Generation of mouse natural killer (NK) cell activity: effect of interleukin-2 (IL-2) and interferon (IFN) on the in vivo development of natural killer cells from bone marrow (BM) progenitor cells

Immune microenvironment of cervical cancer and the role of IL-2 in tumor promotion

The tumor microenvironment (TME) is a heterogeneous mixture of resident and tumor cells that maintain close communication through their secretion products. The composition of the TME is dynamic and complex among the different types of cancer, where the immune cells play a relevant role in the elimination of tumor cells, however, under certain circumstances they contribute to tumor development. In cervical cancer (CC) the human papilloma virus (HPV) shapes the microenvironment in order to mediate persistent infections that favors transformation and tumor development. Interleukin-2 (IL-2) is an important TME cytokine that induces CD8+ effector T cells and NKs to eliminate tumor cells, however, IL-2 can also suppress the immune response through Treg cells. Recent studies have shown that CC cells express the IL-2 receptor (IL-2R), that are induced to proliferate at low concentrations of exogenous IL-2 through alterations in the JAK/STAT pathway. This review provides an overview of the main immune cells that make up the TME in CC, as well as the participation of IL-2 in the tumor promotion. Finally, it is proposed that the low density of IL-2 produced by immunocompetent cells is used by tumor cells through its IL-2R as a mechanism to proliferate simultaneously depleting this molecule in order to evade immune response.

Reduction of perforin, granzyme B, and cytokine interferon gamma by ethanol in male Fischer 344 rats

BACKGROUND

Chronic alcohol consumption can impair the immune system and predispose individuals to an increased risk of cancer and infection. Natural killer (NK) cells are the first line of defense against viral, bacterial, and fungal infections and play an important role in cellular resistance to malignancy and tumor metastasis. We have shown previously that ethanol administration suppresses NK cell cytolytic activity in male Fischer rats. This study analyzed the effects of ethanol on perforin, granzyme B, and the cytokine interferon (IFN)-gamma, factors that modulate NK cell cytolytic activity, to understand the molecular mechanism involved in ethanol's suppression of NK cell activity.

METHODS

A group of male Fischer rats was fed an ethanol-containing diet (8.7% v/v), whereas a control group was pair-fed an isocaloric diet. At the end of 2 weeks, animals were decapitated, and spleen tissues were immediately removed and used for analysis of NK cell cytolytic activity, perforin, granzyme B, and IFN-gamma messenger RNA (mRNA) or protein levels. The mRNA levels of perforin, granzyme B, and IFN-gamma were evaluated by quantitative real-time polymerase chain reaction, and protein levels of these factors were analyzed by Western blot, enzyme-linked immunosorbent assay, or enzymatic activity assay.

RESULTS

Ethanol reduced the NK cell cytolytic activity and decreased the mRNA expression of perforin, granzyme B, and IFN-gamma in ethanol-fed animals when compared with pair-fed animals. Ethanol also significantly reduced the protein levels of perforin and IFN-gamma and the enzyme activity of granzyme B in alcohol-fed animals as compared with pair-fed animals.

CONCLUSIONS

These data suggest that chronic ethanol consumption may suppress NK cell cytolytic activity in male Fischer rats by decreasing the production, activity, or both of granzyme B, perforin, and IFN-gamma.

Therapeutic activity of NK cells against tumors

While it is generally accepted that natural killer (NK) cells, by killing tumor cells in the circulation, represent a first line of defense against metastases, their therapeutic activity against established tumors has been limited. In this review, we describe studies to improve the therapeutic effectiveness of activated NK cells in both animal models and clinical trials to better understand the biological problems that limit their effectiveness.

