Disordered differentiation and cellular senescence in pediatric Hodgkin Reed-Sternberg cells

Hodgkin lymphoma (HL) is characterized by inflammatory lesions with relatively few (typically < 1%) pathogenic Hodgkin Reed-Sternberg (HRS) cells. The scarcity of malignant HRS cells in HL has historically limited characterization of these disease drivers, and pathogenic mechanisms underlying HL are incompletely defined. Using multi-parameter flow cytometry to purify HRS cells and immune cell populations from pediatric HL lesions and control tonsils, we sought to define transcriptional programs in pediatric HRS cells. HRS cells are thought to arise from transformed germinal center B cells. Interestingly, transcriptomic analysis of HRS cells compared to control tonsil CD30+ cells revealed disordered differentiation with multi-lineage gene expression patterns, and primary HRS cells had distinct transcriptomes compared to HL cell lines. Further, transcriptomic analysis revealed increased expression of senescence-related genes and downregulation of pro-apoptotic/mitosis-related genes. Gene expression findings were validated by immunohistochemistry and single cell imaging. In vitro treatment of primary HRS cells with BCL2 inhibitor, venetoclax, augmented induction of apoptosis in HRS cells and other cells of the HL immune microenvironment. These findings support further study of targeting apoptosis resistance as a potential approach to eliminate malignant HRS cells and dismantle inflammatory lesion formation in pediatric HL.