siRNA effectively depletes ZAP-70 without affecting Syk expression in primary CLL cells. (A) Representative ZAP-70 and β-actin immunoblots of primary CLL cells at the indicated time points post-siRNA nucleotransfection with a nonspecific siRNA and ZAP-70 siRNA. (B) Quantification of ZAP-70 expression using ImageJ and calculated as a ratio (siZAP-70/NSC) after normalization to β-actin signal. Time points indicate time after nucleofection (n = 3). (C) Percentage of live (Annexin V⁻, DAPI⁻) CLL cells on day 7 of transfection. Primary CLL samples (n = 7) were transfected with NSC siRNA or ZAP70 siRNA and cultured for 7 days on stroma cells. (D) Representative immunoblots of ZAP-70, Syk, and β-actin of primary purified CLL cells 7 days post-siRNA transfection. (E) Quantification of ZAP-70 and Syk expression, normalized to β-actin, 7 days post-siRNA transfection (n = 7). Statistical analyses were performed using 1-way analysis of variance followed by a 2-tailed paired Student t test. **P < .01. ns, not significant (P > .05).