IFN-γ and indoleamine 2,3-dioxygenase signaling between donor dendritic cells and T cells regulates graft versus host and graft versus leukemia activity

Current perspective on biological properties of plasmacytoid dendritic cells and dysfunction in gut

Plasmacytoid dendritic cells (pDCs), a subtype of DC, possess unique developmental, morphological, and functional traits that have sparked much debate over the years whether they should be categorized as DCs. The digestive system has the greatest mucosal tissue overall, and the pDC therein is responsible for shaping the adaptive and innate immunity of the gastrointestinal tract, resisting pathogen invasion through generating type I interferons, presenting antigens, and participating in immunological responses. Therefore, its alleged importance in the gut has received a lot of attention in recent years, and a fresh functional overview is still required. Here, we summarize the current understanding of mouse and human pDCs, ranging from their formation and different qualities compared with related cell types to their functional characteristics in intestinal disorders, including colon cancer, infections, autoimmune diseases, and intestinal graft-versus-host disease. The purpose of this review is to convey our insights, demonstrate the limits of existing research, and lay a theoretical foundation for the rational development and use of pDCs in future clinical practice.

Identification of novel biomarkers and immune infiltration features of recurrent pregnancy loss by machine learning

Recurrent pregnancy loss (RPL) is a complex reproductive disorder. The incompletely understood pathophysiology of RPL makes early detection and exact treatment difficult. The purpose of this work was to discover optimally characterized genes (OFGs) of RPL and to investigate immune cell infiltration in RPL. It will aid in better understanding the etiology of RPL and in the early detection of RPL. The RPL-related datasets were obtained from the Gene Expression Omnibus (GEO), namely GSE165004 and GSE26787. We performed functional enrichment analysis on the screened differentially expressed genes (DEGs). Three machine learning techniques are used to generate the OFGs. A CIBERSORT analysis was conducted to examine the immune infiltration in RPL patients compared with normal controls and to investigate the correlation between OFGs and immune cells. Between the RPL and control groups, 42 DEGs were discovered. These DEGs were found to be involved in cell signal transduction, cytokine receptor interactions, and immunological response, according to the functional enrichment analysis. By integrating OFGs from the LASSO, SVM-REF, and RF algorithms (AUC > 0.880), we screened for three down-regulated genes: ZNF90, TPT1P8, FGF2, and an up-regulated FAM166B. Immune infiltration study revealed that RPL samples had more monocytes (P < 0.001) and fewer T cells (P = 0.005) than controls, which may contribute to RPL pathogenesis. Additionally, all OFGs linked with various invading immune cells to varying degrees. In conclusion, ZNF90, TPT1P8, FGF2, and FAM166B are potential RPL biomarkers, offering new avenues for research into the molecular mechanisms of RPL immune modulation and early detection.

Understanding recurrent pregnancy loss: recent advances on its etiology, clinical diagnosis, and management

Recurrent pregnancy loss (RPL) has become an important reproductive health issue worldwide. RPL affects about 2%-3% of reproductive-aged women, and makes serious threats to women's physical and mental health. However, the etiology of approximately 50% of RPL cases remains unknown (unexplained RPL), which poses a big challenge for clinical management of these patients. RPL has been widely regarded as a complex disease where its etiology has been attributed to numerous factors. Heretofore, various risk factors for RPL have been identified, such as maternal ages, genetic factors, anatomical structural abnormalities, endocrine dysfunction, prethrombotic state, immunological factors, and infection. More importantly, development and applications of next generation sequencing technology have significantly expanded opportunities to discover chromosomal aberrations and single gene variants responsible for RPL, which provides new insight into its pathogenic mechanisms. Furthermore, based upon patients' diagnostic evaluation and etiologic diagnosis, specific therapeutic recommendations have been established. This review will highlight current understanding and recent advances on RPL, with a special focus on the immunological and genetic etiologies, clinical diagnosis and therapeutic management.

Donor plasmacytoid dendritic cells limit graft-versus-host disease through vasoactive intestinal polypeptide expression

Vasoactive intestinal polypeptide (VIP), an anti-inflammatory neuropeptide with pleiotropic cardiovascular effects, induces differentiation of hematopoietic stem cells into regulatory dendritic cells that limit graft-versus-host disease (GVHD) in allogeneic hematopoietic stem cell transplant (HSCT) recipients. We have previously shown that donor plasmacytoid dendritic cells (pDCs) in bone marrow (BM) donor grafts limit the pathogenesis of GVHD. In this current study we show that murine and human pDCs express VIP, and that VIP-expressing pDCs limit T-cell activation and expansion using both in vivo and in vitro model systems. Using T cells or pDCs from transgenic luciferase+ donors in murine bone marrow transplantation (BMT), we show similar homing patterns of donor pDCs and T cells to the major sites for alloactivation of donor T cells: spleen and gut. Cotransplanting VIP-knockout (KO) pDCs with hematopoietic stem cells and T cells in major histocompatibility complex mismatched allogeneic BMT led to lower survival, higher GVHD scores, and more colon crypt cell apoptosis than transplanting wild-type pDCs. BMT recipients of VIP-KO pDCs had more T helper 1 polarized T cells, and higher plasma levels of granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-α than recipients of wild-type pDCs. T cells from VIP-KO pDC recipients had increasing levels of bhlhe40 transcripts during the first 2 weeks posttransplant, and higher levels of CyclophilinA/Ppia transcripts at day 15 compared with T cells from recipients of wild-type pDCs. Collectively, these data indicate paracrine VIP synthesis by donor pDCs limits pathogenic T-cell inflammation, supporting a novel mechanism by which donor immune cells regulate T-cell activation and GVHD in allogeneic BMT.

Relationship between mucosal TNF-α expression and Th1, Th17, Th22 and Treg responses in Helicobacter pylori infection

Helicobacter pylori (H. pylori)-induced gastric inflammation in the gastric mucosa and significantly increases the risk of developing gastritis and peptic ulcer disease (PUD). The objective of this research is to determine the role of tumor necrosis factor-α (TNF-α) expression in the gastric mucosa of patients with H. pylori-associated gastritis and PUD compared to uninfected patients, and we determined the relation between TNF-α expression and Th1/Th17/Th22, and Treg cells. Fifty-five patients with H. pylori-associated gastritis, 47 patients with H. pylori-associated PUD, and 48 uninfected patients were in this research. Antrum biopsy was used to detect H. pylori, virulence factors and histopathological assessments. Expression of TNF-α in the infected group was significantly higher than the uninfected group. Also, cagA/oipA-positive infected patients induce significantly more TNF-α expression than do cagA/oipA-negative infected patients. Expression of TNF-α was significantly increased in the PUD group than the gastritis group. Notably, TNF-α expression had a significant positive correlation with the frequency of Th1/Th17/Th22 lymphocytes in the PUD group. These findings indicate the importance of increasing TNF-α with Th1, Th17, Th22 responses increase as an important risk factor for PUD in context of H. pylori infection.

Expression of TNF-α was significantly increased in the PUD group than the gastritis group.

Notably, TNF-α expression had a significant positive correlation with the frequency of Th1/Th17/Th22 lymphocytes in the PUD group.

These findings indicate the importance of increasing TNF-α with Th1, Th17, Th22 responses increase as an important risk factor for PUD in context of H. pylori infection.

Murine Models Provide New Insights Into Pathogenesis of Chronic Graft-Versus-Host Disease in Humans

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative therapy for hematologic malignancies, but its success is complicated by graft-versus-host disease (GVHD). GVHD can be divided into acute and chronic types. Acute GVHD represents an acute alloimmune inflammatory response initiated by donor T cells that recognize recipient alloantigens. Chronic GVHD has a more complex pathophysiology involving donor-derived T cells that recognize recipient-specific antigens, donor-specific antigens, and antigens shared by the recipient and donor. Antibodies produced by donor B cells contribute to the pathogenesis of chronic GVHD but not acute GVHD. Acute GVHD can often be effectively controlled by treatment with corticosteroids or other immunosuppressant for a period of weeks, but successful control of chronic GVHD requires much longer treatment. Therefore, chronic GVHD remains the major cause of long-term morbidity and mortality after allo-HCT. Murine models of allo-HCT have made great contributions to our understanding pathogenesis of acute and chronic GVHD. In this review, we summarize new mechanistic findings from murine models of chronic GVHD, and we discuss the relevance of these insights to chronic GVHD pathogenesis in humans and their potential impact on clinical prevention and treatment.

