Regulatory T cells crosstalk with tumor and endothelium through lymphotoxin signaling

Regulatory T cells (Tregs) are suppressors of anti-tumor immunity that exert multifaceted functions by signaling surrounding cells. We revealed Tregs use their high-level surface lymphotoxin (LT)α1β2 to preferentially stimulate LTβ receptor (LTβR) nonclassical NFκB signaling on both tumor and lymphatic endothelial cells (LECs) to accelerate tumor growth and metastasis. Selectively targeting LTβR nonclassical NFκB pathways on both tumors and LECs cocultured with Tregs, inhibited tumor growth and migration in vitro. Further, we identified protumorigenic chemokines and interferon-stimulated response genes selectively driven by LTβR nonclassical NFκB in melanoma cells. Endothelial specific genes related to oncogenic process such as SOX18 and FLRT2 were identified to be driven under LTβR nonclassical NFκB in LECs. Leveraging in vivo Treg LTα1β2 interactions with LTβR on tumor and LECs, transfer of WT but not LTα-deficient Tregs promoted transplanted WT B16F10 growth and tumor cell-derived CXCL1 and CXCL10 secretion in LTβR-deficient host mice, and increased endothelial specific genes related to tumor angiogenesis and lymphangiogenesis, in WT mice bearing LTβR-depleted melanoma. Selectively blocking LTβR nonclassical NFκB pathways remarkably suppressed tumor growth and lymphatic metastasis by reducing tumor cell and LEC-derived CXCL1 and CXCL10 production, restricting Treg and myeloid-derived suppressor cell (MDSC) recruitment to tumor. It also retained intratumoral effector T cells, especially IFNγ ⁺ CD8 T cells by restraining Treg facilitated lymphatic vessel permeability. Our data revealed that Treg LTα1β2 promotes LTβR nonclassical NFκB signaling in tumor cells and LECs providing a rational strategy to modulate Treg-mediated protumorigenic molecules to prevent tumor growth and metastasis.