A macrophage factor enhancing the systemic anti-tumour effect of T lymphocytes

Spleen cells sensitized to tumour cells have an anti-tumour effect on injected syngeneic lymphosarcoma cells in mice. This study shows that this anti-tumour effect can be enhanced by induced peritoneal macrophages and by macrophage-like tumour cells (macrophages). Addition of macrophages to the intraperitoneally injected sensitized spleen cells stimulated the anti-tumour effect. This was observed both with intraperitoneally injected tumour cells and with subcutaneously transplanted tumour cells. The anti-tumour effect is the result of a cooperation between T cells and macrophages. In vitro incubation of immune T-cells with macrophages or macrophage-like cells enhanced the in vivo anti-tumour activity of the sensitized T-lymphocytes. Neither the presence of antigen nor the proliferation of the immune T-cells were a prerequisite to enhance this anti-tumour effect. Our experiments suggest that a macrophage factor is responsible for the enhancement of the anti-tumour effect. Based on the results of this paper and other studies we propose the following sequence of events to explain the anti-tumour effect of injected sensitized T-lymphocytes and macrophages: injected macrophages enhance the anti-tumour effect of sensitized lymphocytes. These stimulated lymphocytes migrate to the tumour located elsewhere and recognize the tumour antigens. Subsequently, the lymphocytes render (host) macrophages in the tumour cytotoxic to tumour cells.