Abnormalities of the Bone Marrow Immune Microenvironment in Patients with Prolonged Isolated Thrombocytopenia after Allogeneic Hematopoietic Stem Cell Transplantation

Repair of dysfunctional bone marrow endothelial cells alleviates aplastic anemia

Aplastic anemia (AA) is a life-threatening disease characterized by bone marrow (BM) failure and pancytopenia. As an important component of the BM microenvironment, endothelial cells (ECs) play a crucial role in supporting hematopoiesis and regulating immunity. However, whether impaired BM ECs are involved in the occurrence of AA and whether repairing BM ECs could improve hematopoiesis and immune status in AA remain unknown. In this study, a classical AA mouse model and VE-cadherin blocking antibody that could antagonize the function of ECs were used to validate the role of BM ECs in the occurrence of AA. N-acetyl-L-cysteine (NAC, a reactive oxygen species scavenger) or exogenous EC infusion was administered to AA mice. Furthermore, the frequency and functions of BM ECs from AA patients and healthy donors were evaluated. BM ECs from AA patients were treated with NAC in vitro, and then the functions of BM ECs were evaluated. We found that BM ECs were significantly decreased and damaged in AA mice. Hematopoietic failure and immune imbalance became more severe when the function of BM ECs was antagonized, whereas NAC or EC infusion improved hematopoietic and immunological status by repairing BM ECs in AA mice. Consistently, BM ECs in AA patients were decreased and dysfunctional. Furthermore, dysfunctional BM ECs in AA patients led to their impaired ability to support hematopoiesis and dysregulate T cell differentiation toward proinflammatory phenotypes, which could be repaired by NAC in vitro. The reactive oxygen species pathway was activated, and hematopoiesis- and immune-related signaling pathways were enriched in BM ECs of AA patients. In conclusion, our data indicate that dysfunctional BM ECs with impaired hematopoiesis-supporting and immunomodulatory abilities are involved in the occurrence of AA, suggesting that repairing dysfunctional BM ECs may be a potential therapeutic approach for AA patients.

Checkpoint Inhibitors in Acute Myeloid Leukemia

The prognosis of acute myeloid leukemia (AML) remains unsatisfactory. Among the reasons for the poor response to therapy and high incidence of relapse, there is tumor cell immune escape, as AML blasts can negatively influence various components of the immune system, mostly weakening T-cells. Since leukemic cells can dysregulate immune checkpoints (ICs), receptor-based signal transductors that lead to the negative regulation of T-cells and, eventually, to immune surveillance escape, the inhibition of ICs is a promising therapeutic strategy and has led to the development of so-called immune checkpoint inhibitors (ICIs). ICIs, in combination with conventional chemotherapy, hypomethylating agents or targeted therapies, are being increasingly tested in cases of AML, but the results reported are often conflicting. Here, we review the main issues concerning the immune system in AML, the main pathways leading to immune escape and the results obtained from clinical trials of ICIs, alone or in combination, in newly diagnosed or relapsed/refractory AML.

Glucocorticoid and glycolysis inhibitors cooperatively abrogate acute graft-versus-host disease

Although glucorticosteroids (GCs) are the standard first-line therapy for acute graft-versus-host disease (aGvHD), nearly 50% of aGvHD patients have no response to GCs. The role of T cell metabolism in murine aGvHD was recently reported. However, whether GCs and metabolism regulators could cooperatively suppress T cell alloreactivity and ameliorate aGvHD remains to be elucidated. Increased glycolysis, characterized by elevated 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), and higher rates of glucose consumption and lactate production were found in T cells from aGvHD patients. Genetic upregulation of PFKFB3 induced T cell proliferation and differentiation into proinflammatory cells. In a humanized mouse model, PFKFB3-overexpressing or PFKFB3-silenced T cells aggravated or prevented aGvHD, respectively. Importantly, our integrated data from patient samples in vitro, in a humanized xenogeneic murine model of aGvHD and graft-versus-leukaemia (GVL) demonstrate that GCs combined with a glycolysis inhibitor could cooperatively reduce the alloreactivity of T cells and ameliorate aGvHD without loss of GVL effects. Together, the current study indicated that glycolysis is critical for T cell activation and induction of human aGvHD. Therefore, the regulation of glycolysis offers a potential pathogenesis-oriented therapeutic strategy for aGvHD patients. GCs combined with glycolysis inhibitors promises to be a novel first-line combination therapy for aGvHD patients.

