Macrophages and neoplasms: new insights and their implication in tumor immunobiology

A history of exploring cancer in context

The concept that progression of cancer is regulated by interactions of cancer cells with their microenvironment was postulated by Stephen Paget over a century ago. Contemporary tumour microenvironment (TME) research focuses on the identification of tumour-interacting microenvironmental constituents, such as resident or infiltrating non-tumour cells, soluble factors and extracellular matrix components, and the large variety of mechanisms by which these constituents regulate and shape the malignant phenotype of tumour cells. In this Timeline article, we review the developmental phases of the TME paradigm since its initial description. While illuminating controversies, we discuss the importance of interactions between various microenvironmental components and tumour cells and provide an overview and assessment of therapeutic opportunities and modalities by which the TME can be targeted.

Effect of farmorubicin both free and associated with poly(butylcyanoacrylate) nanoparticles on phagocytic and NK activity of peritoneal exudate cells from tumor-bearing mice

The effect of Epirubicin (farmorubicin, FR), either free or associated with poly(butylcyanoacrylate) nanoparticles (PBCN) upon the phagocytic and natural killer (NK) activity of peritoneal exudate cells (PECs) harvested from Lewis lung carcinoma (LLC)-bearing-mice was investigated. Phagocytic and NK activity were tested 72 and 96 h, respectively after the last four intraperitoneal (i.p.) injections of the tested compounds have been administered to the mice. Phagocytic activity was evaluated in vitro by phagocytic index and ingestion capacity using a phagocytic assay. NK activity was evaluated in a direct cytotoxic test, in which PECs were used as effector cells while human erythroleukemic K-562 cells were used as target cells. The phagocytic activity of PECs, harvested from tumor-bearing mice, was stimulated after treatment with FR free, FR associated with polymer nanoparticles and with unloaded PBCN. The NK activity of PECs was strongly stimulated by unloaded PBCN. FR both free and encapsulated into the polymer matrix during the polymerization of n-butylcyanoacrylate (n-BCA) stimulated the NK activity of PECs, while FR adsorbed onto nanoparticles restrained it. These results suggest that the association of FR with nanoparticles modifies selectively its immunomodulating ability without producing any significant immunological disturbances. The toxicity of some of FR polymer forms towards PECs, displaying NK activity, probably comes from the enhanced local drug concentration on the membrane surface of the immune cells. However, it is insufficient to preclude the use of nanoparticles as drug delivery system.

Killer dendritic cells: IKDC and the others

Tumors can regress as a result of invading myeloid and lymphoid cells that act in concert. Although the myeloid cells are widely recognized as antigen presenters and lymphoid cells as classical effectors, recent evidence revealed the capacity of dendritic cells (DC) to kill tumor cells. The functional concept of 'natural killer (NK) myeloid DC' is supported by mouse and human in vitro data that may be clinically relevant because human killer DC can contribute to tumor shrinking during topical therapy with toll-like receptor (TLR) agonists. Whether tumor killing by DC is a 'catalyzing' step for efficient crosspresentation and/or a promoting step for an immunogenic cell death pathway remains an open question. We also discuss how interferon-producing killer DC (IKDC) may participate in the control of tumor progression.

Analysis of gene expression in the tumor-associated macrophage

INTRODUCTION

The tumor-associated macrophage (TAM) is at the front line of the host's defense against malignancy and provides an attractive target for immune-modulatory therapy. However, factors present within the tumor microenvironment can alter macrophage phenotype, preventing its cytotoxic activity and reducing its susceptibility to interferon-gamma and lipopolysaccharide-mediated stimulation.

METHODS

Macrophages were isolated from subcutaneous B16 melanoma tumors implanted in C57 BL/6 mice. Wound macrophages were harvested from subcutaneously-implanted PVA sponges, and resting peritoneal macrophages were harvested by peritoneal lavage. Gene expression was analyzed using an Atlas cDNA array (Clontech, Mountain View, CA).

