The immune reaction as a stimulator of tumor growth

Opposing influence of age on the growth and colony-forming ability of mouse melanoma B16 and mammary adenocarcinoma: correlation with natural killer activity

C57B1 and CBA mice of different ages (6, 12, 26 or 35 weeks) received intramuscular inocula of melanoma B16 or mammary adenocarcinoma (MCa), respectively. Median survival time was shorter, the younger the recipients. Tumor enlargement was correspondingly retarded in older mice. This was associated with decrease of natural killer (NK) activity in the spleens. However, the cytotoxicity against fresh syngeneic tumor cells, increased with age in CBA mice. In contrast to the growth of intramuscular tumors, the ability of intravenously injected B16 or MCa cells to form nodules in the lungs was significantly superior in old animals (35 weeks or more), with low levels of NK activity, than in young ones (6 weeks) with high levels of NK activity. Stimulation of NK activity by poly(I).poly(C) reduced the number of MCa colonies by 50% in the lungs of old mice, but had no effect on colony-forming ability in young animals. The observed association of tumor growth with age and NK activity levels may reflect (a) an interplay of tumor-inhibiting and tumor-promoting effects of NK cells, changing with age, and (b) the accessibility of tumor cells, inoculated intramuscularly or captured in the lungs, to these influences.

Host response to myeloma: effect of syngeneic spleen cells on the growth and function of MOPC 104E myeloma in vitro

The effect of coculturing nonadherent and plastic adherent cells from the spleen with MOPC 104E KI81 for short (24 h) and long term (7 days) was investigated. In both culture systems, the effect of the spleen cells on the secretion of IgM by plaque-forming cells assay and growth of the plasmacytoma by cell counts and flow cytometry was measured. In these studies, a low effector:target (E:T) ratio which did not produce cytotoxicity to MOPC 104E cells was used. We observed that while nonadherent spleen cells from normal or MOPC 104E-primed mice inhibited secretion of IgM by the MOPC 104E cells, they stimulated the proliferation of MOPC 104E cells two times faster than MOPC 104E cells cultured alone. Plastic adherent cells from the spleens of normal mice or MOPC 104E-primed mice also inhibited secretion of IgM by the tumor cells as measured by plaque formation, and stimulated proliferation of MOPC 104E in 24 h coculture. Plastic adherent cells from normal nonprimed mice initially stimulated the myeloma to grow, but by 24 h, a large fraction of the population was in the G1 or possibly resting state. The effect of nonadherent and plastic adherent cells on the stem cell activity of MOPC 104E was also tested in 7-day colony-forming assays. Nonadherent cells had no effect on colony-forming units or plaque formation. Plastic adherent cells from normal spleen cells inhibited plaque formation by 68% but had no effect on colony formation. However, plastic adherent cells from spleens of mice primed in vivo with MOPC 104E tumor cells suppressed plaque formation by 98% and also reduced colony formation. The results showed that inhibition by macrophages of IgM production by MOPC 104E cells is independent of cell proliferation. The adherent macrophages from both normal and in vivo-primed spleen cells were Mac.1 positive after 7 days of coculture with MOPC 104E cells. However, the density of Mac.1 was greater on primed macrophages.

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.

Radiostrontium-induced oncogenesis and the role of immunosuppression. I. Influence of 90Sr dose, adult thymectomy and antilymphocyteglobulin treatment on the development of neoplastic and preneoplastic lesions in the skeleton of CBA mice

Ionizing irradiation by incorporated strontium-90 exerts two major effects: it induces tumours (mainly osteosarcomas and lymphoreticular tumours) and depresses the immune system. The interrelation between these functions, i.e. the significance of decreased immunological responsiveness in the oncogenic process, remains unclear. The influence of the 90Sr dose and the role of immune modulation on the tumour yield, were investigated in young adult CBA mice. The animals were exposed to different single doses of 90Sr and, in addition, some groups were subjected to long-term unspecific immune suppression by adult thymectomy (ATx) and/or prolonged antilymphocyteglobulin (ALG) treatment. The present paper (part I) reports on the effects of the treatments on bone tumour responses as reflected by incidence, multiplicity, latency time, histologic characteristics and growth behaviour. The histogenesis of osteosarcomas, as evidenced morphologically by preneoplastic and early neoplastic growth, is illustrated and discussed. The results demonstrate a positive dose-response relationship for osteosarcomas, in which the relative incidences of the various osteosarcoma subtypes were differentially affected. Thus, well-differentiated tumours were gradually replaced by less differentiated types as the dose decreased. A correlation was also observed between the incidence of osteosarcomas and that of assumed preneoplastic lesions in the same bones and sites. Immune suppression by ATx and/or ALG did not distinctly alter the neoplastic or preneoplastic responses at any dose-level of 90Sr.

