Macrophage-dependent, NK-cell-independent "natural" surveillance of tumors in syngeneic mice

Modulation of the immune response to tumors by a novel synthetic compound, (4R)-3-benzoyl-N-[(1R)-1-phenylethyl]-4-thiazolidinecarboxamide (RS-0481)

RS-0481, (4R)-3-benzoyl-N-[(1R)-phenylethyl]-4-thiazolidinecarboxamide, is a compound that can re-establish the function of certain lymphoid cell populations impaired by the presence of a growing tumor in an animal. The compound markedly augmented the tumor-specific cytotoxic T lymphocytes, TDTH (delayed-type hypersensitivity T cells), and the nonspecific lymphokine-activated-killer-cell-like cell responses. It also enhanced the tumor-inhibitory effect of macrophages in tumor-bearing mice, but not in normal mice, indicating that it enhances the antitumor immune responses. Lymphocytes from RS-0481-treated tumor-bearing mice released significantly higher amounts of macrophage-activating factor(s) (MAF) and interleukin-2(IL-2)-like factors in culture compared with lymphocytes from untreated animals. Also, sera from treated tumor bearers showed elevated colony-stimulating factor (CSF) activity. Although the compound did not influence the factor-producing activity in mice without tumor, it enhanced the responsiveness of their bone marrow cells, T cells, and macrophages to CSF, IL-2, and MAF. It seems therefore possible that the compound enhances the responsiveness of immunocompetent cells to cytokines, resulting in a marked augmentation of antitumor T cell responses in tumor-bearing mice. Consistently it inhibited the development of lymph node metastasis of transplanted X5563 plasmacytoma, and we showed that T cells play a decisive role in this inhibition. The compound also counteracted the development of suppressor T cell activity in the spleen of tumor-bearing mice.

Generation of tumoricidal effector cells with a novel potentiator: N-[4-[(4-fluorophenyl)sulfonyl]phenyl] acetamide (CL 259,763)

An effort was made to investigate the effects of a novel immunopotentiator, N-[4-[(4-fluorophenyl)sulfonyl]phenyl]acetamide (CL 259,763), on the generation of tumoricidal effector cells. It was demonstrated that a single oral dose of the compound (100-600 mg/kg) induced in mice a population of peritoneal macrophages capable of inhibiting the growth of tumor cells. These activated macrophages released proteases which seemed responsible for the tumor cell inhibition because the cytostatic activity was abrogated in the presence of protease inhibitors TLCK and aprotinin. On the other hand, addition of catalase and exogenous arginine to the culture failed to alter the effect, suggesting that hydrogen peroxide and arginase did not participate in this system. Although induction of cytolytic T-lymphocytes (CTL) reactive with syngeneic tumor cells was achievable in mice previously sensitized to the tumor, treatment with CL 259,763 rendered these animals even more responsive to tumor antigens resulting in a significant enhancement of tumor cell destruction. The compound was effective in augmenting the CTL response over a rather broad dose range of 25-200 mg/kg. In contrast to these stimulatory effects, the cytolytic activity of natural killer cells seemed not to be affected by the compound. Taken together, CL 259,763 is an orally active immunomodulator capable of inducing tumor inhibitory macrophages and potentiating CTL responses to syngeneic tumor cells and, therefore, may prove clinically useful in the treatment of neoplastic diseases.

Physiological relationships among stress, viruses, and cancer in experimental animals

Anxiety-induced psychoneural stimulation, via the hypothalamic-pituitary axis, activates the adrenal cortex to release corticosteroids, which elicit various alterations of corticoid-sensitive cell-mediated immunologic processes. Stress sensitive murine tumor-host experimental models have been utilized to demonstrate various effects of stress upon aspects of tumor development. Although many of the observed anxiety-induced alterations of tumor-related parameters can be interpreted in terms of corticoid-induced modifications of immune functions, other observations are more difficult to interpret, and may be caused in part by corticosteroid-independent modulation of lymphocyte functions. In the case of tumors induced by oncogenic viruses, anxiety-induced plasma corticoid elevations may also act independently of the immune system to stimulate tumor development via hormone binding sites on proviral DNA. Rigorously controlled environmental and experimental conditions are fundamental for the demonstration and interpretation of stress-related phenomena. Technical prerequisites include protective animal facilities, special handling procedures, the use of nontraumatic stressors, and the recognition of vital psychosocial, coping and timing factors. Various biologic factors, such as sex, genetic substrain differences and common interfering viral infections, must also be controlled or taken into consideration.