RESULTS

TAM demonstrated a pattern of gene expression distinct from both wound and peritoneal macrophage. There is an increase in proliferation-associated genes and in genes encoding the ultrastructural proteins cofillin, zyxin, and vimentin more commonly associated with fibroblast-like cells. In addition, an observed decrease in expression of the CD14 gene, and increase in inhibitory pathways including osteopontin and its receptor CD44, the inositol 1,4,5-triphosphate receptor, and the receptors for interleukin-4 and granulocyte monocyte-colony stimulating factor could explain the resistance of TAM to lipopolysaccharide-mediated stimulation. There was also a significant decrease in the expression of the interferon-gamma second messenger, IRF-1.

CONCLUSIONS

This study has identified a number of pathways involved in the suppression of TAM function. Targeting of these pathways may allow for the generation of more effective immune-modulatory anti-neoplastic therapy.

Growth-stimulating phase of macrophage response to activation: the phenomenon and its implications for tumour growth and immunotherapy

The dynamics of growth-stimulating and cytotoxic activity of mouse peritoneal macrophages (PMo) in response to in vivo and in vitro bacillus Calmette-Guérin (BCG) or bestatin treatment was studied. It was shown that BCG and bestatin induce cytotoxicity in PMo, and that after the cytotoxic response strong growth-stimulating activity develops. PMo, rendered cytotoxic in vivo and afterwards cultivated in vitro, displayed the same switch from a cytotoxic to a growth-stimulating phase. These results suggest that the growth-stimulating phase is the obligatory PMo response to biological response modifiers (BRM) at least to BCG and bestatin. The growth rate of tumours, transplanted into mice during the cytotoxic phase of the response to BCG, was suppressed, whereas tumours transplanted during the growth-stimulating phase were stimulated. It appears that the development of a growth-stimulating phase after the cytotoxic phase of response to activation by BRM could be one of the reasons for the limited effectiveness of immunotherapy based on the application of macrophage activators.

Spindle cell haemangioendothelioma: Probably a benign vascular lesion not a low-grade angiosarcoma

Ten cases of spindle cell haemangioendothelioma (SCH) were analysed clinicopathologically, including an immunohistochemical survey of seven cases and ultrastructural observations on one. There were seven females and three males, ranging from 16 to 76 years of age. All but one lesion developed on the extremities, predominantly on the hands and feet. Six of the ten patients presented multiple nodules or papules which gradually increased in size and number over a long duration. Among them, four patients had undergone operations twice or more, but no metastatic foci were recognized. Histologically, the lesions were composed of dilated vascular spaces and a proliferation of bland-appearing spindle cells and interspersed epithelioid endothelial cells. Ultrastructural and immunohistochemical studies demonstrated that the spindle cells were mainly made up of fibroblastic cells admixed with pericyte-like cells and macrophages. Smooth muscle cells and primitive mesenchymal cells were also present. The clinical and microscopic features suggest that SCH may be a benign vasoformative lesion of a heterochronological multicentric origin.

Effects of doxorubicin on maturation of human monocytes in adherent and non-adherent cultures

Purified human monocytes were cultured for 2 h, 88 h, and 10 days in plastic tubes (adherent) and for 10 days in Teflon foil bags (non-adherent). Monocytes were incubated with doxorubicin by two short-term exposures (750 or 1500 ng/ml) for 1 h or by continuous exposure (75 ng/ml). Maturation was monitored by measuring the intracellular activity of three metabolic enzymes and two acid hydrolases. Expression of receptors for the Fc moiety of immunoglobulin G (FcRI, FcRII, FcRIII), CD14, and HLA-DR was assayed by indirect immunofluorescence with monoclonal antibodies. In the presence of doxorubicin, the adherent capacity, the yield, and the enzyme activities reflecting growth and intermediary metabolism were similar to the control groups. However, doxorubicin reduced the expression of FcRI (32-45%), FcRII (10-26%), CD14 (20-37%), and HLA-DR (25-34%) on the monocyte-derived macrophages. Expression of FcRIII was not detectable after 10 days of culture.

