Tumor-infiltrating Myeloid-derived Suppressor Cells Research Articles

Systemic and local immunosuppression in glioblastoma and its prognostic significance.

The effectiveness of tumor therapy, especially immunotherapy and oncolytic virotherapy, critically depends on the activity of the host immune cells. However, various local and systemic mechanisms of immunosuppression operate in cancer patients. Tumor-associated immunosuppression involves deregulation of many components of immunity, including a decrease in the number of T lymphocytes (lymphopenia), an increase in the levels or ratios of circulating and tumor-infiltrating immunosuppressive subsets [e.g., macrophages, microglia, myeloid-derived suppressor cells (MDSCs), and regulatory T cells (Tregs)], as well as defective functions of subsets of antigen-presenting, helper and effector immune cell due to altered expression of various soluble and membrane proteins (receptors, costimulatory molecules, and cytokines). In this review, we specifically focus on data from patients with glioblastoma/glioma before standard chemoradiotherapy. We discuss glioblastoma-related immunosuppression at baseline and the prognostic significance of different subsets of circulating and tumor-infiltrating immune cells (lymphocytes, CD4+ and CD8+ T cells, Tregs, natural killer (NK) cells, neutrophils, macrophages, MDSCs, and dendritic cells), including neutrophil-to-lymphocyte ratio (NLR), focus on the immune landscape and prognostic significance of isocitrate dehydrogenase (IDH)-mutant gliomas, proneural, classical and mesenchymal molecular subtypes, and highlight the features of immune surveillance in the brain. All attempts to identify a reliable prognostic immune marker in glioblastoma tissue have led to contradictory results, which can be explained, among other things, by the unprecedented level of spatial heterogeneity of the immune infiltrate and the significant phenotypic diversity and (dys)functional states of immune subpopulations. High NLR is one of the most repeatedly confirmed independent prognostic factors for shorter overall survival in patients with glioblastoma and carcinoma, and its combination with other markers of the immune response or systemic inflammation significantly improves the accuracy of prediction; however, more prospective studies are needed to confirm the prognostic/predictive power of NLR. We call for the inclusion of dynamic assessment of NLR and other blood inflammatory markers (e.g., absolute/total lymphocyte count, platelet-to-lymphocyte ratio, lymphocyte-to-monocyte ratio, systemic immune-inflammation index, and systemic immune response index) in all neuro-oncology studies for rigorous evaluation and comparison of their individual and combinatorial prognostic/predictive significance and relative superiority.

Hypoxia and programmed cell death-ligand 1 expression in the tumor microenvironment: a review of the effects of hypoxia-induced factor-1 on immunotherapy.

One useful cancer treatment approach is activating the patient's immune response against the tumor. In this regard, immunotherapy (IT) based on immune checkpoint blockers (ICBs) has made great progress in the last two decades. Although ITs are considered a novel approach to cancer treatment and have had good results in preclinical studies, their clinical success has shown that only a small proportion of treated patients (about 20%) benefited from them. Moreover, in highly progressed tumors, almost no acceptable response could be expected. In this regard finding the key molecules that are the main players of tumor immunosuppression might be helpful in overcoming the possible burdens. Hypoxia is one of the main components of the tumor microenvironment (TME), which can create an immunosuppressive microenvironment in various ways. For example, hypoxia is one of the main factors of programmed cell death ligand-1 (PD-L1) upregulation in tumor-infiltrating Myeloid-Derived Suppressor Cells (MDSCs). Therefore, hypoxia can be targeted to increase the efficiency of Anti-PD-L1 IT and has become one of the important issues in cancer treatment strategy. In this review, we described the effect of hypoxia in the TME, on tumor progression and immune responses and the challenges created by it for IT.

Abstract C174: MerTK as a putative biomarker for treatment response in triple negative breast cancer

