Differential expression of inhibitory and activating CD94/NKG2 receptors on NK cell clones

Lateral plate mesoderm cell-based organoid system for NK cell regeneration from human pluripotent stem cells

Human pluripotent stem cell (hPSC)-induced NK (iNK) cells are a source of off-the-shelf cell products for universal immune therapy. Conventional methods for iNK cell regeneration from hPSCs include embryoid body (EB) formation and feeder-based expansion steps, which are time-consuming and cause instability and high costs of manufacturing. Here, we develop an EB-free, organoid aggregate method for NK cell regeneration from hPSCs. In a short time-window of 27-day induction, millions of hPSC input can output over billions of iNK cells without the necessity of NK cell expansion feeders. The iNK cells highly express classical toxic granule proteins, apoptosis-inducing ligands, as well as abundant activating and inhibitory receptors. Functionally, the iNK cells eradicate human tumor cells via mechanisms of direct cytotoxicity, apoptosis, and antibody-dependent cellular cytotoxicity. This study provides a reliable scale-up method for regenerating human NK cells from hPSCs, which promotes the universal availability of NK cell products for immune therapy.

NK Cells Lose Their Cytotoxicity Function against Cancer Stem Cell-Rich Radiotherapy-Resistant Breast Cancer Cell Populations

Cancer stem cells (CSCs) can be induced from differentiated cancer cells in the tumor microenvironment or in response to treatments and exhibit chemo- and radioresistance, leading to tumor recurrence and metastasis. We previously reported that triple negative breast cancer (TNBC) cells with acquired radioresistance exhibited more aggressive features due to an increased CSC population. Therefore, here, we isolated CSCs from radiotherapy-resistant (RT-R)-TNBC cells and investigated the effects of these CSCs on tumor progression and NK cell-mediated cytotoxicity. Compared to MDA-MB-231 and RT-R-MDA-MB-231 cells, CD24-/low/CD44+ cells isolated from RT-R-MDA-MB-231 cells showed increased proliferation, migration and invasion abilities, and induced expression of tumor progression-related molecules. Moreover, similar to MDA-MB-231 cells, CD24-/low/CD44+ cells recruited NK cells but suppressed NK cell cytotoxicity by regulating ligands for NK cell activation. In an in vivo model, CD24-/low/CD44+ cell-injected mice showed enhanced tumor progression and lung metastasis via upregulation of tumor progression-related molecules and altered host immune responses. Specifically, NK cells were recruited into the peritumoral area tumor but lost their cytotoxicity due to the altered expression of activating and inhibitory ligands on tumors. These results suggest that CSCs may cause tumor evasion of immune cells, resulting in tumor progression.

Dimorphism of HLA-E and its Disease Association

HLA-E is a nonclassical member of the major histocompatibility complex class I gene locus. HLA-E protein shares a high level of homology with MHC Ia classical proteins: it has similar tertiary structure, associates with β2-microglobulin, and is able to present peptides to cytotoxic lymphocytes. The main function of HLA-E under normal conditions is to present peptides derived from the leader sequences of classical HLA class I proteins, thus serving for monitoring of expression of these molecules performed by cytotoxic lymphocytes. However, opposite to multiallelic classical MHC I genes, HLA-E in fact has only two alleles—HLA-E*01:01 and HLA-E*01:03—which differ by one nonsynonymous amino acid substitution at position 107, resulting in an arginine in HLA-E*01:01 (HLA-E^R) and glycine in HLA-E*01:03 (HLA-E^G). In contrast to HLA-E^R,HLA-E^G has higher affinity to peptide, higher surface expression, and higher thermal stability of the corresponding protein, and it is more ancient than HLA-E^R, though both alleles are presented in human populations in nearly equal frequencies. In the current review, we aimed to uncover the reason of the expansion of the younger allele, HLA-E^R, by analysis of associations of both HLA-E alleles with a number of diseases, including viral and bacterial infections, cancer, and autoimmune disorders.