Modulation of human macrophage functions by gangliosides

In human tumors of neuroectodermal origin cell surface expression of individual gangliosides is either increased or decreased relative to comparable normal cells. We have previously shown that gangliosides shed from melanoma cells can immunomodulate T cell activity. Monocytes/macrophages (m/m) are known to play an important role as accessory and effector cells in immune responses. We therefore investigated the effect of exogenous gangliosides derived from melanoma on m/m functions in vitro. Gangliosides commonly expressed on human melanoma such as GM3, GD3, GM2, and GD2 were investigated, as well as GM1, a major component of human neural tissue. Monocytes were isolated from human peripheral blood mononuclear cell populations, treated with gangliosides in vitro, and evaluated in several functional assays. Treatment of m/m with GM2 and GM3 gave the greatest inhibition of Fc receptor expression. GM1 and GD3 on the other hand most inhibited the production of interleukin-1 (IL-1) by m/m. Production of tumor necrosis factor (TNF) like monocytoxin was not affected by incubation with individual gangliosides. These studies suggest that individual melanoma gangliosides have different regulatory effects on m/m functions.

Activation of human monocyte-derived macrophages cultured on Teflon: response to interferon-gamma during terminal maturation in vitro

Macrophages (M phi) are potential antitumor effector cells derived from circulating blood monocytes (mo). Most studies on human mo/M phi biology and function have been performed using immature mo precursor cells. However, the conclusions drawn may be questionable, as mo have to undergo terminal differentiation before they reach relevant tissue sites of inflammation and immune reaction. We have analyzed the ability of mo-derived, teflon-cultured M phi to respond to activating stimuli with an increased tumor cytotoxic effector cell function using recombinant interferon-gamma (IFN-gamma), IFN-alpha 2, granulocyte/macrophage colony stimulating factor (GM-CSF), interleukin(IL) 2, IL 1 alpha, and bacterial lipopolysaccharides (LPS) as mediator molecules. It could be shown that the response of M phi to the most potent activator molecule, IFN-gamma, depends on the terminal differentiation from the mo stage to the mature M phi. Whereas adherent mo could be activated only moderately, M phi increased their cytotoxicity by a factor of up to 400. IFN-gamma activation positively correlated with the effector cell number, the time of incubation and the dosage used. Activation did not depend on the presence of LPS, and was lost within 24 to 48 h. LPS itself activated cells only in the microgram range. IFN-alpha 2 activated M phi only at a two log higher concentration than IFN-gamma; GM-CSF was only slightly effective, whereas M phi incubation with IL 1 alpha or IL 2 did not result in M phi activation. Thus, the ability of human M phi to become activated appears to be a function of cellular maturation and is acquired during the terminal step of M phi differentiation. Teflon-cultured M phi could facilitate studies of the activation of human M phi and may be more suitable cells for adoptive immunotherapy in cancer patients than blood monocytes.

Macrophages associated with murine tumours express plasminogen activator activity

The fibrinolytic activity of cancer cells has been repeatedly implicated in mechanisms of local spread and tumour invasiveness. Mononuclear phagocytes associated with solid tumours might also contribute to fibrin dissolution at the tumour/host interface through the expression of plasminogen activator (PA) activity. We have investigated the PA activity of tumour-associated macrophages (TAM) from 4 transplanted murine tumours in syngeneic hosts; peritoneal macrophages (native and thioglycolate-elicited) from both tumour-bearing and control animals were studied as reference cells. TAM from 3 tumours (MSV, mFS6, MN/MCAI) had basal levels of PA activity (20% plasminogen-independent) comparable to or higher than those of thioglycolate-elicited peritoneal macrophages from the same tumour-bearing animals. TAM isolated from 1 tumour (MS2) had a PA which was very low (60% plasminogen-independent), but higher than the activity of unstimulated peritoneal macrophages. Molecular analysis of PA by SDS-PAGE electrophoresis and fibrin autography revealed in all macrophages a single species having an apparent MW of 48 kDA. It thus appears that, in some experimental neoplasms, tumour cell vicinity may represent an in vivo stimulus for macrophage PA expression.

