Regulation of KIR expression in human T cells: a safety mechanism that may impair protective T-cell responses

CD94-NKG2A receptors regulate antiviral CD8(+) T cell responses

CD8(+) T lymphocytes mediate immunosurveillance against persistent virus infections and virus-induced neoplasia. Polyoma virus, a highly oncogenic natural mouse DNA virus, establishes persistent infection, but only a few mice are highly susceptible to tumors induced by the virus. Mature antiviral CD8(+) T cells expand in tumor-susceptible mice, but their cytotoxic effector activity is nonfunctional in vivo. Here we show that the natural killer cell inhibitory receptor, CD94-NKG2A, is up-regulated by antiviral CD8(+) T cells during acute polyoma infection and is responsible for down-regulating their antigen-specific cytotoxicity during both viral clearance and virus-induced oncogenesis.

Tumor cell recognition by natural killer cells

Natural killer (NK) cells contribute to the immune defense against cancer and viruses. Tumor cells and infected cells that downregulate the HLA class I antigen expression are targets for NK cell responses because NK cell activation is controlled by a repertoire of inhibitory receptors with different HLA class I specificities. The clonal distribution of these inhibitory receptors permits NK cell recognition of target cells that have lost expression of a single HLA-B or HLA-C allotype. Several activation receptors on NK cells have been identified that contribute to tumor cell recognition. One such receptor, NKG2D, is expressed by all NK cells and binds to inducible ligands on tumor cells.

Allogeneic MHC class I ligands and their role in positive and negative regulation of human cytotoxic effector cells

The allogeneic mixed lymphocyte culture (MLC) has served as an important experimental system for elucidating the cellular and molecular basis of human lymphocyte responses. Complex mixtures of lymphocytes are stimulated by disparate alloantigens, inducing cellular activation and generating a cytokine milieu that is an excellent breeding ground for the proliferation and differentiation of many distinct lymphocyte subsets. Cloning of individual lymphocytes following alloactivation has allowed various cytotoxic lymphocytes to be isolated and characterized with respect to phenotype and specificity. These analyses have revealed that all types of cytotoxic effector cells are regulated by interactions with MHC-peptide ligands, however, the consequences of these interactions can result in opposite functional outcomes. In this review we summarize how allogeneic MHC class I-peptide ligands positively or negatively regulate the activities of four distinct groups of cytotoxic lymphocytes and how this information might be transferred into clinical use.

Expression of inhibitory receptors in natural killer (CD3(-)CD56(+)) cells and CD3(+)CD56(+) cells in the peripheral blood lymphocytes and tumor infiltrating lymphocytes in patients with primary hepatocellular carcinoma

The cytolytic responses of NK (CD3(-)CD56(+)) and CD3(+)CD56(+) cells are inhibited by the engagement of the killer inhibitory receptors (p58.1, p58.2, and CD94) with respective ligands on the target cell. The expression of these receptors in peripheral blood lymphocytes (PBLs) (n = 18) and tumor infiltrating lymphocytes (TILs) (n = 7) was examined in patients with primary hepatocellular carcinoma (HCC). There were no differences in the expression of the three inhibitory receptors by both NK and CD3(+)CD56(+) PBLs in patients with HCC compared to that of control NK and CD3(+)CD56(+) PBLs, respectively (all P = NS). However, the expression of p58.1 by NK TILs and by CD3(+)CD56(+) TILs in patients with HCC was significantly decreased compared to that of hepatic lymphocytes of the control subjects (8.9% vs 37.85%, P = 0.047; 4.1% vs 25.2%, P = 0.049, respectively). The expression of p58.2 by CD3(+)CD56(+) TILs and CD94 by NK TILs was also decreased compared to that of hepatic lymphocytes of the control subjects (16.9% vs 73.1%, P = 0.047; 21% vs 49.95%, P = 0.037, respectively). These changes were limited to hepatic TILs, and this observation may reflect an adaptive anti-tumor phenomenon occurring in the microenvironment of HCC.

The analysis of the natural killer-like activity of human cytolytic T lymphocytes revealed HLA-E as a novel target for TCR alpha/beta-mediated recognition

Cytolytic T lymphocytes (CTL) are known to recognize antigen peptides in association with major histocompatibility complex (MHC) class I molecules expressed on target cells. However, a fraction of human CD8(+) CTL has been shown to lyse certain natural killer (NK)-susceptible target cells via still undefined mechanism(s). These CD8(+) T cells, hereafter referred to as NK-CTL, are frequently composed of cells expressing one single TCR Vbeta expansion (different in different individuals), display a memory phenotype and express HLA class I-specific inhibitory NK receptors. Here we show that cell populations or clones of NK-CTL isolated from three healthy donors homogeneously expressed Vbeta16, Vbeta9 and Vbeta3 TCR, respectively. Various clones isolated under limiting dilution conditions from Vbeta16(+) cells of donor 1 displayed identical TCR Vbeta and Valpha rearrangements, thus suggesting a substantial monoclonality of the NK-CTL subset analyzed. NK-CTL lysed a number of NK-susceptible tumor target cells with the exception of those characterized by beta2-microglobulin (beta2m) deficiency. However, the latter targets became susceptible to lysis upon beta2m transfection. Using monoclonal antibodies specific for the relevant TCR Vbeta or beta2m we provide evidence suggesting that target cell lysis by NK-CTL is mediated by the TCR itself upon recognition of beta2m-associated proteins. The cellular distribution of the potential beta2m-associated proteins in susceptible target cells suggested, as a likely candidate for TCR-mediated recognition, the non-classical HLA-E molecule. The use, as target cells, of the murine TAP2-deficient RMA-S cells, either untransfected or transfected with HLA-E, and loaded with an appropriate HLA-E-binding peptide, provided the direct demonstration that HLA-E represents a ligand recognized by the TCR expressed by NK-CTL. This is the first evidence that human TCR alpha/beta can recognize HLA-E molecules, thus revealing a novel type of TCR-mediated recognition, which may offer new insight in immune responses in both normal and disease conditions.

Expression of inhibitory "killer cell lectin-like receptor G1" identifies unique subpopulations of effector and memory CD8 T cells

T cell and natural killer (NK) cell functions are regulated by triggering of activating and inhibitory cell surface receptors. Here, we have studied the expression profile and predicted inhibitory function of mouse "killer cell lectin-like receptor G1" (KLRG1) on CD8 T cells. KLRG1 was present on 1 - 3 % of adult splenic CD8 cells that expressed CD8alpha beta heterodimers as well as a polyclonal TCR Vbeta repertoire indicative of conventional CD8 cells. The majority of KLRG1(+) CD8 cells belonged to the memory pool as determined by extensive phenotypic marker analysis. Spontaneous IFN-gamma production by approximately 20 % of KLRG1(+) CD8 cells identified them as pro-inflammatory effector cells. In contrast to NK cells, Ly49 and KLRG1 expression on CD8cells was found to be mutually exclusive. Therefore, distinct programs regulate KLRG1 expression in CD8 and NK cells. Finally, we provide evidence that KLRG1 triggering interferes with TCRalpha beta-mediated Ca(++) mobilization and cytotoxicity, raising the possibility that KLRG1 functionally participates in down-regulation of CD8 T cell responses.

