Abstract 1593: Neutralization of IL-10 enhances antitumor efficacy of dendritic cell-targeting MIP-3α-gp100 vaccine by way of type-I interferons in B16F10 mouse melanoma model

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. Other studies have provided evidence that IL-10 neutralizing antibodies enhance immunological melanoma therapies by modulating the tolerogenic tumor microenvironment. Here, we report that neutralizing IL-10 enhances the therapeutic anti-melanoma efficacy of a MIP-3α-gp100 DNA vaccine. The current studies utilize the B16F10 syngeneic mouse melanoma model system. The MIP-3α-gp100 DNA vaccine is administered intramuscularly (i.m.) into the tibialis muscle, followed immediately by i.m. electroporation. The standard therapeutic protocol was the following: challenge with lethal dose of B16F10 cells (5x104) on day 0; vaccinate with 50μg vaccine plasmid on days 3, 10, and 17; and administer 150μg of αIL10 antibody intra-tumorally beginning on day 5, once every three days for up to six doses. 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. With this therapeutic protocol, we demonstrate for the first time that a therapy neutralizing IL-10 additively enhances the anti-tumor 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. Furthermore, infiltration into the tumor of plasmacytoid dendritic cells, known to be professional IFNα-producing cells, were enhanced with the combination therapy. 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. In conclusion, 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. Combining this approach with an IL-10 neutralizing antibody therapy that modulates the tolerogenic tumor microenvironment offers promise as a novel melanoma therapy. Citation Format: James Gordy, Kun Luo, Richard Markham. Neutralization of IL-10 enhances antitumor efficacy of dendritic cell-targeting MIP-3α-gp100 vaccine by way of type-I interferons in B16F10 mouse melanoma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1593. doi:10.1158/1538-7445.AM2017-1593