Role of natural killer cells in control of cancer metastasis

Dietary fat and breast cancer metastasis by human tumor xenografts

Human breast cancer cell lines growing as xenografts in athymic nude mice have been used to examine the effects of dietary fat and fatty acids on tumor progression. The estrogen independent MDA-MB-435 cell line has the advantage that it metastasizes consistently to the lungs and forms quantifiable secondary nodules when injected into the mammary fat pads. With these breast cancer cells, the stimulating effects of polyunsaturated omega-6 fatty acids on both primary tumor growth and metastasis were demonstrated; in contrast, the long-chain omega-3 fatty acids were inhibitory. The model can also be adapted to examine dietary fatty acids, and inhibitors of their metabolism, as experimental adjuvant therapy after surgical excision of the primary tumors. Unfortunately, estrogen dependent human breast cancer cells do not metastasize, or do so rarely, in nude mice; in consequence, it is not possible to use the model to study estrogen-fatty acid interactions on the metastatic process. In addition to metastasis from a primary location, intravenous injection of MDA-MB-435 cells into the nude mouse host, particularly when combined with studies using Matrigel-based in vitro invasion assays, permits further dissection of the steps in the metastatic cascade which are influenced by dietary fatty acids. The results obtained by these several approaches have demonstrated distinct roles for the cyclooxygenase and lipoxygenase-mediated products of omega-6 fatty acid metabolism, and suggest new approaches to experimental breast cancer therapy.

Establishment of an experimental liver metastasis model by intraportal injection of a newly derived human pancreatic cancer cell line (KLM-1)

CONCLUSION

It is suggested that this liver metastasis model formed by a highly metastatic variant (KLM-1) is valuable for the study of the liver metastatic processes of human pancreatic cancer.

BACKGROUND

Liver metastasis in the early postoperative period is one of the causes for the poor prognosis of patients with resected pancreatic cancer. Therefore, it is necessary to establish an experimental model to study the mechanisms of liver metastasis in pancreatic cancer.

METHODS

Human pancreatic cancer cell lines (PK-1, PK-9, and KLM-1) were injected into the portal vein of nude mice with or without pretreatment with antiasialo GM1, and colonies of liver metastases were counted for comparison of metastatic ability of these cell lines. Biological and histopathological characteristics of the highly liver metastatic cell line (KLM-1) were compared with its parent cell line (PK-1).

RESULTS

PK-1 cells and PK-9 cells rarely formed liver metastasis foci, but pretreatment with antiasialo GM1 promoted liver metastasis. KLM-1 cells formed liver metastases at the rate of 70% even without antiasialo GM1 pretreatment. KLM-1 cells had such biological characteristics as short doubling time, short lag phase, and resistance to NK cytotoxicity. After intraportal injection of 125I-labeled KLM-1 cells, radioactivity as well as micrometastases were detected in the liver at 72 h.

Inhibition by streptococcal immunopotentiator OK432 of lymph-node metastasis in hamster cheek-pouch carcinoma with enhancement of tumour necrosis factor-alpha and interleukin-6 in serum

A well-known metastic model of human oral cancer employs 9,10-dimethyl-1,2-benzanthracene (DMBA) to induce hamster cheek-pouch carcinoma. Streptococcal immunopotentiator OK432 was studied here for its inhibitory effect on lymph-node metastasis in that model. The intraperitoneal administration of OK432, after excision of cheek-pouch tumours induced by DMBA, resulted in a marked reduction in the incidence of cervical lymph-node metastasis to 7%, a significant decrease beneath the rates observed for control animals not receiving OK432 (40%). OK432 also caused an increased in serum levels of tumour necrosis factor-alpha and interleukin-6 in tumor-bearing hamsters. These results suggest that the immune response may play an important part in the antimetastatic effects of OK432.

Massage therapy is associated with enhancement of the immune system's cytotoxic capacity

Twenty-nine gay men (20 HIV+, 9 HIV-) received daily massages for one month. A subset of 11 of the HIV+ subjects served as a within subject control group (one month with and without massages). Major immune findings for the effects of the month of massage included a significant increase in Natural Killer Cell number, Natural Killer Cell Cytotoxicity, soluble CD8, and the cytotoxic subset of CD8 cells. There were no changes in HIV disease progression markers (CD4, CD4/CD8 ratio, Beta-2 microglobulin, neopterin). Major neuroendocrine findings, measured via 24 hour urines included a significant decrease in cortisol, and nonsignificant trends toward decrease of catecholamines. There were also significant decreases in anxiety and increases in relaxation which were significantly correlated with increases in NK cell number. Thus, there appears to be an increase in cytotoxic capacity associated with massage. Implications for HIV+ men as those with other illnesses, particularly cancer, are discussed.

Natural killer cell activity in patients with pernicious anemia

Patients with pernicious anemia have an estimated risk of gastric adenocarcinoma that ranges from three- to fivefold greater than that of the general population. It has been reported that NK cells may be involved in immunosurveillance against tumor spread. The natural killer cell activity of peripheral blood mononuclear cells was analyzed in 22 patients with pernicious anemia and in 19 healthy controls. Levels of natural killer cell activity against K-562 target cells were similar in control subjects and patients, regardless of gastrin levels and time elapsed since diagnosis. According to quantitative flow cytometry analysis, similar percentages of phenotypically defined NK cells (CD16+) were found in peripheral blood mononuclear cells from patients and healthy controls. Our results show that in pernicious anemia patients, the percentage of NK cells present in peripheral blood mononuclear cells and their lytic activity are normal.

Effects of ethanol on human natural killer cell activity: in vitro and acute, low-dose in vivo studies

Chronic use of ethanol may cause a variety of immunological abnormalities in humans. In this study, we have determined the effects of an acute, low dose of ethanol (0.5 g/kg), administered either intravenously or orally, to normal, nonalcoholic male volunteers, on natural killer cell (NK) activity. We have also examined the effects of a 4-hr incubation with ethanol, in concentrations ranging from 0 to 320 mg/dl, on human NK activity in vitro. NK activity was measured by the 51Cr release assay technique in all of these studies, using peripheral blood mononuclear cells prepared from blood obtained from healthy, nonalcoholic volunteers. Eight subjects received ethanol in vivo; cells from nine subjects were used for the in vitro studies. Blood ethanol concentrations were determined at multiple time points before and after ethanol administration for the in vivo studies; for the in vitro studies, ethanol concentrations were measured from each assay sample both before and after the incubation period. Gas chromatography was used for determinations of both blood alcohol and medium ethanol concentrations. Results of the in vivo studies showed that a single dose of ethanol (0.5 g/kg), administered either intravenously (with resultant peak blood levels transiently up to 89 mg/dl) or orally (with resultant peak blood levels transiently up to 40 mg/dl at the time of the NK assay), did not alter NK activity. However, results of the in vitro studies showed a significant dose-dependent decrease (p < 0.001) in NK activity when ethanol exposure was sustained for 4 hr at concentrations of 80 mg/dl and above.(ABSTRACT TRUNCATED AT 250 WORDS)