Generation and control of metastasis in experimental tumor systems; inhibition of experimental metastases by a tilorone analogue

The role of the chemical compound RMI 10,874DA (3,6-bis[2-(dimethylamino)-ethoxyl]-9H-xanthene-9-one dihydrochloride) in the abrogation of the metastatic spread of tumor cells was studied. Pre-treatment of BALB/c mice with the RMI 10,874DA compound (referred to below as tilorone analogue) completely eliminated lung colonization of an H-2-negative (GR9.B9) MCA-induced fibrosarcoma clone in an experimental metastasis assay. Other murine tumors, including H-2-positive and H-2-negative chemically induced fibrosarcoma clones and B16 melanoma, were also sensitive to the treatment; orally administered tilorone analogue given one day before the i.v. injection of tumor cells markedly inhibited lung colonization. The effect was not due to direct toxicity of tilorone analogue on tumor cells, but instead it was dependent on NK cells; this was suggested by the finding that anti-asialo GM, treatment of mice abrogated the effect of tilorone analogue. Kinetic studies of splenic NK activity in tilorone-treated mice showed a rapid boosting of NK-cell activity, the greatest stimulation occurring the day before removal of splenocytes for 51Cr-release assay against YAC-I target cells. These kinetics correlated with the inhibition of in vivo lung colonization after tilorone analogue treatment. Inhibition of experimental tumor metastasis was dose-dependent and was observed when animals were treated the day before or the day after tumor-cell injection. Furthermore, repeated treatment of mice with this tilorone analogue significantly reduced lung colonization.

Interferon alpha in combination with other biologics: the scientific rationale

Interferon alpha (IFN alpha) has widely pleiotropic effects, on both the immune system and tumour cells, and any of these effects might provide the basis for additive or synergistic effects when administered in combination with other biologics. Some of the main sites of action to consider include the ability of IFN alpha to: inhibit the growth of tumour cells; induce differentiation, and/or MHC expression on tumour cells; and stimulate the activation and/or differentiation of natural killer (NK) cells, cytotoxic T lymphocytes, and cytotoxic macrophages. Other biologics with similar sites of action might be expected to provide additional effects when combined with IFN alpha, and factors with other, complementary anti-tumour effects might synergize. Potentially important therapeutic effects have been observed when IFN alpha has been combined with IFN gamma, interleukin 2, tumour necrosis factor, interleukin 1, monoclonal antibodies, and retinoids. The development of therapeutic strategies on the basis of hypotheses as to how IFN alpha might effectively interact with another biologic, coupled with careful assessment of effects on the tumour cells and/or serial monitoring of immunologic parameters, might be expected to lead most expeditiously to successful therapeutic combinations of IFN alpha with other biologics.

Growth of murine natural killer cells from bone marrow in vitro: role of TNF alpha and IFN gamma

It has been previously shown that natural killer (NK) cell growth can be induced by interleukin-2 (IL-2) in bone marrow (BM) cultures and that other cytokines (CKs), including IL-1 alpha, act synergistically with IL-2. However, as the effect of IL-2 and IL-1 alpha could be due to direct stimulation of NK progenitor cell growth, as well as to the induction of other factors, we analysed the role of the endogenous production of CKs in BM cultures. Results show that mRNAs specific for tumour necrosis factor-alpha (TNF alpha) and interferon-gamma (IFN gamma) are detectable within hours in BM cultures supplemented with IL-2 and IL-1 alpha, and that the amount is higher when both IL-2 and IL-1 alpha are present. Antibodies directed against TNF alpha and IFN gamma abrogate the NK cell development, indicating that these CKs play an essential role. The antibodies, however, had no effect on mature NK cells. Furthermore, pretreatment of BM cells with TNF alpha or IFN gamma before culturing with IL-2, enhances IL-2 responsiveness and NK cell growth. These results suggest that induction of cytokines production may be important for growth of NK cells from BM precursors and that the synergistic effect of IL-1 alpha could be due, at least in part, to increased TNF alpha and IFN gamma production.

