Generation and Characterization of Lymphokine‐activated Killer Cells against Fresh Human Leukemia Cells

Lymphokine‐activated killer (LAK) cells generated from 15 acute leukemia patients in remission showed significant levels of cytotoxicity against Daudi 1A4, a natural killer‐resistant cell line. This indicates that lymphocytes of leukemia patients in remission could respond to interleukin‐2 to generate conventional LAK cells. However, LAK cells caused lysis of autologous leukemia cells at considerably lower levels in seven out of the 15 patients, with the exception of one case (48.6% cytolysis). None of the remaining eight patients exhibited LAK activity against autologous leukemia cells. On the other hand, patients' LAK could lyse allogeneic leukemia cells including those resistant to autologous LAK. Thus, patients' LAK seem not to be defective in lysis of leukemia cells. In the cold target competition analysis, the binding of patients' LAK to leukemia cells could be inhibited by autologous and allogeneic leukemia cell competitors, implying that almost all leukemia cells could be recognized by patients' LAK. Most LAK cells from normal donors showed significant lysis of allogeneic leukemia cells, but some leukemia cells were found to be resistant to lysis. LAK cells against both leukemia cells and Daudi 1A4 were phenotypically heterogenous, and were predominantly observed in the T3(−) fraction in the precursor phase. In the effector phase, whereas LAK activity against leukemia cells was also predominantly shown in the T cell‐depleted fraction, similar levels of LAK activity against Daudi 1A4 were found in both the T cell‐depleted and ‐enriched fractions.