Effects of in vivo modulation of splenic natural killer cell activity on the growth of spleen-seeking tumour variants.

A novel tumour system has been used to study the effect of natural killer cells on tumour growth by using agents which modify natural killer cell activity. The tumour cells are hybridoma cells which secrete antibody specific for red blood cells so that tumour growth can be quantitated by a haemolytic plaque assay. Spleen-seeking variants have been derived from original hybrids which are sensitive to natural killer cells. Treatment of mice with polyinosinic-polycytidylic acid substantially enhanced natural killer cell activity and correlated closely with a reduction in the growth of the hybridoma tumour cells in the spleen and life extension. Conversely, a single injection of anti-asialo GM, antibody resulted in a substantial increase in the number of plaque forming splenic tumour cells and virtual elimination of natural killer cell activity. These data demonstrate the important role of natural killer cells in constraining the growth of a tumour of B cell origin and establishes the usefulness of this tumour model in studying the biology of effects on tumour growth.