Graft-versus-host disease depletes plasmacytoid dendritic cell progenitors to impair tolerance induction

Graft-versus-host disease (GVHD) causes failed reconstitution of donor plasmacytoid dendritic cells (pDCs) that are critical for immune protection and tolerance. We used both murine and human systems to uncover the mechanisms whereby GVHD induces donor pDC defects. GVHD depleted Flt3-expressing donor multipotent progenitors (MPPs) that sustained pDCs, leading to impaired generation of pDCs. MPP loss was associated with decreased amounts of MPP-producing hematopoietic stem cells (HSCs) and oxidative stress-induced death of proliferating MPPs. Additionally, alloreactive T cells produced GM-CSF to inhibit MPP expression of Tcf4, the transcription factor essential for pDC development, subverting MPP production of pDCs. GM-CSF did not affect the maturation of pDC precursors. Notably, enhanced recovery of donor pDCs upon adoptive transfer early after allogeneic HSC transplantation repressed GVHD and restored the de novo generation of donor pDCs in recipient mice. pDCs suppressed the proliferation and expansion of activated autologous T cells via a type I IFN signaling-dependent mechanism. They also produced PD-L1 and LILRB4 to inhibit T cell production of IFN-γ. We thus demonstrate that GVHD impairs the reconstitution of tolerogenic donor pDCs by depleting DC progenitors rather than by preventing pDC maturation. MPPs are an important target to effectively bolster pDC reconstitution for controlling GVHD.

Platelet and Red Blood Cell Transfusions and Risk of Acute Graft-versus-Host Disease after Myeloablative Allogeneic Hematopoietic Cell Transplantation

Transfusion therapy is a critical part of supportive care early after allogeneic hematopoietic cell transplantation (allo-HCT). Platelet and RBC transfusions elicit immunomodulatory effects in the recipient, but if this impacts the risk of acute graft-versus-host disease (aGVHD) has only been scarcely investigated. We investigated if platelet and RBC transfusions were associated with the development of aGVHD following myeloablative allo-HCT in a cohort of 664 patients who underwent transplantation between 2000 and 2019. Data were further analyzed for the impact of blood donor age and sex and blood product storage time. Exploratory analyses were conducted to assess correlations between transfusion burden and plasma biomarkers of inflammation and endothelial activation and damage. Between day 0 and day +13, each patient received a median of 7 (IQR, 5 to 10) platelet transfusions and 3 (IQR, 2 to 6) RBC transfusions (Spearman's ρ = 0.49). The cumulative sums of platelet and RBC transfusions, respectively, received from day 0 to day +13 were associated with subsequent grade II-IV aGVHD in multivariable landmark Cox models (platelets: adjusted hazard ratio [HR], 1.27; 95% confidence interval [CI], 1.06 to 1.51; RBCs: adjusted HR, 1.41; 95% CI, 1.09 to 1.82; both per 5 units; 184 events). For both platelet and RBC transfusions, we did not find support for a difference in the risk of aGVHD according to age or sex of the blood donor. Transfusion of RBCs with a storage time longer than the median of 8 days was inversely associated with aGVHD (HR per 5 units, 0.54; 95% CI, 0.30 to 0.96); however, when using an RBC storage time of ≥14 days as a cutoff, there was no longer evidence for an association with aGVHD (HR, 1.03 per 5 units; 95% CI, 0.53 to 2.00). For platelets, there was no clear association between storage time and the risk of aGVHD. The transfusion burdens of platelets and RBCs were positively correlated with plasma levels of TNF-α, IL-6, and soluble thrombomodulin at day +14. In conclusion, platelet and RBC transfusions in the first 2 weeks after myeloablative allo-HCT were associated with subsequent development of grade II-IV aGVHD. We did not find evidence of an impact of blood donor age or sex or blood product storage time on the risk of aGVHD. Our findings support restrictive transfusion strategies in allo-HCT recipients.

Regulatory T Cells in GVHD Therapy

Graft versus host disease (GVHD) is a common complication and the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Pharmacological immunosuppression used in GVHD prophylaxis and treatment lacks specificity and can increase the likelihood of infection and relapse. Regulatory T lymphocytes (Tregs) play a vital role in restraining excessive immune responses and inducing peripheral immune tolerance. In particular, clinical trials have demonstrated that Tregs can prevent and treat GVHD, without increasing the risk of relapse and infection. Hence, adoptive transfer of Tregs to control GVHD using their immunosuppressive properties represents a promising therapeutic approach. To optimally apply Tregs for control of GVHD, a thorough understanding of their biology is necessary. In this review, we describe the biological characteristics of Tregs, including how the stability of FOXP3 expression can be maintained. We will also discuss the mechanisms underlying Tregs-mediated modulation of GVHD and approaches to effectively increase Tregs’ numbers. Finally, we will examine the developing trends in the use of Tregs for clinical therapy.

Inflammation-induced inhibition of chaperone-mediated autophagy maintains the immunosuppressive function of murine mesenchymal stromal cells

Macroautophagy has been implicated in modulating the therapeutic function of mesenchymal stromal cells (MSCs). However, the biological function of chaperone-mediated autophagy (CMA) in MSCs remains elusive. Here, we found that CMA was inhibited in MSCs in response to the proinflammatory cytokines interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). In addition, suppression of CMA by knocking down the CMA-related lysosomal receptor lysosomal-associated membrane protein 2 (LAMP-2A) in MSCs significantly enhanced the immunosuppressive effect of MSCs on T cell proliferation, and as expected, LAMP-2A overexpression in MSCs exerted the opposite effect on T cell proliferation. This effect of CMA on the immunosuppressive function of MSCs was attributed to its negative regulation of the expression of chemokine C-X-C motif ligand 10 (CXCL10), which recruits inflammatory cells, especially T cells, to MSCs, and inducible nitric oxide synthase (iNOS), which leads to the subsequent inhibition of T cell proliferation via nitric oxide (NO). Mechanistically, CMA inhibition dramatically promoted IFN-γ plus TNF-α-induced activation of NF-κB and STAT1, leading to the enhanced expression of CXCL10 and iNOS in MSCs. Furthermore, we found that IFN-γ plus TNF-α-induced AKT activation contributed to CMA inhibition in MSCs. More interestingly, CMA-deficient MSCs exhibited improved therapeutic efficacy in inflammatory liver injury. Taken together, our findings established CMA inhibition as a critical contributor to the immunosuppressive function of MSCs induced by inflammatory cytokines and highlighted a previously unknown function of CMA.

Post-transplant cyclophosphamide limits reactive donor T cells and delays the development of graft-versus-host disease in a humanized mouse model

Graft-versus-host disease (GVHD) is a major complication of allogeneic haematopoietic stem cell transplantation (allo-HSCT) that develops when donor T cells in the graft become reactive against the host. Post-transplant cyclophosphamide (PTCy) is increasingly used in mismatched allo-HSCT, but how PTCy impacts donor T cells and reduces GVHD is unclear. This study aimed to determine the effect of PTCy on reactive human donor T cells and GVHD development in a preclinical humanized mouse model. Immunodeficient NOD-scid-IL2Rγ^null mice were injected intraperitoneally (i.p.) with 20 × 10⁶ human peripheral blood mononuclear cells stained with carboxyfluorescein succinimidyl ester (CFSE) (day 0). Mice were subsequently injected (i.p.) with PTCy (33 mg kg^-1 ) (PTCy-mice) or saline (saline-mice) (days 3 and 4). Mice were assessed for T-cell depletion on day 6 and monitored for GVHD for up to 10 weeks. Flow cytometric analysis of livers at day 6 revealed lower proportions of reactive (CFSE^low ) human (h) CD3⁺ T cells in PTCy-mice compared with saline-mice. Over 10 weeks, PTCy-mice showed reduced weight loss and clinical GVHD, with prolonged survival and reduced histological liver GVHD compared with saline-mice. PTCy-mice also demonstrated increased splenic hCD4⁺ :hCD8⁺ T-cell ratios and reduced splenic Tregs (hCD4⁺  hCD25⁺  hCD127^lo ) compared with saline-mice. This study demonstrates that PTCy reduces GVHD in a preclinical humanized mouse model. This corresponded to depletion of reactive human donor T cells, but fewer human Tregs.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: I. The 2020 Etiology and Prevention Working Group Report

