Selective proliferation of natural killer cells among monocyte-depleted peripheral blood mononuclear cells as a result of stimulation with staphylococcal enterotoxin B.

In vitro stimulation of monocyte-depleted peripheral blood mononuclear cells with staphylococcal enterotoxin B (SEB) resulted in selective proliferation of cells which express the phenotypic and functional characteristics of natural killer (NK) cells. This culture system provides an easy method for obtaining highly purified NK cells, by sequential incubation of monocyte-depleted cells with SEB and then with interleukin-2 (IL-2). After culture for 4 to 5 days in the presence of SEB, 98 to 100% of the cells expressed the CD16 (Leu11) and HNK-1 (Leu19) antigens. This purification occurred through the death of lymphocytes lacking NK cell markers and marked proliferation of NK cells themselves, which leads to an enrichment of the NK cell population. Activation of NK cells was detected by the appearance of the gamma interferon receptor and IL-2 receptor antigens. This homogeneous population showed the morphology of large granular lymphocytes, were potent effectors of cell-mediated cytotoxicity against K562 and Daudi tumor cell lines, and were able to kill gram-positive and gram-negative bacteria. IL-2 was necessary to maintain the activation and proliferation after SEB stimulation for 4 days. Moreover, the maximum frequency of binding to K562 cells (60.6%) was similar to that recently found (58 +/- 3%) (P. Garcia-Peñarrubia, F. T. Koster, and A. D. Bankhurst, J. Immunol. Methods 118:199-208, 1989) with fresh and highly purified NK cells. This method can be used as a source of highly purified NK cells to study their functional properties and applications to the treatment of cancer.