Stimulation of tumor growth by the immune response

Tumor inhibitory T cell immunity may be largely a transplantation artifact not necessarily dependent upon a lack of Tregs

There exists a very large literature suggesting that T cells come in a variety of species and that without the action of Tregs tumors would seldom survive inhibition by T cell effectors. We believe that much of the evidence supporting the role of Tregs in cancer is compatible with a perhaps simpler hypothesis based upon the demonstration that that small quantities of effector T cells tend to stimulate tumors while larger quantities of seemingly the same cells are inhibitory (an hormesis-like effect). This possibility seems to destroy much of the need to postulate a role for T cell suppressors (Tregs) in cancer, but the exposure of effector T cells to antigen may convert them into Tregs (Tregs do exist). Furthermore, many other data suggest the possibility that immune inhibition of cancer could be a laboratory artifact seldom if ever seen in unmodified nature.

A review of mathematical models of cancer-immune interactions in the context of tumor dormancy

The role of the immune system in tumor dormancy is now well established. In an immune-induced dormant state, potentially lethal cancer cells persist in a state where growth is restricted, to little or no increase, by the host's immune response. To describe this state in the context of cancer progression and immune response, basic temporal (spatially homogeneous) quantitative predator-prey constructs are discussed, along with some current and proposed augmentations that incorporate potentially significant biological phenomena such as the cancer cell transition to a quiescent state or the time delay in T-cell activation. Advances in cancer-immune modeling that describe complex interactions underlying the ability of the immune system to both promote and inhibit tumor growth are emphasized. Finally, the review concludes by discussing future mathematical challenges and their biological significance.

An immune reaction may be necessary for cancer development

Background

The hypothesis of immunosurveillance suggests that new neoplasms arise very frequently, but most are destroyed almost at their inception by an immune response. Its correctness has been debated for many years.

In its support, it has been shown that the incidences of many tumor types, though apparently not all, tend to be increased in immunodeficient animals or humans, but this observation does not end the debate.

Alternative model

There is an alternative to the surveillance hypothesis; numerous studies have shown that the effect of an immune reaction on a tumor is biphasic. For each tumor, there is some quantitatively low level of immune reaction that, relative to no reaction, is facilitating, perhaps even necessary for the tumor's growth in vivo. The optimum level of this facilitating reaction may often be less than the level of immunity that the tumor might engender in a normal subject.

Conclusion

The failure of a tumor to grow as well in the normal as it does in the immunosuppressed host is probably not caused by a lack of tumor-cell killing in the suppressed host. Instead, the higher level of immune response in a normal animal, even if it does not rise to tumor-inhibitory levels, probably gives less positive support to tumor growth. This seems more than a semantic distinction.

Nonlinear dynamics of immunogenic tumors: parameter estimation and global bifurcation analysis

We present a mathematical model of the cytotoxic T lymphocyte response to the growth of an immunogenic tumor. The model exhibits a number of phenomena that are seen in vivo, including immunostimulation of tumor growth, "sneaking through" of the tumor, and formation of a tumor "dormant state". The model is used to describe the kinetics of growth and regression of the B-lymphoma BCL1 in the spleen of mice. By comparing the model with experimental data, numerical estimates of parameters describing processes that cannot be measured in vivo are derived. Local and global bifurcations are calculated for realistic values of the parameters. For a large set of parameters we predict that the course of tumor growth and its clinical manifestation have a recurrent profile with a 3- to 4-month cycle, similar to patterns seen in certain leukemias.

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.

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.

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.

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.

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.

Specific and non-specific immunologic mechanisms of tumor growth facilitation

Specific and non-specific mechanisms of tumor growth facilitation were studied using methylcholanthrene (MCA)-induced fibrosarcomas in C3H/HeJ mice. In early and late stages of tumor growth, mice possessed non-specific, tumor-facilitating cells detected by local adoptive transfer assay (LATA). These cells appeared to be macrophages; they were radioresistant (700 rads), phagocytic, and adherent to plastic. Specific tumor facilitation was induced by treatment either with crude 3M KCl extracts, or with an acidic pIEF fraction (pI 3.5). After treatment with this material, animals displayed facilitated outgrowth of only MCA-F, but not the antigenically distinct MCA-D or MCA-C tumors. Thus in addition to non-specific stimuli, which accelerate neoplastic growth, tumors bear tumor-specific transplantation antigens (TSTA), which induce specific facilitation.