[Passive immunity by splenocyte transfer against amebic meningoencephalitis in mice]

The role of passive cell-mediated transfer of immunity against primary amoebic meningoencephalitis(PAME) in mice was studied. Naegleria fowleri, ITMAP 359, were cultured in CGVS medium. The ICR mice used were six week-old males of average weight of 15 g. Immunization was done by three intraperitoneal injections of l x 10(6) N. fowleri trophozoites at the interval of one week. Splenocytes were obtained from normal and immune mice spleens, and 1 x 10(7) cells were administered intraperitoneally into mice 3 days before challenge infection. Mice were infected intranasally with 7 x 10(4) N. fowleri trophozoites in a 3 microliter suspension under secobarbiturate anesthesia. Transplants of normal or immune splenocytes seem to alter the pattern of the PAME development. The splenocytes transferred from immune mice reduced the mortality rate in the N. fowleri infected mice, as compared with the mice transferred with the same number of normal splenocytes or without splenocyte. The blastogenic response of the splenocytes to both lipopolysaccharide and concanavalin A was elevated on day 7 after infection the mice transinoculated with immune splenocytes. The serum antibody titers in the mice transferred with immune splenocytes were increased gradually from day 7 up to day 20 after infections by mean of ELISA. It is suggested that the transfer of splenocytes from immunized mice conferred immunity against N. fowleri infection.

Organ specificity of tumor metastasis: role of preferential adhesion, invasion and growth of malignant cells at specific secondary sites

The locations of distant secondary tumors in many clinical cancers and animal tumors are nonrandom, and their distributions cannot be explained by simple anatomical or mechanical hypotheses based on the simple lodgment or trapping of tumor cell emboli in the first capillary bed encountered. Evidence from certain experimental tumor systems supports Paget's 'seed and soil' hypothesis on the nonrandom distributions of metastases, in which the unique properties of particular tumor cells ('seeds') and the different characteristics of each organ microenvironment ('soil') collectively determine the organ preference of metastasis. Experimentally, differential tumor cell adhesion to organ-derived microvessel endothelial cells and organ parenchymal cells, differential invasion of basement membranes and organ tissues, and differential responses to organ-derived growth-stimulatory and -inhibitory factors all appear to be important determinants in explaining the organ preference of metastasis. Each tumor system may achieve organ specificity because of its own unique set of multiple metastasis-associated properties and responses to host microenvironments. As neoplasms progress to more highly malignant states multisite metastases are more likely and organ-specific metastases may be masked or circumvented owing to stochastic events, tumor cell diversification, host selection processes, and increased production of tumor autocrine molecules that may modulate adhesion, invasion, growth, and other properties important in metastasis. The importance of each of these properties, however, appears to vary considerably among different metastatic tumor systems. These and other tumor cell and host properties may eventually be used to predict and explain the unique metastatic distributions of certain human malignancies.

Immunologic enhancement of B16 melanoma growth

In certain experimental tumor models, tumor growth is less pronounced in immune deficient animals. Characteristically, tumors such as the murine B16 melanoma and Lewis lung carcinoma (3LL) are weakly antigenic. We proposed that with such tumors that are weakly antigenic, growth is enhanced by T-cell factors. Young mice were inoculated with irradiated B16 cells in complete Freunds adjuvant (CFA) on three occasions, each separated by 2 weeks. Specific antibody (IgG) to B16 membrane antigens was detected by an enzyme-linked immunosorbent assay (ELISA) after the first injection, and it continued to rise for 6 weeks. B16 growth was compared in 20 mice that had received irradiated B16 in CFA or CFA alone by the same schedule previously. Despite the previous sensitization, the rates of tumor appearance and growth were similar. In an additional experiment involving 23 mice that had received B16 immunization, the period of time in which a palpable tumor developed after the injection of viable B16 cells did not correlate with anti-B16 antibody level. It appeared that detectable antibody to B16 antigens was of little consequence. To explain why B16 primary growth and metastases were reduced in immune deficient hosts, we proposed that lymphocytes might enhance tumor growth. To demonstrate this, splenic lymphocytes from tumor-bearing (B16 or 3LL) or control mice were injected with B16 cells into young, immune competent hosts. Tumors (B16) developed earlier and growth was more rapid in mice that received spleen cells from tumor-bearing (B16) mice. Subsequent cell depletion experiments to determine the mediator of tumor enhancement implicated a T-cell fraction that was neither of T-helper nor T-suppressor cell type phenotypically. Immune deficiency states that are associated with dysfunction of those cells that account for tumor enhancement might explain the reduced tumor aggressiveness that is observed frequently in these conditions.

