The nature of the transforming lymphocyte in chronic lymphocytic leukemia

Lymphocyte transformation in vitro was studied with lymphocytes from patients with chronic lymphocytic leukemia (CLL). The responding capacity to phytohemagglutinin (PHA), pokeweed mitogen (PWM) and allogeneic lymphocytes, as well as the stimulating capacity in mixed lymphocyte cultures (MLC), were assessed. Lymphocytes of CLL patients display a depressed and delayed reaction to PHA. In MLC experiments a decreased responding and stimulating capacity could be demonstrated, the latter being reduced to a smaller extent. However, reduced numbers of lymphocytes from normal individuals show a similar reaction pattern with regard to these parameters. By albumin gradient centrifugation the lymphocytes from CLL patients could be separated into a nonresponsive population and other fractions, containing lymphocytes with increased reactivity in comparison with unfractionated cells. It was concluded that the leukemic cells in CLL are completely unresponsive to PHA and PWM and have no MLC activities. All observed in vitro reactivity can be attributed to the small proportion of normal lymphocytes among the leukemic cell population.