GM-CSF and stimulation of monocyte/macrophage function in vivo relevance and in vitro observations

M1 and M2 macrophages: the chicken and the egg of immunity

The purpose of this perspective is to describe a critical advance in understanding how immune responses work. Macrophages are required for all animal life: 'Inhibit' type macrophages in all animals (called M1) can rapidly kill pathogens, and are thus the primary host defense, and 'Heal' type macrophages (M2) routinely repair and maintain tissue integrity. Macrophages perform these activities in all animals without T cells, and also in T cell-deficient vertebrates. Although adaptive immunity can amplify macrophage polarization, the long-held notion that macrophages need to be 'activated' or 'alternatively activated' by T cells is incorrect; indeed, immunology has had it backward. M1/M2-type macrophages necessarily direct T cells toward Th1- or Th2-like activities, respectively. That such macrophage-innate activities are the central directing element in immune responses is a dramatic change in understanding how immune systems operate. Most important, this revelation is opening up whole new approaches to immunotherapy. For example, many modern diseases, such as cancer and atherosclerosis, may not display 'foreign' antigens. However, there are clear imbalances in M1/M2-type responses. Correcting such innate imbalances can result in better health. Macrophages are the chicken and the egg of immunity.

Hypoxia inducible factors-mediated inhibition of cancer by GM-CSF: a mathematical model

Under hypoxia, tumor cells, and tumor-associated macrophages produce VEGF (vascular endothelial growth factor), a signaling molecule that induces angiogenesis. The same macrophages, when treated with GM-CSF (granulocyte/macrophage colony-stimulating factor), produce sVEGFR-1 (soluble VEGF receptor-1), a soluble protein that binds with VEGF and inactivates its function. The production of VEGF by macrophages is regulated by HIF-1α (hypoxia inducible factor-1α), and the production of sVEGFR-1 is mediated by HIF-2α. Recent experiments measured the effect of inhibiting tumor growth by GM-CSF treatment in mice with HIF-1α-deficient or HIF-2α-deficient macrophages. In the present paper, we represent these experiments by a mathematical model based on a system of partial differential equations. We show that the model simulations agree with the above experiments. The model can then be used to suggest strategies for inhibiting tumor growth. For example, the model qualitatively predicts the extent to which GM-CSF treatment in combination with a small molecule inhibitor that stabilizes HIF-2α will reduce tumor volume and angiogenesis.

Modeling the inhibition of breast cancer growth by GM-CSF

M-CSF is overexpressed in breast cancer and is known to stimulate macrophages to produce VEGF resulting in angiogenesis. It has recently been shown that the growth factor GM-CSF injected into murine breast tumors slowed tumor growth by secreting soluble VEGF receptor-1 (sVEGFR-1) that binds and inactivates VEGF. This study presents a mathematical model that includes all the components above, as well as MCP-1, tumor cells, and oxygen. The model simulations are representative of the in vivo data through predictions of tumor growth using different protocol strategies for GM-CSF for the purpose of predicting higher degrees of treatment success. For example, our model predicts that once a week dosing of GM-CSF would be less effective than daily, twice a week, or three times a week treatment because of the presence of essential factors required for the anti-tumor effect of GM-CSF.

High-dose but not low-dose mainstream cigarette smoke suppresses allergic airway inflammation by inhibiting T cell function

Epidemiological studies have identified childhood exposure to environmental tobacco smoke as a significant risk factor for the onset and exacerbation of asthma, but studies of smoking in adults are less conclusive, and mainstream cigarette smoke (MCS) has been reported to both enhance and attenuate allergic airway inflammation in animal models. We sensitized mice to ovalbumin (OVA) and exposed them to MCS in a well-characterized exposure system. Exposure to MCS (600 mg/m(3) total suspended particulates, TSP) for 1 h/day suppresses the allergic airway response, with reductions in eosinophilia, tissue inflammation, goblet cell metaplasia, IL-4 and IL-5 in bronchoalveolar lavage (BAL) fluid, and OVA-specific antibodies. Suppression is associated with a loss of antigen-specific proliferation and cytokine production by T cells. However, exposure to a lower dose of MCS (77 mg/m(3) TSP) had no effect on the number of BAL eosinophils or OVA-specific antibodies. This is the first report to demonstrate, using identical smoking methodologies, that MCS inhibits immune responses in a dose-dependent manner and may explain the observation that, although smoking provokes a systemic inflammatory response, it also inhibits T cell-mediated responses involved in a number of diseases.

Nonspecific immunotherapy with intratumoral lipopolysaccharide and zymosan A but not GM-CSF leads to an effective anti-tumor response in subcutaneous RG-2 gliomas

PURPOSE

Nonspecific stimulation of cells of the immune system may be useful in generating an anti-tumor response for a variety of cancers and may work synergistically with currently available cytotoxic therapies. In this study we examined the response of syngeneic rat gliomas to treatment with several nonspecific stimulators of dendritic cells and macrophages alone or in combination with radiation therapy.