Recurrent Stimulation of Natural Killer Cell Clones with K562 Expressing Membrane-Bound Interleukin-21 Affects Their Phenotype, Interferon-γ Production, and Lifespan

A pattern of natural killer cell (NK cell) heterogeneity determines proliferative and functional responses to activating stimuli in individuals. Obtaining the progeny of a single cell by cloning the original population is one of the ways to study NK cell heterogeneity. In this work, we sorted single cells into a plate and stimulated them via interleukin (IL)-2 and gene-modified K562 feeder cells that expressed membrane-bound IL-21 (K562-mbIL21), which led to a generation of phenotypically confirmed and functionally active NK cell clones. Next, we applied two models of clone cultivation, which differently affected their phenotype, lifespan, and functional activity. The first model, which included weekly restimulation of clones with K562-mbIL21 and IL-2, resulted in the generation of relatively short-lived (5⁻7 weeks) clones of highly activated NK cells. Levels of human leukocyte antigen class II molecule-DR isotype (HLA-DR) expression in the expanded NK cells correlated strongly with interferon-γ (IFN-γ) production. The second model, in which NK cells were restimulated weekly with IL-2 alone and once on the sixth week with K562-mbIL21 and IL-2, produced long-lived clones (8⁻14 weeks) that expanded up to 10⁷ cells with a lower ability to produce IFN-γ. Our method is applicable for studying variability in phenotype, proliferative, and functional activity of certain NK cell progeny in response to the stimulation, which may help in selecting NK cells best suited for clinical use.

NKG2H-Expressing T Cells Negatively Regulate Immune Responses

The biology and function of NKG2H receptor, unlike the better characterized members of the NKG2 family NKG2A, NKG2C, and NKG2D, remains largely unclear. Here, we show that NKG2H is able to associate with the signaling adapter molecules DAP12 and DAP10 suggesting that this receptor can signal for cell activation. Using a recently described NKG2H-specific monoclonal antibody (mAb), we have characterized the expression and function of lymphocytes that express this receptor. NKG2H is expressed at the cell surface of a small percentage of peripheral blood mononuclear cell (PBMC) and is found more frequently on T cells, rather than NK cells. Moreover, although NKG2H is likely to trigger activation, co-cross-linking of this receptor with an NKG2H-specific mAb led to decreased T cell activation and proliferation in polyclonal PBMC cultures stimulated by anti-CD3 mAbs. This negative regulatory activity was seen only after cross-linking with NKG2H, but not NKG2A- or NKG2C-specific monoclonal antibodies. The mechanism underlying this negative effect is as yet unclear, but did not depend on the release of soluble factors or recognition of MHC class I molecules. These observations raise the intriguing possibility that NKG2H may be a novel marker for T cells able to negatively regulate T cell responses.

Modular Activating Receptors in Innate and Adaptive Immunity

Triggering of cell-mediated immunity is largely dependent on the recognition of foreign or abnormal molecules by a myriad of cell surface-bound receptors. Many activating immune receptors do not possess any intrinsic signaling capacity but instead form noncovalent complexes with one or more dimeric signaling modules that communicate with a common set of kinases to initiate intracellular information-transfer pathways. This modular architecture, where the ligand binding and signaling functions are detached from one another, is a common theme that is widely employed throughout the innate and adaptive arms of immune systems. The evolutionary advantages of this highly adaptable platform for molecular recognition are visible in the variety of ligand-receptor interactions that can be linked to common signaling pathways, the diversification of receptor modules in response to pathogen challenges, and the amplification of cellular responses through incorporation of multiple signaling motifs. Here we provide an overview of the major classes of modular activating immune receptors and outline the current state of knowledge regarding how these receptors assemble, recognize their ligands, and ultimately trigger intracellular signal transduction pathways that activate immune cell effector functions.