OK432 inhibits experimental hepatic metastasis of colon adenocarcinoma ACL-15 in F344 rats

The effect of OK432 on hepatic metastasis, induced by inoculating 1 x 10(6) ACL-15 cells from a rat colon adenocarcinoma cell line into the ileocolic vein of male F344 rats, was investigated in this study. Metastases were detected 14 days after inoculation in the control rats, however, pretreatment 3 days prior to the tumor cell inoculation with an anti-asialoGM1 antibody, which eliminates natural killer (NK) cell activity in vitro, increased the number of hepatic metastases, shortened the survival time, and decreased the NK activity of the nonparenchymal liver cells (NPC). In contrast, pretreatment with OK432 2 days prior to tumor inoculation significantly decreased the number of hepatic metastases, prolonged the survival time, and augmented the NK activity of the NPC, although treatment with OK432 3 or 7 days after inoculation did not decrease the number of hepatic metastases. Moreover, NPC from the OK432-pretreated rats had a marked antitumor effect against ACL-15 cells in the Winn's neutralization test. The results of this study indicate that pretreatment with OK432 before tumor cell inoculation inhibits hepatic metastasis in this experimental model, possibly by augmentating liver-associated NK activity.

Natural immunity in breast cancer patients during neoadjuvant chemotherapy and after surgery

Breast cancer is the most common cancer in women. Surgery, and more recently neoadjuvant chemotherapy, are being utilized as the initial treatment for breast cancer; however little is known about their effects on the natural immune system. The natural immune system (natural killer [NK] cells) is thought to be important in immune surveillance, including protection from metastasis during the intravascular tumour seeding that occurs during surgery. To investigate the effects of surgery on the natural immune system, we studied the pre-operative and post-operative peripheral blood lymphocytes (PBL) of 10 patients with stage I or II breast cancer: there was a 71.6 +/- 25.3% post-operative reduction in NK cell function (P < 0.005, Student's paired t-test). To investigate the effects of neoadjuvant chemotherapy and surgery, we examined PBL from five patients with stage III breast cancer: NK cell function dropped 95.7 +/- 1.9% after neoadjuvant chemotherapy, and there was a further 51.0 +/- 23.4% decrease after surgery (P < 0.05, Student's paired t-test). Neither group of patients had decreased numbers of NK cells, changes in the percentage of T helper or suppressor cells, or alterations in the production of cytotoxic factor by NK cells. These findings suggest that the impairment in NK cell function reflects a defect in the ability of NK cells to recognize and/or bind to tumour target cells. We conclude that the initial treatment of breast cancer patients, whether it involves surgery alone or with neoadjuvant chemotherapy, profoundly impairs their natural immune system and could increase the risk of metastasis. Further studies are needed to delineate the mechanism of this derangement in natural immunity and possibly alter its course.

MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide, inhibits the metastasis of haematogenous and non-haematogenous tumours in mice

The antimetastatic effects of MDP-Lys(L18), a lipophilic derivative of muramyl dipeptide (MDP), against three different types of highly metastatic murine tumour cells, B16-BL6 melanoma, colon 26-M3.1 carcinoma and L5178Y-ML25 T lymphoma, were examined in C57BL/6, Balb/c and CDF1 mice, respectively. The administration of 100 micrograms of MDP-Lys(L18) 2 or 4 days before tumour inoculation led to a significant decrease in lung metastasis of B16-BL6 melanoma or colon 26-M3.1 carcinoma cells. MDP-Lys(L18) was also effective in the inhibition of liver metastasis of L5178Y-ML25 lymphoma cells by administration 2 or 4 days before tumour inoculation. The prophylactic effect of 100 micrograms of MDP-Lys(L18) on tumour metastasis was evident for the different administration routes, i.e. subcutaneous, intravenous or intranasal injection, or oral administration. It is of prime interest that oral administration of 1 mg of MDP-Lys(L18) induced a significant decrease in lung metastasis of B16-BL6 melanoma cells. Administration of MDP-Lys(L18) 4 days before assay led to induction of tumoricidal activity by peritoneal macrophages and growth inhibition by the sera against B16-BL6 or L929 cells. When MDP-Lys(L18) was subcutaneously administered five times after tumour inoculation to test therapeutic effect in an experimental and spontaneous metastasis model using B16-BL6 melanoma, the consecutive administrations of MDP-Lys(L18) significantly inhibited lung metastasis in tumour-bearing mice. These results suggest that MDP-Lys(L18) is able to enhance host resistance to reduce tumour metastasis and is a potent immunomodulating agent which may be applied prophylactically or therapeutically for the treatment of cancer metastasis.

Early interactions of cancer cells with the microvasculature in mouse liver and muscle during hematogenous metastasis: videomicroscopic analysis

Biomechanical interactions of cancer cells with the microvasculature were studied using high resolution intravital videomicroscopy. We compared initial arrest of murine B16F10 melanoma and D2A1 mammary carcinoma cells fluorescently labelled with calcein-AM, in low pressure (liver) vs high pressure (cremaster muscle) microvascular beds. Cells were arrested due to size restriction at the inflow side of the microcirculation, penetrating further and becoming more deformed in muscle than liver [median length to width ratios of 3.3 vs 1.3 for D2A1 cells, and 2.5 vs 1.2 for B16F10, at 1 min post-injection (p.i.)]. During the next 2 h many cells became stretched, giving maximum length to width ratios of 68 vs 22.1 (D2A1) and 28 vs 5.6 (B16F10) in muscle vs liver. Ethidium bromide exclusion demonstrated that over 97% of the cells maintained membrane integrity for > 2 h p.i. (In contrast, when an acridine orange labelling procedure was used, membrane disruption of B16F10 cells occurred within 15 min p.i.) Our experiments do not indicate the ultimate fate of the cancer cells, but if cell lysis occurs it must be on a time scale of hours rather than minutes. We report a process of 'clasmatosis' in cancer cells arrested in the microcirculation: large membrane-enclosed fragments (> 3 microns in diameter) became 'pinched off' from arrested cells, in both liver and muscle, often within minutes or even seconds of arrest. The significance of this process is not yet understood. In this study intravital videomicroscopy has thus provided a valuable clarification of the interactions of cancer cells with vessel walls during metastasis.

