Comparison of three isotopic assays of cell-mediated cytotoxicity against mouse tumor cells. I. Basic parameters: baseline controls, target cells, and methods of calculation

Activation of natural resistance against lung metastasis of an adenocarcinoma in T-cell depressed spontaneously hypertensive rats by infection with Listeria monocytogenes

We report here our study of the role of natural host defense mechanisms mediated by macrophages and natural killer (NK) cells in an experimental model of spontaneous pulmonary metastases of a mammary adenocarcinoma SST-2 in spontaneously hypertensive rats (SHR) with congenital T-cell depression. To activate macrophages and NK cells, Listeria monocytogenes (LM) was injected IV into SHR which had received a transplantation of SST-2. To assess the antimetastatic responses induced by LM, the number of lung nodules and the lung weight in SHR were evaluated 30 days after tumor inoculation. The growth of lung metastases, though not of primary tumors, was significantly reduced if 10(7) LM were injected IV into SHR 2, 10 and 20 days after the SC transplantation of 5 X 10(4) or 5 X 10(5) SST-2. An inhibitory effect of LM on pulmonary metastases was also observed in tumor-excised rats, in which the number of lung metastases and the lung weight were enhanced as compared with those in tumor-bearing rats which had not undergone surgery. Peritoneal resident cells which were harvested from rats injected with LM showed a significant augmentation of tumoricidal activity against SST-2 cells as measured by in vitro cytotoxicity. Similarly, the NK activity of spleen cells of SHR injected with LM increased significantly when compared with untreated SHR. These data suggest that the inhibition of metastatic growth, though not of primary tumor growth, was accomplished by the, possibly T-cell independent, activation of macrophages and NK cells.

The effect of immunotherapy with extracted tumor antigens on sinecomitant immunity

The fate of hosts after tumor resection depends upon the level of their sinecomitant immunity, which can destroy residual neoplastic cells. In addition, active specific immunotherapy can stimulate the resistance of mice incompletely resected of large tumors and therefore destined to develop recurrent disease. The studies presented herein, assessing host resistance by in vivo tumor challenge and an in vitro growth inhibition assay (GIA) measuring the effect of splenic lymphocytes on 3H-thymidine incorporation into monolayers of sarcoma cells, revealed an antagonistic relationship between sinecomitant immunity and tumor antigen immunotherapy. Treatment of hosts bearing high levels of endogenous sinecomitant immunity with Fraction 15 pI 5.95 partially purified from 3 M KCl extracts by preparative isoelectric focusing, decreased their resistance to tumor challenge and the capacity of their spleen cells to perform in the in vitro GIA. When sinecomitant immunity was not demonstrable, therapy with tumor antigen induced host resistance. If therapy was delayed until sinecomitant immunity had naturally waned, hosts displayed improved resistance toward secondary challenge. These findings suggest that not only does antigen therapy effect tumor resistance by a mechanism independent of sinecomitant immunity, but also these two mechanisms are mutually antagonistic. Therefore, the design of active specific immunotherapy protocols utilizing tumor antigens may depend on the level of the host endogenous sinecomitant resistance.

Effector and enhancing lymphoid cells in plasmacytoma-bearing mice. I. Methodological studies on the Winn assay

Some parameters of the Winn assay for the detection of tumor-suppressing ("effector") and tumor-enhancing lymphoid cells were studied in BALB/c mice. Spleen cells of mice that were preimmunized with mitomycin-C-treated MOPC-104E plasmacytoma cells were inhibitory in this test system for both the MOPC-104E and the HOPC-I plasmacytomas, thus indicating cross-reactivity. Spleen cells taken from mice 6 days after the surgical removal of 15-day-old MOPC-104E tumors inhibited the growth of lethal doses of MOPC-104E cells in normal recipients, but no inhibition was observed 2 days after the removal of 18-day-old tumors. Spleen cells from mice bearing MOPC-104E for 13 days enhanced tumor growth. This enhancement was not influenced significantly by the wide dose range (from 10(5) to 3 x 10(7)) of MOPC-104E cells used to initiate tumors in the lymphoid cell donors, although tendency for stronger enhancing potential occurred after low tumor doses. When spleen cells from donors bearing MOPC-104E for 10 days were injected at the constant tumor-lymphocyte ratio of 1:30 with increasing numbers of tumor cells (from 5 x 10(5) to 2 x 10(6)), tumor inhibition occurred at the lowest dose only, while no significant effect was observed at higher tumor cell doses. When a constant dose (5 x 10(5)) of tumor cells was injected with spleen cells from 10-day tumor-bearers at tumor/lymphocyte ratios of 1:10, u:40 and 1:160, a significant tumor inhibition occurred only at the ratio of 1:40. The relevance of the Winn test to the study of immune mechanisms in tumor-bearing hosts is discussed.

Studies on the microcytotoxicity test. III. Comparison of [75Se]selenomethionine with [3H]proline, Na2, 51CrO4 and [125I]iododeoxyuridine for pre-labelling target cells in long-term cytotoxicity tests

Four intracellular radioisotope labels, [3H]proline, Na2 51CrO4, [75Se]selenomethionine and [125I]iododeoxyuridine, were evaluated for use in a pre-labelling long-term microcytotoxicity assay for cell-mediated immunity. Adherent rat tumour cells established in tissue culture were used as targets and the basic variables studied were labelling efficiency, toxicity and spontaneous release rates. [125I]Iododeoxyuridine was found unsuitable on account of its high toxicity and correspondingly high spontaneous release rate, and Na2 51CrO4 for its toxicity and low labelling efficiency. Of the two other radiolabels, [75Se]selenomethionine had the advantage over [3H]proline of higher labelling efficiency (especially in Ham's F10 medium), lower toxicity, and being a gamma-emitter. Furthermore, released 75Se was shown to be non-reutilisable and its retention by target cells provided an accurate measure of cell survival in an alloimmune system. Methods of calculating the results of pre-labelling cytotoxicity tests based on the total radioactivity in target cells at the beginning of the assay were found to be invalid.

Studies on the microcytotoxicity test. II. The uptake of amino acids ([3H]leucine or [75Se]methionine) but not nucleosides ([3H]thymidine or [125I]IUdR) or 51CrO24-provides a direct and quantitative measure of target cell survival in the presence of lymphoid cells

We have studied the suitability of various commonly used radioactive materials for the direct post-labeling of adherent rat target cells in long-term cytotoxicity tests. The use of nucleosides at high concentration avoids the necessity of adding fluorodeoxyuridine to enhance nucleoside uptake by target cells, and reduces the degree of non-specific inhibition of nucleoside uptake caused by products released from effector lymphoid cells. However, when [125I]iododeoxyuridine was used for labelling, such inhibition was not completely avoided even at very high nucleoside concentration, necessitating the washing of target cells prior to labelling. Similarly, without prewashing, the uptake of 51CrO24-ions frequently failed to correlate well with the numbers of surviving target cells as assessed by cell counting. On the other hand, radiolabelled amino acids, when present at semi-saturating concentrations, were taken up quantitatively by target cells under all conditions tested. Furthermore, in comparison to [125I]iododeoxyuridine, radioactive amino acids showed little if any toxicity to target cells. The use of the gamma-emitting amino acid analogue, [75Se]selenomethionine, is particularly recommended.