Mitogenic activity elaborated by macrophage-like cell lines acts as competence factor(s) for BALB/c 3T3 cells

The culture medium from several murine macrophage-like cell lines contained a mitogenic activity that functioned synergistically with platelet-poor plasma to induce DNA synthesis in quiescent density-inhibited BALB/c 3T3 fibroblasts. This mitogenic activity was generated by P388D1 (and other established lines of) macrophage-like cells that were cultured either in medium alone or in medium supplemented with platelet-poor plasma. The amount of mitogenic activity produced was directly related to the length of time the macrophage-like cells were maintained in the medium. Serum-free medium conditioned by macrophage-cells did not stimulate DNA synthesis in density-inhibited 3T3 cells in the absence of plasma; however, a transient (4-hr) exposure to serum-free macrophage-conditioned medium allowed quiescent cells to respond to plasma-derived progression factors. The addition of plasma to 3T3 cells that had been treated with the macrophage-conditioned medium brought about DNA synthesis after a 12-hr lag. The mitogenic activity that was in macrophage-conditioned medium bound to DEAE-Sephadex and eluted in a single peak using a linear NaCl gradient. This macrophage-derived competence factor was not mitogenic for lymphocytes and was clearly separated by DEAE-Sephadex chromatography from the major peak of the previously described mitogenic monokine, Interleukin-1 (lymphocyte activating factor).

Resurgence of killing and in vivo protection mediated by lymphocytes cultured from lymph nodes draining Moloney sarcomas

We have previously documented the development and subsequent disappearance of cytolytic activity mediated by lymphocytes from lymph nodes draining Moloney sarcomas destined either to regress or grow progressively. We now report that these tumour-draining lymphnode cells (LNC) that were no longer cytotoxic, spontaneously regenerated peak levels of killing after culture in vitro for 4 days in the absence of exogenous tumour antigen. Cytolytic activity, which was antigenically specific, was mediated by T lymphocytes. Resurgence of cytolytic activity in vitro was accompanied by proliferative changes (DNA synthesis, blast transformation, cell division) which peaked on the 3rd day of culture. Although normal, nonimmune LNC underwent quantitatively similar proliferative changes in culture, the killing that developed was weak and antigenically nonspecific. Transfer of cultured, tumour-draining LNC to immunologically compromised, syngeneic mice conferred complete protection from Moloney sarcoma progression. Adoptive transfer could be delayed for 6 days after tumour induction without loss of protection. These results suggest that there exists in Moloney sarcoma-bearing mice a mechanism that limits the differentiation of pre-killer cells into cytolytically active T lymphocytes, and that such inhibition is eliminated when LNC are explanted into culture.

B-tropic oncornavirus production by BALB/c methylcholanthrene-induced sarcoma cells

Six oncogenic cell lines were established from primary sarcomas that had been induced in thymectomized, aged, BALB/cSt mice by the injection of 3-methylcholanthrene. Of these lines, three produced B-tropic murine leukemia virus (MuLV), i.e. MuLV that would patently infect fibroblasts of BALB/c origin but not those from NIH Swiss mice. One of these lines, M-138, produced large quantities of virus, permitting the isolation of milligram quantities of B-tropic MuLV. Neonatal BALB/c mice injected with the M-138 MuLV developed high plasma levels of the species-specific virion antigen p30, but during 9 months of observation failed to manifest clinical signs of leukemia. Plasma p30 levels of NIH Swiss mice (non-permissive host) that were inoculated also as neonates with the same virus preparation, remained undetectable by radioimmunoassay. Xenotropic MuLV, i.e. that which infects cells of species other than the species of origin, was released by one of the three remaining cell lines. Two of the six original lines have remained free of detectable oncornavirus production. Our results suggest that cell lines that are stable sources of large quantities of B-tropic MuLV may be easily obtainable by the described manipulations. Equally important, however, is the fact that these data re-emphasize the danger that is inherent in assuming that a cell line is virus-free simply because it was isolated from a chemical carcinogen-induced neoplasm