Distribution of the natural killer-related receptor for HLA-C during highly active antiretroviral therapy for human immunodeficiency virus infection

Receptors interacting with Major Histocompatibility Complex class I molecules have been initially found on the surface of human natural killer (NK) cells, where they deliver inhibitory signals to the lysis, being thus defined killer inhibitory receptors (KIR). Subsequently, they were detected also on the surface of T-CD8(+) lymphocytes and are particularly expanded during human immunodeficiency virus (HIV) infection, where they downregulate HIV-specific cytolysis. The expression of KIR recognizing human leukocyte antigen-C alleles was assessed in HIV-infected patients, undergoing highly active antiretroviral therapy (HAART). To this end, the combined expression of CD16/CD56, of CD3 and CD8 as well as of KIR (CD158a and CD158b) surface molecules was analyzed on peripheral blood mononuclear cells by monoclonal antibodies, and flow cytometry. An increase of CD3(+)CD8(+)CD158b(+) cells was found after 6 months of HAART. This finding may have implications for the regulation of T-cell mediated cytolysis during HAART.

Bypassing tumor-specific and bispecific antibodies: triggering of antitumor immunity by expression of anti-FcgammaR scFv on cancer cell surface

We have developed a novel immunostimulatory molecule against tumor cells, composed of an anti-FcgammaRIII (CD16) scFv fused to the platelet-derived growth factor receptor (PDGFR) transmembrane region. This fusion molecule was stably expressed on the tumor cell surface and retained the ability of the parental antibody to bind soluble CD16. Tumor cells expressing anti-CD16 scFv triggered the release of IL-2 by Jurkat-CD 16/gamma cells and of TNFalpha by monocytes when co-cultured with these cells. Furthermore, NK cells could kill scFv-transfected HLA+ class I H1299 lung carcinoma tumor cells, but not the parental cells, indicating that anti-CD16 scFv tumor expression prevents the killer inhibitory receptor (KIR)-mediated inhibition of NK cell cytotoxicity. This anti-CD16 scFv tumor expression also enhanced tumor phagocytosis by IFNgamma-activated macrophages, a mechanism known to induce a protective long-term adaptative immunity to tumors. In vivo Winn tests performed in SCID mice showed that the expression of anti-CD16 scFv on tumor cells, but not of the negative control anti-phOx scFv, prevented tumor cell growth. Thus, expression of FcR antibodies or other FcR-specific ligands on tumor cells represents a novel and potent antibody-based gene therapy approach, which may have clinical applications in cancer

Expression of Fas antigen (CD95) in peripheral blood lymphocytes and in liver-infiltrating, cytotoxic lymphocytes in patients with hepatocellular carcinoma

BACKGROUND

Fas-expressing cytotoxic T lymphocytes (CTLs) are important antitumor immune effector cells in patients with hepatocellular carcinoma (HCC). The role of transforming growth factor beta 1 (TGF-beta1) in modulating the expression of Fas by CTLs is not known in HCC. The objectives of this study were to characterize the expression of Fas by CTLs and natural killer (NK) cells among peripheral blood lymphocytes (PBLs) and tumor-infiltrating lymphocytes (TILs) in patients with HCC and to correlate the association, if any, with serum TGF-beta1 levels.

METHODS

PBLs from 18 patients with HCC and TILs from 5 HCC liver specimens were isolated, and Fas expression was analyzed by three-color flow cytometry. The results were compared with results from normal control volunteers (n = 19 individuals). Serum TGF-beta1 levels in patients with HCC were measured by enzyme-linked immunosorbent assay.

RESULTS

The median percentage of Fas expression by CD3 positive T cells was significantly higher in patients with HCC compared with normal controls (54.37% vs. 32.03%, respectively; P = 0.0036), and this was attributable solely to Fas expression by CD4 positive PBLs (54.46% vs. 34.90%, respectively; P = 0.0234). In contrast, Fas expression was significantly higher in all the subtypes of TILs (CD3 positive, CD4 positive, CD8 positive, NK cells, and natural T cells) compared with controls (all P values were < 0.001). Tumor size was inversely proportional to the TGF-beta1 levels (correlation coefficient [r] = -0.725; P < 0.0001), which were correlated inversely with Fas expression by CD4 positive PBLs (r = -0.516; P = 0.01).

CONCLUSIONS

In patients with HCC, TILs exhibit significantly increased expression of Fas compared with PBLs that may enhance their susceptibility to apoptotic mechanisms. Larger tumors were associated with lower serum TGFbeta1 levels, and this was correlated with greater Fas expression by CD4 positive PBLs.

Distinct mRNA microarray profiles of tolerogenic dendritic cells

Dendritic cells are crucial to the activation as well as suppression of the immune response. Previous reports have illustrated that APC interacting with antigen-specific T suppressor cells become tolerogenic, inducing T helper anergy. To characterize the molecular changes occurring in tolerogenic APC, the mRNA profile of KG-1 dendritic cells exposed to allospecific T helper and T suppressor cells were analyzed. This study now provides evidence that immature dendritic cells stimulated by T suppressor cells differentiate into mature dendritic cells with a distinct phenotype. The identification of Ts induced pathways of dendritic cell differentiation is critical to the development of new therapeutic strategies.

Activating receptors and coreceptors involved in human natural killer cell-mediated cytolysis

