Biology of natural killer cells

Identification of murine natural killer cell subsets with monoclonal antibodies derived from 129 anti-C57BL/6 immune spleen cells

Two hybridomas producing monoclonal antibodies reactive with natural killer cells were selected after fusion of 129 anti-C57BL/6 immune spleen cells with P3X63-Ag8.653 myeloma cells. Treatment of normal or stimulated cells with the 4LO3311 or the 4LO439 mAb and rabbit complement inhibited natural killer and antibody-dependent cellular cytotoxicities, whereas cell lysis mediated by natural cytotoxic cells, cytotoxic T lymphocytes, or activated macrophages was unaffected. Lymphokine-activated killer activity was reduced after complement-mediated treatment of interleukin-2-stimulated spleen cells with the 4LO3311 mAb but not after treatment with the 4LO439 mAb. Similar treatment of spleen cells with either mAb had no effect on the mitogen-induced proliferation of T and B lymphocytes and did not alter the frequency of antibody plaque-forming cells in immune spleen cell suspensions. The 4LO3311 and 4LO439 mAbs thus appear to be specific for NK cells and their progeny. Flow cytometry analysis confirmed that 4LO3311+ and 4LO439+ cells are phenotypically identical to NK-1.1+ cells. The epitope recognized by the 4LO3311 mAb has the same strain distribution as the NK-2.1 alloantigen previously detected with NZB anti-BALB/c antiserum, whereas the 4LO439 mAb appears to identify a new NK cell marker exclusively expressed in mice of C57BL lineage. The relationship of the molecules detected with either the 4LO3311 or the 4LO439 mAb to polymorphic antigens of the Ly series is discussed.

DNA sequence analysis of NKG2, a family of related cDNA clones encoding type II integral membrane proteins on human natural killer cells

We have previously described the isolation of a cDNA clone, designated NKG2, that was expressed in all natural killer (NK) cells tested but not in T or B cells. In the present communication, the original isolate, when used to probe a cDNA library prepared from a CD3- NK cell clone, was found to crosshybridize with a family of transcripts that fell into four distinct groups designated NKG2-A, -B, -C, and -D. Full-length cDNA sequences were determined for each group, and the DNA and inferred peptide sequences were analyzed. All four transcripts encode type II membrane proteins of 215-233 amino acids. NKG2-A and -B peptides appear to be alternative splicing products of a single gene. NKG2-C is highly homologous with group A, having 94% homology in the external (COOH-terminal) domain and 56% homology throughout the internal and transmembrane regions. NKG2-D is distantly but significantly related (21% amino acid homology) to the first three groups. Therefore, NKG2-A, -C, and -D appear to be encoded by distinct genes within a family of NK cell-specific genes. Peptide sequence homology searches demonstrate that the NKG2 peptides are members of a supergene family that includes several other type II membrane proteins. This family is characterized by the presence of a C-type animal lectin domain, and several of its members have demonstrated transmembrane signaling capability.

In vitro infection of natural killer cells with different human immunodeficiency virus type 1 isolates

Natural killer (NK) cells are a discrete subset of leukocytes, distinct from T and B lymphocytes. NK cells mediate spontaneous non-MHC-restricted killing of a wide variety of target cells without prior sensitization and appear to be involved in initial protection against certain viral infections. Depressed NK cell-mediated cytotoxicity, one of the many immunological defects observed in AIDS patients, may contribute to secondary virus infections. Here we report that clonal and purified polyclonal populations of NK cells, which expressed neither surface CD4 nor CD4 mRNA, were susceptible to infection with various isolates of human immunodeficiency virus type 1 (HIV-1). Viral replication was demonstrated by detection of p24 antigen intracellularly and in culture supernatants, by the presence of HIV DNA within infected cells, and by the ability of supernatants derived from HIV-infected NK cells to infect peripheral blood mononuclear cells or CD4+ cell lines. Infection of NK cells was not blocked by anti-CD4 or anti-Fc gamma RIII monoclonal antibodies. NK cells from HIV-infected and uninfected cultures were similar in their ability to lyse three different target cells. Considerable numbers of cells died in HIV-infected NK cell cultures. These results suggest that loss of NK cells in AIDS patients is a direct effect of HIV infection but that reduced NK cell function involves another mechanism. The possibility that NK cells serve as a potential reservoir for HIV-1 must be considered.

CD2 is functionally linked to the zeta-natural killer receptor complex

Natural killer (NK) cells express two distinct surface receptors capable of triggering cytolytic effector function. The first is CD16, an immunoglobulin Fc receptor that allows NK cells to mediate antibody-dependent killing (ADCC). NK cells express CD16 in association with zeta, a signal-transducing subunit that is also a component of the T cell receptor complex. Activation of NK cells via CD16 results in tyrosine phosphorylation of zeta. The second NK cell triggering receptor is CD2, a 50-55-kDa cell surface molecule that is also expressed on T cells. Here we show that NK cell activation induced by mAb reactive with CD2 (either anti-T11.1 alone or with anti-T11.2 in combination) also results in the tyrosine phosphorylation of zeta. Our results indicate that CD2 is functionally linked to the CD16-zeta complex and suggest that the zeta subunit plays a central role in the signal transduction pathways utilized by NK cells.

Binding interactions of murine natural killer cells with the fungal target Cryptococcus neoformans

