The in vivo antitumor effect of i.p. injection of allogeneic spleen cells was investigated. ACI rats were inoculated i.p. with 104 AMC-60 syngeneic fibrosarcoma cells and given injections i.p. of 4 × 107 Wistar spleen cells once a week for 3 wk from 1 day after tumor inoculation. This treatment significantly prolonged the survival period of the tumor-bearing rats. A similar effect was obtained by i.p. injections of Lewis spleen cells. Injection i.p. into ACI rats of spleen cells of these rat strains resulted in the apparent augmentation of cytolytic activity of peritoneal adherent but not of nonadherent cells against AMC-60 tumor cells. The cytotoxicity was exhibited nonspecifically to cells of a variety of tumor lines but not to concanavalin A blasts of ACI spleen cells and was inhibited by the addition of carrageenan. Irradiation (2000 R) of Lewis spleen cells or fractionation of the allogeneic spleen cells using nylon wool columns revealed that a radiosensitive and nylon wool-passed cell population, presumably a T-cell population, of the allogeneic spleen cells is responsible for the augmentation of peritoneal macrophage tumoricidal activity in ACI rats. Further, Lewis spleen cells irradiated at 2000 R neither augmented peritoneal macrophage cytotoxicity nor prolonged the survival period of ACI rats bearing AMC-60 tumor, suggesting that the augmentation of peritoneal macrophage cytotoxicity plays a major role in the in vivo antitumor effect of the allogeneic spleen cell transfer.

ACI rats were given injections i.p. of 4 × 107 Lewis spleen cells. Two days after injection, cells including peritoneal cells of the ACI rats and Lewis spleen cells remaining in the peritoneal cavities were obtained by peritoneal lavages and then incubated for 5 days. Significant blastogenic proliferation was observed, and the supernatant of the culture was shown to be able to render thioglycollate-induced peritoneal macrophages of ACI rats cytotoxic to AMC-60 tumor cells, indicating that a certain cell population of the cell mixture produced a lymphokine(s) resembling macrophage activating factor (MAF) during the incubation. When ACI rats were given injections i.p. of irradiated Lewis spleen cells, neither the blastogenic proliferation nor the generation of MAF activity in the culture supernatant was observed. Indirect immunofluorescence analysis using rabbit anti-ACI and anti-Lewis antisera revealed that as many irradiated Lewis spleen cells were remaining in the peritoneal cavities as normal Lewis spleen cells 2 days after injection into ACI rats. Mixed-leukocyte culture of normal Lewis spleen cells and irradiated ACI nonadherent peritoneal cells resulted in both the blastogenic response and the generation of MAF activity in the culture supernatant, whereas that of irradiated Lewis spleen cells and normal ACI nonadherent peritoneal cells did not. These results strongly suggest that Lewis spleen T-cells, injected i.p. into ACI rats, may produce a variety of lymphokines including MAF in response to the histocompatibility antigens of the ACI rat strain in peritoneal cavities, resulting in the augmentation of peritoneal macrophage turnoricidal activity.

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Supported by a grant-in-aid for cancer research from the Ministry of Education, Science, and Welfare of Japan.

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