Correlation of flow cytometrically determined expression of ZAP‐70 using the SBZAP antibody with IgVH mutation status and cytogenetics in 1,229 patients with chronic lymphocytic leukemia

Background: ZAP‐70 provides an important prognostic information in chronic lymphocytic leukemia (CLL); however, the most appropriate antibody clone and way of analysis have not yet been defined. Methods: We determined ZAP‐70 expression in 1,229 patients with CLL using the SBZAP clone by applying three different ways of analysis (% positive B‐cells, mean fluorescence intensity (MFI) in B‐cells, MFI ratio T‐cells:B‐cells). Results: ZAP‐70 expression was related to somatic hypermutation status of IgVH genes for all three ways of analysis ( P < 0.0001 each). The strongest correlation was found for MFI ratio ( r = −0.475, P < 0.0001); cases with mutated and unmutated IgVH status significantly differed in their mean MFI ratio (6.33 vs. 3.34, P < 0.0001). ZAP‐70 expression was weaker in sole del(13q) (5.44 vs. 4.44, P = 0.001) and stronger in del(11q) (3.31 vs. 5.29, P < 0.0001) and del(6q) (3.29 vs. 5.18, P = 0.005). MFI ratio was significantly related to time to therapy ( P = 0.004, RR = 0.79) in 221 evaluable cases. Multivariate analysis proved MFI ratio ( P = 0.043, RR = 0.64) and CD38 ( P = 0.047, RR = 1.20 per 10%) as only parameters independently related to time to therapy. Conclusions: Determination of ZAP‐70 expression using SBZAP and applying MFI ratio T‐cells:B‐cells results in significant relations to IgVH mutation status, cytogenetics, and outcome and should be further analyzed and considered for routine application in CLL. © 2009 Clinical Cytometry Society