Kinetics of the response of spleen cells from tumor-bearing animals in an in vivo tumor neutralization assay.

The behavior of spleen cells from tumor-bearing mice, vis-à-vis isologous tumor cells, was investigated by means of an in vivo adoptive neutralization test. C3H/eB mice were challenged with tumor cells from a chemically induced fibrosarcoma. Spleens from these animals were removed at weekly intervals following tumor inoculation, mixed with tumor cells, and tested for their influence on tumor growth in syngeneic recipient mice. Two phases in the reactivity of spleen cells from tumor-bearing mice were clearly distinguishable. In a first stage of tumor growth, these mice yielded specific tumor-inhibitory cells conferring protection. Subsequently, the protective activity declined leading to a second phase characterized by tumor enhancement. Both protective and enhancing activities were shown to be mainly dependent on the presence of T cells.