A BAC transgenic mouse was created by using a 155 kb fragment of murine chromosome 14 that had been modified by replacing the start codon of the granzyme B gene with the tamoxifen-dependent recombinase Cre/ERT2 gene. Successful integration of the construct was confirmed through genomic PCR. After crossing to a cre reporter strain and administrating tamoxifen, cre expression was detected in activated CD8 T cells and in NK cells. (J:144174)