Mouse Model Of Immune Thrombocytopenia Research Articles

A novel small molecule phagocytosis inhibitor, KB-208, ameliorates ITP in mouse models with similar efficacy as IVIG.

The characteristic feature of immune cytopenias involves the process of extravascular phagocytosis, wherein macrophages in the spleen and/or liver engage in the destruction of blood cells that have been opsonized by auto- or alloantibodies. Therefore, new treatments that prevent phagocytosis will be advantageous, especially for short-term usage along with alternative options. KB-208, a small molecule drug, previously shown to be efficacious for the in vitro inhibition of phagocytosis was synthesized. A passive antibody mouse model of immune thrombocytopenia (ITP) was used. Three different mouse strains (BALB/c, C57BL/6, CD1) were used to determine the efficacy of KB-208 compared with IVIG to ameliorate the ITP. Toxicity was investigated after 60-day chronic administration of KB-208 by a biochemistry panel, gross necroscopy and histopathology. KB-208 showed similar efficacy to ameliorate the thrombocytopenia compared with IVIG in all three mouse strains. This small molecule drug was effective at 1 mg/kg in ameliorating ITP, in comparison with IVIG at 1000-2500 mg/kg. KB-208 did not affect other blood parameters or elevate serum biochemistry markers of toxicity nor were any abnormal histopathological findings found. KB-208 is similar to IVIG for the amelioration of ITP in multiple mouse strains. Chronic administration of KB-208 for 60 days did not demonstrate in vivo toxicity. These findings indicate that KB-208 is efficacious, without significant in vivo toxicities in mice, and is a potential small molecule candidate for further evaluation to be used in the treatment of ITP and possibly all immune cytopenias where phagocytosis is responsible for the pathophysiology.

Activation of the HMGB1-TLR4 pathway impacts the functionality of bone marrow mesenchymal stem cells and disrupts macrophage polarization in immune thrombocytopenia.

Recent evidence suggests that immune thrombocytopenia (ITP), a common bleeding disorder, is linked to an imbalance in macrophage polarization and impaired bone marrow mesenchymal stem cells (BMSCs). However, the relationship between macrophage polarization imbalance and functional defects in BMSCs, as well as the involvement of associated molecules in BMSCs' defects, is not well understood. This study aimed to investigate the regulatory effects of high mobility group protein 1 (HMGB1) on the physiological functions of BMSCs, specifically in relation to macrophage polarization imbalance. Patients with ITP showed dysregulation in monocyte/macrophage polarization and impaired BMSCs function. HMGB1 was found to have a negative impact on the ability of BMSCs to regulate the imbalance in macrophage polarization, especially when inflammatory factors are present. The MyD88-dependent pathway downstream of BMSCs was found to be significantly enhanced with HMGB1 treatment. Furthermore, treatment with toll-like receptor 4 (TLR4) inhibitors successfully restored the regulatory capacity of BMSCs in ameliorating macrophage polarization imbalance and effectively inhibited the activation of the MyD88-dependent pathway. Meanwhile, infusion of si-TLR4-BMSCs reversed HMGB1-induced platelet dysfunction and reduced over-polarization to M1-like macrophages in the ITP mouse model. Consequently, targeting the HMGB1-TLR4 pathway could be a potential approach to restore the immunoregulatory function of BMSCs.

YAP1 regulates thrombopoiesis by binding to MYH9 in immune thrombocytopenia

AbstractImmune thrombocytopenia (ITP) is a complicated bleeding disease characterized by a sharp platelet reduction. As a dominating element involved in ITP, megakaryocytes (MKs) are responsible for thrombopoiesis. However, the mechanism underlying the dysregulation of thrombopoiesis that occurs in ITP remains unidentified. In this study, we examined the role of Yes-associated protein 1 (YAP1) in thrombopoiesis during ITP. We observed reduced YAP1 expression with cytoskeletal actin misalignment in MKs from patients with ITP. Using an experimental ITP mouse model, we showed that reduced YAP1 expression induced aberrant MK distribution, reduced the percentage of late MKs among the total MKs, and caused submaximal platelet recovery. Mechanistically, YAP1 upregulation by binding of GATA-binding protein 1 to its promoter promoted MK maturation. Phosphorylated YAP1 promoted cytoskeletal activation by binding its WW2 domain to myosin heavy chain 9, thereby facilitating thrombopoiesis. Targeting YAP1 with its activator XMU-MP-1 was sufficient to rescue cytoskeletal defects and thrombopoiesis dysregulation in YAP1+/− mice with ITP and patients. Taken together, these results demonstrate the crucial role of YAP1 in thrombopoiesis, providing potential for the development of diagnostic markers and therapeutic options for ITP.

Iguratimod Could Correct the Defective IL-35-Mediated Megakaryopoiesis in Immune Thrombocytopenia

