PHENOTYPICAL AND FUNCTIONAL ANALYSES OF MONONUCLEAR-CELLS DURING REJECTION OF A TRANSPLANTED MURINE FIBROSARCOMA

Repeated injections of mitomycin C-treated T2 fibrosarcoma cells into tumor-sensitized mice cause regression of a secondary tumor graft and more than 90% of the mice are cured. In the data presented here, an en hancement of the cytolytic cell-mediated activities measured in vitro against the specific T2 targets is shown in lymph nodes draining the t umor and in the spleen during the process of tumor rejection. Histopat hologic studies revealed a rapid and marked accumulation of mononuclea r cells mostly at the periphery of the rejected tumor tissue. A signif icant increase of CD8-positive, asialo GM1-positive and acid phosphata se-positive cells was observed in the rejected tumors whereas CD4-posi tive cells were similarly detected in both progressing and rejected tu mor tissue. As macrophages seemed to be the population presenting the most persistent variation after immunization, the production of TNF-al pha was studied within the tumor site and in the lymphoid tissues duri ng the regression process. Firstly, the presence of TNF-alpha within t he cytoplasm of most of the adherent cell fractions isolated from the spleen and the tumor of immune mice was demonstrated by immunocytochem istry. Next, TNF-alpha mRNA-containing cells were determined by in sit u hybridization of frozen tumor sections and identified essentially as tumor infiltrating macrophages. Finally, the macrophage populations i solated from tumors and from the spleen of immune mice were able to pr oduce in vitro large quantities of TNF-alpha without exogeneous stimul ation. These findings support the role of TNF-alpha in the effector me chanisms contributing to the tumor regression process.