mTOR inhibitor INK128 attenuates dextran sodium sulfate-induced colitis by promotion of MDSCs on Treg cell expansion

Converting "cold" to "hot": epigenetics strategies to improve immune therapy effect by regulating tumor-associated immune suppressive cells

Significant developments in cancer treatment have been made since the advent of immune therapies. However, there are still some patients with malignant tumors who do not benefit from immunotherapy. Tumors without immunogenicity are called "cold" tumors which are unresponsive to immunotherapy, and the opposite are "hot" tumors. Immune suppressive cells (ISCs) refer to cells which can inhibit the immune response such as tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), regulatory T (Treg) cells and so on. The more ISCs infiltrated, the weaker the immunogenicity of the tumor, showing the characteristics of "cold" tumor. The dysfunction of ISCs in the tumor microenvironment (TME) may play essential roles in insensitive therapeutic reaction. Previous studies have found that epigenetic mechanisms play an important role in the regulation of ISCs. Regulating ISCs may be a new approach to transforming "cold" tumors into "hot" tumors. Here, we focused on the function of ISCs in the TME and discussed how epigenetics is involved in regulating ISCs. In addition, we summarized the mechanisms by which the epigenetic drugs convert immunotherapy-insensitive tumors into immunotherapy-sensitive tumors which would be an innovative tendency for future immunotherapy in "cold" tumor.

Dexamethasone promotes renal fibrosis by upregulating ILT4 expression in myeloid-derived suppressor cells

Studies have shown that adoptive transfer of myeloid-derived suppressor cells (MDSCs) can alleviate various inflammatory diseases, including glomerulonephritis, but the long-term effects of the transferred MDSCs are still unclear. In addition, although glucocorticoids exert immunosuppressive effects on inflammatory diseases by inducing the expansion of MDSCs, the impact of glucocorticoids on the immunosuppressive function of MDSCs and their molecular mechanisms are unclear. In this study, we found that adoptive transfer of MDSCs to doxorubicin-induced focal segmental glomerulosclerosis (FSGS) mice for eight consecutive weeks led to an increase in serum creatinine and proteinuria and aggravation of renal interstitial fibrosis. Similarly, 8 weeks of high-dose dexamethasone administration exacerbated renal interstitial injury and interstitial fibrosis in doxorubicin-induced mice, manifested as an increase in serum creatinine and proteinuria, collagen deposition and α-SMA expression. On this basis, we found that dexamethasone could enhance MDSC expression and secretion of the fibrosis-related cytokines TGF-β and IL-10. Mechanistically, we revealed that dexamethasone promotes the expression of immunoglobulin-like transcription factor 4 (ILT4), which enhances the T-cell inhibitory function of MDSCs and promotes the activation of STAT6, thereby strengthening the expression and secretion of TGF-β and IL-10. Knocking down ILT4 alleviated renal fibrosis caused by adoptive transfer of MDSCs. Therefore, our findings demonstrate that the role and mechanism of dexamethasone mediate the expression and secretion of TGF-β and IL-10 in MDSCs by promoting the expression of ILT4, thereby leading to renal fibrosis.

Diverse functions of myeloid-derived suppressor cells in autoimmune diseases

Since myeloid-derived suppressor cells (MDSCs) were found suppressing immune responses in cancer and other pathological conditions, subsequent researchers have pinned their hopes on the suppressive function against immune damage in autoimmune diseases. However, recent studies have found key distinctions of MDSC immune effects in cancer and autoimmunity. These include not only suppression and immune tolerance, but MDSCs also possess pro-inflammatory effects and exacerbate immune disorders during autoimmunity, while promoting T cell proliferation, inducing Th17 cell differentiation, releasing pro-inflammatory cytokines, and causing direct tissue damage. Additionally, MDSCs could interact with surrounding cells to directly cause tissue damage or repair, sometimes even as an inflammatory indicator in line with disease severity. These diverse manifestations could be partially attributed to the heterogeneity of MDSCs, but not all. The different disease types, disease states, and cytokine profiles alter the diverse phenotypes and functions of MDSCs, thus leading to the impairment or obversion of MDSC suppression. In this review, we summarize the functions of MDSCs in several autoimmune diseases and attempt to elucidate the mechanisms behind their actions.

