ZAP-70 protein expression and CD38 positivity in B-cell chronic lymphocytic leukemia.

Background: The clinical course, disease progression, and survival of B-cell chronic lymphocytic leukemia (B-CLL) have been correlated with immunoglobulin heavy-chain variable region mutation status. The biologic parameters 70-kDa zeta-associated protein (ZAP-70) and CD38 expression are easier and faster surrogate markers for mutational status.

Objective: To assess retrospectively ZAP-70 expression in B-CLL cells using flow cytometry and examine its relationship with CD38 expression and the median time from diagnosis to initial therapy.

Methods: Ninety-four unselected patients who had their follow-up in the outpatient clinic from 2004 to 2005 were reviewed for immunophenotyping ZAP-70 and CD38 expression. Direct immunolabeling with clone 2E3.2, isotype IgG2a, enabled easy quantification of ZAP-70 by flow cytometry in association with CD38 expression; in addition, the mean fluorescence intensity ratio (MFIR) of CD19+CD5+ B-CLL cells compared to an isotype control monoclonal antibody was determined.

Results: ZAP-70 expression levels in B-CLL cells varied widely (0.3-99%). The median time to therapy was significantly shorter for the 54 patients with 20% or more ZAP-70+ cells (30 months) than for the 40 patients with less than 20% ZAP-70+ cells (median time to treatment not reached). The optimal MFIR for classifying patients as ZAP-70+ was 2. Thirty-two patients had a threshold of ZAP-70+CD38+ greater than 30%, with a median time from diagnosis to treatment of 19 months. Regardless of CD38 expression level, CD38 and ZAP-70 expressions were significantly associated. The median interval from diagnosis to initial therapy was 16.2 months for ZAP-70+CD38+ patients, 60 months for ZAP-70+CD38- or ZAP-70-CD38+ patients, and had not yet been reached for ZAP-70-CD38- patients.

Conclusion: The association of ZAP-70+CD19+CD5+ B-CLL cells and percentage of CD38+CD19+CD5+ B-CLL cells evaluated by flow cytometry provide reliable methods that could be introduced into a routine diagnostic B-CLL panel to predict outcome.