Spatial and molecular profiling of the mononuclear phagocyte network in Classic Hodgkin lymphoma

Classic Hodgkin lymphoma (cHL) has a rich immune infiltrate, which is an intrinsic component of the neoplastic process. Malignant Hodgkin Reed-Sternberg cells (HRSC) create an immunosuppressive microenvironment by the expression of regulatory molecules, preventing T-cell activation. It has also been demonstrated that mononuclear phagocytes (MNPs) in the vicinity of HRSC express similar regulatory mechanisms in parallel, and their presence in tissue is associated with inferior patient outcomes. MNPs in cHL have hitherto been identified with a small number of canonical markers and are usually described as 'tumor-associated macrophages'. The organization of MNP networks and interactions with HRSC remains unexplored at high resolution. Here, we defined the global immune cell composition of cHL and non-lymphoma lymph nodes, integrating data across single-cell RNA sequencing, spatial transcriptomics, and multiplexed immunofluorescence. We observed that MNPs comprise multiple subsets of monocytes, macrophages and dendritic cells (DCs). Classical monocytes, macrophages and conventional DC2 were enriched in the vicinity of HRSC, but plasmacytoid DCs and activated DCs were excluded. Unexpectedly, cDCs and monocytes expressed immunoregulatory checkpoints PD-L1, TIM-3, and the tryptophan-catabolizing protein IDO, at the same level as macrophages. Expression of these molecules increased with age. We also found that classical monocytes are important signaling hubs, potentially controlling the retention of cDC2 and ThExh via CCR1-, CCR4-, CCR5-, and CXCR3-dependent signaling. Enrichment of the cDC2-monocyte-macrophage network in diagnostic biopsies is associated with early treatment failure. These results reveal unanticipated complexity and spatial polarization within the MNP compartment, further demonstrating their potential roles in immune evasion by cHL.