Immunomodulation of classical and non-classical HLA molecules by ionizing radiation

Radiotherapy has been employed for the treatment of oncological patients for nearly a century, and together with surgery and chemotherapy, radiation oncology constitutes one of the three pillars of cancer therapy. Ionizing radiation has complex effects on neoplastic cells and on tumor microenvironment: beyond its action as a direct cytotoxic agent, tumor irradiation triggers a series of alterations in tumoral cells, which includes the de novo synthesis of particular proteins and the up/down-regulation of cell surface molecules. Additionally, ionizing radiation may induce the release of "danger signals" which may, in turn lead to cellular and molecular responses by the immune system. This immunomodulatory action of ionizing radiation highlights the importance of the combined use (radiotherapy plus immunotherapy) for cancer healing. Major histocompatibility complex antigens (also called Human Leukocyte Antigens, HLA in humans) are one of those molecules whose expression is modulated after irradiation. This review summarizes the modulatory properties of ionizing radiation on the expression of HLA class I (classical and non-classical) and class II molecules, with special emphasis in non-classical HLA-I molecules.

Polymorphism in human cytomegalovirus UL40 impacts on recognition of human leukocyte antigen-E (HLA-E) by natural killer cells

Natural killer (NK) cell recognition of the nonclassical human leukocyte antigen (HLA) molecule HLA-E is dependent on the presentation of a nonamer peptide derived from the leader sequence of other HLA molecules to CD94-NKG2 receptors. However, human cytomegalovirus can manipulate this central innate interaction through the provision of a "mimic" of the HLA-encoded peptide derived from the immunomodulatory glycoprotein UL40. Here, we analyzed UL40 sequences isolated from 32 hematopoietic stem cell transplantation recipients experiencing cytomegalovirus reactivation. The UL40 protein showed a "polymorphic hot spot" within the region that encodes the HLA leader sequence mimic. Although all sequences that were identical to those encoded within HLA-I genes permitted the interaction between HLA-E and CD94-NKG2 receptors, other UL40 polymorphisms reduced the affinity of the interaction between HLA-E and CD94-NKG2 receptors. Furthermore, functional studies using NK cell clones expressing either the inhibitory receptor CD94-NKG2A or the activating receptor CD94-NKG2C identified UL40-encoded peptides that were capable of inhibiting target cell lysis via interaction with CD94-NKG2A, yet had little capacity to activate NK cells through CD94-NKG2C. The data suggest that UL40 polymorphisms may aid evasion of NK cell immunosurveillance by modulating the affinity of the interaction with CD94-NKG2 receptors.

Structural insights into activation of antiviral NK cell responses

Natural killer (NK) cells are key components of innate immune responses, providing surveillance against cells undergoing tumorigenesis or infection, by viruses or internal pathogens. NK cells can directly eliminate compromised cells and regulate downstream responses of the innate and acquired immune systems through the release of immune modulators (cytokines, interferons). The importance of the role NK cells play in immune defense was demonstrated originally in herpes viral infections, usually mild or localized, which become severe and life threatening in NK-deficient patients . NK cell effector functions are governed by balancing opposing signals from a diverse array of activating and inhibitory receptors. Many NK receptors occur in paired activating and inhibitory isoforms and recognize major histocompatibility complex (MHC) class I proteins with varying degrees of peptide specificity. Structural studies have made considerable inroads into understanding the molecular mechanisms employed to broadly recognize multiple MHC ligands or specific pathogen-associated antigens and the strategies employed by viruses to thwart these defenses. Although many details of NK development, signaling, and integration remain mysterious, it is clear that NK receptors are key components of a system exquisitely tuned to sense any dysregulation in MHC class I expression, or the expression of certain viral antigens, resulting in the elimination of affected cells.