Preventing chronic graft-versus-host disease (GVHD) remains challenging because the unique cellular and molecular pathways that incite chronic GVHD are poorly understood. One major point of intervention for potential prevention of chronic GVHD occurs at the time of transplantation when acute donor anti-recipient immune responses first set the events in motion that result in chronic GVHD. After transplantation, additional insults causing tissue injury can incite aberrant immune responses and loss of tolerance, further contributing to chronic GVHD. Points of intervention are actively being identified so that chronic GVHD initiation pathways can be targeted without affecting immune function. The major objective in the field is to continue basic studies and to translate what is learned about etiopathology to develop targeted prevention strategies that decrease the risk of morbid chronic GVHD without increasing the risks of cancer relapse or infection. Development of strategies to predict the risk of developing debilitating or deadly chronic GVHD is a high research priority. This working group recommends further interrogation into the mechanisms underpinning chronic GVHD development, and we highlight considerations for future trial design in prevention trials.

Indole derivatives, microbiome and graft versus host disease

Graft versus host disease is a life-threatening complication following allogeneic hematopoietic stem cell transplantation driven by donor T cells reacting against disparate host antigens. Immune homeostasis within the gut plays a major role in the graft versus host response. Gut microbiota and its metabolites impact gut integrity, inflammation and immune activation within the gut. This review will focus on the role of indoles, a product of microbiota metabolism, on gut homeostasis and our current understanding on how that modulates graft versus host disease.

Human invariant natural killer T cells promote tolerance by preferential apoptosis induction of conventional dendritic cells

Graft-versus-host disease (GvHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. We recently showed in murine studies and in vitro human models that adoptively transferred invariant natural killer T (iNKT) cells protect from GvHD and promote graft-versus-leukemia effects. The cellular mechanisms underlying GvHD prevention by iNKT cells in humans, however, remain unknown. In order to study relevant cellular interactions, dendritic cells (DC) were either generated from monocytes or isolated directly from blood of healthy donors or GvHD patients and co-cultured in a mixed lymphocyte reaction (MLR) with T cells obtained from healthy donors or transplantation bags. Addition of culture-expanded iNKT cells to the MLR-induced DC apoptosis in a cell contact-dependent manner, thereby preventing T-cell activation and proliferation. Annexin V/propidium iodide staining and image stream assays showed that CD4⁺CD8^–, CD4^–CD8⁺ and double negative iNKT cells are similarly able to induce DC apoptosis. Further MLR assays revealed that conventional DC (cDC) but not plasmacytoid DC (pDC) could induce alloreactive T-cell activation and proliferation. Interestingly, cDC were also more susceptible to apoptosis induced by iNKT cells, which correlates with their higher CD1d expression, leading to a bias in favor of pDC. Remarkably, these results could also be observed in GvHD patients. We propose a new mechanism how ex vivo expanded human iNKT cells prevent alloreactivity of T cells. iNKT cells modulate T-cell responses by selective apoptosis of DC subsets, resulting in suppression of T-cell activation and proliferation while enabling beneficial immune responses through pDC.

Recurrent pregnancy loss

Recurrent pregnancy loss is a distressing pregnancy disorder experienced by ~2.5% of women trying to conceive. Recurrent pregnancy loss is defined as the failure of two or more clinically recognized pregnancies before 20-24 weeks of gestation and includes embryonic and fetal losses. The diagnosis of an early pregnancy loss is relatively straightforward, although progress in predicting and preventing recurrent pregnancy loss has been hampered by a lack of standardized definitions, the uncertainties surrounding the pathogenesis and the highly variable clinical presentation. The prognosis for couples with recurrent pregnancy loss is generally good, although the likelihood of a successful pregnancy depends on maternal age and the number of previous losses. Recurrent pregnancy loss can be caused by chromosomal errors, anatomical uterine defects, autoimmune disorders and endometrial dysfunction. Available treatments target the putative risk factors of pregnancy loss, although the effectiveness of many medical interventions is controversial. Regardless of the underlying aetiology, couples require accurate information on their chances of having a baby and appropriate support should be offered to reduce the psychological burden associated with multiple miscarriages. Future research must investigate the pathogenesis of recurrent pregnancy loss and evaluate novel diagnostic tests and treatments in adequately powered clinical trials.

Kinetics of immune cell reconstitution predict survival in allogeneic bone marrow and G-CSF-mobilized stem cell transplantation

The clinical utility of monitoring immune reconstitution after allotransplant was evaluated using data from Blood and Marrow Transplant Clinical Trials Network BMT CTN 0201 (NCT00075816), a multicenter randomized study of unrelated donor bone marrow (BM) vs granulocyte colony-stimulating factor (G-CSF)-mobilized blood stem cell (G-PB) grafts. Among 410 patients with posttransplant flow cytometry measurements of immune cell subsets, recipients of G-PB grafts had faster T-cell reconstitution than BM recipients, including more naive CD4⁺ T cells and T-cell receptor excision circle-positive CD4⁺ and CD8⁺ T cells at 3 months, consistent with better thymic function. Faster reconstitution of CD4⁺ T cells and naive CD4⁺ T cells at 1 month and CD8⁺ T cells at 3 months predicted more chronic graft-versus-host disease (GVHD) but better survival in G-PB recipients, but consistent associations of T-cell amounts with GVHD or survival were not seen in BM recipients. In contrast, a higher number of classical dendritic cells (cDCs) in blood samples at 3 months predicted better survival in BM recipients. Functional T-cell immunity measured in vitro by cytokine secretion in response to stimulation with cytomegalovirus peptides was similar when comparing blood samples from BM and G-PB recipients, but the degree to which acute GVHD suppressed immune reconstitution varied according to graft source. BM, but not G-PB, recipients with a history of grades 2-4 acute GVHD had lower numbers of B cells, plasmacytoid dendritic cells, and cDCs at 3 months. Thus, early measurements of T-cell reconstitution are predictive cellular biomarkers for long-term survival and response to GVHD therapy in G-PB recipients, whereas more robust DC reconstitution predicted better survival in BM recipients.

Coptidis alkaloids extracted from Coptis chinensis Franch attenuate IFN-γ-induced destruction of bone marrow cells

Coptidis alkaloids are the primary active components of Coptis chinensis Franch. Clinical and pharmacodynamic studies have confirmed that Coptidis alkaloids have multiple therapeutic effects including anti-inflammatory, antioxidant and antitumor effects, and they are usually used to treat various inflammatory disorders and related diseases. Mouse bone marrow cells (BMCs) were isolated from BALB/c mice. Immune-mediated destruction of BMCs was induced by interferon (IFN) -γ. High-performance liquid chromatography-electrospray ionization/ mass spectrometry was used to analyze the ingredients of the aqueous extract from Coptis chinensis Franch. The results confirmed that Coptidis alkaloids were the predominant ingredients in the aqueous extract from Coptis chinensis. The functional mechanism of Coptidis alkaloids in inhibiting immune-mediated destruction of BMCs was studied in vitro. After Coptidis alkaloid treatment, the percentages of apoptotic BMCs and the proliferation and differentiation of helper T (Th) cells and regulatory T (Treg) cells were measured by flow cytometry. The expression and distribution of T-bet in BMCs were observed by immunofluorescence. Western blotting analysis was used to assay the expression of key molecules in the Fas apoptosis and Jak/Stats signaling pathways in BMCs. We identified five alkaloids in the aqueous extract of Coptis chinensis. The apoptotic ratios of BMCs induced by IFN-γ were decreased significantly after Coptidis alkaloid treatment. The levels of key molecules (Fas, Caspase-3, cleaved Caspase-3, Caspase-8 and Caspase-8) in Fas apoptosis signaling pathways also decreased significantly after treatment with low concentrations of Coptidis alkaloids. Coptidis alkaloids were also found to inhibit the proliferation of Th1 and Th17 cells and induce the differentiation of Th2 and Treg cells; further, the distribution of T-bet in BMCs was decreased significantly. In addition, the levels of Stat-1, phospho-Stat-1 and phospho-Stat-3 were also reduced after Coptidis alkaloid treatment. These results indicate that Coptidis alkaloids extracted by water decoction from Coptis chinensis Franch could inhibit the proliferation and differentiation of T lymphocytes, attenuate the apoptosis of BMCs, and suppress the immune-mediated destruction of the BMCs induced by pro-inflammatory cytokines.

