Objective To explore the effects of Foxp3 gene transfection on the phenotype and function of CD4

+

CD25

-

  T cells.   Methods The pMSCV-Foxp3 retroviral vector  encoding Foxp3 gene was transfected into PT67 packaging cell line. Virus-containing supernatant was applied to differentiated CD4

+

CD25

-

  T cells

then the cells were sorted with flow cytometry. The expressions of C

D25

CD127

CTLA4 and proliferation of transfected CD4

+

CD25

-

T cells were examined. The effect of transfected CD4

+

CD25

-

  T cells on the proliferation and cytokine production of CD4

+

CD25

-

T cells were examined.   Results Foxp3 gene transfected CD4

+

CD25

-

  T cells could express Foxp3. Transfection of Foxp3 gene upregulated the expressions of CD25 and CTLA-4

but down-regulated CD127 expression. After transfection

the proliferation of CD4

+

CD25

-

T cells was eliminated. IL-2 could not induce the proliferation of transfected T cells. Transfected T cells inhibited the proliferation of CD4

+

CD25

-

   T cells after coculture.   Conclusion CD4

+

CD25

-

  T cells acquired a regulatory phenotype and function after transfected with Foxp3 gene

indicating a key role of Foxp3 in the generation of CD4

+

CD25

+

  regulatory T cells.