Myeloid-derived suppressor cells in the therapy of autoimmune diseases

Myeloid-derived suppressor cells (MDSCs) are well recognized as critical factors in the pathology of tumors. However, their roles in autoimmune diseases are still unclear, which hampers the development of efficient immunotherapies. The role of different MDSCs subsets in multiple sclerosis, inflammatory bowel diseases, rheumatoid arthritis, type 1 diabetes, and systemic lupus erythematosus displayed different mechanisms of immune suppression, and several studies pointed to MDSCs' capacity to induce T-helper (Th)17 cells and tissue damage. These results also suggested that MDSCs could be present in different functional states and utilize different mechanisms for controlling the activity of T and B cells. Therefore, various therapeutic strategies should be employed to restore homeostasis in autoimmune diseases. The therapies harnessing MDSCs could be designed either as cell therapy or rely on the expansion and activation of MDSCs in vivo, or their depletion. Cumulatively, MDSCs are inevitable players in autoimmunity, and rational approaches in developing therapies are required to avoid the adverse effects of MDSCs and harness their suppressive mechanisms to improve the overall efficacy of autoimmunity therapy.

Halofuginone ameliorates systemic lupus erythematosus by targeting Blk in myeloid-derived suppressor cells

Systemic lupus erythematosus (SLE) is a multisystemic, inflammatory autoimmune disease. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells participated in the pathogenesis of SLE. MDSCs has been considered a potential therapeutic target for lupus. As traditional Chinese medicine, Halofuginone (HF) has the extensive immunomodulatory effects on some autoimmune disorders. Our research was dedicated to discovering therapeutic efficacy of HF for lupus to explore novel mechanisms on MDSCs. We found that HF prominently alleviated the systemic symptoms especially nephritis in Imiquimod-induced lupus mice, and simultaneously repaired the immune system, reflected in the alteration of autoantibodies. HF diminished the quantity of MDSCs in lupus mice, and induced apoptosis of MDSCs. Through RNA sequencing performed on the sorted MDSC from lupus mice and HF-treated lupus mice, B lymphoid tyrosine kinase (Blk, a non-receptor cytoplasmic tyrosine kinase) was screened as the target molecule of HF. It's proven that HF had two independent effects on Blk. On the one hand, HF increased the mRNA expression of Blk in MDSCs by inhibiting the nuclear translocation of p65/p50 heterodimer. On the other hand, HF enhanced the kinase activity of Blk in MDSCs through direct molecular binding. We further investigated that Blk suppressed the phosphorylation of downstream ERK signaling pathway to increase the apoptosis of MDSCs. In conclusion, our study illustrated that HF alleviated the disease progression of lupus mice by targeting Blk to promote the apoptosis of MDSCs, which indicated the immunotherapeutic potential of HF to treat lupus.

Myeloid-derived suppressor cells: Cancer, autoimmune diseases, and more

Although cancer immunotherapy using immune checkpoint inhibitors (ICIs) has been recognized as one of the major treatment modalities for malignant diseases, the clinical outcome is not uniform in all cancer patients. Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells that possess various strong immunosuppressive activities involving multiple immunocompetent cells that are significantly accumulated in patients who did not respond well to cancer immunotherapies. We reviewed the perspective of MDSCs with emerging evidence in this review. Many studies on MDSCs were performed in malignant diseases. Substantial studies on the participation of MDSCs on non-malignant diseases such as chronic infection and autoimmune diseases, and physiological roles in obesity, aging, pregnancy and neonates have yet to be reported. With the growing understanding of the roles of MDSCs, variable therapeutic strategies and agents targeting MDSCs are being investigated, some of which have been used in clinical trials. More studies are required in order to develop more effective strategies against MDSCs.