Regulation of tumor development: the biphasic effects of silica and of lipopolysaccharide on natural resistance

The impact on tumor development of the BRM silica and LPS was assessed through analysis of changes in NR parameters in vivo and in vitro. Although injection of the fumed silica Cab-o-sil 3 days before a threshold s.c. inoculum of L5178Y-F9 cells increased the tumor frequency in syngeneic DBA/2 mice, tumors recovered from silica-treated animals exhibited an augmented resistance to NAb and to in vivo NR. Cab-o-sil increased in vivo NR and induced a biphasic modulation of anti-tumor NAb and NK activities. The appearance of more autonomous tumors in Cab-o-sil-treated mice corresponding with a stimulation of NR parameters, suggests that the adjuvant activity of silica also contributes to its co-carcinogenic effect by accelerating tumor development. While injection of LPS 2-3 days before a threshold tumor inoculum lowered the tumor incidence, the survival of tumor cells injected within 1 day of LPS was increased. A corresponding early decrease in NAb activity occurred, in contrast with increases in NK cell and NAb levels previously observed after 5 days. This biphasic effect of LPS on NR effectors assayed in vitro was also seen on in vivo NR. Although their frequency was higher, tumors initiated during the period of LPS-induced NR abrogation exhibited greater reductions in NAb binding and sensitivity to NR than tumors from control mice. These data extend the support for NAb acting against tumor cells in vivo and reveal the dual nature of NR in tumor development, defending against small tumor foci and driving the progression of the surviving neoplasm.

Characterization of tumor progression from threshold tumor inocula: evidence for natural resistance

An examination of the variant generation and selection hypothesis of tumor progression was undertaken using the NK-sensitive, NAb-sensitive SL2-5 lymphoma in the threshold inoculum model of tumor progression. Tumor cells obtained from the i.p. injection site expressed increased heterogeneity for sensitivity to syngeneic NAb and to NR measured in the 131IUdR-labelled tumor elimination assay. Cells retrieved from the s.c. injection site exhibited reductions in sensitivity to NR which correlated with decreases in sensitivity to syngeneic NAb and NK cells in vitro. These data confirm and extend our previous observations with the NK-resistant L5178Y-F9 lymphoma and further substantiate the evidence for the participation of NAb and NK cells in host-mediated anti-tumor resistance. Characterization of the model revealed that the selection for reduced sensitivity to NR in thymus-depleted AT x BM mice and normal animals could not be distinguished, suggesting that thymus-independent mechanisms may be major contributors to the surveillance of nascent tumors. The decreases in susceptibility to NR occurred in a stepwise and time-dependent manner in accord with the sequential multistage concept of progression. Furthermore, the selection for tumor cells which exhibited reductions in sensitivity to NR correlated with selection for increased tumorigenicity, in keeping with the idea that progression is associated with development towards an increasingly autonomous tumor.

Tumor induction by simian virus 40 in mice is controlled by long-term persistence of the viral genome and the immune response of the host

Simian virus 40 (SV40), which transforms mouse cells in vitro, has not been previously observed to cause tumors when injected in immunocompetent mice. We have investigated both the fate of the injected virion in mice and several immunological parameters as potential factors controlling tumorigenicity. We find that although SV40 does not replicate in mouse cells, the viral DNA can persist for many months postinjection; the majority of the viral DNA is found in the cytoplasm, but a small amount of the viral DNA is integrated at multiple sites in the host nuclear DNA. The persistence of the viral genome is independent of the ability of the mouse to mount an SV40 TSTA specific cytotoxic T-cell response and may be attributed to the cytoplasmic location of the majority of the viral genome. However, in long-term studies of SV40-injected mice, genetically identical except for the major histocompatibility complex, we find that tumors were induced in some mice of the H-2d (low cytotoxic T-lymphocyte responder to SV40 TSTA) but not of the H-2k (high responder to SV40 TSTA) haplotype. Thus, a combination of inefficient disposal of the injected virion and inefficient immunological surveillance and elimination of cells containing nuclear SV40 DNA can eventually result in SV40-induced tumors at multiple sites in mice.

