EFFICACY IN A MOUSE MELANOMA MODEL OF A DENDRITIC CELL-TARGETING THERAPEUTIC DNA VACCINE AND ENHANCEMENT OF ITS ACTIVITY BY CO-TREATMENT WITH ANTIBODIES TO NEUTRALIZE INTERLEUKIN-10

Introduction: Vaccines fusing Macrophage Inflammatory Protein-3α (MIP-3α) to an antigen have shown efficacy in malaria, melanoma (prophylactically), and lymphoma models. The MIP-3α component targets nascent peptides to immature dendritic cells by interaction with CCR6, leading to processing, cross-presentation, and the induction of strong immune effector responses. Other studies have provided evidence that IL-10 is integral to the maintenance of the tolerogenic melanoma microenvironment. The therapeutic efficacy and immunogenicity of a DNA vaccine fusing MIP-3α to melanoma differentiation antigen gp100, and the additional effect of neutralizing IL-10 in the tumor, were analyzed in this study. Methods: The B16F10 mouse spontaneous melanoma syngeneic transplantable mouse model system was utilized, with a standard therapeutic protocol: challenge with lethal dose of B16F10 cells (5x104) on day 0; vaccinate by intramuscular electroporation with 50μg vaccine on days three, 10, and 17; and (if used) administer 150μg doses of IL-10 neutralizing antibody (αIL-10) starting day five for every three days intratumorally. Vaccine controlling for MIP-3α contains a mutation abrogating chemokine functionality and is termed dMIP-3α-gp100 or antigen-only vaccine. Efficacy assessed by analyses of tumor size, tumor growth, and mouse survival. Immunogenicity was assessed primarily by flow cytometric methods, including intracellular cytokine staining to assess vaccine-specific T-cell responses. Mechanism of αIL10 was elucidated by gene expression analyses and a knockout mouse model. Results: With this therapeutic protocol, it was demonstrated that MIP-3α-gp100 vaccine significantly slows tumor growth and increases mouse survival compared to antigen-only vaccine. Both CD4+ and CD8+ effector T-cells play a role in protection as determined by T-cell depletion studies, and the vaccine-specific CD8+ tumor infiltrating lymphocyte (TIL) profile correlates with protection. Combining this vaccine with αIL-10 led to further decreases in tumor size and increases in overall survival compared to vaccine alone. Mechanism of effect of αIL10 therapy was shown to be independent of the measured TIL profile. Analysis of tumor lysate transcription levels show significant upregulation of IFN-α4, which is known to have anti-tumor effects. The mechanism was confirmed by observing no therapeutic benefit of αIL-10 in a mouse model with IFNα-receptor knocked out. Conclusions: Efficient targeting of antigen to immature dendritic cells with a chemokine fusion vaccine offers a potential alternative approach to the ex vivo dendritic cell antigen loading protocols currently undergoing clinical investigation. The flexibility and ease of construction of the vaccine make it an excellent platform for inducing immunity to tumor-specific neoantigens. Combining this approach with agents able to modulate the tolerogenic tumor microenvironment offers promise as a novel melanoma therapy