The paradoxical role of MDSCs in inflammatory bowel diseases: From bench to bedside

Myeloid-derived suppressor cells (MDSCs) are a group of bone marrow derived heterogeneous cells, which is known for their immunosuppressive functions especially in tumors. Recently, MDSCs have receiving increasing attention in pathological conditions like infection, inflammation and autoimmune diseases. Inflammatory bowel diseases (IBD) are a series of immune-dysfunctional autoimmune diseases characterized by relapsing intestinal inflammation. The role of MDSCs in IBD remains controversial. Although most studies in vitro demonstrated its anti-inflammatory effects by inhibiting the proliferation and function of T cells, it was reported that MDSCs failed to relieve inflammation but even promoted inflammatory responses in experimental IBD. Here we summarize recent insights into the role of MDSCs in the development of IBD and the potential of MDSCs-targeted therapy.

Mammalian target of rapamycin-novel insight for management of inflammatory bowel diseases

Inflammatory bowel diseases (IBDs), with blurred etiology, show a rising trend and are of global concern. Of various factors involved in IBD pathogenesis and development, inflammation has been shown to play a major role. Recognition of the molecular and cellular pathways that induce IBD is an emerging subject to develop targeted therapies. Mammalian target of rapamycin (mTOR) is one the most common receptors of many inflammatory pathways, including that of IBD. To this end, we intend to overview the mTOR inhibitors for their possible efficacy in present and future approaches to treatment of IBD.

Dual mTORC1/2 inhibitor AZD2014 diminishes myeloid-derived suppressor cells accumulation in ovarian cancer and delays tumor growth

Mechanistic target of rapamycin (mTOR) forms two distinct complexes, mTOR complex 1 (mTORC1) and mTORC2. Here we investigated the antitumor effect of dual mTORC1/2 inhibitor AZD2014 on epithelial ovarian cancer (EOC) and its potential effect on immunosuppressive myeloid-derived suppressor cells (MDSCs). Immunohistochemical analysis of mTORC1 and mTORC2 was performed on a human ovarian cancer tissue microarray. High mTORC2 expression level was associated with shorter survival in EOC, whereas mTORC1 was not correlate with patients' prognosis. AZD2014 suppressed mTOR signaling pathway in ovarian cancer cells, inhibited proliferation and induced G1-phase cell cycle arrest and apoptosis. In tumor-bearing mice, AZD2014 treatment limited tumor growth, reduced peritoneal ascites, and prolonged survival. AZD2014 specifically reduced MDSCs migration and accumulation in EOC peritoneal fluid but not in the spleen. Moreover, subsequent AZD2014 treatment after cisplatin chemotherapy delayed EOC recurrence. Collectively, we observed that high mTORC2 expression level in EOC indicated a poor prognosis. Remarkably, in tumor-bearing mice, AZD2014 diminished MDSC accumulation and delayed tumor growth and recurrence.

The mechanism of rapamycin in promoting asthmatic regulatory T cell differentiation and function

To investigate the mechanism of rapamycin in promoting asthmatic regulatory T cell differentiation . Asthma model was prepared by sensitization and challenge of ovalbumin in mice. Spleen CD4CD25 T cells were sorted from the asthmatic mice and normal mice by ultrahigh speed flow cytometer, and divided into three groups. Transforming growth factor-β and interleukin-2, or combined with rapamycin (final concentration of 500 nmol/L) were given in the model group or the rapamycin group. The levels of Treg cells and CD4CD25 T cells were detected by flow cytometry. The phosphorylation level of downstream proteins of S6 and Akt in the mTORC1/2 signaling pathway were examined by Western blotting. Compared with the model group, the differentiation level of Treg cells in the rapamycin group was significantly increased, the proliferation level of CD4CD25 T cells was decreased, and the phosphorylations of the mTORC1/2 substrates, S6 protein and Akt were decreased （all <0.05）. Rapamycin can promote the differentiation and function of Treg cells via inhibition of the mTORC1/2 signaling pathway.