Influence of in vitro IL-2 or IL-15 alone or in combination with Hsp-70-derived 14-mer peptide (TKD) on the expression of NK cell activatory and inhibitory receptors

NK cells represent a potential tool for adoptive immunotherapy against tumors. Membrane-bound Hsp70 acts as a tumor-specific marker enhancing NK cell activity. Using flow cytometry the effect of in vitro stimulation with IL-2 or IL-15 alone or in combination with Hsp70-derived 14-mer peptide (TKD) on cell surface expression of NK activatory receptors (CD16, NKG2D, NKG2C, NKp46, NKp44, NKp30, KIR2DL4, DNAM-1, and LAMP1) and NK inhibitory receptors (NKG2A, KIR2DL2/L3, LIR1/ILT-2, and NKR-P1A) in healthy individuals was studied. Results were expressed as the percentage of receptor expressing cells and the amount of receptor expressed by CD3(-)CD56(+) cellular population. CD94, NKG2D, NKp44, NKp30, KIR2DL4, DNAM-1, LAMP1, NKG2A, and NKR-P1A were upregulated after the stimulation with IL-2 or IL-15 alone or in combination with TKD. KIR2DL2/L3 was upregulated only by IL-15 and IL-15/TKD. Concurrently, an increase in a number of NK cells positive for CD94, NKp44, NKp30, KIR2DL4, and LAMP1 was observed. IL-15 and IL-15/TKD caused also cell number rise positive for KIR2DL2/L3 and NKR-P1A. Cell number positive for NKG2C and NKG2A was increased only by IL-2 and IL-2/TKD. The diverse effect of IL-2 or IL-15 w or w/o TKD on cell surface expression was observed in CD16, NKp46, and LIR1/ILT-2.

Increased HLA-E expression in white matter lesions in multiple sclerosis

The molecular mechanisms underpinning central nervous system damage in multiple sclerosis (MS) are complex and it is widely accepted that there is an autoimmune component. Both adaptive and innate immune effector mechanisms are believed to contribute to tissue disease aetiology. HLA-E is a non-classical MHC class Ib molecule that acts as the ligand for the NKG2A inhibitory receptor present on natural killer (NK) and CD8+ cells. Peptide binding and stabilization of HLA-E is often considered to signal infection or cell stress. Here we examine the up-regulation of HLA-E in MS brain tissue. Expression is significantly increased in white matter lesions in the brain of MS patients compared with white matter of neurologically healthy controls. Furthermore, using quantitative immunohistochemistry and confocal microscopy, we show increased HLA-E protein expression in endothelial cells of active MS lesions. Non-inflammatory chronic lesions express significantly less HLA-E protein, comparable to levels found in white matter from controls. Increased HLA-E protein levels were associated with higher scores of inflammation. These results suggest the potential for an effect in central nervous system pathogenesis from HLA-E modulation in stressed tissue. Co-localization with infiltrating CD8+ cells implicates a possible role for HLA-E-restricted regulatory CD8+ cells, as has been proposed in other autoimmune diseases.

Ex vivo generated natural killer cells acquire typical natural killer receptors and display a cytotoxic gene expression profile similar to peripheral blood natural killer cells

Ex vivo differentiation systems of natural killer (NK) cells from CD34+ hematopoietic stem cells are of potential importance for adjuvant immunotherapy of cancer. Here, we analyzed ex vivo differentiation of NK cells from cord blood-derived CD34+ stem cells by gene expression profiling, real-time RT-PCR, flow cytometry, and functional analysis. Additionally, we compared the identified characteristics to peripheral blood (PB) CD56(bright) and CD56(dim) NK cells. The data show sequential expression of CD56 and the CD94 and NKG2 receptor chains during ex vivo NK cell development, resulting finally in the expression of a range of genes with partial characteristics of CD56(bright) and CD56(dim) NK cells from PB. Expression of characteristic NK cell receptors and cytotoxic genes was mainly found within the predominant ex vivo generated population of NKG2A+ NK cells, indicating the importance of NKG2A expression during NK cell differentiation and maturation. Furthermore, despite distinct phenotypic characteristics, the detailed analysis of cytolytic genes expressed within the ex vivo differentiated NK cells revealed a pattern close to CD56(dim) NK cells. In line with this finding, ex vivo generated NK cells displayed potent cytotoxicity. This supports that the ex vivo differentiation system faithfully reproduces major steps of the differentiation of NK cells from their progenitors, constitutes an excellent model to study NK cell differentiation, and is valuable to generate large-scale NK cells appropriate for immunotherapy.