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.

Studies on chemically induced tumors in rats: I. Heterogeneity of tumor cells and establishment of syngeneic, tumor-specific cytotoxic T cell clones

Sarcoma P1 was induced in DA rats by DMBA. Anti-P1 antibodies were produced in DA rats, purified via fixed tumor cells and used to induce anti-idiotypic antibodies in syngeneic rats. The anti-idiotypic antibodies were used to generate cytotoxic, P1 specific DA T cells in vitro. These cytotoxic T cells and P1 tumor cells were cloned by limiting dilution. Using the DA anti-P1 specific cytotoxic T cell clones, we were able to characterize 2 types of P1 tumor cell clones, namely those which were susceptible and those which were resistant to the P1 specific cytotoxic T cells. Cytotoxic T cell injected i.v. into syngeneic DA rats could not prevent the development of lethal P1 tumors.

In vivo generation and selection of variants with altered sensitivity to natural resistance (NR): a model of tumor progression

The stability of a cloned murine tumor for sensitivity to NR was examined following growth in vivo in order to test the hypothesis that tumor progression proceeds through the generation and selection of variants. Clonal sensitivity to the [131I]-dUrd elimination assay of NR was assessed for the L5178Y-F9 tumor grown in syngeneic DBA/2 mice or maintained solely in tissue culture. Subclones derived from a tumor obtained from the injection site 3 1/2 weeks after the s.c. inoculation of 25 cells were less sensitive to NR in comparison with subclones derived from cells grown only in vitro. Subclones from the cells grown in vivo exhibited increased heterogeneity in sensitivity to NR in addition to their expanded range of susceptibility to complement-mediated lysis by CBA serum natural antibodies. The extent of the heterogeneity argues against tumor "adaptation" forming the basis for the phenotypic alteration while chromosomal studies eliminate the possibility that a new tumor was induced. These data support the hypothesis that tumor progression proceeds through the random generation of variants and host-mediated selection for the proliferation of clones with an increased ability to survive.

Behavioral--physiological factors in the development and management of cancer

Recent clinical and animal model studies have demonstrated an effect of behavioral variables on the course of cancer. Unrelieved anxiety, helplessness, depression, and the inability to modulate the expression of anger have been implicated as specific predictors of poor prognosis. The endocrinological sequelae of these emotional states may affect certain parameters of cell-mediated immunity involved in host resistance to neoplasia. Both corticosteroids and catecholamines are likely mediators of behavioral effects on immunological function. Hormonal variations may also affect growth of tumors directly, or through nonimmunological tissue specific mechanisms. Behavioral interventions based on elicitation of the relaxation response provide a means of influencing affective and physiological states that may have particular relevance to cancer. Practice of such interventions reduces anxiety and provides a substrate for coping that enhances the patient's sense of control. Such "immunization" against helplessness can forestall depression. Physiological effects of such behavioral interventions occur both on a direct and an indirect level. Elicitation of the relaxation response per se produces physiological alterations consistent with decreased arousal of the sympathetic nervous system. Furthermore, by reducing fear and helplessness, physiological changes related to such dysphoric states may be minimized

Rous sarcoma virus-induced tumors in mice--I. Macrophage-mediated natural cytotoxicity

Lymphoid cells from normal untreated A.SW mice showed a cell-mediated cytotoxicity (CMC) towards Rous sarcoma virus-induced tumor lines in a 48-hr microcytotoxicity assay in vitro, using 3[H]-thymidine prelabeled tumor cells. The tissue distribution of this natural CMC shows high levels of activity in the peritoneal cavity, intermediate levels in bone marrow and spleen, and low levels in lymph node, peripheral blood and thymus. Natural CMC of unstimulated resident peritoneal cells against tumor cells was also found in several strains of mice. This was not dependent on the donor's age, since similar levels appeared in mice aged 1-40 weeks. Passage through nylon wool columns or adherence to the plastic surface of resident peritoneal cells removed cytotoxic activity. By contrast, adherent cell displayed significant CMC levels. Treatment with carbonyl iron powder and magnet decreased peritoneal cell cytotoxicity when performed once and abolished it when repeated. All these results suggest that in mice, natural cytotoxicity against Rous sarcoma virus-induced tumors is primarily mediated by macrophages or macrophage-like cells.

