Somatic hypermutation profiles in stereotyped IGHV4-34 receptors from South American chronic lymphocytic leukemia patients

Abstract

Chronic lymphocytic leukemia (CLL) is the most common mature B-cell neoplasm in the West. IGHV4-34 is one of the most frequently used genes in CLL patients, which usually display an indolent outcome. In this study, we explored the mutational profile of CLL patients expressing IGHV4-34 within different stereotypes and their association with prognostic factors and clinical outcome. A multi-institutional cohort of unselected 1444 CLL patients was analyzed by RT-PCR and bidirectional sequencing. Cytogenetics and molecular cytogenetics analyses were also performed. We identified 144 (10%) IGHV4-34 expressing cases, 119 mutated (M), 44 of them with stereotyped B-cell receptors. Subset #4 was the most frequent (56.8% of cases) followed by subsets #16 (13.6%), #29 (6.8%), and #201 (2.3%), with different distribution among countries. Analysis of somatic hypermutation profile showed significant differences among stereotyped subsets for G28>D/E, P45>S, E55>Q, and S64>I changes (p < 0.01) and high frequency of disruption of the glycosylation motif in the VH CDR2 region. All stereotyped IGHV4-34 cases showed normal karyotypes. Deletion 13q14 as a sole alteration was present in 42.8% of stereotyped cases with a different distribution among subsets. A shorter time to first treatment was found in non-stereotyped vs. stereotyped M-IGHV4-34 patients (p = 0.034). Our results add new information supporting the importance of recurrent amino acid changes at particular positions, contributing to refine the molecular characterization of South American CLL patients.

Keywords: Chronic lymphocytic leukemia; IGHV4-34 gene; Mutational profile; Stereotyped receptors.