Recruitment Of Myeloid-derived Suppressor Cells Research Articles

Regulatory effect of rapamycin on recruitment and function of myeloid-derived suppressor cells in heart failure

BackgroundImmune response and inflammation play important roles in the physiological and pathophysiological processes of heart failure (HF). In our previous study, myeloid-derived suppressor cells (MDSCs), a heterogeneous group of immature myeloid cells with anti-inflammatory and immunosuppressive functions, were shown to exert cardioprotective effects in HF. The pharmacological targeting of MDSCs using rapamycin may emerge as a promising strategy for the prevention and treatment of HF. However, the specific mechanisms underlying rapamycin-induced MDSC accumulation remain unclear. Our study aimed to clarify the effects of rapamycin on the recruitment and function of MDSCs in HF, exploring new therapeutic options for the prevention and treatment of HF. MethodsWe used transverse aortic constriction surgery and isoproterenol injection to establish HF models. Flow cytometry, reverse transcription polymerase chain reaction, transcriptomics and western blot were used to explore the regulation of rapamycin on recruitment and function of MDSCs in HF. Furthermore, rapamycin and granulocyte–macrophage colony-stimulating factor (GM-CSF) were combined to induce exogenous MDSCs from bone marrow cells. ResultsRapamycin promotes the recruitment of MDSCs by inhibiting their maturation and differentiation via suppression of the Wnt signaling in HF mice and enhanced the immunosuppressive function of MDSCs via the NF-κB signaling. Furthermore, exogenous MDSCs induced by rapamycin and GM-CSF can significantly alleviate transverse aortic constriction-induced cardiac dysfunction. ConclusionsThe pharmacological targeting of MDSCs using rapamycin is a promising strategy for the prevention and treatment of HF.

Platelet-activating factor (PAF) promotes immunosuppressive neutrophil differentiation within tumors

Chronic inflammatory milieu in the tumor microenvironment (TME) leads to the recruitment and differentiation of myeloid-derived suppressor cells (MDSCs). Polymorphonuclear (PMN)-MDSCs, which are phenotypically and morphologically defined as a subset of neutrophils, cause major immune suppression in the TME, posing a significant challenge in the development of effective immunotherapies. Despite recent advances in our understanding of PMN-MDSC functions, the mechanism that gives rise to immunosuppressive neutrophils within the TME remains elusive. Both in vivo and in vitro, newly recruited neutrophils into the tumor sites remained activated and highly motile for several days and developed immunosuppressive phenotypes, as indicated by increased arginase 1 (Arg1) and dcTrail-R1 expression and suppressed anticancer CD8 T cell cytotoxicity. The strong suppressive function was successfully recapitulated by incubating naive neutrophils with cancer cell culture supernatant in vitro. Cancer metabolite secretome analyses of the culture supernatant revealed that both murine and human cancers released lipid mediators to induce the differentiation of immunosuppressive neutrophils. Liquid chromatography-mass spectrometry (LC-MS) lipidomic analysis identified platelet-activation factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) as a common tumor-derived lipid mediator that induces neutrophil differentiation. Lysophosphatidylcholine acyltransferase 2 (LPCAT2), the PAF biosynthetic enzyme, is up-regulated in human pancreatic ductal adenocarcinoma (PDAC) and shows an unfavorable correlation with patient survival across multiple cancer types. Our study identifies PAF as a lipid-driven mechanism of MDSC differentiation in the TME, providing a potential target for cancer immunotherapy.

Tumor necrosis factor regulates leukocyte recruitment but not bacterial persistence during Staphylococcus aureus craniotomy infection

BackgroundCraniotomy is a common neurosurgery used to treat intracranial pathologies. Nearly 5% of the 14 million craniotomies performed worldwide each year become infected, most often with Staphylococcus aureus (S. aureus), which forms a biofilm on the surface of the resected bone segment to establish a chronic infection that is recalcitrant to antibiotics and immune-mediated clearance. Tumor necrosis factor (TNF), a prototypical proinflammatory cytokine, has been implicated in generating protective immunity to various infections. Although TNF is elevated during S. aureus craniotomy infection, its functional importance in regulating disease pathogenesis has not been explored.MethodsA mouse model of S. aureus craniotomy infection was used to investigate the functional importance of TNF signaling using TNF, TNFR1, and TNFR2 knockout (KO) mice by quantifying bacterial burden, immune infiltrates, inflammatory mediators, and transcriptional changes by RNA-seq. Complementary experiments examined neutrophil extracellular trap formation, leukocyte apoptosis, phagocytosis, and bactericidal activity.ResultsTNF transiently regulated neutrophil and granulocytic myeloid-derived suppressor cell recruitment to the brain, subcutaneous galea, and bone flap as evident by significant reductions in both cell types between days 7 to 14 post-infection coinciding with significant decreases in several chemokines, which recovered to wild type levels by day 28. Despite these defects, bacterial burdens were similar in TNF KO and WT mice. RNA-seq revealed enhanced lymphotoxin-α (Lta) expression in TNF KO granulocytes. Since both TNF and LTα signal through TNFR1 and TNFR2, KO mice for each receptor were examined to assess potential redundancy; however, neither strain had any impact on S. aureus burden. In vitro studies revealed that TNF loss selectively altered macrophage responses to S. aureus since TNF KO macrophages displayed significant reductions in phagocytosis, apoptosis, IL-6 production, and bactericidal activity in response to live S. aureus, whereas granulocytes were not affected.ConclusionThese findings implicate TNF in modulating granulocyte recruitment during acute craniotomy infection via secondary effects on chemokine production and identify macrophages as a key cellular target of TNF action. However, the lack of changes in bacterial burden in TNF KO animals suggests the involvement of additional signals that dictate S. aureus pathogenesis during craniotomy infection.

