IL9R and neoplasm: To further confirm the importance of the IL-9/IL-9R axis in maintaining low levels of lipid peroxidation and ferroptosis in Tc9 cells, we cocultured Pmel-1 WT, Il9–/–, or Il9r–/– mouse–derived Tc9 cells with B16 tumor cells and observed that mitochondrial activity was lower (Figure 5L), while cellular ROS, lipid peroxidation (Figure 5M), cellular iron levels (Figure 5N), and ferroptosis (Figure 5O) were higher in Tc9 cells from Il9–/– and Il9r–/– mice compared with T cells from WT mice.