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Somatic hypermutation and VH gene usage in mantle cell lymphoma

Abstract:  Mantle cell lymphoma (MCL) is considered to derive from naïve, pregerminal center (GC) CD5+ B‐cells. However, the cell of origin has been questioned in recent studies that showed somatic hypermutations in the immunoglobulin (Ig) variable heavy chain (VH) genes in subsets of MCL. To clarify this issue, we analyzed the IgVH genes for the presence of somatic hypermutations in 51 MCL cases. Twenty percent of the MCL cases displayed somatically mutated VH genes (defined as >2% mutated), whereas 80% showed unmutated VH genes. This finding suggests that MCL is a genetically heterogeneous disease, with the majority of cases originating from unmutated pre‐GC B‐cells and a subset deriving from more mature B‐cells which have been exposed to the GC environment and have undergone somatic hypermutation. A biased VH gene usage has been demonstrated in several B‐cell malignancies; however, this has not yet been investigated in MCL, although VH4‐34 overusage has been indicated by small studies. Interestingly, we found a restricted usage of three individual VH genes in our MCL material; VH4‐34 (22%), VH3‐21 (16%) and VH5‐51 (12%). This novel finding of preferential VH gene usage in half of the MCL cases may suggest an antigen driven process occurring in B‐cells expressing specific VH genes, thus implicating that Ig specificity could be involved in mantle cell lymphoma development.