Biomedical subjects

Daniela Pende

Publications and source records attributed to Daniela Pende.

29 records · Page 2Linked to original sources

PubMed2004

Different checkpoints in human NK-cell activation.

After the discovery, in humans and mice, of inhibitory natural killer (NK) receptors specific for MHC class I molecules, the mechanism by which NK cells kill tumor or virus-infected cells was thought to be clarified: NK cells would kill those target cells that have lost, or underexpress, MHC class I molecules. However, a more complex scenario has recently emerged. For example, certain NK cells express insufficient amounts of triggering receptors, and target cells can lack ligands for such receptors. Thus, it appears that the activation of NK cells and their potentially harmful effector functions are under the control of different checkpoints.

Animals↗

PubMed2004

Learning how to discriminate between friends and enemies, a lesson from Natural Killer cells.

Human Natural Killer cells express a large array of surface receptors that are involved in the regulation of the different NK cell functions. Some of these receptors, by sensing the expression of HLA class I on potential target cells, deliver negative signals that inhibit the NK-mediated killing. In the absence of such inhibitory interactions, other receptors are allowed to transduce activating signals that result in NK-mediated attack of tumor- or virus-transformed cells. The function of these main activating receptors is supported and enhanced by the simultaneous engagement of different co-receptors. Finally, the ability of NK cells to interact with normal, non-transformed other cells such as dendritic cells (DC) appears to crucially contribute to the regulation of both innate and adaptive immune responses.

Histocompatibility Antigens Class I↗

PubMed2003

Identification of PVR (CD155) and Nectin-2 (CD112) as cell surface ligands for the human DNAM-1 (CD226) activating molecule.

Human natural killer (NK) cells express a series of activating receptors and coreceptors that are involved in recognition and killing of target cells. In this study, in an attempt to identify the cellular ligands for such triggering surface molecules, mice were immunized with NK-susceptible target cells. On the basis of a functional screening, four mAbs were selected that induced a partial down-regulation of the NK-mediated cytotoxicity against the immunizing target cells. As revealed by biochemical analysis, three of such mAbs recognized molecules of approximately 70 kD. The other mAb reacted with two distinct molecules of approximately 65 and 60 kD, respectively. Protein purification followed by tryptic digestion and mass spectra analysis, allowed the identification of the 70 kD and the 65/60 kD molecules as PVR (CD155) and Nectin-2 delta/alpha (CD112), respectively. PVR-Fc and Nectin-2-Fc soluble hybrid molecules brightly stained COS-7 cells transfected with the DNAM-1 (CD226) construct, thus providing direct evidence that both PVR and Nectin-2 represent specific ligands for the DNAM-1 triggering receptor. Finally, the surface expression of PVR or Nectin-2 in cell transfectants resulted in DNAM-1-dependent enhancement of NK-mediated lysis of these target cells. This lysis was inhibited or even virtually abrogated upon mAb-mediated masking of DNAM-1 (on NK cells) or PVR or Nectin-2 ligands (on cell transfectants).

Amino Acid Sequence↗

PubMed2003

Cellular and molecular basis of natural killer and natural killer-like activity.

The capability of killing various tumors or cells infected by certain viruses is a property shared by natural killer (NK) cells and by a subset of cytolytic T lymphocytes (CTLs) termed NK-CTL. Recent analysis of the molecular basis in these phenomena, however, revealed rather different molecular mechanisms. Thus, while NK cell cytotoxicity is regulated by a complex balance between activating signals (delivered by non HLA-class I-specific triggering receptors) and inhibitory signals (delivered by HLA-class I-specific receptors) the effector function of NK-CTL reflects the TCR-mediated recognition of the poorly polymorphic HLA-E.

Animals↗

PubMed2003

NKG2D engagement of colorectal cancer-specific T cells strengthens TCR-mediated antigen stimulation and elicits TCR independent anti-tumor activity.