Prognostic Value of Thrombocytopenia in Myelodysplastic Syndromes After Hematopoietic Stem Cell Transplantation

Prolonged isolated thrombocytopenia (PT) is a common complication affecting the outcome of stem cell transplantation. In this study, we undertook a real-world study of 303 myelodysplastic syndrome (MDS) patients who received allogeneic hematopoietic stem cell transplantation (HSCT) between December 2007 and June 2018. 28.4% of MDS patients suffered from PT after HSCT. Survival analysis indicated that PT was associated with worse overall survival (OS) in MDS patients. The 2-year and 5-year OS in MDS patients with PT after HSCT were 49% and 47%, significantly worse than that of 68% and 60% in patients without PT (P=0.005). For RFS, patients with PT did not have an increased risk of disease relapse (P=0.964). After multivariate adjustment, PT was proved to be the independent risk factor associated with the worse OS (HR 1.49, 95% CI 1.00-2.21, P =0.048). We further analyzed risk factors associated with the occurrence of PT in MDS patients. Multiple logistic regression identified grade II-IV aGVHD, extensive chronic GVHD, hemorrhagic cystitis, and CMV activation as significant risk factors for developing PT. Among these variables, the Odds Ratio (OR) of grade II-IV aGVHD was the highest (P =0.001, OR: 2.65, 95% CI: 1.51-4.64). These data indicated the prognostic value of PT in MDS after HSCT. The identification of risk factors for PT may help improve patient management and lead to the design of effective treatment strategies.

Analysis of the Efficacy and Safety of Avatrombopag Combined With MSCs for the Treatment of Thrombocytopenia After Allogeneic Hematopoietic Stem Cell Transplantation

Platelet graft failure (PGF) is a frequent and serious complication after Allogeneic hematopoietic stem cell transplantation (allo-HSCT) and lacks effective treatment strategies, which could affect the prognosis of patients and even cause death. The exact underlying mechanism of PGF remains unclear, and lacks standard treatment. Here, we conduct a retrospective study to evaluate the efficacy and safety of avatrombopag combined with mesenchymal stem cells (MSCs) in 16 patients with thrombocytopenia after allo-HSCT. Patients were administered the following treatment regimen: 20 mg/d avatrombopag; if the PLT count was less than 50×10^{^}9/L for at least 2 weeks, the dose was increased to 40 mg/d; if the PLT count was 200-400×10^{^}9/L, the dose was reduced; and if the PLT count was greater than 400×10^9/L, avatrombopag was terminated. Umbilical cord MSCs (1×10^{^}6 cells/kg) infusion was performed every week for 4-6 weeks. Among the 16 patients, 13 patients (81.3%) achieved a complete response (CR), 2 patients (12.5%) got a partial response (PR), and 1 patient (6.3%) had no response (NR). The median time to obtain CR was 32 (7-426) days after treatment with avatrombopag combined with umbilical cord MSCs. The time to reach 20×10^{^}9/L≤ PLT <50×10^{^}9/L in the 2 patients with PR was 52 and 230 days after treatment, respectively. One patient had a severe pulmonary infection and died of cytomegalovirus pneumonia. Overall, our results indicated that combination of avatrombopag with MSCs can promote platelet recovery after transplantation, thereby improving the survival rate of patients and improving the quality of life of patients after transplantation, and providing a new method and strategy for the treatment of thrombocytopenia after allo-HSCT.

Dysfunctional bone marrow endothelial progenitor cells are involved in patients with myelodysplastic syndromes

BACKGROUND

Myelodysplastic syndromes (MDS) are a group of heterogeneous myeloid clonal disorders characterized by ineffective haematopoiesis and immune deregulation. Emerging evidence has shown the effect of bone marrow (BM) endothelial progenitor cells (EPCs) in regulating haematopoiesis and immune balance. However, the number and functions of BM EPCs in patients with different stages of MDS remain largely unknown.