Natural antibodies carrying a cross-reactive idiotype enhance tumor growth in the rat

A population of Fab fragments was identified in the papain-solubilized fraction of membranes of a rat chemically-induced sarcoma, KMT 17. The Fab fragments were partially purified by gel filtration and column electrophoresis. A rabbit antiserum against the partially purified Fab fragments was raised and shown to be specific for Fab fragments by immunoelectrophoresis. Furthermore, four lines of evidence indicated that the KMT 17 Fab fragments carry a cross-reactive idiotype: (1) the antiserum could bind only with a restricted population of normal Fab fragments having a pl of 6.3; (2) an unrelated antibody (WKA anti-SRBC) showed a weak cross-reactivity (less than 6%); (3) syngeneic antisera against the KMT 17 could bind with the 125I-KMT 17 Fab preparation that was purified by an immunoabsorbent column with the rabbit anti-KMT 17 Fab antiserum (anti-idiotype antibody); (4) the rabbit anti-KMT 17 Fab antiserum could bind with neither heavy nor light chains of WKA IgG. The natural antibody carrying the idiotype was found in normal serum and in various organs as well, especially in the lung of the conventional rats. In addition, the fractions containing Fab fragments (Frll) were shown to enhance tumor growth when injected into syngeneic animals, whereas Fab-free fractions that were separated from the Fab fragments by column electrophoresis showed no enhancing activity. These results strongly suggested that a population of Fab fragments carrying a cross-reactive idiotype was responsible for the enhancement of tumor growth. Mechanisms for the biological function of natural anti-tumor antibodies carrying a cross-reactive idiotype are discussed.

Murine natural anti-tumor antibodies. II. The contribution of natural antibodies to tumor surveillance

The objective of this study was to investigate whether natural anti-tumor antibodies (NAb) contributed to the surveillance of small inocula of syngeneic tumors. Experiments were designed to distinguish between NAb and NK-mediated host resistance. Four approaches were used: (1) the isolation of tumor variants differing in their tumorigenicity and susceptibility to these mechanisms, and to activated macrophages; (2) a comparison of the effects of adjuvants on the modification of both host resistance and the activity of these effectors; (3) the relationship between the ontogeny of the natural resistance mechanisms and tumorigenicity in aged mice; and (4) the use of a Winn-type assay. These studies provided support for a role in natural resistance correlated with both the ability of tumors to bind NAb, and the production of NAb in adjuvant-stimulated mice. Furthermore, the frequency of tumors observed after tumor challenge more closely correlated with the ontogeny of natural antibody than NK cells, and tumors coated with NAb were less tumorigenic than controls. The reduced tumorigenicity of an NK-sensitive tumor, when compared to an NK-resistant variant of the same line, provided evidence for NK-cell-mediated natural resistance in young adult mice. It was concluded that natural resistance to tumors is a complex phenomenon dependent on the tumor phenotype, as well as the activity of several effector mechanisms, and that natural anti-tumor antibody must be considered an important component of host resistance.

Transplantation resistance of drug-treated allogeneic mice against murine lymphomas--II. Studies with various tumor-host combinations

