A targeting vector was designed to insert a cDNA encoding the human diphtheria toxin receptor (HBEGF/DTR) fused to sequences encoding a green fluorescent protein (GFP) equipped with an internal ribosome entery (IRES), IRES-DTR-GFP with a floxed neo into the 3' untranslated region downstream of exon 11 of the Foxp3 gene.