Reactive oxygen species/glutathione dual sensitive nanoparticles with encapsulation of miR155 and curcumin for synergized cancer immunotherapy

Considerable attention has been directed towards exploring the potential efficacy of miR-155 in the realm of cancer immunotherapy. Elevated levels of miR-155 in dendritic cells (DCs) have been shown to enhance their maturation, migration, cytokine secretion, and their ability to promote T cell activation. In addition, overexpression of mir155 in M2 macrophages boost the polarization towards the M1 phenotype. Conversely, miR-155 has the propensity to induce the accumulation of immunosuppressive cells like regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) in the tumor tissue. To account for this discrepancy, it is imperative to get help from a drug that could deal with immunosuppressive effect. Curcumin (CUR) exhibits the capacity to prompt Tregs converse into T helper 1 cells, fostering the polarization of M2 tumor-associated macrophage towards the M1 phenotype, and impeding the recruitment and aggregation of MDSCs within the tumor microenvironment. Nonetheless, CUR is known to exert an immunosuppressive impact on DCs by hindering the expression of maturation markers, cytokines, and chemokines, thereby prevent DCs response to immunostimulatory agents. Hence, a reactive oxygen species/glutathione dual responsive drug conveyance platform (CUR/miR155@DssD-Hb NPs) was devised to co-deliver CUR and miR155, with the aim of exploring their synergistic potential in bolstering a sustained and robust anti-tumor immune response. In vitro and in vivo results have suggested that CUR/miR155@DssD-Hb NPs can effectively inhibit the viability of 4T1 and B16F10 tumor cells, trigger the release of damage associated molecular patterns, stimulate DCs maturation, subsequent activation of CD8+ T cells, diminish immunosuppressive cell populations (MDSCs, Tregs, M2 TAMs and exhausted T cells), promote the formation of long-term immunity and lessen the formation of metastatic nodules in the lungs. In summary, the co-delivery system integrating CUR and miR155 (CUR/miR155@DssD-Hb NPs) demonstrates promise as a promising strategy for the immunotherapy of melanoma and triple negative breast cancer.Graphical abstract

Myeloid‑derived suppressor cells as targets of emerging therapies and nanotherapies (Review).

Breast cancer (BC) is the leading cause of cancer-related mortality among women worldwide. Immunotherapies are a promising approach in cancer treatment, particularly for aggressive forms of BC with high mortality rates. However, the current eligibility for immunotherapy remains limited to a limited fraction of patients with BC. Myeloid-derived suppressor cells (MDSCs), originating from myeloid cells, are known for their dual role in immunosuppression and tumor promotion, significantly affecting patient outcomes by fostering the formation of premetastatic niches. Consequently, targeting MDSCs has emerged as a promising avenue for further exploration in therapeutic interventions. Leveraging nanotechnology-based drug delivery systems, which excel in accumulating drugs within tumors via passive or active targeting mechanisms, are a promising strategy for the use of MDSCs in the treatment of BC. The present review discusses the immunosuppressive functions of MDSCs, their role in BC, and the diverse strategies for targeting them in cancer therapy. Additionally, the present review discusses future advancements in BC treatments focusing on MDSCs. Furthermore, it elucidates the mechanisms underlying MDSC activation, recruitment and differentiation in BC progression, highlighting the clinical characteristics that render MDSCs suitable candidates for the therapy and targeted nanotherapy of BC.

