A loxP element was inserted 347 bp upstream of exon 3, and a cassette containing a loxP site and a FRT-flanked neomycin cassette was inserted 703 bp downstream of exon 4. Chimeric mice were first mated to FLP deleter mice to remove the neomycin cassette, and subsequently to Cre-transgenic mice to remove the floxed alleles. Gene deletion was confirmed by lack of expression in regulatory T cells as determined by quantitative RT-PCR. (J:127791)