PDCD1 and cancer: To further verify the importance of the glutamine transporter SLC25A22 in the immunosuppressive microenvironment of CSCC, we evaluated the expression levels of SLC25A22, the immune checkpoint PD‐1 and CD8, as well as the cytotoxicity of effector CD8+ T cells, in 20 CSCC samples and 3 normal samples with complete clinical and pathological information obtained from the original 44 cancer samples and 18 normal samples (Table S1, Supporting Information).