Abstract 3644: Pancreatic tumor cells that develop within Muc1 knock-out mice generate less immunosuppressive MDSCs in vitro

Abstract

Abstract Epithelial Mucin 1 (MUC1) is a well characterized tumor associated antigen found to be over expressed and aberrantly glycosylated in human pancreatic adenocarcinomas. In recent years, Myeloid- derived suppressor cells (MDSCs), major regulators of the immune response, have been implicated in the progression of cancer. We have recently shown that Muc1 null mice have a higher propensity of MDSCs and are unable to reject allogeneic tumors as effectively as their wild-type counterparts. Here, we studied the effects of tumor derived soluble factors (TDSFs) from pancreatic cancer cell lines that over expressed human MUC1 (KCM) or were null for Muc1 (KCKO) on the generation of MDSCs from bone marrow (BM) cells in vitro. The two cell lines were derived from a spontaneous mouse model of pancreatic ductal adenocarcinoma (PDA) that was bred to the Muc1-null (KCKO) or the human MUC1 transgenic (KCM) mice. BM cells were cultured in complete DMEM supplemented with 10ng/ml GM-CSF and 10ng/ml IL-4 + 30% v/v conditioned media (TCCM) from KCKO or KCM cell lines for 5 days. On day 3, floating cells were removed and fresh media with cytokines and TCCM was added. On day 5, cells were stained for MDSCs and analyzed by flow cytometry. Statistical analysis was performed using GraphPad software and p values were calculated using One-way ANOVA. We observed a significant increase in the monocytic (CD11b+Ly6C+Ly6G-) and the granulocytic (CD11b+Ly6C+LyG+) MDSC subpopulations when naïve BM cells were cultured in the presence of TCCM from KCKO versus KCM cells (p<0.05). Upon further analysis of certain myeloid and granulocytic maturation, activation and immune modulatory markers on the CD11b+Gr1+ MDSCs, we found an up-regulation of CD11c and CD115 molecules on the CD11b+Gr1+ MDSCs generated in the presence of KCKO TCCM but not in the presence of KCM TCCM (p<0.01). This indicated the presence of dendritic cell and macrophage phenotypic markers which arise from the maturation of the monocytic subpopulation. Indeed, we confirmed that the up-regulation of the CD11c and CD115 markers were only found on the monocytic but not on the granulocytic subpopulation when BM cells were treated with KCKO TCCM compared to KCM TCCM (p<0.01). Since the monocytic subpopulation possess most of the immune suppressive activity, we hypothesized that KCKO TCCM induces a more mature monocytic subpopulation of MDSC that may not be immunosuppressive. Thus, when KCKO and KCM cells were injected in vivo in a asyngeneic normal C57BL/6 mice, the KCM cells grew significantly faster than the KCKO cells which were not only slow growing but remained as a stable disease. This could be partially explained by the induction of a less suppressive MDSC phenotype. These findings could lead to therapies that manipulate the immune regulatory cell population maturing into a less immune suppressive state in a tumor setting allowing the body to mount an effective immune response against cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3644. doi:10.1158/1538-7445.AM2011-3644