METHODS

Patients with MDS (N = 30), de novo acute myeloid leukaemia (AML) (N = 15), and healthy donors (HDs) (N = 15) were enrolled. MDS patients were divided into lower-risk MDS (N = 15) and higher-risk MDS (N = 15) groups according to the dichotomization of the Revised International Prognostic Scoring System. Flow cytometry was performed to analyse the number of BM EPCs. Tube formation and migration assays were performed to evaluate the functions of BM EPCs. In order to assess the gene expression profiles of BM EPCs, RNA sequencing (RNA-seq) were performed. BM EPC supporting abilities of haematopoietic stem cells (HSCs), leukaemia cells and T cells were assessed by in vitro coculture experiments.

RESULTS

Increased but dysfunctional BM EPCs were found in MDS patients compared with HDs, especially in patients with higher-risk MDS. RNA-seq indicated the progressive change and differences of haematopoiesis- and immune-related pathways and genes in MDS BM EPCs. In vitro coculture experiments verified that BM EPCs from HDs, lower-risk MDS, and higher-risk MDS to AML exhibited a progressively decreased ability to support HSCs, manifested as elevated apoptosis rates and intracellular reactive oxygen species (ROS) levels and decreased colony-forming unit plating efficiencies of HSCs. Moreover, BM EPCs from higher-risk MDS patients demonstrated an increased ability to support leukaemia cells, characterized by increased proliferation, leukaemia colony-forming unit plating efficiencies, decreased apoptosis rates and apoptosis-related genes. Furthermore, BM EPCs induced T cell differentiation towards more immune-tolerant cells in higher-risk MDS patients in vitro. In addition, the levels of intracellular ROS and the apoptosis ratios were increased in BM EPCs from MDS patients, especially in higher-risk MDS patients, which may be therapeutic candidates for MDS patients.

CONCLUSION

Our results suggest that dysfunctional BM EPCs are involved in MDS patients, which indicates that improving haematopoiesis supporting ability and immuneregulation ability of BM EPCs may represent a promising therapeutic approach for MDS patients.

Thrombocytopenia and Therapeutic Strategies after Allogeneic Hematopoietic Stem Cell Transplantation

Thrombocytopenia following allogeneic hematopoietic stem cell transplantation is a usual complication and can lead to high morbidity and mortality. New strategies, such as the use of another graft versus host-disease prophylaxis, alternative donors, and management of infections, have improved the survival of these patients. The mechanisms are unknown; therefore, the identification of new strategies to manage this potentially serious problem is needed. Thrombopoietin receptor agonists are currently available to stimulate platelet production. Some small retrospective studies have reported their potential efficacy in an allogeneic stem cell transplant setting, confirming good tolerability. Recent studies with higher numbers of patients also support their safety and efficacy in this setting, hence establishing the use of these drugs as a promising strategy for this post-transplant complication. However, prospective trials are needed to confirm these results.

Eltrombopag in the treatment of patients with persistent thrombocytopenia after haploidentical peripheral blood stem cell transplantation: a single-center experience

Persistent thrombocytopenia (PT) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is associated with an increased risk of bleeding and poor survival. The exact pathogenesis underlying PT remains unclear, and its management is difficult. Here we conducted a retrospective study to evaluate the efficacy and safety of eltrombopag (EPAG) in 34 patients with PT after allo-HSCT. Seven patients suffered from prolonged isolated thrombocytopenia (PIT), and 27 had secondary failure of platelet recovery (SFPR). For most patients, the initial dose was 25 mg or 50 mg daily, then adjusted to the maximum dose of 50-100 mg per day according to the response of platelet recovery and toleration of patients. The cumulative incidence (CI) of platelet recovery to at least 20 × 10⁹/L and 50 × 10⁹/L without transfusion support for at least 7 days was 72.1% and 60.7%, respectively. Nineteen (86.4%) of 22 responders were able to taper off the medication; furthermore, the platelet counts remained stable 1 month after withdrawal of EPAG. Although two patients discontinued EPAG during treatment due to headache and nausea, no patients developed grade 3 or 4 toxicities. Hypoplasia of bone marrow and decreased megakaryocytes (MKs) were found to be risk factors for overall response (OR) and complete response (CR) in multivariate analysis, respectively. Overall, our results indicated that EPAG can be used in the treatment of PT and that continuous exposure to EPAG may not be necessary.

