Kinetic study of IK mRNA expression during growth factor–induced CD34⁺ proliferation and differentiation. Isolated CD34⁺ cells were cultured in IMDM containing 10% FCS and a combination of 7 cytokines (IL-1, IL-3, IL-6, SCF EPO, G-CSF, and GM-CSF ). At the indicated times from day 0 to day 8, cells were harvested to study IK expression by semiquantitative RT-PCR. The ratio of IK to GAPDH signals for each sample was 9.6%, 11.2%, 35.9%, 103.6%, 151.6%, and 72.8% from day 0 to day 8.