LDA of NK cell precursor frequency within freshly isolated CD34⁺ HPCs (day 0) or CD34⁺ HPCs cultured for 21 days in KL (day 21/KL) or FL (day 21/FL). CD34⁺ HPCs cultured in KL (*P ≤ .005) or FL (**P ≤ .002) had significantly increased NK cell precursor frequency compared with freshly isolated CD34⁺ HPCs. In addition, the 21-day/FL cultures had significantly greater NK cell precursor frequencies when compared with 21-day/KL culture (#P≤ .01). The results represent the mean ± SEM of three independent experiments.