Expression of ZAP-70 Protein Correlates with Disease Stage in Chronic Lymphocytic Leukemia and is Associated with, but not Generally Restricted to, Non-mutated Ig VH Status

The mutational status of immunoglobulin variable region genes (Ig V H ) is a well established prognostic parameter in chronic lymphocytic leukemia (CLL). Recently, a subset of genes with a characteristic expression profilecorrelating with the mutational status of B-CLLs has been identified. One of the overexpressed genes in the prognostically unfavorable group of CLL patients with unmutated Ig V H genes encodes for the protein tyrosine kinase ZAP-70, which is physiologically involved in T-cell signaling. Since ZAP-70 has been described to be prognostically relevant in CLL, we analyzed the possible relationship of its expression to the mutational status of Ig V H genes as well as to other prognostic factors in CLL and indolent lymphomas The mutational status of Ig V H genes was analyzed by seminested PCR, direct sequencing and comparison with the sequences of the EMBL databases in 60 samples of patients with B-CLL and 18 samples of patients with indolent B-cell malignancies. ZAP-70 protein expression was assessed in all samples by immunoblotting and for semiquantitative analysis the ratio of ZAP-70 to tubulin expression was calculated. ZAP-70 protein was found to be expressed in all investigated B-cell malignancies. Expression levels varied within a wide range in each entity. The highest mean level of ZAP-70 expression was observed in unmutated B-CLLs, however, with broad expression variability. High levels of ZAP-70 expression correlated with higher stage Binet B or C and with unmutated Ig V H genes. Overall survival rates estimated by Kaplan-Meier curves did not differ among patients with high or low ZAP-70 expression. We conclude that ZAP-70 is associated with the mutational status of Ig V H genes, but this expression pattern is not present in all individual cases. Furthermore, high levels of ZAP-70 correlated with Binet stages B or C indicating an involvement of ZAP-70 in mechanisms promoting growth of B-CLL cells.