Document resource
Background CD206 expression marks a substantial proportion of tumor-associated macrophages (TAMs) in many tumors. Although this marker has been associated with the so-called immunosuppressive ‘M2’ phenotype, substantive functional data on the context-dependent roles of CD206+ macrophages in diverse tumor microenvironments are lacking. In particular, how CD206+ macrophage subsets influence CD8 T cell-mediated anti-tumor immunity, either by chemokine-dependent T cell recruitment, or local stimulation/inhibition at the tumor boundary is not clearly determined. We thus made a novel conditional CD206 (Mrc1) knock-in mouse to specifically visualize and/or deplete CD206+ TAM subsets and probe their functions.Methods Our CD206 reporter, comprising of a lox-STOP-lox-Venus (YFP variant)- DTR cassette at the 3’ end of the Mrc1 (CD206) locus, was first used in conjunction with Csf1r Cre to mark and deplete all CD206+ TAMs in specific timeframes. Additionally, we used Retnla (RELM- a)Cre and Lyve-1Cre crossed to the reporter to mark TAMs which are located specifically at the tumor boundary, sharing features of perivascular and tumor-resident macrophages. We used OVA-expressing B78 and MC38 tumor models, which contrast in their baseline T cell infiltration and in responses to immunotherapy. We performed live imaging and post-imaging spatial transcriptomics, focusing on tumor edge, middle and inner regions.Results Early depletion of CD206+ macrophages in Csf1r Cre crossed CD206-reporter mice led to the indirect loss of conventional type I dendritic cells (cDC1), CD8 T cells, and NK cells in tumors. This loss of a tumor-reactive phenotype was mechanistically linked to the robust expression of CXCL9 by CD206+ TAMs, and the recruited Cxcr3-expressing NK and activated CD8 T cells prominently expressing cDC1-supportive Xcl1 and Flt3l. Disrupting this key antitumor axis by depletion of CD206+ TAMs decreased tumor control by antigen-specific T cells in mice. In contrast to the Csf1r Cre cross marking all CD206+ Mono/Macs, the RetnlaCre and Lyve-1Cre marked ~3-5% of TAMs, specifically localized at the tumor margins and distinguished by high expression of RELM-a, FOLR2, LYVE-1 and CD206. Depletion of these tumor edge TAMs in contrasting tumor models led to opposing outcomes on T cell infiltration, associated with distinct phenotypes of these tumor edge TAMs, shaped by their unique extracellular microenvironments.Conclusions These findings negate the unqualified classification of CD206+ macrophages as immunosuppressive by linking them to CXCL9 expression. Further, CD206 hi tumor edge TAMs exist in distinct phenotypes related in different tumors, leading to divergent effects on CD8 T cell infiltration.