The role of the Th1 transcription factor T-bet in a mouse model of immune-mediated bone-marrow failure

Combating bone marrow failure with polymer materials

Bone marrow failure (BMF) has become one of the most studied autoimmune disorders, particularly due to its prevalence both as an inherited disease, but also as a result of chemotherapies. BMF is associated with severe symptoms such as bleeding episodes and susceptibility to infections, and often has underlying characteristics, such as anemia, thrombocytopenia, and neutropenia. The current treatment landscape for BMF requires stem cell transplantation or chemotherapies to induce immune suppression. However, there is limited donor cell availability or dose related toxicity associated with these treatments. Optimizing these treatments has become a necessity. Polymer-based materials have become increasingly popular, as current research efforts are focused on synthesizing novel cell matrices for stem cell expansion to solve limited donor cell availability, as well as applying polymer delivery vehicles to intracellularly deliver cargo that can aid in immunosuppression. Here, we discuss the importance and impact of polymer materials to enhance therapeutics in the context of BMF.

Formononetin reverses Treg/Th17 imbalance in immune-mediated bone marrow failure mice by regulating the PI3K/Akt signaling pathway

BACKGROUND

Severe aplastic anemia (SAA) is a syndrome of bone marrow failure which is life-threatening. Recent studies have demonstrated that CD4 + T cell subsets, including T regulatory (Treg) and T helper 17 (Th17) cells, play a pivotal role in the pathogenesis of SAA. Formononetin (FMN) is a natural compound extracted from the traditional Chinese medicine Huangqi, which has the ability to regulate the imbalance of Treg/Th17 cells in some inflammatory diseases. Nevertheless, the therapeutic effect of FMN in SAA has yet to be definitively established. Therefore, the objective of this research was to investigate the effect of FMN on SAA and elucidate its underlying mechanism.

METHODS

In vivo experiments, the mice were divided into the following five groups: control, model, low-dose FMN, high-dose FMN, and positive control cyclosporine A group. The immune-mediated bone marrow failure (BMF) mouse model was established by the total body X-ray radiation and lymphocyte infusion. After 10 days of continuous administration of FMN, the numbers of Treg/Th17 cells in the bone marrow and spleen were assessed by flow cytometry. The protein expressions of PI3K/Akt pathway in the bone marrow and spleen was assessed by immunohistochemistry and western blotting. In vitro, the impact of FMN on the differentiation of naive CD4 + T cells into Treg cells was investigated by flow cytometry and ELISA.

RESULTS

In comparison with the control group, the model group showed a reduction in bone marrow nucleated cells, a significant decrease in peripheral blood cells, and an altered CD8 + /CD4 + T cell ratio. These findings indicate the successful establishment of a mouse model of immune-mediated BMF. After FMN treatment, there were the increased levels of red blood cells and hemoglobin. In addition, FMN mitigated the bone marrow destruction and restored the CD8 + /CD4 + T cell ratio. Furthermore, in comparison with the control group, the model group showed the decreased levels of Treg cells and the increased levels of Th17 cells. After FMN treatment, there was a significantly increased number of Treg cells and a decreased number of Th17 cells. Additionally, FMN remarkably down-regulated the expression levels of PI3K and Akt proteins in immune-mediated BMF mice.

CONCLUSIONS

FMN alleviates immune-mediated BMF by modulating the balance of Treg/Th17 cells through the PI3K/Akt signaling pathway.

When inflammatory stressors dramatically change, disease phenotypes may transform between autoimmune hematopoietic failure and myeloid neoplasms

Aplastic anemia (AA) and hypoplastic myelodysplastic syndrome are paradigms of autoimmune hematopoietic failure (AHF). Myelodysplastic syndrome and acute myeloid leukemia are unequivocal myeloid neoplasms (MNs). Currently, AA is also known to be a clonal hematological disease. Genetic aberrations typically observed in MNs are detected in approximately one-third of AA patients. In AA patients harboring MN-related genetic aberrations, a poor response to immunosuppressive therapy (IST) and an increased risk of transformation to MNs occurring either naturally or after IST are predicted. Approximately 10%-15% of patients with severe AA transform the disease phenotype to MNs following IST, and in some patients, leukemic transformation emerges during or shortly after IST. Phenotypic transformations between AHF and MNs can occur reciprocally. A fraction of advanced MN patients experience an aplastic crisis during which leukemic blasts are repressed. The switch that shapes the disease phenotype is a change in the strength of extramedullary inflammation. Both AHF and MNs have an immune-active bone marrow (BM) environment (BME). In AHF patients, an inflamed BME can be evoked by infiltrated immune cells targeting neoplastic molecules, which contributes to the BM-specific autoimmune impairment. Autoimmune responses in AHF may represent an antileukemic mechanism, and inflammatory stressors strengthen antileukemic immunity, at least in a significant proportion of patients who have MN-related genetic aberrations. During active inflammatory episodes, normal and leukemic hematopoieses are suppressed, which leads to the occurrence of aplastic cytopenia and leukemic cell regression. The successful treatment of underlying infections mitigates inflammatory stress-related antileukemic activities and promotes the penetration of leukemic hematopoiesis. The effect of IST is similar to that of treating underlying infections. Investigating inflammatory stress-powered antileukemic immunity is highly important in theoretical studies and clinical practice, especially given the wide application of immune-activating agents and immune checkpoint inhibitors in the treatment of hematological neoplasms.