The human C-type lectin-like receptor CLEC-1 is upregulated by TGF-β and primarily localized in the endoplasmic membrane compartment

The orphan receptor CLEC-1 is part of a subfamily of C-type lectin-like receptors, which is encoded in the human natural killer gene complex and comprises several pattern recognition receptors important for innate immune functions. As information on human CLEC-1 is still very limited, we aimed to further characterize this receptor. Similar to another subfamily member, LOX-1, expression of CLEC-1 mRNA was detected in myeloid cells as well as in endothelial cells. CLEC-1 protein displayed N-linked glycosylation and formed dimers. However, in contrast to other members of the subfamily, expression levels were upregulated by transforming growth factor (TGF)-β, but not significantly affected by proinflammatory stimuli. It is intriguing that human CLEC-1 could only be detected intracellularly with a staining pattern resembling endoplasmic reticulum proteins. Neither TGF-β nor inflammatory stimuli could promote significant translocation to the cell surface. These findings are in accordance with a primarily intracellular localization and function of human CLEC-1.

The major histocompatibility complex class Ib molecule HLA-E at the interface between innate and adaptive immunity

The non-classical major histocompatibility complex (MHC) class I molecule human leucocyte antigen (HLA)-E is the least polymorphic of all the MHC class I molecules and acts as a ligand for receptors of both the innate and the adaptive immune systems. The recognition of self-peptides complexed to HLA-E by the CD94-NKG2A receptor expressed by natural killer (NK) cells represents a crucial checkpoint for immune surveillance by NK cells. However, HLA-E can also be recognised by the T-cell receptor expressed by alphabeta CD8 T cells and therefore can play a role in the adaptive immune response to invading pathogens. The recent resolution of HLA-E in complex with both innate and adaptive ligands has provided insight into the dual role of this molecule in immunity.

Neutralizing type I IFN antibodies trigger an IFN-like response in endothelial cells

Neutralizing Abs to type I IFNs are of therapeutic significance, i.e., are currently evaluated for the treatment of autoimmune diseases with pathogenic IFN-alpha production such as for systemic lupus erythematosus. Unexpectedly, we observed that several neutralizing Abs reportedly known to counteract IFN-alpha or IFN-beta activity triggered an "IFN-like" response in quiescent primary human endothelial cells leading to activation of the transcription factor IFN-stimulated gene factor 3 and the expression of IFN-responsive genes. Furthermore, these Abs were found to enhance rather than inhibit type I IFN signals, and the effect was also detectable for distinct other cell types such as PBMCs. The stimulatory capacity of anti-IFN-alpha/beta Abs was mediated by the constitutive autocrine production of "subthreshold" IFN levels, involved the type I IFNR and was dependent on the Fc Ab domain, as Fab or F(ab')(2) fragments potently inhibited IFN activity. We thus propose that a combined effect of IFN recognition by the Ab paratope and the concomitant engagement of the Fc domain may trigger an IFN signal via the respective type I IFNR, which accounts for the observed IFN-like response to the neutralizing Abs. With respect to clinical applications, the finding may be of importance for the design of recombinant Abs vs Fab or F(ab')(2) fragments to efficiently counteract IFN activity without undesirable activating effects.

