Construction and characterization of DNA vaccines encoding the single-chain variable fragment of the anti-idiotype antibody 1A7 mimicking the tumor-associated antigen disialoganglioside GD2

Anti-idiotype antibody, 1A7, functionally mimics the tumor-associated antig en disialoganglioside GD2, which is overexpressed on the surface of a numbe r of neuroectodermal tumors such as melanoma, neuroblastoma, soft tissue sa rcoma, and small cell carcinoma of the lung. Immunization of mice with 1A7 generated the production of anti-GD2 antibodies. In a phase I clinical tria l, immunization of patients with 1A7, mixed with the adjuvant QS21, demonst rated that 1A7 could act as a surrogate antigen for GD2 and induce strong h umoral immune responses in advanced stage melanoma patients. DNA Vaccines h ave recently been shown to invoke humoral as well as cellular responses in injected hosts against the transgene product. To evaluate the efficiency of DNA vaccines encoding anti-idiotype antibodies, we constructed expression plasmids encoding the variable heavy (VH) and variable light (VL) chains of 1A7. The plasmids were made in two configurations, expressing either the V H (pc1A7VHLnVL) or the VL (pc1A7VLLnVH) chain of 1A7 at the amino terminus, linked together by a 15-amino acid linker (Ln). In vitro transcription/tra nslation assays and transfection of CHO-K1 cells with the plasmids demonstr ated that a similar to 30-kDa protein was expressed by both configurations of the single-chain variable fragment. This protein can be specifically pre cipitated by monoclonal anti-GD2 antibody, 14G2a. Following intramuscular i njection in mice, the plasmids were detectable in the injected tissues for at least 3 months and the injected plasmids actively transcribed the single -chain variable fragment 1A7 gene at the injected site. A single, intramusc ular immunization of a group of C57BL/6 mice with pc1A7VLLnVH in phosphate- buffered saline induced humoral immune responses against 1A7 as well as GD2 , the nominal antigen. Multiple immunizations, however, were required to el icit stronger immune responses.