Plasmacytoid dendritic cell biology and its role in immune-mediated diseases

Plasmacytoid dendritic cells (pDCs) are a unique subset of dendritic cells specialised in secreting high levels of type I interferons. pDCs play a crucial role in antiviral immunity and have been implicated in the initiation and development of many autoimmune and inflammatory diseases. This review summarises the latest advances in recent years in several aspects of pDC biology, with special focus on pDC heterogeneity, pDC development via the lymphoid pathway, and newly identified proteins/pathways involved in pDC trafficking, nucleic acid sensing and interferon production. Finally, we also highlight the current understanding of pDC involvement in autoimmunity and alloreactivity, and opportunities for pDC‐targeting therapies in these diseases. These new insights have contributed to answers to several fundamental questions remaining in pDC biology and may pave the way to successful pDC‐targeting therapy in the future.

PRMT5 regulates T cell interferon response and is a target for acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is a T cell-mediated immunological disorder and the leading cause of nonrelapse mortality in patients who receive allogeneic hematopoietic cell transplants. Based on recent observations that protein arginine methyltransferase 5 (PRMT5) and arginine methylation are upregulated in activated memory T cells, we hypothesized that PRMT5 is involved in the pathogenesis of aGVHD. Here, we show that PRMT5 expression and enzymatic activity were upregulated in activated T cells in vitro and in T cells from mice developing aGVHD after allogeneic transplant. PRMT5 expression was also upregulated in T cells of patients who developed aGVHD after allogeneic hematopoietic cell transplant compared with those who did not develop aGVHD. PRMT5 inhibition using a selective small-molecule inhibitor (C220) substantially reduced mouse and human allogeneic T cell proliferation and inflammatory IFN-γ and IL-17 cytokine production. Administration of PRMT5 small-molecule inhibitors substantially improves survival, reducing disease incidence and clinical severity in mouse models of aGVHD without adversely affecting engraftment. Importantly, we show that PRMT5 inhibition retained the beneficial graft-versus-leukemia effect by maintaining cytotoxic CD8+ T cell responses. Mechanistically, we show that PRMT5 inhibition potently reduced STAT1 phosphorylation as well as transcription of proinflammatory genes, including interferon-stimulated genes and IL-17. Additionally, PRMT5 inhibition deregulates the cell cycle in activated T cells and disrupts signaling by affecting ERK1/2 phosphorylation. Thus, we have identified PRMT5 as a regulator of T cell responses and as a therapeutic target in aGVHD.

Local Expression of Indoleamine 2,3, Dioxygenase Prolongs Allogenic Skin Graft Take in a Mouse Model

Background and Objective: Despite the effectiveness of skin autotransplantation, the high degree of immunogenicity of the skin precludes the use of allografts and systemic immunosuppression is generally inappropriate for isolated skin grafts. Indoleamine 2,3 dioxygenase (IDO) is a potent immunoregulatory factor with allo- and autoimmune suppression and tolerance induction properties. This study examines the potential use of locally expressed IDO to prolong the allogeneic skin graft take in a mouse model. Approach: Syngeneic-fibroblasts were transfected with noncompetent IDO viral vector and the level of Kynurenine (Kyn) in conditioned medium was measured as an index for IDO activity. Either 1 or 3 × 10⁶ IDO-fibroblasts were introduced intra/hypo-dermally to the mouse skin. The expression, localization, and functionality of IDO were then evaluated. The cell-injected areas were harvested and grafted on the back of allogeneic mice. The graft survival, immune-cells infiltration, and interaction with dendritic cells were evaluated. Results: The results showed a significant improvement in allogeneic graft take injected with 1 × 106 IDO-fibroblasts (18.4 ± 3.3 days) compared with control (12.2 ± 1.9 days). This duration increased to 35.4 ± 4.7 days in grafts injected with 3 × 10⁶ IDO-expressing cells. This observation might be due to a significantly lower T cells infiltration within the IDO-grafts. Further, the result of a flow cytometric analysis showed that the expression of PD-L1/PD-L2 on CD11c+/eFluor+ cells in the regional lymph nodes of injected skin areas was significantly higher in IDO groups compared with control. Conclusion: These data suggest that allogeneic skin graft survival outcome can be prolonged significantly by local overexpression of IDO without any systemic effect.

Dendritic Cell Regulation of Graft-Vs.-Host Disease: Immunostimulation and Tolerance

Graft-vs.-host disease (GVHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Significant progresses have been made in defining the dichotomous role of dendritic cells (DCs) in the development of GVHD. Host-derived DCs are important to elicit allogeneic T cell responses, whereas certain donor-types of DCs derived from newly engrafted hematopoietic stem/progenitor cells (HSPCs) can amply this graft-vs.-host reaction. In contrast, some DCs also play non-redundant roles in mediating immune tolerance. They induce apoptotic deletion of host-reactive donor T cells while promoting expansion and function of regulatory T cells (Treg). Unfortunately, this tolerogenic effect of DCs is impaired during GVHD. Severe GVHD in patients subject to allo-HSCT is associated with significantly decreased number of circulating peripheral blood DCs during engraftment. Existing studies reveal that GVHD causes delayed reconstitution of donor DCs from engrafted HSPCs, impairs the antigen presentation function of newly generated DCs and reduces the capacity of DCs to regulate Treg. The present review will discuss the importance of DCs in alloimmunity and the mechanism underlying DC reconstitution after allo-HSCT.

Targeting regulation of tryptophan metabolism for colorectal cancer therapy: a systematic review

Colorectal cancer (CRC) is one of the most malignant cancers resulting from abnormal metabolism alterations. As one of the essential amino acids, tryptophan has a variety of physiological functions, closely related to regulation of immune system, central nervous system, gastrointestinal nervous system and intestinal microflora. Colorectal cancer, a type of high-grade malignancy disease, stems from a variety of factors and often accompanies inflammatory reactions, dysbacteriosis, and metabolic disorders. Colorectal cancer accompanies inflammation and imbalance of intestinal microbiota and affects tryptophan metabolism. It is known that metabolites, rate-limiting enzymes, and ARH in tryptophan metabolism are associated with the development of CRC. Specifically, IDO1 may be a potential therapeutic target in colorectal cancer treatment. Furthermore, the reduction of tryptophan amount is proportional to the poor quality of life for colorectal cancer patients. This paper aims to discuss the role of tryptophan metabolism in a normal organism and investigate the relationship between this amino acid and colorectal cancer. This study is expected to provide theoretical support for research related to targeted therapy for colorectal cancer. Furthermore, strategies that modify tryptophan metabolism, effectively inhibiting tumor progression, may be more effective for CRC treatment.

Colorectal cancer (CRC) is one of the most malignant cancers resulting from abnormal metabolism alterations.

Strategies for Enhancing and Preserving Anti-leukemia Effects Without Aggravating Graft-Versus-Host Disease

Allogeneic stem cell transplantation (allo-SCT) is a curable method for the treatment of hematological malignancies. In the past two decades, the establishment of haploidentical transplant modalities make “everyone has a donor” become a reality. However, graft-versus-host disease (GVHD) and relapse remain the major two causes of death either in the human leukocyte antigen (HLA)-matched transplant or haploidentical transplant settings, both of which restrict the improvement of transplant outcomes. Preclinical mice model showed that both donor-derived T cells and natural killer (NK) cells play important role in the pathogenesis of GVHD and the effects of graft-versus-leukemia (GVL). Hence, understanding the immune mechanisms of GVHD and GVL would provide potential strategies for the control of leukemia relapse without aggravating GVHD. The purpose of the current review is to summarize the biology of GVHD and GVL responses in preclinical models and to discuss potential novel therapeutic strategies to reduce the relapse rate after allo-SCT. We will also review the approaches, including optimal donor selection and, conditioning regimens, donor lymphocyte infusion, BCR/ABL-specific CTL, and chimeric antigen receptor-modified T cells, which have been successfully used in the clinic to enhance and preserve anti-leukemia activity, especially GVL effects, without aggravating GVHD or alleviate GVHD.

