Influence of Malignant Cell Clonogenic Capacities and Position Along the Maturation Pathway on Their Susceptibility to Lymphokine-Activated Killer Cell Cytotoxicity

In order to investigate the sensitivity of malignant target cells to lysis by LAK cells according to their clonogenic capacities and their position along the maturation pathway, we compared clonogenic and chromium release cytotoxicity assays performed on human hematopoietic cell lines using Effector: Target ratios of 1:1, 3:1, 6:1, 12:1, 24:1, 48:1 and 96:1, and studied the sensitivity of HL-60 and U937 human cell lines after exposure to different factors including GM-CSF, SCF, IFN, Retinoic acid (RA), DMSO, and TPA which are able to recruit cells into the cell cycle or to induce cell differentiation. There was a good correlation between the lysis of the target cells using 51Cr release and the growth inhibition in semisolid medium. The degree of inhibition was significantly higher using the colony growth assay (p = 0.006). Regarding the effects of culturing cell lines with proliferating and differentiating agents on the sensitivity of these cell lines to LAK cytolysis, a correlation was noted between the proliferative response of the U937 cell line and susceptibility to LAK cell lysis (p = 0.01), while results appeared close to significance with HL-60. The most significant effects were a decreased sensitivity of HL-60 to LAK lysis with RA (p < 0.001) and TPA (p < 0.001), and an increased susceptibility of U937 to LAK lysis with GM-CSF (p < 0.0001). In studies planned to investigate whether susceptibility of treated cells to LAK activity was a consequence of a down-regulation of adhesion molecules expressed on target cell surface, the proportion of cells expressing adhesion molecules was not significantly changed, except for CD54 expression on HL-60 cells which showed a higher expression, after cells were treated with RA or Dmso. We conclude that clonogenic cells are more sensitive to LAK cell lysis and that cell line sensitivity to LAK cytolysis can be modulated by a variety of agents of potential therapeutic use. The poor correlation between adhesion molecules expression and sensitivity to LAK lysis suggests that molecules other than CD54, CD56, CD58, and CD106 may possibly be more central to the processes involved.