Interferon is able to reduce tumor cell susceptibility to human lymphokine-activated killer (LAK) cells

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.

Induction and abrogation of LACK reactive cells in the evolution of human leishmaniasis

Peripheral blood mononuclear cells (PBMC) from cutaneous leishmaniasis patients with ongoing Leishmania aethiopica infection and individuals cured/under treatment from L. infantum or L. donovani infection were stimulated in vitro with LACK, the Leishmania homologue of receptors for activated C kinase. The LACK protein is conserved in related leishmanial species and is expressed both in the promastigote and amastigote stages of Leishmania. Our results show that LACK induced marked NK and some CD8+ cell proliferation in PBMC from cutaneous leishmaniasis patients with active disease. These responses were coupled with high levels of IFN-gamma and IL-10 production. At the concentration tested, the proliferative responses to freeze-thawed Leishmania antigen (Ft-Leish) were higher, while the levels of IFN-gamma were consistently lower than that of LACK. Although cells from individuals cured of leishmaniasis could respond to whole Leishmania lysate by proliferation and IFN-gamma production, there was no evident response to LACK. Ethiopian controls tested at the same time also showed LACK induced proliferation with IFN-gamma and IL-10 responses. Thus LACK reactivity in terms of proliferation and cytokine induction were present in cells from some healthy donors and most of the patients with active lesions, while this response was absent in individuals cured of L. infantum or L. donovani leishmaniasis. Since cure from leishmaniasis often results in life-long protection, and active but not cured patients showed in vitro responses to LACK stimulation, questions arose as to how this highly immunodominant molecule functions during human leishmanisasis. Some possible mechanisms are discussed.

Inefficient protection of human TAP-deficient fibroblasts from autologous NK cell-mediated lysis by cytokines inducing HLA class I expression

We studied HLA class I expression and susceptibility to lysis of activated autologous NK cells in normal and TAP-deficient fibroblasts. These cells were cultured in the presence or absence of cytokines known to increase the surface expression of HLA class I molecules. All the cytokines tested (IFN-alpha, IFN-gamma, TNF-alpha and IFN-gamma + TNF-alpha) increased the expression of HLA class I molecules on fibroblasts after 48-h culture, but on TAP-deficient cells this expression remained very low as compared to that of normal cells. In the presence of IFN-alpha, IFN-gamma or IFN-gamma + TNF-alpha, normal target cells became resistant to lysis by autologous NK cells, whereas this effect was much less pronounced in the case of TAP-deficient fibroblasts. Addition of an anti-HLA class I mAb to fibroblasts treated with cytokines increased lysis of normal but not of TAP-deficient cells. These results suggest that activated TAP-deficient NK cells are strongly cytotoxic to normal autologous cells and that these cells cannot be efficiently protected by cytokines inducing HLA class I expression. Thus, in human TAP deficiency, activated NK cells may contribute to the progressive lung degradation which characterizes the clinical course of these patients.

Engagement of MHC class I proteins on natural killer cells inhibits their killing capacity

We have studied whether engagement of MHC class I (MHC-I) molecules on natural killer (NK) cells can influence the NK killing activity. Human NK effector cells, enriched by nylon wool passage, were incubated with monoclonal antibodies (MoAb) to MHC-I followed by cross-linking with secondary rabbit anti mouse Ig or streptavidin. Cross linking of MHC-I molecules on NK cells resulted in a clear inhibition of the NK activity against the target cells K562, Molt-4 and U937. The inhibitory effect was selective for MHC-I and was not seen with MoAb to MHC-II or CD56 molecules. The inhibition was not mediated via Fc receptors since F(ab)2 fragments of the MHC-I MoAb W6/32 were as effective as the intact antibody. The best inhibition of NK activity was obtained using biotin-labelled F(ab)2 fragments of W6/32 and streptavidin as a cross-linker, where up to 70% reduction in NK cell activity was observed. Antibody dependent cellular cytotoxicity (ADCC) was also inhibited by cross-linking MHC-I molecules on the effector cells. The results show that antibody mediated cross-linking of MHC-I proteins on NK cells can inhibit their killing capacity. This indicates that MHC-I molecules on NK cells can be involved in the regulation of NK cytotoxicity, perhaps by transmitting inhibitory signals into the NK cell.