PI3Kγ inhibition combined with DNA vaccination unleashes a B-cell-dependent antitumor immunity that hampers pancreatic cancer

Phosphoinositide-3-kinase γ (PI3Kγ) plays a critical role in pancreatic ductal adenocarcinoma (PDA) by driving the recruitment of myeloid-derived suppressor cells (MDSC) into tumor tissues, leading to tumor growth and metastasis. MDSC also impair the efficacy of immunotherapy. In this study we verify the hypothesis that MDSC targeting, via PI3Kγ inhibition, synergizes with α-enolase (ENO1) DNA vaccination in counteracting tumor growth.Mice that received ENO1 vaccination followed by PI3Kγ inhibition had significantly smaller tumors compared to those treated with ENO1 alone or the control group, and correlated with i) increased circulating anti-ENO1 specific IgG and IFNγ secretion by T cells, ii) increased tumor infiltration of CD8+ T cells and M1-like macrophages, as well as up-modulation of T cell activation and M1-like related transcripts, iii) decreased infiltration of Treg FoxP3+ T cells, endothelial cells and pericytes, and down-modulation of the stromal compartment and T cell exhaustion gene transcription, iv) reduction of mature and neo-formed vessels, v) increased follicular helper T cell activation and vi) increased “antigen spreading”, as many other tumor-associated antigens were recognized by IgG2c “cytotoxic” antibodies. PDA mouse models genetically devoid of PI3Kγ showed an increased survival and a pattern of transcripts in the tumor area similar to that of pharmacologically-inhibited PI3Kγ-proficient mice. Notably, tumor reduction was abrogated in ENO1 + PI3Kγ inhibition-treated mice in which B cells were depleted.These data highlight a novel role of PI3Kγ in B cell-dependent immunity, suggesting that PI3Kγ depletion strengthens the anti-tumor response elicited by the ENO1 DNA vaccine.

Hepatic recruitment of myeloid-derived suppressor cells upon liver injury promotes both liver regeneration and fibrosis

BackgroundThe liver regeneration is a highly complicated process depending on the close cooperations between the hepatocytes and non-parenchymal cells involving various inflammatory cells. Here, we explored the role of myeloid-derived suppressor cells (MDSCs) in the processes of liver regeneration and liver fibrosis after liver injury.MethodsWe established four liver injury models of mice including CCl4-induced liver injury model, bile duct ligation (BDL) model, concanavalin A (Con A)-induced hepatitis model, and lipopolysaccharide (LPS)-induced hepatitis model. The intrahepatic levels of MDSCs (CD11b+Gr-1+) after the liver injury were detected by flow cytometry. The effects of MDSCs on liver tissues were analyzed in the transwell co-culture system, in which the MDSCs cytokines including IL-10, VEGF, and TGF-β were measured by ELISA assay and followed by being blocked with specific antibodies.ResultsThe intrahepatic infiltrations of MDSCs with surface marker of CD11b+Gr-1+ remarkably increased after the establishment of four liver injury models. The blood served as the primary reservoir for hepatic recruitment of MDSCs during the liver injury, while the bone marrow appeared play a compensated role in increasing the number of MDSCs at the late stage of the inflammation. The recruited MDSCs in injured liver were mainly the M-MDSCs (CD11b+Ly6G−Ly6Chigh) featured by high expression levels of cytokines including IL-10, VEGF, and TGF-β. Co-culture of the liver tissues with MDSCs significantly promoted the proliferation of both hepatocytes and hepatic stellate cells (HSCs).ConclusionsThe dramatically and quickly infiltrated CD11b+Gr-1+ MDSCs in injured liver not only exerted pro-proliferative effects on hepatocytes, but also accounted for the activation of profibrotic HSCs.

Sequence of androgen receptor-targeted vaccination with androgen deprivation therapy affects anti-prostate tumor efficacy

RationaleAndrogen deprivation therapy (ADT) is the primary treatment for recurrent and metastatic prostate cancer. In addition to direct antitumor effects, ADT has immunomodulatory effects such as promoting T-cell infiltration and...

The clinical association of programmed death-1/PD-L1 axis, myeloid derived suppressor cells subsets and regulatory T cells in peripheral blood of stable COPD patients.

Myeloid-derived suppressor cells (MDSCs) have crucial immunosuppressive role in T cell dysfunction in various disease processes. However, the role of MDSCs and their impact on Tregs in COPD have not been fully understood. The aim of the present study is to investigate the immunomodulatory role of MDSCs and their potential impact on the expansion and function of Tregs in COPD patients. Peripheral blood samples were collected to analyze circulating MDSCs, Tregs, PD-1/PD-L1 expression to assess the immunomodulatory role of MDSC and their potential impact on the expansion and function of Treg in COPD. A total of 54 COPD patients and 24 healthy individuals were enrolled in our study. Flow cytometric analyses were performed to identify granulocytic MDSCs (G-MDSCs), monocytic MDSCs (M-MDSCs), Tregs, and the expression of PD-1/PD-L1(L2) on MDSCs and Tregs in peripheral blood. Our results revealed a significantly higher percentage of G-MDSCs and M-MDSCs (p < 0.001) in COPD patients compared to the healthy controls. Additionally, a significantly higher proportion of peripheral blood Tregs was observed in COPD patients. Furthermore, an increased expression of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) on Tregs (p < 0.01) was detected in COPD patients. The expression of PD-1 on CD4+ Tcells and Tregs, but not CD8+Tcells, was found to be increased in patients with COPD compared to controls. Furthermore, an elevated expression of PD-L1 on M-MDSCs (p < 0.01) was also observed in COPD patients. A positive correlation was observed between the accumulation of M-MDSCs and Tregs in COPD patients. Additionally, the percentage of circulating M-MDSCs is positively associated with the level of PD-1 (r = 0.51, p < 0.0001) and CTLA-4 (r = 0.42, p = 0.0014) on Tregs in COPD. The recruitment of MDSCs, accumulation of Tregs, and up-regulation of CTLA-4 on Treg in COPD, accompanied by an increased level of PD-1/PD-L1, suggest PD-1/PD-L1 axis may be potentially involved in MDSCs-induced the expansion and activation of Treg at least partially in COPD.

