Myeloid-derived suppressor cells in mammary tumor progression in FVB Neu transgenic mice

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.

Bone marrow myeloid-derived suppressor cells (MDSCs) inhibit graft-versus-host disease (GVHD) via an arginase-1–dependent mechanism that is up-regulated by interleukin-13

“…[14][15][16] We have used these cytokines to develop a culture system to produce CD11b ϩ Gr1 ϩ MDSCs from whole BM. Phenotypic analysis revealed these cells express IL4R␣ and CD115; both have previously been linked to enhanced suppressive capacity of MDSCs.…”

Differently immunogenic cancers in mice induce immature myeloid cells that suppress CTL in vitro but not in vivo following transfer

“…Mainly investigated in tumor transplantation models, 23,24 only a few studies have analyzed the immunosuppressive effect of iMC in autochthonous tumor models. 5,22,25,26 We think that the analysis of iMC in primary cancer models better reflects the clinical situation. iMC have not yet been analyzed in mice with autochthonous tumors and differences in tumor-reactive T cells.…”

“…17,20 Therefore, iMC subsets (CD11b Among other factors, GM-CSF, IL-6, and VEGF are held responsible for inducing and maintaining suppressive iMC. 5,17,18,21,22 Primary tumor cell lines derived from the 3 models produced, albeit to a different extent, VEGF and IL-6, which were also detectable in sera of tumor-bearing mice ( Figure 5). GM-CSF was not detectable in serum (data not shown) and primary tumor cell lines produced, if at all, only minute amounts of GM-CSF ( Figure 5C).…”

Gain or loss of TGF-β signaling in mammary carcinoma cells can promote metastasis

“…In mouse carcinoma models, the host MDSC cell population is often isolated using the CD11b and GR-1 markers. 78,82,83 Other markers such as F4/80, CD34, CD80 and VEGFR1 have also been identified in the CD11b + GR-1 + MDSC population from tumor bearing mice. 77,83 MDSCs have been isolated in association with tumors derived from various organs currently exemplified using mammary, ovarian, colon, sarcoma, thymoma and lung cancer models.…”

“…77,78,83,84 Further, the recruitment of MDSCs seems to be present in tumors transformed by alternate mechanisms as shown in mammary tumor models produced using transgenic ErbB2 or polyoma virus middle T antigen (PyVmT) expression and through implantation of tumor cells such as the tumorigenic 4T1, CT26, DA3, EL4, LLC, MethA and MC38 cell lines. 77,78,82,84,85 Interestingly, despite a concerted effort to characterize the tumor promoting MDSC populations, relatively little is known about the mechanisms and factors that contribute to their expansion and recruitment in vivo.…”