Topological Analysis Reveals a PD-L1-associated Microenvironmental Niche for Reed-Sternberg Cells in Hodgkin Lymphoma

Signaling between programmed cell death protein 1 (PD-1) and the PD-1 ligands (PD-L1, PD-L2) is essential for malignant Hodgkin Reed-Sternberg (HRS) cells to evade antitumor immunity in classical Hodgkin lymphoma (cHL). Copy number alterations of 9p24.1/()() contribute to robust PD-L1 and PD-L2 expression by HRS cells. PD-L1 is also expressed by nonmalignant tumor-associated macrophages (TAMs), but the relationships among PD-L1 HRS cells, PD-L1 TAMs, and PD-1 T cells remain undefined. We used multiplex immunofluorescence and digital image analysis to examine the topography of PD-L1 and PD-1 cells in the tumor microenvironment (TME) of cHL. We find that the majority of PD-L1 in the TME is expressed by the abundant PD-L1 TAMs, which physically colocalize with PD-L1 HRS cells in a microenvironmental niche. PD-L1 TAMs are enriched for contacts with T cells, and PD-L1 HRS cells are enriched for contacts with CD4 T cells, a subset of which are PD-1 Our data define a unique topology of cHL in which PD-L1 TAMs surround HRS cells and implicate CD4 T cells as a target of PD-1 blockade.