Anti-carcinoembryonic antigen (CEA) immunity induced by a single chain Fv format of an anti-idiotype antibody mimicking CEA

The anti-idiotype monoclonal antibody (mAb), 3H1, was generated by Immunization of mice with the anti-Carcinoembryonic Antigen (CEA) mAb. 8019. To define the minimum structural requirements for antigen mimicry by 3H1, we constructed plasmid vectors for expression of single chain Fv (scFv) variants of 3H1 in Escherichia coli. Variable heavy (VH) and light (VL) chain domains of 3H1 were linked by a 15 amino acid linker (Ln), (Gly,Ser), in two constructs, VH-Ln-VL and VL-LnVH. Ln was omitted in two constructs, VH-VL and VL-VH. Comparisons of the binding of 8019 to purified scFv proteins showed that only VH-Ln-VL had significant activity. Immunization of mice with naked VPI-Ln-VL and VH-Ln-VL conjugated to keyhole limpet hemocyanin (KLH) induced anti-CEA antibodies in mouse sera. These results demonstrate that for antigen mimicry of 3H1 scFv, the presence of Ln is necessary and the domain order should be VH followed by VL.