A genetic approach to idiotypic vaccination for B cell lymphoma.

Idiotypic immunoglobulin expressed by a B cell tumor presents a clear tumor antigen which could be attacked by vaccination of the host. Vaccination with idiotypic protein has been shown to induce protective immunity against lymphoma, but application to patients is limited by the requirement of "personal" vaccines for each patient. A genetic approach enables V-region sequences encoding idiotypic antigen to be rescued from tumor biopsies, and to be assembled as scFv fragments. These can be expressed in bacteria to produce recombinant protein, or used directly as naked DNA vaccines. Intramuscular injection of idiotypic DNA from a mouse B cell lymphoma induces low levels of syngeneic anti-idiotypic antibody in serum. Response can be stimulated by co-injection of DNA plasmids encoding either IL-2 or GM-CSF, and T cells which proliferate in response to idiotypic IgM are generated. However, protection against tumor appears to be blocked by continuing secretion of idiotypic antigen from the persisting vaccine vector, which forms immune complexes with serum antibody. Methods for regulating the level of scFv to engage the immune system, but not to block the effector arm are being investigated. Similar control will be applicable to the cytokine vectors, which can deliver encoded cytokines designed to activate immune pathways for tumor destruction. Experience gained in lymphoma may be extended to other tumors with defined tumor antigens.