HUMAN NATURAL-KILLER (NK) CELLS - REQUIREMENTS FOR CELL-PROLIFERATIONAND EXPANSION OF PHENOTYPICALLY NOVEL SUBPOPULATIONS

Previous studies established that the high density (resting) natural k iller (NK) cell subset (R-NK) of peripheral blood NK cells is unrespon sive to interleukin-2 (IL-2) but can be induced to proliferate when cu ltured with gamma-irradiated malignant melanoma (MM-170) cells or mito mycin-C-treated activated T cells in the presence of an IL-2-condition ed medium (IL-2-CM). This study has examined additional requirements o f this activation process. The induction of proliferation was dependen t on cell to cell contact with metabolically active stimulator cells, although no evidence was obtained that stimulation was effected by sol uble factors produced by the stimulator cells. Compared with IL-2-CM, rIL-2 was an inefficient costimulator for the induction of NK cell pro liferation, suggesting that factors in IL-2-CM were required in additi on to IL-2, but rIL-2 was as efficient as IL-2-CM in maintaining the p roliferation of activated NK cells. Under optimum culture conditions, NK growth of up to 3200-fold occurred during a proliferation cycle of 18 days. Phenotypic analysis of the culture-generated quiescent NK cel ls revealed novel heterogeneity in CD16 (FcgammaRIII) and CD56 (N-CAM) expression. Some NK cells lacked expression of both CD16 and CD56 (as identified using currently available monoclonal antibodies), while ot her NK cells showed differential CD16 epitope expression. Since quiesc ent NK cells can be obtained in large numbers and high purity, they wi ll be a convenient source of NK cells to study the molecular processes involved in initiating NK cell proliferation.