Gene expression comparison between B cells expressing high and low level of Zap-70 mRNA reveals distinct profiles, potential therapeutic targets and new prognostic factors for Chronic Lymphocytic Leukemia

Stamatopoulos B, Equeter C, Haibe-Kains B, Soree A, Sotiriou C, Bron D, Martiat P, Lagneaux L

Background: Chronic Lymphocytic Leukemia (CLL) is a heterogeneous disease characterized by a highly variable clinical course based on the IgVH mutational status currently considered as one of the powerful prognosis factors. Because of the complexity of this analysis, several surrogate genes of this mutational status have been found in the recent years, among them Zap-70 seems to be a reliable prognostic factor.

Methods: We compared three predictive markers (Zap-70, lipoprotein lipase and CD38 expression) in term of treatment-free (TFS) and overall (OS) survival and finally Zap-70 (zeta-associated protein 70) was chosen because of its strong association with the IgVH status and high prognostic values. We developed a quantitative real time PCR to measure Zap-70 mRNA expression in a cohort of 100 patients and to classify patients with high and low Zap-70 expression. Gene expression profiles of high (Zap-70high, n=7) and low (Zap-70low, n=7) mRNA expression were then compared using Affymetrix U133 plus 2.0 genechips representing more than 47000 transcripts.

Results: Among genes differently expressed (P<0.05), only genes with a fold change upper of 1.5 and with a false discovery rate (FDR) lower than 10% were selected. Zap-70, the first gene of the list, was followed by the phosphodiesterase 8A (PDE8A, P<0.0001), integrin alpha 4 (ITGA4, P<0.0001) and some genes of Fc receptor like family (FCRL, P<0.0001). These genes were confirmed in an extended patient cohort (n=80) and were able to separate the patients in term of TFS indicating their relevant clinical predictive power.

Conclusion: CLL cells expressing high and low level of Zap-70 mRNA are characterized by a distinct gene expression profile that reveals new potential therapeutic target, new prognostic factors and genes implicated in cellular activation, adhesion and migration.