mTOR-dependent immunometabolism as Achilles' heel of anticancer therapy

Immune cells are important constituents of the tumor microenvironment and essential in eradicating tumor cells during conventional therapies or novel immunotherapies. The mechanistic target of rapamycin (mTOR) signaling pathway senses the intra- and extracellular nutrient status, growth factor supply, and cell stress-related changes to coordinate cellular metabolism and activation dictating effector and memory functions in mainly all hematopoietic immune cells. In addition, the mTOR complex 1 (mTORC1) and mTORC2 are frequently deregulated and become activated in cancer cells to drive cell transformation, survival, neovascularization, and invasion. In this review, we provide an overview of the influence of mTOR complexes on immune and cancer cell function and metabolism. We discuss how mTOR inhibitors aiming to target cancer cells will influence immunometabolic cell functions participating either in antitumor responses or favoring tumor cell progression in individual immune cells. We suggest immunometabolism as the weak spot of anticancer therapy and propose to evaluate patients according to their predominant immune cell subtype in the cancer tissue. Advances in metabolic drug development that hold promise for more effective treatments in different types of cancer will have to consider their effects on the immune system.

Myeloid-derived suppressor cells in the era of increasing myeloid cell diversity

Myeloid-derived suppressor cells (MDSCs) are pathologically activated neutrophils and monocytes with potent immunosuppressive activity. They are implicated in the regulation of immune responses in many pathological conditions and are closely associated with poor clinical outcomes in cancer. Recent studies have indicated key distinctions between MDSCs and classical neutrophils and monocytes, and, in this Review, we discuss new data on the major genomic and metabolic characteristics of MDSCs. We explain how these characteristics shape MDSC function and could facilitate therapeutic targeting of these cells, particularly in cancer and in autoimmune diseases. Additionally, we briefly discuss emerging data on MDSC involvement in pregnancy, neonatal biology and COVID-19.

Role of intracellular signaling pathways and their inhibitors in the treatment of inflammation

Inflammation is not only a defense mechanism of the innate immune system against invaders, but it is also involved in the pathogenesis of many diseases such as atherosclerosis, thrombosis, diabetes, epilepsy, and many neurodegenerative disorders. The World Health Organization (WHO) reports worldwide estimates of people (9.6% in males and 18.0% in females) aged over 60 years, suffering from symptomatic osteoarthritis, and around 339 million suffering from asthma. Other chronic inflammatory diseases, such as ulcerative colitis and Crohn's disease are also highly prevalent. The existing anti-inflammatory agents, both non-steroidal and steroidal, are highly effective; however, their prolonged use is marred by the severity of associated side effects. A holistic approach to ensure patient compliance requires understanding the pathophysiology of inflammation and exploring new targets for drug development. In this regard, various intracellular cell signaling pathways and their signaling molecules have been identified to be associated with inflammation. Therefore, chemical inhibitors of these pathways may be potential candidates for novel anti-inflammatory drug approaches. This review focuses on the anti-inflammatory effect of these inhibitors (for JAK/STAT, MAPK, and mTOR pathways) describing their mechanism of action through literature search, current patents, and molecules under clinical trials.

The diverse roles of myeloid derived suppressor cells in mucosal immunity

The mucosal immune system plays a vital role in protecting the host from the external environment. Its major challenge is to balance immune responses against harmful and harmless agents and serve as a 'homeostatic gate keeper'. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of undifferentiated cells that are characterized by an immunoregulatory and immunosuppressive phenotype. Herein we postulate that MDSCs may be involved in shaping immune responses related to mucosal immunity, due to their immunomodulatory and tissue remodeling functions. Until recently, MDSCs were investigated mainly in cancerous diseases, where they induce and contribute to an immunosuppressive and inflammatory environment that favors tumor development. However, it is now becoming clear that MDSCs participate in non-cancerous conditions such as chronic infections, autoimmune diseases, pregnancy, aging processes and immune tolerance to commensal microbiota at mucosal sites. Since MDSCs are found in the periphery only in small numbers under normal conditions, their role is highlighted during pathologies characterized by acute or chronic inflammation, when they accumulate and become activated. In this review, we describe several aspects of the current knowledge characterizing MDSCs and their involvement in the regulation of the mucosal epithelial barrier, their crosstalk with commensal microbiota and pathogenic microorganisms, and their complex interactions with a variety of surrounding regulatory and effector immune cells. Finally, we discuss the beneficial and harmful outcomes of the MDSC regulatory functions in diseases affecting mucosal tissues. We wish to illuminate the pivotal role of MDSCs in mucosal immunity, the limitations in our understanding of all the players and the intricate challenges stemming from the complex interactions of MDSCs with their environment.

