Tumor Cytotoxic Factor Research Articles

Metal coordination nanotheranostics mediated by nucleoside metabolic inhibitors potentiate STING pathway activation for cancer metalloimmunotherapy

Activation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is an effective way to initiate an immune response against tumors, and the research on agonists targeting STING has become a new hotspot in the development of antitumor drugs. However, as a novel STING agonist, the limited bioavailability and activation routes of manganese ions (Mn2+) significantly hinder its antitumor effects. To address these challenges, we have designed a metal-coordinated nucleoside metabolic inhibitor (gemcitabine, Gem)-induced metal nanotheranostic (MGP) with PEGylation. This formulation synergistically enhanced the immune response against cancer cells by sensitizing the cGAS-STING pathway and promoting immunogenic cell death (ICD). Modified with PEG derivatives, MGP was efficiently delivered to the tumor site and was internalized by cancer cells. Upon internalization, the release of Mn2+ triggered the activation of the cGAS-STING pathway, while the release of Gem induced DNA damage. On the one hand, the damaged DNA caused by Gem leaked into the cytoplasm, synergistically amplified Mn2+-induced activation of the cGAS-STING pathway, and induced the production of the tumor cytotoxic factor IFN-β. On the other hand, Mn2+-mediated chemodynamic therapy (CDT) exhibited an ICD effect, which further synergized with the activation of the cGAS-STING pathway to promote dendritic cells (DCs) maturation and antigen-specific T cells infiltration. Both in vitro and in vivo studies have demonstrated that MGP nanotheranostics could elicit a robust antitumor effect, especially when combined with anti-PD-1. This study provided a new paradigm for intensifying immune activation by constructing metal coordination nanotheranostics.

C-MET receptor tyrosine kinase as a molecular target in advanced hepatocellular carcinoma.

c-MET is the membrane receptor for hepatocyte growth factor (HGF), also known as scatter factor or tumor cytotoxic factor, a mitogenic growth factor for hepatocytes. HGF is mainly produced by cells of mesenchymal origin and it mainly acts on neighboring epidermal and endothelial cells, regulating epithelial growth and morphogenesis. HGF/MET signaling has been identified among the drivers of tumorigenesis in human cancers. As such, c-MET is a recognized druggable target, and against it, targeted agents are currently under clinical investigation. c-MET overexpression is a common event in a wide range of human malignancies, including gastric, lung, breast, ovary, colon, kidney, thyroid, and liver carcinomas. Despite c-MET overexpression being reported by a large majority of studies, no evidence for a c-MET oncogenic addiction exists in hepatocellular carcinoma (HCC). In particular, c-MET amplification is a rare event, accounting for 4%–5% of cases while no mutation has been identified in c-MET oncogene in HCC. Thus, the selection of patient subgroups more likely to benefit from c-MET inhibition is challenging. Notwithstanding, c-MET overexpression was reported to be associated with increased metastatic potential and poor prognosis in patients with HCC, providing a rationale for its therapeutic inhibition. Here we summarize the role of activated HGF/MET signaling in HCC, its prognostic relevance, and the implications for therapeutic approaches in HCC.

Hepatocyte growth factor twenty years on: Much more than a growth factor

Liver regeneration depends on the proliferation of mature hepatocytes. In the 1980s, the method for the cultivation of mature hepatocytes provided an opportunity for the discovery of hepatocyte growth factor (HGF) as a protein that is structurally and functionally different from other growth factors. In 1991, the scatter factor, tumor cytotoxic factor, and 3-D epithelial morphogen were identified as HGF, and Met tyrosine kinase was identified as the receptor for HGF. Thus, the connection of apparently unrelated research projects rapidly enriched the research on HGF in different fields. The HGF-Met pathway plays important roles in the embryonic development of the liver and the placenta, in the migration of myogenic precursor cells, and in epithelial morphogenesis. The use of tissue-specific knockout mice demonstrated that in mature tissues the HGF-Met pathway plays a critical role in tissue protection and regeneration, and in providing less susceptibility to chronic inflammation and fibrosis. In various injury and disease models, HGF promotes cell survival, regeneration of tissues, and suppresses and improves chronic inflammation and fibrosis. Drug development using HGF has been challenging, but extensive preclinical studies to address its therapeutic effects have provided significant results sufficient for the development of HGF as a biological drug in the regeneration-based therapy of diseases. Clinical trials using recombinant human HGF protein, or HGF genes, are in progress for the treatment of diseases.

