The cDNA encoding the CEA deletion variants DelA1-A2, Del A1, DelB1, DelA2, and DelB2-A3 and the swap variants KO_A, KO_B, KO_C, KI_A, KI_B, and KI_C (see Figures 1, 2, 3, and 4 for domain definition and variant nomenclature) were assembled and amplified by overlapping extension polymerase chain reaction (PCR) using an in-house full-length CEA cDNA clone, pNEO human CEA-GPI, as a template. The CEA variants and the fulllength CEA cDNA were cloned into a mammalian expression vector pcDNA3.1 (Invitrogen).