Immunoglobulin class-switch recombination occurs in mantle cell lymphomas

Mantle cell lymphoma (MCL) is an IgM‐expressing B cell lymphoma that originates from naive B cells and responds poorly to chemotherapy. We show here that several MCLs harbour isotype‐switched subclones. Similar to the situation in normal B cells, in vitro stimulation of MCL cell lines with CD40 ligand (CD40L) and interleukin‐4 induced expression of activation‐induced cytidine deaminase (AID) and germline transcription at the immunoglobulin heavy chain gene locus. Additionally, the occurrence of switch‐circle transcripts and mature IgG transcripts after stimulation indicated ongoing class‐switch recombination in mantle cell lymphoma cell lines. Furthermore, stimulation of primary MCL cells in vitro induced expression of class‐switched IgG mRNA in the tumour cells. Our data indicate that mantle cell lymphomas have retained the ability to undergo class‐switch recombination if appropriate stimuli, such as the CD40 ligand, are provided. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.