Revealing the Evolution of the Tumor Immune Microenvironment in Follicular Lymphoma Patients Progressing Within 24 Months Using Single-cell Imaging Mass Cytometry

Background: The tumor immune microenvironment (TIME) is crucial for follicular lymphoma (FL) pathogenesis and progression. However, TIME evolution during progression of disease within 24 months (POD24) is unknown. Methods: : Spatially-resolved and single-cell image mass cytometry with a panel of 36 meta-tagged antibodies was quantitatively used to dissect the TIME structure in 13 paired FLs at diagnosis and POD24. Results: : Increased CD163 − macrophages with PD-1 ligand upregulation and decreased CD8 + T cells with upregulated LAG3 expression were observed in the follicles during POD24. Spatial interactions demonstrated that FL cells interacted more intimately with macrophages rather than Tregs and less with cytotoxic cells during POD24. Additionally, more CD8 + T cells near FL cells interacted with macrophages but not Tregs during POD24. Notably, macrophages also cooperated with Tregs more frequently to simultaneously hijack the cytotoxic T-cells and protect FL cells, subsequently generating a more immunosuppressive environment in the follicles during POD24. Conclusions: : FL cells reside in a more immune-compromised microenvironment, evading immune-cell attacks during POD24. Novel immunotherapeutic approaches harnessing LAG3, macrophages, and Tregs will be promising to overcome the poor outcomes of patients with FL POD24.