Murine natural killer (NK) cells have been shown to inhibit the growth of the yeastlike organism Cryptococcus neoformans both in vivo and in vitro. An essential first step in NK cell-mediated damage of cryptococcal cells is the binding of the NK cell to the cryptococcal cell. The studies presented here focused on the binding event. Electron photomicrographs and three-dimensional reconstructions of NK cell-C. neoformans conjugates show that NK cells bind to cryptococci through many microvilli. This is in contrast to the broad membrane-membrane interactions which form the binding site of NK cell-YAC-1 tumor cell conjugates. NK cell binding to cryptococci is much slower than NK cell binding to YAC-1 targets. Maximal conjugate formation with cryptococcal targets is reached after 2 h, whereas maximal conjugate formation with YAC-1 targets is obtained after 20 min. Once maximum NK cell-C, neoformans conjugate formation is obtained, another 4 h is required before damage to the cryptococcal cells can be detected with the CFU assay. These data indicate that the binding and action of NK cells on C. neoformans cells requires considerably more time than is necessary for similar events to occur in the NK cell-tumor cell model. NK cell membrane integrity is necessary for NK cells to bind to tumor targets, since some disruption of membrane integrity with 0.1 M dimethyl sulfoxide reduces conjugate formation and tumor cell lysis. In contrast, 0.1 M dimethyl sulfoxide did not diminish NK cell binding to cryptococcal targets; however, it significantly reduced cryptococcal growth inhibition. Although we have observed several differences in NK cell binding to the cryptococcal target compared with NK cell binding to tumor cell targets, there are some similarities in binding interactions of NK cells with the two different targets. Disulfide bonding appears to play a role in the binding of NK cells to both targets, since 5 mM 2-mercaptoethanol, a reagent that reduces disulfide bonds, prevented NK cells from binding to the tumor targets as well as the cryptococcal targets. Actin filaments, components of the cytoskeletal network, must be intact for NK cells to bind to YAC-1 cells or cryptococci. Taken together, our data confirm that binding of NK cells to the cryptococcal target is prerequisite to the stages that result in damage to the cryptococcal cell and that there are similarities and differences in NK cell-binding interactions with structurally different target cells.

Functional p75 interleukin-2 receptor expression on the fresh blast cells in childhood acute lymphoblastic leukemia with natural killer cell properties

Neoplastic cells of childhood acute lymphoblastic leukemia (ALL) with natural killer (NK) cell properties were studied for the expression of p75 interleukin-2 receptors (IL-2R) and the receptor functions. Freshly prepared blast cells from a patient with ALL had NK cell properties: (1) the phenotype such as CD56+, CD2+, E-rosette+, CD3-, and CD19-; and (2) the presence of spontaneous cytotoxicity against NK-sensitive K562 target cells. Although p55 Tac antigen was not detectable, there was the expression of p75 IL-2R on the freshly prepared blast cells: 70% of the cells reacted with Mik-beta 1 monoclonal antibody against p75 IL-2R as determined by flow cytometry. Two-color flow cytometry revealed that the blast cells expressed both p75 IL-2R and NKH-1. NK activity of the blast cells was augmented by their treatment with 1,000 U/ml recombinant IL-2 (rIL-2): the cytotoxicity level as percentage lysis increased to 38.7% from 22.0% when the normal lymphocyte value increased to 62.1% from 46.2%. Although the blast cells possessed no apparent level of proliferative capacity, the addition of 1,000 U/ml rIL-2 yielded a 2.7-fold increase in their thymidine uptake. These results demonstrate the expression of functional p75 IL-2R on the patient's blast cells with NK cell properties.

Activation of CD16+ effector cells by rheumatoid factor complex. Role of natural killer cells in rheumatoid arthritis

The role of natural killer (NK) cells in rheumatoid arthritis (RA) remains unclear. A pathogenetic function of rheumatoid factors (RF) also has not been defined. In the present studies, natural killer (NK) cells were examined as a model for FC gamma receptor type III-positive (FC gamma RIII+) cells, with regard to their interaction with RF. NK cell antigen CD16 (FC gamma RIII) and CD56 expression and functional NK and antibody-dependent cell-mediated cytotoxicity (ADCC) activity were compared in peripheral blood lymphocytes and autologous synovial fluid lymphocytes (SFL) of RA patients. Peripheral blood lymphocytes and SFL showed normal CD56 expression. In contrast, both the frequency and the density of CD16 antigen were decreased in SFL. Furthermore, diminished NK cytotoxicity and a significant decrease in ADCC were observed in SF NK cells. In subsequent in vitro studies with normal fresh NK cells, it was demonstrated that IgG-containing RF complexes from RA patients induced a modulation of FC gamma RIII structure from the NK cell surface, a decrease in NK activity, and a complete loss of ADCC. When purified RF was incubated with NK-enriched cell lines from RA patients, increased transcription and subsequent production of interferon-gamma and tumor necrosis factor alpha were observed. These data suggest a direct involvement of RF complexes in the pathogenetic process of chronic inflammation in RA.

Stimulation of lymphocyte natural cytotoxicity by L-arginine

In vitro L-arginine enhanced natural-killer (NK) and lymphokine-activated-killer (LAK) cell activity; this cytotoxicity was mediated by CD56+ cells. In vivo arginine supplements (30 g/day for 3 days) increased the number of circulating CD56+ cells by a median of 32% in eight volunteers (p less than 0.01); this increase was associated with a mean rise of 91% in NK cell activity (p = 0.003) and of 58% in LAK cell activity (p = 0.001) in thirteen volunteers. These findings have potentially important implications for the modulation of natural cytotoxicity in a wide range of disease states.

Cytolysis of oligodendrocytes is mediated by killer (K) cells but not by natural killer (NK) cells

The cytotoxic activity of killer (K) cells against enriched cultures of bovine oligodendrocytes (BOL) was investigated in multiple sclerosis (MS) and controls. Human K cells mediated cytotoxicity to primary cultures of BOL in the presence of anti-BOL antiserum in all study groups, while BOL were resistant to human natural killer (NK) cells. Cytotoxic activity was significantly reduced in MS when compared to age-matched normal controls but not when compared to other neurologic disease (OND) patients. K cell-mediated lysis of BOL could also be induced with anti-galactocerebroside antibody but not with other antibodies including those specific for OL antigens (myelin basic protein, proteolipid apoprotein, and 2',3'-cyclic nucleotide 3'-phosphodiesterase). Enrichment of the effector population indicated that antibody-dependent cell-mediated cytotoxicity (ADCC) to BOL was mediated by large granular lymphocytes, and the effector population was further characterized by flow cytometry. The effector cells mediating ADCC could be inhibited by protein A of Staphylococcus aureus, and by K562 cells in cold competition assay. These observations indicate that oligodendrocytes are resistant to NK cells but are susceptible to cytolysis mediated by K cells. This may represent a potentially important immune mechanism in the pathogenesis of MS.