PRMT5 regulates epigenetic changes in suppressive Th1-like iTregs in response to IL-12 treatment

Background

Induced regulatory T cells (iTregs) are a heterogeneous population of immunosuppressive T cells with therapeutic potential. Treg cells show a range of plasticity and can acquire T effector-like capacities, as is the case for T helper 1 (Th1)-like iTregs. Thus, it is important to distinguish between functional plasticity and lineage instability. Aplastic anemia (AA) is an autoimmune disorder characterized by immune-mediated destruction of hematopoietic stem and progenitor cells in the bone marrow (BM). Th1-like 1 iTregs can be potent suppressors of aberrant Th1-mediated immune responses such as those that drive AA disease progression. Here we investigated the function of the epigenetic enzyme, protein arginine methyltransferase 5 (PRMT5), its regulation of the iTreg-destabilizing deacetylase, sirtuin 1 (Sirt1) in suppressive Th1-like iTregs, and the potential for administering Th1-like iTregs as a cell-based therapy for AA.

Methods

We generated Th1-like iTregs by culturing iTregs with IL-12, then assessed their suppressive capacity, expression of iTreg suppression markers, and enzymatic activity of PRMT5 using histone symmetric arginine di-methylation (H3R2me2s) as a read out. We used ChIP sequencing on Th1 cells, iTregs, and Th1-like iTregs to identify H3R2me2s-bound genes unique to Th1-like iTregs, then validated targets using CHiP-qPCR. We knocked down PRMT5 to validate its contribution to Th1-like iTreg lineage commitment. Finally we tested the therapeutic potential of Th1-like iTregs using a Th1-mediated mouse model of AA.

Results

Exposing iTregs to the Th1 cytokine, interleukin-12 (IL-12), during early events of differentiation conveyed increased suppressive function. We observed increased PRMT5 enzymatic activity, as measured by H3R2me2s, in Th1-like iTregs, which was downregulated in iTregs. Using ChIP-sequencing we discovered that H3R2me2s is abundantly bound to the Sirt1 promoter region in Th1-like iTregs to negatively regulate its expression. Furthermore, administering Th1-like iTregs to AA mice provided a survival benefit.

Conclusions

Knocking down PRMT5 in Th1-like iTregs concomitantly reduced their suppressive capacity, supporting the notion that PRMT5 is important for the superior suppressive capacity and stability of Th1-like iTregs. Conclusively, therapeutic administration of Th1-like iTregs in a mouse model of AA significantly extended their survival and they may have therapeutic potential.

Stat1 is an inducible transcriptional repressor of neural stem cells self-renewal program during neuroinflammation

A central issue in regenerative medicine is understanding the mechanisms that regulate the self-renewal of endogenous stem cells in response to injury and disease. Interferons increase hematopoietic stem cells during infection by activating STAT1, but the mechanisms by which STAT1 regulates intrinsic programs in neural stem cells (NSCs) during neuroinflammation is less known. Here we explored the role of STAT1 on NSC self-renewal. We show that overexpressing Stat1 in NSCs derived from the subventricular zone (SVZ) decreases NSC self-renewal capacity while Stat1 deletion increases NSC self-renewal, neurogenesis, and oligodendrogenesis in isolated NSCs. Importantly, we find upregulation of STAT1 in NSCs in a mouse model of multiple sclerosis (MS) and an increase in pathological T cells expressing IFN-γ rather than interleukin 17 (IL-17) in the cerebrospinal fluid of affected mice. We find IFN-γ is superior to IL-17 in reducing proliferation and precipitating an abnormal NSC phenotype featuring increased STAT1 phosphorylation and Stat1 and p16ink4a gene expression. Notably, Stat1-/- NSCs were resistant to the effect of IFN-γ. Lastly, we identified a Stat1-dependent gene expression profile associated with an increase in the Sox9 transcription factor, a regulator of self-renewal. Stat1 binds and transcriptionally represses Sox9 in a transcriptional luciferase assay. We conclude that Stat1 serves as an inducible checkpoint for NSC self-renewal that is upregulated during chronic brain inflammation leading to decreased self-renewal. As such, Stat1 may be a potential target to modulate for next generation therapies to prevent progression and loss of repair function in NSCs/neural progenitors in MS.

High-fat-diet induced obesity and diabetes mellitus in Th1 and Th2 biased mice strains: A brief overview and hypothesis

Obesity and diabetes mellitus are common metabolic diseases prevalent worldwide. Mice are commonly used to study the pathogenesis of these two conditions. Obesity and diabetes mellitus are induced by administering a high-fat diet in many studies although other diet-induced models are also used. Several factors may influence the outcome of the studies done to study diet-induced obesity in mice. The immune system plays a crucial role in the susceptibility of mice to develop obesity and metabolic disease. In this article, the reasons for differences in susceptibility to develop obesity and diabetes mellitus in mice in response to high-fat-diet feeding and the influence of immunological bias of the mice strain used in studies are evaluated. Mice strains that induce proinflammatory and Th1-type immune responses are found to be susceptible to high-fat-diet-induced obesity. A few studies which directly compared the effect of a high-fat diet on obesity and diabetic phenotype in Th1- and Th2-biased mice strains were briefly analyzed. Based on the observations, it is proposed that the liver and adipose tissue may respond differently to high-fat-diet feeding regimens in Th1- and Th2-biased mice strains. For instance, in Th1-biased mice, adipose tissue fat content was high both in the baseline as well as in response to a high-fat diet whereas in the liver, it was found to be less. It can be inferred that the immune responses to diet-induced models may provide insights into the pathogenesis of obesity and diabetes mellitus.

