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Alessandro Moretta

Publications and source records attributed to Alessandro Moretta.

83 records · Page 5Linked to original sources
PubMed2002

Crystallization and preliminary crystallographic characterization of the extracellular Ig-like domain of human natural killer cell activating receptor NKp44.

The cytolytic activity of human natural killer (NK) cells is regulated by fine balancing between activating and inhibitory signals related to distinct families of inhibitory and triggering receptor molecules. The recent identification of NKp44, a triggering receptor selectively expressed by activated NK cells and playing an important role in the natural cytotoxicity of these cells, opens the way to the characterization of the mechanisms involved in NKp44-mediated NK-cell activation on a structural basis. For this purpose, the NKp44 extracellular Ig-like domain was cloned, overexpressed, refolded and crystallized. Diffraction intensities were collected to a resolution limit of 2.2 A on a synchrotron source. NKp44 extracellular Ig-like domain crystals belong to the hexagonal space group P6(2)22 (or P6(4)22), with unit-cell parameters a = b = 60.4, c = 197.2 A, gamma = 120 degrees. Evaluation of the crystal packing parameter suggests the presence of one molecule (13.8 kDa) per asymmetric unit, with a solvent volume of 67%.

Amino Acid Sequence↗
PubMed2002

Identification of HLA-E-specific alloreactive T lymphocytes: a cell subset that undergoes preferential expansion in mixed lymphocyte culture and displays a broad cytolytic activity against allogeneic cells.

Previous studies showed that a subset of CD8(+) cytolytic T lymphocytes expressing HLA class I-specific natural killer inhibitory receptors (iNKR) is characterized by the ability to recognize HLA-E and to mediate T cell receptor-dependent killing of different NK cell-susceptible tumor target cells. In this study, we show that this CD8(+) T cell subset can also undergo extensive proliferation in mixed lymphocyte cultures in response to allogeneic cells. Analysis of their cytolytic activity revealed a broad specificity against a panel of allogeneic phytohemagglutinin-induced blasts derived from HLA-unmatched donors. On the other hand, autologous and certain allogeneic phytohemagglutinin blasts were resistant to lysis. We used as target cells the transporter associated with antigen processing (TAP)-2(-/-) murine RMA-S cell line cotransfected with beta2-microglobulin and HLA-E*01033. On loading these cells with different HLA-E-binding peptides derived either from HLA class I leader sequences or viral proteins, we could show that HLA-E-specific cytolytic T lymphocytes recognized many, but not all, peptides analyzed. These data suggest that these cells may recognize, on allogeneic cells, HLA-E with peptides that are not present in the host of origin. In addition to their ability to proliferate in response to allogeneic stimulation and to lyse, most allogeneic cells may have important implications in transplantation and in antitumor immune responses.

Alleles↗
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

Early expression of triggering receptors and regulatory role of 2B4 in human natural killer cell precursors undergoing in vitro differentiation.

In this study we analyzed the progression of cell surface receptor expression during the in vitro-induced human natural killer (NK) cell maturation from CD34(+) Lin(-) cell precursors. NKp46 and NKp30, two major triggering receptors that play a central role in natural cytotoxicity, were expressed before the HLA class I-specific inhibitory receptors. Moreover, their appearance at the cell surface correlated with the acquisition of cytolytic activity by developing NK cells. Although the early expression of triggering receptors may provide activating signals required for inducing further cell differentiation, it may also affect the self-tolerance of developing NK cells. Our data show that a fail-safe mechanism preventing killing of normal autologous cells may be provided by the 2B4 surface molecule, which, at early stages of NK cell differentiation, functions as an inhibitory rather than as an activating receptor.

Antigens, CD↗
PubMed2002

Analysis of natural killer cells in TAP2-deficient patients: expression of functional triggering receptors and evidence for the existence of inhibitory receptor(s) that prevent lysis of normal autologous cells.

Natural killer (NK) cells are characterized by the ability to kill cells that lack HLA class I molecules while sparing autologous normal (HLA class I(+)) cells. However, patients with transporter-associated antigen processing (TAP) deficiency, though displaying strong reductions of HLA class I surface expression, in most instances do not experience NK-mediated autoimmune phenomena. A possible mechanism by which TAP(-/-) NK cells avoid autoreactivity against autologous HLA class I-deficient cells could be based on either quantitative or qualitative defects of surface receptors involved in NK cell triggering. In this study we show that NK cells derived from 2 patients with TAP2(-/-) express normal levels of all known triggering receptors. As revealed by the analysis of polyclonal and clonal NK cells, these receptors display normal functional capabilities and allow the killing of a panel of NK-susceptible targets, including autologous B-LCLs. On the other hand, TAP2(-/-) NK cells were unable to kill either allogeneic (HLA class I(+)) or autologous (HLA class I(-) ) phytohemagglutinin (PHA) blasts even in the presence of anti-HLA class I monoclonal antibody. These data suggest that TAP2(-/-) NK cells express still unknown inhibitory receptor(s) capable of down-regulating the NK cell cytotoxicity on binding to surface ligand(s) expressed by T cell blasts. Functional analyses, both at the polyclonal and at the clonal level, are consistent with the concept that the putative inhibitory receptor is expressed by virtually all TAP2(-/-) NK cells, whereas it is present only in rare NK cells from healthy persons. Another possibility would be that TAP2(-/-) NK cells are missing a still unidentified triggering receptor involved in NK cell-mediated killing of PHA blasts.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
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

Natural killer cells and dendritic cells: rendezvous in abused tissues.

Natural killer (NK) cells and dendritic cells (DCs) are two types of specialized cell of the innate immune system, the reciprocal interaction of which results in a potent, activating cross-talk. For example, DCs can prime resting NK cells, which, in turn, after activation, might induce DC maturation. However, NK cells negatively regulate the function of DCs also by killing immature DCs in peripheral tissues. Moreover, a subset of NK cells, after migration to secondary lymphoid tissues, might have a role in the editing of mature DCs based on the selective killing of mature DCs that do not express optimal surface densities of MHC class I molecules. So, cognate interactions between NK cells and DCs provide a coordinated mechanism that is involved not only in the regulation of innate immunity, but also in the promotion of appropriate downstream adaptive responses for defence against pathogens.

Animals↗
PubMed2002

IFN-gamma protects short-term ovarian carcinoma cell lines from CTL lysis via a CD94/NKG2A-dependent mechanism.

IFN-gamma regulates the immunogenicity of target cells by increasing their expression of HLA class I molecules. This facilitates the T cell receptor-mediated recognition by CD8(+) T cells but decreases target cell sensitivity to lysis by NK cells due to engagement of inhibitory NK receptors. In this study, short-term tumor cell lines from patients with advanced ovarian carcinomas were established. We demonstrate the paradoxical finding that IFN-gamma treatment of these short-term ovarian carcinoma cell lines (OVACs) resulted in resistance of tumor cells to lysis by peptide- and allospecific CD8(+) T cells. Blocking experiments revealed that this phenomenon was dependent on enhanced inhibitory signalling via CD94/NKG2A receptors expressed on the effector cells. This was associated with increased expression of HLA-E mRNA and HLA-G at the protein level in IFN-gamma-treated OVACs. Furthermore, pulsing of untreated OVACs with the leader sequence peptide of HLA-G protected these cells from lysis by CTLs, thus mimicking the inhibitory effect of IFN-gamma. This study provides evidence that CD94/NKG2A receptors play an important role in regulating T cell activity against tumors and shows that IFN-gamma modulation of target cells may shift the balance of triggering and inhibitory signals to T cells, turning off their cytolytic activity.

Antigens, CD↗