CD94-NKG2A recognition of human leukocyte antigen (HLA)-E bound to an HLA class I leader sequence

The recognition of human leukocyte antigen (HLA)-E by the heterodimeric CD94-NKG2 natural killer (NK) receptor family is a central innate mechanism by which NK cells monitor the expression of other HLA molecules, yet the structural basis of this highly specific interaction is unclear. Here, we describe the crystal structure of CD94-NKG2A in complex with HLA-E bound to a peptide derived from the leader sequence of HLA-G. The CD94 subunit dominated the interaction with HLA-E, whereas the NKG2A subunit was more peripheral to the interface. Moreover, the invariant CD94 subunit dominated the peptide-mediated contacts, albeit with poor surface and chemical complementarity. This unusual binding mode was consistent with mutagenesis data at the CD94-NKG2A-HLA-E interface. There were few conformational changes in either CD94-NKG2A or HLA-E upon ligation, and such a "lock and key" interaction is typical of innate receptor-ligand interactions. Nevertheless, the structure also provided insight into how this interaction can be modulated by subtle changes in the peptide ligand or by the pairing of CD94 with other members of the NKG2 family. Differences in the docking strategies used by the NKG2D and CD94-NKG2A receptors provided a basis for understanding the promiscuous nature of ligand recognition by NKG2D compared with the fidelity of the CD94-NKG2 receptors.

The heterodimeric assembly of the CD94-NKG2 receptor family and implications for human leukocyte antigen-E recognition

The CD94-NKG2 receptor family that regulates NK and T cells is unique among the lectin-like receptors encoded within the natural killer cell complex. The function of the CD94-NKG2 receptors is dictated by the pairing of the invariant CD94 polypeptide with specific NKG2 isoforms to form a family of functionally distinct heterodimeric receptors. However, the structural basis for this selective pairing and how they interact with their ligand, HLA-E, is unknown. We describe the 2.5 A resolution crystal structure of CD94-NKG2A in which the mode of dimerization contrasts with that of other homodimeric NK receptors. Despite structural homology between the CD94 and NKG2A subunits, the dimer interface is asymmetric, thereby providing a structural basis for the preferred heterodimeric assembly. Structure-based sequence comparisons of other CD94-NKG2 family members, combined with extensive mutagenesis studies on HLA-E and CD94-NKG2A, allows a model of the interaction between CD94-NKG2A and HLA-E to be established, in which the invariant CD94 chain plays a more dominant role in interacting with HLA-E in comparison to the variable NKG2 chain.

Immune-refractory cancers and their little helpers--an extended role for immunetolerogenic MHC molecules HLA-G and HLA-E?

There is strong evidence to support a role for non-classical MHC class I (class Ib) molecules, most notably HLA-E and HLA-G in tumour immune escape. In this article, we summarize the current knowledge on their expression, regulation and functional relevance in various malignancies, particularly brain tumours. Special emphasis is devoted to the phenomenon that these tolerogenic molecules are expressed by non-transformed cells that are found in close neighborhood to tumour cells representing either parenchymal cells or immune cells attracted to the tumour microenvironment. Here they may act as "natural" or "inducible" suppressors of anti-tumoural immune responses. We thus speculate about the role of HLA-G expressing T cells, a novel population of natural regulatory cells that was identified recently. It is suggested that various cell types within a tumour cooperate in order to inhibit anti-tumour immunity-and that immunetolerogenic HLA-G may play a major role in this context.

Expression of HLA-G in malignant mesothelioma and clinically aggressive breast carcinoma

The aim of the present study was to evaluate HLA-G expression in breast carcinoma and malignant mesothelioma (MM). Malignant breast carcinoma effusions (46) and corresponding solid tumors (39) and 104 MM (26 effusions, 78 solid tumors) were analyzed using immunohistochemistry (IHC). HLA-G protein and mRNA expression were further studied using immunoblotting (IB) and RT-PCR. HLA-ABC expression was analyzed using flow cytometry (FCM). IHC showed predominantly focal HLA-G expression in 12 of 46 (26%) breast carcinoma effusions and 16 of 39 (41%) solid lesions. In MM, 20 of 78 (26%) solid lesions and 14 of 26 (54%) effusions were focally HLA-G positive. Expression in MM was higher in effusions (p=0.008). IB showed more frequent HLA-G expression in MM compared with breast carcinoma effusions, while RT-PCR showed HLA-G mRNA expression in both tumors. FCM showed conserved HLA-ABC expression in 15 of 15 effusions. Breast cancer patients with HLA-G-positive tumor cells had shorter disease-free survival (mean 37 vs 85, median 25 vs 31 months), though not significantly (p=0.14). In conclusion, HLA-G is focally expressed in MM and breast carcinoma, while HLA-ABC expression is conserved. However, the up-regulated expression of HLA-G in MM effusions and its possible association with shorter disease-free survival in advanced stage of breast carcinoma suggest a possible role in immune response evasion in some tumors.