Local induction of a cytotoxic factor in a murine tumour by systemic administration of an antitumour polysaccharide, MGA

When an antitumour mannoglucan prepared from Microellobosporia grisea, MGA was administered i.v. to C3H/He mice bearing the solid MH134 hepatoma, a cytotoxic factor was induced that was detectable in the tumour homogenate by an 8 h cytolysis assay against L-929 fibroblasts. Without MGA treatment, the cytotoxic factor was not detectable in the tumour homogenate. MGA induced the cytotoxic factor in tumour tissue specifically, its level reaching a maximum (24 U ml-1) 3 h after administration of MGA: little if any cytotoxic factor was detectable in homogenates of normal tissues or sera after MGA-treatment. The molecular size of the cytotoxic factor was estimated to be 70-80 kD by gel filtration. It seemed to be a type of tumour necrosis factor because its activity was inhibited by antiserum against murine tumour necrosis factor. From these results, the selective induction of the cytotoxic factor was concluded to be important in the mechanism of the antitumour activity of MGA.

A gelatin sponge model for studying tumor growth: quantitation of tumor cells and leukocytes in the CHO tumor

A gelatin sponge model system for tumor cell inoculation and retrieval of tumor-associated leukocytes is described. Gelatin sponges pre-implanted in nude mice harboring tumorigenic Chinese hamster ovary cells (line CHO) were examined at 2 and 11 days after injection of tumor cells for tumor cell content and leukocyte accumulation after digesting the sponge matrix in collagenase solution. The data indicate a progressive influx of host cells consisting primarily of macrophages, neutrophils and lymphocytes. The total number of viable tumor cells as well as the fraction of surviving tumor cells with clonogenic potential also increased with tumor age. Blank sponges not harboring tumor cells elicited an inflammatory response in the animals which did not change appreciably with length of sponge residence. However, when the sponges were harboring tumor cells, the accumulation of host leukocytes far exceeded that which occurred in blank sponges. This observation suggests a host response directed toward the tumor which is absent in animals bearing blank sponges. Apart from providing anchorage for injected cells, the gelatin sponge, by virtue of its digestibility in collagenase, makes possible the easy retrieval and precise quantitation of tumor-associated host cells.

Characterization of factor XIII containing-macrophages in lymph nodes with Hodgkin's disease

A large number of cells containing subunit a of blood coagulation Factor XIII (FXIII) was detected by immunoperoxidase staining in lymph nodes with Hodgkin's disease. These relatively large, multipolar, mononuclear cells were often found in the immediate vicinity of malignant Hodgkin's cells. Intensive characterization of these cells carried out by immunofluorescent and enzymecytochemical techniques in double- and triple-labelling systems on the same sections clearly demonstrated that they represent tumour-associated macrophages (TAMs). FXIII containing-cells showed alpha-naphtyl acetate esterase (ANAE) positivity, and were labelled by monoclonal anti-Leu M3 antibody, a monocyte/macrophage marker, but not at all or only very weakly by anti-HLA-DR. Neither alkaline phosphatase (ALP) nor adenosine triphosphatase (ATPase) activity could be detected in these cells and surprisingly, they were consistently negative for acid phosphatase (AcP) as well. The presence of FXIII subunit a in tumour-associated macrophages suggests that this cell type might have an important role in the stabilization of fibrin deposits around tumour cells.

The immunological network at the site of tumor rejection

The tumor mass irrespective of its type or location in the body has long been shrouded in mystery and even today we still have only a tentative handle on its secrets. Attempts to manipulate either the tumor cells per se or host-derived leukocytes have, on the whole, not been successful or at best questionable. The ability of the host to respond immunologically to TSTA is well documented, yet again attempts to manipulate this response have been disappointing. One of the problems has been a lack of knowledge concerning the tumor mass and its constituents, such as the intratumor leukocytes, and the significance of their presence to the biological properties of the neoplasm [8,9,80]. The purpose in studying the immunological network is, in part, to try to assign a function to these cells on the premise that lymphoid elements and macrophages have a potential role to play in recognition of TSTA. The advantage of adoptive immunotherapy model systems is that tumor rejection can be achieved under controlled conditions and this allows an analysis of the immunological network and its individual circuits. At the same time, valuable information on the mechanisms of action during adoptive immunotherapy and how best to improve therapeutic protocols is acquired.