Natural killer cells can discriminate between normal cells and cells that do not express adequate amounts of major histocompatibility complex (MHC) class I molecules. The discovery, both in mouse and in human, of MHC-specific inhibitory receptors clarified the molecular basis of this important NK cell function. However, the triggering receptors responsible for positive NK cell stimulation remained elusive until recently. Some of these receptors have now been identified in humans, thus shedding some light on the molecular mechanisms involved in NK cell activation during the process of natural cytotoxicity. Three novel, NK-specific, triggering surface molecules (NKp46, NKp30, and NKp44) have been identified. They represent the first members of a novel emerging group of receptors collectively termed natural cytotoxicity receptors (NCR). Monoclonal antibodies (mAbs) to NCR block to differing extents the NK-mediated lysis of various tumors. Moreover, lysis of certain tumors can be virtually abrogated by the simultaneous masking of the three NCRs. There is a coordinated surface expression of the three NCRs, their surface density varying in different individuals and also in the NK cells isolated from a given individual. A direct correlation exists between the surface density of NCR and the ability of NK cells to kill various tumors. NKp46 is the only NCR involved in human NK-mediated killing of murine target cells. Accordingly, a homologue of NKp46 has been detected in mouse. Molecular cloning of NCR revealed novel members of the Ig superfamily displaying a low degree of similarity to each other and to known human molecules. NCRs are coupled to different signal transducing adaptor proteins, including CD3 zeta, Fc epsilon RI gamma, and KARAP/DAP12. Another triggering NK receptor is NKG2D. It appears to play either a complementary or a synergistic role with NCRs. Thus, the triggering of NK cells in the process of tumor cell lysis may often depend on the concerted action of NCR and NKG2D. In some instances, however, it may uniquely depend upon the activity of NCR or NKG2D only. Strict NKG2D-dependency can be appreciated using clones that, in spite of their NCR(dull) phenotype, efficiently lyse certain epithelial tumors or leukemic cell lines. Other triggering surface molecules including 2B4 and the novel NKp80 appear to function as coreceptors rather than as true receptors. Indeed, they can induce natural cytotoxicity only when co-engaged with a triggering receptor. While an altered expression or function of NCR or NKG2D is being explored as a possible cause of immunological disorders, 2B4 dysfunction has already been associated with a severe form of immunodeficiency. Indeed, in patients with the X-linked lymphoproliferative disease, the inability to control Epstein-Barr virus infections may be consequent to a major dysfunction of 2B4 that exerts inhibitory instead of activating functions.

Human natural killer cell function and receptors

Recent years have witnessed major progress in our understanding of the molecular mechanisms regulating natural killer cell (NK cell) function. These advances stem primarily from the discovery of a number of receptors specific for major histocompatibility complex (MHC) class I and, more recently, of the activating receptors and coreceptors responsible for natural cytotoxicity. Important studies performed over the past year have allowed us to define the evolution of the MHC-specific inhibitory receptors by comparative analysis in different species. The roles of the 'activating natural cytotoxicity receptors', NKG2D and certain coreceptors in the lysis of different tumors have been defined in detail. The mechanism by which the 2B4 coreceptor renders patients with X-linked lymphoproliferative disease unable to control Epstein-Barr virus has been elucidated. Inhibitory receptors identified in NK cells may also be expressed by normal and leukemic myeloid cells, in which they can block cell proliferation and survival. It has also become clear that viruses such as cytomegalovirus have evolved strategies to interfere with NK-cell function to protect themselves from NK-mediated attack.

Expression and function of NK cell receptors in CD8+ T cells

A wide variety of inhibitory and stimulatory NK cell receptors are expressed by some CD8+ cytotoxic T lymphocytes in mice and humans. Recent data address the induction of these receptors on activated or memory CD8+ T cells and have led to hypotheses addressing their function in the CD8+ T cell response.

Epidermal CD8+ T cells in chronic plaque psoriasis are Tc1 cells producing heterogeneous levels of interferon-gamma

The majority of epidermal CD8+ T cells in chronic plaque psoriasis are activated Tc1 cells producing interferon-gamma and no interleukin-4, a small proportion of which express NK-T receptors. To quantitate their level of cytokine production and characterize them further, CD8+ T cells were isolated from epidermal cell suspensions of lesional biopsies from 24 patients with chronic plaque psoriasis. T-cell lines (TCL) were established by culture of CD8+ T cells with feeders and IL-2 for 11 days and expansion with PHA. Ten TCL were stained for surface markers; 6 were cloned with PHA by limiting dilution. Interferon-gamma, interleukin-4 and interleukin-10 production was measured by ELISA after PMA/anti-CD3 activation of 15 TCL and 39 CD8+ T-cell clones. The 10 TCL stained were CD8alphabeta+ (93.3%), T-cell receptor-alphabeta+ (99.5%), costimulatory molecule CD28+ (90.1%), with a small CD8alphaalpha+ population (2.3%). No NK-T-cell receptor CD158a or CD158b expression was detected, whilst CD94 was expressed on 6.2% of cells in 6/9 TCL. All the TCL and 37/39 CD8+ T-cell clones produced interferon-gamma but no or minimal interleukin-4 or interleukin-10. The TCL produced a wide range of interferon-gamma levels (138 to 15,020 pg/ml). Clones from 3 patients showed low levels (60 to 1,410 pg/ml), from 2 patients high levels (6,105 to 43,040 pg/ml) and from 1 patient a wide range (405 to 36,010 pg/ml) of interferon-gamma production. Thus epidermal CD8+ Tc1 cells in chronic plaque psoriasis produce highly heterogeneous levels of interferon-gamma, which may reflect clinical diversity.

TCR gamma delta cytotoxic T lymphocytes expressing the killer cell-inhibitory receptor p58.2 (CD158b) selectively lyse acute myeloid leukemia cells

Cytotoxic T lymphocytes (CTL) are thought to play an important role in the graft-versus-leukemia (GVL) response. Unfortunately, GVL reactivity is often associated with life-threatening graft-versus-host disease (GVHD). Characterization of CTL that selectively attack leukemic cells but not normal cells may lead to the development of adjuvant immunotherapy that separates GVL from GVHD. Here, we describe TCR gamma delta (V gamma 9/V delta 1) CTL, isolated from the peripheral blood of an AML patient after stem cell transplantation (SCT), that very efficiently lysed freshly isolated acute myeloid leukemia (AML) cells and AML cell lines. Interestingly, HLA-matched non-malignant hematopoietic cells were not killed. We revealed that the killer cell-inhibitory receptor (KIR) p58.2 (CD158b) specific for group 2 HLA-C molecules negatively regulates the cytotoxic effector function displayed by these TCR gamma delta CTL. First, an antibody against HLA-C enhances lysis of non-malignant cells. Secondly, stable transfection of HLA-Cw*0304 into the class I-negative cell line 721.221 inhibited lysis. Finally, engagement of p58.2 by antibodies immobilized on Fc gamma R-expressing murine P815 cells inhibits CD3- and TCR gamma delta-directed lysis. Compared to non-malignant hematopoietic cells, AML cells express much lower levels of MHC class I molecules making them susceptible to lysis by p58.2(+) TCR gamma delta CTL. Such KIR-regulated CTL reactivity may have a role in the GVL response without affecting normal tissues of the host and leading to GVHD.

Involvement of inhibitory NKRs in the survival of a subset of memory-phenotype CD8+ T cells

Inhibitory natural killer receptors (NKRs) such as killer cell immunoglobulin-like receptors (KIRs) in humans and Ly49 molecules in mice are expressed on NK cells and recognize multiple major histocompatibility (MHC) class I proteins. In humans and mice, a subset of CD8+ T cells also expresses NKRs and harbors a memory phenotype. Using mice that are transgenic for KIR2DL3 and its cognate HLA-Cw3 ligand, we show that engagement of inhibitory NKRs selectively drives the in vivo accumulation of a subset of memory-phenotype CD8+ T cells that express the beta chain of the interleukin 2 receptor. In vitro, recognition of MHC class I molecules by inhibitory NKRs on T cells down-regulated activation-induced cell death. These results unveil an MHC class I-dependent pathway that promotes the survival of a subset of memory-phenotype CD8+ T cells and also reveal an unexpected biological function for inhibitory NKRs on T cells.