Introduction: IL-35 is an inhibitory cytokine of the IL-12 family, and comprises an EBI3 subunit and a p35 subunit. Previous data indicated that serum levels of IL-35 were significantly lower in immune thrombocytopenia (ITP) patients than in healthy controls. Moreover, the concentration of plasma IL-35 in ITP patients achieving complete response returned to normal, but was not corrected in those who failed to achieve response. However, the underlying pathological function of IL-35 in impaired megakaryopoiesis in ITP remains unexplored. Our study aimed to evaluate the immunoregulatory role of IL-35 in megakaryocytes (MKs) differentiation. Iguratimod, a traditional therapy for inflammatory disorders, has been demonstrated to promote megakaryopoiesis. The effect of iguratimod on the treatment of ITP was retrospectively reviewed. Methods: Bone marrow samples were obtained from newly-diagnosed primary ITP patients and healthy donors. CD34+ cells from ITP patients and healthy donors were differentiated into MKs with and without IL-35 to determine the mechanism of IL-35 in megakaryopoiesis. Iguratimod was added to the culture medium of MKs to determine its function in MKs differentiation. Additionally, ITP mouse model was established to further validate the function of IL-35. Results: In comparison with healthy controls, ITP patients showed lower bone marrow levels of IL-35. IL-35 receptor expression was progressively induced on bone marrow MKs from healthy controls during the differentiation of CD34+ progenitors. In contrast, MKs from ITP patients exhibited defective expression of the IL-35 receptor. We then determined the effect of IL-35 on the megakaryocytic potential of CD34+ progenitor cells in culture medium containing TPO. IL-35 increased the number of medium-sized and large-sized colonies, and increased the total number of CD41+ cells. In IL-35-treated MKs, higher levels of Akt phosphorylation were observed. Pretreatment with LY294002, an inhibitor of Akt phosphorylation, blocked the differentiation of MKs induced by IL-35. LY294002 inhibited proplatelet formation and aggregation of β1-tubulin in MKs stimulated by IL-35. Flow cytometry analysis revealed that platelet production decreased in the LY294002 pretreatment group. These results demonstrated that IL-35 can enhance the proliferation and differentiation of MKs through Akt pathways. The decreased level of bone marrow IL-35 may partially explain the defective megakaryopoiesis in ITP. We then explored the potential causes of the decreased IL-35 levels in ITP. Flow cytometry analysis showed that the percentage of bone marrow iTr35 cells, the primary sources of IL-35, was significantly lower in ITP patients. Furthermore, we cocultured CD4+ T cells with MSCs from healthy controls and ITP patients, respectively. The percentage of iTr35 cells was lower when cultured with ITP-MSCs. These results showed that ITP-MSCs exhibited an impaired capability of inducing iTr35 cells, which might contribute to the reduced level of bone marrow IL-35 in ITP patients. We further investigated the effects of iguratimod on the differentiation of CD34+ progenitors into MKs. When CD34+ cells were cultured with TPO alone, the addition of iguratimod upregulated the expression of IL-35 receptors on MKs from ITP patients and a murine model of this disease, and consequently promoted the formation of MK colonies. In the retrospective study of iguratimod, a total of 68 adult patients with corticosteroid-resistant primary ITP were included. Initial response was achieved in 42/68 (62%) patients, and complete response was achieved in 25/68 (37%) patients. In patients who achieved initial response, the median time to response was 28 days. Sustained response at 6 months was seen in 35/68 (51%). Bleeding symptoms were reduced from 37/68 (54%) patients at baseline to 14/68 (21%) patients at 6 months. Most adverse events were mild (grade 1-2), and there were no grade 4 or worse adverse events in our patients. The most common adverse events were elevated ALT, gastrointestinal disorders, and nausea. Conclusions: ITP-MSCs exhibited an impaired capability of inducing iTr35 cells, which contributed to the reduced level of bone marrow IL-35 in ITP. IL-35 promoted MKs differentiation through the Akt pathway. Iguratimod promoted megakaryopoiesis by inducing the expression of IL-35 receptors on MKs. Iguratimod had good efficacy and safety in the treatment of ITP.

Study on the Treatment of ITP Mice with IVIG Sourced from Distinct Sex-Special Plasma (DSP-IVIG).

Intravenous immunoglobulin (IVIG) is a first-line drug prepared from human plasma for the treatment of autoimmune diseases (AIDs), especially immune thrombocytopenia (ITP). Significant differences exist in protein types and expression levels between male and female plasma, and the prevalence of autoimmune diseases varies between sexes. The present study seeks to explore potential variations in IVIG sourced from distinct sex-specific plasma (DSP-IVIG), including IVIG sourced from female plasma (F-IVIG), IVIG sourced from male plasma (M-IVIG), and IVIG sourced from a blend of male and female plasma (Mix-IVIG). To address this question, we used an ITP mouse model and a monocyte-macrophage inflammation model treated with DSP IVIG. The analysis of proteomics in mice suggested that the pathogenesis and treatment of ITP may involve FcγRs mediated phagocytosis, apoptosis, Th17, cytokines, chemokines, and more. Key indicators, including the mouse spleen index, CD16+ macrophages, M1, M2, IL-6, IL-27, and IL-13, all indicated that the efficacy in improving ITP was highest for M-IVIG. Subsequent cell experiments revealed that M-IVIG exhibited a more potent ability to inhibit monocyte phagocytosis. It induced more necrotic M2 cells and fewer viable M2, resulting in weaker M2 phagocytosis. M-IVIG also demonstrated superiority in the downregulation of surface makers CD36, CD68, and CD16 on M1 macrophages, a weaker capacity to activate complement, and a stronger binding ability to FcγRs on the THP-1 surface. In summary, DSP-IVIG effectively mitigated inflammation in ITP mice and monocytes and macrophages. However, M-IVIG exhibited advantages in improving the spleen index, regulating the number and typing of M1 and M2 macrophages, and inhibiting macrophage-mediated inflammation compared to F-IVIG and Mix-IVIG.

MST4 kinase regulates immune thrombocytopenia by phosphorylating STAT1-mediated M1 polarization of macrophages.

Primary immune thrombocytopenia (ITP) is an autoimmune hemorrhagic disorder in which macrophages play a critical role. Mammalian sterile-20-like kinase 4 (MST4), a member of the germinal-center kinase STE20 family, has been demonstrated to be a regulator of inflammation. Whether MST4 participates in the macrophage-dependent inflammation of ITP remains elusive. The expression and function of MST4 in macrophages of ITP patients and THP-1 cells, andof a macrophage-specific Mst4-/- (Mst4ΔM/ΔM) ITP mouse model were determined. Macrophage phagocytic assays, RNA sequencing (RNA-seq) analysis, immunofluorescence analysis, coimmunoprecipitation (co-IP), mass spectrometry (MS), bioinformatics analysis, and phosphoproteomics analysis were performed to reveal the underlying mechanisms. The expression levels of the MST4 gene were elevated in the expanded M1-like macrophages of ITP patients, and this elevated expression of MST4 was restored to basal levels in patients with remission after high-dose dexamethasone treatment. The expression of the MST4 gene was significantly elevated in THP-1-derived M1 macrophages. Silencing of MST4 decreased the expression of M1 macrophage markers and cytokines, and impaired phagocytosis, whichcould be increased by overexpression of MST4. In a passive ITP mouse model, macrophage-specific depletion of Mst4 reduced the numbers of M1 macrophages in the spleen and peritoneal lavage fluid, attenuated the expression of M1 cytokines, and promoted the predominance of FcγRIIb in splenic macrophages, which resulted in amelioration of thrombocytopenia. Downregulation of MST4 directly inhibited STAT1 phosphorylation, which is essential for M1 polarization of macrophages. Our study elucidates a critical role for MST4 kinase in the pathology of ITP and identifies MST4 kinase as a potential therapeutic target for refractory ITP.

