Proliferation Of Myeloid-derived Suppressor Cells Research Articles

L-arginine and docetaxel synergistically enhance anti-tumor immunity by modifying the immune status of tumor-bearing mice

l-arginine (l-Arg) supplementation has been reported to enhance the function of immune cells, including dendritic cells (DCs) and T lymphocytes, in cancer models thereby countering the suppressive effects of myeloid-derived suppressor cells (MDSCs). The balance of the active immune cells is one factor that determines the progression of cancers in vivo. Docetaxel (DTX), an immunomodulatory chemotherapeutic agent, is now widely used in several types of malignancies including breast cancer. We hypothesized that the combination of DTX and l-Arg would elicit a more robust antitumor response than either molecule alone. To test this hypothesis we utilized BALB/c mice inoculated with 4T1 mammary carcinoma cells. DTX and l-Arg synergistically limited tumor growth in vivo and moderately increased the life span of tumor bearing mice. The anti-tumor effects were associated with the proliferation of splenic CD8+ CTL and CD4+ Th1 effector cells, as well as increased serum levels of interferon gamma. More importantly, DTX+l-Arg effectively increased anti-tumor immunity within the tumor microenvironment. Furthermore, the combined therapy increased the number of myeloid (mDCs) and plasmacytoid (pDCs) dendritic cells, potent activators of the T cell response, and enhanced expression of the maturation markers CD86 and MHC II (required for antigen presentation). The combination therapy also reduced the proliferation of MDSCs. These data suggest that DTX+l-Arg may be a novel therapeutic strategy for breast cancer patients.

Neural innervation stimulates splenic TFF2 to arrest myeloid cell expansion and cancer.

CD11b+Gr-1+ myeloid-derived suppressor cells (MDSCs) expand in the spleen during cancer and promote progression through suppression of cytotoxic T cells. An anti-inflammatory reflex arc involving the vagus nerve and memory T cells is necessary for resolution of acute inflammation. Failure of this neural circuit could promote procarcinogenic inflammation and altered tumour immunity. Here we show that splenic TFF2, a secreted anti-inflammatory peptide, is released by vagally modulated memory T cells to suppress the expansion of MDSCs through CXCR4. Splenic denervation interrupts the anti-inflammatory neural arc, resulting in the expansion of MDSCs and colorectal cancer. Deletion of Tff2 recapitulates splenic denervation to promote carcinogenesis. Colorectal carcinogenesis could be suppressed through transgenic overexpression of TFF2, adenoviral transfer of TFF2 or transplantation of TFF2-expressing bone marrow. TFF2 is important to the anti-inflammatory reflex arc and plays an essential role in arresting MDSC proliferation. TFF2 offers a potential approach to prevent and to treat cancer.

TLR9 ligation in pancreatic stellate cells promotes tumorigenesis.

Modulation of Toll-like receptor (TLR) signaling can have protective or protumorigenic effects on oncogenesis depending on the cancer subtype and on specific inflammatory elements within the tumor milieu. We found that TLR9 is widely expressed early during the course of pancreatic transformation and that TLR9 ligands are ubiquitous within the tumor microenvironment. TLR9 ligation markedly accelerates oncogenesis, whereas TLR9 deletion is protective. We show that TLR9 activation has distinct effects on the epithelial, inflammatory, and fibrogenic cellular subsets in pancreatic carcinoma and plays a central role in cross talk between these compartments. Specifically, TLR9 activation can induce proinflammatory signaling in transformed epithelial cells, but does not elicit oncogene expression or cancer cell proliferation. Conversely, TLR9 ligation induces pancreatic stellate cells (PSCs) to become fibrogenic and secrete chemokines that promote epithelial cell proliferation. TLR9-activated PSCs mediate their protumorigenic effects on the epithelial compartment via CCL11. Additionally, TLR9 has immune-suppressive effects in the tumor microenvironment (TME) via induction of regulatory T cell recruitment and myeloid-derived suppressor cell proliferation. Collectively, our work shows that TLR9 has protumorigenic effects in pancreatic carcinoma which are distinct from its influence in extrapancreatic malignancies and from the mechanistic effects of other TLRs on pancreatic oncogenesis.

Bone marrow mesenchymal stem cells suppress metastatic tumor development in mouse by modulating immune system.

