Suppression of immune response to sheep red blood cells in mice treated with preparations of a tumor cell component and in tumor-bearing mice

Adoptive transfer of immunity induced by semi-allogeneic hybrid cells, against a murine fibrosarcoma

Semi-allogeneic somatic hybrid cells derived from the fusion of a C57BL/6 fibrosarcoma (MCB6-1) and A9 cells (C3H origin) were used to immunize C57BL/6 mice against the parental tumor cells. These hybrid cells expressed H-2 histocompatibility antigen of both parental cells (H-2b and H-2k), and failed to produce tumors in normal C57BL/6 mice. A single i.p. injection of hybrid cells induced anti-tumor immunity which could be transferred to normal C57BL/6 recipient mice by immune spleen or peritoneal cells; the efficient cells were T cells, as this activity was completely abrogated by treatment with anti-Thy-1-2 antiserum and complement. Among immune splenic T cells, only the light-density T cells, obtained after fractionation on Percoll gradient, were effective in the transfer of immunity. Immunity induced by the hybrid cells was specific for MCB6-1 parental tumor cells. This immunity could be transferred during two brief periods, 7 to 12 days, and 40 to 50 days, after hybrid cell injection; there appeared to be an intermediate period, 12 to 40 days after immunization, during which no immunity could be transferred. These results suggest a suppressive mechanism implicated during hybrid cell immunization and interacting with the anti-tumor immune response.

Suppression of T cell-mediated immunity by tumor cells: immunogenicity versus immunosuppression and preliminary characterization of the suppressive factors

In studying the immunogenicity of spleen cells and tumor cells in the generation, of cytotoxic T lymphocyte (CTL) in the allogeneic mixed lymphocyte culture (MLC) or mixed lymphocyte tumor cell culture (MLTC) reactions, we have found that the tumor cells not only appear to be poorly immunogenic, but are also immunosuppressive. This was shown by the ability of the tumor cells or their cell-free extracts to suppress standard MLC reactions. This suppression was acting mainly at the induction phase of the cytotoxic response. It could not interfere with the killing activity of the fully generated CTLs. In a Friend virus-induced leukemia FBL-3 system, at least two major components could be attributed to the cause of immunosuppression; one was of viral origin and the other was of non-viral origin. The viral component was sensitive to UV-irradiation and could be pelleted after ultracentrifugation at 100,000 g. The non-viral component was UV-resistant and was retained in the supernatant fraction after ultracentrifugation. Friend virus and 12 commonly found murine viruses have been excluded as the possible candidates causing the immunosuppression. The immunosuppressive viruses are very likely of endogenous origin and are defective in replication as shown by electromicroscopy, and by the virus focus-inducing and reverse transcriptase assays. These findings indicate that probably all tumor cells possess the immunosuppressive factor(s) which may account for their apparent lack of immunogenicity and the lack of proper immune responses in the tumor-bearing hosts.

Generation of cytotoxic cells in absence of blastogenesis by mouse leukemic cells in mixed cultures

Primary virus-induced murine leukemias and transplantable leukemic cell lines, originally induced by virus, chemical or physical agents, failed to stimulate normal spleen cells differing at the H-2 complex or at Mls locus in the one-way mixed leukocyte culture. Lack of stimulation seems at least partially due to a nonspecific inhibitory effect since in a "three-party" culture system the leukemic cells interfered with the mixed leukocyte reaction (MLR) of normal allogeneic cells. Characterization of the leukemic cell populations used, according to their T or B cell origin, disclosed that in most cases T cell markers were present. Also, no Ia antigens were detected on leukemic cells. Furthermore, using a 51Cr release assay, leukemic cells could sensitize allogeneic normal lymphocytes to kill specifically normal as well as leukemic targets, even when no MLR was detected in parallel cultures.

Leukemia in AKR mice. I. Effects of leukemic cells on antibody-forming potential of syngeneic and allogeneic normal cells

Cells from the spleen, thymus, lymph node, and liver of leukemic AKR mice suppress in vitro antibody responses of normal syngeneic and semiallogeneic cells. This suppression can be mediated by irradiated leukemic cells, requires cell contact between leukemic and normal cells, and may occur at any time during the in vitro culture period. Leukemic AKR cells do not suppress antibody responses of allogeneic cells, even when allogeneic cells have H-2 or background genes homologous with AKR. Leukemic cells do, however, suppress cells that are unable to respond allogeneically to leukemic AKR cells, such as cells of the F1s of AKR. Suppression of normal AKR antibody responses by leukemic AKR cells may be overcome by addition of irradiated allogeneic cells. The fact that leukemic AKR cells are able to suppress normal lymphocyte responses may be of significance in pathogenesis of leukemia in these mice.

Nonspecific immunodepression induced by tumor-cell extracts

The immunodepression induced by tumor extracts in these experiments is characterized by the severe impairement of cell-mediated immunity meaning an alteration of T-cell or macrophage functions or both. This depression is specific to tumor cells and is observed with normal tissue extracts. This model is different from that observed with Ehrlich ascites (7) where the function of the B cells is impaired. The transmission of the immunodepression by thymus-cell or liver-cell extracts of treated mice rules out the involvement of factors like those described by PIKOVSKI (11) and YAMAZAKI (16). On the other hand, the role of suppressor cells in the etiology of the immuno-suppression (5.9) cannot be completely eliminated.