Expression of lineage-restricted protein tyrosine kinase genes in human natural killer cells

The hematopoietic lineage derivation, recognition structures and associated signal transduction pathways of CD3- natural killer (NK) cells have not been identified. Protein tyrosine kinases (PTK) structurally related to the product of the c-src protooncogene are differentially expressed in distinct hematopoietic differentiation lineages and may participate in specific signal transduction pathways. The present study was aimed at characterizing the expression of src-related PTK genes in normal human NK cells and in cells from patients with CD3- granular lymphocyte proliferative disease. CD3- normal NK cells had high levels of transcripts of the lck gene, which is highly expressed in T cells. CD8+ and CD8- NK cells expressed similarly high levels of lck mRNA. In contrast, NK cells expressed very low levels (25-80 times less than monocytes) of mRNA encoding the myelomonocytic PTK hck. NK cells also expressed fyn transcripts (p59fyn reportedly associates with the T cell receptor in T cells) and fgr transcripts, the latter observation confirming a previous report. The pattern of expression of the lineage-restricted PTKs lck and hck in NK cells is consistent with the hypothesis of an ontogenic relationship of this population with the lymphocytic rather than myelocytic differentiation pathway. PTK expressed in NK cells may participate in signal transduction pathways in this cell population.

Molecules and structures involved in the adhesion of natural killer cells to vascular endothelium

The present study was designed to define molecules and structures involved in the interaction of natural killer (NK) cells with the vascular endothelium in vitro. Resting and interleukin 2 (IL-2)-activated NK cells were studied for their capacity to adhere to resting and IL-1-treated human umbilical vein endothelial cells (EC). In the absence of stimuli, NK cells showed appreciable adhesion to EC, with levels of binding intermediate between polymorphs and monocytes. The binding ability was increased by pretreatment of NK cells with IL-2. Using the appropriate monoclonal antibody, the beta 2 leukocyte integrin CD18/CD11a was identified as the major adhesion pathway of NK cells to unstimulated EC. Activation of EC with IL-1 increased the binding of NK cells. In addition to the CD18-CD11a/intercellular adhesion molecule pathway, the interaction of resting or IL-2-activated NK cells to IL-1-activated EC involved the VLA-4 (alpha 4 beta 1)-vascular cell adhesion molecule 1 receptor/counter-receptor pair. No evidence for appreciable involvement of endothelial-leukocyte adhesion molecule was obtained. Often, NK cells interacted either with the culture substrate or with the EC surface via dot-shaped adhesion structures (podosomes) protruding from the ventral surface and consisting of a core of F-actin surrounded by a ring of vinculin and talin. The identification of molecules and microanatomical structures involved in the interaction of NK cells with EC may provide a better understanding of the regulation of NK cell recruitment from blood, their extravasation, and their migration to tissues.

Cytotoxicity and immunocyte markers in cells from the freshwater snail Planorbarius corneus (L.) (Gastropoda pulmonata): implications for the evolution of natural killer cells

The hypothesis that natural killer (NK) cells represent an important form of cell recognition and cytotoxicity leads to the prediction that NK-like activity should be preserved throughout phylogenetic development. This was tested in the invertebrate Planorbarius corneus. Two types of cells can be identified and separated from the hemolymph of this mollusc, i.e. glass-adherent macrophage-like spreading hemocytes (SH) and nonadherent round hemocytes (RH). Only RH are able to lyse the K-562 human target cell line in a short-term NK cytotoxicity test. This NK-like activity, severely reduced after 18 h incubation at 24 degrees C, is preserved by human recombinant interleukin 2. A further analysis of P. corneus hemocytes has been performed by using several mouse anti-human monoclonal antibodies and cytofluorimetric analysis. Unexpectedly, both SH and RH react with several monoclonal antibodies, including those directed against epitopes typical of mammalian NK cells and cell adhesion molecules. On the whole, these data support the hypothesis that a primitive NK-like activity appeared early in evolution and is not shared by phagocytic cells.

Cell-mediated cytotoxicity: ATP as an effector and the role of target cells

Cell-mediated cytotoxicity involves a number of distinct mechanisms as well as the active participation of the target cell. Recently, several investigators have demonstrated that extracellular ATP can act as a cytotoxic effector.

Lymphokine-activated killer cells, natural killer cells and cytokines

In the past year, natural killer cells have been the subject of much active investigation. The analysis of the effect of cytokines on the generation, proliferation and function of natural killer cells, and the definition of the lymphokines that they produce, have been particularly important areas of research in view of their possible application in adaptive immunotherapy, combined with biological response modifiers.

Enhancement of cell-mediated cytotoxicity by Clostridium difficile toxin A: an in vitro study

Cells from the immune system exhibiting cytotoxic activity are able to kill tumor or infected cells in a major histocompatibility complex-restricted (cytotoxic lymphocytes) or non-restricted (natural killer cells) manner. In order to exert such a cytotoxicity they have to bind the target cell and release cytotoxic factors able to induce target cell death. Treatment of human peripheral blood mononuclear cells with toxin A from Clostridium difficile induced an enhancement of the cytotoxic efficiency of these effector cells. Morphological analysis of effector/target cell pairs seems to suggest that this could be related to an increased ability of cytotoxic effectors to establish close and intertwined contacts with target cells. These contacts involve adhesion molecules and lead to the formation of a "closed chamber" which probably improves the efficacy of lytic factors and results in an increased cytotoxicity.

Natural killer function in flow cytometry: identification of human lymphoid subsets able to bind to the NK sensitive target K562

NK cells are a phenotypically, morphologically and functionally heterogeneous population. This has led to the current thought that the non-MHC restricted cytotoxicity is a cellular function that can be associated to different phenotypes. The recognition of the target cell and the conjugate formation is always the first step that eventually leads to the lysis of target. Characterization of the phenotypical pattern of the cells able to bind to K562 targets is the purpose of this study. A multi-parametric flow cytometry binding assay has been employed to identify the different K562-bound lymphocyte subsets. In particular, cells that coexpress the CD16 and CD8 antigens (CD16+8dim+) showed a significantly higher binding capacity than their CD16+8- counterpart. Moreover, the highest binding values have been found in cells that did not express the CD16 antigen at all, but still expressed the CD8dim antigen, such as the small CD8dim+3+ population. These data show that, the NK lytic function being dependent on binding, minor subpopulations must be considered among effector cells, which might correspond to different lytic activities. None of the previously published methodologies that analyze conjugates by flow cytometry or fluorescence microscopy were able to measure the binding capacity of small, double stained, lymphocyte subsets.

