ZAP-70 expression identifies a chronic lymphocytic leukemia subtype with unmutated immunoglobulin genes, inferior clinical outcome, and distinct gene expression profile

Abstract

The presence or absence of somatic mutations in the expressed immunoglobulin heavy chain variable regions (IgVH) of chronic lymphocytic leukemia (CLL) cells provides prognostic information. Patients whose leukemic cells express unmutated IgVH regions (Ig-unmutated CLL) often have progressive disease, whereas patients whose leukemic cells express mutated IgVH regions (Ig-mutated CLL) more often have an indolent disease. Given the difficulty in performing IgVH sequencing in a routine diagnostic laboratory, this prognostic distinction is currently unavailable to most patients. Pilot gene expression profiling studies in patients with CLL identified genes that were differentially expressed between the Ig-unmutated and Ig-mutated CLL subtypes. Here, we have profiled an expanded cohort of 107 patients and show that ZAP-70 is the gene that best distinguishes the CLL subtypes. Ig-unmutated CLL expressed ZAP-70 5.54-fold more highly than Ig-mutated CLL (P < 10 -21 ). ZAP-70 expression correctly predicted IgVH mutation status in 93% of patients. ZAP-70 expression and IgVH mutation status were comparable in their ability to predict time to treatment requirement following diagnosis. In 7 patients, ZAP-70 expression and IgVH mutation status were discordant: 4 Ig-mutated CLLs had high ZAP-70 expression and 3 Igunmutated CLLs had low ZAP-70 expression. Among these ZAP-70 "outliers," those with Ig-mutated CLL had clinical features that are uncharacteristic of this CLL subtype: 2 required early treatment and 2 used a mutated VH3-21 gene, an IgVH gene that has been associated with progressive disease. We developed reverse transcriptase-polymerase chain reaction and immunohistochemical assays for ZAP-70 expression that can be applied clinically and would yield important prognostic information for patients with CLL. IntroductionThe clinical course of chronic lymphocytic leukemia (CLL) is heterogeneous. [1][2][3] Although some patients have an indolent disease without any need for therapeutic interventions, other patients may succumb rapidly despite intensive treatment. There has been an intense search for good prognostic markers in early-stage disease that might facilitate risk-adapted treatment strategies. 4,5 Although cytogenetic abnormalities, especially deletions of 11q and 17p, have been shown to correlate with short survival, 6,7 these changes may not be present in early disease and may only be acquired during disease progression. 8 The presence or absence of somatic mutations in the variable region of the B-cell-receptor heavy chain gene (IgVH) has been shown to distinguish between 2 disease subsets conferring important prognostic information. 9,10 Median survival in patients whose CLL cells express unmutated IgVH genes (Ig-unmutated CLL) ranges between 79 and 119 months. 7,[9][10][11] In contrast, patients whose CLL cells express mutated IgVH genes (Ig-mutated CLL) have a distinctly longer median survival, reaching 293 months in one study, and many may never require treatment. 11 Several lines of evidence indicate that th...

Immunohistochemical detection of ZAP-70 in 341 cases of non-Hodgkin and Hodgkin lymphoma

“…In recent studies, increased ZAP-70 mRNA has been demonstrated in a subset of CLL/SLL cases lacking somatic hypermutation in their IgV genes. [2][3][4] Somatic hypermutation of the Ig genes is a diversification mechanism activated in B cells at the germinal center stage of differentiation. 20 Since somatic hypermutation is a hallmark of B cells which have passed through the germinal center, some investigators have postulated that CLL/SLL associated with unmutated IgV genes is derived from naïve, pre germinal B cells and that CLL/SLL with mutated IgV genes is derived from post germinal B cells.…”

“…However, ZAP-70 is expressed in a subset of cases of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) with unmutated immunoglobulin heavy-chain variable region (IgV H ) genes and is associated with poor clinical outcome. [2][3][4] Few reports have examined ZAP-70 protein expression by immunohistochemical methods in CLL/SLL, and ZAP-70 expression patterns in other types of nonHodgkin and Hodgkin lymphoma has not been defined.…”

Impact of flow cytometry on the diagnosis and characterization of lymphomas, chronic lymphoproliferative disorders and plasma cell neoplasias

“…However, once critical genes and their products are recognized, it may be possible to identify or generate antibodies that can easily detect and quantitate these products or their surrogates using FCM. This course of action has already begun (13,14).…”

Redundant role for Zap70 in B cell development and activation

“…Patients with CLL cells expressing mutated immunoglobulin V H genes (M-CLL) have a good prognosis, whereas those whose CLL cells express unmutated V H genes (U-CLL) have a more aggressive disease with poorer clinical outcome and require more treatment [18,19]. Gene expression profiling has identified key differences between these two disease subtypes and, remarkably, expression of Zap70 is the strongest predictor of the aggressive subtype with poor clinical outcome [20][21][22]. While most M-CLL cases do not express Zap70, a majority of U-CLL cases express the kinase.…”