The natural killer cell-like lytic activity expressed by cytolytic T lymphocytes is associated with the expression of a novel function-associated molecule

Experiments were performed to analyse the natural killer cell (NK)-like cytotoxicity frequently expressed by human antigen-specific cytolytic T lymphocytes (CTL). To this end, several monoclonal antibodies (MoAbs) previously shown to identify a novel function-associated molecule (FAM) involved in human NK function were utilized. Flow cytometry revealed that these MoAbs reacted with the majority of human NK, but only with a subpopulation of CTL isolated from primary mixed lymphocyte cultures. Preincubation of CTL with the MoAbs inhibited the NK-like lysis of K562 targets. Experiments with anti-CD3 MoAb demonstrated that neither the NK-like cytotoxicity of CTL nor the lytic activity of NK were mediated by the CD3 complex. Expression of the novel FAM was found to develop in T-cell cultures at the time that NK-like cytotoxicity was observed. Repeated in vitro antigenic stimulation of CTL was shown to result in loss of NK-like cytotoxicity, as well as loss of the FAM on the CTL surface. Thus, NK-like cytotoxicity displayed by antigen-specific CTL appears to be mediated by a novel FAM that is identical to that structure found on NK.

B30-MDP, a synthetic muramyl dipeptide derivative for tumour vaccination to enhance antitumour immunity and antimetastatic effect in mice

The effect of a muramyl dipeptide derivative (B30-MDP) on the augmentation of antitumour immunity against highly metastatic L5178Y-ML25 mouse lymphoma cells was examined in CDF1 (Balb/c x DBA/2) mice. Mice immunized with a mixture of X-irradiated tumour cells (10(3)) and B30-MDP (100 micrograms) on 7 days prior to challenge by viable tumour cells displayed a significant decrease in metastasis towards the target organs, liver and spleen, compared with that of untreated mice. Immunization of mice with the mixture on day 5 or 7 after tumour challenge, when the level of glutamic-pyruvic transaminase (GPT) and glutamic-oxaloacetic transaminase (GOT) in sera of mice inoculated with viable tumour cells was observed to be normal, caused less metastasis than immunization with X-irradiated tumour cells alone. Sensitization with X-irradiated tumour cells admixed with B30-MDP induced almost two times higher cytotoxicity of spleen cells against L5178Y-ML25 lymphoma cells than sensitization with X-irradiated tumour cells without B30-MDP. In contrast, cytotoxic activity of spleen cells against another target, L1210 lymphoma cells derived from BDF1 mice, was not observed by immunization with X-irradiated L5178Y-ML25 cells with or without B30-MDP. Specific lysis by splenic cells of the immunized mice against L5178Y-ML25 cells decreased to the normal level when T cells were deleted from the immunized spleen cells by the treatment of rabbit anti-mouse Thy1.2 antibody and rabbit complement. These results indicate that B30-MDP is able to augment a specific tumour immunity due to the enhancement of cytotoxicity mediated by T lymphocytes, and is useful as an immunopotentiating agent for active immunization of inactivated tumour cells.

Recombinant fusion polypeptide with cell- and heparin-binding domains of fibronectin inhibits liver metastasis of L5178Y-ML25 lymphoma cells

We have investigated the effect of recombinant polypeptides with cell-binding domain (C-274) or with heparin-binding domain (H-271) and their fusion polypeptide (CH-271) on liver metastasis of murine lymphoid tumor. The polypeptides containing heparin-binding domain, H-271 and CH-271, were able to inhibit liver metastasis when co-injected i.v. with L5178Y-ML25 T-lymphoma cells, while C-274 with cell-binding domain showed much weaker antimetastatic activity. Treatment with H-271 or CH-271 substantially prolonged the survival time of mice injected i.v. with L5178Y-ML25 cells. CH-271, containing cell- and heparin-binding domains, was more antimetastatic than H-271. The reason why CH-271 was more effective in inhibiting liver metastasis than H-271 can not be explained in terms of a difference in the stability in the circulation or in the molecular size of the polypeptide. The polypeptides used in this study did not affect the tumor cell growth or viability in vitro. CH-271 was found to be still active in inhibiting liver metastasis even when natural killer cells or macrophages were removed from this system. Furthermore, multiple administrations of CH-271 after tumor implantation effectively inhibited liver metastasis and enhanced the survival rate as compared with H-271, C-274 and untreated control. Thus, the fusion of H-271 with C-274 (i.e. CH-271) augments the antimetastatic property of H-271, possibly through the interaction between tumor cells and the heparin-binding domain of fibronectin.

Factors determining the ability of cytokine-activated killer cells to lyse human ovarian carcinoma targets

Lysis of human ovarian carcinoma cells by natural killer (NK) cells, interferon-alpha activated NK cells (alpha-NK) and lymphokine-activated killers cells (LAK) was studied using both fresh tumor cells and a cell line (HEY) as targets. A clonogenic assay to measure cell kill was more sensitive than a 4-h 51Cr release assay. Both assays showed that single cells were more effectively lysed than were tumor clumps (spheroids). Freshly isolated tumor cells studied in the 51Cr release assay appeared equally susceptible to lysis by LAK cells whether in the form of clumps or single cells, but NK and alpha-NK effectors appeared much less effective in lysing susceptible target cells when they were in clumps. Tumor cells from some patients showed marked resistance to lysis by NK and alpha-NK cells in fractions enriched for clonogenic cells, even when tested in a single cell-suspension, whereas LAK cells were always cytolytic. These data suggest that intrinsic resistance of ovarian carcinoma to lysis by LAKs is unlikely to explain failure of LAK + IL-2 therapy to eradicate tumor in vivo.

Extracranial metastases of medulloblastoma in adults: literature review

A consecutive series of 30 cases of extracranial medulloblastoma metastases in adults is analysed. The majority of the patients were males with a 3:1 male/female ratio. Bone was the most frequent site of metastases in adults (77%) and children (78%), followed by lymph nodes (33%) in both children and adults. Lung metastases were more common in adults (17%), but liver metastases occurred more frequently in children (15%). Possible routes of spread and development of metastases are discussed, with special emphasis on the role of shunts in tumour seeding. Distant extracranial metastatic spread of medulloblastoma occurs at the rate of 7.1%. Mean interval between operation of the primary tumour and the discovery of metastases was shorter in children (20 months) than in adults (36 months). Survival after the discovery of metastases was also shorter in children (5 months) than in adults (9.5 months). Shunts were associated with an earlier appearance of metastases and with a poorer prognosis. A detailed review of the literature of 119 cases of medulloblastoma with extracranial metastases is provided.

Growth of xenografted head and neck cancer in nude mice pre-treated with whole body irradiation

In an attempt to enhance the primary acceptance rate of human squamous cell carcinoma of the head and neck (HNSCC), nude mice (BALB/c) were given whole body irradiation (WBI) prior to heterotransplantation of tumour specimens. A total of 27 fresh HNSCC biopsies were transplanted, with a take rate of 15%. No difference in primary tumour acceptance rate was found between irradiated and non-irradiated mice. Only one of the accepted tumours established growth both in irradiated and non-irradiated mice. In a second experiment, three previously established tumour lines of HNSCC were re-transplanted to irradiated and non-irradiated mice. As compared with non-irradiated mice, the growth rate was lower in all tumours transplanted to irradiated mice, the difference being statistically significant in two out of the three tumour lines. The results of the study show that attempted immunosuppression by WBI of nude mice prior to tumour implantation does not improve the growth conditions of HNSCC. These findings further emphasise the complexity of the transplantation barrier against human tumour xenografts in nude mice.