Indoles derived from intestinal microbiota act via type I interferon signaling to limit graft-versus-host disease

The intestinal microbiota in allogeneic bone marrow transplant (allo-BMT) recipients modulates graft-versus-host disease (GVHD), a systemic inflammatory state initiated by donor T cells that leads to colitis, a key determinant of GVHD severity. Indole or indole derivatives produced by tryptophan metabolism in the intestinal microbiota limit intestinal inflammation caused by diverse stressors, so we tested their capacity to protect against GVHD in murine major histocompatibility complex-mismatched models of allo-BMT. Indole effects were assessed by colonization of allo-BMT recipient mice with tryptophanase positive or negative strains of Escherichia coli, or, alternatively, by exogenous administration of indole-3-carboxaldehyde (ICA), an indole derivative. Treatment with ICA limited gut epithelial damage, reduced transepithelial bacterial translocation, and decreased inflammatory cytokine production, reducing GVHD pathology and GVHD mortality, but did not compromise donor T-cell-mediated graft-versus-leukemia responses. ICA treatment also led to recipient-strain-specific tolerance of engrafted T cells. Transcriptional profiling and gene ontology analysis indicated that ICA administration upregulated genes associated with the type I interferon (IFN1) response, which has been shown to protect against radiation-induced intestinal damage and reduce subsequent GVHD pathology. Accordingly, protective effects of ICA following radiation exposure were abrogated in mice lacking IFN1 signaling. Taken together, these data indicate that indole metabolites produced by the intestinal microbiota act via type I IFNs to limit intestinal inflammation and damage associated with myeloablative chemotherapy or radiation exposure and acute GVHD, but preserve antitumor responses, and may provide a therapeutic option for BMT patients at risk for GVHD.

Flt3L Treatment of Bone Marrow Donors Increases Graft Plasmacytoid Dendritic Cell Content and Improves Allogeneic Transplantation Outcomes

A higher number of donor plasmacytoid dendritic cells (pDCs) is associated with increased survival and reduced graft-versus-host disease (GVHD) in human recipients of unrelated donor bone marrow (BM) grafts, but not granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood grafts. We show that in murine models, donor BM pDCs are associated with increased survival and decreased GVHD compared with G-CSF-mobilized pDCs. To increase the content of pDCs in BM grafts, we studied the effect of FMS-like tyrosine kinase 3 ligand (Flt3L) treatment of murine BM donors on transplantation outcomes. Flt3L treatment (300 μg/kg/day) resulted in a schedule-dependent increase in the content of pDCs in the BM. Mice treated on days -4 and -1 had a >5-fold increase in pDC content without significant changes in numbers of HSCs, T cells, B cells, and natural killer cells in the BM graft. In an MHC-mismatched murine transplant model, recipients of Flt3L-treated T cell-depleted (TCD) BM (TCD F-BM) and cytokine-untreated T cells had increased survival and decreased GVHD scores with fewer Th1 and Th17 polarized T cells post-transplantation compared with recipients of equivalent numbers of untreated donor TCD BM and T cells. Gene array analyses of pDCs from Flt3L-treated human and murine donors showed up-regulation of adaptive immune pathways and immunoregulatory checkpoints compared with pDCs from untreated BM donors. Transplantation of TCD F-BM plus T cells resulted in no loss of the graft-versus-leukemia (GVL) effect compared with grafts from untreated donors in 2 murine GVL models. Thus, Flt3L treatment of BM donors is a novel method for increasing the pDC content in allografts, improving survival, and decreasing GVHD without diminishing the GVL effect.

Notch inhibition enhances graft-versus-leukemia while reducing graft-versus-host disease

Graft-versus host disease (GVHD) remains the most significant complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Dissociation of graft versus-leukemia (GVL) activity from GVHD has yet to be achieved. In this study, we used γ-secretase inhibitor (GSIs, DAPT) to inhibit Notch signaling in GVHD and GVL murine model. We found that CD11c⁺CD80⁺ dendritic cells (DCs) were up-regulated but did not enhance GVHD. Regulatory T cells (Tregs) and central memory T cells that express high levels of CD62L and CD44 had an expansion after Notch inhibition. Reduced Tumor Necrosis Factor-α and increased Interferon-γ production were found, which might be ascribed to the expansion of Tregs and central memory T cells, and result in increased sensitivity of tumor cells to cytotoxic T lymphocyte activity. Fas Receptor-Fas Ligand interaction plays a critical role in GVL instead of aGVHD. Fas Ligand expressions were similar in recipients with or without Notch inhibition, suggesting that GVL activity was maintained. We showed that Notch inhibition could enhances GVL while reducing GVHD via modulating host DCs and donor T cell activity, and the production of inflammatory cytokines.

Indoleamine 2,3-dioxygenase in endometrial cancer: a targetable mechanism of immune resistance in mismatch repair-deficient and intact endometrial carcinomas

Mismatch repair-deficient endometrial carcinomas are optimal candidates for immunotherapy given their high neoantigen loads, robust lymphoid infiltrates, and frequent PD-L1 expression. However, co-opting the PD-1/PD-L1 pathway is just one mechanism that tumors can utilize to evade host immunity. Another immune modulatory molecule that has been demonstrated in endometrial carcinoma is indoleamine 2,3-dioxygenase (IDO). We herein evaluate IDO expression in 60 endometrial carcinomas and assess results in relation to PD-L1 and mismatch repair status. IDO immunohistochemistry was performed on 60 endometrial carcinomas (20 Lynch syndrome (LS)-associated, 20 MLH1 promoter hypermethylated, and 20 mismatch repair-intact). Eight-five percent of endometrial carcinomas showed IDO tumor staining in >1% of cells. Twenty-five percent were positive in >25% of tumor cells and only 7% exceeded 50% staining. Mismatch repair-deficient cancers were more likely than mismatch repair-intact cancers to be >25% IDO-positive (35% vs. 5% p = 0.024). Differences were amplified when Lynch syndrome-associated cases were evaluated in isolation (50% Lynch syndrome-associated vs. 10% mismatch repair-intact and MLH1-hypermethylated, p = 0.001). Of the four cases showing >50% staining, three were Lynch syndrome-associated and one was MLH1-hypermethylated; no mismatch repair-intact cases had >50% staining. Forty-three percent of IDO-positive tumors were also positive for PD-L1, whereas only two cases showed tumoral PD-L1 in the absence of IDO. In summary, IDO expression is prevalent in endometrial carcinomas and diffuse staining is significantly more common in mismatch repair-deficient cancers, particularly Lynch syndrome-associated cases. Given that the majority of PD-L1 positive cancers also express IDO, synergistic combination therapy with anti-IDO and anti-PD1/PD-L1 may be relevant in this tumor type. Furthermore, anti-IDO therapy may be an option for a small subset of mismatch repair-intact cancers.

An Expanded Neuroimmunomodulation Axis: sCD83-Indoleamine 2,3-Dioxygenase-Kynurenine Pathway and Updates of Kynurenine Pathway in Neurologic Diseases

Many neurologic diseases are related to autoimmune dysfunction and a variety of molecules or reaction pathways are involved in the regulation of immune function of the nervous system. Soluble CD83 (sCD83) is the soluble form of CD83, a specific marker of mature dendritic cell, which has recently been shown to have an immunomodulatory effect. Indoleamine 2,3-dioxygenase (IDO; corresponding enzyme intrahepatic, tryptophan 2,3-dioxygenase, TDO), a rate-limiting enzyme of extrahepatic tryptophan kynurenine pathway (KP) participates in the immunoregulation through a variety of mechanisms solely or with the synergy of sCD83, and the imbalances of metabolites of KP were associated with immune dysfunction. With the complement of sCD83 to IDO-KP, a previously known immunomodulatory axis, this review focused on an expanded neuroimmunomodulation axis: sCD83-IDO-KP and its involvement in nervous system diseases.

