The present application relates to the field of immunology, more particularly to diseases and disorders characterized by insufficient numbers of Foxp3 positive regulatory T cells (Tregs). The mechanisms of the homeostatic processes that regulate the Treg numbers were studied, and it was found that Mcl-expression is critical for Treg survival. As most studies aiming at increasing Treg numbers to modulate immunity only achieve a transient increase, this finding has important therapeutic consequences: combined Mcl-1 and Foxp3 expression results in a stable population of Treg cells; enhancing ...