The potential importance of swainsonine in therapy for cancers and immunology

Swainsonine, an indolizidine alkaloid, was initially used in biomedical research as a tool to investigate the biosynthesis and function of asparagine-linked 'complex' type oligosaccharide moieties of glycoproteins. Recently, swainsonine has generated interest in its potential use as an anticancer agent with reports that it (i) inhibits tumor growth and metastasis, (ii) augments natural killer (NK) and macrophage-mediated tumor cell killing, and (iii) stimulates bone marrow cell proliferation. The antineoplastic activity of swainsonine can be explained at least in part by augmentation of immune effector mechanisms. The potential application of swainsonine as an anticancer agent is discussed.

Host and tumour factors in cancer metastasis

The process of cancer metastasis is sequential and selective and contains stochastic elements. The growth of metastases represents the endpoint of many lethal events that only few tumour cells survive. Primary tumours contain cells with heterogeneous metastatic properties, and the outcome of metastasis depends on the interplay of tumour cells with various host factors. Collectively, then, our studies and most data reported by others have led us to conclude that metastasis is a highly selective process regulated by a number of mechanisms. This belief is contrary to the once widely accepted notion that neoplastic dissemination is the ultimate expression of cellular anarchy. In fact, suggesting that cancer metastasis is a selective process is a more optimistic view in terms of cancer therapy than the one that contends that tumour dissemination is an entirely random event. A selective biological process is regulated by the interaction of tumour cells with their host, and these complex interactions can be studied and manipulated. A better understanding of the complexity of the processes of tumour evolution, progression, and metastasis should lead to improvements in the treatment of cancer.

In vitro immunotoxicology and immunopharmacology: studies on drugs of abuse

The application of immunotoxicology to the toxicologic assessment of drugs of abuse is a field of increasing importance. Interest in the effects of drugs of abuse on the immune system has greatly increased as a result of the AIDS epidemic. If drugs of abuse compromise the immune system, their use may well become a predisposing factor in the development or enhancement of AIDS in high-risk groups. Therefore development and validation of newer methods of assessment of immunotoxicology and their adaptation to routine analysis is an absolute necessity. An important feature in toxicology in general, and in immunotoxicology in particular, is the need to develop in vitro assessment systems. Recent research has provided newer models, data on correlations of immune function variables, and a better understanding of the biologic relevance of certain immune function parameters. This paper analyzes these features in relation to the role of drugs of abuse in the modulation and alteration of the immune system and reviews the various in vitro techniques that could be used to evaluate immunotoxicity.

Orthotopic implantation is essential for the selection, growth and metastasis of human renal cell cancer in nude mice [corrected]

Human neoplasms are heterogeneous for a variety of biological properties that include invasion and metastasis. The presence of a small subpopulation of cells with a highly metastatic phenotype has important clinical implications for diagnosis and therapy of cancer. For this reason, it is important to develop an animal model for the selection and isolation of metastatic variants from human neoplasms and for testing the metastatic potential of human tumor cells. We have implanted human renal cell carcinoma (HRCC) cells (obtained from a surgical specimen) into different organs of nude mice and then recovered the tumors and established each in culture. The 5 established lines differed in their biological-metastatic properties and had a unique karyotype, indicating that growth at different organs selects for different subpopulations of HRCC. Moreover, the HRCC did not metastasize unless they were implanted orthotopically. These findings indicate that the appropriate nude mouse model for studying the biology and therapy of HRCC must be based on the orthotopic implantation of tumor cells.

Natural cell-mediated immunity in the rabbit

Susceptibility and resistance to tumors represent the interplay of many factors. One factor felt to govern the development of tumors is natural killer and natural cytotoxic cellular activity. The constitutional resistance of rabbits to spontaneous tumor development raises questions regarding the activity of natural cell-mediated immunity in this species. We therefore examined the ability of rabbit spleen, lymph node, and peripheral blood lymphocytes to mediate natural killer cell (NK) and natural cytotoxic cell (NC) activity in vitro. Using classical approaches to the study of NK and NC activity, we found no evidence of these activities in leporine spleen, lymph node, and peripheral blood lymphocytes. Preincubation of these cells with IL-2 did not induce such activity. Antibody-dependent cell-mediated cytotoxic reactivity (ADCC), which is believed to be mediated by NK cells, was also undetectable in rabbit lymphocytes. As controls, lymphocytes from other species were capable of mediating NK, NC, and ADCC functions normally in these experiments. Finally, we were unable to identify a population of large granular lymphocytes, the cells believed to mediate NK activity in other animals. Therefore, we could not demonstrate in the rabbit either natural cell-mediated immunity or the population of cells usually associated with natural cell-mediated immunity. If such activity exists in rabbits, it is different from that seen in other animals. More likely, the basis for the natural resistance of rabbits to tumor development must be sought elsewhere.

Phenotypic stability and metastatic behaviour of serially xenografted rat mesotheliomas

Mesotheliomas induced in rats by intrapleural injection of the fibrous zeolite, erionite, were serially transplanted in nude mice for up to ten generations. The cell phenotypes (epithelial or sarcomatous) were well maintained during passaging, as determined morphologically and by the expression of the cytokeratin markers demonstrated in normal mesothelial cells. Some of the tumours occasionally produced metastasis in nude mice. In contrast, a cloned epithelial cell mesothelioma and sarcomatous cell mesothelioma, the original cells of which were isolated in tissue culture, both produced regular multiple metastases when passaged in nude mice. These metastases were frequently found on the visceral pleura, rather than in the lung parenchyma, in nude mice. The high metastatic rate of the xenograph mesotheliomas derived by in vitro isolation of cells from mesotheliomas is atypical of the usual behaviour of xenografts of mesotheliomas.