The tolerogenic role of IFN-γ

Due to its extremely pleiotropic nature, the complex effects of IFN-γ exerted both on immune and non-immune cell types still remain only partially understood. The longstanding view of IFN-γ as being a predominantly inflammatory cytokine is constantly challenged by increasing demonstrations of its direct or indirect regulatory roles. Interferon-γ can exert tolerogenic effects on both innate and adaptive immune cell types, promoting tolerance of various antigen-presenting cells, and augmenting function and differentiation of regulatory T cells, respectively. Its capacity to induce IDO-competence is not limited to immune cells but extends to other cell types such as mesenchymal stem cells, epithelial cells, and tumors. The pro-inflammatory role of IFN-γ in tumor immune surveillance can backfire by directly inducing inhibitory molecule expression, such as PDL-1, on tumor cells. With increasing knowledge regarding the role of different helper T cell subsets in certain autoimmune diseases, the once contradictory observations of disease attenuation by IFN-γ can now be explained by its opposing interplay with other effector cytokines, particularly IL-17. The paradoxically immunosuppressive role of IFN-γ is also becoming evident in the transplantation setting, and graft-versus-host-disease. In the present review, we will discuss the latest findings that help to elucidate this dual role of IFN-γ at a cellular level, and in various pathophysiological states.

miR-153-3p, a new bio-target, is involved in the pathogenesis of acute graft-versus-host disease via inhibition of indoleamine- 2,3-dioxygenase

Acute graft-versus-host disease (aGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Therefore, seeking reliable biomarkers and delineating the potential biological mechanism are important for optimizing treatment strategies and improving their curative effect. In this study, using a microRNA polymerase chain reaction (PCR)-based chip assay, microRNA-153-3p (miR-153-3p) was screened and selected as a potential biomarker of aGVHD. The elevated plasma miR-153-3p levels at +7 d after transplant could be used to predict the upcoming aGVHD. The area under the receiver operating characteristic curve for aGVHD+/aGVHD- patients receiving haploidentical transplant was 0.808 (95% confidence interval, 0.686-0.930) in a training set and 0.809 (95% confidence interval, 0.694-0.923) in a validation set. Interestingly, bioinformatics analysis indicated that indoleamine-2,3-dioxygenase (IDO) is a potential target of miR-153-3p. In vitro study confirmed that IDO could be directly inhibited by miR-153-3p. In a GVHD model, recipient mice injected with a miR-153-3p antagomir exhibited higher IDO expression levels at the early stage after transplantation, as well as delayed aGVHD and longer survival, indicating that the miR-153-3p level at +7 d post-transplant is a good predictor of aGVHD. miR-153-3p participates in aGVHD development by inhibiting IDO expression and might be a novel bio-target for aGVHD intervention.

Rapid reconstitution of NK1 cells after allogeneic transplantation is associated with a reduced incidence of graft-versus-host disease

The balance between immunostimulation and immunoregulation in T cell immunity is achieved by maintaining specific ratios of Th1, Th2, Th3 and Tr1 cells. Here, we investigate levels of type 1 (IFN-gamma; NK1), type 2 (IL-13; NK2), type 3 (TGF-beta; NK3) and regulatory (IL-10; NKr) cytokines in peripheral blood to assess the cytokine profiles of natural killer (NK) cells following human allogeneic hematopoietic stem cell transplantation (allo-HSCT). NK2 and NK3 cell expansion was observed after allo-HSCT; levels of NKr cells reached donor levels at day 15, though levels of NK1 cells were consistently lower than donor levels until day 60 after allo-HSCT. Multivariate analysis showed that a higher level of NK1 cells by day 15 was associated with a lower overall risk of acute graft-versus-host disease (GVHD) (HR 0.157, P=0.010) as well as II-IV acute GVHD (HR 0.260, P=0.059). Furthermore, higher levels of NK1 cells by day 15 were correlated with lower rates of cytomegalovirus (CMV) reactivation (HR 0.040, 0.005-0.348, P=0.003). These results indicate that rapid reconstitution of NK cells, especially NK1 cells, can help prevent the development of GVHD as well as CMV reactivation after allogeneic transplantation.

The Role of MicroRNAs in Myeloid Cells during Graft-versus-Host Disease

The successful treatment of various hematologic diseases with allogeneic hematopoietic cell transplantation is often limited by the occurrence of graft-versus-host disease (GvHD). Several microRNAs (miRs) have recently been shown to impact the biology of GvHD by regulating pro- as well as anti-inflammatory target genes. There is increasing evidence that a single miR can have different effects by preferentially targeting certain genes depending on the cell type that the miR is analyzed in. This review will focus on the role of miRs in myeloid cells during the development of acute and chronic GvHD and autoimmune diseases. Because miRs act on the expression of multiple target genes and may thereby influence the immune system at different functional levels, they are potentially attractive targets for the modification of allogeneic immune responses using miR mimics and inhibitors.

Peritransplantation Red Blood Cell Transfusion Is Associated with Increased Risk of Graft-versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation

More than 90% of allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients receive red blood cell (RBC) or platelet transfusions in the peritransplantation period. We tested the hypothesis that transfusions are associated with the development of severe (grade III-IV) acute graft-versus-host disease (aGVHD) or mortality after allo-HSCT in a retrospective study of 322 consecutive patients receiving an allogeneic bone marrow or granulocyte colony-stimulating factor-mobilized blood stem cell graft for a hematologic malignancy. Counting transfused RBC and platelet units between day -7 pretransplantation and day +27 post-transplantation, but excluding transfusions administered after a diagnosis of aGVHD, yielded medians of 5 RBC units and 2 platelet units transfused. Sixty-three patients (20%) developed a maximal grade III-IV aGVHD with onset up to day +150 post-transplantation (median aGVHD onset of 28 days). HLA mismatch (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.2 to 4.7; P = .01), and transfusion of more than the median number of RBC units (HR, 2.1; 95% CI, 1.1 to 3.7; P = .02) were independently associated with greater risk of grade III-IV aGVHD in a multivariable analysis model. Disease risk strata (HR, 1.7; 95% CI, 1.2 to 2.4 for high risk versus low risk; P = .005) and transfusion of more than the median number of RBC units (HR, 1.4; 95% CI, 1.0 to 2.0; P = .054) were independently associated with inferior overall survival. These data support our hypothesis that peritransplantation RBC transfusions are associated with the risk of developing severe aGVHD and worse overall survival following allo-HSCT, and suggest that strategies to reduce routine RBC transfusion may favorably reduce the incidence and severity of GVHD.

The IDO inhibitor 1-methyl tryptophan activates the aryl hydrocarbon receptor response in mesenchymal stromal cells

The catabolism of tryptophan (Trp) by indoleamine 2,3-dioxygenase (IDO) is a key step in tolerance effected by a variety of cell types, including mesenchymal stromal cells (MSCs). Trp catabolism generates molecules known as kynurenines, whose tolerance mechanisms involve activation of the Aryl Hydrocarbon Receptor (AHR). A synthetic analog of Trp, 1-methyl tryptophan (1MT), is a selective inhibitor of IDO enzymatic activity being utilized in cancer immunotherapy trials. We hypothesized 1MT might activate AHR independently of its effects on IDO. We demonstrate MSCs express AHR protein, and that in vitro treatment with 1MT causes AHR nucleotranslocation. Upon analyzing mRNA, we observed transcriptional upregulation of cytochrome p450 1a1 and 1b1 by 1MT racemic mixture (R-MT), consistent with AHR-activation. RNA-sequencing identified Nrf2, MAPK12 and IL-1a as downstream targets of 1MT. We demonstrate 1a1 and 1b1 activation by 1MT in IDO+ MSC following interferon-γ (IFN-γ) activation, suggesting AHR signaling is uncoupled from IDO catalytic function. Such a mechanism of action for 1MT may extend its usage to a wider range of patients, irrespective of tumor IDO expression. These observations support a novel paradigm by which AHR-activating compounds like 1MT can be used in cancer immunotherapy to stimulate a pro-inflammatory response.