Monocytic myeloid-derived suppressive cells mitigate over-adipogenesis of bone marrow microenvironment in aplastic anemia by inhibiting CD8+ T cells

Aplastic anemia (AA) is a blood disorder resulted from over-activated T-cell related hematopoietic failure, with the characterization of hypocellularity and enhanced adipogenic differentiation of mesenchymal stroma cells (MSCs) in bone marrow (BM). However, little is known about the relationship between immune imbalance and polarized adipogenic abnormity of BM microenvironment in this disease entity. In the present study, we differentiated BM-MSCs into osteoblastic or adipogenic lineages to mimic the osteo-adipogenic differentiation. Activated CD8⁺ T cells and interferon-γ (IFN-γ) were found to stimulate adipogenesis of BM-MSCs either in vitro or in vivo of AA mouse model. Interestingly, myeloid-derived suppressive cells (MDSCs), one of the immune-regulating populations, were decreased within BM of AA mice. We found that it was not CD11b⁺Ly6G⁺Ly6C^- granulocytic-MDSCs (gMDSCs) but CD11b⁺Ly6G^-Ly6C⁺ monocytic-MDSCs (mMDSCs) inhibiting both T cell proliferation and IFN-γ production via inducible nitric oxide synthetase (iNOS) pathway. Single-cell RNA-sequencing (scRNA-seq) of AA- and mMDSCs-treated murine BM cells revealed that mMDSCs transfusion could reconstitute BM hematopoietic progenitors by inhibiting T cells population and signature cytokines and decreasing immature Adipo-Cxcl12-abundant reticular cells within BM. Multi-injection of mMDSCs into AA mice reduced intra-BM T cells infiltration and suppressed BM adipogenesis, which subsequently restored the intra-BM immune balance and eventually prevented pancytopenia and hypo-hematopoiesis. In conclusion, adoptive transfusion of mMDSCs might be a novel immune-regulating strategy to treat AA, accounting for not only restoring the intra-BM immune balance but also improving stroma's multi-differentiating microenvironment.

Acquired severe aplastic anaemia: how medical therapy evolved in the 20th and 21st centuries

The progress in aplastic anaemia (AA) management is one of success. Once an obscure entity resulting in death in most affected can now be successfully treated with either haematopoietic stem cell transplantation (HSCT) or immunosuppressive therapy (IST). The mechanisms that underly the diminution of haematopoietic stem cells (HSCs) are now better elucidated, and include genetics and immunological alterations. Advances in supportive care with better antimicrobials, safer blood products and iron chelation have greatly impacted AA outcomes. Working somewhat 'mysteriously', anti-thymocyte globulin (ATG) forms the base for both HSCT and IST protocols. Efforts to augment immunosuppression potency have not, unfortunately, led to better outcomes. Stimulating HSCs, an often-sought approach, has not been effective historically. The thrombopoietin receptor agonists (Tpo-RA) have been effective in stimulating early HSCs in AA despite the high endogenous Tpo levels. Dosing, timing and best combinations with Tpo-RAs are being defined to improve HSCs expansion in AA with minimal added toxicity. The more comprehensive access and advances in HSCT and IST protocols are likely to benefit AA patients worldwide. The focus of this review will be on the medical treatment advances in AA.

Minimal role of interleukin 6 and toll-like receptor 2 and 4 in murine models of immune-mediated bone marrow failure

Immune aplastic anemia (AA) results from T cell attack on hematopoietic cells, resulting in bone marrow hypocellularity and pancytopenia. Animal models have been successfully developed to study pathophysiological mechanisms in AA. While we have systemically defined the critical components of the adaptive immune response in the pathogenesis of immune marrow failure using this model, the role of innate immunity has not been fully investigated. Here, we demonstrate that lymph node (LN) cells from B6-based donor mice carrying IL-6, TLR2, or TLR4 gene deletions were fully functional in inducing severe pancytopenia and bone marrow failure (BMF) when infused into MHC-mismatched CByB6F1 recipients. Conversely, B6-based recipient mice with IL-6, TLR2, and TLR4 deletion backgrounds were all susceptible to immune-mediated BMF relative to wild-type B6 recipients following infusion of MHC-mismatched LN cells from FVB donors, but the disease appeared more severe in IL-6 deficient mice. We conclude that IL-6, TLR2, and TLR4, molecular elements important in maintenance of normal innate immunity, have limited roles in a murine model of immune-mediated BMF. Rather, adaptive immunity appears to be the major contributor to the animal disease.

Human T-bet Governs Innate and Innate-like Adaptive IFN-γ Immunity against Mycobacteria

Inborn errors of human interferon gamma (IFN-γ) immunity underlie mycobacterial disease. We report a patient with mycobacterial disease due to inherited deficiency of the transcription factor T-bet. The patient has extremely low counts of circulating Mycobacterium-reactive natural killer (NK), invariant NKT (iNKT), mucosal-associated invariant T (MAIT), and Vδ2+ γδ T lymphocytes, and of Mycobacterium-non reactive classic TH1 lymphocytes, with the residual populations of these cells also producing abnormally small amounts of IFN-γ. Other lymphocyte subsets develop normally but produce low levels of IFN-γ, with the exception of CD8+ αβ T and non-classic CD4+ αβ TH1∗ lymphocytes, which produce IFN-γ normally in response to mycobacterial antigens. Human T-bet deficiency thus underlies mycobacterial disease by preventing the development of innate (NK) and innate-like adaptive lymphocytes (iNKT, MAIT, and Vδ2+ γδ T cells) and IFN-γ production by them, with mycobacterium-specific, IFN-γ-producing, purely adaptive CD8+ αβ T, and CD4+ αβ TH1∗ cells unable to compensate for this deficit.

