CEACAM5 and infection: To test this hypothesis, CHO cells were infected with lentivirus constructs directing the expression of full-length CEA (CHO FL CEA) or the CEA splice variant (CHO SV CEA), or both concurrently after sequential infection of cells with the CEA splice variant then the full-length CEA (CHO FL+SV CEA); full-length CEA and CEA splice variant protein expression were verified by western blotting (Figure S1).