PDCD1 and cancer: Therefore,KRAS/LKB1 mutations in cancer cells not only establish a non-T cell, inflamed TME including reduced infiltration of CD3+, CD4+, CD8+ T cells and low expression of PD-1, but also help the cancer cells to cope with harsh conditions in the TME, when metabolites such as arginine become limited depending on the immune status (Figure 2D).