Correlation of "sneaking through" of tumor cells with specific immunological impairment of the host.

The preferential take of tumors after small-size inocula of transplantable tumor cells has been described for many systems. The phenomenon has been named "sneaking through" or "dilution escape". Using a BALB/c mastocytoma, we have analyzed the immunological parameters accompanying sneaking through that can be observed upon injection of 10(1) to 10(3) living cells. Mice can also be conditioned by injection of low, subimmunogenic numbers of irradiated cells to show increased tumor incidences upon injection of living cells in doses two orders of magnitude above the sneaking through dose. The general immune reactivity of the animals is not impaired under these conditions. However, determinant-specific unresponsiveness is found which can be transferred by spleen cells and therefore seems to be actively maintained. It is concluded that sneaking through of tumor cells is the result of specific immunological impairment of the host's immune system by subimmunogenic small-size inocula of tumor cells.