Moreover, the expansion of TIL-Tregs and their ability to suppress the immune system rely heavily on mitochondrial metabolic activity.271 For example, the capacity of Tregs in suppressing cancer-fighting immunity is determined by complex III of mitochondria.272 During differentiation of Treg cells, fusion of mitochondria triggered by transforming growth factor-beta1 (TGFβ1) is a checkpoint which directs reprogramming of metabolic processes.273,274 PGC1α participates in mitochondrial biogenesis and mitochondrial dynamics. The gene discussed is TGFB1; the disease is cancer.