Molecular cloning of MIS, a myeloid inhibitory siglec, that binds protein-tyrosine phosphatases SHP-1 and SHP-2

We describe the molecular cloning and characterization of a novel myeloid inhibitory siglec, MIS, that belongs to the family of sialic acid-binding immunoglobulin-like lectins. A full-length MIS cDNA was obtained from murine bone marrow cells. MIS is predicted to contain an extracellular region comprising three immunoglobulin-like domains (V-set amino-terminal domain followed by two C-set domains), a transmembrane domain and a cytoplasmic tail with two immunoreceptor tyrosine-based inhibitory motif (ITIM)-like sequences. The closest relative of MIS in the siglec family is human siglec 8. Extracellular regions of these two siglecs share 47% identity at the amino acid level. Southern blot analysis suggests the presence of one MIS gene. MIS is expressed in the spleen, liver, heart, kidney, lung and testis tissues. Several isoforms of MIS protein exist due to the alternative splicing. In a human promonocyte cell line, MIS was able to bind Src homology 2-containing protein-tyrosine phosphatases, SHP-1 and SHP-2. This binding was mediated by the membrane-proximal ITIM of MIS. Moreover, MIS exerted an inhibitory effect on FcgammaRI receptor-induced calcium mobilization. These data suggest that MIS can play an inhibitory role through its ITIM sequences.

Recognition of tumor cells by the innate immune system

There has been a rapid increase in our understanding of the cellular components of the innate immune system, the receptors used to distinguish changes in homeostasis, and how these components integrate into an anti-tumor effector response. Recently, significant progress has been made in the identification of ligands for receptors that activate NK cells, and the results have implications for the recognition of tumor cells.

Effect of granulocyte colony-stimulating factor mobilization on phenotypical and functional properties of immune cells

Some phenotypic and functional properties of lymphocytes from bone marrow or peripheral blood stem cell donors were compared in a randomized study. Lymphocyte subsets were analyzed by immunocytometry in blood harvested from bone marrow donors (n = 27) and from peripheral blood stem cell donors before and after granulocyte colony-stimulating factor mobilization (n = 23) and in bone marrow and peripheral blood stem cell grafts. Granulocyte colony-stimulating factor mobilization increased the blood T and B, but not NK, lymphocyte counts. All lymphocyte counts were approximately 10-fold higher in peripheral blood stem cell grafts than in bone marrow grafts. Analysis of CD25, CD95, HLA-DR, and CD45RA expression shows that T-cell activation level was lower after granulocyte colony-stimulating factor mobilization. Similarly, granulocyte colony-stimulating factor reduced by twofold to threefold the percentage of interferon-gamma, interleukin-2, and tumor necrosis factor-alpha-secreting cells within the NK, NK-T, and T-cell subsets and severely impaired the potential for interferon-gamma production at the single-cell level. mRNA levels of both type 1 (interferon-gamma, interleukin-2) and type 2 (interleukin-4, interleukin-13) cytokines were approximately 10-fold lower in peripheral blood stem cell grafts than in bone marrow grafts. This reduced potential of cytokine production was not associated with a preferential mobilization of so-called "suppressive" cells (CD3+CD4-CD8-, CD3+CD8+CD56+, or CD3+TCRVA24+CD161+), nor with a modulation of killer cell receptors CD161, NKB1, and CD94 expression by NK, NK-T, or T cells. Our data demonstrate in a randomized setting that quantitative as well as qualitative differences exist between a bone marrow and a peripheral blood stem cell graft, whose ability to produce type 1 and type 2 cytokines is impaired.

CD4(+) cutaneous T-cell lymphoma cells express the p140-killer cell immunoglobulin-like receptor

Tumor cells of patients with cutaneous T-cell lymphoma (CTCL) have the cell surface phenotype of mature T-helper lymphocytes, and it may be impossible to differentiate them from nonmalignant lymphocytes in skin and blood. Until now, no specific cell membrane marker of CTCL has been reported. In the current study, it is reported for the first time that CTCL cells express the major histocompatibility complex class I binding p140-killer cell immunoglobulin-like receptor, which has been described on a minor subset of natural killer lymphocytes and on a marginal circulating CD8(+) T lymphocyte subset. Interestingly, the molecular characterization of this KIR expressed by CTCL allowed us to isolate a novel allelic form of p140-KIR3DL, resulting in 4 amino acid substitutions, 3 in the extracellular immunoglobulin-like domain of the protein and one in the cytoplasmic region. This finding is likely to be important both for the pathophysiology and for the clinical treatment of patients with CTCL.

Regulation of inhibitory and activating killer-cell Ig-like receptor expression occurs in T cells after termination of TCR rearrangements

A small fraction of T cells expresses killer-cell Ig-like receptors (KIR), a family of MHC class I-specific receptors that can modulate TCR-dependent activation of effector functions. Although KIR(+) cells are enriched within Ag-experienced T cell subsets, the precise relationships between KIR(+) and KIR(-) T cells and the stage of KIR induction on these lymphocytes remain unclear. In this study, we compared KIR(-) and KIR(+) alphabeta T cell clones, sorted by means of the CD158b (KIR2DL2/KIR2DL3/KIR2DS2) specific mAb GL183. We isolated several pairs of CD158b(+) and CD158b(-) alphabeta T cell clones sharing identical productive and nonproductive TCR transcripts. We showed that expression of functional KIR on T cells is regulated after termination of TCR rearrangements. Transcriptional regulation of KIR genes was documented in multiple T cell clones generated from the same donor, and the presence of KIR transcripts was also detected in KIR(-) T cells. These results document a complex regulation of KIR expression in T cells at both pre and posttranscriptional levels, under the control of yet undefined signals provided in vivo.

Induction of hyporesponsiveness and impaired T lymphocyte activation by the CD31 receptor:ligand pathway in T cells

CD31 is a member of the Ig superfamily expressed on various cell types of the vasculature, including a certain subpopulation of T lymphocytes. Previous reports suggest that interaction of CD31 with its heterophilic ligand on T cells (T cell CD31 ligand) plays a regulatory role in T lymphocyte activation. Here we demonstrate that a soluble rCD31-receptorglobulin (CD31Rg) specifically down-regulated the proliferation of human peripheral blood CD31(-) T lymphocytes stimulated via CD3 and CD28 mAbs. Notably, engagement of the T cell CD31 ligand by CD31Rg during primary stimulation also induced a prolonged unresponsive state in T cells. Retroviral transduction of CD31 into CD31(-) Th clones resulted in a significant inhibition of their proliferative capacity. When cocultured with purified CD31(-) T lymphocytes, irradiated CD31-transduced Th clones counterregulated the CD3/CD28-mediated activation of these cells. Furthermore, primary stimulation in the presence of CD31-transduced Th clones induced a comparable state of hyporesponsiveness in the T cell responders as the soluble CD31Rg. Thus, by counterregulating the activation of cognate T lymphocytes, CD31-expressing T cells might contribute to the establishment and maintenance of peripheral tolerance.