mTOR inhibitor INK128 promotes wound healing by regulating MDSCs

Background

Skin wounds in diabetic patients hardly recover. Accumulating evidence has shown that mammalian target of rapamycin (mTOR) pathway and myeloid-derived suppressor cells (MDSCs) are involved in inflammatory-related response. INK128 is a novel mTOR kinase inhibitor in clinical development. However, the exact roles of MDSCs and INK128 in healing wound of diabetic patients are unclear.

Methods

Mice models of normal, diabetic, and diabetic+INK128 were constructed. Bone marrow (BM)-derived macrophages and RAW264.7 cell line co-cultured with MDSCs, which were induced at different conditions. Flow cytometry, western blot, quantitative real-time PCR, and immunohistochemical analysis were performed.

Results

Diabetic mice (DM) had a slower recovery rate, thinner epidermis and dermis, and less blood vessels than those of normal mice. MDSCs were abnormally accumulated in DM, mTOR was activated in MDSCs of DM, and the cells were treated with high glucose. Moreover, mTOR signaling inhibitor INK128 could promote wound healing through reducing the MDSCs. MDSC function was disordered in DM and high-glucose environments, while INK128 could help retrieve their function. Furthermore, high glucose and other factors in DM could promote M-MDSC differentiation to M1 pro-inflammatory macrophage cells, thus inhibiting wound healing. The differentiation, which was dependent on mTOR signaling, could be reversed by INK128.

Conclusion

INK128 is potential to be developed as a clinical strategy to promote wound healing of diabetic patients.

Regulating T Cell Population Alleviates SLE by Inhibiting mTORC1/C2 in MRL/lpr Mice

It’s well known that the mammalian target of rapamycin (mTOR) exerts a critical role in the regulator of immune cells and is associated with T cells dysfunction in patients with systemic lupus erythematosus (SLE). Antigen-induced T-cell proliferation via mTORC1 suppressed by Rapamycin has been used to improve SLE primarily. Previously it has showed that INK128, a highly potent, specific orally inhibitor of mTORC1 and mTORC2, significantly attenuates SLE in pristine-induced lupus mice. Herein we compared the cure effects of INK128 and rapamycin on lupus mice. We treated MRL/lpr mice with INK128 or rapamycin at 12 weeks-age. The effect of the two inhibitors on the lupus mice was determined by immunohistochemistry. The effect of the two inhibitors on T cell populations was investigated by flow cytometry. The mTOR signaling was measured by Western Blot. INK128 remarkably alleviated SLE by reducing splenomegaly, renal inflammation and damage, and resuming T-cell dysfunction. The more effective of INK128 on SLE than rapamycin. INK128 effectively suppressed mTORC1 and mTORC2 activity in T cells, but rapamycin just suppressed mTORC1 activity. Thus, our results show that INK128 is can effectively alleviate SLE and be used as one of the potential clinical therapeutic candidates for SLE.

Role of myeloid-derived suppressor cells in the promotion and immunotherapy of colitis-associated cancer

Colitis-associated cancer (CAC) is a specific type of colorectal cancer that develops from inflammatory bowel disease (IBD). Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that are essential for the pathological processes of inflammation and cancer. Accumulating evidence indicates that MDSCs play different but vital roles during IBD and CAC development and impede CAC immunotherapy. New insights into the regulatory network of MDSCs in the CAC pathogenesis are opening new avenues for developing strategies to enhance the effectiveness of CAC treatment. In this review, we explore the role of MDSCs in chronic inflammation, dysplasia and CAC and summarize the potential CAC therapeutic strategies based on MDSC blockade.