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

Intratumoral T lymphocytes were recovered sequentially after induction of regressing or progressing Moloney sarcomas in BALB/c mice and were assayed quantitatively for their ability to kill specifically the tumor (MSC) cells used for induction. The cytolytic activities of the two lymphocyte populations described two distinct biphasic kinetic profiles that were similar in amplitude and duration but separated from each other by 4-6 days. In progressing neoplasm, there was a rapidly occuring accumulation of T lymphocytes highly cytolytic for MSC cells. This response, however, was not sustained and disappeared in association with the onset of unchecked tumor growth. In contrast, T lymphocyte cytolytic activity developed more slowly in regressing sarcomas and attained peak levels coincident with the beginning of tumor regression. Similar changes in cytolytic activity characterized T lymphocytes in lymph nodes draining tumors. When cultured in vitro for 4 days, non-cytotoxic T lymphocytes from regional lymph nodes draining progressing sarcomas regained very high levels of cytolytic activity. Such restitution was diminished, however, if MSC cell lysates, macrophages or macrophages fed MSC cell lysates were present during the culture period. These experiments provided presumptive evidence that T lymphocyte-mediated cytolytic activity was lost in progressively growing Moloney sarcomas as a consequence of suppression in vivo of the genesis and/or functional expression of cytolytic T lymphocytes, perhaps by macrophages and/or soluble tumor antigen.

Inflammatory cells in solid murine neoplasms. IV. Cytolytic T lymphocytes isolated from regressing or progressing Moloney sarcomas

Highly purified suspensions of intratumoral T lymphocytes, recovered 11 and 13 days after induction of regressing or progressing Moloney sarcomas, were compared in their ability to lyse specifically the MSC cells used for tumor induction. Cytolytic activity, expressed in terms of lytic units/10(6) T cells, was similar for intratumoral T cell suspensions obtained 11 days after induction of either regressing (3.1 +/- 1.3 LU/10(6) T cells) or progressing (4.3 +/- 1.8) neoplasms. By 13 days post-induction, regressing tumors contained T lymphocytes with an increased cytolytic activity (11.1 +/- 4.5) whereas those from progressing tumors were strikingly less able to kill MSC cells (less than or equal to 0.2). This dramatic loss in cytotoxicity could not be attributed to errors associated with the enzymatic disaggregation method, inhibition by copurified endogenous tumor cells, or immunosuppression induced by viral infection. The changes in functional activity of intratumoral T lymphocytes from the two types of sarcoma appeared to be correlated with the stage of neoplasia. In this model system, cytolytic activity of T lymphocytes increased during spontaneous tumor regression whereas losses in cytotoxicity occurred coincident with the onset of inexorable progression.

Isolation of T-lymphocytes from disaggregated tumors, with high purity and good percentage recovery

A combination of two cell separation methods was utilized for the isolation of thymus-derived lymphocytes (TL) from enzymatically disaggregated tumors. Passage through Sephadex G-10-glass bead columns to remove adherent cell types followed by exposure to IgG-coated sheep red blood cell monolayers for removal of Fc receptor-bearing inflammatory cells provided functional TL suspensions of high purity with good percentage recovery.

Inflammatory cells in solid murine neoplasms. III. Cytotoxicity mediated in vitro by macrophages recovered from disaggregated regressing Moloney sarcomas

Macrophages (Mphi) were recovered from disaggregated, spontaneously regressing Moloney sarcomas for in vitro testing of their cytotoxic capabilities. At a 3:1 ratio, Mphi in monolayers efficiently killed (51Cr release) a variety of tumor target cells without regard to antigenic specificity. Within 24 hr most of their cytolytic potential was lost. Killing could be restored, however, if Mphi were replated at higher cell densities. A soluble, heat-stable, dialyzable inhibitor of thymidine incorporation, which did not interfere with cellular proliferation, also was produced by Mphi recovered from Moloney sarcomas. The finding of such a competitive inhibitor, probably cold thymidine, in supernatants further opened to question the validity of radioisotope incorporation into DNA as a measure of Mphi-mediated cytostasis. The data presented suggest that Mphi may participate in the regression process by directly killing tumor cells, thus complementing the antigen-specific cytolytic capabilities of the T lymphocytes that are also found in large numbers within regressing Moloney sarcomas.