Effects of a stable prostacyclin analogue on platelet activity and on host immunocompetence in mice

The stable prostacyclin (PGI2) analogue, iloprost, is a potent inhibitor of both tumor cell-induced platelet aggregation and of experimental metastasis in mice. To explore possible mechanisms of antimetastatic effect of iloprost, we measured the effect of this drug on both platelet aggregation and immunocompetence in the mouse. Iloprost (4 x 10(-8) M) inhibited platelet aggregation as induced by a mixture of collagen and epinephrine for at least 180 minutes of incubation, and completely reversed platelet aggregation when added during the second wave of aggregation. In addition, aggregation of platelets obtained from iloprost-treated mice (0.2 mg/kg) was completely inhibited for at least 90 minutes of incubation. Moreover, iloprost pretreatment in vivo counteracted tumor cell-induced thrombocytopenia. Thus, mouse platelets were equally sensitive to the inhibitory effect of iloprost on aggregation as platelets of other species including humans. Effects of iloprost on parameters of host immunocompetence that may influence tumor growth and metastasis formation were also evaluated. Iloprost treatment increased significantly macrophage cytostasis to tumor cells, natural killer (NK) lytic activity of spleen cells and T-cell mediated cytotoxicity ex vivo. These results suggested that the antimetastatic effect of iloprost in the mouse may be attributable to multiple mechanisms including inhibition of platelet aggregation and stimulation of certain host immune functions.

Antitumor effects of a new interleukin-2 slow delivery system on methylcholanthrene-induced fibrosarcoma in mice

The interleukin-2 (IL-2) mini-pellet, the carrier material of which is a biocompatible and biodegradable atelocollagen refined from bovine skin, contains 1 x 10(6) units of IL-2 and can release IL-2 slowly in vivo by diffusion and dissolution. We have evaluated the antitumor effects of the IL-2 mini-pellet on an established solid murine tumor, methylcholanthrene-induced fibrosarcoma (Meth A). The subcutaneous administration of the IL-2 mini-pellet alone on days 8 and 11 after tumor inoculation significantly inhibited tumor growth. A significant inhibition was also seen when it was combined with the intravenous injection of 5 x 10(7) lymphokine-activated killer (LAK) cells, in comparison to the untreated controls. Moreover, therapy with the IL-2 mini-pellet alone or in combination with LAK cells also prolonged the survival of mice bearing Meth A fibrosarcoma. In order to determine the precise mechanism of action of these antitumor effects, we tested splenocytes of treated mice for cytotoxic activity in vitro and investigated tumor tissues by an immunohistochemical method. On day 2 after the administration of the IL-2 mini-pellet, the lytic activity of splenocytes against both YAC-1 and JTC-11 cells (i.e. NK and LAK activity) was significantly augmented, and on day 7 a massive accumulation of lymphocytes, which were mainly like Thy1+ and/or asialo-GM1+ LAK cells, was seen in the tumor. These findings indicate that the IL-2 mini-pellet is an appropriate system for local administration of IL-2 and can induce LAK-like effector cells at the target site.

Cyclosporin A inhibition of interleukin 2 gene expression, but not natural killer cell proliferation, after interferon induction in vivo

The IFN inducer, poly(I:C), elicits acute NK cell blastogenesis and proliferation in vivo. The role of IL-2 in mediating this proliferation was investigated in the studies presented here. Blast NK cells were isolated from poly(I:C)-treated, T cell-deficient athymic mice. Dividing cells, incorporating [3H]thymidine, were enriched in the J11d- low density populations isolated from poly(I:C)-treated mice, and were characterized as NK by the following criteria: (a) they were eliminated by treatment with anti-AGM1 in vivo; and (b) they directly mediated lysis of NK-sensitive target cells in a single cell cytotoxicity assay with autoradiography. These poly(I:C)-induced blast NK cells were responsive to IL-2, but, when compared with in vivo activated T cells, responsiveness required 1,000-fold higher concentrations of the factor. The technique of in situ hybridization was used to evaluate induction of IL-2 gene expression after poly(I:C) treatment in vivo. Treatment of euthymic, athymic, and severe combined immunodeficient mice with poly(I:C) activated IL-2 gene expression in a small percentage of spleen leukocytes. The transcription-positive cells were enriched in low density cell populations. These findings demonstrate that IL-2 transcription occurs after IFN induction in vivo, and suggest that an endogenous source of IL-2 exists other than the mature T cell. To assess the IL-2 dependence of in vivo NK cell expansion, poly(I:C)-treated athymic mice were given cyclosporin A (CsA), an agent that regulates IL-2 production at the level of gene transcription. The drug resulted in an 85-100% reduction in the percentages of cells transcribing IL-2. In contrast, CsA administration did not block IFN-enhanced NK cell cytolytic activity, expansion of large granular lymphocyte numbers, or NK cell proliferation. These findings demonstrate that although the proliferation of blast NK cells can be supported by IL-2, IL-2 is not an important mediator of IFN-induced NK cell expansion. Moreover, they establish that the acute proliferation of NK cells in response to IFNs is CsA insensitive.

