NK cell colony formation from human fetal thymocytes

We established a clonal cell culture system for human natural killer (NK) c ells from fetal thymoctes . Thymocytes of 16 to 22 gestational weeks were c ultured in methylcellulose in the presence of interleukin (IL)-7, IL-15, an d steel factor (SF), After 14 days in incubation, large, diffuse colonies c onsisting of small cells,were identified. Cells in the colonies vr-ere medi um- to large-sized granular lymphocytes, expressing CD56 but not CD3, and r evealed lytic activity against K562 cells, Colony-forming units (CFU)NK wer e enriched in lineage negative (Lin(-)) CD34(++) subpopulations of fetal th ymocytes, whereas a smaller number of CFU-NK also existed in Lin(-)CD34(+) and Lin(-)CD34(-) subpopulations. Cytokine requirement for the WR cell colo ny formation was examined under serum-free conditions. As a single agent, o nly IL-15, but not IL-2, IL-7, or SF, supported NK cell colony formation. I L-15 had synergy with IL-7 and SF independently, and the maximal number of colonies were obtained when the three cytokines were present. IL-2 also sup ported NK cell colony formation in the presence of SF, When IL-2 was added to cultures containing IL-15 alone, IL-15 plus SF, or IL-15, SF, and IL-7, the numbers of NK cell colonies were reduced relative to those without IL-2 , These results indicate that IL-2 may regulate IL-15-responsive Nti cell p rogenitors. This clonal culture system will be a useful tool in the investi gation of NK cell ontogeny, (C) 1999 International Society for Experimental Hematology, Published by Elsevier Science Inc.