H. Murine naïve CD4 T cells (CD62L+/CD25-/CD4+) from WT and USP44-/- mice (n=2-3/group/experiment) were FACS purified and activated in vitro for four days by CD3/CD28 cross-linking antibodies (1ug and 4ug/ml, respectively) in the presence of 100 U/ml IL-2 and the indicated dose of TGF-β. Down-regulation of FOXP3 was observed in USP44-/- mice by intracellular immunostaining and flow cytometry. 