Differential sensitivity of head and neck cancers to non-major histocompatibility-restricted killer cell activity

Cell lines derived from squamous cell carcinoma of the upper aerodigestive tract (head and neck cancer) were phenotypically characterized with regard to differential sensitivity to nonmajor histocompatibility restricted (non-MHCr) killer cell activity. Requirements for detectable lysis of the cell lines in a standard chromium release assay included either isolation of fresh enriched Leu 19+ large granular lymphocytes (both Leu 19+CD3+ and Leu 19+CD3- populations) or interleukin-2 (IL-2) stimulation of peripheral blood lymphocytes (PBL). In neither circumstance could lytic activity be identified among Leu 19- populations. With PBL IL-2 stimulation significant differential sensitivity to lysis expressed by the head and neck cancer cell lines (P less than 0.001 by analysis of variance) was identified and maintained regardless of PBL source, i.e., PBL from healthy controls and three differing populations of head and neck cancer patients categorized by disease status and treatment. One factor associated with a cell line's increased sensitivity was degree of tumor differentiation, poorly differentiated tumors (as defined by intermediate filament cytochemical staining [decreased keratin and increased vimentin]) being more sensitive. Furthermore, as tumor cell lytic sensitivity increased, major histocompatibility complex (MHC)-class I antigen expression diminished concurrently. In 1 of 4 cell lines tested, however, pretreatment of tumor cells with interferon-gamma induced diminished lytic sensitivity independent of changes in MHC-class I expression, indicating factors not related to MHC-class I expression are likewise relevant. In previous studies we defined the in vivo prognostic significance of non-MHCr killer cell cytotoxicity activity against K562 targets, diminished activity being principally predictive of metastatic disease development in persons with poorly differentiated head and neck cancers. This report extends these observations by demonstrating in vitro that poorly differentiated head and neck cancer target cells are highly sensitive to changes in lytic function expressed by Leu 19+ non-MHCr effector cells.

Augmentation of antimetastatic activity of interferon and tumor necrosis factor by heparin

Interferon (IFN) and tumor necrosis factor (TNF) suppress the development of experimental metastasis and when used together, TNF and IFN show synergistic activity. However, the use of TNF is limited by its ability to initiate inappropriate hemostasis. Hemostatic effects are exaggerated by the procoagulant activity of certain tumor cell lines. Therapy with anticoagulants are indicated to block the effects of tumor cell products as well as chemotherapeutic side effects. Heparin is a glycosaminoglycan with diverse biological activity, including the ability to rapidly accelerate the inactivation of active clotting factors. The present studies have explored the therapeutic effects of combining heparin with TNF or interferon on experimental metastasis in mice using a melanoma cell line (B16BL6). Our data indicate that continued heparinization augments the antitumor activity of both interferon and TNF. Alterations of the hemostatic and immune systems play a role in the producing the observed effect.

Inhibition of lymphokine-activated killer cell generation by blocking factors in sera of patients with head and neck cancer

Cytolytic activation of peripheral blood lymphocytes by recombinant interleukin-2 (rIL-2) in patients with squamous cell carcinoma (SCC) of the head and neck may be inhibited by serum blocking factors, and this could influence therapeutic efficacy. Peripheral blood lymphocytes from 21 patients with this disease and 17 controls were incubated with 10-1000 U rIL-2 for 6 days in supplemented complete medium (containing 10% fetal calf serum) or the same medium plus 10% autologous serum. After washing the effector cells, we determined their cytotoxicity against K562 and MDA1386, a lymphokine-activated-killer(LAK)-sensitive SCC cell line, using a 51Cr-release assay. Patient sera inhibited LAK-generated lysis of both MDA1386 and K562, while control sera from healthy persons inhibited LAK-generated lysis of MDA1386. The blocking activity of patient sera tended to be greater than that of control sera. The sera of patients with untreated or recurrent disease and those who were free of disease had equivalent inhibitory capacity. The serum blocking factor acted in a dose-dependent manner, and inhibition was overcome by increasing the dose of rIL-2. Levels of circulating immune complexes (measured by the C1q binding method) did not correlate significantly with inhibition. A clinical protocol of repeated plasma exchange in patients with advanced and recurrent squamous cell carcinoma of the head and neck allowed sequential study of one patients's serum before, during, and after treatments. Plasmapheresis removed serum inhibitory factors, albeit temporarily. The activity of serum blocking factors in patients with this disease can be modulated by increasing doses of rIL-2 and by plasma exchange. This modulation may be important to improving clinical response rates for patients undergoing immunotherapy.

Origin and biology of cancer metastasis

Metastasis, the spread of cells from a primary neoplasm to distant sites where they grow, contributes to the death of most cancer patients. The process of metastasis is not random. Rather, the process consists of a series of linked, sequential steps that must be completed by tumor cells if a metastasis is to develop. Thus, metastatic cells must succeed in invasion and embolization, survive in the circulation, arrest in a distant capillary bed, and extravasate into and multiply in organ parenchyma. Although some of the steps in this process contain stochastic elements, as a whole metastasis favors the survival and growth of a few subpopulations of cells that preexist within the parent neoplasm. Moreover, metastases can have a clonal origin, and different metastases can originate from the proliferation of single cells. The outcome of metastasis depends on the interaction of metastatic cells with different organ environments. Organ-specific metastases have been demonstrated in a variety of experimental tumor systems, and even within one organ, site-specific tumor growth can be found. The conclusion that metastasis is a highly selective process that is influenced by both the intrinsic properties of tumor cells and by host factors is optimistic. A selective process is regulated and therefore can be studied and then manipulated.

Influence of ethanol consumption on natural killer cell activity in mice

Alcohol is a known suppressant to the immune system, and alcoholics frequently have impaired humoral and cell-mediated immunity. Several studies indicate that alcohol modulates natural killer (NK) cell activity. NK cells provide important defense against certain infectious diseases, spontaneously arising tumors and, in particular, to blood-borne metastasizing tumor cells. Evaluation of the effects of alcohol on NK cells is complicated by many factors including: the level and duration of alcohol abuse, polydrug use, the subject's age, and nutritional and health status. This study examined the effects of 1 and 2 weeks of alcohol consumption on baseline and interleukin 2 (IL-2) stimulated murine NK cell activity. Well nourished female C57BL/6 mice were given continuous access to 20% w/v ethanol as the sole fluid source and consumed about 40% of their total caloric intake as ethanol. Splenic baseline and IL-2 stimulated NK cell activity were significantly lower in ethanol-consuming groups compared to control groups after the 1- and 2-week test periods. The average daily intake of ethanol, blood alcohol concentration, and the percentage of ethanol-derived calories were not associated with the decreased NK cell activity of the experimental animals; nor did any other measured parameter appear to serve as an indicator of ethanol modulation of splenic NK cell activity. Whether this immunosuppression results from the "direct" modulation of ethanol or from indirect factors is presently unknown.

In vivo selection of human renal cell carcinoma cells with high metastatic potential in nude mice

Studies were made to determine whether the orthotopic implantation of human renal cell carcinoma cells (HRCC) into nude mice will produce distant metastases, thus allowing for the selection of variant cells with high metastatic potential. The parental SN12C line was established in culture from a surgical specimen of HRCC. The renal subcapsule (RSC) of adult nude mice was injected with SN12C cells; the mice were killed when they became moribund. Cell lines were established from either single or multiple lung HRCC metastases. The intravenous injection of many (but not all) of the metastasis-derived lines produced significantly more experimental metastases than did the parental cells. The injection of cells into the RSC demonstrated that, in general, cells derived from spontaneous metastases were more metastatic than cells of the parental line. Hence adult nude mice can be used to select HRCC cells with high metastatic potential. These HRCC variant lines offer a good model for studying the cell properties of metastatic HRCC.