Interferon-gamma regulates inflammatory cell death by targeting necroptosis in experimental autoimmune arthritis

Interferon γ (IFN-γ) induces an inflammatory response and apoptotic cell death. Rheumatoid arthritis (RA) is a systemic inflammatory disease associated with increased levels of inflammatory mediators, including tumour necrosis factor α (TNF-α) and T helper (Th) 17 cells, and downregulation of apoptosis of inflammatory cells. We hypothesized that IFN-γ would reduce inflammatory cell death in vitro and that loss of IFN-γ would aggravate inflammation in vivo. IFN-γ downregulated necroptosis and the expression of cellular FLICE-like inhibitory protein (cFLIP_L) and mixed lineage kinase domain-like (MLKL). However, loss of IFN-γ promoted the production of cFLIP_L and MLKL, and necroptosis. IFN-γ deficiency increased Th17 cell number and upregulated the expression of IL-17 and TNF-α. Expression of MLKL, receptor interacting protein kinase (RIPK)1, and RIPK3 was increased in the joints of mice with collagen-induced arthritis (CIA). Compared with wild-type mice with CIA, IFN-γ^−/− CIA mice showed exacerbation of cartilage damage and joint inflammation, and acceleration of MLKL, RIPK1, and RIPK3 production in the joints. IFN-γ deficiency induced the activation of signal transducer and activator of transcription 3. These results suggest that IFN-γ regulates inflammatory cell death and may have potential for use in the treatment of RA.

Immune roles of dendritic cells in stem cell transplantation

Dendritic cells (DCs) are professional antigen-presenting cells and initial stimulators for immune response. DCs can shape their functions based on their immune states, which are crucial for the balance of immunity and tolerance to preserve homeostasis. In the immune response involved in stem cell transplantation, DCs also play important roles in inducing immune tolerance and antitumor immunity. After the rapid development of stem cell transplantation technology in recent years, the risks of graft rejection, tumor recurrence, and tumorigenicity are still present after stem cell transplantation. It is important to understand the mechanisms of DC-mediated immune tolerance and stimulation during stem cell transplantation. In this review, we will summarize and analyze the regulatory mechanisms of DCs in stem cell transplantation and their application in clinical settings. It may help to promote the innovation in basic theories and therapeutic approaches of stem cell transplantation.

Administration of a vasoactive intestinal peptide antagonist enhances the autologous anti-leukemia T cell response in murine models of acute leukemia

Vasoactive intestinal peptide (VIP) is a neuroendocrine peptide hormone that has potent anti-inflammatory activities. VIP signaling through its receptor VPAC1 on T cells leads to reduced proliferation and a reduction in pro-inflammatory cytokine secretion. We report here that inhibition of the VIP pathway with a peptide antagonist significantly enhances a T-cell-dependent, autologous anti-leukemia response in murine models of acute myeloid leukemia and T lymphoblastic leukemia. Subcutaneous administration of the VIP antagonist, VIPhyb, resulted in reduced tumor burden and significantly enhanced survival (30-50% survival) over vehicle-treated controls (0-20% survival). The T cells in mice treated with VIPhyb expressed lower levels of the co-inhibitory PD-1 and secreted higher levels of IFNγ. Furthermore, T cells from VIPhyb-treated survivors were protective against C1498 following adoptive transfer. These data highlight the potential for the VIP pathway as a novel target for immunomodulation in settings of hematological malignancies.

Chemo-Immunotherapy: Role of Indoleamine 2,3-Dioxygenase in Defining Immunogenic Versus Tolerogenic Cell Death in the Tumor Microenvironment

In certain settings, chemotherapy can trigger an immunogenic form of tumor cell death. More often, however, tumor cell death after chemotherapy is not immunogenic, and may be actively tolerizing. However, even in these settings the dying tumor cells may be much more immunogenic than previously recognized, if key suppressive immune checkpoints such as indoleamine 2,3-dioxygenase (IDO) can be blocked. This is an important question, because a robust immune response to dying tumor cells could potentially augment the efficacy of conventional chemotherapy, or enhance the strength and duration of response to other immunologic therapies. Recent findings using preclinical models of self-tolerance and autoimmunity suggest that IDO and related downstream pathways may play a fundamental role in the decision between tolerance versus immune activation in response to dying cells. Thus, in the period of tumor cell death following chemotherapy or immunotherapy, the presence of IDO may help dictate the choice between dominant immunosuppression versus inflammation, antigen cross-presentation, and epitope spreading. The IDO pathway thus differs from other checkpoint-blockade strategies, in that it affects early immune responses, at the level of inflammation, activation of antigen-presenting cells, and initial cross-presentation of tumor antigens. This "up-stream" position may make IDO a potent target for therapeutic inhibition.

The Kynurenine Pathway Is a Double-Edged Sword in Immune-Privileged Sites and in Cancer: Implications for Immunotherapy

The term “immune privilege” was originally coined to describe the suppression of inflammatory responses within organs protected by anatomic barriers, ie, the eyes, brain, placenta, and testes. However, cellular and metabolic processes, which orchestrate immune responses, also control inflammation within these sites. Our current understanding of tolerogenic mechanisms has extended the definition of immune privilege to include hair follicles, the colon, and cancer. By catabolizing tryptophan, cells expressing the enzyme indoleamine-2,3-dioxygenase produce kynurenine metabolites, which orchestrate local and systemic responses to control inflammation, thus maintaining immune privilege. This review highlights the double-edged role played by the kynurenine pathway (KP), which establishes and maintains immune-privileged sites while contributing to cancer immune escape. The identification of the underlying molecular drivers of the KP in immune-privileged sites and in cancer is essential for the development of novel therapies to treat autoimmunity and cancer and to improve transplantation outcomes.

Modulation of Immune Checkpoints and Graft-versus-Leukemia in Allogeneic Transplants by Antagonizing Vasoactive Intestinal Peptide Signaling

The goal of allogeneic bone marrow transplantation (allo-BMT) is elimination of leukemia cells through the graft-versus-leukemia (GvL) activity of donor cells, while limiting graft-versus-host disease (GvHD). Immune checkpoint pathways regulate GvL and GvHD activities, but blocking antibodies or genetic inactivation of these pathways can cause lethal GVHD. Vasoactive intestinal peptide (VIP) is an immunosuppressive neuropeptide that regulates coinhibitory pathways; its role in allo-BMT has not been studied. We found VIP transiently expressed in donor NK, NK-T, dendritic cells, and T cells after allo transplant, as well as host leukocytes. A peptide antagonist of VIP signaling (VIPhyb) increased T-cell proliferation in vitro and reduced IL10 expression in donor T cells. Treatment of allo-BMT recipients with VIPhyb, or transplanting donor grafts lacking VIP (VIP-KO), activated donor T-cells in lymphoid organs, reduced T-cell homing to GvHD target organs, and enhanced GvL without increasing GvHD in multiple allo-BMT models. Genetic or ex vivo depletion of donor NK cells or CD8⁺ T cells from allografts abrogated the VIPhyb-enhanced GvL activity. VIPhyb treatment led to downregulation of PD-1 and PD-L1 expression on donor immune cells, increased effector molecule expression, and expanded oligoclonal CD8⁺ T cells that protected secondary allo transplant recipients from leukemia. Blocking VIP signaling thus represents a novel pharmacologic approach to separate GvL from GvHD and enhance adaptive T-cell responses to leukemia-associated antigens in allo-BMT. Cancer Res; 76(23); 6802-15. ©2016 AACR.

Programming of donor T cells using allogeneic δ-like ligand 4-positive dendritic cells to reduce GVHD in mice

Alloreactive T cells play a critical role in eliminating hematopoietic malignant cells but are also the mediators of graft-versus-host disease (GVHD), a major complication that subverts the success of allogeneic hematopoietic stem cell transplantation (HSCT). However, induction of alloreactive T cells does not necessarily lead to GVHD. Here we report the development of a cellular programming approach to render alloreactive T cells incapable of causing severe GVHD in both major histocompatibility complex (MHC)-mismatched and MHC-identical but minor histocompatibility antigen-mismatched mouse models. We established a novel platform that produced δ-like ligand 4-positive dendritic cells (Dll4(hi)DCs) from murine bone marrow using Flt3 ligand and Toll-like receptor agonists. Upon allogeneic Dll4(hi)DC stimulation, CD4(+) naïve T cells underwent effector differentiation and produced high levels of interferon γ (IFN-γ) and interleukin-17 in vitro, depending on Dll4 activation of Notch signaling. Following transfer, allogeneic Dll4(hi)DC-induced T cells were unable to mediate severe GVHD but preserved antileukemic activity, significantly improving the survival of leukemic mice undergoing allogeneic HSCT. This effect of Dll4(hi)DC-induced T cells was associated with their impaired expansion in GVHD target tissues. IFN-γ was important for Dll4(hi)DC programming to reduce GVHD toxicities of alloreactive T cells. Absence of T-cell IFN-γ led to improved survival and expansion of Dll4(hi)DC-induced CD4(+) T cells in transplant recipients and caused lethal GVHD. Our findings demonstrate that Dll4(hi)DC programming can overcome GVHD toxicity of donor T cells and produce leukemia-reactive T cells for effective immunotherapy.

