PDC and neoplasm: Interestingly, the Restifo group showed that the lung may be a tumor-permissive organ due to the tissue-specific expression of oxygen-sensing prolyl-hydroxylase (PHD) proteins in a preclinical model and that changes in extracellular oxygen tension induced Treg quantity and function through an increase in PHD proteins and a local reduction in HIF1α, which correlated with increased intrapulmonary metastasis [63].