Carcinoembryonic antigen (CEA) mimicry by an anti-idiotypic scFv isolated from anti-Id 6.C4 hybridoma

Since carcinoembryonic antigen (CEA) is expressed during embryonic life, it is not immunogenic in humans. The use of anti-idiotypic (Id) antibodies as a surrogate of antigen in the immunization has been considered a promising strategy for breaking tolerance to some tumor associated antigens. We have described an anti-Id monoclonal antibody (MAb), designated 6.C4, which is able to mimic CEA functionally. The anti-Id MAb 6.C4 was shown to elicit antibodies that recognized CEA in vitro and in vivo. In the present study, we sought to verify whether a single chain (scFv) antibody obtained, the scFv 6.C4, would retain the ability to mimic CEA. Two scFv containing the variable heavy and light chain domains of 6.C4 were constructed with a 15-amino acid linker: one with and another without signal peptide. DNA immunization of mice with both forms of scFv individually elicited antibodies able to recognize CEA.