Abstract 4975: The role of the Ikaros transcription factor in regulatory T cell (Treg) development and function in a murine pancreatic adenocarcinoma model.
Authors: Nelson Nadine , Jerald Maya , Pendleton Laura , Szekeres Karoly , Vohra Nasreen , Pilon-Thomas Shari , Ghansah Tomar 
Published: August 2014

Abstract
Pancreatic cancer (PC) is currently the only major form of cancer that still has survival rates in the single digits. The limited success of cancer therapies in treating pancreatic cancer has been primarily due to the immunosuppressive tumor microenvironment. In particular, there is an increased prevalence of regulatory T cells (Tregs) (CD4+CD25+CD127−), which suppress anti-tumor immune responses in PC tumor-bearing (TB) hosts. Tregs express the Forkhead BoxP3 (FoxP3) gene, which is critical for their suppressive function. Studies have shown that Ikaros, a zinc finger transcription factor, is an important regulator of T lymphocyte development and function. The regulation of Ikaros’ expression and function is controlled by post-translational modification events. Deficiencies in Ikaros are observed in various T cell leukemias and lymphomas. However, little is known about the possible role of Ikaros in regulating immune cell development in response to solid cancers. In this study, we aim to identify the role of Ikaros in regulating Treg homeostasis and function in a pancreatic tumor microenvironment. Therefore, using our murine model of pancreatic cancer, we isolated splenocytes from TB and control mice and performed flow cytometry and magnetic activated cell sorting (MACS) to immunophenotype and enrich T cell populations for in vivo and in vitro analyses. Also, we performed quantitative real-time PCR (qRT-PCR) and western blot analyses to evaluate Ikaros and FoxP3 mRNA and protein expression in whole and enriched CD3+ T cells from TB and control splenocytes. Our results showed that effector T cell percentages (CD4+ and CD8+) were significantly lower in splenocytes from TB mice compared to control. However, our results also showed a significant expansion of Tregs in splenocytes from TB mice compared to control. In addition, enriched TB Tregs (CD4+CD25+) suppressed antigen-specific CD8+T cell immune responses in a dose-dependent manner, in vitro. Preliminary qRT-PCR results revealed no significant difference in Ikaros mRNA expression; whereas, Ikaros protein expression was reduced in TB whole splenocytes compared to control. Also, Ikaros protein expression was reduced in TB enriched CD3+ T cells compared to control. Furthermore, our results showed an increase in FoxP3 protein expression in TB CD3+ T cells compared to control. These findings suggest that the pancreatic tumor microenvironment potentially down-regulates Ikaros’ protein expression, which may contribute to the expansion of Tregs and their suppression of CD8+T cell (anti-tumor) immune responses.
Citation Format: Nadine Nelson, Maya Jerald, Laura Pendleton, Karoly Szekeres, Nasreen Vohra, Shari Pilon-Thomas, Tomar Ghansah. The role of the Ikaros transcription factor in regulatory T cell (Treg) development and function in a murine pancreatic adenocarcinoma model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4975. doi:10.1158/1538-7445.AM2013-4975