Influence of Tumour Growth on the Evolution of Cytotoxic Lymphoid Cells in Rats Bearing a Spontaneously Metastasizing Syngeneic Fibrosarcoma

Regional and distant lymph node cells, thoracic duct cells and peripheral blood lymphocytes from rats bearing a spontaneously metastasizing and apparently non-immunogenic sarcoma were assayed for cytotoxic activity on microcultures of tumour cells at 7, 14 and 21 days of tumour growth. In the regional lymph nodes detectable cytotoxicity was present at 7 days and the overall activity remained constant at 14 and 21 days. At Day 7 of tumour growth the cytotoxic cell population in the regional node was tumour specific in its cytotoxic effect, very radiosensitive and could not be removed by nylon wool column purification. In contrast the cells in the regional nodes at Day 21 were nonspecifically cytotoxic and could be completely removed by nylon wool treatment. In the peripheral blood, cytotoxic lymphoid cells not removed by nylon wool, were detectable at all stages of tumour growth. The thoracic duct lymph cells were, however, without cytotoxic activity throughout the period of tumour growth studied. Distant lymph node cells were assayed for cytotoxicity and it was found that they acquired significant cytocidal properties only late in tumour growth. The sera from tumour-bearing rats were tested for inhibitory activity on the cytotoxicity of Day 7 regional lymph nodes from tumour-bearing rats. It was found that a specific inhibitor appeared in the serum and that its activity increased with tumour growth. The possible contributions of the changes in lymph node cytotoxicity and the development of specific serum inhibitors to continued growth and dissemination of the tumour are discussed.