Resveratrol inhibits AhR/Notch axis and reverses Th17/Treg imbalance in purpura by activating Foxp3.

Resveratrol has been reported to reverse the imbalance of T helper 17/regulatory T (Th17/Treg) by inhibiting the aryl hydrocarbon receptor pathway to treat immune thrombocytopenia. However, the regulation mechanism of the Notch signaling pathway by resveratrol has not been reported in purpura. This study is aimed to explore the mechanism of resveratrol ultrafine nanoemulsion (Res-mNE) in immune thrombocytopenia. The immune thrombocytopenia mouse model was constructed to explore the effect of RES-mNE on immune thrombocytopenia. Cluster of differentiation 4 (CD4+) T cells were isolated and treated with different medications. CD4+ T cells were induced to differentiate into Th17 cells and Treg cells. Flow cytometry was used to detect the proportion of Th17 cells and Treg cells. The secretion was measured by the enzyme-linked immunosorbent assay (ELISA). Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and western blot were used to detect the mRNA and protein levels. Th17 cells, IL-17A and IL-22 increased in the immune thrombocytopenia mouse model, and the Treg cells and IL-10 decreased. Res-mNE promoted Treg cell differentiation and IL-10 secretion in CD4+ T cells while inhibiting Th17 cell differentiation and IL-17A and IL-22 levels. The AhR activator 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reversed the effect of Res-mNE. Notch inhibitors reduced the ratio of Th17/Treg differentiation. Res-mNE activated the expression of Foxp3 by mediating AhR/Notch signaling to reverse the imbalance of Th17/Treg differentiation in immune thrombocytopenia. Taken together, our findings demonstrated that RES-mNE inhibited the AhR/Notch axis and reversed Th17/Treg imbalance by activating Foxp3.

β2-adrenergic receptor agonist corrects immune thrombocytopenia by reestablishing the homeostasis of T cell differentiation

BackgroundThe sympathetic nerve is known to regulate immune responses in autoimmunity. Aberrant T cell immunity plays a vital role in immune thrombocytopenia (ITP) pathogenesis. The spleen is the primary site of platelet destruction. However, little is known whether and how splenic sympathetic innervation and neuroimmune modulation contribute to ITP pathogenesis. ObjectivesTo determine the sympathetic distribution in the spleen of ITP mice and the association between splenic sympathetic nerves and T cell immunity in ITP development, and to evaluate the treatment potential of β2-adrenergic receptor (β2-AR) in ITP. MethodsChemical sympathectomy was performed in an ITP mouse model with 6-hydroxydopamine and treated with β2-AR agonists to evaluate the effects of sympathetic denervation and activation. ResultsDecreased sympathetic innervation in the spleen of ITP mice was observed. Significantly increased percentages of Th1 and Tc1 cells and reduced percentages of regulatory T cells (Tregs) were also observed in ITP mice with chemical sympathectomy (ITP-syx mice) relative to mice without sympathectomy (controls). Expression of genes associated with Th1, including IFN-γ and IRF8, was significantly upregulated, whereas genes associated with Tregs, including Foxp3 and CTLA4, were significantly downregulated in ITP-syx mice compared with controls. Furthermore, β2-AR restored the percentage of Tregs and increased platelet counts at days 7 and 14 in ITP mice. ConclusionOur findings indicate that decreased sympathetic distribution contributes to ITP pathogenesis by disturbing the homeostasis of T cells and that β2-AR agonists have potential as a novel treatment for ITP.

S290: ATRA CAN CORRECT DEFECTIVE HIF-1Α/S1P AXIS-MEDIATED CYTOSKELETAL REORGANIZATION IN PROPLATELET FORMATION OF ITP

Background: Bone marrow physiological hypoxia plays a crucial role in haematopoietic stem cell homeostasis. Hypoxia inducible factor (HIF) is central to mediating the cellular response to hypoxia. HIF-1α expression was decreased in the bone marrow of patients with immune thrombocytopenia (ITP), and HIF-1α activation was shown to enhance megakaryopoiesis in mice. Recent studies suggest that “inside-out” signalling by S1P in megakaryocytes (MKs) plays a critical role in proplatelet formation (PPF) (Blood, 2013; J EXP MED, 2012). Our previous data indicated that impaired PPF contributed to the development of thrombocytopenia in ITP. To further explore the underlying mechanism of impaired PPF in ITP, we found that HIF-1α/S1P axis-mediated cytoskeletal reorganization was defective in the PPF of ITP. All-trans retinoic acid (ATRA), which has been shown to be a promising treatment option for ITP patients in our clinical studies (Blood, 2021; Lancet haematology, 2017; Lancet haematology, 2021), could restore cytoskeletal reorganization and correct impaired PPF. Aims: This study aimed to explore the role of hypoxia inducible factor-1α (HIF-1α) in proplatelet formation (PPF) and the underlying mechanisms of ATRA treatment in ITP patients. Methods: Thirty consecutive patients with newly diagnosed ITP and 30 healthy donors were included in our study. MKs were isolated from bone marrow samples. Targeted and untargeted metabolomic profiling through metabolomic analysis was performed to explore the relationship between the metabolome and ITP. Confocal microscopy and transmission electron microscopy were used to observe the PPF and cytoskeleton structure of ITP MKs. An ITP mouse model was established to observe the therapeutic effects of ATRA in the PPF. Results: In the present study, we observed that MKs displayed altered cytoskeletal reorganization and impaired proplatelet formation (PPF) in ITP patients. Targeted and untargeted metabolite profiling revealed a decreased sphingosine-1-phosphate (S1P) level in ITP. Downregulated sphingosine kinase 2 (SPHK2) expression in MKs accounted for the low level of S1P in ITP. S1P is essential for S1P receptor 1 (S1PR1) and Rac1 activation, Src family kinases (SFKs) activity, and subsequent cytoskeletal reorganization and PPF regulation. Moreover, we demonstrated that HIF-1α mediated SPHK2 activation and S1P production. Decreased HIF-1α levels were found in the MKs of patients with ITP, contributing to impaired PPF. We then investigated the effect of ATRA on PPF in ITP patients. ATRA upregulated HIF-1α and SPHK2 expression, increased S1P production and corrected impaired PPF in vitro. In an ITP mouse model, ATRA alleviated thrombocytopenia and restored cytoskeletal reorganization. ATRA corrected impaired PPF by upregulating HIF-1α expression. The exposure of ITP MKs to selective RARα (AM580) or RARγ (BMS961) agonists did not change PPF. However, the treatment of ITP MKs with a selective RARβ agonist (CD2314) significantly increased PPF. Furthermore, we found that the effect of ATRA on enhancing PPF in ITP MKs was reversed in the presence of an RARβ antagonist (CD2665). These data suggest that impaired PPF in ITP MKs is corrected by ATRA in a RARβ-dependent manner. Summary/Conclusion: Together, our data show that the HIF-1α/S1P axis mediates altered cytoskeletal reorganization and impaired PPF in ITP and suggest that ATRA correction of impaired PPF is a potential mechanistic explanation for the clinical efficacy of ATRA in ITP.

