cell line

HLA-G is a non-classical HLA class Ib molecule primarily expressed in trophoblast cells, and is thought to play a key role in the induction of materno-fetal tolerance during pregnancy. In addition, the HLA-G gene provides a suitable leader sequence peptide capable of binding to HLA-E. However, the existence of placentas homozygous for the HLA-G*0105N null allele suggests that HLA-G1 might not be essential for fetal survival. To investigate whether expression of the HLA-G*0105N allele supports HLA-E cell surface expression, we transfected the HLA-G*0105N gene into JAR trophoblast cells. Flow cytometry analysis showed that HLA-G*0105N-transfected cells express surface HLA-E to a similar extent as the unmutated HLA-G gene, whereas HLA-G1 cell surface expression was undetectable. Using the NKL cell line in a standard (51)Cr release assay, the HLA-E molecules were found to inhibit natural killer lysis, through a mechanism partially dependent on CD94/NKG2A-mediated recognition.

Cutting edge: engagement of CD160 by its HLA-C physiological ligand triggers a unique cytokine profile secretion in the cytotoxic peripheral blood NK cell subset

CD160 is an Ig-like activating NK cell receptor expressed on the majority of circulating NK cells. This population corresponds to the nonproliferating, highly cytolytic, CD56dimCD16+ subset. CD160 engagement by HLA-C molecules mediates cytotoxic function. In this study, we report that upon specific activation by the physiological ligand HLA-C, or Ab cross-linking, CD160+ peripheral blood NK cells produce IFN-gamma, TNF-alpha, and IL-6. This unique CD160-mediated cytokine production differs from the one observed after CD16 engagement whose expression is also restricted to the CD56dim cytotoxic NK cell subset. As already reported for the CD160-mediated cytotoxic effector function, CD160-mediated cytokine production by peripheral blood-NK cells is negatively controlled by the killer Ig-like receptor CD158b. Thus, the CD160 receptor represents a unique triggering surface molecule expressed by cytotoxic NK cells that participates in the inflammatory response and determines the type of subsequent specific immunity.

Dialogue materno-fœtal et implantation embryonnaire humaine : des concepts qui évoluent

Multiple immunogical mechanisms allow fetal allograft tolerance. In this review, we first describe the maternal and embryological side in order to expose the dangers for the embryo enabling the development of materno-fetal strategies that will allow fetal survival and growth.

Analysis of the natural killer mediated immune response in metastatic renal cell carcinoma patients

Metastatic renal cell carcinomas (MRCC) are considered as immunogeneic tumors on the basis of the clinical responses observed in patients treated by IL-2. However, renal cell carcinoma patients are also characterized by alterations of the immune response that may compromise the immunotherapeutic approaches. In our study, we have studied the phenotype and the functional capacities of peripheral NK cells in a panel of neprectomized metastatic renal cell carcinoma patients. NK cells were harvested by negative immunoselection from fresh peripheral blood samples. In most of MRCC patients analysed (23/28), the expression of NCR (NKp46 and NKp30) was similar to that of donors. Lytic capacities by activated immunoselected NK cells from MRCC patients assessed against K562 and 3 renal tumor cell lines were in the range of that observed in NK cells from normal donors. HLA-I- renal tumor cells UOK23 were killed with a good efficiency, whereas HLA-I renal tumor cells were more resistant. Although LFA-1/ICAM-1 interaction potentiates RCC cell lysis, HLA-I/NKR interaction clearly decreased RCC cell susceptibility to NK cells. In addition, proliferation of NK cells from MRCC patients in response to cytokines was altered.

HLA-G modulates immune responses by diverse receptor interactions

HLA-G regulates immune responses as it binds different receptors expressed on natural killer (NK) cells, T cells and myeloid cells. HLA-G1 can inhibit NK- and T-cell-mediated lysis of target cells by its interaction with the inhibitory receptors ILT2 and ILT4. Engaging KIR2DL4 triggers different reactions depending on the activation state of the effector cells. The indirect recognition of HLA-G as peptide presented by HLA-E and recognized by the CD94/NKG2 receptor family might further power the battle between the immune system and tumor cells. Secreted HLA-G5 can also bind CD8 and induces Fas/Fas ligand-mediated apoptosis in activated CD8+ lymphocytes.