Evidence for the presence of an inactive precursor of human hepatocyte growth factor in plasma and sera of patients with liver diseases

Human hepatocyte growth factor (hHGF), which is now known to be the same protein as the scatter factor and the tumor cytotoxic factor, is a heterodimeric protein with one heavy chain and one light chain linked together by a disulfide bond, and is thought to be involved in liver regeneration. Using an enzyme-linked immunosorbent assay (ELISA) and Western blot analysis, we found that a significant amount of single chain precursor of hHGF (pro-hHGF) was present in plasma of patients with fulminant hepatic failure (FHF) and that normal human serum contained a protease or proteases that convert pro-HGF to a heterodimeric (mature) form of hHGF. We also showed that the processing protease activity for hHGF was suppressed by such serine protease inhibitors as leupeptin, antipain, and aprotinin, and that sera of patients with liver diseases such as fulminant hepatic failure, acute hepatitis, chronic hepatitis, and cirrhosis contained not only pro-hHGF but also the protease. This is the first report showing the presence of pro-hHGF in human blood, and our observations suggest that hHGF is synthesized and secreted from the hHGF-producing cells as an inactive pro-hHGF after hepatic injuries, and the pro-hHGF is then converted to an active heterodimeric form of hHGF in the blood. It is also suggested that plasma of patients with liver diseases contains an active protease or proteases that convert pro-hHGF to a mature form of hHGF.

Evidence for the presence of an inactive precursor of human hepatocyte growth factor in plasma and sera of patients with liver diseases

Human hepatocyte growth factor (hHGF), which is now known to be the same protein as the scatter factor and the tumor cytotoxic factor, is a heterodimeric protein with one heavy chain and one light chain linked together by a disulfide bond, and is thought to be involved in liver regeneration. Using an enzyme-linked immunosorbent assay (ELISA) and Western blot analysis, we found that a significant amount of single chain precursor of hHGF (pro-hHGF) was present in plasma of patients with fulminant hepatic failure (FHF) and that normal human serum contained a protease or proteases that convert pro-hHGF to a heterodimeric (mature) form of hHGF. We also showed that the processing protease activity for hHGF was suppressed by such serine protease inhibitors as leupeptin, antipain, and aprotinin, and that sera of patients with liver diseases such as fulminant hepatic failure, acute hepatitis, chronic hepatitis, and cirrhosis contained not only pro-hHGF but also the protease. This is the first report showing the presence of pro-hHGF in human blood, and our observations suggest that hHGF is synthesized and secreted from the hHGFproducing cells as an inactive pro-hHGF after hepatic injuries, and the pro-hHGF is then converted to an active heterodimeric form of hHGF in the blood. It is also suggested that plasma of patients with liver diseases contains an active protease or proteases that convert pro-hHGF to a mature form of hHGF.

Ultrastructural location of human hepatocyte growth factor in human liver

Human hepatocyte growth factor has been purified from the plasma of patients with fulminant liver failure, but where this factor is produced in organs or cells of subjects with liver diseases is unknown. Therefore, we used a monoclonal antibody to human hepatocyte growth factor to stain cells in three normal and 29 diseased liver tissues by immunohistochemical techniques. By light microscopy, the immunostained cells seemed to be polymorphonuclear leukocytes because of their segmented nuclei. Some biliary epithelial cells also were stained. Electron microscopy confirmed that the immunostained cells with segmented nuclei were polymorphonuclear leukocytes and that the stained grains were on the membranes of rough endoplasmic reticulum, around specific or azurophilic granules and in the cell sap. Stained grains in the biliary epithelial cells were found sporadically on the inside and outside of the membranes of rough endoplasmic reticulum near the nuclei. Human hepatocyte growth factor is now known to be the same protein as scatter factor and tumor cytotoxic factor, both of which are produced by human fibroblasts in culture, but our results suggest that polymorphonuclear leukocytes in diseased livers are one cellular source of circulating human hepatocyte growth factor. The immunostaining properties of biliary epithelial cells in diseased livers also suggest that the cells produce and secrete human hepatocyte growth factor.

