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Chronic lymphocytic leukemia (CLL) is characterized by low CD20 expression, in part explained by an epigenetic-driven downregulation triggered by mutations of the NOTCH1 gene. In the present study, by taking advantage of a wide and well-characterized CLL cohort (n=537), we demonstrate that CD20 expression is downregulated in SF3B1-mutated CLL to an extent similar to NOTCH1-mutated CLL. In fact, SF3B1-mutated CLL cells show common features with NOTCH1- mutated CLL cells, including a gene expression profile enriched in NOTCH1-related gene sets and elevated expression of the active intracytoplasmic NOTCH1. Activation of the NOTCH1 signaling and downregulation of surface CD20 in SF3B1-mutated CLL cells correlate with overexpression of an alternatively spliced form of DVL2, a component of the Wnt pathway and negative regulator of the NOTCH1 pathway. These findings were confirmed by separately analyzing the CD20dim and CD20bright cell fractions from SF3B1-mutated cases as well as by DVL2 knockout experiments in CLL-like cell models. Together, the clinical and biological features that characterize NOTCH1-mutated CLL may also be recapitulated in SF3B1-mutated CLL, contributing to explain the poor prognosis of this CLL subset and providing the rationale for expanding therapies based on novel agents to SF3B1-mutated CLL.

In chronic lymphocytic leukemia the balance between the pro-apoptotic and anti-apoptotic members of the bcl-2 family is involved in the pathogenesis, chemorefractoriness and clinical outcome. Moreover, the recently proposed anti-bcl-2 molecules, such as ABT-199, have emphasized the potential role of of bcl-2 family proteins in the context of target therapies. We investigated bax/bcl-2 ratio by flow cytometry in 502 patients and identified a cut off of 1.50 to correlate bax/bcl-2 ratio with well-established clinical and biological prognosticators. Bax/bcl-2 was 1.50 or over in 263 patients (52%) with chronic lymphocytic leukemia. Higher bax/bcl-2 was associated with low Rai stage, lymphocyte doubling time over 12 months, beta-2 microglobulin less than 2.2 mg/dL, soluble CD23 less than 70 U/mL and a low risk cytogenetic profile (P