All-trans-retinoic acid shifts Th1 towards Th2 cell differentiation by targeting NFAT1 signalling to ameliorate immune-mediated aplastic anaemia

Severe acquired aplastic anaemia (AA) is a serious disease characterised by autoreactive T cells attacking haematopoietic stem cells, leading to marrow hypoplasia and pancytopenia. Immunosuppressive therapy combined with antithymocyte globulin and ciclosporin can rescue most patients with AA. However, the relapse after ciclosporin withdrawal and the severe side effects of long-term ciclosporin administration remain unresolved. As such, new strategies should be developed to supplement current therapeutics and treat AA. In this study, the possibility of all-trans-retinoic acid (ATRA) as an alternative AA treatment was tested by using an immune-mediated mouse model of AA. Results revealed that ATRA inhibited T-cell proliferation, activation and effector function. It also restrained the Fas/Fasl pathway, shifted Th1 towards Th2 cell development, rebalanced T-cell subsets at a relatively high level and corrected the Th1/Th2 ratio by targeting NFAT1 signalling. In addition, ATRA inhibited Th17 cell differentiation and promoted regulatory T-cell development. Therefore, ATRA was an effective agent to improve AA treatment outcomes.

Human gingiva tissue-derived MSC ameliorates immune-mediated bone marrow failure of aplastic anemia via suppression of Th1 and Th17 cells and enhancement of CD4+Foxp3+ regulatory T cells differentiation

Accumulating evidence has revealed that human gingiva-derived mesenchymal stem cells (GMSCs) are emerging as a new line of mesenchymal stem cells and may have the potential to control or even treat autoimmune diseases through maintaining the balance between Th and Treg cells. Given that GMSCs have a robust immune regulatory function and regenerative ability, we investigated the effect of GMSCs on preventing T cell-mediated bone marrow failure (BMF) in a mouse model. We observed that GMSCs markedly improved mice survival and attenuated histological bone marrow (BM) damage. Moreover, we found GMSCs significantly reduced cell infiltration of CD8+ cells, Th1 and Th17 cells, whereas increased CD4+Foxp3+ regulatory T cells (Tregs) differentiation in lymph nodes. GMSCs also suppressed the levels of TNF-α, IFN-γ, IL-17A and IL-6, but IL-10 was increased in serum. The live in vivo imaging identified that GMSCs can home into inflammatory location on BM. Our results demonstrate that GMSCs attenuate T cell-mediated BMF through regulating the balance of Th1, Th17 and Tregs, implicating that application of GMSCs may provide a promising approach in prevention and treatment of patients with aplastic anemia.

Panaxdiol Saponins Component Promotes Hematopoiesis and Modulates T Lymphocyte Dysregulation in Aplastic Anemia Model Mice

OBJECTIVE

To investigate the potential efficacy of panaxadiol saponins component (PDS-C) in the treatment of aplastic anemia (AA) model mice.

METHODS

Totally 70 mice were divided into 7 groups as follows: normal, model, low-, medium-, high-dose PDS-C (20, 40, 80 mg/kg, namely L-, M-, H-PDS-C), cyclosporine (40 mg/kg), and andriol (25 mg/kg) groups, respectively. An immune-mediated AA mouse model was established in BALB/c mice by exposing to 5.0 Gy total body irradiation at 1.0 Gy/min, and injecting with lymphocytes from DBA mice. On day 4 after establishment of AA model, all drugs were intragastrically administered daily for 15 days, respectively, while the mice in the normal and model groups were administered with saline solution. After treatment, the peripheral blood counts, bone marrow pathological examination, colony forming assay of bone marrow culture, T lymphocyte subpopulation analysis, as well as T-bet, GATA-3 and FoxP3 proteins were detected by flow cytometry and Western blot.

RESULTS

The peripheral blood of white blood cell (WBC), platelet, neutrophil counts and hemoglobin (Hb) concentration were significantly decreased in the model group compared with the normal group (all P<0.01). In response to 3 dose PDS-C treatment, the WBC, platelet, neutrophil counts were significantly increased at a dose-dependent manner compared with the model group (all P<0.01). The myelosuppression status of AA was significantly reduced in M-, H-PDS-C groups, and hematopoietic cell quantity of bone marrow was more abundant than the model group. The colony numbers of myeloid, erythroid and megakaryocytic progenitor cells in the model group were less than those of the normal mice in bone marrow culture, while, PDS-C therapy enhanced proliferation of hematopoietic progenitor cells by significantly increasing colony numbers (all P<0.01). Furthermore, PDS-C therapy increased peripheral blood CD3⁺ and CD3⁺CD4⁺ cells and reduced CD3⁺CD8⁺ cells (P<0.05 or P<0.01). Meanwhile, PDS-C treatment at medium- and high doses groups also increased CD4⁺CD25⁺FoxP3⁺ cells, downregulated T-bet protein expression, and upregulated GATA-3 and FoxP3 protein expressions in spleen cells (P<0.05).

CONCLUSION

PDS-C possesses dual activities, promoting proliferation hematopoietic progenitor cells and modulating T lymphocyte immune functions in the treatment of AA model mice.

[Tetramethylpyrazine promotes bone marrow repair in a C57 mouse model of X-rayinduced immune-mediated bone marrow failure]

OBJECTIVE

To observe the therapeutic effect of tetramethylpyrazine on immune-mediated bone marrow failure (BMF) induced by different doses of X-ray exposure in C57 mice.

METHODS

C57BL6 mice were randomized into 4 groups, including a blank control group and 3 X-ray exposure groups with X-ray exposure at low (5.0 Gy), moderate (5.75 Gy), and high (6.5 Gy) doses. After total body irradiation with 0.98 Gy/min X-ray. The mice as recipient received injections of 4×106 lymphocytes from DBA/2 mice via the tail vein within 4 h. The survival rate of the recipient mice, peripheral blood cell counts, bone marrow nucleated cell count, and bone marrow pathology were examined at 14 days after the exposure. In the subsequent experiment, C57 mice were exposed to 5.0 Gy X-ray and treated with intraperitoneal injection of tetramethylpyrazine at the low (5 mg/mL), moderate (10 mg/mL), or high (20 mg/mL) doses (12 mice in each group) for 14 consecutive days, and the changes in BMF were observed.

