Variable heavy-chain gene analysis of follicular lymphomas: subclone selection rather than clonal evolution over time

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Abstract
To investigate B-cell receptor evolution in follicular lymphomas (FLs), immunoglobulin variable heavy chain (VH) gene regions of 3 FLs were analyzed at different time points. One FL with a high somatic mutation load and intraclonal VH gene diversity was investigated in situ. VH gene transcripts were amplified and sequenced from samples of approximately 50 tumor cells isolated from frozen tissue sections by laser microdissection. Interestingly, the mutation pattern of the prevalent subclone in the relapse biopsy was virtually identical to that of a subclone isolated by microdissection from the presentation biopsy 9 years earlier. In a second FL, proof was obtained that the subclone that dominated the relapse sample had already been present in the initial biopsy. The finding that subclones found in the relapses of these FLs had not evolved over time but were preexistent, challenges the concept of antigen-driven B-cell receptor evolution during disease course.