A survey of in vivo growth characteristics and spontaneous metastasizing potentials of C3H mouse mammary tumors

This investigation examined the relationship between spontaneous metastasizing potential, immunogenicity and growth rate in 34 C3H/He mammary carcinomas. The main purpose of our studies was to examine the hypothesis that a tumor's metastasizing potential is affected by its immunogenicity. The tumors were studied during serial intra-mammary transplantations, starting with tissue from autochthonous, spontaneous pulmonary metastases. The results show that there was no correlation between metastasizing potential and tumor immunogenicity, and no correlation between metastasizing potential and tumor growth rate. Moreover, metastasizing potential was not related to invasive behavior, because histological examination showed that all of the metastases grew extensively within pulmonary vessels and displayed no tendency to active extravasation.

Effect of photodynamic therapy on anti-tumor immune defenses: comparison of the photosensitizers hematoporphyrin derivative and chloro-aluminum sulfonated phthalocyanine

The effects of the two photosensitizers chloroaluminum sulfonated phthalocyanine (ClAlSPc) and hematoporphyrin derivative (HpD) on the functional activities of macrophages and natural killer (NK) cells, two immunocyte populations implicated in the control of tumor development and spread, have been investigated. Murine peritoneal macrophages treated in vivo with ClAlSPc or HpD at 10 mg/kg body weight showed no impairment of Fc-mediated phagocytic capacity and only minor disturbances of in vitro tumoricidal/tumoristatic function. The NK cell activity of splenocytes obtained from photosensitizer-treated mice, assayed 24 or 48 h after i.v. injection of ClAlSPc or HpD at 10 mg/kg was unaffected compared to controls. However significant inhibition of NK activity was observed when splenocytes obtained from mice with or without subcutaneous Colo 26 tumors, treated with ClAlSPc plus laser therapy (675 nm) were used as effector cells. The results show that impairment of some anti-tumor activity can be observed in phthalocyanine treated or phthalocyanine + laser-treated animals but this relatively minor impairment may augur well for the use of systemic phthalocyanine administration in photodynamic therapy.

Liver sinusoidal blood containing natural killer-like cells

Rat liver sinusoidal washout cells were examined. These cells, which are marginated in sinusoids, could be washed out by simple flushing of the vasculature with culture media without enzymes and under physiological portal pressure. They revealed, in comparison to peripheral blood mononuclear cells, high cytotoxic activity commonly attributed to the natural killer (NK) and natural cytotoxic (NC) cells, and were found to be anti-asialo-GM1-negative. Liver sinusoidal cytotoxic cell (LSCC) activity has been found to be associated with the large granular lymphocytes in low-density cells in OX8-positive as well as in OX8-negative populations. The mononuclear cells washed out from the liver microvasculature could be stimulated with NK-sensitive targets to release soluble factors which selectively lyse YAC-1 tumour cells and inhibit growth of normal haematopoietic granulocyte-macrophage colony-forming cells in vitro. The cytotoxic cell population in the liver turned out to be blood-borne in origin and not resident. Our findings suggest that liver sinusoidal cytotoxic cells represent an NK population with a predilection for marginating in the liver and may be important in eliminating tumour or virus infected cells passing through the liver from the circulation. The mechanism of their accumulation in liver sinusoids remains unclear.

Effects of the immunomodulator PSK on growth of human prostate adenocarcinoma in immunodeficient mice

Tumor growth alterations were studied using an immunomodulator, PSK. Four human prostate tumor lines were grown in two types of immunodeficient mice. Two of the lines were selected because they are able to metastasize to lungs in host animals. Outbred NIH Swiss athymic mice having normal natural killer cells and athymic Beige mice deficient in natural killer cells were used as animal hosts. PSK treatment was given to tumor-bearing hosts to some animals soon after solid tumors were injected and to others after solid tumors were well-established. Low dose cyclophosphamide was given to some animals to decrease host natural killer cells and polyinosinic-polycytidylic acid (poly I:C) was given to other animals to increase natural killer cell activity. Measurement of tumor doubling times, host survival and metastatic capabilities showed that either poly I:C or PSK treatment in NIH Swiss animals soon after tumor cells were injected significantly increased tumor doubling times and host survival and decreased the incidence and number of metastatic lung lesions. Two of the tumor lines incapable of metastasizing in NIH Swiss mice were metastatic in the Beige athymic, natural killer-cell-deficient animals.

Sensitivity of locally recurrent rat mammary tumour cell lines to syngeneic polymorphonuclear cell, macrophage and natural killer cell cytolysis

Using a recently developed model for studying the biology of locally recurrent (LR) mammary tumours in the 13762NF rat mammary adenocarcinoma system, we examined the sensitivity to polymorphonuclear cell, macrophage and natural killer cell cytolysis. The parental MTF7(T20) cell line; the 'primary' tumours which arose following subcutaneous inoculation into the mammary fat pad, sc1 and sc3; and the local recurrences (following surgical excision) LR1 and LR1a from sc1, and LR3 from sc3 were all cells generally resistant to specific PMN cytolysis. LPS-activated macrophages caused 25.1%, 38.7% and 58.8% specific cytolysis in MTF7, sc1 and LR1 cells, respectively at E:T of 20:1 and 72 h co-incubation. LR1a, sc3 and LR3 lysis ranged from 0-4.4% under the same conditions. Non-activated macrophages did not lyse any of the cell lines. Locally recurrent and 'primary' tumour cell lines were also not lysed by naive NK cells (range 0.5-4.0% cytolysis). NK cells activated with bropirimine, a potent immunomodulator currently being studied in clinical trials, and/or interleukin-2 were mildly more effective at killing LR cells. Our results show that locally recurrent tumours exhibit heterogeneous sensitivities and are different from 'primary' tumour cells in sensitivities to immune cell killing, but they are not necessarily more or less sensitive. Results with bropirimine-activated or IL-2-activated NK cells emphasize that nonspecific activation is insufficient to eliminate all tumour subpopulations.

