Indoleamine 2,3-dioxygenase 1 (IDO1) inhibition is another metabolic approach promoting Vγ9Vδ2 T-cell cytotoxicity against human breast cancer cells and pancreatic ductal adenocarcinoma (PDAC) cells by enhancing perforin production (150), degranulation, and cytokine production (151). The gene discussed is IDO1; the disease is breast cancer.