Abstract 3184: Tumor-entrained dendritic cells promote ICOS/ICOSL-dependent Th17-like responses in pancreatic adenocarcinoma

BACKGROUND: Ranking 4th among cancer-related deaths worldwide, pancreatic adenocarcinoma (PDAC) boasts a dismal prognosis. The robust immune infiltrate that comprises its tumor microenvironment (TME) can influence disease progression. Tumor rejection by T lymphocytes relies on proper guidance by dendritic cells (DCs). This antigen-education is manifested by the DCs’ expression of co-stimulatory factors, such as ICOS-ligand (ICOSL). In this study, we plan to elucidate the mechanisms used by PDAC-entrained DC to modify T cell effector function and differentiation. METHODS: To establish our in vivo model, either PBS or 2.5e+5 “FC1242” murine PDAC cells derived from the tumor of a KPC mouse (LSL-KrasG12D; Trp53R172H; pdxCre/+) were injected into the distal pancreata of C57BL/6J (WT) mice. After 20 days, mice were euthanized and the spleen and tumor were assayed. DC phenotype was determined by flow cytometry (FC). DC function was assessed by mixed-leukocyte reactions (MLR) and peptide-specific proliferation assays, +/- neutralizing mAbs against ICOSL or ICOS. Supernatant cytokines were assessed at 84h using cytometric bead assays (CBA). Intracellular cytokines were analyzed by FC after 5h re-stimulation with PMA/IMN. To assess in vivo proliferation, 2.5e+6 of both OT1 and OT2 T cells labeled with CFSE or CPD, respectively, were co-injected into WT mice and challenged with 5e+5 OVA-loaded DC after 24h. Proliferation was assessed 4 days post-DC inoculation. RESULTS: Splenic FC1242-DC had lower expression of MHC2 and CD83, while tumor-infiltrating DC (TME-DC) displayed higher levels of each, relative to controls. TME-DC also exhibited higher expression of ICOSL, CD80, and CD86. Despite no difference in ICOSL expression between splenic groups, MHC2 and CD83 were substantially lower on ICOSL+ DC of FC1242 spleen, while highest on that of the TME, relative to controls. We found a higher fraction of CD11b+ myeloid DC (mDC) and a lower fraction of cross-presenting CD8α+ DC (xDC) in both tumor-bearing groups relative to controls. FC1242-mDC expressed higher CD80 and PDL1 than sham-mDC, while FC1242-xDC displayed lower CD80 and no difference in PDL1. Also, tumor-entrained DC had a diminished propensity for CD8+ T cell expansion in vitro and in vivo, resulting in lower Granzyme B, IFNγ, and TNFα. Interestingly, DC tumor-entrainment improved CD4+ T cell expansion and augmented IL-17A, IL-6, G-CSF secretion, while diminishing IFNγ, TNFα, IL-13, and IL-2. Blockade of the ICOS-pathway hindered IL17 production, and amplified production of IFNγ and TNFα by T cells. CONCLUSION: This study suggests that DC possess a vital role as liaisons between the TME and cell-mediated immunity. Furthermore, Th17 cells in the TME can accelerate PDAC progression. This makes the ICOS-pathway especially attractive, as it can modify anti-tumor immunity while circumventing the barriers of drug-delivery to the TME. Citation Format: Rocky M. Barilla, Raul Caso, Antonina Avanzi, Anjlee Panjwani, Xiaopei L. Zeng, Steve Matthews, Daniel M. Tippens, Lena Tomkoetter, Elliot M. Levie, Alejandro Torres-Hernandez, Donnele Daley, George Miller. Tumor-entrained dendritic cells promote ICOS/ICOSL-dependent Th17-like responses in pancreatic adenocarcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3184. doi:10.1158/1538-7445.AM2015-3184