Ultrastructural location of human hepatocyte growth factor in human liver

Human hepatocyte growth factor has been purified from the plasma of patients with fulminant liver failure, but where this factor is produced in organs or cells of subjects with liver diseases is unknown. Therefore, we used a monoclonal antibody to human hepatocyte growth factor to stain cells in three normal and 29 diseased liver tissues by immunohistochemical techniques. By light microscopy, the immunostained cells seemed to be polymorphonuclear leukocytes because of their segmented nuclei. Some biliary epithelial cells also were stained. Electron microscopy confirmed that the immunostained cells with segmented nuclei were polymorphonuclear leukocytes and that the stained grains were on the membranes of rough endoplasmic reticulum, around specific or azurophilic granules and in the cell sap. Stained grains in the biliary epithelial cells were found sporadically on the inside and outside of the membranes of rough endoplasmic reticulum near the nuclei. Human hepatocyte growth factor is now known to be the same protein as scatter factor and tumor cytotoxic factor, both of which are produced by human fibroblasts in culture, but our results suggest that polymorphonuclear leukocytes in diseased livers are one cellular source of circulating human hepatocyte growth factor. The immunostaining properties of biliary epithelial cells in diseased livers also suggest that the cells produce and secrete human hepatocyte growth factor. (HEPATOLOGY 1994;19:1157–1163.)

BIOLOGIC EFFECT OF HUMAN HEPATOCYTE GROWTH-FACTOR ON HUMAN GASTRIC-CARCINOMA CELL-LINES

Biologic effect of human hepatocyte growth factor (hHGF), which is now known to be the same protein of scatter factor and tumor cytotoxic factor, on gastric cancer cell lines were examined. hHGF messenger RNA expression was undetectable in human gastric cancer cell lines TMK-1 (poorly differentiated adenocarcinoma) and MKN-28 (well differentiated adenocarcinoma). Human fetal lung fibroblast cell line MRC-5 and human stomach derived fibroblast ST-Fib expressed high levels of hHGF mRNA. hHGF production was also confirmed in the culture media of the fibroblast cell lines by enzyme linked immunosorbent assay. Interestingly, TMK-1, having weak expression of E-cadherin, showed marked scattering on 0.1% collagen gel with hHGF (10 ng/ml). The same scattering activity was also observed with fibroblast conditioned medium or with stomach derived fibroblast ST-Fib co-culture. Contrarily, well differentiated adenocarcinoma cell line MKN-28 maintaining strong E-cadherin expression did not show this morphologic change. The expression of c-met proto-oncogene, which encodes the receptor for hHGF, and the biochemical character of hHGF receptor did not differ significantly between TMK-1 and MKN-28. On the other hand, Western blot analysis using specific antibody to phosphotyrosine revealed a difference in phosphoprotein pattern between the two cell lines. These results indicate that hHGF produced by the stromal fibroblasts has a histologic type-specific morphogenic activity on gastric cancer cells with different expression of E-cadherin in a paracrine manner in vivo and a different post-receptor signal transduction mechanism.

Enhancement of human hepatocyte growth factor production by interleukin-1 alpha and -1 beta and tumor necrosis factor-alpha by fibroblasts in culture.

Human hepatocyte growth factor (hHGF) was first purified from plasma of patients with fulminant hepatic failure (Gohda, E., Tsubouchi, H., Nakayama, H., Hirono, S., Sakiyama, O., Takahashi, K., Miyazaki, H., Hashimoto, S., and Daikuhara, Y. (1988) J. Clin. Invest. 81, 414-419) and is now identified to be the same protein as the scatter factor (Weidner, K. M., Arakaki, N., Hartmann, G., Vandekerckhove, J., Weingart, S., Rieder, H., Fonatsch, C., Tsubouchi, H., Hishida, T., Daikuhara, Y., and Birchmeier, W. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 7001-7005) and tumor cytotoxic factor (Shima, N., Nakao, M., Ogaki, F., Tsuda, E., Murakami, A., and Higashio, K. (1991) Biochem. Biophys. Res. Commun. 180, 1151-1158), and it is known to be produced by fibroblasts in culture. Here we report that inflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) stimulate production of hHGF from human embryonic lung fibroblasts, MRC-5, and human gingival fibroblasts, GF-5. Recombinant human IL-1 alpha (rhIL-1 alpha) and recombinant human TNF-alpha (rhTNF-alpha) increased hHGF levels in culture supernatants of MRC-5 and GF-5 cells dose-dependently as determined by an enzyme-linked immunosorbent assay for hHGF. The half-maximal stimulatory concentrations of rhIL-1 alpha and rhTNF-alpha were about 1ng/ml and 10 units/ml, respectively. rhIL-1 beta showed almost the same effect as IL-1 alpha on stimulation of production of immunoreactive hHGF from the two cell lines. However, rhIL-6 failed to show the stimulatory effect on hHGF production by the cells in the range of 2-200 units/ml. Human interferon-beta and -gamma also did not show the stimulatory activity. Stimulation of hHGF production was observed 6-12 h after addition of rhIL-1 alpha or rhTNF-alpha and lasted at least 48 h, and the observed stimulation of hHGF production by cytokines was suppressed by addition of corresponding antiserum. hHGF mRNA levels of MRC-5 cells increased by addition of rhIL-1 alpha and rhTNF-alpha in a dose-dependent manner as determined by Northern blot analysis using cDNA for hHGF as a probe. In addition, results from nuclear run-off transcription experiments showed that the two cytokines regulated increasing hHGF gene expression at transcriptional levels rather than a change in mRNA stability. These observations indicate that the inflammatory cytokines modulate the production and secretion of hHGF by fibroblasts and may play an important role for tissue repair and regeneration.