Improved function and balance in T cell modulation by endothelial cells in young people

Elderly individuals exhibit unbalanced bone marrow (BM) effector T cell subset differentiation, such as increased T helper type 1 (Th1) and T cytotoxic type 1 (Tc1) cell frequencies, but the underlying mechanism is still unclear. Endothelial cells (ECs), which are instructive components of the BM microenvironment, exhibit the phenotype of semi-professional antigen-presenting cells and regulate T cell recruitment and activation. Thus, we compared the frequency and function of BM ECs, especially their capacity to regulate effector T cell subsets, between young and elderly healthy individuals, and explored the underlying mechanism of this immunomodulatory discrepancy. Although the young and elderly EC percentages were comparable, young ECs showed fewer reactive oxygen species and better migratory and tube-forming abilities than elderly ECs. Notably, increased T cell activation molecules and inflammatory cytokines were found in elderly ECs which regulated T cells to differentiate into more proinflammatory T cells, including Th1 and Tc1 cells, than young ECs.

Hematopoietic Stem Cell Niche During Homeostasis, Malignancy, and Bone Marrow Transplantation

Self-renewal and multidirectional differentiation of hematopoietic stem cells (HSCs) are strictly regulated by numerous cellular components and cytokines in the bone marrow (BM) microenvironment. Several cell types that regulate HSC niche have been identified, including both non-hematopoietic cells and HSC-derived cells. Specific changes in the niche composition can result in hematological malignancies. Furthermore, processes such as homing, proliferation, and differentiation of HSCs are strongly controlled by the BM niche and have been reported to be related to the success of hematopoietic stem cell transplantation (HSCT). Single-cell sequencing and in vivo imaging are powerful techniques to study BM microenvironment in hematological malignancies and after HSCT. In this review, we discuss how different components of the BM niche, particularly non-hematopoietic and hematopoietic cells, regulate normal hematopoiesis, and changes in the BM niche in leukemia and after HSCT. We believe that this comprehensive review will provide clues for further research on improving HSCT efficiency and exploring potential therapeutic targets for leukemia.

Different subsets of haematopoietic cells and immune cells in bone marrow between young and older donors

Young donors are reported to be associated with better transplant outcomes than older donors in allogeneic hematopoietic stem cell transplantation (allo-HSCT), but the mechanism is still unclear. The current study compared the different subsets of haematopoietic stem cells (HSCs) and their progenitors as well as immune cells in bone marrow (BM) between young and older donors. The frequencies of HSCs, multipotent progenitors (MPPs) and myeloid progenitors, including common myeloid progenitors (CMPs) and megakaryocyte-erythroid progenitors (MEPs), were decreased, whereas those of lymphoid progenitors, including multi-potent lymphoid progenitors (MLPs) and common lymphoid progenitors (CLPs), were increased in the BM of young donors compared with in that of older donors. Lower reactive oxygen species (ROS) levels were observed in BM HSCs and six progenitor lines in young donors. Furthermore, young donors demonstrated higher frequencies of naive T cells and immune suppressor cells, such as alternative macrophages (M2) and lower frequencies of memory T cells and immune effectors, including T helper-1 and T cytotoxic-1 cells, in BM than older donors. Multivariate analysis demonstrated that donor age was independently correlated with BM HSC frequency. Although further validation is required, our results suggest that the differences in the frequency and immune differentiation potential of HSCs in BM between young donors and older donors may partly explain the different outcomes of allo-HSCT.