Abstract 3880: LYTAC targeting galectin-1 to enhance radioimmunotherapy of cancers in the upper aerodigestive tract

Abstract Non-small cell lung cancer (NSCLC) and head and neck cancer (HNC), ranking respectively as a leading cause of cancer-related death and the sixth most common cancer worldwide. Despite treatment advancements, there's a pressing need for more effective strategies to improve survival and quality of life for NSCLC and HNC patients. Carolyn Bertozzi group recently reported in Nature the groundbreaking protein degraders named lysosome-targeted chimeras (LYTACs), which have bispecific binding affinity that drives cell-surface endocytic receptors to drag membrane or extracellular oncogenic proteins to lysosomes for degradation. They have successfully targeted critical oncoproteins such as epidermal growth factor receptor (EGFR) and more. However, current degradation demonstration was limited to in vitro cancer cells, LYTACs' impact on immune cell modulation and their therapeutic potentials in preclinical animal models remain unknown and require extensive evaluation before venturing to clinical trials.Our group and others have identified galectin-1 (Gal-1) as a multifaceted immunosuppressive biomarker overexpressed in NSCLC and HNC. By interacting with glycosylated receptors (e.g. CD45) on immune cells, it results in apoptosis of cytotoxic T cells, expansion of regulatory T cells, and intratumoral recruitment of myeloid-derived suppressor cells. Despite promising as an immune checkpoint target, effective anti-Gal-1 therapies are currently absent in clinical trials.Through histopathological analyses, we have confirmed substantial LYTAC receptor (cation-independent mannose-6-phosphate receptor, CI-M6PR) expression in ~200 HNC and ~400 NSCLC patient samples. Collaborating with Bertozzi group, we have developed the first Gal-1 targeting LYTAC named G-M6Pn which triggers significant target protein degradation in various human HNC and NSCLC cell lines. Such efficient Gal-1 degradation leads to significant immunosuppression reversal by stimulating CD8+ T cell and natural killer (NK) cell activation while dampening regulatory T cell (Treg) activity in both cell experiments and humanized mouse tumor models, resulting in excellent tumor/metastases control and survival improvement on both NSCLC and HNC models. When synergized with stereotactic ablative radiotherapy, the antitumor immune responses are further amplified and G-M6Pn also mediates ‘abscopal effect’ inhibiting non-irradiated tumors. This study thus contributes to expediting clinical translation of LYTACs as novel immune checkpoint degraders to improve personalized radio-immunotherapy of cancer. Citation Format: Yuyan Jiang, Green Ahn, Mobeen Rahman, Hongbin Cao, Carolyn Bertozzi, Qunh Le. LYTAC targeting galectin-1 to enhance radioimmunotherapy of cancers in the upper aerodigestive tract [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3880.

Abstract 1593: Intercellular network in immune suppressive microenvironment of pancreatic cancer

Abstract Despite constant efforts to improve treatment, the prognosis remains poor, with an overall survival rate of 6% (ranges from 2% to 9%) due to lack of efficient chemotherapy, radiotherapy, and targeted therapy. Immune checkpoint inhibitors (ICIs) has been reported to be effective in various solid cancers, such as melanoma, lung cancer, and renal cell carcinoma. However, pancreatic ductal adenocarcinoma (PDAC) is resistant against ICIs. The responsiveness of immune therapy is mainly determined by immune tumor microenvironment (TME) composed of tumor-infiltrating lymphocytes (TIL) and stromal cells. PDAC possesses unique TME, which is abundant of fibrosis, termed of desmoplasia, and the role of fibrosis in constructing immune suppressive TME remains unclear. First, in this study, to examine the immunological characteristics of TME, we constructed an integrated data base of TIL profiling, RNA-seq and whole exome seq using 31 fresh resected tissues of PDAC. An unsupervised clustering of based on numbers and percentages of 12 TIL types analyzed by flow cytometry showed that PDAC was divided into 2 types of cluster (myeloid cell-, T cell-dominant type), and the prognosis of myeloid type was significantly poorer than T cell-type. Myeloid type contained the high frequency of myeloid cell lineage including monocytes, macrophages and myeloid-derived suppressor cells (MDSC). Only MDSCs were significantly associated with poor prognosis among various immune cell types. Furthermore, gene enrichment analysis identified activated and suppressed pathways in each immune type, and in myeloid cell-dominant type, the immune-related pathways were significantly down-regulated. Then, to understand the characteristics of MDSCs infiltrated into pancreatic cancer tissues, single cell RNA-seq with surgical specimens was performed, and the analysis showed that a specific subtype of MDSCs infiltrated into cancer tissues. In addition, activation status of cancer-associated fibroblasts (CAFs) was related with MDSC recruitment and activation, indicating that the interaction between MDSCs and CAFs is crucial to create MDSC-rich TME. Inhibition of interaction between MDSCs and CAFs is expected to overcome immunosuppressive TME can be a therapy in PDAC. Citation Format: Kazunori Aoki, Hironori Fukuda, Yukihiro Mizoguchi, Kosuke Arai. Intercellular network in immune suppressive microenvironment of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1593.