The nature and significance of tumour-associated mast cells

The role of the mast cell in tumour growth was examined in the rat with the use of a transplanted sarcoma. Mast cells were found at the periphery of the tumours and in fibrovascular trabeculae within the tumour mass. Histochemical studies showed that these cells contained an immature proteoglycan molecule, in contrast to normal mast cells. The mast cells appeared to be of the connective tissue phenotype and their local occurrence correlated with an anteroposterior difference in tumour growth. Mast cell enhancement of tumour proliferation was demonstrated by the addition of mast cells to the initial tumour inoculum and by pharmacological inhibition of mast cell degranulation.

Tumor cell metastasis

Local tissue invasion and the formation of metastatic lesions are characteristic properties of many malignant tumors. The formation of metastases is a complex process involving the passage of tumor cells from the site of the primary bulk tumor through successive connective tissue barriers, ultimately resulting in the growth of secondary tumor cell colonies in distinct target organ locations. At many stages in the metastatic process, tumor cells interact with multiple components of the extracellular matrix. Recently, the importance of basement membrane as a barrier to invasive cells has been recognized. In the course of the transition from in situ to invasive carcinoma, normal or dysplastic epithelial cells residing on a basement membrane are replaced by neoplastic cells which subsequently invade the basement membrane and enter the underlying stroma. Once in the stroma, tumor cells can then penetrate the walls of blood vessels or the lymphatic system and enter into the circulation. Circulating tumor cells next arrest in the lumina of small vessels, invade the vessel wall, and leave the circulation. These cells are now directly exposed to the extracellular matrix of a target organ where they may grow to form secondary tumors. Throughout the metastatic process tumor cells are thus in contact with, and are potentially responsive to, various components of the extracellular matrix. This review provides a survey of the recent advances in our understanding of the interactions of metastatic tumor cells with the extracellular matrix. Specifically, the role of basement membrane as a barrier to metastatic tumor cells is examined.

Generation of Epstein-Barr virus antigen-specific suppressor T cells in vitro

Immunosuppression is a commonly observed phenomenon in Epstein-Barr virus (EBV)-associated disorders and malignancies. The purpose of this study was to determine whether EBV antigens could generate suppressor cell activity in vitro. Peripheral blood lymphocytes (PBL) were first treated with various concentrations of EBV antigens or culture medium for 5 days and then with mitomycin C. The cells were then washed and tested for their ability to abrogate the blastogenic response of fresh, autologous PBL to previously determined optimal concentrations of EBV antigens. It was found that excess of both EBV antigens tested (soluble antigen and virus particles) induced suppressor cells, while optimal antigen concentrations failed to do so. In addition, PBL incubated with excess of EBV antigens for 10 days, without mitomycin treatment, inhibited the response of fresh autologous lymphocytes to EBV antigens. The generated suppressor cells were found to be antigen-specific since they inhibited the response of sensitized lymphocytes to the inducing antigen only. Moreover, experiments performed using purified lymphocyte subpopulations indicated that the suppressor activity was associated with T-cell populations. Using T-cells specific monoclonal antibodies, we further determined that the inhibitory activity was due to suppressor (OKT 8+) T-lymphocytes; treatment of T-lymphocyte populations (exhibiting suppressor activity) with OKT 8 antibody and complement abrogated the inhibitory effect of these populations on the response of sensitized lymphocytes to EBV antigens. Taken together, these observations suggest that similar suppressor cells may be at least partly responsible for the immunosuppression observed in patients with an antigenic overload, particularly during persistently active virus infection or malignancy.

