Both Id3⁻ and Id3⁺ FL cells recovered after culture on S17 stroma retain the capacity to develop into NK cells. Cells harvested after coculture of transduced FL cells on a monolayer of S17 stroma were further cultured in a cytokine combination consisting of Flt-3L, IL-7, and IL-15. Ten days later, cell suspensions were analyzed by flow cytometry for cell surface expression of CD19 and CD56 antigens. The markers were set to exclude greater than 98% of cells stained with irrelevant control antibodies.