The biological differences between ovarian serous carcinoma and diffuse peritoneal malignant mesothelioma

Recent improvements in immunohistochemistry panels used for differentiating ovarian serous carcinoma/primary peritoneal carcinoma (OC/PPC) from diffuse malignant peritoneal mesothelioma (DMPM) have resulted in improved diagnostic rates for these tumors in both cytological and histological material. However, little is known about the biological characteristics that differentiate these two cancer types. We performed a comparative analysis of cancer-associated molecule expression data for a cohort consisting of up to 270 serous OC/PPC specimens (only peritoneal lesions) and 32 peritoneal MM. The molecules studied were nerve growth factor receptors (p75, p-TrkA), angiogenic factors (VEGF, IL-8, bFGF, heparanase), laminin receptors (the 67-kDa receptor and the alpha 6 integrin subunit), proteases (MMP-2), immune response mediators (HLA-G), and signaling molecules (the MAPK members ERK, JNK, and p38). The methods used were immunohistochemistry, Western blotting, and RT-PCR. DMPM specimens showed significantly higher expression of p75 (P < 0.001), p-TrkA (P < 0.001), and bFGF (P < 0.001), and significantly lower expression of the 67-kDa receptor (P < 0.001), alpha 6 integrin subunit (P = 0.025), VEGF (P < 0.001), IL-8 (P < 0.001), and HLA-G (P = 0.039) compared with OC/PPC. DMPM specimens showed higher activation ratio (phosphorylated/total enzyme ratio) of all three MAPK members (ERK, P = 0.017; JNK, P < 0.001; p38, P = 0.009) compared with OC/PPC. These data document significant differences in the expression of cancer- and metastasis-associated molecules in MM compared with ovarian carcinoma, and suggest that different biological pathways are involved in tumorigenesis and disease progression in these two tumors.

Switch from inhibitory to activating NKG2 receptor expression in HIV-1 infection: lack of reversion with highly active antiretroviral therapy

BACKGROUND

HIV-1 infection is characterized by increase in inhibitory receptors and loss of activating receptors on natural killer (NK) cells, resulting in loss of cell activity. Exceptionally, for an inhibitory receptor, the proportion of NK cells bearing CD94-NKG2A decreases during HIV-1 infection. It is not understood whether HIV-1 itself or other concomitant infections drive these changes.

OBJECTIVES

To investigate the relationship between HIV-1 viraemia and changes in C-type lectin-like receptor expression in NK cells and to investigate the effect of highly active antiretroviral therapy (HAART) on these changes.

METHODS

Three cohorts of patients were studied: (1) before, during and after treatment interruption in aviraemic and viraemic patients receiving HAART (n = 15); (2) HIV-1-positive treatment-naive individuals (n = 13); and (3) HIV-1-positive individuals receiving successful HAART for a minimum of 1 year without interruption (n = 11). Flow cytometry was used to study the expression of NKG2A before and after treatment interruption and to define expanded populations of NK cells in untreated and treated HIV-1-positive individuals. Assays were performed in vitro to assess the cytotoxicity of the expanded populations.

