PRF1 and myalgic encephalomeyelitis/chronic fatigue syndrome: Metabolic features and immune cell dysfunction in ME/CFS T cells, such as decreased mitochondrial membrane potential, glycolytic impairments, lower granzyme A/perforin production, and now higher levels of fatty acid oxidation, are also consistent with an exhausted T cell state, common in chronic viral infections and cancer [23,51,53,87].