SDC4 and carcinoma: Consistent with a Carcinoma 3–T cell niche in SCC, robust signaling to Tregs was facilitated through multiple ligand–receptor interactions, encompassing TNFSF9‐TNFRSF9 and CXCL16‐CXCR6, as well as PTN‐SDC4, PVR‐CD96, and PVR‐TIGIT (Figure 5A).