Abstract A13: Optimization of a dendritic cell-targeting MIP3α-antigen fusion vaccine in the B16F10 mouse melanoma model

Background: The chemokine MIP-3α (CCL20) binds to CCR6 found on immature dendritic cells. Vaccines fusing MIP-3α to gp100 have been shown to be effective in therapeutically alleviating melanoma in mouse models. However, that protection was not complete. To optimize the therapy, our laboratory is exploring two avenues. First, we added agents designed to modulate the tolerogenic tumor microenvironment. Here, we report that neutralizing IL-10 at the tumor site enhances the therapeutic anti-melanoma efficacy of a MIP-3α-gp100 DNA vaccine. Secondly, we are optimizing the antigenic profile of the vaccine to help reduce the probability of immunoediting processes leading to tumor therapy escape. Methods: The current studies utilize the B16F10 syngeneic, transplantable, mouse melanoma model system. The MIP-3α-antigen DNA vaccine is administered intramuscularly (i.m.) into the tibialis muscle, followed immediately by i.m. electroporation. Constructs utilized include MIP-3α fused to gp100 alone or in addition to TRP-2. Vaccinations are given therapeutically, beginning at day 3 or 5 post challenge. Tumor sizes, growth, and survival were all assessed. Treatment responses were characterized by flow cytometric analysis of tumor infiltrate. Vaccine-specific T-cells were delineated by gp10025-33 stimulation followed by intracellular cytokine staining for IFN-γ and assessment by flow cytometry. The mechanism of αIL-10 efficacy was explored by RT-PCR and confirmed with a knockout mouse model. Results: With this therapeutic protocol, we demonstrate for the first time that by either neutralizing IL-10 or adding a second antigen to our construct, we are able to enhance the antitumor efficacy of a MIP-3α-gp100 vaccine, leading to significantly smaller tumors, slower growing tumors, and overall increases in mouse survival. Surprisingly, the additive effects of αIL-10 were not shown to be directly mediated by any T-cell parameter tested, including vaccine-specific tumor infiltrating lymphocytes (TILs), total TILs of either CD4+ or CD8+ subset, regulatory T-cells, granzyme positive T-cells, and others. We discovered, however, that IFNα-4 transcripts in the tumor were significantly upregulated in mice given vaccine and αIL-10 compared to vaccine alone. A mouse model with IFNαR1 knocked out eliminated the protection provided by αIL-10, demonstrating that the additional therapeutic value of αIL-10 is primarily mediated by type-I interferons. The immunologic details of the added TRP2 antigen are currently being explored. 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. Adding multiple antigens or combining this approach with an IL-10 neutralizing antibody therapy that modulates the tolerogenic tumor microenvironment both enhance vaccine efficacy. Further potential therapy optimization currently undergoing investigation offers promise for this line of investigation to become a novel melanoma therapy. Citation Format: James T. Gordy, Kun Luo, Richard B. Markham. Optimization of a dendritic cell-targeting MIP3α-antigen fusion vaccine in the B16F10 mouse melanoma model [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A13.