RESULTS

X-ray exposure, especially at the high dose, resulted in significantly lowered survival rate in the mouse models of BMF at 14 days. As the X-ray dose increased, the mice showed significantly reduced peripheral blood counts of red blood cells, white blood cells, platelets and lowered bone marrow nucleated cell counts with obvious bone marrow congestion and reduction of nucleated cells (P < 0.05 or 0.001). In the mice exposed to 5.0 Gy X-ray, tetramethylpyrazine at the high dose most obviously increased bone marrow nucleated cells (P < 0.01) and red blood cells (P < 0.001), and even at the low dose, tetramethylpyrazine significantly increased the counts of white blood cells (P < 0.05) and platelets (P < 0.01) following the exposure. Tetramethylpyrazine dose-dependently alleviated bone marrow hyperemia, increased bone marrow nucleated cell counts, and lowered Fas protein expression in the bone marrow.

CONCLUSIONS

X-ray irradiation at 5.0 Gy is suitable for establish mouse models of immune-mediated BMF. Tetramethylpyrazine promotes bone marrow repair by regulating Fas cell apoptosis signals, which further expands the traditional Chinese medicine theory of "removing blood stasis to create new."

T-cell expression of Bruton's tyrosine kinase promotes autoreactive T-cell activation and exacerbates aplastic anemia

The role of Bruton’s tyrosine kinase (BTK) in BCR signaling is well defined, and BTK is involved in B-cell development, differentiation, and malignancies. However, the expression of Btk in T cells and its role in T-cell function remain largely unknown. Here, we unexpectedly found high expression and activation of BTK in T cells. Deficiencies in BTK resulted in the impaired activation and proliferation of autoreactive T cells and ameliorated bone marrow failure (BMF) in aplastic anemia. Mechanistically, BTK is activated after TCR engagement and then phosphorylates PLCγ1, thus promoting T-cell activation. Treatment with acalabrutinib, a selective BTK inhibitor, decreased T-cell proliferation and ameliorated BMF in mice with aplastic anemia. Our results demonstrate an unexpected role of BTK in optimal T-cell activation and in the pathogenesis of autoimmune aplastic anemia, providing insights into the molecular regulation of T-cell activation and the pathogenesis of T-cell-mediated autoimmune disease.

Dysregulated miR34a/diacylglycerol kinase ζ interaction enhances T-cell activation in acquired aplastic anemia

Acquired aplastic anemia is an idiopathic paradigm of human bone marrow failure syndrome, which involves active destruction of hematopoietic stem cells and progenitors by cytotoxic T cells in the bone marrow. Aberrant expression of microRNAs in T cells has been shown to lead to development of certain autoimmune diseases. In the present study, we performed a microarray analysis of miRNA expression in bone marrow CD3⁺ T cells from patients with aplastic anemia and healthy controls. Overexpression of miR34a and underexpression of its target gene diacylglycerol kinase (DGK) ζ in bone marrow mononuclear cells were validated in 41 patients and associated with the severity of aplastic anemia. Further, the level of miR34a was higher in naïve T cells from patients than from controls. The role of miR34a and DGKζ in aplastic anemia was investigated in a murine model of immune-mediated bone marrow failure using miR34a^−/− mice. After T-cell receptor stimulation in vitro, lymph node T cells from miR34a^−/− mice demonstrated reduced activation and proliferation accompanied with a less profound down-regulation of DGKζ expression and decreased ERK phosphorylation compared to those from wild-type C57BL6 control mice. Infusion of 5 × 10⁶ miR34a^−/− lymph node T cells into sublethally irradiated CB6F1 recipients led to increased Lin^-Sca1⁺CD117⁺ cells and less vigorous expansion of CD8⁺ T cells than injection of same number of wild-type lymph node cells. Our study demonstrates that the miR34a/DGKζ dysregulation enhances T-cell activation in aplastic anemia and targeting miR34a may represent a novel molecular therapeutic approach for patients with aplastic anemia.

The intestinal microbiota determines the colitis-inducing potential of T-bet-deficient Th cells in mice

Conflicting evidence has been provided as to whether induction of intestinal inflammation by adoptive transfer of naïve T cells into Rag^-/- mice requires expression of the transcription factor T-bet by the T cells. Here, we formally show that the intestinal microbiota composition of the Rag^-/- recipient determines whether or not T-bet-deficient Th cells can induce colitis and we have resolved the differences of the two microbiomes, permissive or non-permissive to T-bet-independent colitis. Our data highlight the dominance of the microbiota over particular T cell differentiation programs in the pathogenesis of chronic intestinal inflammation.