Abstract Triple Negative Breast Cancer (TNBC) is characterized by the lack of estrogen, progesterone, and HER2 receptors. TNBC is a highly invasive subtype of breast cancer, with limited targeted therapies. Current therapeutic options for TNBC patients include surgery, chemotherapy, and radiation but disease recurrence is common. Anti-PD-1 and anti-PD-L1 therapeutic antibodies have been approved for the treatment of TNBC in combination with chemotherapy, but biomarkers for response and new therapeutic targets are still needed. The receptor tyrosine kinase MerTK has been associated with many types of cancer and is highly expressed in TNBC. To investigate the role of MerTK in TNBC, we created a syngeneic cell line (4T1) overexpressing MerTK to evaluate tumor growth, the tumor immune microenvironment (TIME), and response to immune checkpoint inhibitors (ICIs) in vivo. First, we tested the effect of MerTK on tumor growth in vivo by inoculating the 4T1 cell line, which has very low MerTK expression, and two 4T1 MerTK-overexpressing clones into eight Balb/c mice per group subcutaneously on the flank. We measured tumor growth over 27 days and found that MerTK-overexpressing tumors exhibited a statistically significant delay in tumor growth when compared to the parental 4T1 tumors. This indicates that MerTK may be inducing a hotter TIME in MerTK overexpressing tumors, as this slowed growth was not observed in athymic nude mice. To test this hypothesis, we evaluated the TIME of these tumors by flow cytometry, which revealed robust expansion of macrophage, natural killer cell and T cell compartments, and reduction in tumor-infiltrating myeloid derived suppressor cells. These results suggest that MerTK is playing a yet unidentified role in promoting infiltration of anti-tumor immune cells into the TIME and excluding pro-tumor immune cells. Further, we saw robust changes in genes associated with cytokine signaling pathways including CD38, CCL2 and CCL5 by Nanostring nCounter analysis in MerTK-overexpressing 4T1 cells compared to parental 4T1 cells. Finally, there is evidence that hotter tumors respond well to ICI therapy, and we hypothesized that MerTK-overexpressing tumors would exhibit a significant response to ICI when compared to parental 4T1 tumors. Indeed, our data showed a robust and durable response marked by a significant reduction in tumor growth in the MerTK-overexpressing tumors compared to parental 4T1 tumors in Balb/c mice when treated with either anti-PD-L1 or anti-CTLA-4 antibodies. Together, these results suggest that MerTK overexpression could serve as a predictive biomarker for response to immune therapy in patients with TNBC. Citation Format: Bridget E Mehall, Mari Iida, Kourtney L Kostecki, Jillian M Adams, Deric L Wheeler. MerTK as a putative biomarker for treatment response in triple negative breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C174.

Impacts of Combining Pulsed Low Dose Rate Radiotherapy (PLDR) and Anti-PD-1 Antibody on Tumor Growth and Its Mechanism for Lung Cancer in Mice

As an emerging anti-tumor strategy, Immunotherapies has been approved for the treatment of a variety of tumors. Recent data suggest that the efficacy of radiotherapy in various cancers can be augmented when combined with immune checkpoint blockade. Then, pulsed low dose rate radiotherapy (PLDR) is a new radiotherapy segmentation method. Therefore, this study investigated the inhibitory effect of PLDR combined with anti-PD-1 antibody on lung cancer in mice and its impact on tumor immune microenvironment. By transplanting murine LLC cells into the right leg of C57BL/6 mice with immune activity, a transplanted subcutaneous tumor model was established. The mice were randomly divided into five groups: control, conventional radiotherapy (RT)±anti-PD-1 antibody (mAb),PLDR±anti-PD-1 antibody (mAb). RT was delivered as a dose of 5 × 2 Gy whereas PLDR involved delivering a dose of 2 Gy as 10 pulses of 0.2 Gy, each 3 minutes apart and lasting for 5 days. Anti-PD-1 antibody and isotype control were administered intraperitoneally once every three days at a dose of 5mg/kg, three times in total. The tumor, blood and tumor-draining lymph nodes (TDLNs) were harvested after treatment, and a single cell suspension was prepared for flow cytometry to analyze the changes in the immune microenvironment of the tumor tissue, the expression of PD-L1. PD-1 and the activated systemic immune response; Finally, this study explored a mechanism able to explain the observed synergy of combined therapy. PLDR combined with anti-PD-1 antibody can better inhibit the growth of tumor than RT,PLDR and RT combined group. Survival analysis demonstrated a statistically significant advantage for PLDR+anti-PD-1 than other groups. Median survival with PLDR+anti-PD-1mAb was 63d compared with 54d with RT+anti-PD-1mAb,41d with RT and 40d with PLDR and 33 with control. Meanwhile both RT and PLDR induced up-regulation of PD-L1 expression on tumor surface and PD-1 expression on lymphocytes. Then, the frequency of CD4+,CD8+T cells were higher in the PLDR combined treatment group in tumor blood and draining lymph nodes, and synergistically reduce the local accumulation of tumor-infiltrating myeloid-derived suppressor cells (MDSCs) than others. Finally, the main reason for the better tumor inhibition effect of PLDR combined group is that it upgrades the number and activity of CD8+T cells in tumor. PLDR combined with anti-PD-1 antibody can result in better tumor growth inhibition and significantly delay the survival time of mice, which was mainly through the cytotoxic T cell-dependent mechanism, meanwhile increasing the infiltration of CD4 + and CD8 +T-cells in tissues.

