Human Platelets Effectively Kill K‐562 Cells, a Chronic Myelogenic Leukemia Cell Line, in vitro

The cytotoxic effect of isolated human platelets on leukemic cells has been examined in order to investigate the role of platelets in host defense systems. K‐562 cells (a chronic myelogenic leukemia cell line) showed significant change in their morphology and were killed when they were incubated with platelets in serum‐free medium for several hours at 37°C, a condition where no killing of normal peripheral lymphocytes occurred. Some protease inhibitors inhibited the cytotoxicity of platelets against K‐562 cells. Our results suggest that platelets may be involved in host defense against neoplasia and that certain proteases are implicated in the cytotoxic effect of platelets.