Inflammatory cells in solid murine neoplasms. II. Cell types found throughout the course of Moloney sarcoma regression or progression

Regressing and progressing Moloney sarcomas, induced in BALB/c mice by the injection of cultured sarcoma cells (MSC)1, were sampled for histologic analysis and then disaggregated using mixtures of trypsin, collagenase and DNAse or collagenase and DNAse alone. The types of inflammatory cells (IC) found in resultant cell suspensions were determined 6, 11, 14 and 18 days post inoculation. Inflammatory infiltrates were composed almost exclusively of three cell types; neutrophils, T lymphocytes and macrophages. The extent to which each was found in tumors was related to the time post inoculation. Neutrophils were part of an early acute inflammatory response seen in both developing regressing and progressing sarcomas. The onset of regression was associated histologically with the appearance within tumors of a mononuclear inflammatory infiltrate. T lymphocytes and macrophages were the principal constituents. A higher percentage of T lymphocytes was recovered at all sampling times from regressing, compared to progressing, sarcomas. During development of the mononuclear inflammatory infiltrate there were relatively more large T cells in regressing, than in progressing tumors, and the percentage of macrophages was higher. Thereafter, the proportion of macrophages in the recovered cell population was approximately the same for both types of tumor. Such equality was more apparent than real, however, since IC were restricted to the peripheries of progressing sarcomas after the acute inflammatory phase, but continued to be found throughout regressing neoplasms. The effective ratio of macrophages and T lymphocytes to tumor cells therefore was much lower in progressing sarcomas than was suggested by percentage figures. The data presented support the concept that T lymphocytes are instrumental in causing the regression of Moloney sarcomas, possibly through interactions with macrophages.

Studies on the role of macrophages in regulation of growth and metastasis of murine chemically induced fibrosarcomas

Murine solid tumors were shown to contain 9-54% medium to large non-malignant cells bearing receptors for immunoglobulin Fc. These cells rapidly adhered to plastic surfaces, were trypsin-resistant, were capable of phagocytosis of latex particles and were sensitive to the lytic effects of anti-macrophage serum and complement. Purified Fc-receptor-positive cells failed to produce tumors, which strongly suggested that they were macrophages. When tumor-cell suspensions, depleted of macrophages by adherence to plastic surfaces, were injected subcutaneously into normal syngeneic mice, the tumors displayed an increased potential for metastasis. By contrast, control animals which received tumor-cell suspensions containing their normal complement of macrophages invariably developed progressive localized tumors. The survival times of mice infected with macrophage-depleted tumor-cell suspensions were significantly shorter (p less than 0.05) than those for animals inoculated with intact tumor-cell suspensions. These studies confirm the existence of a substantial number of macrophages within progressing syngeneic murine solid tumors and strongly suggest a regulatory role for the macrophages in the growth and metastasis of the tumor.

Receptor sites for antigen-antibody complexes on cells derived from solid tumors: detection by means of antibody sensitized sheep erythrocytes labeled with technetium-99m

Surface receptor sites for the Fc portion of antigen-antibody complexes were demonstrated on cells derived from three methylcholanthrene-induced fibrosarcomas, one of strain C3H and two of strain BALB/c origin, two spontaneously occurring malignant melanomas (B16 in strain C57BL/6 and Harding-Passey in strain BALB/c mice), a Moloney sarcoma virus-induced tumor of strain BALB/c origin and the Walker 256 carcinosarcoma of Holtzman rats. Primary cell cultures derived from these tumors adsorbed technetium-99m labeled, antibody-sensitized sheep erythrocytes (99mTc EA) as determined either by visual scoring of adherence or radioisotopic quantitation. Depending upon the tumor tested, from 20% to greater than 95% of the target cells absorbed 99mTc EA. All cells lost their reactivity after 1 or 2 passages in vitro, but this was regained after a single passage in vivo. Indicator erythrocytes coated with F(ab')2 fragments of the sensitizing sheep erythrocytes (SRBC) antiserum did not adhere thereby demonstrating that the hemadsorption required an intact Fc portion of the antibody molecule. Adherence of 99mTc EA was blocked by soluble immune complexes prepared with ovalbumin and rabbit antibody directed against it and Escherichia coli 055:B5 lipopolysaccharide and mouse antibody directed against it. Normal rabbit or mouse serum, immune serum, or antigen alone did not block adherence of 99mTc EA thereby demonstrating that the receptors had greater affinity for immune complexes than for either antigen or antibody alone. The existence of membrane receptors on tumor-derived cells which react with the Fc portion of antigen-antibody complexes may provide an explanation for the mechanism by which immune complexes are capable of blocking cell-mediated tumor cell destruction irrespective of whether the receptors are on the tumor cells themselves or on admixed lymphocytes and macrophages.