IDO in the Tumor Microenvironment: Inflammation, Counter-Regulation, and Tolerance

Indoleamine 2,3-dioxygenase (IDO) has immunoregulatory roles associated with tryptophan metabolism. These include counter-regulation (controlling inflammation) and acquired tolerance in T cells. Recent findings reveal that IDO can be triggered by innate responses during tumorigenesis, and also by attempted T cell activation, either spontaneous or due to immunotherapy. Here we review the current understanding of mechanisms by which IDO participates in the control of inflammation and in peripheral tolerance. Focusing on the tumor microenvironment, we examine the role of IDO in response to apoptotic cells and the impact of IDO on Treg cell function. We discuss how the counter-regulatory and tolerogenic functions of IDO can be targeted for cancer immunotherapy and present an overview of the current clinical progress in this area.

IFN-γ-mediated hematopoietic cell destruction in murine models of immune-mediated bone marrow failure

Interferon gamma (IFN-γ) has been reported to have both negative and positive activity on hematopoietic cells, adding complexity to the interpretation of its pleiotropic functions. We examined the effects of IFN-γ on murine hematopoietic stem cells (HSCs) and progenitors in vitro and in vivo by using mouse models. IFN-γ treatment expanded bone marrow (BM) c-Kit(+)Sca1(+)Lin(-) (KSL) cell number but reduced BM KLCD150(+) and KLCD150(+)CD48(-) cells. IFN-γ-expanded KSL cells engrafted poorly when tested by competitive repopulation in vivo. KSL, KLCD150(+), and KLCD150(+)CD48(-) cells from IFN-γ-treated animals all showed significant upregulation in Fas expression. When cocultured with activated T cells in vitro, KSL and KLCD150(+) cells from IFN-γ-treated donors showed increased apoptosis relative to those from untreated animals, and infusion of activated CD8 T cells into IFN-γ-injected animals in vivo led to partial elimination of KSL cells. Exposure of BM cells or KSL cells to IFN-γ increased expression of Fas, caspases, and related proapoptotic genes and decreased expression of Ets-1 and other hematopoietic genes. In mouse models of BM failure, mice genetically deficient in IFN-γ receptor expression showed attenuation of immune-mediated marrow destruction, whereas effector lymphocytes from IFN-γ-deficient donors were much less potent in initiating BM damage. We conclude that the activity of IFN-γ on murine hematopoiesis is context dependent. IFN-γ-augmented apoptotic gene expression facilitates destruction of HSCs and progenitors in the presence of activated cytotoxic T cells, as occurs in human BM failure.

Plasmacytoid dendritic cells in allogeneic hematopoietic cell transplantation: benefit or burden?

Plasmacytoid dendritic cells (pDCs) bridge innate and adaptive immune responses and have important roles in hematopoietic engraftment, GvHD and graft-versus-leukemia responses following allogeneic hematopoietic cell transplantation (HCT). In addition, pDCs mediate antiviral immunity, particularly as they are the body's primary cellular source of type I interferon. Given their pleiotropic roles, pDCs have emerged as cells that critically impact transplant outcomes, including overall survival. In this article, we will review the pre-clinical and clinical literature, supporting the crucial roles that pDCs assume as key immune effector cells during HCT.

Severity of DSS-induced colitis is reduced in Ido1-deficient mice with down-regulation of TLR-MyD88-NF-kB transcriptional networks

Indoleamine 2,3 -dioxygenase 1 (IDO1) catalyzes L-tryptophan to kynurenine in the first and rate-limiting step of tryptophan metabolism. IDO1 is expressed widely throughout the body, with especially high expression in colonic intestinal tissues. To examine the role of IDO1 in the colon, transcriptome analysis was performed in both Ido1^−/− and Ido1^+/+ mice. Gene set enrichment analysis identified the Inflammatory Response as the most significant category modulated by the absence of IDO1. This observation prompted us to further investigate the function of IDO1 in the development of tissue inflammation. By using DSS-induced experimental colitis mice models, we found that the disease in Ido1^−/− mice was less severe than in Ido1^+/+ mice. Pharmacological inhibition of IDO1 by L-1MT attenuated the severity of DSS-colitis as well. Transcriptome analyses revealed that pathways involving TLR and NF-kB signaling were significantly down-regulated by the absence of IDO1. Furthermore, dramatic changes in TLR and NF-kB signaling resulted in substantial changes in the expression of many inflammatory cytokines and chemokines. Numbers of inflammatory cells in colon and peripheral blood were reduced in IDO1 deficiency. These findings suggest that IDO1 plays important roles in producing inflammatory responses and modulating transcriptional networks during the development of colitis.

Role of indoleamine 2,3-dioxygenase in health and disease

IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1’s catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.

Higher frequency of regulatory T cells in granulocyte colony-stimulating factor (G-CSF)-primed bone marrow grafts compared with G-CSF-primed peripheral blood grafts

BACKGROUND

Regulatory T cells (Treg) in allografts are important for the prevention of graft-versus-host disease (GVHD) post-transplantation. The aim of this study was to compare the contents of Tregs and effector T cells in granulocyte colony-stimulating factor (G-CSF)-primed bone marrow grafts (G-BM) and peripheral blood grafts (G-PB).

METHOD

G-BM and G-PB were obtained from 20 allogeneic donors. T-cell subgroups, including conventional T cells and different types of Treg cells, as well as the percentage of Ki67 expression on CD4(+)CD25(high)Foxp3(+) Treg cells, were analyzed using flow cytometry. The levels of interferon-γ (IFN-γ) and interleukin-17 (IL-17) secreted by T cells stimulated with PMA and ionomycin were also determined by flow cytometry.

RESULTS

The percentage of CD4(+)CD25(high)CD127(-/dim)CD62L(+) Treg cells was significantly higher in the G-BM group, with higher proportions of CD45RA(+) naïve Treg cells and higher expression of CD69 on Treg cells in G-BM (P < 0.05). The percentage of Ki67 expression in CD4(+)CD25(high)Foxp3(+) Treg cells in G-BM was significantly higher than that on G-PB. The suppressive functions of Treg cells in inhibiting T-cell activation were comparable between G-BM and G-PB. The proportions of CD4(+)CD25(-)CD69(+) Treg subsets as well as Th1 cells in G-BM were also significantly higher than those in G-PB (P < 0.001). The proportions of conventional T cells and Th17 effector cells were comparable in G-BM compared with those in G-PB. Thus, the ratio of conventional T cells and CD4(+)CD25(high)CD127(-/dim) regulatory T cells were lower in G-BM than that in G-PB (P = 0.014).

CONCLUSION

In addition to the much higher T-cell counts in G-PB grafts that may contribute to more severe GVHD, the higher frequency of Treg cells and lower ratio of conventional T cells to Treg cells in G-BM compared with G-PB grafts might reduce GVHD post-transplantation in G-BM compared with G-PB transplantation.

Recent advances on cellular therapies and immune modulators for graft-versus-host disease

The efficacy of allogeneic hematopoietic stem cell transplantation is counterbalanced by the occurrence of life-threatening immune-mediated complications, such as graft-versus-host disease (GVHD), a multistep disease which is reportedly fatal to approximately 15% of transplant recipients. It is now established that T-cell-dendritic cell interactions, T-cell activation, release of proinflammatory cytokines and T-cell trafficking partake in GVHD pathogenesis. This article will focus on the most recent strategies aimed at preventing/treating GVHD by manipulating components of the innate and adaptive immune response from both the donor and the host.