Interleukin 2-induced proliferation of murine natural killer cells in vivo

The growth factor, IL-2, was administered to mice to evaluate the in vivo responsiveness of NK cells to this factor. The immediate effects of this factor on NK cells were determined by examining cytotoxic activity at 18-24 h after a single treatment with rIL-2. Although moderate doses of rIL-2 (3 x 10(4) U) could be shown to activate existing cytotoxic cells on a per cell basis, higher doses (10(6) U) were required to elicit blast size killer cells. The elicited killer cells were characterized as NK cells by the following criteria: (a) they were readily induced in athymic mice; (b) they mediated killing of NK-sensitive YAC-1 target cells but not NK-resistant P815 target cells; and (c) they expressed the NK cell determinants asialo ganglio-n-tetraosylceramide and NK1.1, but not the T cell determinants CD3, L3T4, or Lyt-2. High-dose IL-2 treatment induced not only the appearance of blast size NK cells, but also the expansion of this population. After treatments, the number of large granular lymphocytes and the number of NK1.1+ cells were increased at least twofold. Analysis of DNA content within the NK1.1+ cell subset demonstrated that IL-2 preferentially drove NK1.1+ cells into S and G2/M phases of the cell cycle. The in vivo elicited blast lymphocytes were examined by Northern blot analysis and in situ hybridization for expression of the IL-2-R p55 alpha chain gene. As previous work from this laboratory has demonstrated that NK cells proliferate in response to IFNs and IFN inducers in vivo, blast lymphocytes were also prepared after IFN treatments. The NK cells were not induced to express detectable levels of the alpha chain gene under any of the conditions examined. Blast T lymphocytes, isolated at times during viral infections when IL-2 production can be demonstrated in vitro, were induced to transcribe the alpha chain gene. Treatments of euthymic mice with high-dose IL-2 also induced transcription of the alpha chain gene in 41% of the non-B blast lymphocytes, but only background percentages of the NK1.1+ cells expressed the alpha chain gene. Transcription of the alpha chain gene was not induced in the NK cell-abundant athymic mice after IL-2 treatment. All of the in vivo elicited blast lymphocytes were induced to express IFN-gamma. Taken together, these data definitively demonstrate that IL-2 can induce NK cell proliferation and expansion in vivo. They also show that exposure to IL-2 in vivo, either by administration or endogenous production of the factor, induces transcription of the IL-2-R alpha chain gene in populations of cells containing T cell subsets. The results suggest, however, that murine NK cells are not induced to express high levels of the alpha chain gene in response to IL-2 in vivo.

Effect of Biostim (RU 41.740) on natural killer cell generation from bone marrow precursors

We have evaluated the possible effect of RU 41.740 (Biostim), a mixture of two glycoproteins extracted from K. pneumoniae, on the in vitro interleukin-2 (IL-2)-induced generation of NK cells from bone marrow (BM) precursors and on the in vivo reconstitution of splenic NK activity in lethally irradiated (9 Gy) and BM reconstituted mice. Our results show that RU 41.740 is able to augment the generation of NK cells when added (1-0.01 micrograms/ml) to normal or 5-fluorouracil-resistant BM, cultured in the presence of recombinant IL-2. Also, in vivo treatment of lethally irradiated mice, transplanted with syngeneic BM cells, with RU 41.740 (1-0.1 mg/kg i.v.) from day 0 through day 4 after BM graft, resulted in a significant augmentation of NK activity reconstitution.

