Development of natural killer cells from lymphohematopoietic progenitors of murine fetal liver.

We established a clonal culture system which supports the growth of murine immature natural killer (NK) cells. When we plated day 14 fetal thymocytes in methylcellulose media containing interleukin 2 (IL-2), IL-7 and steel factor (SF), we observed diffuse colonies which could not be classified into known colony types. Cells in the colonies were blast-like and expressed Thy-1 and CD25 but not lineage-specific markers. Cells in the colonies developed into NK1.1+ cells in fetal thymus organ culture indicating that the colonies consist of immature NK cells. We then examined the colony-forming ability of fetal liver cells. The combination of IL-2, IL-7 and SF with or without IL-11 supported formation of few immature NK cell colonies from purified progenitors. Interestingly, addition of IL-11 to the culture stimulated formation of mixed colonies consisting of immature NK cells, B cells, macrophages and/or mast cells. The clonal origin of the mixed NK cell colonies was confirmed by micromanipulation of the colony-forming cells. This culture assay should facilitate the analysis of the pathway and cytokine regulation of NK cell development.