Differentiation of NK1.1+, Ly49+ NK Cells from flt3+ Multipotent Marrow Progenitor Cells

Abstract

AbstractTo delineate factors involved in NK cell development, we established an in vitro system in which lineage marker (Lin)−, c-kit+, Sca2+ bone marrow cells differentiate into lytic NK1.1+ but Ly49− cells upon culture in IL-7, stem cell factor (SCF), and flt3 ligand (flt3L), followed by IL-15 alone. A comparison of the ability of IL-7, SCF, and flt3L to generate IL-15-responsive precursors suggested that NK progenitors express the receptor for flt3L. In support of this, when Lin−, c-kit+, flt3+ or Lin−, c-kit+, flt3− progenitors were utilized, 3-fold more NK cells arose from the flt3+ than from the flt3− progenitors. Furthermore, NK cells that arose from flt3− progenitors showed an immature NK1.1dim, CD2−, c-kit+ phenotype as compared with the more mature NK1.1bright, CD2+/−, c-kit− phenotype displayed by NK cells derived from flt3+ progenitors. Both progenitors, however, gave rise to NK cells that were Ly49 negative. To test the hypothesis that additional marrow-derived signals are necessary for Ly49 expression on developing NK cells, flt3+ progenitors were grown in IL-7, SCF, and flt3L followed by culture with IL-15 and a marrow-derived stromal cell line. Expression of Ly49 molecules, including those of which the MHC class I ligands were expressed on the stromal or progenitor cells, as well as others of which the known ligands were absent, was induced within 6–13 days. Thus, we have established an in vitro system in which Ly49 expression on developing NK cells can be analyzed and possibly experimentally manipulated.