Functional heterogeneity of Leu 19"bright"+ and Leu 19"dim"+ lymphokine-activated killer cells.

The functional heterogeneity of human lymphokine-activated killer (LAK) cells was characterized using LAK effector cells generated in vivo during rIL-2 therapy and separated by FACS into Leu 19"bright"+ and Leu 19"dim"+ subsets. The Leu 19"bright"+ subset mediated significantly greater levels of LAK lytic activity against NK-resistant COLO 205 target cells compared to Leu 19"dim"+ effector cells in chromium release assays. Single cell cytotoxicity assays showed that the Leu 19"bright"+ LAK effector cell subset contained a significantly higher percentage of cells capable of binding to and lysing COLO 205 or K562 target cells compared to the Leu 19"dim"+ subset. Furthermore, individual Leu 19"bright"+ LAK effector cells exhibited a more rapid rate of COLO 205 target cell lysis when compared to Leu 19"dim"+ LAK effector cells. In vitro culturing of Leu 19"bright"+ or Leu 19"dim"+ cells from normal donors with 1500 U/ml rIL-2 resulted in significantly greater levels of proliferation and LAK effector activity by Leu 19"bright"+ cells. Furthermore, whereas 86% of normal Leu 19"bright"+ cells maintained a Leu 19"bright"+ phenotype after rIL-2 stimulation, only 24% of Leu 19"dim"+ cells developed a Leu 19"bright"+ phenotype. These data demonstrate that Leu 19"bright"+ LAK cells are significantly more potent effectors than Leu 19"dim"+ cells due to quantitative and qualitative differences in the LAK effector cells contained within these subsets. Furthermore, these data indicate that Leu 19"bright"+ LAK cells that develop during rIL-2 therapy are derived from Leu 19"bright"+ precursor cells.