Detection of autoantibodies to killer immunoglobulin-like receptors using recombinant fusion proteins for two killer immunoglobulin-like receptors in patients with systemic autoimmune diseases

OBJECTIVE

To investigate the existence of autoantibodies to killer immunoglobulin-like receptors (KIRs), especially p58.1 (KIR2DL1) and p58.2 (KIR2DL3), in patients with systemic autoimmune diseases.

METHODS

Sera from 30 patients with systemic lupus erythematosus (SLE), 30 patients with rheumatoid arthritis (RA), 22 patients with Behçet's disease, and 20 healthy control subjects were tested for anti-p58.1 and anti-p58.2 antibodies by Western blot analysis using recombinant p58.1 and p58.2 proteins. Furthermore, clinical features and laboratory data were compared between the anti-p58.1/58.2 antibody-positive and -negative patients.

RESULTS

Anti-p58.1 antibodies were detected in 7 (23.3%) of the 30 patients with SLE, 9 (30%) of the 30 patients with RA, and 6 (27.3%) of the 22 patients with Behçet's disease. Anti-p58.2 antibodies were detected in the same 22 patients who were positive for the anti-p58.1 antibodies. None of the serum samples from the healthy donors were positive for antibodies to the recombinant p58.1 or p58.2 molecules. Compared with the anti-p58.1/ 58.2 antibody-negative patients, the anti-p58.1/58.2 antibody-positive patients had significantly elevated levels of serum IgG in all 3 diseases tested, an accelerated erythrocyte sedimentation rate in RA and SLE, and decreased white blood cell counts in RA.

CONCLUSION

This report is the first to describe the presence of autoantibodies to KIR2DL (p58.1 and p58.2) in the sera of patients with systemic autoimmune diseases. Considering the correlation with several clinical features, these autoantibodies may be involved in the pathologic process of the autoimmune diseases.

Differential expression of CD28 and CD94/NKG2 on T cells with identical TCR beta variable regions in primary melanoma and sentinel lymph node

NK cell tolerance is maintained by the interaction of killer inhibitory receptors with self MHC class I gene products. A subset of T cells also express killer inhibitory receptors, but the functional significance of this is unclear. Here we demonstrate that the expression of the C-lectin-like killer inhibitory receptor CD94 / NKG2 on T cells depends on the state of differentiation during the immune response to solid tumors. To this end we identified clonally expanded T cells which were present both in the sentinel lymph node of primary melanoma, as well as in the tumor itself. In situ characterization of such T cell clonotypes revealed that within the early stages of T cell activation, i. e. priming in the lymph node, T cells did not express CD94 / NKG2 whereas the same T cell clones expressed high levels of CD94 / NKG2 having reached the effector state at the tumor site. Moreover, while the phenotype of these T cell clones was CD28high in the lymph node only CD28low or CD28- T cells were found within the tumor. Double staining for CD94 and CD28 conformed that CD94 / NKG2-expressing cells were preferentially CD28-. Thus, T cells may down-regulate CD28 and up-regulate NK receptors as consequence of prolonged activation for cytolytic effector function. It is likely that NK receptors are involved in peripheral regulatory mechanisms avoiding overwhelming immune responses and immunopathology, particularly in situations of long-lasting immune activation.

Functional inhibitory receptors expressed by a cutaneous T cell lymphoma-specific cytolytic clonal T cell population

Inhibitory receptors on natural killer cells and on a minority of T lymphocytes are major histocompatibility complex class Ia or Ib specific. We have previously reported several tumor-specific cytotoxic T cell clones infiltrating a CD4(+) V beta 13(+) cutaneous T cell lymphoma. These clones mediated a specific major histocompatibility complex class I-restricted cytotoxic activity toward the uncultured tumor cells and autologous long-term tumor T cell lines. In this study, we cultured with interleukin-2 the peripheral blood lymphocytes of the same patient a few weeks before invasion of the blood by tumor cells. We report the rapid and selective expansion of a CD8(+) V beta 13(+) lymphoid population. This population was clonal, as it expressed a unique T cell receptor-V beta junctional region. V beta 13(+) tumor cells and V beta 13(+) reactive T cells were shown to have different junctional sequences. The CD8(+) reactive clone was functional, as it had a specific autologous tumor-specific, human leukocyte antigen-A2 restricted, cytotoxic activity. This clone coexpressed high levels of CD158a, CD158b, p70, and CD94/NKG2A inhibitory receptors. Interestingly, we found that anti-CD158a and anti-CD158b monoclonal antibodies could inhibit anti-CD3 redirected cytotoxicity mediated by the reactive clonal population. Further, an anti-human leukocyte antigen-B/C monoclonal antibody enhanced the specific cytotoxic activity of the clone against autologous tumor cells. These results are the first evidence that inhibitory receptor expression can lead to the inhibition of cutaneous T cell lymphoma-specific T cell responses.

Non-MHC-restricted CD4+ T lymphocytes are regulated by HLA-Cw7-mediated inhibition

Natural killer cells (NK cells) represent an important component of innate immunity with the capacity to kill many tumor and virus-infected cells. The discovery of several classes of killer cell inhibitory receptors expressed by NK cells that bind specific MHC class I ligands on target cells provides detailed insight into the regulation of NK cells. Inhibitory receptors deliver negative signals following MHC ligand binding that abrogate cytotoxicity and, thus, determine the specificity of NK effector cell function. Here, we describe a novel subset of human memory CD4(+) T lymphocytes that display an NK-like pattern of regulation. These CD4(+) T cells display non-MHC-restricted cytotoxicity that is governed by HLA-Cw7 mediated inhibition. In NK cells, such specificity is associated with expression of the inhibitory receptor p58.2. In contrast, neither p58.2 nor other known inhibitory receptors were detected on these non-MHC-restricted CD4(+) T cells. This suggests that these cells are regulated by a hitherto unknown inhibitory receptor. The finding that interactions with MHC molecules downregulate the function of these CD4(+) T cells suggests that these non-MHC-restricted T cells may function to detect and eliminate cells with aberrant MHC expression.