Previous studies showed that treatment of mice with 5(3,3'-dimethyl-1-triazeno)-amidazole-4-carboxamide (DTIC) plus cyclophosphamide (Cy) produce profound depression of classical allograft responses and impairment of endogenous cell proliferation similar to that detectable in lethally-irradiated mice. However efficient localized graft resistance was found in the spleen of drug-treated hybrid or allogeneic mice challenged with lymphoma cells. The present report describes the genetic patterns of this type of natural resistance [hereafter called drug-resistant inhibition of tumors (DRIT) in various tumor-host combinations DRIT was evaluated measuring the extent of 125I-5-iodo-2'-deoxyuridine (125IUdR) uptake in the spleen and liver of leukemic hosts. The results of the experiments performed with two H-2d (i.e. L1210 and LSTRA), one H-2b (i.e. L5MF-22) and one H-2a (i.e. LAF-17) lymphomas inoculated into drug-treated recipients pointed out that: (a) tumor cell proliferation was markedly inhibited in the spleen and weakly or not impaired in the liver of D end Hh-1-incompatible euthymic or nude mice responder for the hh system; (b) no resistance was found in the spleen and liver of Hh-1-compatible B10.A (2R) mice against L5MF-22 lymphoma or of SJL recipients genetically non-responder for the Hh system, against LSTRA cells; (c) splenic resistance against L1210 leukemia was detectable in Hh-compatible B10.A or B10.A (5R) mice; (d) splenic and liver resistance was found in Hh-incompatible but genetically Hh non-responder SJL or C3H mice against L5MF-22 or LSTRA lymphomas, respectively. These results showed that the genetic patterns of the DRIT system parallels the Hh-type immunity in certain tumor-host combinations [(a) and (b)] but not in others [(a) and (d)], as previously detected in lethally-irradiated mice. It is concluded that genetically-controlled lymphoma graft resistance can be retained by mice treated with high doses of antitumor drugs, capable of abrogating classical T-dependent transplantation immunity.

Transplantation resistance of drug-treated hybrid or allogeneic mice against murine lymphomas. I. Immunopharmacology studies

Sequential treatment of mice with non-lethal doses of 5(3,3'-dimethyl-l-triazeno)-imidazole-4-carboxamide (DTIC) and cyclophosphamide (Cy) was found to produce long-term inhibition of endogenous cell proliferation in the spleen and profound impairment of classical allograft responses, similar to that detectable in lethally irradiated mice. Studies were carried out with drug-treated (i.e. treated with DTIC + Cy) conventional or nude mice inoculated with lymphoma cells homozygous for the H-2b or H-2d haplotype. Transplantation resistance in various tumour-host combinations was studied in terms of survival times after tumor challenge or lymphoma cell proliferation in spleen and liver, measured by the uptake of DNA precursor 125I-labelled 5-iodo-2'-deoxyuridine ([125I]dUrd). The results of in vivo transplantation immunity tests or in vitro tests of generation of cytotoxic lymphocytes confirmed that classical T-dependent allograft responses were abrogated by drug treatment of H-2-incompatible hosts. However, localized resistance against lymphoma graft, mainly at spleen level, was found in drug-treated hybrid mice, or conventional and "nude" allogeneic recipients, as judged by [123I]dUrd uptake inhibition. Resistance presumably regulated, at least in part by the Hh (hemopoietic histocompatibility) system, was abrogated by pretreatment with carrageenan, an antimacrophage agent. In addition, treatment with DTIC + Cy did not abrogate NK activity of mice when the in vitro cytotoxicity test was conducted 5 h after Cy administration, i.e. at the time used for tumor challenge in vivo. It was concluded that selected immunological functions (i.e., antilymphoma natural resistance insensitive to DTIC + Cy, called drug-resistant inhibition of tumors, DRIT) possibly of non-T origin, similar to those detectable in lethally-irradiated mice, can be retained by hosts subjected to high doses of certain anti-tumor agents.

In vitro NK-activity and in vivo resistance to leukemia: studies of beige, beige//nude and wild-type hosts on C57BL background