Suppression of Hematopoietic Primitive Cells in Patients with Secondary Failure of Platelet Recovery after Acute Graft-versus-Host Disease

Secondary failure of platelet recovery (SFPR) can occur after allogeneic hematopoietic stem cell transplantation (alloHSCT), and 20% of cases are related to acute graft-versus-host disease (aGVHD). The underlying mechanisms of this association are unclear, however. The aim of the present study was to investigate the potential mechanisms of SFPR secondary to aGVHD, which may provide a new therapeutic strategy for these patients. A total of 468 patients with malignant hematologic disease who underwent alloHSCT were included. Sixty-six patients developed SFPR after alloHSCT, and in 45 of these 66 patients (68.2%), SFPR was secondary to grade II-IV aGVHD (SFPR/aGVHD). Compared with patients with good graft function (GGF), patients with SFPR had poor overall survival (20.72% versus 88.01%; P < .0001). Grade II-IV aGVHD was identified as an independent risk factor for SFPR in multivariate analysis (hazard ratio, 9.512; P < .0001). We observed reduced erythroid and megakaryocyte colony formation in bone marrow (BM) samples isolated from SFPR/aGVHD patients, consistent with the lower frequency of megakaryocyte and erythrocyte progenitors in BM. Levels of the inflammatory cytokines IL-2R and TNF-R1 were significantly higher in the SFPR/aGVHD group compared with the GGF group (P = .002 and .001, respectively), as were the frequencies of proinflammatory T helper subsets. Furthermore, the pathways that regulate hematopoiesis and immune responses were universally underexpressed in CD34⁺ cells isolated from SFPR/aGVHD patients. Differentially expressed genes were significantly enriched in the hematopoietic cell lineage pathway and other pathways involved in both immune responses and megakaryopoiesis. In summary, we found that both the immune microenvironment and compromised proliferation of hematopoietic primitive cells contribute to the development of SFPR secondary to aGVHD, and our data provide new insight into the mechanisms of SFPR in the context of aGVHD.

Incidence, Risk Factors, and Outcomes of Primary Prolonged Isolated Thrombocytopenia after Haploidentical Hematopoietic Stem Cell Transplant

The aim of this study was to evaluate the incidence, risk factors, and outcomes of primary prolonged isolated thrombocytopenia (PT) after haploidentical hematopoietic stem cell transplant (haplo-HSCT). We retrospectively analyzed patients who received haplo-HSCT for various hematologic malignancies at Peking University Institute of Hematology between January 2015 and December 2016. Of the 918 patients, 93 (10.1%) developed primary PT. We designed a propensity score method-based study. For each primary PT patient control subjects (1:3) were selected using a propensity score-matching method. A total of 372 recipients were enrolled in the study: 93 in the PT group and 279 in the control group. Multivariate analysis showed that age older than 25 years (P = .002), median mononuclear cells (P = .000), median CD34⁺ counts (P = .003), history of grades II to IV acute graft-versus-host disease (GVHD; P = .000), and Epstein-Barr virus (EBV) infection after haplo-HSCT (P = .016) were independent risk factors for primary PT. Primary PT was significantly associated with higher transplant-related mortality (TRM; P < .001), inferior overall survival (P = .001), and disease-free survival (P = .005). In conclusion, the incidence of primary PT after haplo-HSCT was 10.1%. Primary PT was associated with poorer survival and higher TRM along with older age, grades II to IV acute GVHD, and EBV infection after haplo-HSCT.

Prophylactic oral NAC reduced poor hematopoietic reconstitution by improving endothelial cells after haploidentical transplantation

