A restriction digest was performed on both the CEACAM1-4S PCR product and the pCl-neo plasmid (Promega, Madison, WI, USA) using EcoRI and SalI (New England Biolabs, Ipswich, MA, USA). Following digestion, the plasmid and the PCR product were dephosphorylated using Antarctic phosphatase (New England Biolabs), heat-treated to inactivate the phosphatase, and run on a 1% agarose gel. Bands corresponding to the plasmid DNA and CEACAM1-4S PCR product were purified using the Geneclean spin kit (Qbiogene, Morgan Irvine, CA, USA). The CEACAM1-4S PCR product was ligated into the pCI-neo plasmid using T4 DNA ligase (New England Biolabs). Ligated plasmid was transformed into One Shot OmniMax 2 T1 Phage-Resistant Cells (Invitrogen) according to the manufacturer's protocol. Transformed cells were plated onto LB/ CARB plates and resulting colonies were screened by PCR using forward and reverse primers for CEACAM1-4S (see above). Plasmid DNA from four CEACAM1-4S positive clones was isolated using the Qiagen Endofree maxiprep kit (Valencia, CA, USA) and submitted for DNA sequencing to the W.M. Keck Biotechnology Laboratory at Yale University (New Haven, CT).