The cDNA for human PDCD1, encompassing sequence from kozak through translational stop and the last 2 exons of a mouse metallothionein gene including the terminal intron followed by a neo mini-gene flanked by loxP sites replaced the coding portion of murine exon 1 in order to maintain correct splicing of the fusion transcript. Flow cytometric protein expression analysis confirmed absence of targeted protein expression. (J:126829)