Highly oncolytic adherent lymphocytes: therapeutic relevance for leukemia

We have generated and characterized a highly oncolytic adherent lymphocyte subset (A-LAK) from eight leukemic patients with non-lymphocytic leukemia (NLL) in remission and one NLL patient in relapse. Our studies demonstrated that A-LAK was superior in its oncolytic activity (tested in a 3-h 51Cr release assay) to conventionally prepared (LAK) and non-adherent (NA) IL-2 cultures. No activity was observed by this highly oncolytic subset against normal bone marrow (BM). A-LAK also displayed highest proliferative activity in 7-11 day cultures (5- to 58-fold expansion) in comparison to LAK (0.7- to 2.7-fold) or NA (1.0- to 2.6-fold) cultures. Analysis of phenotype of unseparated, NA and adherent (A-LAK) lymphocytes 24 h after IL-2 activation showed that the A-LAK was composed predominantly of high intensity (bright) CD11a+ (LFA-1) lymphocytes (75 +/- 4.8%) when compared to the other two populations (12 +/- 2.1%). Similarly, A-LAK contained higher proportion of CD11b (CR3 receptor)-positive lymphocytes (39 +/- 2.1%) than unseparated and NA lymphocytes (11 +/- 1.4%). Double marker phenotypic studies showed that A-LAK cultures were heterogeneous and distribution of individual lymphocyte subsets differed among NLL patients. While in A-LAK culture of some patients the CD56+, CD3- natural killer (NK) cell subset was predominant, CD3+, CD56- lymphocyte subset was prevalent in others. Highest A-LAK lytic activity was always correlated with highest NK cell content. Characterization studies (using the complement-depletion technique) showed that independently of the distribution of lymphocytes in A-LAK cultures, CD16+, CD56+, CD3- NK cell subset displayed highest oncolytic effect. CD5+ subset also participated in cytotoxic function. These observations indicated that A-LAK may represent a new therapeutic approach to treatment of leukemia.

Ultrastructure of cell mediated cytotoxicity

Contact dependent cell mediated cytotoxicity has been found to be executed by lymphocytes, macrophages, and even granulocytes. Cytotoxic effector cells of the lymphatic lineage are divided into cytotoxic T lymphocytes (CTL), mediating MHC related cytotoxicity, and in effectors mediating non-MHC restricted cytotoxicity such as natural killer (NK) cells, T lymphocytes displaying NK-like activity and lymphokine activated killer (LAK) cells. In morphologic studies these cells are hardly to be distinguished: they all show features of large granular lymphocytes (LGLs), which are characterized by a low nuclear to cytoplasmic ratio and azurophilic granules. Ultrastructurally lysosomal granules, showing an electron dense core that is either surrounded by numerous small vesicles or by a small electron translucent halo, have been found. Pore-forming proteins such as perforin, as well as serine esterases and proteoglycans have been pointed out in these granules. Specialties are parallel tubular arrays (PTA) in NK cells and nuclear inclusion bodies in LAK cells. Morphologically two types of killing event may be distinguished. In one way membrane lesions develop at the surface of target cells upon binding of effector cells and in advanced stages of cytolysis the target cells are surrounded by a completely disintegrated membrane. The nuclei, however, show only minor changes. In the other way, called apoptosis, the cell membrane of the targets remains intact, but the nucleus and cell organelles very early disintegrate intracellularly. Whether these morphologically different types of cell killing correspond to the functionally different pathways of cell mediated cytotoxicity remains to be resolved.

Fibronectin facilitates the migration of human natural killer cells

The interaction of lymphocytes with the extracellular matrix plays an important role in the immune defence against tumor cells and virus-infected cells. We have examined the effect of matrix proteins on the migration of large granular lymphocytes (LGL) through 3-microns pores in Nuclepore filters in a Boyden invasion chamber. Fibronectin bound on the filter surface significantly increased (p less than 0.001) the capacity of LGL to migrate, whereas soluble fibronectin did not. In addition, a significantly higher (p less than 0.001) percentage of LGL was capable of migration through fibronectin-coated filters than through untreated filters. With fibronectin-coated filters, a strong enrichment of CD16+ and CD56+CD3- cells with LGL morphology and reduction of CD3+ cells was found among migrating cells when the incubation time was 4 h or less. Later agranular lymphocytes, mainly CD3+ T lymphocytes, also started to migrate. Laminin coating of filters also facilitated migration, and when filters were coated with both fibronectin and laminin the increase in migration was equal to the sum of the increases induced by each protein alone. Interactions between cell surface and the Arg-Gly-Asp (RGD) peptide sequence of many matrix proteins had no role in the LGL migration through untreated filters. However, when filters were coated with either fibronectin or laminin, or with both, peptide containing the RGD sequence reduced migration to the level of untreated filters, whereas an Arg-Gly-Glu control peptide had no effect. Our results show that unstimulated LGL/natural killer cells are capable of rapid migration through matrix-coated porous membranes, and that interactions between cell surface receptors and the RGD sequence of fibronectin and probably laminin are utilized in this process.

Phenotypic analysis of a resting subpopulation of human peripheral blood NK cells: the FcR gamma III (CD16) molecule and NK cell differentiation

A subpopulation of human peripheral blood natural killer (NK) cells, defined by sedimentation at Percoll high buoyant densities (P greater than 1.0635-1.0640 g/ml) and unresponsiveness to interleukin-2 (IL-2), contained two distinct populations based on the intensity of CD16 (FcR gamma III) expression, namely CD16dim and CD16bright. This resting subpopulation of NK cells differed from the total population of peripheral blood NK cells, by containing a larger proportion of CD16dim cells, by the total absence of CD56bright CD16- cells, and by an inability to respond to high concentrations (500 U/ml) of rIL-2 despite the expression of an intermediate affinity (p70) IL-2R. Both CD16dim and CD16bright NK cells expressing high affinity IL-2R were initially generated following co-culture of resting NK cells with gamma-irradiated MM-170 cells and IL-2, but CD16bright NK cells became the dominant cell type later in culture. The CD16 molecule was not involved in the differentiation of resting NK cells since solid-phase-bound anti-CD16 monoclonal antibody neither enhanced nor inhibited NK cell generation. These studies demonstrate that the resting subpopulation of peripheral blood NK cells expresses a unique CD16 profile, that CD16 expression increases during NK cell generation, and that CD16 is not involved in the differentiation process.