Abstract 7521: Tumor NLRP3 inflammasome activity mediates resistance to Anti-PD-1 immunotherapy in advanced gastroesophageal cancer

Abstract The addition of anti-PD-1 immunotherapy to the therapeutic armamentarium of advanced gastroesophageal (GE) cancer patients has resulted in modest improvements in clinical outcomes for a subset of patients. More robust predictive biomarkers to guide patient management and to select optimal combination immunotherapy strategies for the individual patient are needed. Our previous studies indicate that the tumor-intrinsic NLRP3 inflammasome-HSP70 signaling axis promotes the recruitment of granulocytic myeloid-derived suppressor cells (PMN-MDSCs) and drives resistance to anti-PD-1 immunotherapy. The KEYLargo phase II clinical trial evaluated the efficacy of pembrolizumab (pembro) in combination with capecitabine/oxaliplatin (CAPOX) in HER2-negative advanced GE cancer patients. An 8-day lead-in period of pembro monotherapy in 36 advanced GE cancer patients allowed for the acquisition of blood and tumor tissue specimens to determine which immune-mediated alterations within the tumor microenvironment correlated with resistance to anti-PD-1 immunotherapy. Baseline and on-treatment specimens were collected for HSP70 ELISA, immunofluorescence microscopy, spatial transcriptomics, NLRP3 FISH, IHC, and NLRP3-ASC proximity ligation assays (PLA) to measure NLRP3 pathway activity levels. All data was correlated with best objective response, progression-free survival (PFS), and overall survival (OS). Tumor-infiltrating CD8+ T cells and PMN-MDSCs were increased in responders and non-responders, respectively. While PD-L1 CPS failed to associate with response, elevated baseline NLRP3 PLA activity correlated with increased tumor-infiltrating PMN-MDSCs (P = 0.001) and resistance to pembro/CAPOX therapy (P = 0.01). Only non-responding tumors exhibited an increase in NLRP3 PLA activity and NLRP3 amplification. Transcriptional studies revealed tumors with enhanced NLRP3 activity to exhibit decreased expression of the NLRC5 transactivator, MHC class I antigen presentation genes, and an increase in the NK cell negative regulator, HLA-G. Baseline plasma HSP70 levels correlated with tumor NLRP3 activity (P = 0.043) and with resistance to pembro/CAPOX therapy (P = 0.001). Elevated baseline NLRP3 PLA activity and amplification were associated with diminished PFS (P = 0.008) and OS (P = 0.009). In additional studies, pharmacologic inhibition of the NLRP3 inflammasome suppressed PMN-MDSC recruitment, upregulated MHC class I, and reversed anti-PD-1 resistance in an orthotopic model of GE cancer. Together, these findings implicate tumor-intrinsic NLRP3-HSP70 signaling as an important mediator of anti-PD-1 resistance in advanced GE cancer. The NLRP3-HSP70 pathway is a promising source of therapeutic targets and biomarkers capable of improving treatment outcomes for this patient population. Additional clinical studies are warranted. Citation Format: Nagendra Yarla, Kaylee Howell, Y-Van Nguyen, Donna Niedwiecki, Hope Uronis, John Strickler, Nicholas C. DeVito, Bala Theivanthiran, Brent A. Hanks. Tumor NLRP3 inflammasome activity mediates resistance to Anti-PD-1 immunotherapy in advanced gastroesophageal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7521.