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)

A concept of immune regulation of somatic cell differentiation

On the basis of several lines of experimental evidence a hypothesis is advanced on autoimmune regulation of somatic cell differentiation in an immunologically mature organism ("self-anti-self" hypothesis of differentiation). There are supposed to be clones of lymphocytes interacting via their antigen-recognizing receptors with autologous differentiation antigens on various target cells. This interaction would modify the genetically determined rate of cell differentiation. Some implications of the hypothesis are discussed in relation to immunological memory, tolerance etc. In particular, the new concept might imply similarity (or identity) of the genes coding for autologous differentiation antigens and those responsible for the idiotypes of antigen-recognizing lymphocyte receptors.

Two different primary lung malignancies after a successful kidney transplantation

A patient with two histologically different primary pulmonary malignancies occurring simultaneously ten months after a successful cadaveric renal transplantation is reported. One tumor was an adenocarcinoma of the left lung and the other an oat cell carcinoma of the right lung. The differentiation of the two tumors was made by a fluorescein-conjugated antikeratin antibody staining technique. No tumor was present at the time of transplantation as judged from chest examinations. Ten months after transplantation a left-sided pleural effusion caused by the adenocarcinoma occurred simultaneously with a small infiltrate in the apex of the right lung. Simultaneous development of two histologically different lung tumors is unusual, and even more rare after renal transplantation.

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.

Cell surface molecules and tumor metastasis. Regulation of metastatic phenotypic diversity

Metastatic tumor cells are characterized by quantitative alterations in cell surface and other properties that confer to these cells their abilities to invade, disseminate, implant, survive and grow at secondary sites. Metastasis is also determined by a variety of host factors that prevent, allow or even stimulate metastatic processes. The emergence of diversified cell subpopulations in malignant tumors insures that some cells will ultimately become highly metastatic, resulting in tumor progression towards characteristics which are the most favorable for survival and growth. Unknown mechanisms appear to stimulate and then to control phenotypic diversification of tumor cell subpopulations. These mechanisms may be altered by genetic (mutational) and/or epigenetic (non-mutational) modifications that individually influence cells within a malignant neoplasm.

Analysis of the growth characteristics of a primary BALB/c IgG plasmacytoma

Spontaneously arising and chemically or virally induced tumors usually cannot be analyzed in the early stages of tumorigenesis. Growth characteristics of these tumors thus are not available and it is unknown whether their expansion at any stage is influenced by the immune system. We have developed the following strategy to evaluate possible deviations from exponential growth in initial stages when a tumor is not yet manifest and in order to overcome the two main objections against most experiments in tumor immunology: use of possibly selected transplantable tumors and high initial cell doses. BALB/c mice received 0.5 ml of Pristane intraperitoneally three times within 16 weeks. This treatment induces plasmacytomas in 58% of the animals within 1 year. Mice were bled twice a week beginning with the 5th week after the last injection and sera were stored. Guinea-pig anti-idiotypic antibodies were raised against the IgG myeloma protein of a plasmacytoma developing in mouse 6-15 and a radioimmunoassay was set up. Sera of mouse 6-15 were then tested in retrospect for appearance and increase of the myeloma idiotype Id 6-15. We followed this idiotype thus for 19 weeks from a concentration of about 10 micrograms/ml up to 3 mg/ml serum. Plasmacytoma 6-15 cell growth was calculated from the Id 6-15 levels. In early phases wave-like fluctuations were found, possibly due to varying ratios of secretor to total plasmacytoma 6-15 cells. This phase was followed by an exponential increase in secretor cell number. At no time was there evidence for anti-idiotypic auto-antibodies against Id 6-15. The data are discussed in connection with possibly early activation of cellular components of the immune system.

