Myeloid landscape profiling identifies DLBCL-specific suppressive macrophages colocalized with blood endothelial cells

Diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) are the two most common B-cell lymphomas and are characterized by a dynamic crosstalk between tumor B cells and a heterogeneous tumor-supportive microenvironment, including immune, endothelial, and stromal components. Despite their recognized impact on the pathogenesis and prognosis of B-cell lymphoma, tumor-associated macrophages (TAM) have not been extensively explored in these diseases. Herein, we investigated mononuclear phagocyte (MNP) heterogeneity at the single-cell level and the activation profile of MNP, stromal, and endothelial compartments in B-cell lymphoma lymph nodes compared to reactive secondary lymphoid organs. This was achieved using a combination of mass cytometry, single-cell RNA sequencing, in silico and spatial imaging approaches. Our findings revealed a lymphoma-specific pattern of TAM and blood endothelial cell (BEC) co-activation. Furthermore, we identified in DLBCL a spatial interaction between Annexin A1 (ANXA1)-expressing BEC and formyl-peptide receptor (FPR1/2) and S100A9-expressing monocytes/macrophages. This crosstalk is associated with an immunosuppressive tumor microenvironment and an adverse prognosis in two cohorts of DLBCL patients.