Induction of tumoricidal macrophages from bone marrow cells of normal mice or mice bearing a colony-stimulating-factor-producing tumor

Nonadherent cells of the bone marrow of C3H/HeN mice were incubated for 3 days with the culture supernatant of an L-929 cell line containing macrophage-colony-stimulating factor. Approximately, 70% of the cells became phagocytic, adherent to plastic dishes and positive for nonspecific esterase staining. The adherent cells exhibited a weak tumoricidal activity against syngeneic mammary carcinoma cells, and the cytotoxicity was strongly augmented by the addition of bacterial lipopolysaccharide to the cytotoxicity assay. The cytotoxicity induced by lipopolysaccharide was also shown to be mediated by Thy1.2- and asialo-GM1+ cells, and was abrogated by the addition of carrageenan. Macrophage-colony-stimulating-factor-producing (D66) and nonproducing (A23) variants were separated from the MM48 tumor line in in vitro culture following limiting dilution. There was no difference between these two variants in either the in vitro growth rate or the susceptibility to macrophage-mediated cytotoxicity. C3H/HeN mice inoculated i.p. with D66 survived longer than did those inoculated i.p. with A23. C3H/HeN mice bearing D66 or A23 as an ascitic form were given i.p. injections of Nocardia rubra cell wall skeleton (N-CWS). N-CWS significantly prolonged the survival period of mice bearing D66, whereas it exhibited no apparent antitumor effect on mice bearing A23. The increase in the cell number of D66 in the peritoneal cavity was significantly retarded, compared with that of A23. In contrast, the number of peritoneal macrophages increased more in D66-bearing mice than in A23-bearing mice. The increase in the peritoneal macrophage number was further augmented by an i.p. injection of N-CWS. Peritoneal macrophages of D66-bearing mice exhibited apparent tumoricidal activity against MM48 tumor cells in the presence of lipopolysaccharide, and the cytotoxicity was significantly augmented by i.p. injection of N-CWS. On the other hand, the responsiveness of peritoneal macrophages to lipopolysaccharide was found to be poor in A23-bearing mice and the tumoricidal activity was only weakly augmented by N-CWS. These results strongly suggest that M-CSF plays an important role not only in the maturation of macrophage progenitors but also in the induction and the accumulation of activated macrophages.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.

Lymphokine-activated killer cells derived from murine bone marrow: age-associated difference in precursor cell populations demonstrated by response to interferon

We have previously demonstrated that the majority of precursor cells of lymphokine-activated killer (LAK) cells in spleens from both young and old mice reside in the natural killer (NK) cell or pre-NK cell populations. In the present study, we examined the induction of LAK cell activity in bone marrow cells from young and old mice and its modulation by interferon (IFN). Bone marrow cells from either young (6-9 weeks) or old (20-26 months) mice were cultured with 1000 U/ml of human recombinant interleukin 2 (rIL-2) for 5 days. The cells were harvested and tested for their cytotoxicity against NK-resistant fresh tumor cells (MCA-102) in a 51Cr release assay. As with spleen cells, bone marrow cells from old and young mice developed comparable levels of activity. Phenotypic analysis showed that virtually all of the LAK precursor cells were asialo GM1+ and most of the effector cells expressed Thy-1, regardless of the age of the mice. Inclusion of IFN-gamma during the culture with rIL-2 augmented the activity induced in bone marrow of young mice, but, in contrast, inhibited the generation of LAK activity from bone marrow cells of old mice. These results demonstrate a differential sensitivity of LAK precursor (or pre-NK) cells of old and young mice to interferon.

