Ex vivo activation of killer monocytes (AKM) and their application to the treatment of human cancer

Re-education of Tumor-Associated Macrophages by CXCR2 Blockade Drives Senescence and Tumor Inhibition in Advanced Prostate Cancer

Tumor-associated macrophages (TAMs) represent a major component of the tumor microenvironment supporting tumorigenesis. TAMs re-education has been proposed as a strategy to promote tumor inhibition. However, whether this approach may work in prostate cancer is unknown. Here we find that Pten-null prostate tumors are strongly infiltrated by TAMs expressing C-X-C chemokine receptor type 2 (CXCR2), and activation of this receptor through CXCL2 polarizes macrophages toward an anti-inflammatory phenotype. Notably, pharmacological blockade of CXCR2 receptor by a selective antagonist promoted the re-education of TAMs toward a pro-inflammatory phenotype. Strikingly, CXCR2 knockout monocytes infused in Pten^pc−/−; Trp53^pc−/− mice differentiated in tumor necrosis factor alpha (TNF-α)-releasing pro-inflammatory macrophages, leading to senescence and tumor inhibition. Mechanistically, PTEN-deficient tumor cells are vulnerable to TNF-α-induced senescence, because of an increase of TNFR1. Our results identify TAMs as targets in prostate cancer and describe a therapeutic strategy based on CXCR2 blockade to harness anti-tumorigenic potential of macrophages against this disease.

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CXCR2 blockade drives re-education of tumor-associated macrophages (TAMs)

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Infusion of CXCR2-KO monocytes in tumor-bearing mice blocks tumor progression

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PTEN deletion sensitizes tumor cells to TNF-α-induced senescence and growth arrest

Kupffer cells and pit cells are not effective in the defense against experimentally induced colon carcinoma metastasis in rat liver

The present study was performed to investigate processes involved in circumvention of the immune system by advanced stages of tumor growth in the liver. The efficacy of Kupffer cells and pit cells against cancer cells was tested in vivo in an experimental model of colon carcinoma metastasis in rat liver. Liver tumors were induced by administration of CC531 colon cancer cells into the vena portae. After 3 weeks, livers were obtained and partly fixed for electron microscopic procedures or frozen in liquid nitrogen for enzyme and immunohistochemistry at the light microscope level. The activation status of Kupffer cells was studied by expression of Ia-antigen (MHC class II) and by measurement of glucose-6-phosphate dehydrogenase (G6PDH) activity in the cells in situ as a measure of production of reactive oxygen species. Large numbers of Kupffer cells were found in liver parenchyma surrounding colon carcinomas when compared with levels in control livers, but these cells were not activated. Large numbers of activated monocytes and macrophages, cytotoxic T cells but only a few pit cells were found to be recruited to the boundary between liver parenchyma and tumors or their stroma. In those areas where cancer cells invaded liver parenchyma, only newly recruited macrophages and some Kupffer cells were present but few cytotoxic T cells or pit cells were found. The low activation status of Kupffer cells both in terms of production of reactive oxygen species and Ia-antigen expression and the absence of significant numbers of pit cells at tumor sites suggest that Kupffer cells and pit cells do not play a significant role in advanced stages of tumor growth. High levels of prostaglandin E2 were detected in the parenchyma of livers containing tumors and transforming growth factor beta was detected in the stroma of the tumors, therefore suggest that cytotoxicity of newly recruited monocytes, macrophages and cytotoxic T cells may be limited in these stages because of local production of these immunosuppressive factors.

