Stereotyped Subset #4 In Chronic Lymphocytic Leukemia Is Associated With Distinct Gene and Microrna Transcriptional Profile

Chronic lymphocytic leukemia (CLL) is a lymphoproliferative disorder characterized by the monoclonal accumulation of B lymphocytes and a variable clinical course. Specific B-Cell Receptor (BCR) utilized by leukemic cells may influence disease progression and outcome. Highly homologous BCR, “stereotyped BCR”, are expressed in a recurrent fraction of patients with CLL and in some cases they were associated with distinct biological and clinical features. Stereotyped subset #4 have been reported to exhibit a favorable clinical course and to be the most frequent stereotyped BCR among the IGHV mutated (IGHV-M) cases. In this study we performed a comprehensive clinical, biological and molecular characterization of leukemic cells from 16 patients utilizing stereotyped subset #4 BCR (IGHV4-34) among a representative prospective cohort of 462 Binet stage A CLL patients enrolled in O-CLL1 protocol (clinicaltrial.gov identifier NCT00917540). In all cases, biological and molecular analyses were performed in peripheral CD19⁺ B-cells. All subset #4 patients were characterized by lower CD38 expression, unique IGHV-M configuration and absence of NOTCH1 and SF3B1 mutations. None subset #4 patients showed unfavorable cytogenetic deletions (i.e del11q23 and del17p13). Gene expression profiling (GEP) analysis was performed on 217 patients, including 9 subset #4 cases for whom RNA material was available. Supervised analysis comparing subset #4 vs all other patients (208) revealed 14 differentially expressed genes. Furthermore subset #4 patients were characterized by a significant downregulation of WDFY4, MEF2A and upregulation of PDGFA, FGFR1 and TFEC genes when compared with the remaining IGHV-M patients. miRNA profiles were analyzed in 229 patients including 10 subset #4 patients for whom RNA material was available. A specific miRNA expression pattern involving the upregulation of miR-497 and miR-29c was found in subset# 4 cases. Furthermore, we demonstrated that transfection of the miR-497 mimic in primary leukemic CLL cells induces, after 48 and/or 72 h, a downregulation of BCL2, known to be a validated target in different solid cancers. Our data provide a contribution to the biological definition of CLL patients with specific stereotyped IGHV4-34 BCR and identify for the first time distinct gene and miRNA expression profiles associated with this subset, providing further evidence of the putative leading role of HCDR3 conformation in CLL.