ABSTRACT
One of the most important problems in tumor immunology studies is the in vivo role of natural killer (NK) cells and, as a consequence, the regulation of NK cell development and activity. It has been demonstrated that cells and soluble factors, including cytokines and hormones, are able to modulate NK activity by regulating both the reactivity of mature effector cells and the growth and differentiation of their precursors. One of the most interesting aspects of the in vitro generation of NK cells was the study of the role of different soluble factors, possibly involved in this process. In fact, while interleukin (IL)-2 was necessary for NK cell generation it is clear that other factors are involved in the first phase of differentiation and acquisition of IL-2-responsiveness. This suggests that, as in the rat, differentiation of mouse NK cells in addition to IL-2 needs other factors which are present in the CM.