CD8+ T cells rapidly acquire NK1.1 and NK cell-associated molecules upon stimulation in vitro and in vivo

NKT cells express both NK cell-associated markers and TCR. Classically, these NK1.1+TCRalphabeta+ cells have been described as being either CD4+CD8- or CD4-CD8-. Most NKT cells interact with the nonclassical MHC class I molecule CD1 through a largely invariant Valpha14-Jalpha281 TCR chain in conjunction with either a Vbeta2, -7, or -8 TCR chain. In the present study, we describe the presence of significant numbers of NK1.1+TCRalphabeta+ cells within lymphokine-activated killer cell cultures from wild-type C57BL/6, CD1d1-/-, and Jalpha281-/- mice that lack classical NKT cells. Unlike classical NKT cells, 50-60% of these NK1.1+TCRalphabeta+ cells express CD8 and have a diverse TCR Vbeta repertoire. Purified NK1.1-CD8alpha+ T cells from the spleens of B6 mice, upon stimulation with IL-2, IL-4, or IL-15 in vitro, rapidly acquire surface expression of NK1.1. Many NK1.1+CD8+ T cells had also acquired expression of Ly-49 receptors and other NK cell-associated molecules. The acquisition of NK1.1 expression on CD8+ T cells was a particular property of the IL-2Rbeta+ subpopulation of the CD8+ T cells. Efficient NK1.1 expression on CD8+ T cells required Lck but not Fyn. The induction of NK1.1 on CD8+ T cells was not just an in vitro phenomenon as we observed a 5-fold increase of NK1.1+CD8+ T cells in the lungs of influenza virus-infected mice. These data suggest that CD8+ T cells can acquire NK1.1 and other NK cell-associated molecules upon appropriate stimulation in vitro and in vivo.

Overexpression of CD1d by keratinocytes in psoriasis and CD1d-dependent IFN-gamma production by NK-T cells

The MHC class I-like protein CD1d is a nonpolymorphic molecule that plays a central role in development and activation of a subset of T cells that coexpress receptors used by NK cells (NK-T cells). Recently, T cells bearing NK receptors were identified in acute and chronic lesions of psoriasis. To determine whether NK-T cells could interact with epidermal cells, we examined the pattern of expression of CD1d in normal skin, psoriasis, and related skin disorders, using a panel of CD1d-specific mAbs. CD1d was expressed by keratinocytes in normal skin, although expression was at a relatively low level and was generally confined to upper level keratinocytes immediately beneath the lipid-rich stratum corneum. In contrast, there was overexpression of CD1d in chronic, active psoriatic plaques. CD1d could be rapidly induced on keratinocytes in normal skin by physical trauma that disrupted barrier function or by application of a potent contact-sensitizing agent. Keratinocytes displayed enhanced CD1d following exposure to IFN-gamma. Combining CD1d-positive keratinocytes with human NK-T cell clones resulted in clustering of NK-T cells, and while no significant proliferation ensued, NK-T cells became activated to produce large amounts of IFN-gamma. We conclude that CD1d can be expressed in a functionally active form by keratinocytes and is up-regulated in psoriasis and other inflammatory dermatoses. The ability of IFN-gamma to enhance keratinocyte CD1d expression and the subsequent ability of CD1d-positive keratinocytes to activate NK-T cells to produce IFN-gamma, could provide a mechanism that contributes to the pathogenesis of psoriasis and other skin disorders.

Expression of Ly49A on T cells alters the threshold for T cell responses

In this study we investigated the balance between activating and inhibitory signals during T cell activation. We have used transgenic mice in which CD8+ T cells expressed an inhibitory receptor, Ly49A, and a specific activating alphabeta TCR. This TCR recognizes an lymphocytic choriomeningitis virus peptide in combination with H-2Db. We observed a quantitative influence on cellular responses that depended upon the activating signals received through the TCR and the inhibitory signals received through Ly49A. By varying the peptide concentration given to stimulating cells or target cells, we could adjust the amount of ligand available to trigger the TCR. At low doses of peptide, Ly49A-expressing T cells were unresponsive on target cells that expressed H-2Dd, but responded against target cells without H-2Dd. However, this inhibition could be overcome by increasing the peptide concentration or by addition of anti-Ly49A F(ab')2 fragments. Thus, rather than behaving as simple "off" switches, our data indicate that Ly49 receptors modulate T cell signaling so that higher amounts of activating signals are required for effector-cell responses.

Transgenic expression of Ly49A on T cells impairs a specific antitumor response

Inhibitory MHC receptors determine the reactivity and specificity of NK cells. These receptors can also regulate T cells by modulating TCR-induced effector functions such as cytotoxicity, cytokine production, and proliferation. Here we have assessed the capacity of mouse T cells expressing the inhibitory MHC class I receptor Ly49A to respond to a well-defined tumor Ag in vivo using Ly49A transgenic mice. We find that the presence of Ly49A on the vast majority of lymphocytes prevents the development of a significant Ag-specific CD8+ T cell response and, consequently, the rejection of the tumor. Despite minor alterations in the TCR repertoire of CD8+ T cells in the transgenic lines, precursors of functional tumor-specific CD8+ T cells exist but could not be activated most likely due to a lack of appropriate CD4+ T cell help. Surprisingly, all of these effects are observed in the absence of a known ligand for the Ly49A receptor as defined by its ability to regulate NK cell function. Indeed, we found that the above effects on T cells may be based on a weak interaction of Ly49A with Kb or Db class I molecules. Thus, our data demonstrate that enforced expression of a Ly49A receptor on conventional T cells prevents a specific immune response in vivo and suggest that the functions of T and NK cells are differentially sensitive to the presence of inhibitory MHC class I receptors.

Sequential analysis of HLA-C-specific killer cell inhibitory receptor (CD158b) expressing peripheral blood mononuclear cells during chronic graft-versus-host disease

We have sequentially investigated the expression of natural killer cell inhibitory receptors (KIRs) for HLA-C (CD158b) on peripheral blood mononuclear cells (PBMC) in three patients with extensive chronic graft-versus-host disease (cGVHD) after allogeneic bone marrow transplantation (alloBMT). Clinical symptoms of cGVHD were not cured and worsened in the first patient whose CD158b-positive cells increased to 18.5% during cGVHD and decreased to 9.4% at 8 months after transplantation. On the other hand, cGVHD was cured and did not relapse in the second patient whose CD158b-positive cells increased up to 45.9% during cGVHD and sustained 19.4% at 8 months after transplantation. In contrast, CD158b-positive cells were less than 10% during the course of cGVHD in the third patient, and her cGVHD did not respond to treatment. Therefore, it appears that chronic allostimulation augments the expansion of CD158b-positive cells and these expanded CD158b-positive cells may have some role in the control of alloresponse in some patients.