EXPERIMENTAL DESIGN

RG-2 gliomas were implanted subcutaneously and treated with intratumoral (IT) injections of the toll-like receptor (TLR) ligands lipopolysaccharide (LPS) and zymosan A (ZymA) and the cytokine granulocyte-macrophage colony stimulating factor (GM-CSF). Combination treatment with IT LPS and single-fraction external beam radiotherapy (EBRT) was also evaluated.

RESULTS

Treatment with IT LPS and ZymA delayed tumor growth compared to saline controls. Multiple doses of both substances were superior to single doses, and led to complete tumor regression in 71% (LPS) and 50% (ZymA) of animals. GM-CSF showed no anti-tumor effects in this study. Combinations of IT LPS and EBRT appeared to have a synergistic effect in delaying tumor growth. Rechallenge studies and IT LPS treatment of RG-2 tumors in nude rats suggested the importance of T cells in this treatment paradigm.

CONCLUSIONS

Direct IT treatment with the TLR ligands LPS and ZymA are effective in generating an anti-tumor response. These treatments may synergize with cytotoxic therapies such as EBRT, and appear to require T cells for a successful outcome.

Preoperative granulocyte/macrophage colony-stimulating factor (GM-CSF) increases hepatic dendritic cell numbers and clustering with lymphocytes in colorectal cancer patients

Despite surgery with curative intent, approximately 30% of colorectal carcinoma patients will develop liver metastases during follow-up. Synchronous occult micrometastases, tumor cell shedding into the portal circulation and postoperative immune impairment have all been suggested to facilitate outgrowth of liver metastases. In experimental models, increases in both number of resident macrophages of the liver, the so-called Kupffer cells (KC), and tumoricidal capacity of KC were observed after pretreatment with granulocyte/macrophage colony-stimulating factor (GM-CSF), a potent immuno-stimulatory agent. Following perioperative recombinant human GM-CSF (rhGM-CSF), we previously showed activation of the systemic immune response in the postoperative period, which is normally transiently down-modulated after surgery. Therefore, in this pilot study, effects of preoperative rhGM-CSF administration on the composition of human liver immune cell population were evaluated in patients undergoing surgery for colorectal cancer. No difference in KC numbers of rhGM-CSF-treated patients was observed. Importantly, however, a 6-fold increase in dendritic cell (DC) numbers was observed compared to control patients, as quantified by immunohistochemistry of liver biopsies, taken during laparotomy. Furthermore, direct contact between liver CD8+ cells and DC was significantly enhanced in rhGM-CSF-treated patients. Both increases in DC numbers and DC interaction with CD8+ T cells suggest enhanced immunological activation, which may reduce liver metastases formation and ultimately improve survival after initial colorectal surgery.

An alternative flow cytometry strategy for peripheral blood dendritic cell enumeration in the setting of repetitive GM-CSF dosing

BACKGROUND

Enumeration of circulating peripheral blood dendritic cells (DCs) is complicated by the absence of a unique cell surface marker expressed on all DC subsets and by the use of various biological adjuvants to modulate the DC compartment, including granulocyte macrophage colony stimulating factor (GM-CSF). Common methods employ a cocktail of antibodies, typically including anti-CD14, to define a lineage negative, MHC class II positive, putative DC population. Reported flow cytometry protocols include highly variable gating strategies and DC identification criteria. Increasing appreciation of DC pleiomorphism, GM-CSF biology, and recognition of CD14 expression in some DC subsets led us to consider an alternative lineage cocktail to improve identification of the circulating DC pool.

METHODS

Standard whole blood staining with appropriate fluorochrome conjugated antibodies to MHC class II and either standard CD14 containing, or an alternate CD66acde containing, lineage cocktail was performed on samples obtained from normal donors and breast cancer patients before and after administration of dose-dense, cytotoxic chemotherapy with daily GM-CSF hematopoetic growth factor support. Putative DCs were enumerated by standard flow cytometry. Data set differences were evaluated using two tailed Mann-Whitney or Wilcoxon signed rank tests. Cellular morphology was examined in cell-sorted populations from post GM-CSF samples.

RESULTS

Use of either antibody cocktail defined comparably sized lineage negative, MHC class II positive populations in normal donors and at baseline in cancer patients. However, selection of lineage negative subsets with increasing MHC class II expression levels yielded larger putative DC populations identified with the alternate cocktail. Both cocktails yielded highly reproducible data. Use of the alternate cocktail: 1) yielded a putative DC population, post GM-CSF that was more homogenous and consistent with DCs, 2) resulted in less data variation across gating strategies, and 3) resulted in more uniform and concordant longitudinal data, consistent with established GM-CSF biological activity.

