CD274 and esophageal squamous cell carcinoma: Overall, analyses of both myeloid and lymphoid compartments highlight the immunosuppressive nature of the ESCC microenvironment: i) Both CD4+ and CD8+ T cell compartments express various immune checkpoints in a tumor-specific manner; ii) Treg cells are more enriched in tumor samples; iii) M2-like macrophages (Mac_1, Mac_2 and Mac_3) express anti-inflammatory factors, and even the M1-like subset (Mac_5) expresses PD-L1 specifically in tumor samples; iv) Different monocyte subsets express immune-regulatory and pro-tumoral factors.