IFN-treatment of B16-F1 versus B16-F10: relative impact on non-adaptive and T-cell-mediated immune defense in metastatic spread

Treatment of tumor cells with interferon-gamma (IFN) frequently reduces their susceptibility towards NK cells and results in augmented expression of MHC antigens, which may increase immunogenicity of tumor cells. Depending on the relative strength of these opposing effects, i.e. escape from non-adaptive immune defense versus facilitated activation of T-cell-mediated defense, IFN-treatment may be beneficial or disadvantageous for the tumor-bearing host. This is demonstrated for the variants F1 and F10 of the B16 melanoma, which differ in metastasizing capacity. IFN-treatment of B16-F1 melanoma cells significantly reduced susceptibility towards non-adaptive immune defense, and increased metastasizing potential. On the other hand, H2K antigen expression was augmented by a factor of 50; concomitantly, lysability by CTL was increased, together with the number and expansion rate of cytotoxic T-cell precursors (CTLp) recruited after immunization with IFN-treated B16-F1. The benefit of increased antigenicity and immunogenicity outweighed the disadvantage or reduced susceptibility towards non-adaptive immune defense. B16-F10 cells were less susceptible to NK cells, expression of MHC antigens was found to be stronger and they were more immunogenic than B16-F1 cells. After IFN-treatment, susceptibility to non-adaptive immune defense was further reduced. Expression of MHC antigens as well as antigenicity and immunogenicity were only moderately augmented. As a consequence, the decreased susceptibility to non-adaptive immune defense was dominating in the tumor bearing host and could not be counterbalanced by immunization with IFN-treated B16-F10 cells. We interpret these data to show that a precise knowledge of the relative decrease in susceptibility to non-adaptive immune defense, the relative increase in MHC antigen expression, antigenicity and immunogenicity may allow a more precise prognosis of the influence of IFN on metastatic capacity in the B16 system, and eventually also in a clinical therapeutic regimen.

The biology of melanoma metastasis

The process of cancer metastasis is sequential and selective and contains stochastic elements. The growth of melanoma metastases represents the endpoint of many lethal events that few tumor cells can survive. Primary tumors consist of multiple subpopulations of cells with heterogeneous metastatic properties, and the outcome of metastasis depends on the interplay of metastatic tumor cells with various host factors. This viewpoint is more optimistic than that of metastasis as a random process. A selective biological process is regulated by the interaction of tumor cells with their host, and these complex interactions can now be studied and manipulated.

A new experimental metastasis model in athymic nude mice, the human malignant melanoma LOX

The human tumor line LOX was established as an s.c. xenograft in nude mice from a lymph-node metastasis of a patient with malignant melanoma. I.v. injection into adult nude mice of single-cell suspensions prepared from xenografts resulted in progressively growing lung tumor colonies that killed the animals. No difference in colony formation was seen between cells taken from lung colonies and s.c. xenografts. An in vitro cell line, LOX-L, was established from lung colonies, and the monolayer cells, detached with EDTA, retained the same ability to form experimental lung metastases. In a total of 14 experiments, 82 of 89 mice receiving 1 X 10(6) viable tumor cells died with a mean survival time of 34.1 +/- 4.8 days. Long-term passaging in vivo and in vitro did not result in any alteration of the lung-colonizing potential of the LOX cells, whereas trypsinization of the cells before i.v. injection reduced lung colony formation. The life span was inversely related to the number of LOX cells injected, permitting estimation of the cell kill caused by chemotherapy. Mice injected i.v. with the LOX cells showed the same relative response to cis-diamminedichloroplatinum (CDDP) and mitozolomide (MZA) as did animals carrying s.c. xenografts. The LOX cells have shown a remarkable stability and similarity to the cells of the patient's tumor with respect to morphology, karyotype and chemosensitivity. The LOX model may be useful for testing effects of therapy on lung micro- and macrometastases, and the activity of antimetastatic agents, as well as for studying mechanisms involved in the metastatic process.

Response to flavone acetic acid (NSC 347512) of primary and metastatic human colorectal carcinoma xenografts

The antitumour activity of flavone acetic acid (FAA) was evaluated against two human colorectal carcinoma (HCC) lines, HCC-P2988 and HCC-M1410, transplanted into nude mice. On repeated i.v. injection of 200 mg kg-1 every 4 days FAA was moderately active against the s.c. growing HCC-P2988. HCC-M1410 transplanted s.c. was almost unresponsive in the same experimental conditions. In contrast, FAA (200 mg kg-1 i.v. every 4 days, repeated three times) significantly reduced liver tumour colonies produced by the HCC-M1410 cells injected intrasplenically into nude mice. These findings suggest that FAA has potential activity against human colorectal carcinoma, particularly against liver metastases.

Use of NeoR B16F1 murine melanoma cells to assess clonality of experimental metastases in the immune-deficient chick embryo

Recent work on molecular and genetic aspects of metastasis has emphasized the need for assays in immune-deficient animal hosts. The commonly used assays in athymic nude mice may not always be appropriate, and assays in other hosts are required. We have developed a metastasis assay in the naturally immune-deficient chicken embryo. As part of our characterization of this assay we have examined the clonality of individual experimental (i.v.-derived) metastases in this host. For these studies we developed a cell line, B16-Neo, from parental B16F1 murine melanoma cells. B16-Neo cells carry a stable drug-resistance marker, the bacterial neo gene, which confers resistance to the drug G418, but are unaltered in experimental metastatic properties in the chick embryo relative to parental B16F1 cells. We observe that the majority of individual liver tumors that arise following i.v. injection of mixtures of these cells contain cells of a single marker phenotype and are likely to be clonal in origin. These results are similar to those obtained by others for metastases in immune-competent mice, suggesting similar mechanisms of metastasis formation in these two systems. In both hosts it should be noted, however, that a small but significant proportion of metastases appear not to be clonal in origin.

Pulmonary tumor colony formation following i.v. inoculation of six human colorectal carcinoma xenografts in young gnotobiotic athymic mice

The lung colonizing potential of 6 xenografted human colorectal adenocarcinomas following tail vein inoculation of tumor cell suspensions into gnotobiotic 3-4-week-old congenitally athymic mice was investigated. One of the lines, CRCo2, was of particular interest, as apparently distinctive lung colonizing phenotypes, large (greater than 2.5 mm diameter) and small (less than 1 mm diameter) colonies were identified, and variant lines with greater, equal, or lesser ability to grow in the lungs relative to the sc tumor of origin were observed. Another line, CRCo1, was also able to grow well in the lungs following tail vein inoculation, but subsequent cycles of lung tumor recovery and reinoculation i.v. did not result in an enhancement of the tumor's lung colonizing ability relative to the initial i.v. inoculation of the sc carried tumor. Scattered lung colonies were observed following i.v. inoculation of sc carried xenografts in three of the four other lines, but we could not consistently recover lung colonies with these tumors. The data are in accord with the clinical observation that pulmonary metastasis is not a high frequency event in human colorectal carcinoma, illustrating the selective nature and experimental utility of this model of metastasis. Further, there were indications of the inefficient and/or random nature of the metastatic process in some of the tumors, while in others, evidence for both effectively higher and lower metastatic variants were found, as might be predicted in heterogeneous tumor cell populations.