Decrease in lymphokine-activated killer sensitivity of a human renal-cell carcinoma cell line after cytokine treatment

Recent studies have shown that cytokine treatment of tumor cells alters the sensitivity of these cells to lymphokine-activated killer (LAK) cells, depending on the cell line. In this study, we analyzed the decrease in LAK sensitivity of a human renal-cell carcinoma cell line (SMKT-R-3). The LAK sensitivity of SMKT-R-3 was decreased by treatment with a combination of interferon gamma (IFN gamma) and tumor necrosis factor (TNF). However, the cytokine treatment increased the expression of intercellular adhesion molecule-1 (ICAM-1) on the renal-cell carcinoma cell surface. The conjugate-formation assay also confirmed a slight increase in the binding rate of LAK cells to the renal-cell carcinoma cells. When actinomycin D (a protein synthesis inhibitor) was added to the culture medium prior to treatment with IFN gamma and TNF, the LAK sensitivity of SMKT-R-3 recovered to the level demonstrated by the cells that had not received any cytokine treatment. These results suggest that the effect of cytokines in reducing LAK sensitivity of SMKT-R-3 is mediated by protein synthesis occurring when LAK cells are bound to SMKT-R-3 cells.

Intercellular adhesion molecule-1 expression by bladder cancer cells: functional effects

The role of intercellular adhesion molecule-1 (ICAM-1) and its ligand, leukocyte function-associated antigen-1 (LFA-1), in the interaction between bladder cancer cells and lymphokine activated killer (LAK) cells was investigated. Expression and modulation of ICAM-1 by cytokine treatment was assessed by immunocytometry and Northern blot analysis. Four of five human bladder cancer cell lines expressed ICAM-1 constitutively and responded to cytokine stimulation. Expression of ICAM-1 was upregulated most consistently by treatment with interferon-gamma (IFN gamma) and tumor necrosis factor-alpha (TNF alpha), cytokines that are released into the urine after intravesical BCG treatment. In contrast, interleukin-1 and phorbol myristate acetate exhibited variable effects on ICAM-1 expression, and interferon-alpha had no effect. The adherence of LAK cells to bladder cancer cell monolayers and LAK cell-mediated cytolysis were then studied. Monoclonal antibodies to ICAM-1 and LFA-1 significantly decreased the binding of LAK cells to the cell lines that express ICAM-1 (37 to 75% reduction, p < 0.05), and cytokine treatment (IFN gamma, TNF alpha) of these cells enhanced ICAM-1 dependent adherence (18 to 39% increase, p < 0.05). In contrast, these manipulations had no effect on the binding of LAK cells to the UMUC3 cell line, which does not express ICAM-1. Monoclonal antibodies to LFA-1 decreased LAK cell mediated cytolysis of the bladder cancer cells from 27 to 65% (p < 0.05), but anti-ICAM-1 antibodies were much less effective (0 to 25% decrease in cytolysis). Cytokine treatment (IFN gamma, TNF alpha) of the tumor cells did not significantly increase LAK cell-mediated cytolysis, despite upregulation of ICAM-1. These data demonstrate that ICAM-1 plays a role in the binding of LAK cells to bladder cancer cells but is only marginally involved in the process of LAK cell-mediated cytolysis. These findings suggest that adhesion molecules may be important mediators of the immune response to bladder cancer after intravesical BCG therapy.

Intercellular adhesion molecule-1 expression induced by interleukin (IL)-1 beta or an IL-1 beta fragment is blocked by an IL-1 receptor antagonist and a soluble IL-1 receptor

The effects of a recombinant human interleukin-1 (IL-1) receptor antagonist (IL-1ra) and a recombinant human soluble IL-1 receptor (sIL-1R) on cytokine-induced intercellular adhesion molecule-1 (ICAM-1) expression in a human glioblastoma cell line and a neuroblastoma cell line were determined. Cells were incubated with IL-1 beta, tumor necrosis factor (TNF) alpha and interferon (IFN) gamma. Cells were also tested under identical conditions with an IL-1 beta synthetic peptide fragment (IL-1 beta 208-240) previously shown to possess biological activity. IL-1 beta, TNF alpha and IFN gamma potentiated ICAM-1 expression in both cell lines in a dose-related manner. The IL-1 beta 208-240 fragments, corresponding to the rabbit, rat and human sequences, enhanced ICAM-1 expression in glioblastoma cells at high doses. ICAM-1 expression induced by IL-1 beta, rabbit IL-1 beta 208-240 and human IL-1 beta 208-240 was blocked by the IL-1ra, while TNF alpha- and IFN gamma-induced ICAM-1 expression were not. ICAM-1 expression induced by IL-1 beta and human IL-1 beta 208-240 was also blocked by the sIL-1R. Our findings suggest that IL1 beta 208-240 acts as an IL-1 beta agonist in enhancing ICAM-1 expression in vitro and that this effect is receptor-mediated.

