Spatial and molecular profiling of classic Hodgkin lymphoma reveals an immunosuppressive mononuclear phagocyte network

Abstract Although a lymph node infiltrated by classic Hodgkin lymphoma (cHL) is mostly composed of nonneoplastic immune cells, the malignant Hodgkin Reed-Sternberg cells (HRSC) successfully suppress an anti-tumor immune response, creating a cancer-permissive microenvironment. Accordingly, unleashing the dormant immune cells, for example by checkpoint inhibition, has been a central focus of recent therapeutic advances for this disease. Despite the efficacy of PD-1 blockade in relapsed cHL, a significant proportion of patients have suboptimal or non-durable responses, which may reflect HRSC and microenvironmental adaptation.Here, we profiled the global immune cell composition of normal and diseased lymph nodes by singlecell RNA sequencing, as a basis for interrogating the immediate vicinity of HRSC. We did so regionally and at cellular resolution, using spatial transcriptomics and multiplexed immunofluorescence, on fixed cHL tissue sections. It is established that tumor associated macrophages (TAMs) are associated with inferior outcomes following combination chemotherapy, but the function, interactions, and distribution of TAMs, and other mononuclear phagocytes, have not been fully explored.Our analyses revealed specific immune cells and functional states associated with HRSC. We discovered a non-random spatial organization of immunoregulatory mononuclear phagocytes (TAMs and classical monocytes) around HRSC, which express the immune checkpoints PD-L1, TIM-3, and the tryptophan-catabolizing protein IDO1. Dendritic cells (DC), key antigen presenting cells, are regionally polarized according to subtype. Specific DCs are spatially associated with the HRSC ‘neighborhood’ (cDC2), but plasmacytoid DCs and ‘activated’ DCs are excluded. These findings provide a basis for rational targeting and activation of the anti-tumor immune response in cHL.