Studies with a spontaneous murine tumour--I. Indetectibility of host immune resistance with tumour-activated elaboration of T cell stimulatory lymphokines in vitro

A spontaneous tumour SP/N-1 which arose in a BALB/c female mouse and histologically consistent with breast origin was studied in vivo and in vitro to assess host responses to the tumour. Examination by means of the established methods of tumour cell challenge and cell transfer assays following 'immunization' of the isogeneic host against the tumour failed to provide clear evidence of host recognition and reactivity. Cell transfers conducted using critical numbers of tumour cells in which tumour to spleen cell ratios of up to 1:1000 were employed did not show any sign of antitumour activity within the pretreated host spleen cells. Nor was there any evidence of host resistance when presensitized mice were challenged with graded doses of tumour cells ranging from 10(4) cells, with no take of tumours, to 5 X 10(4) cells, with total acceptance of the tumour by the challenged mice. Despite failures to demonstrate clear immune recognition of tumour by the above criteria, normal spleen cells when incubated with the tumour cells in vitro elaborated factors with stimulatory and possibly suppressive properties. At least one of these factors was shown to stimulate T cells as evidenced by stimulation of DNA synthesis in thymocytes. This could be shown readily in the presence of a submitogenic concentration of Con A.

Immune response to polyoma tumor cells in mice--III. Stimulation of tumor cell growth in vitro by spleen cells from immunized animals

We have evaluated the stimulation of target cell growth in vitro by spleen cells from mice which were immunized with polyoma-transformed cells and other tumor and non-tumor antigens. Stimulation was particularly seen under conditions of immunization that were suboptimal for the production of specific cytotoxicity. Significant stimulation of polyoma target cell growth was observed by lymphocytes from mice immunized against 10(5) Py 4198 tumor cells. This stimulation of target cell growth was not confined to polyoma-transformed cells only. Cells transformed by SV40, H-MuSV and non-transformed cells like 3T3 and embryo fibroblasts were also stimulated. Immunization of mice with syngeneic embryo fibroblasts also resulted in stimulation of tumor cell growth by the spleen cells from the immunized mice. However, the growth stimulation was less consistent and did not occur in all target cells tested. The specificity of immunostimulation was further studied with the Moloney sarcoma virus (M-MuSV) system; an antigenically distinct tumor system. Spleen cells from M-MuSV tumor-bearing mice stimulated cell growth in vitro not only against MuSV-transformed cells but also with SV40-transformed and polyoma-transformed cells as targets. Significant stimulation of target cell growth was also observed by spleen cells from mice that were immunized against 'non-pertinent' antigens, e.g. sheep red blood cells and allogeneic (C57B 1/6) spleen cells.

Cyclophosphamide-induced leukopenia and suppression of limb regeneration in the adult newt, notophthalmus viridescens

Cyclophosphamide (cytoxan), a clinical immunosuppressant, produced a marked, persistent leukopenia (greater than 40% reduction) in adult newts in contrast to a transient, milder leukopenia accompanying amputations without cytoxan treatments. In addition, cytoxan suppressed the formation of regeneration blastemata initially: however, blastema formation occurred if a second amputation was performed two or more weeks following the cessation of cytoxan treatments. The failure of the leukopenias of these latter cases to be corrected suggests that although a cytoxan-induced leukopenia is correlated with the absence of forelimb regeneration, this leukopenia is not, of itself, a sufficient condition to inhibit regeneration.

Enhancement of Lewis lung carcinoma growth by sera or spleen cells from tumour-bearing mice

Lewis lung carcinoma(3LL) cells grafted in syngeneic adult C57BL/6 mice produced local tumours associated with lung metastasis in 78% of recipients. Adult thymectomized, lethally irradiated, bone marrow cell-reconstituted animals (B mice) were more resistant since this tumour grew in only 46% of recipients and especially the weight of lung metastasis was almost 8 times less than in normal animals. Sera from tumour-bearing mice transferred into B mice enhanced tumour incidence and weight of metastasis to the level observed in normal mice. In vitro cultured 3LL cells displayed an intense mitogenic activity as measured by 3H-thymidine incorporation. Addition into these cultures of serum from tumour-bearing animals did not alter this activity. Addition of normal spleen cells in a ratio 40/1 reduced this mitogenic activity to a half or a third. Spleen cells from tumour-bearing mice, either normal or serum-enhanced B mice, mixed in vitro with 3LL cells, produced a 4-fold increase of mitogenic activity of the latter. These results indicate that the lymphoid system may contribute to the growth and spreading of 3LL tumours.

Escape of tumours from immunological destruction

This paper reviews the mechanisms of tumour escape from immune destruction that have been delineated in the past 2 decades. Current evidence indicates that the principal escape mechanisms are (i) weak or absent immunogenicity (ii) immunosuppression by tumour antigens or antigen-antibody complexes (iii) induction of suppressor cells and (iv) production of immunosuppressive factors. A classification of tumour escape mechanisms is presented.