Eradication of mouse melanoma by combined treatment with recombinant human interleukin 2 and recombinant murine interferon-gamma

Successful immunotherapy of early s.c. or i.p. (B16) melanoma in syngeneic C57BL/6 (B6) mice was achieved with s.c. peri-lesional injections (for s.c. tumors) or i.p. injections (for i.p. tumors) of recombinant human interleukin 2 (rIL-2) and recombinant murine interferon-gamma (rIFN-gamma). Over a 28-day period, rIL-2 and rIFN-gamma were injected 14 times. Results with this combination were additive with s.c. tumors and synergistic with i.p. tumors. Treatment with 6,250 U-25,000 U of rIL-2 and 2 micrograms of rIFN-gamma began 1-3 days after s.c. inoculation of melanoma. On day 50, 87% (72/83) of mice thus treated were completely free of tumor. None of the 78 control mice (tumor + buffer) survived. Of mice receiving either rIL-2 or rIFN-gamma alone, 59% (47/79) and 53% (44/83), respectively, were tumor-free. I.p. tumors were also eradicated by i.p. injections of rIL-2 (50,000 U) with rIFN-gamma (5, 10, and 15 micrograms) as judged by absence of tumor in 81% (21/26) of mice autopsied between days 45 and 65. No control mice survived, and only 17% (2/12) and 20% (6/30) given either rIL-2 or rIFN-gamma separately (i.p.) were tumor-free. Doses of rIFN-gamma from 1-4 micrograms were more beneficial in eliminating 1-day s.c. melanomas than were higher doses, and local s.c. treatment was far superior to distant or systemic treatment. Non-adherent peritoneal or splenic cells from mice bearing 6-day-old i.p. melanomas and treated with one or both lymphokines on days 3 and 4 were used in cytotoxicity assays in vitro. Significant cytotoxicity against cultured melanoma cells was displayed by cells harvested from lymphokine-treated mice, but there was no evidence of the synergism observed with combination treatment of i.p. tumors in vivo. rIFN-gamma inhibited proliferation of melanoma cells in vitro, whereas rIL-2 stimulated proliferation at 1,000 U/ml. Plating efficiency was increased by at least 30% by culture with 100 U or 1,000 U of rIL-2/ml and both concentrations neutralized the inhibitory effect of 0.05 ng/ml of IFN-gamma, but not of 0.5 or 5.0 ng/ml.

Fifty cases of human immunodeficiency virus (HIV) infection: immunoultrastructural study of circulating lymphocytes

The peripheral lymphocytes of 50 cases of human immunodeficiency virus (HIV) infection (13 of acquired immune deficiency syndrome (AIDS), 17 of AIDS related complex (ARC), and 20 healthy carriers) were studied immunoultrastructurally. The prevalence of "tubuloreticular structures" and "tubular confronting cisternae" increased with the progression of the disease. Numerous tubular confronting cisternae were noted in patients presenting with a high serum acid labile alpha-interferon values. The patients with depressed natural killer cell activity were characterised by circulating immature natural killer cells with abundant multivesicular bodies that were devoid of "parallel tubular arrays". With an immunogold staining technique the location of HIV antigen was detected ultrastructurally, both at the surface of "hand-mirror" natural killer cell lymphocytes and inside vacuolised cells, probably corresponding to infected T4 lymphocytes. These findings indicate the usefulness of electron microscopic techniques in evaluating the pathology and the pathogenetic outcome of AIDS.

Role of interferons in natural killer cell generation from primitive bone marrow precursors

We studied the possible role of interferons (IFNs) on the interleukin-2 (IL-2)-dependent development of mouse natural killer (NK) cells from undifferentiated bone marrow (BM) precursors. Results indicate that alpha-IFN is able to synergize with IL-2 in the induction of lytic effectors. The stimulating effect of alpha-IFN is dose-dependent and is also obtained when BM cells are pretreated shortly before culturing. The precursor cells are resistant to treatment with 5-fluorouracil (FU, 150 mg/kg i.v.). Treatments which have been shown to eliminate more differentiated cells but spare less differentiated BM precursors, are asialoGM1-, Thy1+, Lyt1- and Lyt2-. Effector cells generated by culturing with IL-2 and alpha-IFN are typical NK cells in that they lyse only NK-susceptible targets. These are Thy1+, asialoGM1+, Lyt5+, Lyt1- and Lyt2-. These data suggest that alpha-IFN may represent a maturational signal for the generation of NK cells from undifferentiated BM precursors.