CD200R1 and skin squamous cell carcinoma: Using cutaneous squamous cell carcinoma (cSCC) models, Khan et al. demonstrated that CD200/CD200R signaling upregulates the expression of collagen proteinase Cathepsin K (Ctsk) from tumor infiltrating myeloid lineages in the TME, including CD200R-expressing MDSCs and TAMs (Figure 2I) [86].