Effector and enhancing lymphoid cells in plasmacytoma-bearing mice. II. Dynamic changes during tumor progression

The Winn assay was used for the study of effector (tumor-inhibiting) and enhancing (tumor-promoting) lymphoid cells in BALB/c mice bearing MOPC-104E plasmacytomas. Kinetic studies with thymus, lymphnode, spleen and bone-marrow cells revealed that spleen, lymph node and to a lesser extent bone-marrow cells from 7- and 10-day tumor-bearers inhibited MOPC-104E growth, while at day 13 all three cell populations enhanced tumor growth. However, at day 16 strong tumor inhibition was observed again by spleen cells and to a lesser extent by lymph-node cells and thymocytes. Peritoneal cells from normal and tumor-bearing (7 and 10 days) animals enhanced tumor growth significantly. Separation of spleen cells on nylon wool columns showed that at 10 days the effector cells were T lymphocytes, but at a later stage (35 days) a different effector mechanism was present in the spleen. Treatment of MOPC-104E recipients with carrageenan or silica had little influence on tumor growth, but marked tumor inhibition occurred after lethal irradiation and bone-marrow reconstitution. This latter observation, together with the finding that bone-marrow, lymph node and peritoneal cells from normal donors enhanced tumor growth in several experiments, suggests that this plasmacytoma, like hormone-dependent tumors, requires lymphocyte-derived growth factors.

Reproducibility and relation to specific and non-specific anti-tumor resistance of the tumor "sneaking through" phenomenon

The reproducibility and immunological specificity of the tumor "sneaking through" phenomenon and enhancement of tumor growth were studied in syngeneic and random-bred Syrian hamsters by means of a quantitative modification of the transplantation test. After primary challenge the phenomenon was neither observed in normal animals nor in animals effectively immunized against tumor. However, it was regularly observed in some "immune" animals after secondary challenge. In primary challenge of animals "sneaking through" phenomenon was most often observed in animals pretreated with large doses of heat-inactivated tumor cells. This characteristic could not be transferred with serum of pretreated animals. In contrast to specific tumor immunity, the "sneaking through" pbenomenon appeared to be immunologically non-specific. This was observed in cross-transplantation tests with tumor cells bearing different TSTAs. Thus, TSTA is not an inducer and apparently not a target for a response leading to enhancement of tumor growth in pretreated hamsters. Experiments demonstrating enhanced tumor growth in pretreated animals at the same time demonstrate two other possibly more essential findings: (1) normal animals are naturally resistant to transplantation of 1 to about 1 x 10(3) (or more) tumor cells; and (2) this resistance can be totally abrogated by the pretreatment of normal animals with tumor cell preparations. The preliminary data demonstrate that abrogation of natural anti-tumor resistance in adult hamsters subsequently inoculated with SV40 leads to rapid development of primary tumors in such animals. The development of specific anti-tumor immune response in animals treated with inactivated tumor cell preparations was also studied. Significant non-specific inhibition of sponse in Syrian hamsters treated with inactivated syngeneic tumor cells was observed. The data obtained are considered to demonstrate two anti-tumor defense systems in the animal, i.e., non-specific natural resistance and specific anti-tumor immunity. The first seems to be responsible for elimination of low numbers of tumor cells in the normal organism and also to be esseitial for effective induction and functioning of the specific anti-tumor immunity.

[Cell mediated immunity in cervical cancer patients: evaluation by in vitro leukocyte-migration-inhibition-assay (author's transl)]

Cellular mediated immune reactions (CMI) against tumour associated antigens are the demonstration of an interrelationship between tumour and tumour host. They are related to the stage and prognosis of the disease. 41 patients with cervical cancer were tested by leukocyte-migration-inhibition test. Cryostat sections of 10 micron of the tumour-tissue, gained by excision or curettage and histologically defined, were taken as tumour antigens. The test was performed in Sykes-Moore-Chamber as so-called one-way-test with the lymphocytes/leukocytes and macrophagen of the tumour patient. Reactions against autologous and homologous tumour tissue and against recall antigens (tuberculin and varidase) were tested. There was no overall diminution of cellular mediated immune reactions. CMI was demonstrated in 69.7% (inhibition in 30.3%, stimulation in 39.4%) in the autologous and in 51.3% in the homologous system (21.6% inhibition, 29.7% stimulation).

[Limits and possibilities of neoplasm immunotherapy]

Immunological treatment of malignant human tumors has so far met with little success. Based on methods and insights obtained by investigation of corresponding animal models, this article attempts to elucidate the reasons for this failure and to suggest ways and means to improve immunotherapeutic approaches to human neoplasms.

Progression of the immune response to solubilized tumor antigens

Local adoptive transfer assays (LATA) were used to analyze and compare the progression of the immune response in C3H/HeJ mice to irradiated tumor cell vaccine and to crude 3M KCl solubilized antigens extracted from a syngeneic methylcholanthrene-induced fibrosarcoma. Sequential LATA performed 2, 6, 9, 12 and 15 days after soluble antigen pretreatment of spleen cell donors revealed a sinusoidal evolution of lymphoid cell activity. An initial brief period of potent tumor facilitation (days 6-9) was followed by a phase of tumor neutralization (days 9-12) which decayed by day 15. On the other hand, spleen cells from donors sensitized with irradiated tumor cells exhibited consistent tumor neutralization which was sustained throughout 15 days. Thus the tumor growth facilitation observed only in CSA-treated donors may represent a qualitative difference in the immune state induced by soluble, as opposed to cellular, forms of tumor antigen.

