Degradation of ZAP-70 mediated by Hsp90 inhibitors is specific and is not induced by cytotoxic chemotherapy in vitro. ZAP-70⁺ and ZAP-70^-CLL cells (n = 10) were treated with 17-AAG (100 nM) and 2-Fluoro-Ara-A (2.5 μM) for 48 hours. Flow cytometry was used to assess apoptosis (top panels) and ZAP-70 expression (bottom panels) on each sample. Control samples were incubated with media-DMSO as indicated. Error bars indicate the mean value for each group. P values were calculated using a one-way analysis of variance (ANOVA) with Bonferroni posttest analysis.