Integrated Epigenetic and Transcriptional Single-Cell Analysis of t(11;14) Multiple Myeloma and Its BCL2 Dependency.

The translocation t(11;14) occurs in 20% of multiple myeloma (MM) patients and results in the upregulation of CCND1. Nearly two-thirds of t(11;14) MM cells are BCL2 primed and highly responsive to the oral BCL2 inhibitor venetoclax. While it is evident that this unique sensitivity to venetoclax depends on the BH3-proapoptotic protein priming of BCL2, the biology underlying t(11;14) MM dependency on BCL2 is poorly defined. Importantly, the epigenetic regulation of t(11;14) transcriptomes and its impact on gene regulation and clinical response to venetoclax remains elusive. In this study, by integrating ATACseq and RNAseq at the single-cell level in primary MM samples, we have defined the epigenetic regulome and transcriptome associated with t(11;14) MM. A "B cell-like" epigenetic signature was enriched in t(11;14) MM, confirming its phylogeny link to B cell rather than plasma cell biology. Of note, a loss of a "B cell-like" epigenetic signature with a gain of canonical plasma cell transcription factors was observed at the time of resistance to venetoclax. In addition, MCL1 and BCL2L1 copy number gains and structural rearrangements were linked to venetoclax resistance in t(11;14) MM patients. To date, this is the first study in which both scATAC-seq and scRNA-seq analysis are integrated into primary MM cells to obtain a deeper resolution of the epigenetic regulome and transcriptome associated with t(11;14) MM biology and venetoclax resistance.