A survey of ethylnitrosourea-induced rat gliomas for the presence of tumour rejection antigens expressed in vivo

Transplanted lines of seven F-344 (Fischer) rat malignant gliomas induced transplacentally with ethylnitrosourea (ENU) were surveyed by in vivo immunoprotection assays for the presence of tumour rejection antigens. These gliomas were representative of commonplace histological types of human primary brain tumours and were analyzed in early transplantation passages. The classical tumour ligation method of immunizing animals was attempted with five glioma lines, but was found unusable in four of these because of a high incidence of local tumour recurrences and distant metastases. In most experiments the animals were immunized by repeated inoculations of heavily-irradiated tumour cells. Two gliomas, a glioblastoma multiforms and a mixed astrocytoma-ependymoma, demonstrated weak but statistically significant tumour rejection responses. Immunization with three other tumours, a mixed oligodendroglioma-astrocytoma and two glioblastomas multiforme, led to enhanced outgrowth of the challenge cell inocula. Neither a rejection nor an enhancement response was observed in assays of the remaining two neoplasms, a glioblastoma multiforme and a mixed astrocytoma-oligodendroglioma. Immunization with a 3-methylcholanthrene-induced urinary bladder carcinoma line, used as a control in assays of six gliomas, had no effect on the outgrowth of transplanted glioma cells. These results suggest that ENU-induced malignant rat gliomas do not uniformly elicit strong tumour-rejection responses in vivo.

Macrophages and methylthio groups in lymphocyte proliferation

Macrophages are shown to replace methylthio disulfides in supporting in vitro proliferation of three cell lines previously characterized as methylthio-dependent. Macrophages have the capacity to generate methylthio groups from methylthioadenosine. It is hypothesized that macrophages stimulate cell proliferation both in normal immune systems and in certain cancers by providing an abundance of methylthio groups. Fetal calf serum is shown to contain methylthio groups. It appears that, in cell cultures containing fetal calf serum, sulfhydryl compounds stimulate cell proliferation by making the methylthio groups in the serum available to the cells.

[Inhibition of tumoral graft growth by pretreatment with normal or heat-modified tumoral cells]

The intravenous injection of Ehrlich tumour cells (TC) into Swiss mice, or BP8-fibrosarcoma cells into C3H mice, caused no intra-organ dissemination of the tumour but resulted in increasing resistance of animals to these two tumours. The percentage of mice protected against a regularly lethal dose of TC given intraperitoneally (i.p.) increased with the dose and the number of immunizing injections to the i.p. challenge. However, after high or repeated doses a cancerous nodule sometimes developed at the site of intravenous injections (penis vein), which caused death of the animal, not by extension of the tumour but by urethral occlusion. Moderate heating (46, 49.5 or 52 degrees C) of the TC did not impair their immunogenicity but prevented their multiplication in normal mice. It was thus possible, by intradermal injections of heated TC, to protect mice against a dose of intact TC. The efficiency of prophylaxis depended on the temperature to which the cells were exposed (optimal temperature depending on the type of tumour), on the number of injections and on the medium in which the cells were suspended. When Freund's complete adjuvant was used, all mice were protected against tumour ascites following challenge.

Immunoglobulins associated with human tumours in vivo: IgG concentrations in eluates of colonic carcinomas

The concentrations of IgG in acidic and 3MKCl eluates of resected colonic carcinomas and adjacent normal tissue were determined by radioimmunoassay. The mean concentration of IgG was significantly higher in both acidic and KCl eluates of primary Dukes Stage C tumours than Dukes Stage A tumours. These results provide direct evidence for increased fixation of IgG in vivo by human colonic cancers which had metastasized. Our results also raise the possibility that IgG is more tightly bound to the Stage C tumours. It is likely that this tumour-associated Ig represents antibody to tumour antigens or antigen-antibody complexes, bound to Fc receptors in the tumour.

