ZAP-70 Expression, VH-Mutation Status, Genomic Aberrations and Prognosis in Chronic Lymphocytic Leukemia.

The VH status is a strong prognostic marker in chronic lymphocytic leukemia (CLL). ZAP-70, a zeta associated tyrosine kinase physiologically expressed by T-cells, is overexpressed in VH unmutated CLL and could therefore serve as a surrogate marker for the VH status. We analyzed ZAP-70 expression (n=96), the VH status (n=75) and genomic aberrations (n=84) in a single center CLL cohort to study associations among these parameters and to assess their relative prognostic value. ZAP-70 expression was measured by 4-colour flow cytometry (CD5, CD19, CD3/56, ZAP-70) applying an unconjugated anti-ZAP-70-antibody (Upstate, clone 2F3.2) according to Crespo et al., NEJM 2003. ZAP-70 expression was positive (cut-off 20%) in 67% and negative in 33% of cases. VH was mutated in 33% and unmutated in 67% of cases. Unfavorable genomic aberrations (17p−, 11q−) were more frequently observed in cases with unmutated VH (46 vs. 9%) and in ZAP-70 positive cases (39 vs. 20%), while favorable genomic aberrations (13q− as single aberration) occurred more frequently in VH mutated (48 vs. 17%) and ZAP-70 negative subgroups (50 vs. 18%). ZAP-70 expression predicted the VH status in 84% of cases. At a median follow up time of 47 months (m), the median treatment free survival (TFS) of ZAP-70 positive and negative cases was 31 and 86 m (p=.057). The median TFS of the VH unmutated and VH mutated subgroups were 24 and 172 m (p<.001). Within the follow up time 10 deaths occurred. Of these, 8 cases exhibited high ZAP-70 expression and an unmutated VH, whereas 2 cases showed discordant results. Overall, discordant results for ZAP-70 expression and VH status were identified in 12 cases (ZAP-70 positive/VH mutated, 8 cases; ZAP-70 negative/VH unmutated, 4 cases). Of the 8 VH mutated cases with high ZAP-70 expression, only 1 case exhibited unfavorable genomic aberrations, 4 remained in stable disease, 4 developed progressive disease, 3 patients required therapy, and 1 of these 3 died within follow up time. Two of the 3 patients who required therapy, including the patient who died, showed a mutated V3-21 gene rearrangement, associated with an unfavorable outcome. Among the 4 cases with an unmutated VH and low ZAP-70 expression, 2 cases exhibited unfavorable genomic aberrations, 3 cases required therapy, 1 of these 3 died, and for one patient no clinical data were available. In summary, the imbalanced distribution of high risk genomic aberrations was similar when comparing the subgroups according to ZAP-70 expression and VH status. In our series an unmutated VH status predicted for shorter TFS, whereas high ZAP-70 expression did not reach significance. ZAP-70 expression was associated with unmutated VH, but a substantial number of cases showed discordant results for ZAP-70 expression and VH status. The pattern of genomic aberrations and the clinical course of the discordant cases were typical for their respective VH status. Compared to ZAP-70 expression the VH status appeared to be more informative in the prediction of the clinical course in our series of CLL patients.