Development and persistence of cytolytic T lymphocytes in regressing or progressing Moloney sarcomas

Cytotoxic activity of lymphocytes infiltrating progressive and regressive tumor variants from a rat colonic cancer

Two tumor cell variants (PROb and REGb) isolated from a single chemically-induced rat colon adenocarcinoma were previously shown to differ in their tumorigenicity. When injected into syngeneic BDIX rats, PROb cells induce progressive tumors whereas REGb cells give rise to tumors which always regress. PROb and REGb variants also differ in their capacity to induce an immune response in the syngeneic host. Regression of REGb tumors could have been mediated by cytotoxic effector cells acting at the tumor site. To test this hypothesis, the cytolytic activity of non-adherent lymphoid cells isolated from PROb and REGb tumors and from the spleen of the same animals were compared. The same number of infiltrating lymphocytes was recovered per gram of PROb or REGb tumor. The cytolytic activity of tumor infiltrating lymphocytes, as that of spleen lymphocytes, was predominantly non specific, as demonstrated by their ability to kill YAC-1 cells, an NK-sensitive cell line. PROb cells were relatively resistant to the cytotoxic activity of spleen or tumor infiltrating lymphocytes. In the regressing REGb tumors, the cytotoxic activity of tumor infiltrating lymphocytes to homologous cells or to YAC-1 cells was low and significantly inferior to that of the corresponding spleen lymphocytes. These results suggest that the cytotoxic activity of lymphocytes was impaired at the local, intratumoral level, even in spontaneously regressing tumors.

T-cell responses at the host: tumour interface

The evidence considered here reinforces the conclusion that T-cell responses to tumours involve complex cellular interactions. An attempt to summarize some of these interactions is shown. This emphasizes that not only are the interactions between the effector cell populations complicated, but that the target cell surface is also subject to variation and modification as a result of the immune response. A feature that also emerges from these studies is that most cells apparently responding to or infiltrating a tumour do not necessarily participate in its destruction, and it is in this area that experimental tumour systems have particular value. This also perhaps explains the preoccupation of experimentalists with the identification of 'the' effector cell crucial to tumour rejection. However, there is heterogeneity between systems in terms of the type of rejection response induced, but a logical basis for this heterogeneity is not established. If experimental studies could define the nature of the immune response generated by a tumour in the context of the biological features of the tumour itself, this could lead to the prediction of the immunogenicity and potential for induction of a rejection response for that tumor. Clearly, experimental tumour systems do not provide an exact reflection of the situation with human tumours. However, they may provide systems that illuminate particular aspects of the human response, and give precedents to guide the interpretation of data derived from human systems. This form of assessment is still at an early stage, but developments in the experimental field should provide a framework for the development and exploitation of T-cell responses to tumours.

Immunology of tumor infiltrating lymphocytes

Frequently peripheral blood lymphocytes (PBL) do not reflect the tumor host relationship and cell mediated immunity in the PBL does not often correlate with prognosis. The tumor infiltrating lymphocytes (TIL) interact most closely with the tumor cells and are likely to more accurately reflect tumor host interactions. These studies indicate that TIL from pulmonary tumors are similar to PBL so far as their cell surface markers are concerned. The percentage of T-cells, B-cells, helper cells, suppressor cells, and NK cells are similar in the two compartments. However, the TIL are markedly suppressed in their functional capacity as measured by their proliferative and cytotoxic activity. In addition, natural killer (NK) cell activity is markedly diminished in TIL as opposed to the PBL. In addition, the direct injection of BCG into these tumors reverses this phenomenon by significantly increasing T-cell and NK cell functional activity. Thus, the microenvironment of the tumor profoundly affects the immunologic relationship between the tumor and the host.

Enhancement of tumor growth in mice: evidence for the involvement of host macrophages

Intratumor host cells of methylcholanthrene-induced fibrosarcoma(s) were shown to enhance the in vivo outgrowth of syngeneic homologous tumors (MC1A, Mc2A, Mc2B) but not two heterologous T-lymphomas (EL4 and TLX9) in the Winn adoptive transfer assay. This enhancing activity was not restricted only to the latent period of tumor growth but was also observed during the period of active in vivo tumor proliferation. Tumor enhancement was mediated by a population of cells adherent to nylon wool and glass and insensitive to irradiation (with 850 rads) or to treatment with anti-Thy 1.2 serum and complement. Macrophages from peritoneal exudates of normal mice, used as control host cell population, showed similar tumor-enhancing activity. These findings suggest that tumor infiltrating host cells, predominantly macrophages appear to be the cell type responsible for tumor enhancement and active promotion of tumor growth (in vivo).