Myeloid-derived suppressor cells deficient in cholesterol biosynthesis promote tumor immune evasion

Cancer immunotherapy targeting myeloid-derived suppressor cells (MDSCs) is one of the most promising anticancer strategies. Metabolic reprogramming is vital for MDSC activation, however, the regulatory mechanisms of cholesterol metabolic reprogramming in MDSCs remains largely unexplored. Using the receptor-interacting protein kinase 3 (RIPK3)-deficient MDSC model, a previously established tumor-infiltrating MDSC-like model, we found that the cholesterol accumulation was significantly decreased in these cells. Moreover, the phosphorylated AKT-mTORC1 signaling was reduced, and downstream SREBP2-HMGCR-mediated cholesterol synthesis was blunted. Interestingly, cholesterol deficiency profoundly elevated the immunosuppressive activity of MDSCs. Mechanistically, cholesterol elimination induced nuclear accumulation of LXRβ, thereby promoting LXRβ-RXRα heterodimer binding of a novel composite element in the promoter of Arg1. Furthermore, itraconazole enhanced the immunosuppressive activity of MDSCs to boost tumor growth by suppressing the RIPK3-AKT-mTORC1 pathway and impeding cholesterol synthesis. Our findings demonstrate that RIPK3 deficiency leads to cholesterol abrogation in MDSCs, which facilitates tumor-infiltrating MDSC activation, and highlight the therapeutic potential of targeting cholesterol synthesis to overcome tumor immune evasion.

Abstract 6257: Developing HDAC inhibitors as immunomodulators

Abstract Immune checkpoint inhibitors (ICIs) are standard of care for several solid tumor types, including renal cell carcinoma (RCC). However, the clinical success of these therapies is dampened by the fact that the majority of patients demonstrate either inherent resistance to treatment or develop secondary resistance following an initial response. One key mechanism of tumor-driven ICI resistance is the generation and recruitment of suppressive immune cell types, including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), which coordinate to suppress anti-tumor T cell responses. Thus, there is a critical need for the development of novel combination strategies aimed at mitigating the presence and function of suppressive immune cells to improve the efficacy of ICIs in the clinic. Our laboratory has previously demonstrated that histone deacetylase inhibition (HDACi) is associated with a decrease in both the number and function of tumor-infiltrating Tregs and MDSCs in the RENCA tumor model. Thus, the overall goal of these studies both preclinically and clinically is to investigate the impact of the immunomodulatory effects of HDACi in combination with ICI therapy, with the overall hypothesis that HDACi will improve the efficacy of anti-PD1 therapy in RCC. Our pre-clinical data support this hypothesis by demonstrating increased tumor control and survival in RENCA tumor-bearing mice when treated with a combination of anti-PD1 and HDACi compared to single agent therapy. These increases were also associated with an increase in the activation state of anti-tumor immune cells, as demonstrated by increased surface expression of MHC Class II molecules on macrophages and a decrease in phenotypically defined monocytic MDSCs. ATACseq and RNAseq data generated from combination-treated animals also outline a gene expression signature associated with both myeloid and T cell activation. Interestingly, our clinical studies also afforded us the opportunity to investigate potential biomarkers associated with responder status, which will allow us to better predict patient outcomes and administer therapies accordingly. Accumulating evidence from two independent clinical trials run by our group suggests that high levels of suppressive CD11b+HLA-DRlo MDSCs at baseline in the peripheral blood is associated with lack of clinical response to the combination of HDACi and ICI. Overall, these data support the rationale for the combination of ICI and HDACi in the clinic, and provide a potentially useful biomarker through which we can predict the success of combination therapy. Citation Format: Sean Colligan, Li Shen, Christopher Rupert, Jonathan Bard, Roberto Pili. Developing HDAC inhibitors as immunomodulators [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6257.

The Voltage-Gated Hv1 H+ Channel Is Expressed in Tumor-Infiltrating Myeloid-Derived Suppressor Cells.

