Studies with full length CEA and the splice variant were carried out in CHO cells due to their ease of infection with lentiviral constructs and their subsequent selection of CEA-expressing cells using flow cytometry. To demonstrate the killing specificity of MEDI-565 for CEA positive human tumor cells, we examined numerous human cancer cell lines for CEA expression and for their ability to be killed by MEDI-565 activated T cells. Consistent with the specificity observed for CHO cells, MEDI-565 mediated the killing of human tumor cells that expressed CEA, but not those that did not express cell surface CEA ( Figure S2 ). Additionally, a control BiTE did not induce T cell lysis of CEA positive or negative cell lines.