T cell targeting in cancer therapy

Targeting of immune cells by bispecific antibodies has proven a powerful tool for the investigation of cellular cytotoxicity, lymphocyte activation and induction of cytokine production, as well as to represent an innovative form of immunotherapy for the treatment of cancer. The hallmark of this approach is the use of the specificity of monoclonal antibodies to join target and immune cells by virtue of the dual specificity of bispecific antibodies for the two entities. More precisely the bispecific antibody has two different binding sites, which are capable of recognizing tumor associated antigens on the one hand and lymphocyte activation sites on the other. This process of crosslinking results in the activation of the lymphocyte and triggering of its lytic machinery, as well as lymphokine production. A major advantage of this therapeutic modality is, that use is made of the normal cellular immune defence system and therefore is only associated with minor toxicity. The distinct lymphocyte populations, which can be used for adoptive immunotherapy and the various bispecific antibody preparations, as well as the chimeric immunoglobulin/T cell receptor construction are the major topics of this review.

Characterization of effector-target conjugates for cloned human natural killer and human lymphokine activated killer cells by flow cytometry

The present studies demonstrate that the intracellular fluorochromes calcein and hydroethidine can be used for quantification of effector-target conjugates involving cloned human natural killer (NK) or interleukin-2 (IL-2) activated human lymphokine activated killer (LAK) cells by dual color flow cytometry without potential artifacts that might result from extensive modification of effector and/or target cell membranes. Cloned NK cells and LAK cells form conjugates with cultured cell lines regardless of susceptibility to lysis. The strength of the interactions in these conjugates was investigated using a variable speed vortexer. Even relatively gentle vortexing disrupted most conjugates involving fresh human peripheral blood lymphocytes (PBL) but only about one-fourth of conjugates between K-562 cells and human PBL that had been cultured with or without IL-2 by this treatment. The rate of conjugate formation for LAK cells was determined to be about 3 times faster than for cloned NK cells, and both rates are considerably faster than the reported rate of formation of cytotoxic T lymphocyte (CTL) target conjugates. The differences in the rate of conjugate formation are apparently not related to target cell specificity, since LAK cells form conjugates with susceptible and resistant cell lines at comparable rates. When effector-target conjugates are incubated at 37 degrees C in the absence of calcium--thereby precluding lysis--the percentage of conjugated LAK or cloned NK cells decreases logarithmically with time. These results suggest that an initial equilibrium between free and conjugated lymphocytes gradually shifts in favor of unconjugated cells.

Identification of four subsets of human CD3-CD16+ natural killer (NK) cells by the expression of clonally distributed functional surface molecules: correlation between subset assignment of NK clones and ability to mediate specific alloantigen recognition

In previous studies we identified a surface molecule (termed GL183) capable of mediating cell activation and selectively expressed by a subset of human CD3-CD16+ natural killer (NK) cells. In this study we analyzed whether other subset-specific functional molecules were expressed in GL183- NK cells. To this end, mice were immunized with the PE29 (CD3-CD16+GL183-) NK clone. Monoclonal antibodies (mAbs) were selected by screening the hybridoma supernatants for their ability to trigger the cytolytic activity of clone PE29 against the human myelomonocytic leukemia U937. The EB6 mAb (IgG1) triggered the PE29 clone, but not a GL183+ clone used as a control. EB6+ cells ranged between 1 and 13% of peripheral blood lymphocytes and were largely included in the CD3-CD16+CD56+ cell populations (only less than 2% of EB6+ cells were CD3+). Analysis of resting or activated CD3-CD16+ populations, or clones for the expression of EB6 or GL183 mAbs, allowed us to identify four distinct, phenotypically stable, NK subsets (EB6+GL183-; EB6+GL183+; EB6-GL183+; EB6-GL183-). Similar to GL183 mAb, the EB6 mAb selectively triggered the NK subset expressing the corresponding surface antigen to lyse human tumor cell lines including U937, IGROV-I, M14, and A549. In addition, EB6 mAb sharply inhibited the cytolytic activity of EB6+ clones against P815, M12, and P3U1 murine target cells. In EB6+GL183+ ("double-positive") clones both EB6 and GL183 mAb inhibited the redirected killing of P815 cells induced by anti-CD16, anti-CD2 mAbs and phytohemagglutinin (PHA). Similar to GL183 molecules, molecules precipitated by EB6 mAb were represented by either single 58-kD chain or double chains of 55 and 58 kD (with no detectable differences in EB6+GL183- or EB6+GL183+ clones). In sequential immunoprecipitation experiments using the double-positive clones CEG52 and CA25.50, preclearing of cell lysates with EB6 or GL183 mAb removed only EB6 or GL183 molecules, respectively, thus indicating that the two antigenic determinants are carried by two distinct molecules. Peptide map analysis indicated that EB6 (or GL183) molecules precipitated from double-positive clones were identical to the corresponding molecules isolated from single-positive ones. On the other hand, comparison of the EB6 and GL183 maps revealed peptides that were unique to each molecule, although most of the major peptides migrated to identical positions. We further investigated whether correlation existed between the phenotypic assignment of NK clones and their ability to mediate specific lysis of normal allogeneic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Susceptibility or resistance to lysis by alloreactive natural killer cells is governed by a gene in the human major histocompatibility complex between BF and HLA-B

The specificity recognized on normal allogeneic cells by a given alloreactive (1-anti-A) natural killer clone is controlled by a gene locus termed EC1. Because the EC1 locus was previously shown to be located on chromosome 6, families characterized by a recombinant major histocompatibility complex haplotype were analyzed to map this locus more precisely. The breakpoint of recombination was studied by standard HLA typing, complement typing, and restriction fragment length polymorphism analysis of a series of genes located between the complement cluster genes and HLA-B within the major histocompatibility complex region. Three of 10 families analyzed were informative. From the data obtained, the EC1 locus maps between BF and HLA-B and presumably is one of the normal genes recently described in this region.

