In addition to such naturally occurring pTreg cells that continuously develop in peripheral lymphoid tissues of nonmanipulated mice, Foxp3+ pTreg cells can be artificially generated in vivo from post-thymic, initially naive CD4+Foxp3− T cells in experimental settings of lymphopenia-driven proliferation (7, 8) and subimmunogenic antigen administration (9, 10). The gene discussed is FOXP3; the disease is lymphopenia.