Enhancement or inhibition of tumor growth by interferon: dependence on treatment protocol

MSC cells are tumor cells originally induced in BALB/c mice by Moloney sarcoma virus. In these studies we demonstrated that, although these tumor cells are sensitive in vitro both to lysis by NK or NK-like cells and to the growth-inhibitory effect of murine L-cell interferon (IFN), the growth of the tumor in vivo could be either inhibited or enhanced by IFN. The outcome of in vivo IFN treatment was dependent on the timing and route of IFN administration relative to tumor challenge. IFN given systematically at the same time as tumor challenge resulted in enhancement of primary tumor formation, rate of tumor growth and subsequent progressive tumor growth. In contrast, IFN administered at the site of tumor inoculation on days 1-3 after tumor challenge inhibited tumor formation and growth. Histopathology of tissue sections obtained from the site of tumor challenge confirmed these results. Similar studies performed in mice given 450 rads of X-irradiation showed that IFN could still inhibit tumor growth when administered at the site of tumor inoculation on days 1-3 after tumor challenge. IFN administered simultaneously with tumor challenge, however, did not enhance tumor growth in irradiated mice. These results are consistent with the interpretation that 1) inhibition of MSC-induced tumor growth by IFN has a radioresistant component and 2) the enhancement of MSC-induced tumor formation by IFN is dependent on interaction with a radiosensitive population of cells, possibly lymphoid cells.

Characterization of lymphocyte subsets in spontaneous mouse mammary tumors and host lymphoid organs

The subsets of small lymphocytes (surface Igm-positive or B, Thy-I-positive or T and "double-negative" or null) appearing within spontaneous mammary tumors of C3H retired breeder female mice and in various lymphoid organs of the host at different stages of tumor development were characterized directly using a radioautographic method. Tumor-bearing mice showed early transient splenomegaly and progressive atrophy of the thymus. The proportion of T small lymphocytes increased with tumor age within the tumor and in the spleen, blood and thymus; then, except in the spleen, these proportions declined again by 8 weeks of tumor growth. The incidence of B small lymphocytes showed no change in the tumor or thymus; there was an increase in the blood after 3 weeks, and a small decrease in the spleen after 7 weeks. At all the sites examined, the proportion of null small lymphocytes declined from an initial high level observed in the elderly tumor-free control mice, and then recovered to control levels after 7 weeks. The absolute numbers of T and null cells in the spleen changed in parallel to their proportions, while splenic B-cell numbers increased at 1-3 weeks. In the thymus the absolute numbers of all subsets decreased, with a late recovery of null cell numbers. Age-matched control mice showed higher proportions of null cells in the spleen, blood and thymus, and lower proportions of T cells in the blood and spleen, than did young normal mice. This spontaneous tumor appears to be characterized by an increase in T cells, rather than in null cells, as observed for rapidly growing transplanted tumors. The null cell rise in the present case takes place before the clinical appearance of tumors. In both cases, however, tumor-infiltrating B cells exhibited low levels of surface Ig, possibly related to a low level of maturation. The functional significance of these findings remains to be determined.

Effect of non-steroidal anti-inflammatory drugs of Moloney sarcoma virus inoculated mice

Chronic administration of phenylbutazone, flufenamic acid and a new, potent non-steroidal anti-inflammatory agent ITF (3-methyl-5-benzoyl-amino-isothiazole-4-carboxy-p-ethoxyphenylamine) to BALB/c mice inoculated with a Moloney sarcoma virus resulted in a stimulation of tumor growth and increased severity of disease. This treatment, however, had no effect on the spontaneous regression of tumors. Indomethacin in a dose of 5.0 or 2.5 mg per kg suppressed the MSV-induced tumor growth, but this effect was apparently connected with the high toxicity of this drug for mice.