Hemostatic mechanism of the effect of Jianpi Yiqi Shexue decoction on vascular factors in immune thrombocytopenia model mice

To explore the hemostatic mechanism of Jianpi Yiqi Shexue decoction (JYSD) by regulating vascular factors in an immune thrombocytopenia (ITP) mouse model. An ITP mouse model was established by the passive-immune modeling method, and interventional drugs used were prednisone tablets and JYSD. The platelet count; vascular activity–related factors vWF, VCAM-1, and TM; and VEGF and bFGF were used as observational indicators. On the 8th day of administration, compared with the model group, platelet counts in the prednisone and JYSD groups increased (both P < .001). Compared with the control group, the levels of vWF, VCAM-1, and TM in the other groups were lower (all P < .05). The VCAM-1 level in the JYSD group was higher than that in the prednisone group ( P = .012), but without significant difference compared with the model group ( P = .051). The TM level in the JYSD group was the lowest ( vs. the model group, P = .047; vs. the prednisone group, P = .006). Compared with the control group, the IOD values of VEGF and bFGF in the other three groups were lower (all P < .01). The IOD values of VEGF in the prednisone and JYSD groups were both higher than those in the model group ( P = .002 and P < .001, respectively). The IOD values of bFGF among the model, prednisone, and JYSD groups were not statistically significant ( P > .05). A vascular factor disorder is involved in the pathogenesis of ITP. JYSD can increase the platelet count, upregulate VEGF expression, and reduce the TM level. JYSD has the same effect as prednisone tablets in regulating platelet, vWF, VEGF, and bFGF, with a stronger effect in normalizing VCAM-1 and TM levels. The hemostatic mechanism of JYSD is closely related to the effective balance of vascular factors.

Ker-050, an Inhibitor of TGF- β Superfamily Signaling, Promoted Thrombopoiesis and Reversed Immune Thrombocytopenia in a Mouse Model of Disease

KER-050 is a modified ActRIIA ligand trap that is designed to inhibit the activity of the TGF-β ligands, including activin A, activin B, GDF8 and GDF11, that act through the SMAD2/3 signaling cascade. Notably, in a Phase 1 clinical study we observed that, in addition to increases in red blood cells and hemoglobin, treatment with KER-050 elicited a robust and sustained increase in platelets (PLTs) in healthy volunteers. While ActRII ligand traps have been shown to increase erythropoiesis in preclinical and clinical studies, their role in thrombopoiesis has not yet been well-elucidated.A variety of conditions exist where hematopoiesis is impaired and cytopenia persists, including comorbidities associated with aging, diseases causing ineffective hematopoiesis such as myelodysplastic syndrome (MDS) and myelofibrosis (MF), and acute bleeding. Thrombocytopenia can arise from primary or secondary causes due to multiple etiologies and treatments are limited, aiming at treating the root cause of disease or replacing PLTs through transfusion. Therefore, there is an unmet medical need for more targeted treatments to correct thrombocytopenia. Here, in a series of preclinical studies, we investigated the mechanism of action of KER-050 on thrombopoiesis and evaluated its ability to accelerate recovery from acute platelet depletion.First, we examined how RKER-050 (a research form of KER-050) affected thrombopoiesis under homeostatic conditions. We observed that a single intraperitoneal dose of RKER-050 (10 mg/kg) to 11-week-old mice resulted in a 2-fold increase in PLTs compared to vehicle-treated mice 12 hours after treatment. The timing of the effect is suggestive of a direct effect of RKER-050 on terminal platelet maturation. Additionally, there was a 35% increase in the number of bone marrow (BM) megakaryocyte (Mk) progenitors (Lin -; sca1 -; cKit -; CD41 + cells), demonstrating that RKER-050 affected earlier stages of the PLT formation process. We also evaluated the effect of RKER-050 on the polyploidization of Mks, a hallmark of Mk differentiation. At 24 hours after treatment with RKER-050, there was an increase in BM CD41 + cells with ploidy greater than 16N compared to vehicle-treated mice, demonstrating that RKER-050 treatment resulted in a greater number of Mk that are potentially primed for platelet production. Taken together, these data are consistent with RKER-050 affecting multiple stages of thrombopoiesis in a preclinical model.We next tested whether RKER-050 affects PLTs in a mouse model of immune thrombocytopenia (IT) where antibodies directed against mouse GPIbα result in acutely reduced PLT numbers. In this model, mice receiving anti-GPIbα had a 25% reduction in PLT number at 4 days post-dose compared to IgG control-treated mice. At this point, the anti-GPIba cohort was divided into receiving either a single dose of vehicle or RKER-050. On day 7 following anti-GPIbα treatment, PLT counts in vehicle-treated mice were 62% lower compared to IgG-control-treated mice. In contrast, the GPIbα-mediated effect on PLT count was stabilized in the anti-GPIbα + RKER-050 group, which had 55% more platelets compared to the anti-GPIba + vehicle group. These data suggest that RKER-050 promoted thrombopoiesis in mice even under conditions when the system is acutely challenged and potentially could promote faster recovery from thrombocytopenia. Additionally, we observed a 25% increase in the number of CD41 + cells in the BM of the RKER-050-treated group compared to the vehicle-treated group at day 10 after PLT depletion, suggesting that under acute thrombocytopenia, RKER-050 treatment promoted differentiation of Mks as a mechanism of the accelerated recovery in platelet-depleted mice.In summary, our preclinical data demonstrate a potentially novel effect of RKER-050 on thrombopoiesis. RKER-050 treatment resulted in a rapid increase in PLTs, consistent with an effect on terminal maturation. Treatment also increased the number of Mk progenitors and increased the number of polyploid Mks, demonstrating an effect on early stages of thrombopoiesis. These findings support that RKER-050-targeted ligands regulate multiple stages of the thrombopoiesis pathway in mice. Additionally, our data demonstrate that KER-050 has the potential to accelerate the rate of PLT recovery due to acute depletion, and could represent a potential novel treatment option for thrombocytopenia in patients with MDS, MF and IT. DisclosuresFeigenson: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Nathan: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Lamora: Keros Therapeutics: Current Employment. Fisher: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Tseng: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Seehra: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company. Lachey: Keros Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees.

