Landscape of immunoglobulin heavy chain γ gene class switch recombination in patients with adult T-cell leukemia–lymphoma

摘要

We are currently conducting the multicenter prospective study “Monitoring of immune responses following mogamulizumab-containing treatment in patients with adult T-cell leukemia–lymphoma (ATL)” (MIMOGA), (Trial registration number: UMIN000008696).1-4 We previously reported the importance of humoral immune measures, such as the proportion of CD2-CD19+ B cells in peripheral blood mononuclear cells (PBMC), for the outcome of ATL patients.5 Subsequently, we demonstrated that lower immunoglobulin G (IgG) B-cell diversity in PBMC was a significant unfavorable prognostic factor for overall survival (OS) in patients.6 In that study, we had focused on the diversity-generating mechanism for the IgG variable regions. Therefore, here we focused on the diversity-generating mechanism in the IgG constant region, namely class switch recombination (CSR),7- 9 and explored its detailed status in ATL patients. The present investigation was affiliated with the MIMOGA study, and 81 ATL patients were enrolled according to the criteria used in that previous study.5,6 Unbiased amplification and high-throughput sequencing of the immunoglobulin heavy chain γ (IGHG) genes was conducted using PBMC at enrollment in the MI-MOGA study.6,10 The sequence reads whose immunoglobulin heavy chain constant (IGHC) region was determined to be assigned to immunoglobulin heavy constant γ P were excluded from the analysis. IGHG unique reads, with identical IGHV (variable), IGHD (diversity) and IGHJ (joining) gene usage and identical deduced amino acid sequences of the CDR3 complementarity determining region 3 (CDR3), were designated “VDJ/CDR3 identical unique reads”. Among IGHG unique reads in PBMC, the percentage of VDJ/CDR3 identical reads which were shared between two or more different subclass genes was designated “the percentage of CSR of IGHG unique reads in PBMC”, abbreviated to “CSR of IGHG”. In practice, the CSR of IGHG was calculated as follows: the total number of VDJ/CDR3 identical unique reads which were shared between two subclass genes (IGHG3-IGHG1, IGHG3-IGHG2, IGHG3-IGHG4, IGHG1-IGHG2, IGHG1-IGHG4, or IGHG2-IGHG4), or three subclass genes (IGHG3-IGHG1-IGHG2, IGHG3-IGHG1-IGHG4, IGHG3-IGHG2-IGHG4, or IGHG1-IGHG2-IGHG4), or four subclass genes (IGHG3-IGHG1-IGHG2-IGHG4) was divided by the total number of IGHG unique reads.