Abstract B66: Blockade of PD-1 signaling in tumor-associated dendritic cells results in compensatory IL-10 release maintaining immune suppression in ovarian cancer microenvironments.
Authors: Lamichhane Purushottam , Karyampudi Lavakumar , Shreeder Barath , Krempski James , Bahr Deborah , Block Matthew , Knutson Keith 
Published: May 2016

Abstract
PD-1 and PD-L1 form a major inhibitory axis that acts to suppress tumor-rejecting effector responses. In addition to its expression and inhibitory functions in T and B cells, PD-1 has also been shown to be expressed on and hence impact the functions of cells of innate arm, such as dendritic cells (DCs), primarily at the tumor site but not in the periphery. Our aim in this study was to identify tumor-associated factor(s) responsible for PD-1 regulation on DCs and investigate how DCs in the tumor microenvironment respond to anti-PD-1-based immunotherapy. Both bone marrow-derived dendritic cells (BMDCs) as well as murine ovarian tumor ascites-derived DCs were used in the studies. Using in vitro cultures, we show that the cytokine IL-10; which is expressed in abundance in many malignancies including ovarian cancer, is potent regulator of PD-1 expression on DCs. Based on inhibition and siRNA knockdown studies; we show that IL-10 mediated PD-1 expression depends on STAT3 activation. Treatment of DCs with IL-10 also led to an increase in expression of PD-L1 on surface of DCs as well as an increase in release of soluble PD-L1. Antibody-mediated blockade of PD-1 on DCs led to greatly increased production of IL-10 (&gt; 4 fold) in cultures in vitro. Furthermore, treatment of tumor bearing mice with anti-PD-1 antibody led to a significant increase of IL-10 in ascites (&gt; 6 fold) and periphery (&gt; 4 fold). This compensatory release of IL-10 correlated with a further increase in PD-1 expression on DCs both in vitro and in vivo. In in vivo studies, while the blockade of PD-1 or IL-10 neutralization as monotherapy were ineffective, blockade of PD-1 and IL-10 neutralization as combination therapy augmented the anti-tumor response in ovarian tumor bearing mice; leading to a decrease in tumor growth and a significant increase in survival. These results show that the IL-10 and PD-1 pathways intersect with DCs in the tumor microenvironment. PD-1 blockade on DCs leads to compensatory release of IL-10 resulting in the maintenance of immunosuppression, and a combination regimen of PD-1 blockade and IL-10 neutralization has therapeutic benefit in ovarian tumors. These results serve as catalyst to explore the feasibility/efficacy of exploiting these targets in clinical settings for treatment of human ovarian cancer.
Citation Format: Purushottam Lamichhane, Lavakumar Karyampudi, Barath Shreeder, James Krempski, Deborah Bahr, Matthew Block, Keith Knutson. Blockade of PD-1 signaling in tumor-associated dendritic cells results in compensatory IL-10 release maintaining immune suppression in ovarian cancer microenvironments. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B66.