Agar capillary clonogenic microassays for cellular immunocytotoxic activities in human leukaemia and lymphoma

Current concepts of immunotherapeutic approaches in leukemias and lymphomas using activated cytotoxic lymphocytes and macrophages are briefly reviewed. Defective cellular immunocytotoxic activities and effects of interleukins and chemotherapeutic drugs thereupon are discussed. In vitro assays to measure lymphokine-activated killer (LAK) and natural killer (NK) cell activities suffer from various problems, depending on the quality of the endpoints. Our clonogenic microassay for LAK cell activity, using agar-containing glass capillaries, avoids some of the potential artifacts and offers several advantages that are discussed. As an example the stimulatory effect of low mafosfamide concentrations on the LAK cell activity versus K562 human myeloid leukemia cells is demonstrated. Thus, our clonogenic LAK microassay provides a valid tool for preclinical screening of immunomodulatory agents.

Mechanism of interferon gamma-induced protection of human gliosarcoma cells from lymphokine-activated killer lysis: division of lymphokine-activated killer cells into natural killer- and T-like cells

The mechanism by which interferon gamma (IFN-gamma) decreases the susceptibility of the established cultured gliosarcoma line Gl-1 to lymphokine-activated killer (LAK) lysis was analyzed. The results of monolayer depletion and lectin-dependent cellular cytotoxicity assays by LAK cells revealed that the resistance to LAK lysis of IFN-gamma-treated Gl-1 cells is manifested at the stage of LAK cell target recognition alone. We have also divided LAK cells into populations of phenotypically natural killer (NK)- and T-like cells with monoclonal antibodies and complement, respectively. We have used these cells to examine the mechanism of IFN-gamma-induced protection of Gl-1 cells from LAK lysis in cold target inhibition, monolayer depletion, and direct binding assays. The results revealed that NK-like cells do not recognize IFN-gamma-treated Gl-1 cells as efficiently as they do untreated targets, whereas T-like cells show the opposite tendency. In conclusion, we have demonstrated that the IFN-gamma induced protection of tumor cells from LAK lysis is predominantly regulated by the target recognition of NK-like cells. On the other hand, IFN-gamma-treated tumor cells may bind to T-like cells but fail to trigger them to initiate further stages for lysis as effectively as NK-like cells.

TNF impairs in vivo and in vitro natural killer (NK) susceptibility of B16 melanoma cells

Tumour necrosis factor alpha (TNF) is a multipotent cytokine which affects many biological properties of both normal and neoplastic cells. Here we show that treatment with TNF reduces B16-A melanoma cell susceptibility to normal and in vivo- and in vitro-activated NK cell-mediated killing. This resistance is associated with an enhancement of B16-A metastatic potential in normal syngeneic mice, but not in anti-asialo GM1-treated animals, further supporting the NK dependence of TNF-induced enhancement of metastatic ability. A significant increase of MHC class I expression on B16-A murine melanoma cells is observed after TNF treatment. In all these effects TNF interacts positively with interferon gamma (IFN gamma). Taken together, these results indicate that TNF treatment negatively affects the susceptibility of B16-A murine melanoma to NK effectors in vivo and in vitro. This decreased susceptibility may be related, at least in part, to enhanced expression of MHC class I antigens on tumour cells.

Diverse effect of cytokine treatment of tumor cells on specific versus non-specific cytotoxicity

The effect of IFN-gamma and TNF-alpha treatment of an ovarian carcinoma line on the sensitivity to lysis by specific CTL clones and non-specific Tumor Associated Lymphocytes (TAL), isolated from the ascites fluid, was analyzed. The in vitro established TAL line displayed a non-specific lytic activity against the autologous tumor as well as against several allogeneic tumor lines. Pretreatment with IFN-gamma alone, or in combination with TNF-alpha, rendered the carcinoma line less susceptible to lysis by the autologous TAL line. Conversely, susceptibility to lysis by tumor specific T cell clones, isolated from the TAL line, was increased as a result of cytokine pretreatment. Several TCR-alpha/beta+, CD8+ T-cell clones showing a more specific pattern of lysis against the autologous tumor were isolated. Lysis of the autologous tumor by these clones involved the TCR-alpha/beta via a MHC-class I restricted mechanism dependent on the adhesion molecules ICAM-1 and LFA-3, as inferred from antibody blocking studies. The enhanced sensitivity to specific CTL clones seen after cytokine treatment may be related to the enhanced expression of ICAM-1 molecules on the ovarian carcinoma. These results have implications for cytokine based immunotherapy, where IFN-gamma may enhance the effects of tumor associated specific CTL while decreasing that of non-specific effector cells.

