MCL1 and B-cell chronic lymphocytic leukemia: Moreover, a significant amount of phosphorylated STAT3 on Tyr705 was localized in the nucleus of CLL cells (Figure 1H,I), where this protein can exert its function as a transcription factor through the activation of pro-survival genes [40,41] and anti-apoptotic factors [3,4], such as Mcl-1 and Bcl-2 [7], both over-expressed in CLL (Figure S4), underpinning the role of STAT3 in CLL pathogenesis.