ANTI-IDIOTYPIC CDR3 VACCINATION AGAINST CHRONIC B-CELL LYMPHOMA: DNA VACCINE STRATEGY

B-cell lymphomas express tumor-specific immunoglobulin. Its variable region [idiotype (Id)] can be considered a tumor-specific antigen and a target for vaccine immunotherapy. Promising results have been obtained in clinical studies of Id vaccination using Id proteins or naked DNA Id vaccines. Several reports have indicated that the immunodominant epitopes of the clone-specific Ig lie mainly in the CDR3. We have previously demonstrated the possibility of using the short peptide encompassing the CDR3 of immunoglobulin heavy chain (VH-CDR3) as a target for eliciting a tumor specific immune response via DNA-based vaccination. DNA immunization of outbred mice with different patient-derived VH-CDR3 peptides elicited antibodies able to recognize native antigens on individual patient's tumor cells. In the present study, we evaluated the humoral and cellular immune response recruited by VL-CDR3-directed DNA vaccines using the murine 38C13 B-cell lymphoma tumor as a model system. The nucleic acid sequence of the idiotypic IgM (38C-Id) light chain was analyzed and the region corresponding to the CDR3 sequence was chosen for the production of a synthetic mini-gene. A high-level expression bicistronic plasmid DNA vaccine was designed to express both the short VL-CDR3 and the mouse IL-2 sequences. IL-2 was chosen as immunomodulating cytokine to enhance T cell-mediated immune response, to improve antigen-specific T cell proliferation, differentiation and Ig secretion of antigen-activated B cells. Vaccination of syngenic C3H/HeN mice with the described plasmid DNA vaccine was found to generate an immune response to the 38C13 tumor, inducing both specific circulating antibodies and specific cytotoxic T-cell (CTL) activity. Combined, our data indicates that a novel CDR3-based DNA vaccine can be improved and used to develop a protective vaccine against B-cell lymphoma. We have recently developed multiple complementary strategies to enhance the efficacy of a CDR3-based DNA vaccine. The first utilizes in vivo electroporation to increase the uptake of vaccine given intramuscularly and to yield powerful humoral and cellular responses. The second one entails the use of plasmid containing a DNA nuclear targeting sequence. The combination of both approaches has been reported to increase plasmid DNA vaccine delivery and expression, thus improving the antigen dose achievable in vivo. The third imply the use of a pathogen-derived sequence, proven to be potent adjuvants for several different DNA vaccines when fused to the tumor antigen in the expression vector. Lastly, we have developed a DNA vaccine encoding artificial strings of defined epitopes. The efficacy of the fusion gene vaccine and the epitope string DNA vaccine, in term of anti-idiotypic response and protection against B-cell lymphoma, will be tested and evaluated.