Abstract A83: The role of Ikaros in effector and regulatory T cell homeostasis in a murine pancreatic cancer model

Abstract

Abstract The alternatively spliced transcription factor Ikaros is crucial for normal lymphocyte development. Ikaros plays a role as a tumor suppressor in murine T cells. In pancreatic cancer hosts, the balance between effector and regulatory T cells is lost, leading to immunosuppression and reduced anti-tumor immunity. In this study, we aim to identify the role of Ikaros in regulating effector CD4+ and CD8+ and regulatory T cell homeostasis in a pancreatic tumor microenvironment. Using our murine heterotopic model of pancreatic cancer, we isolated splenocytes from tumor-bearing (TB) and control mice and performed western blot and qRT-PCR analyses to evaluate Ikaros mRNA and protein expression, respectively. Flow cytometry analyses were also used to immunophenotype T cell populations in splenocytes from control and TB mice. Next, magnetic activated cell sorting (MACS) was used to sort CD3+ T cells from TB and control splenocytes for western blot analyses of Ikaros expression. We also carried out in vitro and in vivo experiments using apigenin, a plant flavonoid and protein kinase inhibitor with anti-inflammatory, anti-tumor and anti-proliferative properties, to shed insight into how Ikaros may be regulated and its involvement in T cell development. Our results showed no difference in Ikaros mRNA expression but reduced expression of all Ikaros isoforms in splenocytes from TB mice compared with controls. Ikaros protein expression was also downregulated in sorted TB T cells, compared with control. Analyses of T cells by flow cytometry revealed a significant decrease in effector CD4+ and CD8+ T cell percentages but an increase in CD4+CD25+ regulatory T cells (Treg) in TB splenocytes compared with controls. In vitro, treatment of splenocytes with apigenin stabilized Ikaros' protein expression. In the presence of Panc02 cells, Ikaros protein expression was downregulated. However, the addition of apigenin to the co-culture blocked this downregulation. These correlated with in vivo findings that showed partial reversal of some Ikaros isoforms in TB mice treated with apigenin. Apigenin treatment also significantly increased CD4+ and CD8+ T cell percentages but decreased Treg percentages. We are currently performing experiments to determine how Ikaros may be regulated in T cells and its effect on their functions. Thus far, our findings suggest that PC progression is associated with reduced Ikaros expression, which may lead to loss of T cell homeostasis and thus, dampened anti-tumor immune responses. Citation Format: Nadine Nelson, Shengyan Xiang, Xiaohong Zhang, Karoly Szekeres, Ghansah Tomar. The role of Ikaros in effector and regulatory T cell homeostasis in a murine pancreatic cancer model. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A83.