Abstract 6861: PIK3CA activating mutation promotes an immune suppressive microenvironment in squamous cell carcinoma

Abstract Head and neck squamous cell carcinoma (HNSCC) is a leader in cancer incidence worldwide. Recently, immunotherapies such as immune checkpoint blockade (ICB) have offered great promise in treating many solid tumors, including HNSCCs, that are refractory to chemotherapy and radiation. Challengingly, HNSCC patients often relapse following ICB treatment due to the lack of a thorough understanding of the mechanisms underlying cancer immune evasion. These disparities in patient outcomes strongly suggest the existence of genetic variations that underlie their distinct responses to ICB. Although the specific oncogenic mutations responsible for driving relapse in SCC patients remain unclear, it is imperative to grasp the mechanisms of cancer immune evasion in individuals with specific genetic profiles to enhance the precision of immunotherapy. Cancer immune evasion has emerged as a hallmark of cancer and is facilitated by a highly complex tumor microenvironment (TME). We aim to understand the genetic basis shaping the immune suppressive TME and hypothesize that oncogenic driver mutations play a dominant role in preventing the immune clearance of transformed cells by reprogramming the immune landscape in the tumors. To determine the critical genetic signatures enriched in SCC patients that can impact anti-tumor immunity, we analyzed TCGA data which revealed a strong negative correlation between PIK3CA level and CD8 T cell signatures. We have identified that activating mutations in the PIK3CA gene, found in 20% of HNSCCs, promote rapid tumor relapse after initial response to anti-PD-L1 and anti-CTLA-4 ICB treatments. Utilizing single-cell analysis, quantitative immune profiling, and multiplexed imaging, our lab showed that tumor-initiating cells (TICs) in SCCs can have an intricate dialogue with myeloid-derived suppressor cells (MDSCs) where TICs secrete factors to enhance MDSC recruitment and suppressive function on cytotoxic T cells. Additionally, our data supports that the tumor interstitial fluid (TIF) of PIK3CA mutant SCC tumors can enhance the suppressive activity of MDSCs on cytotoxic T cells. These results suggest that the acquisition of PIK3CA mutation may trigger TICs to release additional factors to further modify MDSC activities. A critical method by which MDSCs suppress T cells is through the production and respiratory burst of reactive oxygen species (ROS). RNA sequencing revealed that PIK3CA mutant SCCs have multiple mechanisms of increasing ROS in the TME and specifically in MDSCs, while simultaneously upregulating lipid metabolism genes, such as SCD1, to protect itself from MDSC-derived ROS. This study reveals a potential strategy for targeting PIK3CA mutant SCCs as a promising precision immunotherapy to enhance the efficacy of ICB treatments. Citation Format: Benjamin T. Nicholson, Weijie Guo, Yuxuan Miao. PIK3CA activating mutation promotes an immune suppressive microenvironment in squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6861.

Shuangshen Granules Suppress Myeloid-derived Suppressor Cell-mediated Lung Premetastatic Niche Development by Targeting Sphingosine-1-Phosphate Receptor-1/Signal Transducer, Activator of Transcription 3 Signaling

Abstract Background: Shuangshen granules (SSGs) are extensively utilized for the treatment of lung cancer in China and have been reported to possess tumor-protective and anti-metastatic effects. Therefore, it is crucial to understand the precise mechanism. Building upon the findings of our previous study, the objective of the present study was to explore the impact of SSGs on the sphingosine-1-phosphate receptor-1 (S1PR1)/signal transducer and activator of transcription 3 (STAT3) axis, as well as the recruitment of myeloid-derived suppressor cells (MDSCs) during the formation of the premetastatic niches (PMNs). Methods: In a mouse xenograft model utilizing Lewis lung carcinoma (LLC) cells that express green fluorescent protein (GFP), the initiation of lung metastasis was monitored every three days until day 35 following transplantation. Lung metastasis, MDSC recruitment, the expression of PMN and S1PR1/STAT3 axis biomarkers, as well as the blood levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and transforming growth factor-β (TGF-β) were assessed in the SSG treatment and control groups. Results: The LLC cells did not reach the lung until 14–17 days following subcutaneous implantation, which was concurrent with the formation of lung PMNs. SSG significantly postponed the initiation of lung metastasis and reduced the recruitment of MDSCs to the lung PMNs. SSG also suppressed the S1PR1/STAT3 axis in tumor tissues, bone marrow, and lung PMNs. Additionally, SSG suppressed the blood levels of GM-CSF and TGF-β, as well as the PMN markers, matrix metalloproteinase-9 and versican. Conclusion: Our findings suggested that SSG suppressed the development of MDSC-mediated PMNs by inhibiting the S1PR1/STAT3 axis, consequently postponing the initiation of lung metastasis.

Modulation of myeloid-derived suppressor cell functions by oral inflammatory diseases and important oral pathogens.

The oral cavity presents a diverse microbiota in a dynamic balance with the host. Disruption of the microbial community can promote dysregulation of local immune response which could generate oral diseases. Additionally, alterations in host immune system can result in inflammatory disorders. Different microorganisms have been associated with establishment and progression of the oral diseases. Oral cavity pathogens/diseases can modulate components of the inflammatory response. Myeloid-derived suppressor cells (MDSCs) own immunoregulatory functions and have been involved in different inflammatory conditions such as infectious processes, autoimmune diseases, and cancer. The aim of this review is to provide a comprehensive overview of generation, phenotypes, and biological functions of the MDSCs in oral inflammatory diseases. Also, it is addressed the biological aspects of MDSCs in presence of major oral pathogens. MDSCs have been mainly analyzed in periodontal disease and Sjögren's syndrome and could be involved in the outcome of these diseases. Studies including the participation of MDSCs in other important oral diseases are very scarce. Major oral bacterial and fungal pathogens can modulate expansion, subpopulations, recruitment, metabolism, immunosuppressive activity and osteoclastogenic potential of MDSCs. Moreover, MDSC plasticity is exhibited in presence of oral inflammatory diseases/oral pathogens and appears to be relevant in the disease progression and potentially useful in the searching of possible treatments. Further analyses of MDSCs in oral cavity context could allow to understand the contribution of these cells in the fine-tuned balance between host immune system and microorganism of the oral biofilm, as well as their involvement in the development of oral diseases when this balance is altered.

