CDK9 and acute myeloid leukemia: Finally the Gandhi laboratory reported, although in CLL not AML, that stroma-driven resistance to apoptosis of CLL cells was associated with a cascade of transcriptional events that included increased phosphorylation of RNA Pol II on serine residues at positions 2 and 5 (the phosphorylation site of CDK9), leading to increased rate of global RNA synthesis, and amplification of Mcl-1 transcript levels55.