IntroductionBone marrow mesenchymal stem cells (BMSCs) have been studied extensively because of their potential use in clinical therapy, regenerative medicine, and tissue engineering. However, their application in tumor therapy remains yet in preclinical stage because of the distinct results from different researches and vagueness of their functional mechanism. In this study, the influence of BMSCs on tumor growth was observed and the potential mechanism was investigated.MethodTwo animal models, H22 ascitogenous hepatoma in BALb/c mouse and B16-F10 pulmonary metastatic melanoma in C57 mouse, were adopted in experience in vivo and treated with BMSCs by intravenous injection. The percentage of Gr-1+CD11b+ myeloid-derived suppressor cells (MDSCs) and IFN-γ+ T cells were observed in peripheral blood (PB) and bone marrow (BM) by Flow Cytometry. BMSCs were co-cultured in vitro with tumor cells and MDSCs in a tumor conditioned medium separately in order to illustrate the mechanism.ResultsOur results demonstrated that BMSCs treatment caused a delayed tumor growth and a prolonged survival in both tumor models, the homing fraction of BMSCs in BM was 2% - 5% in 24–72 hours after transfusion and the percentage of Gr-1+CD11b+ MDSCs was downregulated in peripheral blood and BM. Meanwhile, IFN-γ+ T lymphocytes in PB increased. In vitro co-culture showed that BMSCs inhibited the induction and proliferation of MDSCs in tumor conditioned medium, whereas they didn’t affect the proliferation of B16-F10 and H22 cells by in vitro co-culture. Both in vivo and in vitro results showed that BMSCs have a systemic suppressive effect on MDSCs.ConclusionOur data suggest that BMSCs has suppressive effect on tumor and is feasible to be applied in cancer treatment. BMSCs inhibiting MDSCs induction and proliferation is likely one of the mechanism.

Bone marrow mesenchymal stem cells suppress ascitogenous hepatoma progression in BALB/c mouse through reducing myeloid-derived suppressor cells.

Bone marrow mesenchymal stem cells (BMSCs) and myeloid-derived suppressor cells (MDSCs) can be mobilized from bone marrow (BM) into blood stream and home in tumor stroma, where they either help or hinder tumor growth. The issue of whether BMSCs could affect MDSCs in ascitogenous hepatoma BALB/c mice, thus influencing their functional activity, remains unclear. In this study, we demonstrated that after transfusion into ascitogenous hepatoma BALB/c mice, the homing fraction of BMSCs in BM was 2%-5% in 24-72 h and the percentage of Gr-1+CD11b+ MDSCs was downregulated in peripheral blood (PB) and BM. Meanwhile, IFN-γ+ T lymphocytes in PB increased. As a result of such immunoregulation, BMSCs treatment caused a delayed tumor growth and a prolonged survival in H22 ascitogenous hepatoma model. Because the proliferation of H22 cells was not affected by in vitro coculture with BMSCs, this observation is likely due to a systemic suppressive effect on the host MDSCs. We also demonstrated that BMSCs inhibited the induction and proliferation of MDSCs from hematopoietic stem cells (HSCs) in an in vitro tumor conditioned medium. Thus, our findings show for the first time that BMSCs are potentially inhibitor during MDSCs induction and proliferation and that when injected intravenously into tumor bearing mice they might be effective antitumor agents suitable for cancer therapy.

MiR-34a expands myeloid-derived suppressor cells via apoptosis inhibition

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population and show significant expansion under pathological conditions. microRNA plays important roles in many biological processes, whether microRNAs have a function in the expansion of MDSCs is still not very clear. In this study, miR-34a overexpression can induce the expansion of MDSCs in bone marrow chimera and transgenic mice model. The experimental results suggest that miR-34a inhibited the apoptosis of MDSCs but did not affect the proliferation of MDSCs. The distinct mRNA microarray profiles of MDSCs of wild type and miR-34a over-expressing MDSCs combined with the target prediction of miR-34a suggest that miR-34a may target genes such as p2rx7, Tia1, and plekhf1 to inhibit the apoptosis of MDSCs. Taken together, miR-34a contributes to the expansion of MDSCs by inhibiting the apoptosis of MDSCs.

