Genomic Analyses of Flow-sorted Hodgkin Reed Sternberg Cells Reveal Complementary Mechanisms of Immune Evasion.
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Classical Hodgkin lymphoma (cHL) is composed of rare malignant Hodgkin Reed Sternberg (HRS) cells within an extensive, but ineffective, inflammatory/immune cell infiltrate. HRS cells exhibit near-universal somatic copy gains of chromosome 9p/9p24.1 which increase expression of the PD-1 ligands. To define genetic mechanisms of response and resistance to PD-1 blockade and identify complementary treatment targets, we performed whole exome sequencing of flow cytometry-sorted HRS cells from 23 excisional biopsies of newly diagnosed cHLs including 8 EBV+ tumors. We identified significantly mutated cancer candidate genes (CCGs) as well as somatic copy number alterations and structural variations and characterized their contribution to disease-defining immune evasion mechanisms and NF-KB, JAK/STAT and PI3K signaling pathways. EBV- cHLs had a higher prevalence of genetic alterations in the NF-KB and MHC class I antigen presentation pathways. In this young cHL cohort (median age of 26), we identified a predominant mutational signature of spontaneous deamination of CpGs ... (Show More)