IL-2 can stimulate the growth of NKs, however, when Tregs and NKs are cocultured, Tregs can inhibit the proliferation of NKs by competing with IL-2 [33, 34], indicating that the affinity between Tregs and IL-2 may be dominant, which can weaken the immune ability and facilitate the escape of tumor cells (Figure 1). Here, IL2 is linked to neoplasm.