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)1{beta}2 to preferentially stimulate LT{beta} receptor (LT{beta}R) nonclassical NF{kappa}B signaling on both tumor and lymphatic endothelial cells (LECs) to accelerate tumor growth and metastasis. Selectively targeting LT{beta}R nonclassical NF{kappa}B 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 LT{beta}R nonclassical NF{kappa}B in melanoma cells. Endothelial specific genes related to oncogenic process such as SOX18 and FLRT2 were identified to be driven under LT{beta}R nonclassical NF{kappa}B in LECs. Leveraging in vivo Treg LT1{beta}2 interactions with LT{beta}R on tumor and LECs, transfer of WT but not LT-deficient Tregs promoted transplanted WT B16F10 growth and tumor cell-derived CXCL1 and CXCL10 secretion in LT{beta}R-deficient host mice, and increased endothelial specific genes related to tumor angiogenesis and lymphangiogenesis, in WT mice bearing LT{beta}R-depleted melanoma. Selectively blocking LT{beta}R nonclassical NF{kappa}B 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 IFN{gamma}+ CD8 T cells by restraining Treg facilitated lymphatic vessel permeability. Our data revealed that Treg LT1{beta}2 promotes LT{beta}R nonclassical NF{kappa}B signaling in tumor cells and LECs providing a rational strategy to modulate Treg-mediated protumorigenic molecules to prevent tumor growth and metastasis.