Waldenström macroglobulinemia cells as models for the regulation of human IgM 2252298

Abstract Introduction Waldenström macroglobulinemia (WM) is a B cell lymphoma distinguished by the overproduction of a monoclonal IgM antibody and the lack of class switch recombination (CSR). Despite the presence of apparently normal CSR machinery, it remains unknown why WM B cells fail to undergo CSR or what mechanisms regulate the overproduction of IgM. To date, three WM cell lines (BCWM.1, MWCL-1, and RPCI-WM1) have been generated from different patients. Each cell line secretes a monoclonal IgM, though at varying levels. The regulation of human IgM transcription relies on studies of polyclonal B cells from tonsils or peripheral blood, making it challenging to study regulation at the transcriptional level. Methods Through bulk RNA sequencing of B cell receptors (BCRs), we have identified V, (D), and J gene segment usage in the heavy (H) and light (L) chains of each cell line. We performed PacBio HiFi whole-genome sequencing on each WM cell line to verify the regions spanning the immunoglobulin loci and their associated regulatory regions. Results BCR sequencing identified a single dominant IGH and IGK/L rearrangement in each line, consistent with their clonal origin, along with only infrequent secondary rearrangements (< 30 reads). The ratio of light- to heavy-chain (L:H) transcripts ranged from 20—100 across the cell lines and correlated with the level of secreted IgM. Analysis of the PacBio data confirmed that the intronic regulatory sequence between the rearranged VDJ and constant regions is conserved in BCWM.1 and RPCI-WM1 but is disrupted by a gap in MWCL-1. Methylation profiles derived from the PacBio kinetic signals were broadly similar across the IGH region in all three cell lines, indicating that large-scale methylation differences are unlikely to account for variation in IgM expression. Conclusion The availability of monoclonal WM cell lines, coupled with BCR and PacBio sequencing, provides a platform to study the regulation of human IGH. Funding Source n/a Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)