Differences in non-MHC restricted cytotoxic activities of human peripheral blood lymphocytes after transfusion with allogeneic leukocytes or platelets possessing class I and/or class II MHC molecules

MHC-unrestricted cytotoxic activity of peripheral blood lymphocytes (PBL) from 4-6 healthy donors was investigated before and after transfusion with allogeneic leukocytes or platelets. Natural killer and lectin-dependent cellular cytotoxicity (LDCC) of PBL was tested against K562 and Raji target cells in a 4-h and 16-h 51Cr-release assay, respectively. After allotransfusion with leukocytes, we found increased cytotoxic activity of each donor's PBL against all the three targets on day 3 or 7. The highest non-specific cytotoxic activity was detected against the relatively NK resistant Raji target cells. The increase of cytotoxic activity was lowest against the LDCC target (PHA-treated Raji) cells. On the contrary, no changes in cytotoxic activity against any targets were observed after allotransfusion with platelets (possessing class I HLA antigens but no HLA class II molecules). Our results suggest that HLA class II molecules, presumably by inducing immune responses, are essential for activation/generation of non-specific killing of tumor targets after leukocyte transfusion. Thrombocytes, known to be less immunogenic than leukocytes, are not effective in in vivo enhancing of non-specific cytotoxicity. Cellular activation of PBL following leukocyte allotransfusion was confirmed by detection of elevated serum neopterin and beta-2-microglobulin levels on day 3. This was not the case after platelet allotransfusion. In addition, the expression of ICAM-1 antigen (as a molecule involved directly in MHC-unrestricted cytotoxicity) was also found to be increased in two donors' PBL on day 3 after leukocyte transfusion in contrast to transfusion with platelets.

Interleukin 2 gene transfer into tumor cells abrogates tumorigenicity and induces protective immunity

To study the effects of localized secretion of cytokines on tumor progression, the gene for human interleukin 2 (IL-2) was introduced via retroviral vectors into CMS-5 cells, a weakly immunogenic mouse fibrosarcoma cell line of BALB/c origin. Secretion of low levels of IL-2 from the tumor cells abrogated their tumorigenicity and induced a long-lasting protective immune response against a challenge with a tumorigenic dose of parental CMS-5 cells. Co-injection of IL-2-producing CMS-5 cells with unmodified tumor cells inhibited tumor formation even when highly tumorigenic doses of CMS-5 cells were used. Cytolytic activity in mice injected with parental CMS-5 cells was transient and was greatly diminished 3 wk after injection, as commonly observed in tumor-bearing animals. However, in mice injected with IL-2-producing cells, tumor-specific cytolytic activity persisted at high levels for the duration of the observation period (at least 75 d). High levels of tumor-specific cytolytic activity could also be detected in parental CMS-5 tumor-bearing animals 18 d after inoculation with tumor cells, if IL-2-producing CMS-5 cells but not unmodified parental tumor cells were used as targets. These studies highlight the potential advantages of localized secretion of cytokines mediated via gene transfer to induce potent anti-tumor immune responses.

Cytotoxic events taking place in the lung of patients with HIV-1 infection. Evidence of an intrinsic defect of the major histocompatibility complex-unrestricted killing partially restored by the incubation with rIL-2

To characterize the cytotoxic events taking place in the lung of patients with HIV-1 infection, we studied the cells recovered from the bronchoalveolar lavage (BAL) of nine patients with AIDS, seven patients with AIDS-related complex, and two patients with lymphadenopathy. Phenotypic analysis was coupled to a series of functional evaluations of nonspecific cytotoxic abilities performed on lung effectors, including their property to bind K-562 targets, to release natural killer cytotoxic factor (NKCF), and to become cytotoxic following in vitro activation with rIL-2. Our results demonstrated that lung cells bearing the NK-related CD16, CD56, and CD57 antigens were quantitatively increased, irrespective of the disease stage. The majority of the cells also coexpressed the CD3 molecule and the alpha/beta T cell receptor (TCR), notably the phenotype characterizing MHC-unrestricted cytotoxic T cells. From a functional point of view, a severe impairment of the spontaneous cytotoxic ability was demonstrated in most patients. Evaluation at the single cell level showed a normal percentage of the effector/target conjugates formed by HIV-1 lymphocytes. The release of NKCF was undetectable in patients with AIDS even following lectin stimulation, whereas BAL cells from patients with earlier infection produced and/or could be triggered to release discrete amounts of NKCF by incubation with PHA. Studies designed to activate lung cytotoxic cells with rIL-2 showed that in most patients the stimulation of effector cells with rIL-2 enhanced the spontaneous killing and elicited a lymphokine-activated killer (LAK) phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

Monocyte-mediated suppression of IL-2-induced NK-cell activation. Regulation by 5-HT1A-type serotonin receptors

In the present study, the effects of serotonin on human natural killer (NK)-cell responsiveness to interleukin 2 (IL-2) was investigated. Concomitant treatment of human lymphocytes, enriched for NK effector cells by Percoll density-gradient centrifugation, with serotonin and IL-2 yielded a synergistic activation of NK-cell cytotoxicity (NKCC) in the presence but not in the absence of monocytes. The monocyte-dependent, regulatory effects of serotonin and/or IL-2 were prostaglandin-independent and could be reconstituted when monocytes, recovered by countercurrent centrifugal elutriation (CCE), were added to purified NK effector cells. The effects of serotonin on baseline and IL-2-activated NK cells were mimicked by the 5-HT1A receptor-specific agonists 8-OH-DPAT and (+)-ALK. Our data suggest that serotonin regulates NK-cell responsiveness to IL-2 via 5-HT1A receptors.