Reg4 and complement factor D prevent the overgrowth of E. coli in the mouse gut

The expansion of Enterobacteriaceae, such as E. coli is a main characteristic of gut inflammation and is related to multiple human diseases. However, how to control these E. coli overgrowth is not well understood. Here, we demonstrate that gut complement factor D (CFD) plays an important role in eliminating E. coli. Increased E. coli, which could stimulate inflammatory macrophages to induce colitis, were found in the gut of CFD deficient mice. We also showed that gut Reg4, which is expressed in gut epithelial cells, stimulated complement-mediated attack complexes to eliminate E. coli. Reg4 deficient mice also had increased E. coli. The dominant E. coli were isolated from colitis tissues of mice and found to be sensitive to both CFD- and Reg4-mediated attack complexes. Thus, gut Reg4- and CFD-mediated membrane attack complexes may maintain gut homeostasis by killing inflammatory E. coli.

Qi et al. show that gut complement factor D (CFD) plays an important role in eliminating Escherichia coli, using gut specific CFD null mice. They find that E. coli isolated from inflamed guts are sensitive to both CFD and Reg4-mediated attack complexes. This study provides insights into how the level of E. Coli is kept low in the gut to prevent its inflammation.

Regulations of Glycolytic Activities on Macrophages Functions in Tumor and Infectious Inflammation

Macrophages differentiated into a classically activated (M1) or alternatively activated phenotype (M2) in infection and tumor, but the precise effects of glycolysis and oxidative phosphorylation (OXPHOS) metabolic pathway remain unclear. Herein, the effects of glycolysis or OXPHOS on macrophage polarizations were investigated using a pharmacological approach in mice. 2-Deoxy-D-glucose (2-DG) treatments, which blocks the key enzyme hexokinase of glycolysis, efficiently inhibits a specific switch to M1 lineage, decreasing the secretion of pro-inflammatory cytokines and expressions of co-stimulatory molecules associated with relieving infectious inflammation in vitro and in vivo. Glycolytic activation through the hypoxia-inducible factor-1α (HIF-1α) pathway was required for differentiation to the M1 phenotype, which conferred protection against infection. Dimethyl malonate (DMM) treatment, which blocks the key element succinate of OXPHOS, efficiently inhibits a specific switch to M2 lineage when macrophages receiving M2 stimulation, decreasing the secretion of anti-inflammatory cytokine and CD206 expressions. Mitochondrial dynamic alterations including mitochondrial mass, mitochondrial membrane potential (Dym) and ROS productions were critically for differentiation to the M2 phenotype, which conferred protection against anti-tumor immunity. Glycolysis is also required for macrophage M2 differentiation. Thus, these data provide a basis for a comprehensively understanding the role of glycolysis and OXPHOS in macrophage differentiation during anti-infection and anti-tumor inflammation.

Glucocorticoids Promote the Onset of Acute Experimental Colitis and Cancer by Upregulating mTOR Signaling in Intestinal Epithelial Cells

The therapeutic effects of glucocorticoids on colitis and colitis-associated cancer are unclear. In this study, we investigated the therapeutic roles of glucocorticoids in acute experimental ulcerative colitis and colitis-associated cancer in mice and their immunoregulatory mechanisms. Murine acute ulcerative colitis was induced by dextran sulfate sodium (DSS) and treated with dexamethasone (Dex) at different doses. Dex significantly exacerbated the onset and severity of DSS-induced colitis and potentiated mucosal inflammatory macrophage and neutrophil infiltration, as well as cytokine production. Furthermore, under inflammatory conditions, the expression of the glucocorticoid receptor (GR) did not change significantly, while mammalian target of rapamycin (mTOR) signaling was higher in colonic epithelial cells than in colonic immune cells. The deletion of mTOR in intestinal epithelial cells, but not that in myeloid immune cells, in mice significantly ameliorated the severe course of colitis caused by Dex, including weight loss, clinical score, colon length, pathological damage, inflammatory cell infiltration and pro-inflammatory cytokine production. These data suggest that mTOR signaling in intestinal epithelial cells, mainly mTORC1, plays a critical role in the Dex-induced exacerbation of acute colitis and colitis-associated cancer. Thus, these pieces of evidence indicate that glucocorticoid-induced mTOR signaling in epithelial cells is required in the early stages of acute ulcerative colitis by modulating the dynamics of innate immune cell recruitment and activation.