Upregulation of IL4-induced gene 1 enzyme by B2 cells during melanoma progression impairs their antitumor properties.

B cells present in human cutaneous melanoma have been associated with protective or detrimental effects on disease progression according to their phenotype. By using the RET model of spontaneous melanoma and adoptive transfer of B16 melanoma cells, we show that immature and follicular B2 (B2-FO) cells exert a protective effect on melanoma progression by promoting the generation of effector memory T cells and limiting the recruitment of polymorphonuclear myeloid-derived suppressor cells. Unfortunately, this beneficial effect progressively wanes as a consequence of enhanced expression of the IL4-induced gene 1 (IL4I1) enzyme by immature B cells and B2-FO cells. Endogenous IL4I1 selectively decreases CXCR5 expression in splenic immature B cells, subverting their trafficking to primary tumors and enhancing the production of IL-10 by B2 cells, thereby promoting an immunosuppressive microenvironment. Accordingly, B2 cells from RET IL4I1KO mice more efficiently controlled B16 melanoma growth than B2 cells from IL4I1-competent RET mice. Collectively, immature B cells and B2-FO cells are key actors in the control of melanoma growth, but their mobility and functions are differently impaired by IL4I1 overexpression during melanoma progression. Thus, our present data strongly urge us to associate an IL4I1 antagonist with current immunotherapy to improve the treatment of metastatic melanoma.

Chidamide improves gefitinib treatment outcomes in NSCLC by attenuating recruitment and immunosuppressive function of myeloid-derived suppressor cells

Clinical resistance to EGFR tyrosine kinase inhibitors in non-small-cell lung cancer (NSCLC) remains a significant challenge. Recent studies have indicated that the number of myeloid-derived suppressor cells (MDSCs) increases following gefitinib treatment, correlating with a poor patient response in NSCLC. Our study revealed that gefitinib treatment stimulates the production of CCL2, which subsequently enhances monocyte (M)-MDSC migration to tumor sites. Chidamide, a selective inhibitor of the histone deacetylase subtype, counteracted the gefitinib-induced increase in CCL2 levels in tumor cells. Additionally, chidamide down-regulated the expression of CCR2 in M-MDSCs, inhibiting their migration. Furthermore, chidamide attenuated the immunosuppressive function of M-MDSCs both alone and in combination with gefitinib. Chidamide also alleviated tumor immunosuppression by reducing the number of M-MDSCs in LLC-bearing mice, thereby enhancing the antitumor efficacy of gefitinib. In conclusion, our findings suggest that chidamide can improve gefitinib treatment outcomes, indicating that MDSCs are promising targets in NSCLC.

Abstract A020: Molecular basis of immune suppressive microenvironment specified by cancer-associated fibroblasts in pancreatic cancer

Abstract Despite constant efforts to improve treatment, the prognosis remains poor, with an overall survival rate of 6% (ranges from 2% to 9%) due to lack of efficient chemotherapy, radiotherapy, and targeted therapy. Immune checkpoint inhibitors (ICIs) has been reported to be effective in various solid cancers, such as melanoma, lung cancer, and renal cell carcinoma. However, pancreatic ductal adenocarcinoma (PDAC) is resistant against ICIs. The responsiveness of immune therapy is mainly determined by immune tumor microenvironment (TME) composed of tumor-infiltrating lymphocytes (TIL) and stromal cells. PDAC possesses unique TME, which is abundant of fibrosis, termed of desmoplasia, and the role of fibrosis in constructing immune suppressive TME remains unclear. First, in this study, to examine the immunological characteristics of TME, we constructed an integrated data base of TIL profiling, RNA-seq and whole exome seq using 31 fresh resected tissues of PDAC. An unsupervised clustering of based on numbers and percentages of 12 TIL types analyzed by flow cytometry showed that PDAC was divided into 2 types of cluster (myeloid cell-, T cell-dominant type), and the prognosis of myeloid type was significantly poorer than T cell-type. Myeloid type contained the high frequency of myeloid cell lineage including monocytes, macrophages and myeloid-derived suppressor cells (MDSC). Only MDSCs were significantly associated with poor prognosis among various immune cell types. Furthermore, gene enrichment analysis identified activated and suppressed pathways in each immune type, and the immune-related pathways were significantly down-regulated in myeloid cell-dominant type. Then, to understand the characteristics of MDSCs infiltrated into pancreatic cancer tissues, single cell RNA-seq with surgical specimens was performed, and the analysis showed that a specific subtype of MDSCs infiltrated into cancer tissues. In addition, activation status of cancer-associated fibroblasts (CAFs) was related with MDSC recruitment and activation, indicating that the interaction between MDSCs and CAFs is crucial to create MDSC-rich TME. Inhibition of interaction between MDSCs and CAFs is expected to overcome immunosuppressive TME can be a novel immunotherapy in PDAC. Citation Format: Kazunori Aoki, Hironori Fukuda, Eri Hashimoto, Kosuke Arai. Molecular basis of immune suppressive microenvironment specified by cancer-associated fibroblasts in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A020.

