Whilst Th1-like Treg cells can be potent suppressors of the activity, proliferation, and memory formation of CD8 effector T cells27 and IFNγ-mediated STAT1 activation in Treg cells can promote Treg cell function in alloantigen tolerized mice25, IFNγ can also promote Treg cell fragility or lineage instability in the tumor microenvironment26. Here, STAT1 is linked to neoplasm.