Effects of protein kinase inhibitors on the mitogenic activity of human hepatocyte growth factor on rat hepatocytes in primary culture

To evaluate the role of protein phosphorylation reactions in signal transduction of human hepatocyte growth factor (hHGF), now known to be the same protein as the scatter factor and tumor cytotoxic factor, we examined the effects of various inhibitors of protein kinases on the mitogenic activity of hHGF on rat hepatocytes in primary culture. Genistein, a specific inhibitor of tyrosine kinase, dose-dependently inhibited the effect of hHGF in stimulating DNA synthesis of hepatocytes. By contrast, 1-(5-isoquinolinesulfonyl)-2- methylpiperazine (H7), a specific inhibitor of protein kinase C, potentiated the stimulatory effect of hHGF on DNA synthesis of hepatocytes. H7 was effective at over 2 micrograms/ml and potentiated the effect of hHGF over 2-fold at 20 micrograms/ml. On the other hand, an inhibitor of Ca++/calmodulin-dependent protein kinase inhibited both the basal and hHGF-stimulated DNA synthesis in the cells, whereas an inhibitor of cyclic nucleotide-dependent protein kinases had little effect on the action of hHGF. These results suggest that tyrosine phosphorylation is required for stimulation of hepatocyte DNA synthesis by hHGF and that the action of hHGF is negatively regulated by protein kinase C activation.

TGF-β is a potent inhibitor of hepatocyte growth factor secretion by human fibroblasts

Transforming growth factor-β 1 (TGF-β 1) inhibited secretion of human hepatocyte growth factor (hHGF), which is also known as scatter factor or fibroblast-derived tumor cytotoxic factor, by MRC-5 cells. The effect was detectable at as little as 10 pg/ml and was more potent than that of dexamethasone. Complete inhibition was observed after 12 h in the presence of 5 ng/ml of TGF-β 1. Phorbol 12-myristate 13-acetate-induced secretion of hHGF from human skin fibroblasts was also suppressed by TGF-β 1. TGF-β 2 inhibited hHGF secretion by MRC-5 cells to the same extent as TGF-β 1, but other growth factors such as epidermal growth factor and acidic and basic fibroblast growth factors had only a slight or null inhibitory effect.

ELISA for F-TCF (human hepatocyte growth factor/hHGF)/fibroblast-derived tumor cytotoxic factor antigen employing monoclonal antibodies and its application to patients with liver diseases

For determination of fibroblast-derived tumor cytotoxic factor, F-TCF (human hepatocyte growth factor/hHGF), sensitive two-step sandwich enzyme-linked immunosorbent assay (ELISA) employing monoclonal antibodies was developed. Microplates were coated with monoclonal antibody (P1C8) and bound F-TCF was quantitated with the second monoclonal antibody (P2D6) linked to peroxidase. The standard curve for F-TCF was found to be linear in the range of 0.16 to 10 ng of F-TCF per ml. The assay was specific for F-TCF but not for plasminogen. The assay can be used for determination of F-TCF antigen in both human plasma and serum. The variation of absorbance was little in duplicate samples. Recoveries of exogenous F-TCF added to serum or plasma samples showed theoretical values. F-TCF antigen levels in 21 healthy volunteers was found to be 0.56 +/- 0.43 ng/ml. In contrast, mean F-TCF levels in patients with liver diseases were all higher than those of healthy subjects. This ELISA system has the advantage of using a sensitive and reproducible set of monoclonal antibodies, and is a useful method for monitoring F-TCF levels in patients with liver diseases.