HLA antigen expression and malignant mesothelioma

The expression of HLA antigens by a tumor may determine its progression and metastatic potential by influencing the immune response to that tumor. The upregulation of HLA antigen expression on some cell types by interferons (IFNs) may contribute to their antitumor activity. Malignant mesothelioma (MM) is a tumor that has a poor prognosis and is unaffected by conventional therapy, although immunotherapy has not been adequately assessed. In this study, we have examined the constitutive and IFN-inducible expression of class I and class II HLA antigens on MM cell lines using indirect immunofluorescence and Northern blotting. All MM cell lines constitutively expressed class I, but not class II, surface antigen, and all three class I loci (HLA-A, HLA-B, and HLA-C) were expressed. The MM cell lines were heterogeneous in their response to the IFNs. Treatment with IFN-alpha marginally increased class I surface expression, but not class II. Class I mRNA was, however, clearly increased in all cell lines after IFN-alpha treatment, suggesting that class I surface antigen was already maximally expressed. IFN-gamma increased class I mRNA expression in all but one cell line and induced DR expression on three of the cell lines. DQ-beta, but not DQ-alpha, mRNA was inducible in the same three cell lines, but DQ surface antigen was never demonstrable.(ABSTRACT TRUNCATED AT 250 WORDS)

Human small-cell lung-cancer cells are cytokine-resistant but NK/LAK-sensitive

We have studied the effects of 8 cytokines and their combinations on the in vitro growth of 10 human small-cell cancer lines (SCLC). Interferon-alpha and gamma (IFN-alpha and gamma) caused significant but slight growth inhibition over a 7-day incubation period. However, none of the other 6 cytokines, tumor necrosis factor (TNF), lymphotoxin (LT), interleukin-1 beta (IL-1 beta) interleukin-2 (IL-2), transforming growth factor-beta 1 (TGF-beta 1), or granulocyte colony-stimulating factor (G-CSF), modified SCLC cell proliferation. In contrast, all 10 lines were sensitive to lysis by natural killer (NK) and lymphokine-activated killer (LAK) cells. Sensitivity to LAK cells could be increased by pretreatment of SCLC cells with IFN-gamma. As resistance to the cytostatic/cytotoxic activity of some cytokines has been associated with autocrine production of cytokines, we screened the SCLC lines for cytokine mRNAs. Within the limits of detection of the assay we found no expression of TNF, TGF-beta 1, IL-1 beta or IL-6 mRNA in the 10 SCLC lines.

Increased susceptibility of IFN-gamma-treated neuroblastoma cells to lysis by lymphokine-activated killer cells: participation of ICAM-1 induction on target cells

We have investigated the effect of interferon-gamma (IFN-gamma) treatment of neuroblastoma cells on the susceptibility to lysis by lymphokine-activated killer (LAK) cells and examined the participation of cell-adhesion molecules on the target cells in LAK cell lysis. Untreated neuroblastoma cells expressed lymphocyte-function-associated antigen 3 (LFA-3) and neural-cell-adhesion molecule (NCAM), but did not express MHC-class-I, MHC-class-II, or intercellular-adhesion molecule I (ICAM-I). IFN-gamma treatment of neuroblastoma cells induced the expression of MHC-class-I and ICAM-I antigens, but did not affect the expression of MHC-class-II, LFA-3, and NCAM. This was accompanied by an increased susceptibility to lysis by LAK cells. Anti-ICAM-I antibody inhibited partially the increased sensitivity of IFN-gamma-treated neuroblastoma cells to LAK cell lysis, and blocked completely the increase in binding of LAK cells observed after IFN-gamma treatment of the target cells. These results suggest that the increased LAK sensitivity of IFN-gamma-treated neuroblastoma cells is partially attributable to the induction of ICAM-I on neuroblastoma cells and indicate that post-binding events also play a role in the increased sensitivity to LAK cell lysis observed after IFN-gamma treatment.

Effect of IFN-gamma treatment and in vivo passage of murine tumor cell lines on their sensitivity to lymphokine-activated killer (LAK) cell lysis in vitro; association with H-2 expression on the target cells

Interferon-gamma (IFN-gamma) treatment or in vivo passage of the murine YAC-1 lymphoma resulted in reduced sensitivity to in vitro lysis by syngeneic murine spleen cells cultured in rIL-2 (LAK-cells). IFN-gamma treatment also rendered the murine B16 melanoma less sensitive to lysis by syngeneic LAK cells, whereas in vivo passage did not alter LAK sensitivity. The reduction in sensitivity to lysis correlated with enhanced expression of cell surface H-2 on the target cells. The possible role of H-2 was studied with a beta 2-microglobulin-deficient, and thus H-2-deficient, variant of the YAC-1 lymphoma. This variant line remained H-2 negative even after IFN-gamma treatment or in vivo passage, and was highly sensitive to LAK-cell-mediated lysis, even after IFN-gamma treatment or in vivo passage. The present results are discussed in relation to IFN-gamma and in vivo induced modulation of MHC class-1 molecules on target cells and the possible consequences for interaction with activated as well as "natural" effector cells.