Separation and Functional Studies of the Human Lymphokine-activated Killer Cell

Cell separation studies were undertaken in an attempt to purify the lymphokine-activated killer (LAK) precursor cell. Null cells, prepared by the sequential depletion of monocytes, T- and B-lymphocytes from human peripheral blood mononuclear cells, were found to be potent mediators of LAK activity. Such preparations were Leu-11⁺ but Leu-4^- and displayed high levels of natural killer activity. Incubation of these cells with recombinant interleukin 2 (IL-2) for periods in excess of 24 h induced LAK lysis of fresh tumor targets which were resistant to lysis by unstimulated null effectors. In contrast, lymphocytes which formed high affinity rosettes with sheep RBC (E+ lymphocytes) were poor mediators of both natural killer and LAK activity. Interleukin 2 stimulated null cells, retained a Leu-11% Leu-4^- phenotype, and expressed only low levels of receptors for IL-2 and transferrin. An increase in the number of binding sites, on null cells but not on T-cells, for Vicia rillosa lectin with IL-2 stimulation was noted. Following IL-2 stimulation, null and T-cells were able to conjugate to K562 and fresh tumor but not to autologous lymphoblast targets.