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. Disclosures: No relevant conflicts of interest to declare.