Myeloid-derived suppressor cells (MDSCs) are key determinants of the immunosuppressive microenvironment in tumors. As ion channels play key roles in the physiology/pathophysiology of immune cells, we aimed at studying the ion channel repertoire in tumor-derived polymorphonuclear (PMN-MDSC) and monocytic (Mo-MDSC) MDSCs. Subcutaneous tumors in mice were induced by the Lewis lung carcinoma cell line (LLC). The presence of PMN-MDSC (CD11b+/Ly6G+) and Mo-MDSCs (CD11b+/Ly6C+) in the tumor tissue was confirmed using immunofluorescence microscopy and cells were identified as CD11b+/Ly6G+ PMN-MDSCs and CD11b+/Ly6C+/F4/80-/MHCII- Mo-MDSCs using flow cytometry and sorting. The majority of the myeloid cells infiltrating the LLC tumors were PMN-MDSC (~60%) as compared to ~10% being Mo-MDSCs. We showed that PMN- and Mo-MDSCs express the Hv1 H+ channel both at the mRNA and at the protein level and that the biophysical and pharmacological properties of the whole-cell currents recapitulate the hallmarks of Hv1 currents: ~40 mV shift in the activation threshold of the current per unit change in the extracellular pH, high H+ selectivity, and sensitivity to the Hv1 inhibitor ClGBI. As MDSCs exert immunosuppression mainly by producing reactive oxygen species which is coupled to Hv1-mediated H+ currents, Hv1 might be an attractive target for inhibition of MDSCs in tumors.

S-1 eliminates MDSCs and enhances the efficacy of PD-1 blockade via regulation of tumor-derived Bv8 and S100A8 in thoracic tumor.

Myeloid-derived suppressor cells (MDSCs) have been known to play a pivotal role in the induction of immune tolerance, which limits the benefits of immune checkpoint inhibitors (ICIs). Recent studies revealed that several chemotherapeutic agents decreased tumor-infiltrating MDSCs. Therefore, combination therapy with cytotoxic chemotherapeutic agents and ICIs was approved for first-line treatment for lung cancer. However, the impact of chemotherapeutic agents on MDSCs and an optimal partner of ICIs has not been fully investigated in thoracic tumors, including lung cancer and malignant pleural mesothelioma. In the present study, we found that treatment with 5-FU and its oral formulation, S-1, suppressed tumor progression and inhibited the accumulation of MDSCs in thoracic tumor-bearing mice. Tumor-infiltrating T cells and dendritic cells were significantly expanded in S-1-treated mice. 5-FU suppressed the ability of tumor cells to recruit MDSCs, while it did not suppress the survival and differentiation of mouse MDSCs in vitro. We also revealed that 5-FU or S-1 significantly downregulated the expression of tumor-derived Bv8 and S100A8. The knockdown of Bv8 or S100A8 in tumor cells suppressed tumor growth and MDSC recruitment in vivo. Furthermore, in comparison with pemetrexed, administration of S-1 improved the synergistic therapeutic efficacy of anti-PD-1 antibodies with or without carboplatin. Our findings revealed a novel mechanism wherein S-1 primed a favorable tumor microenvironment to provide the rationale for combination therapy with S-1 and ICIs as the optimal therapy for thoracic cancer.

Prognostic stratification based on the levels of tumor-infiltrating myeloid-derived suppressor cells and PD-1/PD-L1 axis in locally advanced rectal cancer.

Although rectal cancer remains somewhat sanctuary to the contemporary immunotherapy, there is increasing knowledge on clinical implications of anti-tumor immunity. This study evaluated the prognostic relevance of two immune-inhibitory functions, myeloid-derived suppressor cells (MDSCs) and programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis. Study cohort is comprised of 165 patients with locally advanced rectal cancer who underwent neoadjuvant chemoradiotherapy followed by definitive resection. Using postsurgical tissue microarrays, the number of MDSCs, PD-1+/CD8+ tumor-infiltrating lymphocyte (TIL) ratio, and PD-L1 expression scores in stromal immune cells and tumor cells were assessed. Positive correlation was observed between the PD-1+/CD8+ TIL ratio and number of MDSCs (P < 0.001). The greater the immune infiltrates, the higher the PD-L1 immune cell score (P < 0.001). MDSCHigh, PD-1+/CD8+ TILHigh, PD-L1 immune cell scoreLow, and PD-L1 tumor H-scoreHigh were associated with worse disease-free survival (DFS) (P < 0.001, P = 0.042, 0.047, and P < 0.001, respectively). To integrate the adverse effects of MDSCHigh, PD-1+/CD8+ TILHigh, and either PD-L1 immune cell scoreLow (set I) or tumor H-scoreHigh (set II), prognostic risks were stratified according to the number of factors: 0, 1, and 2-3 (P < 0.001 for I and II). On multivariate analyses, patients with multiple risk factors for set I and II had worse prognosis (P < 0.001; 2-3 vs. 0 for models I and II), and the two prognostic models had acceptable predictability. In this study, integration of the prognostic impact of MDSCs and PD-1/PD-L1 stratified the long-term risks of patients with locally advanced rectal cancer. Thus, further exploration could be focused to the identified subset of patients carrying worse prognosis, where potential benefits could be derived by targeting the two components contributing to the immunosuppressive microenvironment.

