SOD3 induces a HIF-2α-dependent program in endothelial cells that provides a selective signal for tumor infiltration by T cells.

Background: Tumor-infiltrating lymphocytes (TILs), mainly CD8 cytotoxic T lymphocytes (CTL), are linked to immune-mediated control of human cancers and response to immunotherapy. Tumors have nonetheless developed specific mechanisms that selectively restrict T cell entry into the tumor microenvironment. The extracellular superoxide dismutase (SOD3) is an anti-oxidant enzyme usually downregulated in tumors. We hypothesize that upregulation of SOD3 in the tumor microenvironment might be a mechanism to boost T cell infiltration by normalizing the tumor-associated endothelium.

Results: Here we show that SOD3 overexpression in endothelial cells increased in vitro transmigration of naïve and activated CD4 and CD8 T cells, but not of myeloid cells. Perivascular expression of SOD3 also specifically increased CD4 and CD8 effector T cell infiltration into tumors and improved the effectiveness of adoptively transferred tumor-specific CD8 T cells. SOD3-induced enhanced transmigration in vitro and tumor infiltration in vivo were not associated to upregulation of T cell chemokines such as CXCL9 or CXCL10, nor to changes in the levels of endothelial adhesion receptors such as intercellular adhesion molecule-1 (ICAM-1) or vascular cell adhesion molecule-1 (VCAM-1). Instead, SOD3 enhanced T cell infiltration via HIF-2α-dependent induction of specific WNT ligands in endothelial cells; this led to WNT signaling pathway activation in the endothelium, FOXM1 stabilization, and transcriptional induction of laminin-α4 (LAMA4), an endothelial basement membrane component permissive for T cell infiltration. In patients with stage II colorectal cancer, SOD3 was associated with increased CD8 TIL density and disease-free survival. SOD3 expression was also linked to a T cell-inflamed gene signature using the COAD cohort from The Cancer Genome Atlas program.

Conclusion: Our findings suggest that SOD3-induced upregulation of LAMA4 in endothelial cells boosts selective tumor infiltration by T lymphocytes, thus transforming immunologically "cold" into "hot" tumors. High SOD3 levels are associated with human colon cancer infiltration by CD8 T cells, with potential consequences for the clinical outcome of these patients. Our results also uncover a cell type-specific, distinct activity of the WNT pathway for the regulation of T cell infiltration into tumors.