In search of the 'missing self': MHC molecules and NK cell recognition

Natural killer (NK) cells can defend an organism against a variety of threats, probably using several different strategies to discriminate between normal and aberrant cells. According to the 'missing self' hypothesis, one function of NK cells is to recognize and eliminate cells that fail to express self major histocompatibility complex (MHC) class I molecules. In this article Hans-Gustaf Ljunggren and Klas Kärre review in vivo studies with H-2-deficient targets that support this hypothesis. In vitro studies, some of which have given conflicting results, are interpreted within a multiple choice model for NK cell recognition. The authors derive testable predictions for how MHC class I molecules act in cases where they control a rate-limiting step in the NK cell-target interaction.

Lysis of myotubes by alloreactive cytotoxic T cells and natural killer cells. Relevance to myoblast transplantation

The aim of this study was to investigate the susceptibility of human myotubes to lysis by the two major types of cytotoxic effector cells, CD3+CD8+ cytotoxic T cells (CTL) and CD16+CD56+ natural killer (NK) cells. The myoblasts preparations used as target cells were greater than 90% pure as assessed by immunostaining with the Leu19 monoclonal antibody (MAb) that cross-reacts with the neural cell adhesion molecule N-CAM. Allospecific CTL lines were generated from mixed lymphocyte cultures, and freshly isolated allogeneic and autologous peripheral blood cells were used as a source of NK cells. The cytotoxicity was observed under phase optics and by immunoelectron microscopy, and was quantitated with a chromium release assay. Myotubes were efficiently killed by allospecific CTL and by autologous and allogeneic NK cells. The killing by CTL was inhibited with an anti-class I HLA MAb, and the killing by NK cells was inhibited by depleting peripheral blood cells of CD16+ cells with anti-CD16 MAb and complement. The results have important implications for myoblast transplantation, an experimental therapy of muscular dystrophy.

The generation of natural killer (NK) cells from NK precursor cells in rat long-term bone marrow cultures

In this report, we describe a novel long-term bone marrow culture (LTBMC) system to study the origin and generation of natural killer (NK) cells from NK precursors. Rat bone marrow was cultured for 4 wk in RPMI 1640 with 5% fetal calf serum and 2-mercaptoethanol to allow the formation of an adherent stromal cell layer containing NK precursor cells. After addition of interleukin 2 (IL-2), the LTBMC generated high numbers (up to 100-fold expansion in 7 d) of pure 3.2.3+ large granular lymphocytes with lytic activity against NK-sensitive and -resistant tumor targets, as well as antibody-dependent cellular cytotoxicity. NK activity in LTBMC could be detected 3 d after addition of as little as 1 U/ml rIL-2, whereas lymphokine-activated killer activity was found 5 d after addition of at least 10 U/ml rIL-2. In vivo depletion and in vitro complement lysis studies showed that the NK precursor cells in LTBMC did not express the NK-associated surface markers asialo GM1 or 3.2.3. We also found that LTBMC cells did not exhibit colony growth in granulocyte/macrophage or spleen colony-forming unit assays. The generation of NK cells from NK precursors required, in addition to IL-2, a second growth/maturation factor(s), which was present in the conditioned medium of the LTBMC. This LTBMC system provides a unique in vitro model to study the development of NK cells from precursor cells, the role of the bone marrow stromal microenvironment in this development, and the lineage relationship of NK cells to other hematopoietic cells.

Specific tolerance induction across a xenogeneic barrier: production of mixed rat/mouse lymphohematopoietic chimeras using a nonlethal preparative regimen

The development of safe methods for inducing donor-specific tolerance across xenogeneic barriers could potentially relieve the critical shortage of allograft donors that currently limits the applicability of organ transplantation. We report here that such tolerance can be induced in a xenogeneic combination (rat----mouse) using a nonmyeloablative and nonlethal preparative regimen. Successful induction of chimerism and donor-specific transplantation tolerance required pretreatment of recipients with monoclonal antibodies (mAbs) against NK1.1, Thy-1.2, CD4 and CD8, followed by administration of 3 Gy whole body radiation (WBI), 7 Gy thymic irradiation, and infusion of T cell-depleted rat bone marrow cells (BMC). Rat cells appeared among peripheral blood lymphocytes (PBL) of such recipients by 2-3 wk, and rat T cells by 2-5 wk following bone marrow transplantation (BMT). Donor-type rat skin grafts placed 4 mo after BMT were accepted, while simultaneously placed non-donor-type rat skin grafts were promptly rejected. In addition to its clinical potential, the ability to induce donor-specific tolerance across xenogeneic barriers using such a nonlethal preparative regimen provides a valuable model for the study of mechanisms of xenogeneic transplantation tolerance.

A cell-to-cell mediated interaction involving monocytes and non-T/CD16+ natural killer (NK) cells is required for histamine H2-receptor-mediated NK-cell activation

Histamine (10(-4) to 10(-7) M) augmented natural killer cell cytotoxicity (NKCC) of human CD16+, non-T lymphocytes in vitro against the NK-sensitive target cells K562 erythroleukaemic, Molt-4 lymphoma, Chang liver cells and against Epstein-Barr virus (EBV)-transformed, NK-insensitive Daudi B-lymphoblastoid target cells by a mechanism of action involving a prostaglandin- and interleukin 1 (IL-1)-independent accessory function of monocytes. No evidence for the production of intermediary, NK-enhancing cytokines by histamine was obtained, indicating a cell-to-cell mediated interaction between monocytes and NK cells as a plausible mechanism of action for the NK-augmenting effect. Monocytes recovered by countercurrent centrifugal elutriation (CCE), but not monocytes recovered by adherence, reconstituted the effect of histamine when added to non-adherent NK cells. The development of NKCC in response to histamine was time-dependent with (i) an induction phase, dependent on the presence of accessory monocytes and ongoing histamine H2-receptor activation (half-maximal response required approximately 30 min treatment of large granular lymphocyte (LGL)-enriched lymphocytes and monocytes with histamine), and (ii) an effector phase, independent of the presence of monocytes or histamine receptor activation. Histamine-activated mononuclear cells (MNC) continued to exert augmented cytotoxicity for at least 8 h after removal of histamine and monocytes. In several experiments, histamine-activated NK-effector cells killed greater than 90% of the target cells at low baseline NKCC. We suggest that histamine may have a role in non-specific tumour defence by regulating an earlier unrecognized interplay between monocytes and NK cells.

