Updated project metadata. Recent data have shown that Hypermethylated in cancer 1 (HIC1) is an important contributor to iTreg cell development and function. Using affinity-purification and tandem mass spectrometry we systematically characterized the HIC-1 interactome in human iTreg cells. On the basis of these data, we have shown that HIC1 is a part of FOXP3-RUNX1-CBFβ protein complex that regulates Treg signature genes and is indispensable for the suppressive function of FOXP3+ regulatory T cells. SRM was used to validate HIC1 interactors