[Show abstract][Hide abstract] ABSTRACT: Myeloid-derived suppressor cells (MDSCs) increase during tumor growth and following cytoreductive therapy resulting in immune dysfunction and tumor escape from host control. We report organ- and tumor-specific expansion of MDSCs, differences in their molecular and membrane phenotypes and T-cell suppressive activity. A significant increase in MDSCs was observed within the spleen, peripheral blood (PB), bone marrow (BM), lungs, and livers of mice bearing orthotopic 4T1, but not CI66 mammary tumors. The PB of 4T1 TB mice had the highest frequency of MDSCs (78.6±2.1%). Similarly, the non-parenchymal cells (NPCs) in the tumor tissue, livers and lungs of 4T1 tumor-bearing (TB) mice had an increased MDSCs frequency. Studies into Gr-1 and Ly-6C staining of MDSCs revealed significant increases in CD11b+Gr-1(dull)Ly-6C(high) and CD11b+Gr-1(bright)Ly-6C(low) subsets. The frequency of MDSCs inversely correlated with the CD3+ T-cell frequency in the spleen, and blood of 4T1 TB mice and was associated with a significant decrease in splenic and NPCs IFN-γ and IL-12 transcript levels, as well as significantly increased levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), stem cell factor (SCF), granulocyte colony-stimulating factor (G-CSF), interleukin-10 (IL-10), interleukin-13 (IL-13), arginase-1 (ARG-1), nitric oxide synthase (NOS-2), vascular endothelial growth factor-A (VEGF-A) transcripts. In summary, MDSCs are significantly increased not only in lymphoid organs, but also in parenchymal organs including lungs and livers of TB mice, where they may facilitate metastasis to these organ sites.
Full-text · Article · Mar 2011 · International immunopharmacology
[Show abstract][Hide abstract] ABSTRACT: Mouse mammary tumor virus-Neu (MMTV/neu) transgenic mice on an FVB-background (FVB-neuN) have increased numbers of myeloid derived suppressor cells (MDSCs) and regulatory T-cells (T-regs) in the spleen during mammary tumor induction and progression. Using this transgenic tumor model, we assessed the therapeutic activity of sunitinib, a multi-targeted, tyrosine kinase (TK) inhibitor and its effects on immune-regulatory cells. Our preliminary results show that sunitinib at 40mg/kg/day, p.o. (per os), delayed the time to tumor induction and reduced the incidence and growth of tumors in FVB-neuN mice. In association with its therapeutic activity, sunitinib reduced the absolute number of splenic T-reg cells (CD4(+)CD25(+)CD62L(+)) and MDSCs (CD11b(+)Gr1(+)) that were increased during tumor progression with less activity in mice with gross tumors. A significant decrease in the absolute number of splenic T-regs, dendritic cells (DCs), MDSCs and hematopoietic progenitors (Lin(-)Sca1(+)CD90(dull)) was observed following sunitinib treatment. The frequency of splenic T-regs and hematopoietic progenitors, but not MDSCs was also reduced by sunitinib treatment. Additionally immune-regulatory cytokines and enzymes were down regulated by sunitinib treatment, including TGFbeta and NOS2 in the spleen cells of sunitinib treated mice as compared to untreated tumor bearing (TB) mice. We conclude that sunitinib has therapeutic activity, in association with the down regulation of MDSCs and T-regs and has a trend towards the normalization of the inflammatory cytokine levels induced by tumor progression and growth. Based on these results, we suggest that sunitinib reduction of immune suppressive cells is a critical part of its adjuvant immune therapeutic activity.
