Competition for cytotoxic immune capacity against a 'syngeneic' mouse tumour distributed at two sites.

Normal C3H mice will develop fatal ascites after the intraperitoneal injection of as few as 100 BP8 cells. However, mice can be immunized so that they can specifically reject an intraperitoneal challenge of 10(7) of these C3H-derived tumour cells. This paper investigates a phenomenon in which the capacity of immunized mice to reject an intraperitoneal challenge of tumour cells is lost between two to seven days after tumour cells have been given subcutaneously. Investigation of this temporary loss of capacity to reject the intraperitoneal challenge of tumour suggests that this might be due to the attraction of cytotoxic immunity to the site of subcutaneous injection. The possibility that this phenomenon is due to blocking factors, tumour overload, suppressor cells or enhancing antibody has been investigated but experimental results are given which do not favour these explanations.