FOXP3 and autoimmune disease: Mutation of the transcription factor Forkhead box P3 (Foxp3) leads to fatal autoimmune diseases in mice and humans.1, 2 Although Foxp3 was initially shown to be a key transcription factor in the control of regulatory T-cell (Treg) function,3 there are an increasing number of reports describing the functions of Foxp3 in other cell types.