Full-text · Article · Oct 2009 · International immunopharmacology
[Show abstract][Hide abstract] ABSTRACT: Female mice transgenic for the rat proto-oncogene c-erb-B2, under control of the mouse mammary tumor virus (MMTV) promoter (neuN), spontaneously develop metastatic mammary carcinomas. The development of these mammary tumors is associated with increased number of GR-1(+)CD11b(+) myeloid derived suppressor cells (MDSCs) in the peripheral blood (PB), spleen and tumor. We report a complex relationship between tumor growth, MDSCs and immune regulatory molecules in non-mutated neu transgenic mice on a FVB background (FVB-neuN). The first and second tumors in FVB-neuN mice develop at a median of 265 (147-579) and 329 (161-523) days, respectively, resulting in a median survival time (MST) of 432 (201 to >500) days. During tumor growth, significantly increased number of MDSCs is observed in the PB and spleen, as well as, in infiltrating the mammary tumors. Our results demonstrate a direct correlation between tumor size and the number of MDSCs infiltrating the tumor and an inverse relationship between the frequency of CD4(+) T-cells and MDSCs in the spleen. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assessment of enzyme and cytokine transcript levels in the spleen, tumor, tumor-infiltrating non-parenchymal cells (NPCs) and mammary glands revealed a significant increase in transcript levels from grossly normal mammary glands and tumor-infiltrating NPCs during tumor progression. Tumor NPCs, as compared to spleen cells from wild-type (w/t) mice, expressed significantly higher levels of arginase-1 (ARG-1), nitric oxide synthase (NOS-2), vascular endothelial growth factor (VEGF-A) and significantly lower levels of interferon (IFN)-gamma, interleukin (IL)-2 and fms-like tyrosine kinase-3 ligand (Flt3L) transcript levels. Transcript levels in the spleens of tumor-bearing (TB) mice also differed from normal mice, although to a lesser extent than transcript levels from tumor-infiltrating NPCs. Furthermore, both spleen cells and NPCs from TB mice, but not control mice, suppressed alloantigen responses by syngeneic control spleen cells. Correlative studies revealed that the number of MDSCs in the spleen was directly associated with granulocyte colony stimulating factor (G-CSF) transcript levels in the spleen; while the number of MDSCs in the tumors was directly correlated with splenic granulocyte macrophage stimulating factor (GM-CSF) transcript levels, tumor volume and tumor cell number. Together our results support a role for MDSCs in tumor initiation and progressive, T-cell depression and loss of function provide evidence which support multiple mechanisms of MDSC expansion in a site-dependent manner.
Full-text · Article · Jun 2009 · Cancer Immunology and Immunotherapy
[Show abstract][Hide abstract] ABSTRACT: The tumor microenvironment is heterogeneous for the expansion and infiltration by myeloid derived suppressor cells (MDSCs) which has been hypothesized to be dependent on tumor burden. We report a relationships between tumor size, MDSCs and T-cells; using four murine mammary tumors to assess tumor growth, infiltration and gene expression. Our analysis of cellular infiltration into tumors and gene expression used collagenase dissociated tumors and density gradient isolation of non-parenchymal cells (NPCs). The frequency of splenic and peripheral blood (PB) MDSCs was tumor dependent resulting in a significantly increased number of MDSCs. The MDSC frequency inversely correlated with the frequency of CD3+ lymphocytes in the spleen, independent of the tumor studied and directly correlated with tumor burden. Tumor growth up-regulated cyclooxygenase-2 (COX-2), vascular endothelial growth factor-A (VEGF-A), granulocyte (G-) and granulocyte-monocyte-colony stimulating factor (GM-CSF), arginase-1 (ARG-1), and nitric oxide synthase-2 (NOS-2) transcription in the tumor and spleens (not VEGF-A). The frequency of splenic MDSCs directly correlated with splenic COX-2, NOS-2, and ARG-1 message levels, while COX-2 and NOS-2 transcript levels inversely correlated with splenic CD3+ cell frequency. COX-2 mRNA levels also directly correlated with the ARG-1 and NOS-2 transcript levels from tumor-infiltrating leukocytic cells, supporting prostaglandin E2 as a regulator of ARG-1 and NOS-2 transcription. In summary, MDSC numbers in the spleen and tumor microenvironment are tumor dependent, directly correlating with tumor size and inversely correlating with T-cell number. MDSCs are also directly associated with VEGF-A and G-CSF transcript levels suggesting multiple mechanisms for MDSC regulation and COX-2, NOS-2 and ARG-1 supporting multiple mechanisms of T-cell suppression.
Full-text · Article · May 2009 · International immunopharmacology