For instance, Ouaknine Krief et al. (2019) found that high baseline citrulline level (≥20 μM) in blood plasma, which reflects proper intestinal epithelial cell function, was associated with better response and clinical benefit to the ICI therapy and longer progression-free survival (PFS) and overall survival (OS) in patients with advanced non-small cell lung cancer (NSCLC) receiving the anti-PD-1 therapy [8]. The gene discussed is PDCD1; the disease is non-small cell lung carcinoma.