ZAP-70 EXPRESSION AS A SURROGATE FOR IMMUNOGLOBULIN-VARIABLEREGION MUTATIONS IN CHRONIC LYMPHOCYTIC LEUKEMIA

The mutational status of immunoglobulin heavy-chain variable-region (Ig VH) genes in the leukemic cells of chronic lymphocytic leukemia (CLL) is an important prognostic factor in this disease. We investigated whether the expression of ZAP-70 by CLL cells correlated with the Ig VH mutational status, disease progression, and survival. The expression of ZAP-70 was analyzed in T-cell and B-cell lines, and in the peripheral blood samples from 56 patients with CLL using flow-cytometry, western blotting, and immunohistochemistry. The results were correlated with the Ig VH mutational status and clinical outcome. ZAP-70 was detected by flow-cytometric analysis in the cells of the T-cell lineage and in the leukemic cells from 32 of 56 patients with CLL. In all patients in whom at least 20% of the leukemic cells were positive for ZAP-70, Ig VH gene was nonmutated, whereas Ig VH mutations were found in 21 of 24 patients in whom less than 20% of the leukemic cells were positive for ZAP-70 (p < 0.001). Concordant results were obtained when ZAP-70 expression was assessed by immunohistochemistry or western blotting. The level of ZAP-70 expression did not change over time (median, 37 months) in sequential samples from 30 patients with CLL. Patients with Binet stage A CLL who had at least 20% ZAP-70-positive leukemic cells experienced more rapid progression and poorer survival than those with less than 20% ZAP-70-positive cells. Among patients with CLL, the expression of ZAP-70, as detected by flow-cytometric analysis, correlated with Ig VH mutational status, disease progression, and survival.