Modulation of Immunosuppression by Oligonucleotide-Based Molecules and Small Molecules Targeting Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that exert suppressive function on the immune response. MDSCs expand in tumor-bearing hosts or in the tumor microenvironment and suppress T cell responses via various mechanisms, whereas a reduction in their activities has been observed in autoimmune diseases or infections. It has been reported that the symptoms of various diseases, including malignant tumors, can be alleviated by targeting MDSCs. Moreover, MDSCs can contribute to patient resistance to therapy using immune checkpoint inhibitors. In line with these therapeutic approaches, diverse oligonucleotide-based molecules and small molecules have been evaluated for their therapeutic efficacy in several disease models via the modulation of MDSC activity. In the current review, MDSC-targeting oligonucleotides and small molecules are briefly summarized, and we highlight the immunomodulatory effects on MDSCs in a variety of disease models and the application of MDSC-targeting molecules for immuno-oncologic therapy.

Lactobacillus maintains healthy gut mucosa by producing L-Ornithine

Gut mucosal layers are crucial in maintaining the gut barrier function. Gut microbiota regulate homeostasis of gut mucosal layer via gut immune cells such as RORγt (+) IL-22(+) ILC3 cells, which can influence the proliferation of mucosal cells and the production of mucin. However, it is unclear how gut microbiota execute this regulation. Here we show that lactobacilli promote gut mucosal formation by producing L-Ornithine from arginine. L-Ornithine increases the level of aryl hydrocarbon receptor ligand L-kynurenine produced from tryptophan metabolism in gut epithelial cells, which in turn increases RORγt (+)IL-22(+) ILC3 cells. Human REG3A transgenic mice show an increased proportion of L-Ornithine producing lactobacilli in the gut contents, suggesting that gut epithelial REG3A favors the expansion of L-Ornithine producing lactobacilli. Our study implicates the importance of a crosstalk between arginine metabolism in Lactobacilli and tryptophan metabolism in gut epithelial cells in maintaining gut barrier.

Correlation between toll-like receptor 4 and nucleotide-binding oligomerization domain 2 (NOD2) and pathological severity in dogs with chronic gastrointestinal diseases

Toll-like receptor 4 (TLR4), nucleotide-binding oligomerization domain 2 (NOD2), and TNF-α play important roles in human inflammatory bowel diseases. The aim of this study was to elucidate the relationship between Toll-like receptor 4, NOD2, and TNF-α and the severity of chronic gastrointestinal diseases in dogs. We examined the expression levels of TLR4, NOD2, and TNF-α in the stomach, duodenum, ileum, colon, and rectum obtained from 21 dogs with chronic gastrointestinal disease, including inflammatory bowel disease, high-grade lymphoma, food responsive enteropathy, chronic pancreatitis, low-grade lymphoma, inflammatory colorectal polyp, and chronic colitis. Next, we demonstrated whether there is good correlation between the expression levels of TLR4, NOD2, and TNF-α and the histopathological analysis of each sample. We found that the level of TLR4 expression in the ileum of dogs with chronic gastrointestinal disease was positively associated with the histopathological severity. We also found that the level of NOD2 expression in the duodenum, stomach, and rectum was positively associated with the histopathological severity. However, there was no correlation between TNF-α expression in the 5 regions tested in this study and the histopathological severity. These findings indicate that TLR4 and NOD2 are remarkably associated with the severity of chronic gastrointestinal disease in dogs.