Flavopiridol induces ER stress in CLL cells. Real-time RT-PCR for XBP1, IRE1, GRP78, and CHOP in CLL cells (n = 10) collected from patients undergoing flavopiridol treatment. P values were calculated for comparisons between gene expression in pretreatment samples versus samples collected at the end of infusion (4.5 hours). P = .0008 for IRE1. P = .0016 for XBP1. P = .033 for GRP78. For all real-time RT-PCR experiments described here and in the following figures, we used CD52 as control housekeeping gene.