DNA VACCINES AGAINST LYMPHOMA - PROMOTION OF ANTIIDIOTYPIC ANTIBODY-RESPONSES INDUCED BY SINGLE-CHAIN FV GENES BY FUSION TO TETANUS TOXIN FRAGMENT-C

Idiotypic determinants can act as tumor-associated Ags for B cell lymp homa. Vaccination with idiotypic protein and adjuvant is known to indu ce specific protection against lymphoma challenge in mice, largely med iated by anti-idiotypic Ab. For facilitating the approach for patients , the V-H and V-L genes used to encode the individual idiotypic determ inants of each tumor can be obtained by PCR and assembled as single ch ain Fv (scFv). DNA vaccines containing scFv sequences alone induce low and poorly reproducible levels of anti-idiotypic Ab, likely to be ins ufficient to suppress tumor in patients. In addition, it may be necess ary to break tolerance to Id in tumor bearers. By fusing the gene for fragment C of tetanus toxin to the C terminus of human scFv, we have p romoted the anti-scFv Ab response in mice by >50-fold in three of thre e cases. The induced Abs are mainly against idiotypic determinants, an d react specifically with patients' tumor cells, indicating optimal fo lding of the scFv molecule in the fusion protein. For both antigenic c omponents of the DNA vaccine, the Ige subclass distribution showed a r elative increase in IgG2a as compared with vaccination with IgM protei n in adjuvant, In patients, the fusion gene should both promote anti-i diotypic Ab and induce Abs against fragment C of tetanus toxin. The Ta tter response would provide a potentially useful comparative measure o f the ability of patients to respond to conventional Ag delivered via DNA.