Detection of the cytotoxic effect of tumor cells against the targets of normal killers

: The cells of 2 mouse leukemias (L-1212 and EL-4), the cells of mouse sarcoma (MX-11) and blood lymphocytes from 5 subjects with chronic leukemia were shown to damage the membrane of K-562 and EL-4 cells maintained in vitro. The membrane damage manifested in the rise of the permeability by the pancreatic ribonuclease molecules (m. m. 12,000 d). Experiments with tumor cell suspension fractionation have shown that such permeability cannot be attributed to the admixture of lymphocytes and macrophages to the tumor effector cells. Experiments with cold inhibition have revealed that the damage of the target cell membrane can be produced only by the contact of the tumor cell with the target. It is not related to the deterioration of target metabolism in the presence of a considerable number of tumor cells, or to the accumulation of any toxic products in the culture medium.