Specific Inhibition of the VEGFR-3 Tyrosine Kinase by SAR131675 Reduces Peripheral and Tumor Associated Immunosuppressive Myeloid Cells

Myeloid derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) represent prominent components in cancer progression. We previously showed that inhibition of the VEGFR-3 pathway by SAR131675 leads to reduction of TAM infiltration and tumor growth. Here, we found that treatment with SAR131675 prevents the accumulation of immunosuppressive blood and splenic MDSCs which express VEGFR-3, in 4T1 tumor bearing mice. Moreover we showed that soluble factors secreted by tumor cells promote MDSCs proliferation and differentiation into M2 polarized F4/80+ macrophages. In addition, cell sorting and transcriptomic analysis of tumor infiltrating myeloid cells revealed the presence of a heterogeneous population that could be divided into 3 subpopulations: (i) immature cells with a MDSC phenotype (GR1+/CD11b+/F4/80−); (ii) “immuno-incompetent” macrophages (F4/80high/CD86neg/MHCIILow) strongly expressing M2 markers such as Legumain, CD206 and Mgl1/2 and (iii) “immuno-competent”-M1 like macrophages (F4/80Low/CD86+/MHCIIHigh). SAR131675 treatment reduced MDSCs in lymphoid organs as well as F4/80High populations in tumors. Interestingly, in the tumor SAR131675 was able to increase the immunocompetent M1 like population (F4/80low). Altogether these results demonstrate that the specific VEGFR-3 inhibitor SAR131675 exerts its anti tumoral activity by acting on different players that orchestrate immunosuppression and cancer progression in a tumoral context: MDSCs in peripheral lymphoid organs and TAMs infiltrating the tumor.

Trp53 inactivation in the tumor microenvironment promotes tumor progression by enhancing MDSC differentiation (P2073)

Abstract Inactivation of the tumor suppressor p53 is one of the leading causes of cancer as p53 inactivation via somatic mutations occurs in 50% of human cancers and sometimes in other cells of the tumor microenvironment (TME). Recent studies by our laboratory and others showed that innate and adaptive immunities are skewed towards pro-inflammation in hosts lacking p53 function. As chronic inflammation plays a vital role in tumor initiation, progression, and metastases, we hypothesized that p53 inactivation in the TME favors tumorigenesis by promoting inflammation. In this study, we compared the growth of subcutaneously inoculated B16F1 melanoma in p53null and WT mice. Tumor growth in p53null mice was greatly accelerated, correlating with marked increases in CD11b+Gr-1+ myeloid-derived suppressor cells (MDSCs), FoxP3+ regulatory T cells, and a loss of effector function, compared with those in WT mice. This augmented immunotolerance in tumor bearing p53null mice was associated with an enhanced MDSC proliferation, an increased frequency of myeloid progenitors in the peripheral lymphoid tissues, and a marked elevation of serum inflammatory cytokines/chemokines, compared with those of WT mice. Together, these results support our hypothesis and reveal a previously unappreciated function for p53 in maintaining an immunological microenvironment that suppresses tumor initiation and progression.

Abstract 4363: Tumor regulation of myeloid-derived suppressor cell proliferation, circulation and apoptosis.

Abstract In response to stress, myeloid progenitor cells (MPCs) mobilize and establish sites of extramedullary hematopoiesis (EMH) within lymphoid and parenchymal organs. We report that the spleens of 4T1 mammary tumor-bearing (TB) mice are the primary site of MPC proliferation resulting in extensive EMH in association with decreased apoptosis, increased myeloid cell survival, and increased hematopoietic growth factor (GF) transcription by the tumor cells. MPC trafficking and survival differs between TB and naïve mice with leukocyte arrest in the lungs of naïve mice and accumulation in the splenic red pulp of TB mice with little marrow or tumor arrest or proliferation. Indeed, despite the high levels of GF transcription by tumor cells MDSC apoptosis in tumors is very high perhaps due to the high levels of NOS2 in the tumor microenvironment. Further myeloid proliferation directly correlates with the decrease in T-cell frequency, which is associated with extrathymic, but not thymic T-cell proliferation. In summary, tumor cytokines regulate a dynamic relationship between MPCs and T-cells regulating their proliferation, trafficking, accumulation, apoptosis, and survival. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4363. doi:1538-7445.AM2012-4363