“…In the clinical oncology, during the "countdown period, " usually few days before the CAR T cell therapy, a lymphodepleting conditioning regimen is administered. Lymphodepleting conditioning regimens, comprising IL-2, cyclophosphamide, and fludarabine, are most often used before CAR T cells infusion, allowing for bigger T cell expansion and survival (62)(63)(64)(65)(66)(67)(68). During this period, lymphodepleting regimen eradicates homeostatic cytokine sinks, such as IL-7, IL-2, and IL-15, eliminates unwanted immunosuppressive cells, such as regulatory T cells and myeloid-derived suppressor cells and downregulates indoleamine 2,3-dioxygenase (IDO) in tumor cells (67,69).…”