Enhancement of growth of a radiation-induced lymphoma by T cells from normal mice

The effect of lymphocytes from normal mice on the growth of a syngeneic, radiation-induced, T-cell-derived lymphoma was investigated. Thymus and spleen cells enhanced the growth of admixed lymphoma cells in a reproducible manner. Growth enhancement was manifested by the earlier appearance and higher final incidence of tumours. Lymphocytes also enhanced the growth of radiation-damaged lymphoma cells. The enhancing activity of spleen cells was predominantly a property of T cells, since it was abolished by treatment with anti-theta serum plus complement and significantly less in spleen cells of nude mice. Tumour-enhancing thymocytes seem to belong to the immature thymic subpopulation, as indicated by their binding to peanut agglutinin.

Development of carcinogen-induced skin tumors in mice with varied states of immune capacity

The incidence of tumor formation in MCA-treated skin grafted onto maximally immunosuppressed mice that had been restored to varying extents with normal spleen cells was significantly greater in the mice with intermediate immune capacities than in those that had either minimal or maximal capacities. A similar biphasic tumor incidence curve was observed when MCA-treated skin was grafted onto mice of varying immune capacities, produced by thymectomy and varying doses of whole-body irradiation. Significantly more tumors occurred in the mice given moderate doses of irradiation than in tohse given higher or lower doses. That both of these procedures were actually able to induce discrete levels of immunocompetence was demonstrated by measuring skin allograft rejection times. The immunomodulated mice were observed to have skin graft rejection times which strongly correlated with the number of immunologically competent spleen cells transferred into them. The outgrowth potential of syngeneic normal mammary epithelial cells grafted into cleared mammary fat pads was similar in both immunologically altered and normal control mice, showing that immunoaltered and normal control mice were equally able to support the growth of transplanted normal tissues. These results, which conform with the predictions of the immunostimulation hypothesis, suggest that the immune response is able to stimulate as well as inhibit oncogenesis.

Distant metastasis facilitated by BCG: spread of tumour cells injected in the BCG-primed site

Tumour metastasis in BCG-pretreated mice was studied using a methylcholanthrene-induced fibrosarcoma in C3H/He mice. When tumour cells were injected into the BCG-primed site, distant metastasis occurred in the lungs and the popliteal lymph node, through this tumour did not metastasize in normal mice. Such metastases were increased in proportion to the number of tumour cells injected into the BCG-primed site, and developed soon after tumour challenge. Concomitant immunity developed well in the mice bearing such metastases, but did not inhibit metastatic growth. Experiments using 125I-labelled SRBC or tumour cells revealed that such cells egressed rapidly from the BCG-primed site. When the tumour was inoculated into the contralateral foot to the BCG-primed site, the incidence and the number of metastases was reduced. Furthermore, BCG infection induced an increase of platelet count. I.v. injection of this tumour induced marked thrombocytopenia in normal mice. Administration of pentoxifylline, a methylxanthine derivative before tumour challenge reduced such metastases. These findings suggest that the changes in peripheral blood, such as increased platelet count and increased release of tumour cells from the injection site, facilitated distant metastasis in BCG-pretreated mice.

Perturbation of the growth kinetics of C3H mouse mammary carcinoma by irradiation of tumour and host and by attempted pre-immunization of host

The kinetics of development and subsequent growth of a C3H mouse mammary tumour after implantation of 10(6) cells was quantified by observation and statistical analysis of latent period and growth rate for different categories of tumour. These comprised control tumours, tumours recurring after large single doses of X-rays alone and in combination with misonidazole, tumours developing from cells implanted both outside and within the sites of tumours previously cured by irradiation, tumours developing from cells implanted in heavily irradiated skin, and tumours developing from cells taken from tumours recurring after irradiation and re-implanted in untreated skin. The kinetics of development and growth of tumours in host animals previously treated by i.p. injection of killed tumour cells was also quantified. The results confirm that tumour development and growth is significantly perturbed by irradiation of host tissues both before and after tumour transplantation, and that this perturbation involves an extended latent period, a slower average rate of growth and a less uniform pattern of growth. These effects result from localized radiation damage to host tissues, are not attributable to residual damage to irradiated tumour cells, and are not markedly dose-dependent within the dose range 25--80 Gy. These results are consistent with the complete sterilization of host endothelial cells by doses of 25 or more. In marked contrast to the growth-slowing effect of irradiation, the treatment of host animals by previous injection of radiation-killed tumour cells led to a reduced latent period and a faster average rate of growth.