MDSCs use a complex molecular network to suppress T-cell immunity in a pulmonary model of fungal infection.

Paracoccidioidomycosis (PCM) is a systemic endemic fungal disease prevalent in Latin America. Previous studies revealed that host immunity against PCM is tightly regulated by several suppressive mechanisms mediated by tolerogenic plasmacytoid dendritic cells, the enzyme 2,3 indoleamine dioxygenase (IDO-1), regulatory T-cells (Tregs), and through the recruitment and activation of myeloid-derived suppressor cells (MDSCs). We have recently shown that Dectin-1, TLR2, and TLR4 signaling influence the IDO-1-mediated suppression caused by MDSCs. However, the contribution of these receptors in the production of important immunosuppressive molecules used by MDSCs has not yet been explored in pulmonary PCM. We evaluated the expression of PD-L1, IL-10, as well as nitrotyrosine by MDSCs after anti-Dectin-1, anti-TLR2, and anti-TLR4 antibody treatment followed by P. brasiliensis yeasts challenge in vitro. We also investigated the influence of PD-L1, IL-10, and nitrotyrosine in the suppressive activity of lung-infiltrating MDSCs of C57BL/6-WT, Dectin-1KO, TLR2KO, and TLR4KO mice after in vivo fungal infection. The suppressive activity of MDSCs was evaluated in cocultures of isolated MDSCs with activated T-cells. A reduced expression of IL-10 and nitrotyrosine was observed after in vitro anti-Dectin-1 treatment of MDSCs challenged with fungal cells. This finding was further confirmed in vitro and in vivo by using Dectin-1KO mice. Furthermore, MDSCs derived from Dectin-1KO mice showed a significantly reduced immunosuppressive activity on the proliferation of CD4+ and CD8+ T lymphocytes. Blocking of TLR2 and TLR4 by mAbs and using MDSCs from TLR2KO and TLR4KO mice also reduced the production of suppressive molecules induced by fungal challenge. In vitro, MDSCs from TLR4KO mice presented a reduced suppressive capacity over the proliferation of CD4+ T-cells. We showed that the pathogen recognition receptors (PRRs) Dectin-1, TLR2, and TLR4 contribute to the suppressive activity of MDSCs by inducing the expression of several immunosuppressive molecules such as PD-L1, IL-10, and nitrotyrosine. This is the first demonstration of a complex network of PRRs signaling in the induction of several suppressive molecules by MDSCs and its contribution to the immunosuppressive mechanisms that control immunity and severity of pulmonary PCM.

Concomitant NAFLD Facilitates Liver Metastases and PD-1-Refractory by Recruiting MDSCs via CXCL5/CXCR2 in Colorectal Cancer

Background and AimsBoth Non-alcoholic fatty liver disease (NAFLD) and colorectal cancer (CRC) are prevalent worldwide. The effect of concomitant NAFLD on the risk of colorectal liver metastasis (CRLM) and its mechanisms have not been definitively elucidated. MethodsWe observed the effect of concomitant NAFLD on CRLM in the mouse model, and explored the underlying mechanisms of specific myeloid-derived suppressor cells (MDSCs) recruitment, then tested the therapeutic application based on the mechanisms; finally we validated our findings in the clinical samples. ResultsHere we prove that in different mouse models, NAFLD induces F4/80+ Kupffer cells to secret chemokine CXCL5, then recruits CXCR2+ myeloid-derived suppressor cells (MDSCs) to promote the growth of CRLM. CRLM with NAFLD background are refractory to the anti-PD-1 monoclonal antibody treatment, but when combined with Reparixin, an inhibitor of CXCR1/2, dual-therapy cures the established CRLM in mice with NAFLD. Our clinical studies also indicate that fatty liver diseases increase the infiltration of CXCR2+ MDSCs, as well as the hazard of liver metastases in CRC patients. ConclusionsCollectively, our findings highlight the significance of a selective CXCR2+/CD11b+/Gr-1+ subset myeloid cells in favoring the development of CRLM with NAFLD background, and identify a pharmaceutic medicine which is already available for the clinical trials and potential treatment.