Tumor-derived chemotactic factor(s) from human ovarian carcinoma: evidence for a role in the regulation of macrophage content of neoplastic tissues

Supernatants from freshly disaggregated human ovarian carcinomas maintained in vitro for 24 hr, from primary ovarian carcinoma cultures (4-6 days in culture) and from established ovarian cancer cell lines were examined for chemotactic activity on blood monocytes in blind-well chemotaxis chambers. Tumor-cell culture supernatants induced migration of peripheral blood monocytes across polycarbonate filters with considerable heterogeneity among different tumors. Induction of migration occurred only in the presence of a gradient between the lower and upper compartments of the chamber. Chemotactic activity was characterized by means of supernatants from primary ovarian carcinoma cultures. Chemotactic factor(s) was (were) produced in serum-free conditions and the production was inhibited by emetine but not by mitomycin C. The activity was destroyed by exposure to proteolytic enzymes and by heating at 100 degrees C but was unaffected by RNase, DNase, lipase and exposure to extreme pH values or heating at 56 degrees C. Upon fractionation on Sephadex G 75, the activity eluted as a single peak in the cytochrome C region, corresponding to an apparent molecular weight of about 12 kd. The percentage of macrophages was assessed in 25 freshly disaggregated tumor specimens. Ovarian carcinomas were heterogeneous in their macrophage content with values ranging from 4 to 36%. A significant (r = 0.62; p = 0.00097), though far from absolute, correlation was found between chemotactic activity of culture supernatants and percentage of tumor-associated macrophages. Tumor-derived chemotactic factor(s) could be one of the mechanisms involved in the regulation of the macrophage content of human ovarian carcinomas.

Bronchoalveolar lavage and the immunology of primary lung cancer

Bronchoalveolar lavage (BAL) is a powerful tool with which the immunology of the lung in health and disease can be studied. This technique has been successfully used to characterize localized humoral and cell-mediated responses in sarcoidosis and a number of other interstitial pneumonitides. In contrast, BAL in patients with lung cancer has resulted in some confusion regarding the extent and type of local and systemic immunity in these patients. This review summarizes some of the data obtained from these patients via BAL, but does not attempt to explain the reported discrepancies. The objective of this review is rather to identify gaps which exist in our knowledge of the environmental factors influencing pulmonary immunity in primary lung cancer.

Cancer metastasis: experimental approaches, theoretical concepts, and impacts for treatment strategies

It has been the purpose of this article to describe recent advances in cancer metastasis research. Clinical realities and experimental approaches to the study of underlying basic mechanisms of metastasis formation were discussed. Wherever possible, results were reported which led to the development of theoretical concepts. Such results and concepts were finally evaluated in light of their possible impact for the design of new treatment strategies. Experimental findings from many diverse research fields were summarized with the help of tables, figures, and references. It was concluded that the process of metastasis is a dynamic event that can be described as a sequence of interrelated steps. Experimental results indicated that malignant cells that migrate and disseminate from the primary organ to distant sites and there eventually develop into metastases have to survive a series of potentially lethal interactions. Intimate tumor-host interactions were reported to take place all along the metastatic process. They were elucidated at the steps of angiogenesis, invasion, organ interaction, dormancy, tumor rejection, and tumor immune escape. The outcome of such tumor-host interactions seemed to depend on intrinsic properties of the tumor cells themselves as well as on the responsiveness of the host. Metastasis does not appear as a merely random process. Both clinical and experimental studies revealed that the whole process can be described more appropriately in terms of stochastic, sequential, and selective events, each of which is controlled and influenced by a number of mechanisms. With regard to therapeutic intervention, a selective event offers more possibilities than a random one because it is governed by rules that can be exploited experimentally. Various impacts from experimental studies for the design of antimetastatic cancer treatment strategies were discussed. Sequential steps of the metastatic cascade could become new therapy targets. Conventional empirically derived treatment modalities should become flanked by methods aimed more specifically at critical steps of cancer spread in order to prevent progression of the disease. This is where basic research on mechanisms could make significant contributions to therapy planning in the future. Furthermore, possible negative effects of surgery, radiotherapy, and adjuvant chemotherapy or immunotherapy that could result in enhancement of metastatic progression need to be critically evaluated to limit them as much as possible.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of high or low metastatic related tumor lines with normal or lymphokine-activated syngeneic peritoneal macrophages: in vitro analysis of tumor cell binding and cytostasis