The bg mutation in C57BL mice causes a partial impairment of NK activity, and has therefore been proposed as a model to evaluate the in vivo function of NK cells. In the present report, we studied natural resistance against the ascitic lines of one chemically and two virally induced syngeneic leukemias in C57BL bg/bg mice and their phenotypically normal heterozygous +/bg littermates. S.c. threshold inocula of all three leukemia lines grew faster and caused death earlier in bg/bg than in +/bg mice, and two of the lines were rejected completely at a significantly higher frequency in +/bg control animals. The +/bg mice also eliminated [125I]-IdUrd-labelled leukemia cells at a faster rate than bg/bg mice, as measured by pulmonary, hepatic and splenic radioactivity retained 18-30 h after i.v. injection. Direct splenic killing of 51Cr-labelled leukemia cells was also studied in vitro, and was found to be severely depressed in bg/bg compared to +/bg. This natural killer activity was independent of adherent cells and showed a rapid, but transient, increase after inoculation of the tumor cell doses used in the transplantation tests. It was also possible to study the bg mutation in T-cell-free mice, by combining it with the nu mutation on a C57BL background. The NK activity of such beige-nude mice was found to be partially impaired compared to nude (non-beige) or wild-type animals, but higher than that of beige (non-nude) mice. Our results suggest that NK cells may be responsible for elimination of small numbers of tumor cells in the intact syngeneic host. The further use of beige and beige-nude mice in studies of transplanted and primary tumors is discussed.

Silica-induced malignant histiocytic lymphoma: incidence linked with strain of rat and type of silica

It has already been established that a single intrapleural inoculation of crystalline silica (quartz) produces malignant lymphomas of histiocytic type (MLHT) in Wistar-derived rats. It has now been shown that after treatment with Min-U-Sil, rats of the Alderley Park strain have a tumour incidence of 35%, whereas the incidence in Agus rats is 5% and in PVG 8%. There was also a significant difference in the incidence of MLHT caused by injecting different samples of crystalline silica, particularly of tridymite. There was correlation between cytotoxicity to mouse peritoneal macrophages and tumour incidence, except for one dust (DQ12). Zeta potential, number of particles and their size range were considered, but the incidence does not show a clear correlation with these measurements. The results are discussed.

The generation of tumor heterogeneity in vivo

In order to determine whether host factors may contribute to the generation of tumor heterogeneity, the phenotypic stability of cells from a cloned tumor was examined during proliferation in tissue culture and in the syngeneic host. Growth of this cloned tumor was initiated both in vivo and in vitro, and the tumor populations were sampled at different time intervals by subcloning. The susceptibility of these tumor subclones to the cytotoxic action of natural antibodies and complement was used as a marker of their membrane phenotype. The extent of phenotypic variation of the clones in one sample was considered to be a measure of tumor heterogeneity. Following these procedures, we observed that a clone of the L5178Y murine lymphoma maintained its homogeneity during 5 months of in vitro culture. In contrast, a single passage of the same tumor clone for 3 1/2 weeks or 3 months in the syngeneic host resulted in the generation of a population of cells exhibiting a significant increase in heterogeneity. This relative instability of tumor phenotype in vivo suggests that the host milieu may allow the generation of tumor heterogeneity. Genetic or epigenetic mechanism(s) may be involved although the high frequency of new phenotypes argues against a role for somatic mutation.

H-2 associated resistance to leukaemia transplantation: natural killing in vivo

Natural resistance in vivo was studied by injecting non-immunized mice with leukaemia cells prelabelled with the thymidine analogue 131I-iododeoxyuridine. There was a decrease in the survival of the leukaemia cell inoculum as determined by whole-body gamma counting, and a failure of the leukaemia cells to survive in the spleens of mice which were not H-2 identical with the transplant. H-2-associated resistance could be measured within 24 h of leukemia inoculation and was strongest in the spleen and absent from the liver. Although all strains of mice tested were able to resist H-2 non-identical cells, resistance in irradiated (800--900 R) mice was restricted to certain strains and their F1 hybrids, notably those of the C57BL family. Resistance in both non-irradiated and irradiated mice was not due to classical immunological rejection. Mice with either genetic or induced T-cell deficiency showed full resistance, and circulating preformed antibody could not account for the rejection observed. Treatment with silica or with 89Sr abrogated natural resistance in non-irradiated as well as irradiated animals; these treatments had previously been shown to abolish both bone-marrow graft rejection in irradiated mice and in vitro natural killing. Resistance against leukaemia transplantation in irradiated C57BL mice appeared to depend on Hh-1 (H-2D) incompatibility between the host and the graft, again suggesting that bone-marrow graft rejection, and perhaps natural killer activity, is a subset of a more general paraimmune or non-adaptive rejection mechanism.