Fc gamma receptor type III (CD16) is included in the zeta NK receptor complex expressed by human natural killer cells

We recently reported that CD3- natural killer (NK) cells express the zeta chain of the T-cell receptor complex (zeta NK) in association with higher molecular weight structures whose expression differs between individual NK cell clones. Because NK cell cytolytic activity is known to be triggered by perturbation of the type III Fc gamma receptor (CD16), we sought to determine whether this activating molecule is included in the zeta NK molecular complex. Biochemical evidence for a physical association between CD16 and zeta NK was obtained by comparing immunoprecipitates formed using monoclonal antibodies reactive with each of these molecules by SDS/polyacrylamide gel electrophoresis, immunoblotting, and peptide mapping. In both clonal and polyclonal populations of CD3- NK cells, CD16 and zeta NK specifically associated with one another. Functional evidence for a specific association between CD16 and zeta NK in intact cells was obtained by demonstrating a coordinate down-modulation of both of these molecules induced by either phorbol 12-myristate 13-acetate or monoclonal antibodies reactive with CD16. Our results suggest that Fc gamma receptor type III (CD16) is included in the zeta NK complex and that this complex is likely to play an important role in NK cell activation.

Augmentation of mouse natural killer (NK) activity by GM-1/P, a processed form of monosialoganglioside GM-1

We describe the immunomodulatory activity of GM-1/P a processed form of GM-1 (monosialoganglioside) extracted from ox brain, purified and physically modified. We examined the effect of in vivo and in vitro treatment of GM-1/P on natural (NK) activity and its ability to induce the production of interleukin-2 (IL-2) in the mouse. In vivo treatment with GM-1/P (1 mg/Kg, i.v., day-1) resulted in a marked increase and in a change of distribution of NK activity, which was associated with lower density Percoll fractions. Marked increase was already observed at 18 hrs and then declined by day 4. In vitro treatment with GM-1/P (2 micrograms/ml) enhanced NK activity of B6 spleen cells, already after 6 hours of incubation, remaining at plateau levels within 18 hours. A role of IL-2 in this enhancement was suggested by the ability of an anti-IL-2 rabbit antiserum to abolish in vitro increased cytotoxicity. The presence of IL-2 in the supernatants of splenocytes from GM-1/P (1mg/Kg, i.v., ,day-1) treated mice stimulated with Con A or Con A plus TPA for 48 hrs was evaluated by proliferation of an IL-2 dependent CTLL cell line. GM-1/P by itself was unable to stimulate IL-2 production; however it markedly increased IL-2 production induced by Con A or Con A plus TPA.

Flavone acetic acid antitumour activity against a mouse pancreatic adenocarcinoma is mediated by natural killer cells

Flavone acetic acid (FAA) is one of the most active antitumour agents against mouse solid tumours. A number of reports favour the hypothesis that FAA could behave as a biological response modifier; in fact FAA stimulates natural killer (NK) cells, induces secretion of type I interferon and synergizes with interleukin-2 to increase NK/lymphokine-activated killer (LAK) activity in vivo. However, there is no conclusive evidence that the antitumour activity of FAA is mediated via the modulation of NK/LAK cells. The present study was designed to evaluate whether the reported activation of NK cells is instrumental in FAA antitumour activity. FAA (180 mg/kg, i.v. on days 3, 7 and 11 after tumour implant) was significantly effective in inhibiting the subcutaneous growth of the pancreatic adenocarcinoma PAN/03 in C57/Bl mice. After 132 days the number of tumour-free survivors was 36%, whereas in the control group receiving no treatment, or in the group of mice treated with 10 micrograms/mouse of alpha-asialo-GM1 the value was only 0 or 6.7%, respectively. The combination of FAA and alpha-asialo-GM1 resulted in only 6% tumour-free mice. In parallel experiments, splenocytes and peritoneal cells from C57/B1 mice were tested in a standard cytotoxicity NK assay. While animals treated with FAA showed a significant increase in NK activity, those injected with alpha-asialo-GM1 had very low levels, and the combined treatment of FAA and alpha-asialo-GM1 resulted in a lower or similar NK activity compared to that in untreated mice. The fact that the abrogation of the NK-stimulating effect of FAA is accompanied by a lack of anti-tumour activity indicates that, at least in this experimental model, FAA is likely to act via an immunomodulatory mechanism.

Mechanisms of target cell killing by natural killer cells

Understanding of the lytic process of NK cells has been greatly advanced in the past decade. However, the definition of the primary event required for lysis has been elusive. The recent enthusiasm about the granule exocytosis/PFP model of membrane damage has been tempered by the multitude of factors that cytotoxic effector cells can secrete and the observation of rapid nuclear degradation before membrane damage which is not well explained by the PFP model. Logically, one would expect that this array of cytotoxic, cytostatic and immunoregulatory factors are secreted for a purpose, and should, therefore, be involved in the lysis of target cells. Further studies are necessary to define the role of each of these factors in plasma membrane and nuclear damage. Additional experiments to determine whether these two events are related will be necessary. On the basis of information currently available, one could hypothesize that after recognition of foreign cells, the NK cell is not single-minded in its delivery of lethal factors. The end result is that target cell lysis may occur because of many factors acting not only on the target cell itself but also on other components of the host immune response.

Natural killer cells and their precursors in mice with severe combined immunodeficiency

Our studies with scid mice have clarified the relationship between T cells and NK cells. C.B-17 scid mice have normal frequency of transplantable NK progenitors in their bone marrow which develop into fully functional NK cells. Spleens of scid mice contain mature NK cells which are phenotypically and functionally indistinguishable from NK cells found in normal mice. These cells retain their TCR genes in germline configuration and do not transcribe the CD3 genes. Thus, NK cells are distinct from the earliest identifiable cells committed to the T-lineage. In addition to the spleen, the thymus of scid mice also contains mature NK cells. These cells constitute a small proportion of the thymus cell population and can be clearly distinguished from the majority of cells, which have the phenotype and molecular characteristics of very early T-lineage cells. There is no evidence that NK cells within the thymus are derived in situ from a common NK/T precursor. Together these data support the hypothesis that NK cells form an independent lineage.