Lymphoma‐associated mutations in autoreactive memory B cells of patients with Sjögren's syndrome

We recently demonstrated that normal memory B lymphocytes carry a substantial number of de novo mutations in the genome. Here, we performed exome‐wide somatic mutation analyses of bona fide autoreactive rheumatoid factor (RF)‐expressing memory B cells retrieved from patients with Sjӧgren's syndrome (SS). The amount and repertoire of the de novo exome mutations of RF B cells were found to be essentially different from those detected in healthy donor memory B cells. In contrast to the mutation spectra of normal B cells, which appeared random and non‐selected, the mutations of the RF B cells were greater in number and enriched for mutations in genes also found mutated in B‐cell non‐Hodgkin lymphomas. During the study, one of the SS patients developed a diffuse large B‐cell lymphoma (DLBCL) out of an RF clone that was identified 2 years earlier in an inflamed salivary gland biopsy. The successive oncogenic events in the RF precursor clone and the DLBCL were assessed. In conclusion, our findings of enhanced and selected genomic damage in growth‐regulating genes in RF memory B cells of SS patients together with the documented transformation of an RF‐precursor clone into DLBCL provide unique novel insight into the earliest stages of B‐cell derailment and lymphomagenesis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.