The plasmid containing the full-length CEA sequence was purchased from Open Biosystems (Thermo Fisher Scientific, Huntsville, AL). The CEA complementary DNA (cDNA) was subcloned using sequence specific primers into a modified version of the lentiviral vector pCDH1-CMV-MCS-EF1-Puro (System Biosciences, Mountain View, CA) in which the puromycin-resistance casette was replaced with a blasticidin-resistance cassette (pCDH1-CMV-MCS-EF1-Blast) and the CEA sequence was verified by DNA sequencing. The plasmid containing the sequences of the CEA splice variant (cDNA clone DKFZp781M2392) was purchased from ImaGenes GmbH (Source BioScience UK Limited, Nottingham, UK) in association with B Bridge International (Cupertino, CA). The CEA splice variant was cloned into the puromycin resistance lentiviral vector pCDH1-HCS1-EF1-Puro (System Biosciences) using sequence-specific primers and the resulting clones were sequence-verified.