A fibroblast-derived tumor cytotoxic factor/F-TCF(hepatocyte growth factor/HGF) has multiple functions in vitro

We previously demonstrated that a tumor cytotoxic factor(F-TCF) purified from the culture broth of human embryonic lung diploid fibroblast, IMR-90 cells was one of the human hepatocyte growth factors (hHGFs). In the present report, we demonstrate its biological functions. F-TCF showed moderate cytotoxicity on human tumor cell lines KB, BG-1, MCF-7 and Hs913 T, and strong cytotoxity on mouse tumor cell lines Sarcoma 180, Meth A sarcoma and P388. On the contrary, F-TCF was a potent mitogen not only for adult rat hepatocytes, but also for human endothelial cells, HUVEC and human melanocytes. Moreover, F-TCF induced the differentiation of premyelocyte leukemia, HL-60 cells into morphologically granulocyte-like cells. These biological functions suggest that F-TCF is an effector molecule responsible for inflammation and repair in injured tissues including tumor and liver.

Identity of a tumor cytotoxic factor from human fibroblasts and hepatocyte growth factor

Human embryonic lung diploid fibroblast, IMR-90 cells secreted a tumor cytotoxic factor. The fibroblast-derived tumor cytotoxic factor (F-TCF) has a cytotoxic activity to Sarcoma 180 and a cytostatic and degenerative activities to KB cells. F-TCF has been purified about 540,000-fold with 23.3% recovery from 75 liters of the conditioned medium containing 5% newborn calf serum. The purified F-TCF is a basic glycoprotein with isoelectric point values of 7.4 to 8.6. It was stable in the pH range from 6.0 to 9.0 and was stable at the heating temperature of 60°C for 10 min, but completely inactivated by reducing it with 2-mercaptoethanol. F-TCF has molecular weight of 76 to 80 kD on SDS-PAGE under non-reducing conditions and is a heterodimer consisting of a large α subunit with 52 to 56 kD and a small β subunit with 30 to 34 kD. F-TCF was identified as one of human hepatocyte growth factors by the physicochemical properties including N terminal and a few internal amino acid sequences. We have confirmed that F-TCF has an ability to dramatically stimulate DNA synthesis in adult rat hepatocytes in the low dose range of 1 to 10 ng/ml.

Effector mechanism of human monocyte-mediated cytotoxicity: role of a new tumor cytotoxic factor distinct from interleukin 1 and tumor necrosis factor alpha.

Human blood monocytes activated to the tumoricidal state were previously found to release a factor(s) responsible for tumor cell killing. The activity of the tumor cytotoxic factor(s) (TCF) was determined by release assay of radioactivity from human A375 melanoma cells. On fractionation of the supernatant of activated monocytes by Ultrogel AcA34 and TSK-G3000SW gel chromatographies two major peaks of the material with TCF activity with MWs of 30,000 and 15,000, called TCF-I and TCF-II, respectively were obtained. TCF-II could be neutralized by polyclonal anti-IL-1 beta antiserum, but anti-IL-1 alpha antiserum did not neutralize either factor. TCF-I was separated by ampholine column electrofocusing into three major fractions with TCF activity at pI 5, 6 and 6.8, named TCF-1 alpha, TCF-1 beta and TCF-1 gamma, respectively. The cytotoxic and IL-1 activities of TCF-1 alpha were neutralized by anti-IL-1 alpha serum, whereas those of TCF-1 beta and TCF-1 gamma were not completely neutralized by anti-IL-1 alpha or anti-IL-1 beta antiserum. On DEAE ion-exchange chromatography (TSK DEAE 5PW) TCF-I beta gave two peaks with TCF activity (TCF-I beta 1 and TCF-I beta 2). TCF-I beta 1 was slightly neutralized by anti-TNF alpha antibody, but TCF-I beta 2 was not affected by antisera against IL-1 alpha and IL-1 beta, or anti-TNF alpha antibody, thus ruling out the possibility that tumor necrosis factor (TNF alpha) might be involved in tumor cell killing mediated by TCF-I beta 2. These results indicate that human monocyte-mediated cytotoxicity against human A375 melanoma cells is mediated in part by a tumor cytotoxic factor (TCF; MW, 30,000; pI 6), differing from IL-1 and TNF alpha.