Blood Stem Cell Activity Is Arrested by Th1-Mediated Injury Preventing Engraftment following Nonmyeloablative Conditioning

T cells are widely used to promote engraftment of hematopoietic stem cells (HSCs) during an allogeneic hematopoietic cell transplantation. Their role in overcoming barriers to HSC engraftment is thought to be particularly critical when patients receive reduced doses of preparative chemotherapy and/or radiation compared with standard transplantations. In this study, we sought to delineate the effects CD4⁺ cells on engraftment and blood formation in a model that simulates clinical hematopoietic cell transplantation by transplanting MHC-matched, minor histocompatibility-mismatched grafts composed of purified HSCs, HSCs plus bulk T cells, or HSCs plus T cell subsets into mice conditioned with low-dose irradiation. Grafts containing conventional CD4⁺ T cells caused marrow inflammation and inhibited HSC engraftment and blood formation. Posttransplantation, the marrows of HSCs plus CD4⁺ cell recipients contained IL-12-secreting CD11c⁺ cells and IFN-γ-expressing donor Th1 cells. In this setting, host HSCs arrested at the short-term stem cell stage and remained in the marrow in a quiescent cell cycling state (G₀). As a consequence, donor HSCs failed to engraft and hematopoiesis was suppressed. Our data show that Th1 cells included in a hematopoietic allograft can negatively impact HSC activity, blood reconstitution, and engraftment of donor HSCs. This potential negative effect of donor T cells is not considered in clinical transplantation in which bulk T cells are transplanted. Our findings shed new light on the effects of CD4⁺ T cells on HSC biology and are applicable to other pathogenic states in which immune activation in the bone marrow occurs such as aplastic anemia and certain infectious conditions.

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.

Immune-mediated bone marrow failure in C57BL/6 mice

We established a model of immune-mediated bone marrow (BM) failure in C57BL/6 (B6) mice with 6.5 G total-body irradiation followed by the infusion of 4-10 × 10(6) lymph node (LN) cells/recipient from Friend leukemia virus B/N (FVB) donors. Forty-three percent of animals succumbed, with surviving animals showing marked declines in blood neutrophils, red blood cells, platelets and total BM cells at 8 to 14 days following LN cell infusion. Lowering the total-body irradiation dose to 5 G or altering the LN source from FVB to BALB/cBy donors failed to produce BM destruction. Affected animals showed significant expansion and activation of CD8 T lymphocytes in both the blood and BM; cytotoxic T cells had elevated Fas ligand expression and were oligoclonal, mainly displaying Vβ7 and Vβ17 T cell receptors. There were significant increases in blood plasma interferon γ and tissue necrosis factor α in affected animals. Chemokine ligands CCL3, CCL4, CCL5, CCL20, CXCL2, and CXCL5 and hematopoietic growth factors G-CSF, M-CSF, GM-CSF, VEGF were also elevated. In B6 mice carrying a Fas gene mutation, BM failure was attenuated when they were infused with FVB LN cells. Our model establishes a useful platform to define the roles of individual genes and their products in immune-mediated BM failure.

New therapeutic approaches for protecting hematopoietic stem cells in aplastic anemia

Aplastic anemia (AA) is an immune-mediated and life-threatening form of acquired bone marrow failure (BMF), characterized by development and expansion of self-reactive T cells. These T cells cause continuous destruction of hematopoietic stem cells (HSCs), progenitors, and mature blood cells, leading to severe and if left untreated fatal marrow hypoplasia and pancytopenia. Standard treatment options for patients with AA include: (1) immunosuppressive therapy (IST) with anti-thymocyte globulin and cyclosporine A which targets self-reactive T cells, or (2) matched sibling or unrelated BM transplant (BMT). The IST treatment is often not effective due to poor response to therapy or disease relapse after IST. Also, BMT is not an option for many patients due to their age, comorbidities, and the lack of histocompatible donor. This necessitates development and testing of novel approaches to reduce severity of AA and to efficiently treat patients with refractory and relapsed AA. Immune-mediated AA was reproduced in animals, including mouse lymphocyte infusion models, which are used to study further etiology and pathophysiology of AA and test new drugs and approaches in treating and managing AA. In these mouse models the immune correlates and pathologic features of AA are strikingly similar to features of severe human AA. In this article we (a) briefly review standard and developing approaches for treating AA and (b) describe development and testing of novel treatment approach with a potential to safely reduce BM hypoplasia and significantly decrease the loss of HSCs in mouse lymphocyte infusion model of AA.

Th2 lymphocytes migrating to the bone marrow under high-altitude hypoxia promote erythropoiesis via activin A and interleukin-9

The mechanism of accelerated erythropoiesis under the hypoxic conditions of high altitude (HA) remains largely obscure. Here, we investigated the potential role of bone marrow (BM) T cells in the increased production of erythrocytes at HA. We found that mice exposed to a simulated altitude of 6,000 m for 1-3 weeks exhibited a significant expansion of BM CD4+ cells, mainly caused by increasing T helper 2 (Th2) cells. Using a coculture model of BM T cells and hematopoietic stem/progenitor cells, we observed that BM CD4+ cells from hypoxic mice induced erythroid output more easily, in agreement with the erythroid-enhancing effect observed for Th2-condition-cultured BM CD4+ cells. It was further demonstrated that elevated secretion of activin A and interleukin-9 by BM Th2 cells of hypoxic mice promoted erythroid differentiation of hematopoietic stem/progenitor cells and the growth of erythroblasts, respectively. Our study also provided evidence that the CXCL12-CXCR4 interaction played an important role in Th2 cell trafficking to the BM under HA conditions. These results collectively suggest that Th2 cells migrating to the BM during HA exposure have a regulatory role in erythropoiesis, which provides new insight into the mechanism of high altitude polycythemia.