CONCLUSION

An alternative lineage negative cocktail substituting anti-CD66 antibody for anti-CD14 is a viable option for enumerating the circulating DC population, potentially more accurately defining the circulating DC pool by including CD14 positive immature DCs, and thus, may give more reliable data, particularly in the setting of sustained GM-CSF administration.

Therapeutic potential of Kupffer cells in prevention of liver metastases outgrowth

Development of liver metastases is a frequent complication in the course of gastro-intestinal malignancies. After entering the liver via the portal circulation, blood-borne tumor cells that have been seeded from primary colorectal cancer, are first encountered by Kupffer cells (KC), which line the liver sinusoids. KC represent approximately 10% of all liver cells, and have the ability to kill tumor cells. As such, they may play an important intrinsic role in the protection against outgrowth of hepatic metastases. Furthermore, the cytotoxic function of KC is increased upon stimulation with various biological response modifiers, such as interferon-gamma, granulocyte macrophage-colony stimulating factor, antibodies and muramyl dipeptides. Therefore, enhancement of KC cytotoxic functions may represent an attractive treatment modality to prevent development of liver metastases in the clinical setting.

TREM-1, MDL-1, and DAP12 expression is associated with a mature stage of myeloid development

The triggering receptor expressed on myeloid cells (TREM-1) and the myeloid DAP12-associating lectin (MDL-1) are two recently identified receptors which associate non-covalently with DAP12 to form receptor complexes involved in monocytic activation and inflammatory response. In this study, we investigated whether the expression of TREM-1, MDL-1, and DAP12 correlated with myelomonocytic differentiation. Northern and RT-PCR revealed a strong expression of TREM-1, MDL-1, and DAP12 in peripheral blood-derived CD14(+) mature monocytes in contrast to undifferentiated bone marrow CD34(+) stem cells, and in the differentiated versus undifferentiated U937 cells. TREM-1 and MDL-1 RNA expression was also more elevated in adult than fetal tissues and in normal than malignant cells. These findings suggest that the TREM-1/DAP12 and MDL-1/DAP12 signaling pathways are features of mature differentiated myelomonocytic cells. In addition, expression of an alternative mRNA TREM-1 splice variant (TREM-1sv) was detected that might translate into a soluble receptor with potential as a regulator of myeloid activation.

Combined IL-12 and GM-CSF gene therapy for murine hepatocellular carcinoma

Among various immunotherapeutic approaches, interleukin-12 (IL-12) is particularly appealing because of its superior antitumor effects, which have been demonstrated in preclinical as well as clinical studies. However, IL-12 therapy was often accompanied by severe side effects due mainly to the supranormal induction of interferon-gamma. To optimize the therapeutic efficacy and lower the side effects of IL-12, we have investigated the antitumor activity of combined IL-12 and granulocyte-macrophage colony-stimulating factor (GM-CSF) gene therapy in a highly malignant and poorly immunogenic murine hepatocellular carcinoma model. Using a versatile hydrodynamics-based DNA delivery method, we showed that the combined gene delivery of IL-12 and GM-CSF induced very strong antitumor cellular immunity and achieved significant therapeutic efficacy, whereas each cytokine gene alone yielded appreciable but less effects. We also observed that the combined therapy induced lower levels of interferon-gamma than did IL-12 alone. These results suggest that combined IL-12 and GM-CSF therapy can render a stronger antitumor effect as well as lowering potential side effects.

Cytokine modulated cell-membrane bound tumour necrosis factor expression is associated with enhanced monocyte-mediated killing of human leukaemic targets

Cytokines such as interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) activate monocytes both in vitro and in vivo. We therefore studied whether the anti-leukaemic activity of monocytes could be augmented by IL-3 alone or in combination with GM-CSF. Using normal human monocytes stimulated with IL-3, GM-CSF, LPS or combinations of growth factor and LPS, we studied their cytotoxic activity against leukaemic cell-lines and primary AML blasts. IL-3 like GM-CSF, augmented the expression and secretion of TNF but did not prime for further expression and secretion of TNF in response to LPS. Neither GM-CSF or IL-3 increased the expression or secretion of TNF receptor p55 (TNF-Rp55), although both agents increased expression of TNF receptor p75 (TNF-Rp75). Monocyte-mediated cytotoxicity (MMC) against K562 and U937 cell-lines was increased by both GM-CSF and IL-3 stimulation, and both cytokines primed monocytes for increased killing of K562 and KG-1 cell-lines as well as primary AML blasts in response to LPS. The mechanism of action of MMC was largely confirmed to be via surface-bound TNF, although other TNF-independent mechanisms must have been involved.