Functional changes in human lymphocytes and monocytes after in vitro incubation with arginine

Human lymphocytes and monocytes obtained from healthy nonsmoking volunteers, were activated by in vitro incubation with excess arginine. Natural killer cell (NK) activity was increased three-fold after in vitro incubation with 64×10 2μg/ml of arginine and 4×10 2μg/ml of arginine induced 1.5 fold increase of human monocytes-mediated(HM) cytotoxicity. Production of tumor cytotoxic factor (TCF) from human monocytes significantly increased after in vitro incubation with arginine (8×10 2 and 32×10 2μg/ml) for 24 hr. At high concentrations of arginine, in vitro growth of tumor cells was evidently suppressed. These results suggest that arginine action against tumor cells is due to, in part, not only via the enhancement of host immune functions (NK activity and HM cytotoxicity) but also direct effect to tumor cells.

A monosaccharide precursor of Escherichia coli lipid A has the ability to induce tumor-cytotoxic factor production by a murine macrophage-like cell line, J774.1.

A monosaccharide precursor of Escherichia coli lipid A, designated lipid X, which is a diacylglucosamine 1-phosphate with beta-hydroxymyristoyl groups at positions 2 and 3, was shown to have the ability to induce the production of tumor necrosis factor (TNF)-like tumor-cytotoxic factor by a murine macrophage-like cell line, J774.1. This cytotoxic factor was released from J774.1 cells grown in the presence of lipid X and related compounds, and it was assayed as to its lytic activity against [3H]thymidine-labeled L929 cells. Dose-response studies revealed that lipid X induced the production of smaller amounts of the tumor-cytotoxic factor than LPS at low concentrations, but it induced that of considerable amounts at and over 1 microgram/ml. Elimination of 1-phosphate or 3-O-beta-hydroxymyristoyl group from lipid X completely prevented the induction of producing this factor by the macrophages. Therefore, it is suggested that both 1-phosphate and 3-O-beta-hydroxymyristoyl groups are essential for the biologic activity of lipid X, as to the induction of the tumor-cytotoxic factor production in the macrophages.

Kinetics and Function of Tumor Cytotoxic Factor(s) Produced by Human Blood Monocytes Activated to the Tumoricidal State<xref ref-type="fn" rid="FN2">2</xref>

Human monocytes obtained from healthy volunteers and isolated by centrifugal elutriation were not cytotoxic to allogeneic tumorigenic cells. These freshly isolated monocytes were rendered tumoricidal following interaction in vitro for 24 hours with greater than 0.01 micrograms lipopolysaccharide (LPS)/ml or over 1 microgram nor-muramyl dipeptide/ml. Monocytes activated by this procedure produced a soluble factor that lysed tumor cells. Full expression of tumor cell lysis required a minimum of 18 hours' exposure of tumor cells to the factor. The degree of tumor cytotoxic factor (TCF) production was closely related to the intensity of monocyte activation to become tumoricidal. Significant production of TCF by monocytes was detected in the supernatants after treatment for 3 hours with LPS. TCF was also released by activated monocytes when cocultivated with tumorigenic cells. Similarly, the level of TCF production correlated with the monocyte density. TCF destroyed human allogeneic tumor cell lines (melanoma, glioblastoma, colon carcinoma, prostatic carcinoma, and breast carcinoma), but it did not affect nontumorigenic cell lines (lung and skin fibroblasts). TCF activity was not blocked by superoxide dismutase, catalase, or protease inhibitors; it was destroyed by being heated at 100 degrees C for 2 minutes. The ability of activated monocytes to release TCF could enhance host defense against cancer.

In vitro cytotoxicity to various human tumor cell lines of a tumor cytotoxic factor(s) produced by human alveolar macrophages.

When human alveolar macrophages (AM) obtained by lavage of the lungs of healthy donors were incubated in medium with or without lipopolysaccharide (LPS) they released a factor(s) with tumor cell killing activity. This tumor cytolytic and/or cytotoxic factor(s) (TCF) was assayed by measuring its effect in inhibiting target cell growth. TCF activity was not observed in the supernatant from cultures of LPS-treated hematopoietic malignant cell lines (monocytic leukemia, B-cell leukemia and T-cell leukemia cell lines). Human TCF was significantly cytotoxic to 13 of 15 solid-tumor cell lines tested and to 7 of 9 hematopoietic malignant cell lines, but not to two different normal, nontumorigenic cell lines. TCF-rich supernatants contained low levels of interferon (IFN) activity that were not significantly cytotoxic to A-375 melanoma cells. Human TCF and IFN-alpha or IFN-beta had additive cytotoxic effects. These data suggest that human TCF released by activated human AM may be of potential use in the treatment of malignant disseminated diseases.