Activated monocytes kill malignant brain tumor cells in vitro

The purpose of our study was to investigate the susceptibility of human glioblastoma multiforme (GBM) cells to lysis by human peripheral-blood monocytes following activation with biological response modifiers (BRM) and to lysis by various BRMs directly. Cytotoxic effects were determined using a monocyte-/BRM-mediated tumor cytotoxicity assay. Human peripheral-blood monocytes from healthy donors were activated in vitro by incubation for 24 h with different BRMs such as gamma- and beta-interferon (gamma, beta-IFN), lipopolysaccharide (LPS), muramyldipeptide (MDP) and tumor necrosis factor-alpha (TNF-alpha) in varying concentrations and combinations. Seven human GBM cell lines as well as an adenocarcinoma brain metastasis cell line and a malignant melanoma cell line served as target cells. Radiolabeled target cells were cocultivated with activated monocytes or with BRMs directly. Cytotoxicity was calculated after 72 h of cocultivation. High levels of cytotoxicity were mediated by monocytes activated with beta-IFN in six out of eight brain tumor cell lines and with TNF-alpha in five cell lines. The combination of two BRMs, in particular the combination of gamma-IFN + beta-IFN and gamma-IFN + TNF-alpha, was associated with an enhanced monocyte mediated lysis exceeding LPS control, whereas the combination of gamma-IFN + MDP was very effective against the metastasis cell line. Monocyte-mediated cytotoxicity against tumor target cells was up to ten fold higher than direct cytotoxicity of soluble BRMs. Our data indicate that BRM-stimulated peripheral-blood monocytes exert cytotoxic properties against human glioblastoma cells in vitro, which exceed those of BRMs alone up to ten fold. The higher tumoricidal activities observed after stimulation with combined BRMs suggest mutual promoting mechanisms of BRMs acting on the stimulation of lyctic activity in human peripheral blood monocytes.

Mechanism for the recruitment of macrophages to cancer site. In vivo concentration gradient of monocyte chemotactic activity

BACKGROUND

Tumor stroma is characterized by the development of new blood vessels, an inflammatory cell infiltration, and a fibrotic reaction. The inflammatory component of tumor stroma plays an important role in the modulation of tumor expansion. In this respect, macrophages constitute a major part of the inflammatory cell infiltration and can exert cytotoxic activity against tumor cells. The accumulation of macrophages in the vicinity of the tumor suggests their recruitment from circulating blood monocytes through the local release of chemotactic factors for monocytes.

METHODS

To detect the existence of a concentration gradient of monocyte chemotactic activity (MCA) between the tumor vicinity and blood vessels, malignant pleural effusions defined by the local presence of cancer cells were evaluated for quantification of MCA.

RESULTS

Unlike nonmalignant pleural effusions, malignant pleural effusions were characterized by the presence of increased levels of MCA, and in lung adenocarcinoma (a cancer with high inflammatory cell infiltration), pleural levels of MCA were significantly greater than in small cell lung carcinoma (a cancer with low inflammatory cell reaction). An MCA concentration gradient between pleural fluid and plasma was present in malignant effusions because pleural MCA levels in all cancer types were significantly greater than MCA levels in the plasma of the same patients.

CONCLUSIONS

Thus, an increased local level of MCA is a feature of cancers with high inflammatory cell infiltration, and the presence of an in vivo concentration gradient of MCA suggests the direct role of this biologic activity in recruiting blood monocytes to the cancer site.

Up-regulation of natural killer activity of human immunodeficiency virus-infected patients by in vitro-differentiated macrophages

Patients with acquired immunodeficiency syndrome (AIDS)-related complex and asymptomatic individuals seropositive for human immunodeficiency virus (HIV) have depressed natural killer (NK) activity. Normal human macrophages cultured for 3-7 days significantly up-regulated the NK activity of mononuclear cells obtained from the blood of asymptomatic HIV-seropositive individuals and patients with AIDS. Following a 4-hr incubation of patients' cells with in vitro-differentiated macrophages, the greatest augmentation of NK activity was seen in asymptomatic HIV-seropositive individuals who were receiving treatment with azidothymidine. Stimulation of macrophage immunoregulatory activities or adoptive immunotherapy with ex vivo-activated monocytes may be beneficial in HIV-infected patients.