A Novel Allogeneic Cell Therapy That Targets Pathogenic Autoantibodies for the Treatment of Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet counts (<100x10 9/L) and increased risk of bleeding. ITP is predominantly driven by immunoglobulin G (IgG)-autoantibodies directed against platelet surface antigens resulting in platelet destruction by the spleen and/or impaired platelet production by bone marrow megakaryocytes. Approximately 60% of ITP patients have measurable levels of anti-platelet autoantibodies in plasma and about 70% of them have autoantibodies directed against the fibrinogen receptor glycoprotein (GP) IIbIIIa.Current treatment strategies for ITP include non-specific immunosuppression (steroids, rituximab), inhibition of platelet clearance (immunoglobulins, splenectomy, anti-D immunoglobulin, and the Syk inhibitor fostamatinib) and stimulation of platelet production (thrombopoietin receptor agonists). In addition, therapeutics targeting the neonatal Fc receptor, responsible for IgG recycling, are under clinical investigation for ITP. Despite these treatment options, some patients with ITP are refractory or have inadequate responses to existing therapy.Here we describe a novel allogeneic cellular therapy, entitled platelet-like cells (PLC), that specifically targets pathogenic IgG for the treatment of thrombocytopenia in ITP. PLC are produced by differentiating a human induced pluripotent stem cell (hiPSC) line into megakaryocyte-like cells (MLC) which are further processed in a proprietary bioreactor that mimics the bone marrow environment and induces the release of anucleate PLC which are then cryopreserved. Analyses of PLC demonstrate sizes ranging between 65 nm and 10 μm. Expression of GPIIbIIIa protein as measured by enzyme-linked immunosorbent assay (ELISA) is evident in all particle sizes. PLC were administered intravenously (IV) into NOD-scid IL2Rgamma null (NSG) mice to evaluate their pharmacokinetics and biodistribution. PLC were rapidly cleared from the mouse circulation and predominantly distributed to the mouse liver where they colocalized primarily with Kupffer cells. PLC clearance through the liver was significantly inhibited by pre-treating mice with liposomes expressing phosphatidylserine (PS), indicating that one mechanism of PLC clearance is dependent on PS exposure on the PLC outer plasma membrane.The ability of PLC to bind anti-GPIIbIIIa autoantibodies was evaluated in an in vitro assay where PLC were incubated with ITP patient plasmas and subsequently removed by centrifugation and filtration. The concentration of anti-GPIIbIIIa autoantibodies remaining in the plasmas decreased following PLC treatment (96.6% ± 2.4%).The ability of PLC to clear anti-human GPIIbIIIa antibodies in circulation was evaluated by using a passive mouse model of ITP. Here, a fluorescently labeled mouse anti-human GPIIbIIIa monoclonal antibody (PAB-1) was dosed intravenously (IV) into NSG mice to achieve a circulating level of antibody comparable to those observed in ITP patients. The GPIIbIIIa antibody persisted in circulation for over 24 hours following a single dose in untreated mice and did not induce clearance of mouse platelets. Following administration of PLC in the passive ITP model, a decrease in antibody fluorescence in blood was observed within 2 minutes and full antibody clearance was observed at 3 hours post dosing. Furthermore, clearance of the antibody was observed to be both dose responsive and specific since PLC treatment did not affect the antibody concentration of an isotype matched control antibody. PLC activity in clearing the anti-GPIIbIIIa antibody was observed in all particle sizes. Fluorescence quantification of liver and spleen tissue demonstrated that PLC driven anti-GPIIbIIIa antibody clearance occurred preferentially in the liver. Taken together, these data indicate that by specifically binding and rapidly removing anti-platelet antibodies from circulation, PLC may disrupt the platelet degradation mechanisms underlying ITP pathogenesis and restore platelet counts. DisclosuresPatel-Hett: PlateletBio: Current Employment. Giannini: Platelet Biogenesis: Current Employment. Peters: Platelet Biogenesis: Current Employment. Dykstra: Platelet Biogenesis: Current Employment. Lehmann: Platelet Biogenesis: Current Employment. Russo: Platelet Biogenesis: Current Employment. Kohnke: Platelet Biogenesis: Current Employment. Carpenter: Platelet Biogenesis: Current Employment. Tomczak: Platelet Biogenesis: Current Employment. Lazarus: Platelet Biogenesis: Consultancy. Masuko: Platelet Biogenesis: Current Employment. Leung: Platelet Biogenesis: Current Employment. Meredith: Platelet Biogenesis: Current Employment. Pete: Platelet Biogenesis: Current Employment. Lee: Platelet Biogenesis: Current Employment. Falb: Platelet Biogenesis: Current Employment.