The immunomodulatory role of all-trans retinoic acid in tumor microenvironment.

Retinoids are essential nutrients for human beings. Among them, all-trans retinoic acid (ATRA), considered one of the most active metabolites, plays important roles in multiple biological processes. ATRA regulates the transcription of target genes by interacting with nuclear receptors bonded to retinoic acid response elements (RAREs). Besides its differentiation-inducing effect in the treatment of acute promyelocytic leukemia and some solid tumor types, its immunoregulatory role in tumor microenvironment (TME) has attracted considerable attention. ATRA not only substantially abrogates the immunosuppressive effect of tumor-infiltrating myeloid-derived suppressor cells but also activates the anti-tumor effect of CD8 + T cells. Notably, the combination of ATRA with other therapeutic approaches, including immune checkpoint inhibitors (ICIs), tumor vaccines, and chemotherapy, has been extensively investigated in a variety of tumor models and clinical trials. In this review, we summarize the current understanding of the role of ATRA in cancer immunology and immunotherapy, dissect the underlying mechanisms of ATRA-mediated activation or differentiation of different types of immune cells, and explore the potential clinical significance of ATRA-based cancer therapy.

Abstract 1345: p300/CBP bromodomain inhibitor CCS1477 enhances the efficacy of immune checkpoint blockade therapy in cancer treatment

Abstract Background: Blockade of programmed death-ligand 1 (PD-L1) by therapeutic antibodies has shown to be a promising strategy in cancer therapy, yet clinical response in many types of cancer is limited. Tumor cells secrete PD-L1 through exosomes or splice variants, which has been described as a new mechanism for the resistance to PD-L1 blockade therapy in multiple cancers. Our previous findings showed that the histone acetyltransferases p300/CBP could be recruited to the promoter of CD274 (encoding PD-L1) to regulate the expression of PD-L1. P300/CBP inhibition abrogated this process and reduced the secretion of exosomal PD-L1 by blocking the transcription of CD274, which combined with the anti-PD-L1 antibody to reactivate T cells function for tumor attack. In this study we have tested the outcome of combined immune checkpoint inhibitors with CCS1477, a novel p300/CBP bromodomain inhibitor, in pre-clinical models of prostate cancer and melanoma. Results: CCS1477 significantly decreased human prostate (DU145/PC-3) and melanoma (A375/SK-MEL-28) cancer cell line PD-L1 expression, as well as exosome secreted PD-L1 after 24 hours treatment. Moreover, consistent with these findings in vitro, CCS1477 (2.5mg//kg) also reduced PD-L1 expression in a syngeneic mouse prostate model (TRAMP-C2) and syngeneic mouse melanoma model (B16-F10). Meanwhile, CCS1477 treatment significantly increased tumor-infiltrating CD8+ and CD4+ T cells in syngeneic mouse models. Monotherapy treatment with CCS1477 or immune checkpoint inhibitors (anti-PD-L1 antibody for prostate cancer or anti-PD-L1 and anti-CTLA4 antibody for melanoma) resulted in significant but modest efficacy. Strikingly, the combination of immune checkpoint inhibitors with CCS1477 showed robust synergistic responses resulting in tumor regression. Mechanistically, CCS1477 treatment induced significant loss of H3K27 acetylation from super-enhancers of CD274, which subsequently induced a significant reduction of PD-L1 expression and exosome secreted-PD-L1. Also, we found that CCS1477 treatment significantly decreased the abundance of circulating and tumor-infiltrating myeloid-derived suppressor cells (MDSCs), which are known to play important roles in tumor immune evasion by inhibiting T cell’s activation. Reduction of MDSCs and exosome secreted-PD-L1 preserved T-cell function and elicited robust immunotherapy response combined with immune checkpoint blockade agents. Conclusions: These observations illuminate a clinically relevant hypothesis for combining CCS1477 with immune checkpoint blockade in the treatment of cancer. Citation Format: Jinghui Liu, Xinyi Wang, Katelyn Jones, Nigel Brooks, Neil Pegg, Xiaoqi Liu. p300/CBP bromodomain inhibitor CCS1477 enhances the efficacy of immune checkpoint blockade therapy in cancer treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1345.

