RT-PCR of individual granulocyte-macrophage colonies derived from CML cells after culture in the pre-CFU assay. (A) Lanes 1 to 10: PCR of ten individual colonies derived from cells cultured in SCF alone for 14 days, then transferred into the CFU-GM assay for 14 days. Lane 11 is a CFU-GM culture medium negative control. (B) Lanes 1 to 8: PCR of eight individual colonies derived from cells cultured in 4HGF for 14 days, then transferred into the CFU-GM assay for 14 days. Lane 9 is a CFU-GM culture medium negative control.