Blockade of the Neonatal Fc Receptor (FcRn) Represents an Effective Mechanism for the Removal of Pathogenic Autoantibodies in Primary Immune Thrombocytopenia

Introduction: The neonatal Fc receptor, FcRn is ubiquitously expressed, & is responsible for maintaining the half-life of IgG & albumin, by rescuing these proteins from intracellular lysosomal degradation. Blockade of the interaction of FcRn with IgG would be expected to prevent salvage of both non-pathogenic and pathogenic IgG. Patients with primary immune thrombocytopenia (ITP) have autoantibodies against platelet membrane proteins such as the cell adhesion receptor CD61/CD41 (GPIIb/IIIa). Rozanolixizumab (a high affinity IgG4 monoclonal antibody (mAb) that specifically inhibits IgG binding to FcRn) is currently being evaluated in phase 2 clinical studies in patients with ITP. The aim of the current study was to understand the in vitro properties of rozanolixizumab & to explore the in vivo effects of a surrogate anti-mouse FcRn mAb (murinized “4464”) in a mouse model of ITP.Methods: The affinity of rozanolixizumab for FcRn was tested using surface plasmon resonance technology (Biacore), with the antibody captured by an anti-Fc immobilized on the sensor chip & soluble FcRn in solution, whilst the affinity of fluorescently labelled rozanolixizumab for human FcRn expressed on the surface of Madin-Darby canine kidney (MDCK) cells was measured by flow cytometry. Recycling & transcytosis of human IgG (hIgG) was also assessed in FcRn-transfected MDCK cells. For IgG tracking experiments, endothelial & epithelial cell lines were incubated with an AF647-conjugated IgG for 24 hours in the presence or absence of rozanolixizumab. Prior to imaging, nuclei were labelled using Hoechst at 37°C & cells were then visualized by fluorescence microscopy. Phagocytosis of anti-human MHC I (W6/32)-coated platelets by THP-1 cells was assessed by flow cytometry at 1 hour. The effect of rozanolixizumab on IgG recycling in vivo was assessed in the human FcRn-transgenic (hFcRn-Tg) mouse: hIgG at 500mg/kg was administered IV to mice on day 1 & dosed with antibodies on day 2; serial bleeds were then taken at multiple time points post antibody dosing & levels of hIgG, albumin & rozanolixizumab were quantified using LC-MS/MS. For the induction of ITP in mice, animals received an anti-CD41 antibody (MWReg30), delivered by osmotic minipump (~1µg of antibody delivered every 24 hours) & the anti-mouse FcRn mAb (4464) was administered at 30mg/kg either on days 0, 2 & 4 (prophylactic dosing) or on days 3 & 5 (therapeutic dosing); IVIg (1g/kg) was also evaluated & control mice received either PBS or an isotype-matched control mAb (101.4). Daily blood samples were taken to assess platelet numbers.Results: Rozanolixizumab has a high affinity for FcRn in a protein-protein (Biacore) assay with a KD of ~25pM at both pH6.0 & pH7.4; in the cell-based assay, the affinity was 1nM at both pH's. Rozanolixizumab efficiently inhibited the recycling & transcytosis of IgG in human FcRn-transfected MDCK cells (IC50 0.4nM & 1.1nM, respectively). Confocal microscopy experiments showed that there was an increased accumulation of IgG in cells in the presence of rozanolixizumab, relative to an isotype control mAb, & that the IgG was co-localized in lysosomes where it appeared to be degraded. FcRn has been postulated to play a direct role in phagocytosis, but the phagocytosis of opsonized platelets by THP-1 cells was unaffected by blockade with rozanolixizumab. Treatment with rozanolixizumab resulted in a dose-dependent accelerated clearance of hIgG in the hFcRn-Tg mouse; hIgG levels in all treated groups were significantly lower vs PBS controls from 24 hours post-dosing until the end of the experiment 8 days post dosing (p<0.01). No effect on albumin levels occurred in these mice. In the mouse model of ITP, both prophylactic & therapeutic treatment regimens with 4464 resulted in an increased number of platelets compared to control animals that received either PBS or 101.4. Animals that received 4464 from day 0 had significantly greater platelet numbers than control animals on days 4 & 5 (p<0.05); therapeutic dosing gave a significantly greater platelet number than control animals on day 5 (p<0.05).Conclusion: Rozanolixizumab is a high affinity mAb that inhibits the IgG recycling function of FcRn in vitro &in vivo . An anti-mouse FcRn mAb demonstrated efficacy in a mouse model of ITP. These data support the evaluation of rozanolixizumab in patients with ITP, & a phase 2 clinical study is currently ongoing in this patient population. DisclosuresEddleston:UCB Pharma: Employment. Greenslade:UCB Pharma: Employment. Qureshi:UCB Pharma: Employment. West:UCB Pharma: Employment. Atherfold:UCB Pharma: Employment. Amirkhosravi:UCB Pharma: Research Funding. Desai:UCB Pharma: Research Funding. Rivera-Amaya:UCB Pharma: Research Funding. Smith:UCB Pharma: Consultancy, Equity Ownership. Shock:UCB Pharma: Employment.

PRN1008, a Reversible Covalent BTK Inhibitor in Clinical Development for Immune Thrombocytopenic Purpura

PRN1008 is an oral, reversible covalent inhibitor of Bruton's tyrosine kinase (BTK) in clinical development for the treatment of multiple autoimmune diseases. BTK is an essential signaling element downstream of the B cell receptor (BCR), Fc-gamma receptor and Fc-epsilon receptor pathways. BTK activation is critical for B cell activation and maturation. BTK also regulates antibody mediated activation of other immune cells, such as macrophages, neutrophils and mast cells through Fc receptor signaling.Treatment with PRN1008 in vitro profoundly inhibited B cell activation and blocked antibody mediated activation of immune cells via Fc receptor signaling. In preclinical studies, PRN1008 demonstrated a significant dose-dependent reduction of platelet-loss in an anti-CD41 induced mouse model of immune thrombocytopenia. In addition, PRN1008 showed rapid and significant anti-inflammatory effects in an antibody driven rat arthus model and in spontaneous autoantibody-mediated canine pemphigus foliaceus. The preclinical data suggest that PRN1008 could reduce platelet destruction via inhibition of autoantibody/Fc-gamma receptor signaling in splenic macrophages, and also affect autoantibody generation through effects on B-cell activation, to diminish platelet loss in ITP.Platelets express high levels of BTK, however alternative signaling pathways exist which bypass BTK signaling to retain normal platelet functions. The effect of PRN1008 on platelet function was assessed in vitro in both normal healthy volunteer and ITP patient platelets using a standard panel of platelet agonists. In contrast to ibrutinib, treatment with PRN1008 at clinically relevant concentrations did not impact collagen-induced platelet aggregation in either normal or ITP patient platelet samples, or interfere with responses to all other platelet agonists tested. In the clinic, PRN1008 has been well tolerated. Thrombocytopenia, bleeding or bruising signals have not been reported. An analysis of platelet counts from the ongoing 12 week study of pemphigus vulgaris (NCT02704429) showed no evidence of an effect of PRN1008 on platelet counts in the normal range.Principia Biopharma is developing PRN1008 for the treatment of autoimmune diseases including ITP, blistering skin diseases such as pemphigus vulgaris and other immunologic disorders where autoantibodies and/or B-cell signaling are pathogenic. DisclosuresLangrish:Principia Biopharma: Employment. Bradshaw:Principia Biopharma: Employment. Owens:Principia Biopharma: Employment. Campbell:Principia Biopharma: Employment. Francesco:Principia Biopharma: Employment. Karr:Principia Biopharma: Employment. Murray:Principia Biopharma: Employment. Quesenberry:Principia Biopharma: Employment. Smith:Principia Biopharma: Consultancy. Taylor:Principia Biopharma: Consultancy. Zhu:Principia Biopharma: Employment. Nunn:Principia Biopharma: Employment. Gourlay:Principia Biopharma: Employment.