Inhibition of myeloid-derived suppressive cell function with all-trans retinoic acid enhanced anti-PD-L1 efficacy in cervical cancer

PD-1/PD-L1 inhibitor treatments are relatively inefficacious in advanced cervical cancer patients. The presence of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment may be one significant barrier to efficacy. It has been shown that all-trans retinoic acid (ATRA) can differentiate MDSCs into mature myeloid cells. However, whether ATRA suppression of MDSCs function could enhance PD-L1 blockade-mediated tumor immunotherapy remains unknown. Here, the frequency of tumor-infiltrating MDSCs in cervical cancer patients was measured. ATRA was used to target MDSCs both in vitro and in tumor-bearing mice. The impact of ATRA on the human cell line HeLa was also investigated. The frequency of MDSCs and T cells was determined by flow cytometry. The expression of immunosuppressive genes was measured with quantitative real time-PCR and infiltration of immune cells was assessed by immunohistochemical examination. We found that tumor-infiltrating PD-L1+ MDSCs were more prevalent in cervical cancer patients. Blockade of PD-L1 expression in MDSCs with anti-PD-L1 antibody cannot relieve the suppressive activity of MDSCs induced by HeLa cells, while ATRA efficiently abrogated the suppressive activity of MDSCs. Furthermore, ATRA had no effect on PD-L1 expression in HeLa cells in vitro. In in vivo treatment, ATRA decreased MDSCs accumulation and increased the frequency of CD8+ T cells in BALB/C mice with U14 cervical tumors. Importantly, a combination treatment of ATRA and anti-PD-L1 antibody further delayed U14 tumor growth and increased the proportion of CD62L−CD8+ T cells, CD62L−CD4+ T cells, CD107a+CD8+ T cells as well as IFN-γ and TNF-α levels in tumors. Our results provide a rationale for the use of ATRA to suppress MDSCs and enhance anti-PD-L1 cancer immunotherapy in cervical cancer.

An innate IL-25-ILC2-MDSC axis creates a cancer-permissive microenvironment for Apc mutation-driven intestinal tumorigenesis.

Interleukin-25 and group 2 innate lymphoid cells (ILC2s) defend the host against intestinal helminth infection, and are associated with inappropriate allergic reactions. IL-33-activated ILC2s were previously found to augment protective tissue-specific pancreatic cancer immunity. Here, we showed that intestinal IL-25-activated ILC2s created an innate cancer-permissive microenvironment. Colorectal cancer (CRC) patients with higher tumor IL25 expression had reduced survival, and increased IL-25R-expressing tumor-resident ILC2s and myeloid-derived suppressor cells (MDSCs) associated with impaired anti-tumor responses. Ablation of IL-25-signalling reduced tumors, virtually doubling life-expectancy in an Apc-mutation-driven model of spontaneous intestinal tumorigenesis. Mechanistically, IL-25 promoted intratumoral ILC2s, which sustained tumor-infiltrating MDSCs to suppress anti-tumor immunity. Therapeutic antibody-mediated blockade of IL-25-signalling decreased intratumoral ILC2s, MDSCs and adenoma/adenocarcinoma, while increasing anti-tumor adaptive T cell and IFNγ-mediated immunity. Thus, the roles of innate epithelium-derived cytokines IL-25 and IL-33, and ILC2s in cancer cannot be generalized. The pro-tumoral nature of the IL-25-ILC2 axis in CRC highlights this pathway as a novel therapeutic target against CRC.

Myeloid-derived suppressor cells promote tumor growth and sorafenib resistance by inducing FGF1 upregulation and fibrosis

BackgroundConsiderable evidence implicates myeloid-derived suppressor cells (MDSCs) promote tumor progression and drug resistance. Sorafenib is the standard first-line therapy for advanced hepatocellular carcinoma (HCC). Clinical evidence indicates that sorafenib resistance is associated with increased MDSCs, by which MDSCs exerts these effects is obscure. This study aimed to investigate the mechanism of sorafenib resistance mediated by MDSCs. MethodsA syngeneic mouse-liver cancer cell line BNL was subcutaneously injected to build a tumor-bearing mouse model, and syngeneic MDSCs were adoptive transferred into the tumor-bearing mouse. Tumor tissue was obtained, and transcriptomic analysis of the tumor was carried out on RNAseq data. A coculture system was used to verify the crosstalk between MDSCs and BNL cells. ResultsAdoptive MDSCs transfer into tumor-bearing mice induced an increase of tumor-infiltrating MDSCs, which led to tumor growth and impaired antitumor activity of sorafenib in BNL HCC models. MDSCs transfer contributed to tumor fibrosis and tumor-associated fibroblast (CAF) activation, associated with fibroblast growth factor (FGF1) upregulation. In contrast, MDSC depletion by anti-Ly6G+ reduced fibrosis and increased sorafenib antitumor efficacy. Intriguingly, tumor-infiltrating MDSCs barely expressed FGF1. IL-6 derived from MDSCs increased FGF1 expression in BNL liver cancer cells, and anti-IL-6 attenuated this effect in vitro. MAPK pathway, one of the sorafenib targets, is the downstream signaling of FGF1 and is reactivated by MDSCs-mediated FGF1 upregulation. ConclusionsOur finding demonstrated that MDSCs led to tumor growth and sorafenib resistance via FGF1 upregulation and subsequent indirect CAF activation. We offered a novel mechanism of MDSCs-driven HCC progression and sorafenib resistance.

