IDO1 and renal cell carcinoma: Immune-suppressive components in the RCC microenvironment such as T regulatory cells (Tregs), macrophages, myeloid-derived suppressor cells (MDSCs), and cells expressing indoleamine 2,3-dioxygenase (IDO1) were lower in responders, though not significantly (n = 7, 10; p = 0.16, 0.29, 0.39, 0.41) (Figure S2D).