Roles of the SHP-1 tyrosine phosphatase in the negative regulation of cell signalling

The critical role for the SH2 domain-containing SHP-1 tyrosine phosphatase in regulating haemopoietic cell behaviour was initially revealed by data linking SHP-1 deficiency to the systemic autoimmunity and severe inflammation exhibited by motheaten mice. This discovery laid the groundwork for the identification of SHP-1 as an inhibitor of activation-promoting signalling cascades and for the coincident demonstration that protein tyrosine phosphatases (PTPs) such as SHP-1 show considerable specificity with respect to the mechanisms whereby they modulate the biochemical and biological sequelae of extracellular simulation. As outlined in this review, SHP-1 has now been implicated in the regulation of a myriad of signalling cascades and cell functions. As a result, the cumulative data generated from studies of this PTP have elucidated not only the functional relevance of SHP-1, but also a number of novel paradigms as to the molecular mechanisms whereby signalling cascades are regulated so as to either augment or abrogate specific cell behaviours.

Killer cell activating receptors function as costimulatory molecules on CD4+CD28null T cells clonally expanded in rheumatoid arthritis

Expansion of CD4+CD28null T cells is a characteristic finding in patients with rheumatoid arthritis. Despite lacking CD28 molecules, these unusual CD4 T cells undergo clonal proliferation and form large and long-lived clonal populations. They produce high levels of IFN-gamma, exhibit autoreactivity, and have cytolytic function. The mechanisms facilitating the expansion and longevity of CD4+CD28null T cell clones in vivo are unknown. Here, we report that CD4+CD28null, but not CD4+CD28+, T cells express MHC class I-recognizing receptors normally found on NK cells. CD4+CD28null T cells preferentially expressed killer cell activating receptors (KAR), often in the absence of killer cell inhibitory receptors. Cross-linking of KAR molecules enhanced the proliferative response to TCR-mediated stimulation, but not the cytolytic function of CD4+CD28null T cells, suggesting different signaling pathways in CD4 T cells and NK cells. Triggering of KAR signaling led to the phosphorylation of several cellular targets, although the pattern of phosphorylation differed from that induced by the TCR. Aberrant expression of KAR molecules in the absence of inhibitory receptors and in the appropriate HLA setting may lead to the clonal outgrowth of autoreactive CD4+CD28null T cells commonly seen in rheumatoid arthritis.

Characterization of gammadelta T cells expressing CD158b, a killer cell inhibitory receptor, in a patient with chronic CD4(+) lymphocytopenia and disseminated Mycobacterium intracellulare infection

A population of Vdelta1(+)Vgamma9(-) gammadelta T cells that represented almost the totality (84%) of circulating lymphocytes in a patient with chronic, non-HIV-related, CD4 lymphocytopenia complicated by a disseminated Mycobacterium intracellulare infection was characterized. These gammadelta(+) T cells expressed a single killer inhibitory receptor (CD158b) and their phenotype (CD8(+)CD57(+)CD27(-)CD28(-)) indicated that, although CD45RA(+), they were not naive. However, the absence of large granular lymphocyte morphology, the impaired proliferative activity, the high susceptibility to apoptosis, and the total lack of cytotoxic ability suggested that these gammadelta cells were in a resting state. A high percentage of the cells did not harbor the CD11b integrin alpha chain and exhibited a decreased capability to bind endothelial cells. This defect might represent the mechanism whereby they remained trapped in the circulation.

Dissimilar anti-tumour reactions induced by tumour cells engineered with the interleukin-2 or interleukin-15 gene in nude mice

Interleukin (IL)-15 shares immuno-stimulatory properties with IL-2 and is a potent inducer of natural killer (NK) cell function. The major histocompatibility complex (MHC) class I-negative human small cell lung cancer (SCLC) cell line N592, engineered to express a modified IL-15 cDNA (N592/IL-15), secreted biologically active IL-15 (300-500 pg/ml), capable of boosting T-cell proliferation and NK activity 'in vitro'. The effect of IL-15 gene transfer on natural immunity 'in vivo' was assessed by xenotransplants in nude mice and compared with that of the IL-2 gene. N592 cells engineered with IL-2 (N592/IL-2) were promptly rejected, while N592/IL-15 displayed a significant delay in tumour growth and a slightly reduced take rate. However, in NK-depleted nude mice, N592/IL-15 displayed the same growth kinetics as unmodified N592 cells, and N592/IL-2 grew with slightly reduced kinetics. An impressive reactive cell infiltration, consisting mainly of macrophages and granulocytes, was associated with N592/IL-2 tumour rejection, while a more evident recruitment of NK cells was found in N592/IL-15 tumours. In both N592 transfected tumours, we found expression of chemoattractant molecules, such as granulocyte macrophage-colony stimulating factor (GM-CSF) and monocyte chemoattractant protein (MCP)-1, while macrophage inflammatory protein (MIP)-2 was produced by endothelial cells only in N592/IL-2 tumours. In this tumour, very few and severely damaged microvessels were found, while microvessels were numerous in N592/IL-15 tumours. The potent recruitment of NK cells mediated by IL-15 gene transfer suggests its possible therapeutic use in tumours lacking MHC class I.

BCR-ABL directed immunotherapy: a virtual reality?

Nearly ten years of research on the feasibility of specific immunotherapy targeting the junctional regions of BCR-ABL has considerably increased our knowledge of which MHC alleles might present BCR-ABL peptides, yet has failed to provide us with definite proof of appropriate processing of the hybrid oncoprotein into such antigenic peptides. This paper intends to provide an overview of the current state of affairs as well as to delineate limitations and future directions of this line of research.

Regulation of T cell function by NK cell receptors for classical MHC class I molecules

Inhibitory receptors for MHC class I molecules were initially characterised on NK cells. Human and mouse NK cell receptors (NKRs) are also expressed on T cells, predominantly on a subset of memory-phenotype CD8(+) T cells. This review focuses on the precise determination of interactions between NKRs and MHC class I, as well as on the unexpected in vivo function of NKRs on T cells.

Expression of CD94/NKG2 subtypes on tumor-infiltrating lymphocytes in primary and metastatic melanoma

Natural killer receptors are expressed both on natural killer populations and subpopulations of T cells, mainly alpha/beta TCR+CD8+ T cells. We have characterized the expression of the C-type lectin natural killer receptor CD94/NKG2 on tumor-infiltrating lymphocytes in primary and metastatic melanoma lesions. By immunohistochemistry, 5-10% of the tumor-infiltrating lymphocytes, both in primary and metastatic lesions, expressed CD94. More than 95% of these CD94+ cells coexpressed CD8 and the percentage of CD94 expression within the CD8+ cell population ranged from 5 to 20% with a higher expression in metastatic lesions. CD94/NKG2 exists both in an inhibitory and an activating form; thus, it was necessary to determine whether the inhibitory CD94/NKG2-A/B, the activating CD94/NKG2-C/E, or both were expressed on tumor-infiltrating lymphocytes. Reverse transcription-polymerase chain reaction using specific primers for NKG2-A/B and C/E mRNA revealed the presence of NKG2-C/E in all primary and metastatic lesions. In contrast, the inhibitory NKG2-A/B was only present in 50% of primary tumors whereas 80% of tumor-infiltrating lymphocytes in metastatic lesions expressed these transcripts. In healthy humans, the mean number of inhibitory natural killer receptors is higher than that of activating receptors, but the opposite was true for tumor-infiltrating lymphocytes in melanoma. The reversal of the ratio of inhibitory to activating natural killer receptors among tumor-infiltrating lymphocytes suggests a regulated event due to either specific factors within the tumor microenvironment, preferential homing of T cell subsets, or certain stages of T cell activation.