Peritoneal macrophages from normal DBA/2 mice were found to bind significantly more cells of a syngeneic low metastatic lymphoma line (Eb) than cells of a high metastatic variant (ESb) derived therefrom. These differences were observed in three different assays, at 4 degrees C and at 37 degrees C, and at various ratios of macrophages to tumor cells. Upon co-culture with normal macrophages, a tumor cytostatic effect was consistently observed with Eb but not with ESb tumor cells. Further experiments indicated that macrophages exerted their growth inhibitory effect via direct tumor cell contact. Pre-treatment of tumor cells with neuraminidase or pre-treatment of macrophages with lens culinaris lectin increased the numbers of macrophages binding Eb and ESb tumor cells. Addition of D-galactose or D-mannose at 50 mM concentration led to an increase of tumor cell binding and tumor cytostatic activity. Taken together, these results suggest (i) that carbohydrates play a role in tumor cell recognition by macrophages and (ii) that the differences observed between Eb and ESb tumor cells may be due to differences in the expression of carbohydrates. Pre-activation of the macrophages by lymphokine(s) led to a short increase in their tumor cell binding capacity. Lymphokine activation resulted in a strong but also short-lived increase of tumor cytostatic potential. This was effective against both the low and the high metastatic tumor line.

Suggestive evidence that the highly metastatic variant ESb of the T-cell lymphoma Eb is derived from spontaneous fusion with a host macrophage

Two lines of evidence are reported which suggest that the highly metastatic variant ESb of the T-cell lymphoma Eb is derived from spontaneous fusion with a host macrophage. Firstly, ESb cells are shown to express the macrophage differentiation antigen Mac-1 which was not found on Eb cells or on any other tumor cells tested except the macrophage tumor line Pu5. Secondly, the progression from low to high metastatic capacity could be reproduced in vitro following hybridization of thioguanine-resistant Eb cells (EbTGR) with syngeneic bone-marrow-derived macrophages. Two HAT medium-selected hybrid tumor lines (Eb-F1 and Eb-F2) could be established. They were found to express cell surface markers of both parental lines: T lymphoid differentiation antigens from T-lymphoma and macrophage antigens (Mac-1, class II MHC antigens) from the normal cell fusion partner. The antigens were identified on the hybrids and subclones thereof by means of monoclonal antibodies and 3 different detection assays: cytofluorography, complement-dependent cytotoxicity and immunoprecipitation followed by gel electrophoresis. Animals inoculated s.c. with the parental line EbTGR developed local tumors but not metastases and survived for more than 40 days. In contrast, animals inoculated similarly with Eb-F1 or Eb-F2 cells quickly developed metastases in visceral organs and died as early as 10-14 days following inoculation. In many but not all respects, the in vitro-derived T-lymphoma-macrophage hybrids resembled the spontaneous in vivo-derived variant ESb. These findings, together with the presence of Mac-1 antigen on ESb cells, suggest (1) that ESb variant cells may be derived from spontaneous fusion with a host cell, most likely a macrophage and (2) that somatic cell fusion may be an important mechanism of genetic rearrangements leading to metastatic variants. The new highly metastatic tumor lines which were developed under well-defined in vitro conditions, and their subclones, may become very useful tools for studying the contribution of specific genetic traits and of membrane-related structures to various steps of the metastatic process.

