CD4 and breast cancer: In addition to the aforementioned reduction of cytokine production, cell cycling and anti-leukemic activity and increase of apoptosis rate (Fig. 3b; Supplementary Fig. 8a–d), increased levels of other immune checkpoints (e.g., Tim-3 and CTLA-4) were also observed in the CD4+ and CD8+ spleen T cells from the Mir142−/−BCR-ABL mouse compared to those from the Mir142+/+BCR-ABL mouse (Supplementary Fig. 14e, f), suggesting T cell exhaustion in the BC mouse.