Lenalidomide therapy induces p21 expression in CLL cells in vivo. (A-B) CLL blood mononuclear cells from 5 different patients were collected prior therapy (Pre) and 15 days after lenalidomide treatment (Post). All patients received 2.5 mg daily for the first 7 days, and 5 mg daily for the subsequent 7 days. Protein were extracted from all samples and analyzed for p21 and GAPDH expression by immunoblot. (A) Shows the immunoblot data for all 5 patients tested. (B) Shows the densitometry analysis quantifying the expression of p21 protein in the 5 patient samples shown in (A). The expression of p21 has been normalized to GAPDH. **P < .001 (Student t test).