• Shohei Kikuchi, Akinori Wada, Yusuke Kamihara, Yoshimi Nabe, Tomoki Minemura, Jun Murakami, Nam H Dang, and Tsutomu Sato.
• Department of Hematology, Toyama University School of Medicine, Toyama, Japan.
• Medicine (Baltimore). 2022 Dec 23; 101 (51): e32260e32260.

AbstractBiclonal gammopathy (BG) is a rare phenomenon in which 2 M proteins are detected in the same patient, with 2 major hypotheses regarding its etiology. One potential explanation is that completely different malignant B-cell clones produce different M proteins, while the other is that there is a malignant clone that produces both M proteins simultaneously. In this study, we examined 2 cases of B-cell malignancy with BG and found that some cells were double positive for both M proteins by immunofluorescence and flow cytometry. However, most of the remaining cells were single positive cells that produced only one of the M proteins. We hypothesized that double positive cells were in the process of transitioning from 1 single positive cell to another single positive cell, and that class switch recombination (CSR) would be involved as a mechanism. We then examined the expression of activation induced cytidine deaminase (AICDA), which is responsible for CSR, and found that lymphoma/myeloma cells in 2 BG patients were positive for AICDA by immunostaining. Our study is the first report suggesting that AICDA may be involved in the pathogenesis of BG.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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