STAT3 and diffuse large B-cell lymphoma: We then focused on DLBCL and measured the level of STAT3 phosphorylation, a target of CDK5,16 at serine 727 (S727) in samples of DLBCL cells: as expected, DLBCL cell lines showed a higher level of phosphorylation compared to B lymphocytes (Figures 1a and d).