Abstract TMEM-016: DENDRITIC CELL VACCINATION AND INHIBITION OF TUMOR–ASSOCIATED IMMUNE SUPPRESSION

PURPOSE: Th17 cell infiltration correlates with markedly prolonged overall survival among ovarian cancer patients, prompting the question of whether Th17 cells could be induced or expanded to therapeutic advantage. To address this question, a phase I clinical trial to test the safety and immunogenicity of Th17-inducing dendritic cell (DC) vaccination for stage IIIC–IV ovarian cancer patients (Clinicaltrials.gov NCT02111941) is nearing its accrual goal (n = 22). Interim analyses show that 8 of 9 patients completing the induction phase of five DC vaccinations mounted Th17 and antibody responses to FRα target antigen. These results are encouraging, but we found that ovarian tumor-associated CD14 + macrophages strongly suppress Th17-inducing DC-stimulated tumor antigen-specific Th1/Th17 effector CD4 + T cells responses. The purpose of this project was to elucidate the mechanisms by which ovarian tumor ascites CD14 + cells suppress DC-stimulated T cell responses, and to explore innovative strategies for alleviation of CD14 + cell-mediated immune suppression, or redirection of CD14 + cells from a suppressive phenotype to a pro-inflammatory phenotype. EXPERIMENTAL PLAN: Primary ovarian ascites CD14 + myeloid cells were tested for their ability suppress DC-stimulated tumor antigen-specific CD4 + T cell responses in contact or transwell coculture assays. Ascites fluid and ascites CD14 + cells were screened for expression of key chemokines and cytokines associated with T cell migration and immune suppression. Ascites CD14 + cells were also screened for PD-L1 expression, indoleamine 2,3-dioxygenase (IDO) activity, and key signaling pathways that determine the balance between M1 and M2 function. We also tested the ability of small molecule inhibitors to block key functions and alleviate immune suppression. SUMMARY OF RESULTS : Ovarian ascites CD14 + cells suppress DC-stimulated CD4 + T cell responses at least in part through expression of IL-10 and IDO. PD-L1 and PD-1 are consistently expressed by ascites CD14 + cells. Flow cytometric phosphoprotein assays with ascites CD14 + cells (n = 9) revealed consistent activation of Akt S473 , ERK1/2 T202/Y204 , CREB S133 and STAT3 S727 . Ovarian tumor-associated CD14 + macrophages consistently show high activity of a non-canonical STAT3 signaling pathway revealed by phosphorylation of S 727 rather than the canonical Y 705 phosphorylation seen in the classical JAK-STAT3 pathway. This innovative finding is consistent for every patient sample tested to date - canonical STAT3 Y705 is absent. Inhibition of p38 T180/Y182 MAPK signaling reduced expression of IL-10, RANTES, MIP-1β and IP-10. CCL22 (MDC) expression was also limited by p38 inhibition, but markedly elevated by blockade of JAK1/2 signaling. Inhibition of c-Kit and PI3K/Akt signaling showed a trend towards reduced K/T ratios, whereas inhibition of STAT3 reduced kynurenine production, suggesting that IDO activity is regulated at least in part by non-canonical STAT3 S727 signaling. CONCLUSIONS : Multiple pathways regulate mechanisms of immune suppression by ovarian tumor ascites CD14 + myeloid cells. The p38 MAPK pathway regulates IL-10 expression, consistent with our published work on DC function. The non-canonical STAT3 S727 pathway may also play a central role in regulating immune function by myeloid cells in the tumor microenvironment. These studies are of fundamental importance for development of adjuvant treatments to enhance the clinical efficacy of Th-17-inducing DC vaccination for ovarian cancer. Citation Format: Martin J Cannon, PhD. DENDRITIC CELL VACCINATION AND INHIBITION OF TUMOR–ASSOCIATED IMMUNE SUPPRESSION [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr TMEM-016.