Mutated IgHV1-69 gene usage represents a distinct subgroup associated with indolent disease in chronic lymphocytic leukemia

Abstract

Biased IgHV gene usage in chronic lymphocytic leukemia (CLL) is well documented and suggests antigen involvement in leukemogenesis. IgHV1-69 is one of the most frequently rearranged IgHV genes in CLL and the majority of IgHV1-69 cases lack somatic hypermutation and display poor prognosis. However, its independent prognostic impact remains uncertain given reports showing a low proportion of mutated IgHV1-69 cases and stereotyped IgHV1-69 subsets with divergent clinical outcome. We assessed the frequency and clinical significance of IgHV1-69 gene usage in a cohort of 330 CLL patients. Functional IgHV1-69 gene rearrangements were detected in 32 cases (9.7%), 31 of which were characterised further. Seven (22.6%) were found to have undergone somatic hypermutation. This subgroup had shorter and more diverse complementarity determining region 3 (CDR3) sequences compared with unmutated IgHV1-69 cases. In addition, mutated IgHV1-69 gene status was associated with lower cell surface CD38 expression and less progressive disease as monitored by Binet staging, lymphocyte doubling time and requirement of chemotherapeutic intervention. To conclude, we present data confirming that IgHV1-69 gene rearrangements in CLL are not exclusively associated with unmutated IgHV status. In addition, we show that a somatically hypermutated subgroup may demonstrate more indolent characteristics despite the general association of IgHV1-69 gene usage with aggressive disease.

Keywords:

• CLL
• IgHV gene usage
• somatic hypermutation
• CDR3
• prognosis