Natural cytotoxicity receptors that trigger human NK-cell-mediated cytolysis

Natural killer (NK) cells can detect whether cells have undergone tumour transformation or viral infection. The discovery of specific inhibitory receptors for major histocompatibility complex class I molecules clarified the basis of this discrimination. However, the receptors responsible for NK-cell triggering in the process of natural cytotoxicity remained elusive until recently. Here, Alessandro Moretta and colleagues describe the identification and characterization of several such receptors.

Zinc-altered immune function and cytokine production

Although the intriguing role of zinc as an essential trace element for immune function is well established, particular progress in determining the molecular principles of action of this ion was made recently. Leukocyte responsiveness is delicately regulated by zinc concentration. Zinc deficiency as well as supraphysiologic levels impair immune function. Furthermore, the activities of many immunostimulants frequently used in immunologic studies are influenced by zinc concentration. Therefore, our knowledge from in vitro studies is widely dependent on the zinc concentration, and when not in physiologic range, immunologic responses are artificially low. Decreased production of TH1 cytokines and interferon-alpha by leukocytes in the healthy elderly person is correlated with low zinc serum level. The defect in interferon-alpha production is reconstituted by the addition of physiologic amounts of zinc in vitro. Interestingly, zinc induces cytokine production by isolated leukocytes. Zinc induces monocytes to produce interleukin-1, interleukin-6 and tumor necrosis factor-alpha in peripheral blood mononuclear cells and separated monocytes. This effect is higher in serum-free medium. However, only in the presence of serum does zinc also induce T cells to produce lymphokines. This effect on T cells is mediated by cytokines produced by monocytes. Stimulation also requires cell-to-cell contact of monocytes and T cells. Information is presented to illustrate the concepts that the zinc concentration must be taken into account whenever in vitro studies are made or complex alterations of immune functions are observed in vivo.

Increased expression of non-functional killer inhibitory receptor CD94 in CD8+ cells of myeloma patients

Different MHC class I-specific killer inhibitory receptors (KIRs) are expressed in vivo by a minor fraction of activated memory CD8+ cells. It has been postulated that KIRs may 'fine-tune' specific responses by altering their threshold of activation by the TCR-CD3 complex. We have previously shown that, in multiple myeloma (MM) patients, a large fraction of peripheral blood CD8+ cells display the phenotype of chronically activated memory T cells (CD38+, HLA-DR+, CD25-, CD45R0+, CD28-). We investigated the expression of KIRs on MM T cells and determined their possible influence on cytolytic responses elicited via the CD3-TCR complex. The expression of CD94, a molecule that is part of a heterodimeric KIR recognizing the non-classical MHC surface HLA-E molecule, was almost threefold higher in MM T cells than in age-matched normal control subjects (P < 0.0001). CD94 expression was preferentially confined to CD8+ cells but not restricted to activated (HLA-DR+) and/or memory (CD45R0+) T cells. Unlike normal T cells, in which CD94 is assembled with glycoproteins of the NKG2 family to form functional receptors with activating or inhibitory properties, most CD94+ MM T cells were devoid of both the NKG2-A and NKG2-C glycoproteins detected in the inhibitory or activating form respectively. CD94 blockade did not significantly affect either T-cell proliferation or cytotoxic T-lymphocyte generation induced by the myeloma-derived cell lines NCI and RPMI 8226. Similarly, the cytolytic activity induced by direct anti-CD3-mediated targeting of MM T cells to FCR+ P815 target cells was unaffected by the addition of anti-CD94 and/or anti-NKG2-A/C monoclonal antibodies (mAbs). These data indicate that the large majority of MM CD8+ cells do not express a functional CD94 receptor. Thus, their ability to 'fine-tune' an appropriate immune response against tumour cells can be impaired.

Surface receptors delivering opposite signals regulate the function of human NK cells

The effector function of NK cells is regulated by a number of positive and negative signals. The receptors involved in the negative regulation of NK cells are known since several years: they are represented by different families of MHC-specific receptors characterized by ITIM sequences in their cytoplasmic tail. In contrast, the surface molecules responsible for NK cell activation in the process of natural cytotoxicity and tumor cell lysis have remained elusive until recently. Three distinct NK-specific molecules termed 'natural cytotoxicity receptors' (NCR) have recently been identified and cloned. They play a complementary role in mediating NK cell activation in the interaction and lysis of most tumor cells. They are associated with different ITAM-containing adaptor proteins mediating signal transduction. Molecular cloning revealed novel members of the Ig superfamily displaying a limited homology with known human receptors.

Expression of HLA-C-specific natural killer cell receptors (CD158a and CD158b) on peripheral blood mononuclear cells after allogeneic bone marrow transplantation

We investigated the expression of natural killer cell receptors (NKRs) for HLA-C on peripheral blood mononuclear cells (PBMCs) in 23 allogeneic bone marrow transplantation (allo-BMT) patients to analyse the role of NKRs in alloresponse concerning graft-versus-host disease (GVHD). CD158a expression was low and there was little change in the expression after allo-BMT. Also, there was no difference in the proportion of CD158a+/CD3- after allo-BMT. In contrast, the proportion of CD158b+/CD3- cells, mainly NK cells, increased in the early stage (< 2 months) after allo-BMT and then gradually decreased (3.3 +/- 2.6% before BMT vs. 15.4 +/- 8. 6% in the early stage after BMT, 8.5 +/- 4.9% during the period 3-6 months after BMT and 7.0 +/- 3.0% > 6 months after BMT; P < 0.05). However, CD158b expression on CD3+ T cells increased 3 months after allo-BMT (1.1 +/- 1.1% before BMT vs. 5.1 +/- 7.7% during the period 3-6 months after BMT and 3.0 +/- 2.4% > 6 months after BMT, P < 0. 05). The highest percentages of CD158 expression in patients without chronic GVHD (cGVHD) and those with cGVHD were compared. The percentage of CD158b+/CD3+ cells and also that of CD158b+/CD8+ cells were significantly increased in patients with cGVHD compared with those in patients without cGVHD (2.6 +/- 2.0% vs. 8.0 +/- 11.2% and 2.3 +/- 1.5% vs. 8.3 +/- 11.7% respectively; P < 0.05). The exact clinical relevance of these CD158b-expressing cells is not clear. However, there is an interesting possibility that CD158b-expressing cells play some role in the regulation of GVHD after allo-BMT.