Lack of inhibition of the TPO-induced differentiation response by GF109203X. UT-7/mpl 1101C cells were incubated for 4 days with either 2 ng/mL GM-CSF (left), 2 ng/mL GM-CSF + 10 nmol/L PMA TPO (center), or with 10 nmol/L TPO (right), in the absence or presence of 3 μmol/L GF109203X. GpIIb expression and DNA content were analyzed by flow cytometry as described in Materials and Methods. In the top panels the open traces correspond to the fluorescence distributions of samples stained with a control IgG1, and the filled traces correspond to parallel samples stained with the MoAb Tab.