Immunological properties of a single-chain fragment of the anti-idiotypic antibody ACA125

Cancer Immunol Immunother. 2000 Jul;49(4-5):186-92. doi: 10.1007/s002620000126.


Vaccination with anti-idiotypic antibodies has been described as a promising concept for treatment of several malignant diseases. The murine monoclonal anti-idiotypic antibody ACA125 imitates a specific epitope of the tumor-associated antigen CA125 expressed by 80% of ovarian carcinomas. In the first clinical trial it could be shown that mAb ACA125 is able to elicit anti-anti-idiotypic antibodies (Ab3) with anti-CA125 specificity in patients with advanced ovarian cancer. In order to improve the capabilities of anti-idiotype vaccines we generated a genetically engineered single-chain fragment (scFv) ACA125 composed of heavy- and light-chain variable regions connected by a flexible linker. The antigenicity of scFv ACA125 was demonstrated by immunizing rats i.p. with scFv or complete mAb in complete/incomplete Freund's adjuvants (CFA/IFA) or precipitated by aluminium hydroxide. Negative control groups included applications of irrelevant mouse IgG or adjuvants alone. Anti-anti-idiotypic antibodies (Ab3) directed against the mAb ACA125 as well as specific anti-CA125 antibodies (Ab1') could be detected in all animals treated with scFv in CFA/IFA. Nevertheless, antibody titers were lower than when the complete mAb ACA 125 was used. Suprisingly, an increase of specificity could not be observed in scFv-immunized animals, which had been expected because of the lack of heavy- and light-chain constant regions that could raise rather unspecific anti-isotypic and anti-allotypic rat anti-(mouse Ig) antibodies (RAMA). In contrast, the RAMA responses detected in these rats were even stronger than those following immunization with complete mAb ACA125. In conclusion, the anti-idiotypic scFv ACA125 alone cannot improve the immunogenic features of the corresponding mAb, but provides a useful tool for the further development of genetic vaccines.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aluminum Hydroxide / pharmacology
  • Animals
  • Antibodies, Anti-Idiotypic / immunology*
  • Antibodies, Monoclonal / immunology*
  • Antibody Formation / immunology
  • Antibody Specificity
  • Dose-Response Relationship, Immunologic
  • Electrophoresis, Polyacrylamide Gel
  • Escherichia coli / metabolism
  • Female
  • Freund's Adjuvant / pharmacology
  • Immunoglobulin G / immunology
  • Mice
  • Ovarian Neoplasms / metabolism
  • Rats
  • Rats, Sprague-Dawley


  • Antibodies, Anti-Idiotypic
  • Antibodies, Monoclonal
  • Immunoglobulin G
  • Aluminum Hydroxide
  • Freund's Adjuvant