The NKG2D receptor is expressed by human NK, gammadelta T and alpha/beta T lymphocytes and its engagement results in the stimulation of effector cells. We evaluated the role of NKG2D receptor in anti-colorectal cancer (CRC) immune response. The cell surface expression of stress-inducible NKG2D ligands MICA/B (MHC class I-related chain molecules A/B) and ULBP (UL16 binding protein) by a panel of CRC lines was evaluated by flow cytometry. MICA and ULBP2/3 were widely expressed by the analyzed lines, with a minority of them being also ULBP-1+, whereas MICB was undetectable. CD8+ and CD4+ HLA-restricted anti-tumor T cell clones of a CRC patient were used to evaluate whether NKG2D engagement could mediate tumor recognition. Three out of four CD8+ T cell clones recognized the autologous tumor with a marginal NKG2D engagement, a finding that was correlated with the weak expression of NKG2D ligands by the autologous tumor. On the contrary, NKG2D triggering of these CD8+ T cell clones induced recognition of allogeneic CRC lines showing high expression of MICA and ULBP. A costimulatory role of NKG2D was observed with one CD4+/NKG2D+ T cell clone when stimulated by tumors sharing the HLA class II alleles and expressing NKG2D ligands. Taken together these data indicate that the engagement of NKG2D, depending on the expression of its ligands by target cells, can influence the pattern of anti-tumor reactivity by T lymphocytes.

CD8-Positive T-Lymphocytes↗

PubMed2002

Major histocompatibility complex class I-related chain A and UL16-binding protein expression on tumor cell lines of different histotypes: analysis of tumor susceptibility to NKG2D-dependent natural killer cell cytotoxicity.

NKG2D, together with NKp46 and NKp30, represents a major triggering receptor involved in the induction of cytotoxicity by both resting and activated human natural killer cells. In this study, we analyzed the expression and the functional relevance of MHC class I-related chain A (MICA) and UL16 binding protein (ULBP), the major cellular ligands for human NKG2D, in human tumor cell lines of different histological origin. We show that MICA and ULBP are frequently coexpressed by carcinoma cell lines, whereas MICA is expressed more frequently than ULBP by melanoma cell lines. Interestingly, the MICA(-) ULBP(+) phenotype was detected in most T cell leukemia cell lines, whereas the MICA(-) ULBP(-) phenotype characterized all acute myeloid leukemia and most B-cell lymphoma cell lines analyzed. These results, together with functional experiments, based on monoclonal antibody-mediated blocking of either NKG2D or its ligands, showed that killing of certain MICA(-) cell tumors is at least in part NKG2D dependent. Indeed, leukemic T cells as well as certain B-cell lymphomas were killed in a NKG2D-dependent fashion upon recognition of ULBP molecules. Moreover, ULBP could induce NKG2D-mediated NK cell triggering also in tumors coexpressing MICA. Our data suggest that the involvement of NKG2D in natural killer cell-mediated cytotoxicity strictly correlates with the expression and the surface density of MICA and ULBP on target cell tumors of different histotypes.

Carrier Proteins↗

PubMed2002

Defective expression and function of natural killer cell-triggering receptors in patients with acute myeloid leukemia.

The cytolytic function of natural killer (NK) cells is induced by the engagement of a series of activating receptors and coreceptors some of which have recently been identified and collectively termed natural cytotoxicity receptors (NCRs). Here, we analyzed the cytolytic function of NK cells obtained from patients with acute myeloid leukemia (AML). In sharp contrast with healthy donors, in most (16 of 18) patients with AML the majority of NK cells displayed low NCR surface density (NCR(dull)). This phenotype correlated with a weak cytolytic activity against autologous leukemic cells that could not be reversed by the monoclonal antibody-mediated disruption of HLA class I/killer immunoglobulinlike receptor interaction. The remaining 2 patients were characterized by NK cells having an NCR(bright) phenotype. Surprisingly, although displaying NCR-mediated cytolytic activity, these NCR(bright) NK cells were unable to kill autologous leukemic blasts. Importantly, the leukemic blasts from these 2 patients were also resistant to lysis mediated by normal NCR(bright) allogeneic NK cells. Our study suggests that in most instances the inability of NK cells to kill autologous leukemic blasts is consequent to low NCR surface expression. In few cases, however, this failure appears to involve a mechanism of tumor escape based on down-regulation of ligands relevant for NCR-mediated target cell recognition.

Acute Disease↗

PubMed2002

Human natural killer cells: their origin, receptors and function.

The term of "natural killer" (NK) cells was originally assigned on a merely functional basis to lymphoid cells capable of lysing certain tumors in the absence of prior stimulation. However, both their origin and the molecular mechanism(s) involved in their function remained a mystery for many years 1. Regarding their origin, clear evidence has now been provided both in mouse and in man that NK and T cells may derive from a common precursor 2-5. Thus, mature NK cells can be obtained in vitro from CD34(+) cells isolated from umbilical cord blood, bone marrow (BM) and even human thymus 6 when cultured in the presence of appropriate feeder cells or IL-15. The molecular mechanism allowing NK cells to discriminate between normal and tumor cells, predicted by the "missing self hypothesis" 7, has been clarified only in recent years. Thus, NK cells recognize MHC class I molecules through surface receptors delivering signals that inhibit, rather than activate, NK cells. As a consequence, NK cells lyse target cells that have lost (or express insufficient amounts of) MHC class I molecules, as frequently occurs in tumors and in cells infected by certain viruses.