Immunosuppressive tumor microenvironment in uterine serous carcinoma via CCL7 signal with myeloid-derived suppressor cells.

Serous carcinoma of the uterus (USC) is a pathological subtype of high-grade endometrial cancers, with no effective treatment for advanced cases. Since such refractory tumors frequently harbor antitumor immune tolerance, many immunotherapies have been investigated for various malignant tumors using immuno-competent animal models mimicking their local immunities. In this study, we established an orthotopic mouse model of high-grade endometrial cancer and evaluated the local tumor immunity to explore the efficacy of immunotherapies against USC. A multivariate analysis of 62 human USC cases revealed that the tumor-infiltrating cell status, few CD8+ cells and abundant myeloid-derived suppressor cells (MDSCs), was an independent prognostic factor (P < 0.005). A murine endometrial cancer cell (mECC) was obtained from C57BL/6 mice via endometrium-specific deletion of Pten and Tp53, and another high-grade cell (HPmECC) was established by further overexpressing Myc in mECCs. HPmECCs exhibited higher capacities of migration and anchorage-independent proliferation than mECCs (P < 0.01, P < 0.0001), and when both types of cells were inoculated into the uterus of C57BL/6 mice, the prognosis of mice bearing HPmECC-derived tumors was significantly poorer (P < 0.001). Histopathological analysis of HPmECC orthotopic tumors showed serous carcinoma-like features with prominent tumor infiltration of MDSCs (P < 0.05), and anti-Gr-1 antibody treatment significantly prolonged the prognosis of HPmECC-derived tumor-bearing mice (P < 0.05). High CCL7 expression was observed in human USC and HPmECC, and MDSCs migration was promoted in a CCL7 concentration-dependent manner. These results indicate that antitumor immunity is suppressed in USC due to increased number of tumor-infiltrating MDSCs via CCL signal.

Anti-PD1 antibody enhances the anti-tumor efficacy of MUC1-MBP fusion protein vaccine via increasing Th1, Tc1 activity and decreasing the proportion of MDSC in the B16-MUC1 melanoma mouse model

In previous studies, we have obtained a notable anti-tumor efficacy of the recombinant MUC1-MBP vaccine in the process of mouse B16-MUC1 melanoma treatment. However, the tumor cannot be eliminated completely. We found that the tumor inhibition rate decreased from 81.67% (five immunizations) to 43.67% (eight immunizations) after more than five immunizations, indicating persistent vaccine stimulation may activate immunosuppressive factors. In the present study, we revealed that programmed cell death 1 (PD1), an inhibitory molecule suppressing T cell function, expressed on splenic and tumor-infiltrating T cells were up-regulated by the vaccine. Therefore, to optimize the anti-tumor efficacy of the vaccine, we employed combination immunotherapy with MUC1-MBP vaccine and αPD1 (anti-PD1 antibody). Results showed that combination immunotherapy induced a more remarkable anti-tumor efficacy, the tumor clearance being increased to 80% from 20% which obtain by MUC1-MBP vaccine immunizations. To investigate the possible underlying mechanism, IFN-γ secretion and cytotoxic T lymphocyte (CTL) cytotoxicity were measured by enzyme-linked immunosorbent assay (ELISA) and xCELLigence real-time cell analyzer (RTCA) respectively. T cell subsets and immunosuppressive cells in the mouse spleen and tumor microenvironment were analyzed by FACS. Results showed that the proportion of splenic CD8+T cells and tumor infiltration was increased and the activity of CTL killing, T helper 1 (Th1), Type 1 CD8+T (Tc1) was enhanced, indicating that the anti-tumor efficacy enhanced by combination immunotherapy was mainly through boosting CD8+T cells mediated anti-tumor cellular immunity. Additionally, combination immunotherapy significantly decreased the splenic and tumor-infiltrating myeloid derived suppressor cells (MDSCs). These results demonstrated that combination immunotherapy with MUC1-MBP vaccine and αPD1 was capable to invoke a more potent anti-tumor immune response and provide a foundation for further research.

