Effect of interleukin 2 on cytotoxic effectors: II. Long-term culture of NK cells

The present study reports the establishment of an NK (natural killer) cell line, designated as IL2-CE1. This cell line was maintained in active growth in culture with the supplementation of interleukin 2 (IL2). The cells gave cytotoxicity against a variety of murine tumors. There was no detectable cytotoxicity against three human tumors tested. The reactivity obtained with the murine tumors was generally correlated with the sensitivity of these tumor cells to NK cytotoxicity. With few exceptions, the reactivity was much higher for NK-sensitive targets like YAC and RL♂ 1 cells. There was very little cytotoxicity against NK-resistant targets like P815 and HFL/d. The reactivity of the effectors against YAC was susceptible to trypsin treatment and this effect was reversible. In determining the surface markers of IL2-CE1 cells, it was shown that over 90% of the cells had Thy-1.2 antigen despite their resistance to the lytic effect of anti-Thy-1.2 antibody. There were no detectable surface Ig or Fc receptors. Therefore, the IL2-CE1 cells were consistent with being NK cells. Although these cells gave high levels of cytotoxicity against murine tumors, in the tumor neutralization tests the IL2-CE1 cells failed to give any protection against an immunosensitive leukemic line, FBL-3. After the IL2-CE1 cells were cloned, it was found that different NK clones showed variations in their fine specificity. Our finding supports the presence of different populations or subsets of NK cells. Establishment of these NK clones in long-term culture should be helpful for the detailed characterization of the NK cells and aid in the determination of their significance in the immune surveillance against neoplasia.