Adaptation, Physiological↗

PubMed2002

Human NK cells and their receptors.

The past decade has witnessed important progress in our understanding of how natural killer (NK) cells function. This is primarily consequent to the identification and functional characterization of MHC-specific inhibitory receptors that allow NK cells to discriminate between normal cells and potentially harmful cells that have lost or express insufficient amounts of MHC class I molecules. More recently, a number of activating receptors or coreceptors have been identified that are involved in the process of natural cytotoxicity but may also play a role in the direct recognition of pathogen-associated structures. Surprisingly, none of the triggering receptors identified in NK cells appears to be involved in the "NK-like activity" of a subset of CD8(+) cytolytic T lymphocytes. In this case, lysis of NK-susceptible tumor target cells is the result of the TCR alpha/beta-mediated recognition of HLA-E. The potent cytolytic activity of NK cells as well as their unique mode of functioning may be exploited in therapy. An important breakthrough is the recent report that "alloreactive" NK cells, generated in haploidentical bone marrow transplantation in patients with acute myeloid leukemias, may efficiently prevent leukemic relapses as well as graft rejection and graft-vs.-host disease. This may lead to a true revolution in bone marrow transplantation, based on the exploitation of appropriate HLA-Cl I mismatches that can put NK cells in action.

Antigens, CD↗

PubMed2002

Haemophagocytic lymphohistiocytosis: proposal of a diagnostic algorithm based on perforin expression.

Haemophagocytic lymphohistiocytosis (HLH) is a rare, fatal disorder of early infancy. Mutations of the PRF1 gene have been identified in a subset of patients. However, the distinction between the different genetically determined and environmental subtypes of the disease remains a major issue to be solved. This may result in delayed or inappropriate application of bone marrow transplantation (BMT). We propose an algorithm that uses a combination of three rapid laboratory tests, i.e. perforin expression by peripheral lymphocytes, assessment of the behaviour of the 2B4 lymphocyte receptor and natural killer (NK) cell activity, to identify the different subgroups of HLH. In 19 patients diagnosed according to current criteria, we tested perforin expression, 2B4 receptor function and NK cell activity. PRF1 mutations were found in all seven patients showing absent perforin expression. In one male with abnormal behaviour of the 2B4 receptor, SH2D1A mutation confirmed the diagnosis of X-linked lymphoproliferative disease. Four patients with normal NK cell activity had evidence of associated infections. Of the seven with impaired NK cell activity, two had a probable genetically determined subtype of HLH and five appeared as sporadic, infection-associated cases. Improving the diagnostic approach may restrict the use of BMT, the only recognized curative treatment, to HLH patients with a documented poor prognosis while patients with milder disorders may be treated less intensively. Our flow chart could also lead to better selection of patients for specific gene analysis.

Algorithms↗

PubMedDate not supplied

Downregulation and/or release of NKG2D ligands as immune evasion strategy of human neuroblastoma.

Neuroblastoma (NB) is a pediatric extracranial tumor characterized by downregulation of human leukocyte antigen class I and defects of the antigen processing machinery, two features that make it an appropriate target for natural killer (NK)-mediated lysis. NKG2D is an activating immunoreceptor expressed by cytotoxic T lymphocytes and NK cells. The ligands for NKG2D are the major histocompatibility complex class I-related chain (MIC)A and MICB glycoproteins, and the UL-16-binding proteins (ULBPs). Here, the expression of NKG2D ligands was investigated in human primary NB tumors and cell lines because scanty information is available on this issue. MICA, MICB, and ULBP transcripts were found in most tumors and cell lines. MICA protein was detected in some NB cell lines but not in primary tumors. A soluble form of MICA (sMICA) was identified in most patient sera and in some cell line supernatants. sMICA downregulated surface NKG2D in normal peripheral blood CD8(+) cells and decreased NK-mediated killing of MICA(+) NB cells. MICB was detected exclusively in the cytosol of primary tumors and cell lines. Approximately 50% of primary tumors expressed ULBP-2, but not ULBP-1 or -3. ULBP-3 was expressed in 5 of 9 cell lines, ULBP-2 in 2 of 9, whereas ULBP-1 was never detected. These studies delineate novel potential pathways of tumor escape and immunodeficiency in NB.

CD8-Positive T-Lymphocytes↗