Somatic Hypermutational Status and Gene Repertoire of Immunoglobulin Rearrangements in Chronic Lymphocytic Leukemia

Abstract

Immunoglobulin molecule is the key component of B cell receptor (BCR), which governs the survival, differentiation and function of normal B lymphocytes, but accu‐ mulating data suggest that, in the case of chronic lymphocytic leukaemia (CLL), it is also involved in the pathogenesis and clinical course of the disease. CLL is a malig‐ nancy of mature CD5+ CD19+ CD23+ sIgMlow B lymphocytes and is characterized by extremely heterogeneous clinical course, which varies from indolent to rapidly pro‐ gressive. Somatic hypermutational status of immunoglobulin heavy chain variable genes (IGHV) defines two CLL subtypes, mutated (M‐CLL) and unmutated (U‐CLL). U‐CLL patients suffer from more aggressive disease, characterized by shorter time to treatment, progression‐free survival and overall survival in comparison to M‐CLL patients. Since these correlations are not dependent on the clinical stage and since there is no interconversion between subtypes, IGHV mutational status is currently the most reliable prognostic marker in CLL. Several lines of evidence indicate that both M‐CLL and U‐CLL arise from an antigen‐experienced cell of origin. Immunogenetic studies have revealed CLL‐biased usage of immunoglobulin variable region genes, as well as the existence of highly homologous, ‘stereotyped’ BCRs in CLL clones, strongly implying the role of antigenic drive in the development and evolution of the disease. Keywo