Ezh2 regulates transcriptional and posttranslational expression of T-bet and promotes Th1 cell responses mediating aplastic anemia in mice

Acquired aplastic anemia (AA) is a potentially fatal bone marrow (BM) failure syndrome. IFN-γ-producing Th1 CD4(+) T cells mediate the immune destruction of hematopoietic cells, and they are central to the pathogenesis. However, the molecular events that control the development of BM-destructive Th1 cells remain largely unknown. Ezh2 is a chromatin-modifying enzyme that regulates multiple cellular processes primarily by silencing gene expression. We recently reported that Ezh2 is crucial for inflammatory T cell responses after allogeneic BM transplantation. To elucidate whether Ezh2 mediates pathogenic Th1 responses in AA and the mechanism of Ezh2 action in regulating Th1 cells, we studied the effects of Ezh2 inhibition in CD4(+) T cells using a mouse model of human AA. Conditionally deleting Ezh2 in mature T cells dramatically reduced the production of BM-destructive Th1 cells in vivo, decreased BM-infiltrating Th1 cells, and rescued mice from BM failure. Ezh2 inhibition resulted in significant decrease in the expression of Tbx21 and Stat4, which encode transcription factors T-bet and STAT4, respectively. Introduction of T-bet but not STAT4 into Ezh2-deficient T cells fully rescued their differentiation into Th1 cells mediating AA. Ezh2 bound to the Tbx21 promoter in Th1 cells and directly activated Tbx21 transcription. Unexpectedly, Ezh2 was also required to prevent proteasome-mediated degradation of T-bet protein in Th1 cells. Our results demonstrate that Ezh2 promotes the generation of BM-destructive Th1 cells through a mechanism of transcriptional and posttranscriptional regulation of T-bet. These results also highlight the therapeutic potential of Ezh2 inhibition in reducing AA and other autoimmune diseases.

NOTCH signaling in immune-mediated bone marrow failure of aplastic anemia

Severe aplastic anemia is a rare bone marrow failure disease with the majority of cases caused by aberrant immune destruction of blood progenitors. Although the Th1-mediated pathology of aplastic anemia is well-described, the molecular mechanisms that drive disease progression remain ill-defined. The NOTCH signaling pathway mediates Th1 differentiation in the presence of polarizing cytokines, an action requiring enzymatic processing of NOTCH receptors by γ- secretase. We used a mouse model of aplastic anemia to demonstrate that expression both of intracellular NOTCH1 (NOTCH1(IC)) and T-BET, a key transcription factor regulating Th1 differentiation, were increased in T cells in the spleen and bone marrow during active disease. Conditionally deleting NOTCH1 or administering γ-secretase inhibitors (GSI) in vivo, attenuated disease and rescued mice from lethal bone marrow failure. In peripheral T cells from patients with untreated aplastic anemia, NOTCH1(IC) was significantly elevated and was detected at the TBX21 promoter, showing NOTCH1 directly regulates the gene encoding T-BET. Treating patients' cells ex vivo with GSI lowered NOTCH1(IC) levels, decreased the level of NOTCH1 detectable at the TBX21 promoter, and also decreased T-BET expression, indicating NOTCH1 signaling is responsive to GSI during active disease. Collectively, these results identify NOTCH1 signaling as a primary driver of Th1-mediated pathogenesis in aplastic anemia and may represent a novel target for therapeutic intervention.

Aplastic anemia: what have we learned from animal models and from the clinic

Aplastic anemia (AA) is currently perceived as an immune-mediated disease in which aberrant effector cells recognize and destroy primitive marrow elements, resulting in pancytopenia. The immune hypothesis is based on clinical observations of responsiveness of AA to immunomodulatory agents such as anti-thymocyte globulin (ATG) and the requirement of cyclosporine to maintain response; evidence of an immune system in disarray provided by abnormal regulatory, TH1, TH17, and expanded CD8(+) T-cell populations, and animal models of immune-mediated marrow destruction, where many of the observed clinical and in vitro alterations can be confirmed and expanded. Murine models mimicking AA have used exposure to agents that result in marrow destruction through a direct toxic effect, but models that explore antigenic disparities between strains have resulted in immune-mediated destruction of the marrow, more closely modeling human AA. Many experiments in mice have helped confirm and elucidate specific mechanisms of marrow destruction. However, clinical development of regimens in AA has not relied on establishing their success in murine model. Instead, drugs and their combinations investigated in AA were those shown clinically to be active in AA, in other hematologic diseases, or in other specialties such as in rheumatology, and solid and bone marrow transplantation. In this review, the evolution of murine models and their clinical relevance in AA are discussed.

Therapeutic targeting of NOTCH signaling ameliorates immune-mediated bone marrow failure of aplastic anemia

Notch1 signaling sustains the proinflammatory behavior of Th1 cells, implicated in the development of aplastic anemia in humans and mice.

Severe aplastic anemia (AA) is a bone marrow (BM) failure (BMF) disease frequently caused by aberrant immune destruction of blood progenitors. Although a Th1-mediated pathology is well described for AA, molecular mechanisms driving disease progression remain ill defined. The NOTCH signaling pathway mediates Th1 cell differentiation in the presence of polarizing cytokines, an action requiring enzymatic processing of NOTCH receptors by γ-secretase. Using a mouse model of AA, we demonstrate that expression of both intracellular NOTCH1^IC and T-BET, a key transcription factor regulating Th1 cell differentiation, was increased in spleen and BM-infiltrating T cells during active disease. Conditionally deleting Notch1 or administering γ-secretase inhibitors (GSIs) in vivo attenuated disease and rescued mice from lethal BMF. In peripheral T cells from patients with untreated AA, NOTCH1^IC was significantly elevated and bound to the TBX21 promoter, showing NOTCH1 directly regulates the gene encoding T-BET. Treating patient cells with GSIs in vitro lowered NOTCH1^IC levels, decreased NOTCH1 detectable at the TBX21 promoter, and decreased T-BET expression, indicating that NOTCH1 signaling is responsive to GSIs during active disease. Collectively, these results identify NOTCH signaling as a primary driver of Th1-mediated pathogenesis in AA and may represent a novel target for therapeutic intervention.

