Abstract 2198: The anti-tumor enhancement of a dendritic-cell targeting MIP3α-Gp100-Trp2 DNA vaccine by IFNα and 5-Aza-2'-deoxycytidine treatments correlates with intratumoral CCL19 but not CCL21 expression

Abstract Background: The chemokine MIP-3α (CCL20) binds to CCR6 on immature dendritic cells (DCs). DNA vaccines fusing MIP-3α to melanoma-associated antigens gp100 and/or tyrosinase-related protein 2 (Trp2) have delayed tumor growth and increased survival time in the B16F10 mouse melanoma model system compared to vaccines lacking the chemokine. To further enhance the therapeutic effects of the vaccine, our laboratory has added type-I interferon (IFNα) and 5-Aza-2'-deoxycitidine (5Aza) to the therapy. Here, we report that the enhancement previously seen by the combination of IFNα, 5Aza, and a MIP-3α-Gp100-Trp2 (MGpTrp2) DNA vaccine correlates with increases of tumor-infiltrating CD8+T-cells (CD8 TILs) and intratumoral expression of CCL19 but not CCL21. Methods: Beginning on day five post-transplantation of B16F10 melanoma, vaccine was administered intramuscularly (i.m.) by electroporation. CpG adjuvant was given two days later. 5Aza was given intraperitoneally at 1mg/kg and IFNα therapy either intratumorally or i.m. as noted. Tumor sizes, tumor growth, and mouse survival were assessed. Tumor lysate gene expression levels and tumor-infiltrating lymphocytes (TILs) were assessed by qRT-PCR and flow cytometry with intracellular cytokine staining, respectively. Results: Previous work has shown that the combination of IFNα, 5Aza, and MGpTrp2 led to significantly reduced tumor burden and overall increases in mouse survival dependent upon all three components. The addition of 5Aza and IFNα to the vaccine affected T-cell tumor infiltration, increasing the proportion of CD3+CD8+ cells in gated TILs by 92% over vaccine alone (p<0.0001), which correlated with tumor size (r2: 0.507; p<0.0001). Interferon stimulated genes such as Mx1, MHC1, CXCL10, and GranzymeB were modestly upregulated in the tumor lysate. However, CCL19, normally expressed constitutively in lymphoid tissues, was upregulated 10-fold compared to vaccine alone (p<0.0001) and was correlated with tumor size (r2: 0.195; p=0.002). The CCL19 receptor, CCR7, was upregulated to a lesser degree (5-fold over vaccine; p<0.001), and interestingly its partner chemokine CCL21 did not have significantly different expression patterns across groups (p=0.14 to vaccine). Conclusions: Efficient targeting of antigen to immature dendritic cells with a chemokine-fusion vaccine offers a potential alternative approach to classic and dendritic cell-based vaccines. Combining this approach with IFNα and 5Aza treatments significantly improved vaccine efficacy. This enhancement was correlated with CD8+ TIL recruitment and with the expression of the T-cell trafficking chemokine CCL19. 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, Avinaash K. Sandhu, Samuel K. Ayeh, Aakanksha Kapoor, Emily Kim, Petros C. Karakousis, Richard B. Markham. The anti-tumor enhancement of a dendritic-cell targeting MIP3α-Gp100-Trp2 DNA vaccine by IFNα and 5-Aza-2'-deoxycytidine treatments correlates with intratumoral CCL19 but not CCL21 expression [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2198.