RESULTS

Increases in plasma HIV-1 RNA during treatment interruption in aviraemic HAART-treated individuals did not influence the proportion of NK cells carrying the complex CD94-NKG2A. Loss of NKG2A NK cells corresponded to the dramatic expansion of a distinct population of cells expressing a functional activating CD94-NKG2C receptor with skewed expression of killer cell immunoglobulin-like receptor family and natural cytotoxicity receptors.

CONCLUSION

Changes in the NK cell repertoire during HIV-1 infection were not a result of HIV-1 viraemia alone but resembled those associated with concomitant infections.

Expression of MHC class I receptors confers functional intraclonal heterogeneity to a reactive expansion of gammadelta T cells

NK cell receptors for MHC class I molecules (MHC-NKR) can be expressed by T cell subsets. The restricted repertoire and phenotypic characteristics of MHC-NKR(+) T cells indicate that expression of MHC-NKR is acquired upon antigenic challenge and might promote expansion of T cells. Previous studies performed on in vitro generated alphabeta T cell clones concluded that MHC-NKR expression was not a clonal attribute. Here, we examined a massive monoclonal expansion of a non-leukemic gammadelta T cell population found in the peripheral blood of a lung-transplanted patient who suffered from a cytomegalovirus infection. Despite their monoclonality, these T cells displayed a heterogeneous and stable in vivo Ig- and lectin-like MHC-NKR phenotype. Twenty percent of the cells displayed a CD94(+)NKG2A(+) phenotype, and 10% were labeled with an anti-CD158b1/b2/j monoclonal antibody. A CD158b/j(+) gammadelta T cell clone derived in vitro from patient's peripheral blood lymphocytes was shown to express the activating form CD158j (KIR2DS2), which once cross-linked stimulated the clone cytolytic function and costimulated the TCR-induced production of cytokines, independently of the killer-activating receptor-associated protein (KARAP). In conclusion, heterogeneity of MHC-NKR expression confers a functional intraclonal diversity that may participate to induction of specific gammadelta T cell effector functions or proliferation upon pathogen challenge.

Interactions between NKG2x immunoreceptors and HLA-E ligands display overlapping affinities and thermodynamics

The NKG2x/CD94 family of C-type lectin-like immunoreceptors (x = A, B, C, E, and H) mediates surveillance of MHC class Ia cell surface expression, often dysregulated during infection or tumorigenesis, by recognizing the MHC class Ib protein HLA-E that specifically presents peptides derived from class Ia leader sequences. In this study, we determine the affinities and interaction thermodynamics between three NKG2x/CD94 receptors (NKG2A, NKG2C, and NKG2E) and complexes of HLA-E with four representative peptides. Inhibitory NKG2A/CD94 and activating NKG2E/CD94 receptors bind HLA-E with indistinguishable affinities, but with significantly higher affinities than the activating NKG2C/CD94 receptor. Despite minor sequence differences, the peptide presented by HLA-E significantly influenced the affinities; HLA-E allelic differences had no effect. These results reveal important constraints on the integration of opposing activating and inhibitory signals driving NK cell effector functions.

Molecular determinants regulating the pairing of NKG2 molecules with CD94 for cell surface heterodimer expression

The lytic capacity of a NK cell is regulated, in part, by the balance in cell surface expression between inhibitory CD94/NKG2A and activating CD94/NKG2C heterodimers. We demonstrate that, in the absence of DAP12, rhesus monkey NKG2A is preferentially expressed at the cell surface with CD94 due to a single amino acid difference in the transmembrane of NKG2A and NKG2C. Furthermore, in the context of an NKG2A transmembrane, the stalk domain of NKG2C was found to enhance heterodimer formation with CD94 compared with the stalk domain of NKG2A. In the presence of DAP12, the ability of NKG2C to compete for cell surface CD94 heterodimerization is enhanced and approaches that of NKG2A. Finally, allelic differences that affect the ability of rhesus NKG2A to reach the cell surface with CD94 could also be mapped to the transmembrane. These differences in the ability of inhibitory and activating NKG2 molecules to reach the cell surface provide a mechanism for the regulation of NK cell activity.