Procoagulant activity of macrophages associated with different murine neoplasms

Mononuclear phagocytes, an integral part of the lymphoreticular infiltrate of human and experimental tumors, might contribute to tumor-associated fibrin deposition through the development of procoagulant activity (PCA). We have investigated PCA of tumor-associated macrophages (TAM) in 6 transplanted murine tumors in syngeneic hosts; peritoneal macrophages from tumor-bearing and control animals were studied also, as reference cell populations. PCA was evaluated by a one-stage clotting assay immediately after preparation and following incubation in the absence and in the presence of endotoxin. TAM from 5 poorly immunogenic tumors (mFS6, MN/MCA1, R 80/44, M109 and MS2) had basal PCA levels comparable to or somewhat lower than those of peritoneal macrophages from the same animals. Similar PCA was found in peritoneal macrophages from both control and tumor-bearing animals. Unlike peritoneal macrophages, TAM in all instances failed to respond with increased PCA when exposed to endotoxin in vitro. Failure to respond to endotoxin could not be ascribed to contaminating tumor cells or their products, to the presence of suppressive macrophage populations or to the lack of lymphocyte "help". TAM from a strongly immunogenic, regressing tumor (MSV sarcoma), in contrast to its non-immunogenic variant, MS2, and to the 4 other tumors mentioned above, expressed high levels of PCA immediately after isolation. The latter did not increase further following in vitro stimulation with endotoxin. When MSV sarcomas were induced in nude mice, TAM showed PCA levels similar to those of the euthymic hosts, suggesting that the procoagulant response was largely independent of T-cell-mediated immunity.

Effect of hydrocortisone on the macrophage content, growth and metastasis of transplanted murine tumors

Hydrocortisone (HC) reduced the macrophage content of four murine tumors to less than half of control values. Since HC causes monocytopenia and inhibits the recruitment of mononuclear phagocytes at sites of inflammation but does not affect the viability and proliferative capacity of macrophages, this finding suggests that the maintenance of macrophage levels in growing tumors is in part dependent upon the entry into the neoplasm of circulating monocytes. HC inhibited the growth of these tumors. The effect of HC was most marked on the mFS6 and MN/MCA1 sarcomas and 3LL carcinoma, with only marginal inhibition in the M109 carcinoma. HC augmented spontaneous and/or artificial (i.v.) metastasis in these tumor models. Cells from metastatic foci of the mFS6 sarcoma and M109 carcinoma inoculated i.m. were as susceptible to HC as cells from primary tumors. The effects of HC on macrophage content, growth and metastasis of the M109 carcinoma and mFS6 sarcoma were similar in mice with defective T-cell function (nude or thymectomized) or defective NK activity (beige or antiasialo GM1-treated) and in controls. The in vitro growth of the mFS6 and MN/MCA1 sarcomas was not modified by HC. Some inhibition of tumor-cell proliferative capacity was observed with the 3LL and M109 tumors. Tumor cell had high-affinity binding sites for glucocorticoid hormones, but these were not correlated to susceptibility in vivo. Thus it is unlikely that a direct interaction of HC with tumor cells accounts for the inhibition of tumor growth observed in vivo. To evaluate whether HC affected tumor growth by reducing the macrophage content of tumors, mFS6 sarcoma cells were transplanted, mixed with peritoneal macrophages into normal or HC-treated mice. Macrophages did not affect the growth of tumor cells in normal mice, whereas in HC-treated animals lesions from mixtures of macrophages and sarcoma cells appeared earlier and weighed more than those from tumor cells alone or tumor cells and thymocytes. However, macrophages did not reconstitute growth of the other sarcoma (MN/MCA1) in HC-treated mice. These results are consistent with the hypothesis that HC inhibited growth of some poorly immunogenic transplanted murine tumors, at least in part, by interfering with the macrophage levels in neoplastic tissues, tumor-associated macrophages providing the conditions for optimal tumor-cell proliferation at least in some neoplasms.

Relationship of tumor leucocytic infiltration to host defense mechanisms and prognosis

The interface between the tumor and the host is often the site of leucocytic infiltration. We will examine the idea that the infiltrating leucocytes of human and experimental tumors are components of the host immunological defense against the tumor, and that the presence of the infiltrate is a marker of favorable prognosis. Leucocytes could infiltrate tumors because of an active immune response, either nonspecific or specifically directed to tumor-associated antigens. Leucocyte influx may also occur because of chemotactic factors secreted by the tumor cells. Some tumors release factors which enhance vascular permeability and permit improved access by leucocytes to the tumor focus. The consequences of leucocytic infiltration include tumor cell cytolysis, cytostasis, or stimulation of proliferation. The present state of our knowledge of the interactions between tumor cells and infiltrating leucocytes precludes broad generalization of mechanisms. Further study will probably reveal that the mechanisms are diverse, and that there are some systems in which immune interactions occur at this interface and others in which they do not.