Mesenchymal Stem Cells Improve Platelet Counts in Mice with ITP

INTRODUCTION: Patients with chronic refractory immune thrombocytopenia (ITP) have the high risk of death and complications, which urge us to seek for new treatment alternatives. Currently, bone marrow-derived mesenchymal stem cells (BMSCs) have been extensively utilized for autoimmune diseases. However, it is still lack of evidence in vivo about the therapeutic benefits and the possible underlying mechanisms of BMSCs in ITP, which is also known as an acquired autoimmune disease. In this study, we transplanted BMSCs into a passive ITP mouse model to explore the therapeutic effects and immunosuppressive mechanisms of BMSCs in ITP disease.METHODS: The passive ITP mouse model was induced by dose-escalation injection of monoclonal antibody MWReg30. Mice were randomly divided into two groups: experimental group (2-4×106 BMSCs were injected into each ITP mouse through the tail vein on Day 3) and control group (ITP mice). PLT counts were enumerated by an automatic blood cell counter. The serum levels of cytokines (IL-10 and TGF-β1) were examined by ELISAs and the frequency of Treg cells by flow cytometry. The statistical analysis was processed by SPSS software version 19.0.RESULTS: We successfully induced a passive ITP mouse model with very low levels of PLT counts for 8 days (PLT counts were reduced to half of the initial values by 24 hours and were relatively constant throughout the study). The PLT counts in experimental group on Day 4 to Day 8 were (263±17)×109/L, (482±35)×109/L, (367±38)×109/L, (385±107)×109/L, and (317±48)×109/L, which were significantly higher than those in control group [ (159±19)×109/L, (238±20)×109/L, (175±32))×109/L, (129±7)×109/L, and (170±16)×109/L, respectively ]. The levels of serum TGF-β1 and IL-10 were significantly higher in experimental group compared with the control group [ (116.61±12.59)pg/ml and (348.89±44.49)pg/ml vs. (72.78±15.70) pg/ml and (134.61±27.59)pg/ml; p <0.05]. The ratios of Treg cells both in splenocytes and peripheral blood were significantly higher after transplantation of BMSCs [ (15.79±0.55)% and (6.37±0.45)% vs. (10.25±0.55)% and (4.80±0.26)%; p<0.05].CONCLUSIONS: BMSCs transplantation is an effective treatment for ITP in mice. The key mechanisms underlying the positive therapeutic impact may due to the BMSCs secreting suppressive cytokines TGF-β1 and IL-10 and increasing the proportion of Treg cells, which play key roles in both the maintenance of immune tolerance and the inactivation of macrophage. DisclosuresNo relevant conflicts of interest to declare.

Helicobacter pylori Regulates the Apoptosis of Human Megakaryocyte Cells via NF-κB/IL-17 Signaling.

ObjectiveTo investigate the role of Helicobacter pylori (HP) on the regulation of NF-κB/IL-17 signaling, mechanisms underlying apoptosis in human megakaryocyte cell lines Dami.MethodsFirstly, the mouse model of immune thrombocytopenia (ITP) was established. Then, the mice were subjected to gastric perfusion with HP. Next, the changes in platelet and bone marrow megakaryocyte classification were assessed in each group. Human megakaryocyte Dami cells were treated with HP in vitro for 3, 6, or 9 h; and the rates of apoptosis in each group were then evaluated with flow cytometry. Fluorescent quantitative PCR and Western blotting were implemented for assessing the expression of Bcl-2 and Bax, which are related to apoptosis, and p65, which is associated with the NF-κB pathway. The expression of these proteins was also evaluated after treatment with PDTC, an inhibitor of the NF-κB pathway inhibitor.ResultsIn vivo, exogenous administration of HP was found to increase the optical density value for the anti-HP antibody in HP-infected BALB/c mice. Meanwhile, the platelet counts in the HP-infected ITP mice model were significantly reduced compared with non-infected ITP mice. In vitro, the apoptotic rate of Dami cells increased gradually with the prolongation of the exposure to HP; the most noticeable change was at 6 h, and there was a significant difference between 0 h and 6 h. The expression of Bax, p-p65, and IL-17 also increased progressively with the prolongation HP exposure, while the expression of anti-apoptotic Bcl-2 protein decreased gradually, especially at 6 h, and the expression of total p65 did not change significantly compared with baseline. Anecdotally, these effects were reversed by the application of pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB signaling.ConclusionHP can promote platelet destruction in ITP mice, and the underlying mechanisms may be related to accelerating apoptosis of megakaryocytes by the activation of the NF-κB/IL-17 pathway.