The effect of the immune status of the TAR mouse on the growth and metastasis of tumour xenografts

Mice thymectomised at 3-4 weeks of age and subsequently given whole-body irradiation (9 Gy) under cytosine arabinoside cover (TAR mice) provide an alternative model to the athymic nude (nu+/nu+) mouse for studying the biological characteristics of tumour xenografts. In the present study we have evaluated the repopulation events in the bone marrow and spleen following whole body irradiation of TAR mice, and analysed immune competence up to 98 days following irradiation. Repopulation of both bone marrow and spleen was evident in the weeks following whole body irradiation, and an initial increase in the relative proportion of T-lymphocytes present in the spleen was followed by a decrease in the percentage of lymphocytes expressing T-cell markers, which remained below the level observed in control mouse spleen cell preparations. TAR mice exhibited a decreased ability to respond to a non-specific T-cell mitogen and to elicit a T-cell dependent antibody response to influenza viral antigen. Both TAR and control mice possessed macrophages which could be activated to the tumouricidal state, and natural killer activity of TAR mice was enhanced greater than 3-fold above control values. The ability of TAR mice to accept tumour xenografts decreased with the increasing time interval between irradiation and subcutaneous implantation of tumour cells, and (in some instances) spontaneous regression was observed. In addition, a hamster tumour cell line possessing high metastatic potential in its syngeneic host was shown to metastasise to the regional lymph node, lungs, liver, kidneys and spleen of TAR mice from a cell inoculum implanted subcutaneously immediately after irradiation; however, with increasing time between irradiation and inoculation of tumour cells tumour metastasis decreased. The ability of TAR mice to support the growth and metastasis of tumour xenografts would appear to inversely correlate with the increase in natural killer cell activity following irradiation.

Growth and metastatic behavior of human tumor cells implanted into nude and beige nude mice

The growth and metastatic behavior of several human tumor lines grown in adult nude mice, nude mice pretreated with antiserum against asialo GM1 glycoprotein, and beige nude mice were studied. The cell lines were all injected s.c. and i.v. A human colon carcinoma line was also injected into the spleen, and two human renal carcinoma lines were injected into renal subcapsule. All the tumor lines grew as fast or faster in adult nude mice compared with beige nude mice. There were no discernible differences in the production of experimental lung metastasis among the three groups of mice, but human colorectal carcinoma cells and human renal carcinoma cells produced more metastases in nude mice than in beige nude mice after intrasplenic or renal subcapsule injection, respectively. In vitro cytotoxicity assays confirmed that adult nude mice had high levels of natural killer (NK) cell activity whereas nude mice pretreated with anti-asialo GM1 serum and beige nude mice did not. The in vitro NK cell activity of nude mice was demonstrable against mouse lymphoma cells but not against human leukemia cells which were sensitive to lysis by human NK cells. These results suggest that the implantation of human tumor cells into beige nude mice, which are deficient in NK cell activity does not provide an advantageous model for the study of growth and metastasis of human neoplasms.

Enhancement of pulmonary metastasis of murine fibrosarcoma NR-FS by ozone exposure

The effects of ozone exposure on the metastasis of a fibrosarcoma (NR-FS) that arose spontaneously in a C3H/He mouse was studied. Male C3H/He mice were exposed to 0.8, 0.4, 0.2, and 0.1 ppm ozone for 1, 3, 5, 7, and 14 d. After the exposure periods, the mice were infused intravenously with NR-FS cells. At 2 wk postinfusion, the lungs were examined for colony development of metastasis. A significantly higher rate of pulmonary metastasis than that of normal mice was observed in the ozone-exposed mice. The enhancement of metastasis due to ozone exposure varied with length of exposure and concentration of ozone. When 1 X 10(5) cells of NR-FS were injected into the tail veins of mice, the maximal enhancement (459%) of pulmonary metastasis was observed in the mice exposed to 0.8 ppm ozone for 1 d. A longer period of exposure to 0.8 ppm ozone also enhanced pulmonary metastasis, although the prolonged exposure (14 d) gradually suppressed the enhancement (268%). In the mice exposed to the lower concentration of ozone, a lower rate of the lung matastasis was observed; even in the mice exposed to 0.1 ppm ozone for the period of from 1 to 14 d, a significantly higher rate of metastasis than that of nonexposed mice was observed.

The cytolytic and regulatory role of natural killer cells in experimental neoplasia

NK cells are defined here as cells, other than macrophages and polymorphonuclear leucocytes, from non-immunized animals (or humans) which are cytotoxic for neoplastic and non-neoplastic targets in the absence of specific antibody. Though not requiring antibody, they may function as K cells in ADCC. This definition includes cells activated nonspecifically by such agents as IFN and IL-2. Murine NK cells may be subdivided into two types by differences in the kinetics of target-cell lysis. Those we label Type 1 correspond roughly to what others have called NKA, NKL or simply NK cells; those of Type 2 to NKB, NKS and NC cells. Type 1 cells express various antigens, including NK-1, Thy-1 (50%), Ly-1 (25%), Qa-3, Qa-4, Qa-5, Ly-5, Ly-6, Ly-10, Ly-11 and asialo-GM1, not expressed by Type 2 cells, whereas Mac-1 may be expressed by both types. At least some NK cells appear to be pre-thymic cells which, in the presence of a thymus, can differentiate into T cells. The level of NK activity is influenced by the age and genetic background of the mouse, the organ from which the cells are obtained, and a variety of experimental manipulations. Type 1 activity is increased by IFN and IL-2; Type 2 activity by IL-3. IFN appears to be concerned in the development of spontaneous NK activity in young mice. Many experiments have shown that NK cells may inhibit the growth of tumours which are sensitive to NK cells of the same type in vitro. Inhibitory cells which suppress NK activity may play an important regulatory role in vivo. There is still uncertainty about how NK cells recognize their targets. Possibilities discussed are: (1) specific interacting molecules; (2) more diffuse properties of target cell membranes; (3) absence of MHC-coded self-recognition markers. Certainly, the presence of a Class 1 MHC molecule is not necessary. NK killing appears to be mediated by cytotoxins released by NK cells. In vivo, NK cells contribute to limiting the development of transplanted and primary tumours, and metastasis from established tumours. NK cells seem well qualified to act as a first-line defence against neoplasia, and may kill cells not killed by T cells. Transfer of NK cells may be of value in the treatment of cancer.

Interferon-mediated protection of B16 melanoma cells from cytotoxicity by activated macrophages

Corynebacterium parvum-activated macrophages (M phi), purified by adherence, were cytotoxic for B16 melanoma cells maintained in vitro. Pretreatment of the melanoma cells for 18 hr with interferon-alpha/beta or -gamma (IFN-alpha/beta or -gamma) caused a reduced susceptibility of the B16 cells to M phi-mediated cytotoxicity. The IFN-induced protective effect of B16 cells from cytotoxic M phi was found to be dose dependent. In addition, IFN-gamma was more protective than IFN-alpha/beta. The protective effect observed with partially purified IFN was reproduced by using highly purified IFN-alpha/beta or recombinant IFN-gamma. Monoclonal antibodies to IFN-gamma neutralized the protective effect provided by IFN-gamma. These results show that the susceptibility of a tumor cell line to killing by activated M phi can be altered by IFN pretreatment.