Experimental bone marrow failure in mice ameliorated by OCH via tippling the balance of released cytokines from Th1 to Th2

BACKGROUND

OCH was reported to stimulate natural killer T (NKT) cells to produce predominantly T helper type 2 (Th2) cytokines. The present study was attempted to evaluate potential protection of OCH on acquired bone marrow failure syndromes (BMFS) in mice model.

METHODS

BMFS in mice model was established by exposure to sublethal irradiation followed by infusion with 5 × 10(6) B6 lymph nodes cells. Mice were injected intraperitoneally (I.P.) with either OCH or α-galactosylceramide (α-GC) at a dose of 100 µg kg(-1) twice a week for two weeks after post-irradiation. The control mice were I.P. with vehicle alone (10% dimethyl sulfoxide in phosphate-buffered saline). Meanwhile, anti-interleukin-4 (anti-IL-4) monoclonal antibody (mAb) (500 µg/animal) was given I.P. 2 hours prior to vehicle or OCH administration. Both interferon-γ (IFN-γ) and IL-4 levels in the serum were measured by enzyme-linked immunosorbent assay. Colony-forming unit-granulocyte-macrophage (CFU-GM) by bone marrow (BM) mononuclear cells was counted. The percentage of NKT cell in BM cells and intracellular cytokines were determined by flow cytometry.

RESULTS

The treatment of OCH in vivo decreased the IFN-γ/IL-4 ratio in the serum, and increased the transformation of NKT cells into NKT2 cells. The treatment of OCH in vitro increased the colonies of CFU-GM.

CONCLUSION

Our data suggests that OCH ameliorated immune-mediated BMFS in CByB6F1 mice via activation of NKT cells, and shifting the balance from Th1 to Th2.

MHC class II upregulation and colocalization with Fas in experimental models of immune-mediated bone marrow failure

OBJECTIVE

To test the hypothesis that γ-interferon (IFN-γ) promotes major histocompatibility complex (MHC) class II expression on bone marrow (BM) cell targets that facilitate T-cell-mediated BM destruction in immune-mediated BM failure.

MATERIALS AND METHODS

Allogeneic lymph node (LN) cells were infused into MHC- or minor histocompatibility antigen-mismatched hosts to induce BM failure. MHC class II and Fas expression and cell apoptosis were analyzed by flow cytometry. MHC class II-Fas colocalization was detected by ImageStream Imaging Flow Cytometry and other cell-to-cell associations were visualized by confocal microscopy. T-cell-mediated BM cell apoptosis and effects of IFN-γ on MHC class II-Fas colocalization on normal BM cells were studied using cell culture in vitro followed by conventional and imaging flow cytometry.

RESULTS

BM failure animals had significantly upregulated MHC class II expression on CD4(-)CD8(-)CD11b(-)CD45R(-) residual BM cells and significantly increased MHC class II-Fas colocalization on BM CD150(+) and CD34(+) hematopoietic cells. MHC class II(+)Fas(+) BM cells were closely associated with CD4(+) T cells in the BM of affected animals, and they were significantly more responsive to T-cell-mediated cell apoptosis relative to MHC class II(-)Fas(-) BM cells. Infusion of IFN-γ-deficient LN cells into minor histocompatibility antigen-mismatched recipients resulted in no MHC class II-Fas upregulation and no clinically overt BM failure. Treatment with recombinant IFN-γ significantly increased both MHC class II-Fas coexpression and colocalization on normal BM cells.

CONCLUSIONS

Elevation of the inflammatory cytokine IFN-γ-stimulated MHC class II expression and MHC class II-Fas colocalization, which may facilitate T-cell-mediated cell destruction.

Th17 immune responses contribute to the pathophysiology of aplastic anemia

T helper type 17 (Th17) cells have been characterized based on production of interleukin-17 (IL-17) and association with autoimmune diseases. We studied the role of Th17 cells in aplastic anemia (AA) by isolating Th17 cells from patients blood (n = 41) and bone marrow (BM) mononuclear cells (n = 7). The frequency and total number of CD3(+)CD4(+)IL-17-producing T cells were increased in AA patients at presentation compared with healthy controls (P = .0007 and .02, respectively) and correlated with disease activity. There was an inverse relationship between the numbers of Th17 cells and CD4(+)CD25(high)FoxP3(+) regulatory T cells (Tregs) in the blood of AA patients. Concomitant with the classical Th1 response, we detected the presence of CD4(+) and CD8(+) IL-17-producing T cells in a mouse model of lymph node infusion-induced BM failure. Although anti-IL-17 treatment did not abrogate BM failure, early treatment with the anti-IL-17 antibody reduced the severity of BM failure with significantly higher platelet (P < .01) and total BM cell (P < .05) counts at day 10. Recipients that received anti-IL-17 treatment had significantly fewer Th1 cells (P < .01) and more Treg cells (P < .05) at day 10 after lymph node infusion. Th17 immune responses contribute to AA pathophysiology, especially at the early stage during disease progression.

Lethal graft-versus-host disease in mouse models of T cell receptor gene therapy

The transfer of T cell receptor (TCR) genes can be used to induce immune reactivity toward defined antigens to which endogenous T cells are insufficiently reactive. This approach, which is called TCR gene therapy, is being developed to target tumors and pathogens, and its clinical testing has commenced in patients with cancer. In this study we show that lethal cytokine-driven autoimmune pathology can occur in mouse models of TCR gene therapy under conditions that closely mimic the clinical setting. We show that the pairing of introduced and endogenous TCR chains in TCR gene-modified T cells leads to the formation of self-reactive TCRs that are responsible for the observed autoimmunity. Furthermore, we demonstrate that adjustments in the design of gene therapy vectors and target T cell populations can be used to reduce the risk of TCR gene therapy-induced autoimmune pathology.