Effect of FL and KL on the proliferation of CD34⁺ CD38^dim cells and CD34⁺ CD38⁺ in liquid culture. CD34⁺ CD38^dim cells and CD34⁺ CD38⁺ cells from normal marrow were cultured in [IL-3 + IL-6] alone or with FL, KL, or [KL + FL]. The figure shows the maximum fold cell expansion obtained in each of 6 or 7 independent experiments as well as the mean ± SD for each condition. Note that the marked variability of CD34⁺ CD38^dim cell expansion in [IL-3 + IL-6 + FL] was largely overcome when cells were cultured in [IL-3 + IL-6 + KL + FL].