IVIg increases interleukin-11 levels, which in turn contribute to increased platelets, VWF and FVIII in mice and humans

The mechanisms of action of intravenous immunoglobulins (IVIg) in autoimmune diseases are not fully understood. The fixed duration of efficacy and noncumulative effects of IVIg in immune thrombocytopenia (ITP) and acquired von Willebrand disease (AVWD) suggest other mechanisms besides immunological ones. Additionally to the peripheral destruction of platelets in ITP, their medullary hypoproduction emerged as a new paradigm with rescue of thrombopoietin receptor agonists (TPO-RA). In an ITP mouse model, interleukin (IL)-11 blood levels increase following IVIg. IL-11 stimulates the production of platelets and other haemostasis factors; recombinant IL-11 (rIL-11) is thus used as a growth factor in post-chemotherapy thrombocytopenia. We therefore hypothesized that IVIg induces IL-11 over-production, which increases platelets, VWF and factor VIII (FVIII) levels in humans and mice. First, in an ITP mouse model, we show that IVIg or rIL-11 induces a rapid increase (72h) in platelets, FVIII and VWF levels, whereas anti-IL-11 antibody greatly decreased this effect. Secondly, we quantify for the first time in patients with ITP, AVWD, inflammatory myopathies or Guillain-Barré syndrome the dramatic IL-11 increase following IVIg, regardless of the disease. As observed in mice, platelets, VWF and FVIII levels increased following IVIg. The late evolution (4weeks) of post-IVIg IL-11 levels overlapped with those of VWF and platelets. These data may explain thrombotic events following IVIg and open perspectives to monitor post-IVIg IL-11/thrombopoietin ratios, and to assess rIL-11 use with or without TPO-RA as megakaryopoiesis co-stimulating factors to overcome the relative hypoproduction of platelets or VWF in corresponding autoimmune diseases, besides immunosuppressant.

Tacrolimus ameliorates thrombocytopenia in an ITP mouse model.

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by lower platelet count resulting from immune cells-mediated platelet clearance. Tacrolimus is an immunosuppressive agent which selectively inhibits T cell activation. Whether tacrolimus plays a role in ITP remains unclear. This study aimed to investigate the effect of tacrolimus on ITP in mice. An ITP mouse model was established by injection of rat anti-mouse integrin GPIIb/CD41 immunoglobulin and treated with tacrolimus followed by isolation of peripheral blood mononuclear cells and plasma. The mRNA expression of T-bet, GATA3, and Foxp3 was measured by RT-PCR, and level of IFN-γ, IL-12p70, IL-4, IL-13, and TGF-β in plasma was measured by ELISA. Tacrolimus inhibited antiplatelet antibody-mediated platelet clearance in ITP mouse model. Meanwhile, tacrolimus-treated ITP mice displayed a significant decrease in the mRNA expression of T-bet and plasma level of IFN-γ and IL-12p70 compared with ITP mice but without differences when compared with normal mice. Furthermore, the expression of GATA3, Foxp3, and plasma level of IL-4 and TGF-β were upregulated in tacrolimus-treated ITP mice without significant differences to normal mice (except TGF-β). Tacrolimus prevents antiplatelet antibody-mediated thrombocytopenia in ITP mice possibly through regulating T cell differentiations, suggesting it might be a novel approach for preventing ITP.

Downregulation of microRNA-155-5p prevents immune thrombocytopenia by promoting macrophage M2 polarization via the SOCS1-dependent PD1/PDL1 pathway

AimsWe set about to investigate the potential role of microRNA-155-5p (miR-155-5p) in the development of immune thrombocytopenia (ITP), an idiopathic deficiency of blood platelets. Main methodsInitially, RT-qPCR and Western blot analyses were carried out to determine the expression of miR-155-5p and SOCS1 in peripheral blood mononuclear cells (PBMCs) and macrophages from ITP patients. We undertook gain- and loss- function methods by transfection of macrophages and PBMCs with treated plasmids. The expression patterns of platelet-related factors were measured by ELISA, and the expressions of PD1, PDL1, and macrophage M2 marker CD206 and CD86 were also measured. The relationship between miR-155-5p and SOCS1 was determined using the dual-luciferase reporter gene assay. We also established an ITP mouse model to explore the roles of miR-155-5p and SOCS1 in vivo. Key findingsmiR-155-5p was up-regulated, while SOCS1 was down-regulated in PBMCs and macrophages from ITP patients. SOCS1 was indicated as a target of miR-155-5p. Inhibition of miR-155-5p or up-regulation of SOCS1 facilitated macrophage M2 polarization as demonstrated by an increased M2/M1 ratio and suppressed expression of platelet-related factors. Furthermore, silencing of SOCS1 promoted ITP progression through blocking the PD1/PDL1 pathway, whilst upregulation of miR-155-5p remarkably increased the platelet abundance and suppressed SOCS1 expression in ITP model mice. SignificanceSilencing of miR-155-5p could promote PD1/PDL1 pathway-mediated macrophage M2 polarization and prevent ITP via up-regulation of SOCS1, thus relieving ITP.

Three-Dimensional Culture of Umbilical Cord Mesenchymal Stem Cells Effectively Promotes Platelet Recovery in Immune Thrombocytopenia.

Mesenchymal stem cells (MSCs) can effectively regulate immune cell functions and therefore are promising for the treatment of autoimmune disorders, such as immune thrombocytopenia (ITP). Recent research has shown that three-dimensional (3D) culture method have many advantages over conventional culture with respect to MSC secretion and immunogenicity. In this study, 2D and 3D cultured MSCs were used to evaluate cytokine secretion, extracellular matrix (ECM) gene expression, immune regulatory activity, and therapeutic effects in a mouse model of ITP. MSCs cultured on scaffolds had higher expression levels of immune regulatory genes, such as IDO1, HLA-G, and PTGS2, and greater inhibitory activity against lymphocyte activation that those of 2D-MSCs. In addition, 3D-MSCs exhibited higher ECM expression and greater protection against interferon-γ (IFN-γ)-induced apoptosis. In a mouse study, ITP was induced by guinea pig anti-mouse platelet serum injections. Based on enzyme-linked immunosorbent assays, serum levels of the suppressive cytokine interleukin (IL)-10 were higher and IFN-γ levels were lower after intravenous injection with 3D-MSCs and with 2D-MSCs. Additionally, 3D-MSCs improved the body weight, spleen index, and platelet index relative to those for 2D-MSCs. Bone marrow homing was also significantly enhanced in the 3D group. Therefore, the 3D culture of MSCs is an effective technique for the treatment of ITP.