Metabolic reprograming of MDSCs within tumor microenvironment and targeting for cancer immunotherapy.

A number of emerging studies in field of immune metabolism have indicated that cellular metabolic reprograming serves as a major administrator in maintaining the viability and functions of both tumor cells and immune cells. As one of the most important immunosuppressive cells in tumor stroma, myeloid-derived suppressor cells (MDSCs) dynamically orchestrate their metabolic pathways in response to the complicated tumor microenvironment (TME), a process that consequently limits the therapeutic effectiveness of anti-cancer treatment modalities. In this context, the metabolic vulnerabilities of MDSCs could be exploited as a novel immune metabolic checkpoint upon which to intervene for promoting the efficacy of immunotherapy. Here, we have discussed about recent studies highlighting the important roles of the metabolic reprograming and the core molecular pathways involved in tumor-infiltrating MDSCs. In addition, we have also summarized the state-of-the-art strategies that are currently being employed to target MDSC metabolism and improve the efficacy of antineoplastic immunotherapy.

Abstract 1626: PMC309, a highly selective anti-VISTA antibody enhances T cell activation through blocking the interaction of T cells and myeloid derived suppressor cells (MDSC)

Abstract TME (tumor microenvironment) consists of blood &amp; lymphatic vessels, stromal cells, and immune cells such as lymphocytes, macrophages, and antigen-presenting cells (APC). Cellular interactions among various immune cell types within TME regulate tumor growth, metastasis, and resistance to cancer therapy. V-domain Ig suppressor of T cell activation (VISTA) is a negative checkpoint regulator highly expressed on tumor-infiltrating myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAMs) and VISTA blockade could enhance antitumor immunity in TME. PMC-309 binding to VISTA expressing cells is highly selective and the selectivity is maintained even in the low pH conditions that mimic TME. Binding of PMC-309 on MDSC cells enhances the secretion of IFN-γ, TNF-α, and IL-2 in Mixed Lymphocyte Reaction (MLR) settings. In in vivo study, PMC-309 suppressed tumor growth, which was further attenuated with an anti-PD1 antibody. The anti-tumor activity was associated with enhanced T cell activation, increased secretion of pro-inflammatory cytokines, and increased penetration of tumor-infiltrating leukocytes (TIL) into TME. Patients who became resistant to anti-CTLA-4 and anti-PD(L)1 antibody showed increased expression of VISTA, suggesting that anti-VISTA therapeutics can help to treat the patients who do not respond well to other immuno-oncology drugs. We are developing PMC-309 as a next generation immuno-oncology (IO) agent, which can convert immunologically cold into hot tumors as a mono- or combo- therapy with other IO agent. Citation Format: Cheon Ho Park, Sang Soon Byun, Jin Yong An, Sun Hyung Ha, Hye Rim Han, Nu Ri Kang, Beom Yong Park, Eun Ah Lee, Hyun Sun Park, Jin-San Yoo, Weon Sup Lee. PMC309, a highly selective anti-VISTA antibody enhances T cell activation through blocking the interaction of T cells and myeloid derived suppressor cells (MDSC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1626.

Myeloid-Derived Suppressor Cells as Therapeutic Targets in Uterine Cervical and Endometrial Cancers

Uterine cervical and endometrial cancers are the two most common gynecological malignancies. As demonstrated in other types of solid malignancies, an increased number of circulating or tumor-infiltrating myeloid-derived suppressor cells (MDSCs) have also been observed in uterine cervical and endometrial cancers, and increased MDSCs are associated with an advanced stage, a short survival, or a poor response to chemotherapy or radiotherapy. In murine models of uterine cervical and endometrial cancers, MDSCs have been shown to play important roles in the progression of cancer. In this review, we have introduced the definition of MDSCs and their functions, discussed the roles of MDSCs in uterine cervical and endometrial cancer progression, and reviewed treatment strategies targeting MDSCs, which may exhibit growth-inhibitory effects and enhance the efficacy of existing anticancer treatments.

Targeting Myeloid-Derived Suppressor Cells in Ovarian Cancer.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that exhibit immunosuppressive activity. They also directly stimulate tumor cell proliferation, metastasis, and angiogenesis. In ovarian cancer, there are increased numbers of circulating or tumor-infiltrating MDSCs, and increased frequencies of MDSCs are associated with a poor prognosis or an advanced clinical stage. Moreover, in murine models of ovarian cancer, MDSC depletion has shown significant growth-inhibitory effects and enhanced the therapeutic efficacy of existing anticancer therapies. In this review, we summarize the current knowledge on MDSC biology, clinical significance of MDSC, and potential MDSC-targeting strategies in ovarian cancer.