Inhibition of the growth of lymphoid tumours in syngeneic athymic (nude) mice

A comparison of the growth of a number of BALB/c tumours in BALB/c, BALB/c.nu/ + (heterozygous nude) and BALB/c.nu (homozygous) nude mice has shown that a majority of BALB/c lymphoid tumours grow at a significantly reduced rate in BALB/c.nu mice. The three non-lymphoid BALB/c tumours (carcinomas and sarcomas) tested and a minority of lymphoid tumours, however, grew as well, or better, in the BALB/c.nu mice. Furthermore a correlation, without exception to date, has emerged from a comparison between the susceptibility of a tumour cell line to in vitro lysis by spleen cells from syngeneic nude mice and its growth in vivo in syngeneic nude mice. Only those lymphoid tumour cell lines lysed in vitro show the reduced growth rate in syngeneic nude as compared to syngeneic normal mice. Tumour cell lines, both lymphoid and non-lymphoid, which are resistant to in vitro lysis do not show the reduced in vivo growth rate in syngeneic nude mice. Both the in vivo and in vitro effect can be partially abolished by irradiating the nude mice prior to use, suggesting that a radiation-sensitive non-T-cell surveillance of lymphoid tumours is operating in nude mice. While the identity of the antigens is still unknown, the specificity of the phenomena suggest that C-type RNA oncogenic viral determined antigens are involved.

Comparison of autochthonous and allogeneic breast-tumour cells in tests for lymphocyte immunity to human tumours

Lymphocytes from 10 patients with breast carcinoma were seeded in autologous serum, on autochthonous tumour cells and allogeneic tissue-cultured breast tumour cell lines. In 4 patients, the anti-tumour cell cytotoxicity against at least one of 3 breast tumour cell lines differed significantly from that against autochthonous tumour cells. Further study of these 4 individuals (using their previously frozen lymphoid cells and sera) showed that these differences occurred because serum which decreased ("blocked") lymphocyte anti-tumour cytotoxicity when applied to one tumour cell line, could either have no effect or potentiate it when applied to another, without any consistent pattern vis-à-vis target-cell susceptibility to these different humoral effects.

Temporal analysis of cellular cytotoxicity and humoral factors during progession and regression of Rous sarcomas in Japanese quails

Temporal appearance of cellular cytotoxicity and humoral activities including blocking and arming activities during the entire course of Rous sarcoma development in Japanese quails was examined by microcytotoxicity assay with comparison of animals bearing regressing tumors induced by a moderate dose of virus (regressors) and animals bearing growing tumors induced by a large dose of virus (progressors). Cellular cytotoxicity of the spleen cells in regressors was detected in a biphasic pattern; the first phase being observed as early as 3-5 days post inoculation (p.i.), followed by an eclipse period between 7-10 days p.i. which was the time of active tumor growth, and the second phase occurring after 12 days p.i. when the tumor had attained the maximum size. In progressors, only the first phase was observed. Instead, a stimulatory effect of the spleen cells on growth of target cells was noticed. Arming activity which confers cytotoxic activity on the normal spleen cells was demonstrated in the sera of regressors in the similar biphasic pattern as the cellular cytotoxicity; the early activity being present at 3 days p.i., and the late one after 19 days p.i. The former was detected by pre-incubation of serum with effector cells in microcytotoxicity assay and the latter by pre-incubation with target cells. In progressors, only the early arming activity which reacts with effector cells was demonstrated. Blocking activity which abrogates cellular cytotoxicity was demonstrated in both regressors and progressors but in different patterns of appearance, that is, blocking activity in regressors was only transiently demonstrated only by pre-incubation with effector cells at the time of maximum tumor growth, while the activity in progressors seemed to persist after the tumor reached the maximum size. Since the earlier activity was found to be effective at effector cell level, and the later one at both effector and target cell levels, participation of blocking factors of different types in progressors was also suggested.

Immunological studies of women with primary breast carcinoma

Lymphocytes from disease-free women and women with primary breast carcinoma were comparable vis-a-vis their capacity to inactivate breast tumor cells in vitro. Sera from comparable numbers of women in each of these two groups either blocked, potentiated or left unaffected the anti-tumor-cell cytotoxicity of their lymphoctes. As such, the results cast doubt on the validity of the hypothesis that there is a positive correlation between the presence of humoral blocking factors and in vivo tumor progression.