Poor graft function (PGF) and prolonged isolated thrombocytopenia (PT) remain life-threatening complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Endothelial cells (ECs) play a crucial role in regulating hematopoiesis in the bone marrow (BM) microenvironment. However, whether the impaired BM ECs are responsible for defective hematopoiesis in PGF and PT patients requires clarification, and clinical management is challenging. Two prospective clinical trials were included in the current study. In the first trial (N = 68), PGF and PT patients demonstrated defective BM ECs pre-HSCT and impaired BM EC dynamic reconstitution at early time points post-HSCT, which was positively correlated with reactive oxygen species (ROS) levels. Receiver operating characteristic curves showed that BM EC < 0.1% pre-HSCT could identify high-risk patients with PGF and PT. The second trial enrolled patients (N = 35) with EC < 0.1% who accepted oral N-acetyl-l-cysteine (NAC; 400 mg 3 times per day) from -14 days pre-HSCT to +2 months post-HSCT continuously, whereas the remaining EC ≥ 0.1% patients (N = 39) received allo-HSCT only. Prophylactic NAC intervention was safe and effective in preventing the occurrence of PGF and PT in EC < 0.1% patients by promoting the dynamic reconstitution of BM ECs and CD34+ cells, along with reducing their ROS levels, which was further confirmed by in situ BM trephine biopsy analyses. These findings suggest that the impaired BM ECs pre-HSCT are responsible for the defective hematopoiesis in PGF and PT patients. Therefore, improvement of BM ECs through prophylactic NAC intervention may be a promising therapeutic approach to promote hematopoietic reconstitution post-HSCT. This trial was registered at www.clinicaltrials.gov as #NCT03236220 and #NCT02978274.

G-CSF-induced macrophage polarization and mobilization may prevent acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Macrophages (MΦs) are an important immune cell population that are essential for tissue homeostasis and disease pathogenesis. MΦs are now classified as either M1, which produce pro-inflammatory cytokines, or M2, which produce antiinflammatory cytokines. The impact of granulocyte colony-stimulating factor (G-CSF) on MΦs in humans is unclear. Moreover, little is known about the association between MΦ subsets in allografts and the occurrence of acute graft-versus-host disease (aGVHD) in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the current study, we found that the M1/M2 ratio was markedly decreased in both G-CSF-treated bone marrow (post-BM) and G-CSF-treated peripheral blood from healthy donors. Post-BM MΦs exhibited reduced migration and increased phagocytosis. Moreover, post-BM MΦs reduced the percentage of Th1 and Tc1 lineages and increased the percentage of Th2, Tc2, and Treg lineages. Patients who received BM grafts with a higher M1/M2 ratio exhibited a higher incidence of grade 2-4 aGVHD. In summary, our data indicate that G-CSF decreases the M1/M2 ratio in BM grafts from healthy donors, which may contribute to preventing the occurrence of grade 2-4 aGVHD in patients after allo-HSCT.

Platelet number and graft function predict intensive care survival in allogeneic stem cell transplantation patients

Despite significant advances in the treatment of complications requiring intensive care unit (ICU) admission, ICU mortality remains high for patients after allogeneic stem cell transplantation. We evaluated the role of thrombocytopenia and poor graft function in allogeneic stem cell recipients receiving ICU treatments along with established prognostic ICU markers in order to identify patients at risk for severe complications. At ICU admission, clinical and laboratory data of 108 allogeneic stem cell transplanted ICU patients were collected and retrospectively analyzed. Platelet counts (≤ 50,000/μl, p < 0.0005), hemoglobin levels (≤ 8.5 mg/dl, p = 0.019), and leukocyte count (≤ 1500/μl, p = 0.025) along with sepsis (p = 0.002) and acute myeloid leukemia (p < 0.0005) correlated significantly with survival. Multivariate analysis confirmed thrombocytopenia (hazard ratio (HR) 2.79 (1.58-4.92, 95% confidence interval (CI)) and anemia (HR 1.82, 1.06-3.11, 95% CI) as independent mortality risk factors. Predominant ICU diagnoses were acute respiratory failure (75%), acute kidney injury (47%), and septic shock (30%). Acute graft versus host disease was diagnosed in 42% of patients, and 47% required vasopressors. Low platelet (≤ 50,000/μl) and poor graft function are independent prognostic factors for impaired survival in critically ill stem cell transplanted patients. The underlying pathophysiology of poor graft function is not fully understood and currently under investigation. High-risk patients may be identified and ICU treatments stratified according to allogeneic stem cell patients' individual risk profiles. In contrast to previous studies involving medical or surgical ICU patients, the fraction of thrombocytopenic patients was larger and low platelets were a better differentiating factor in multivariate analysis than any other parameter.

Poor graft function after allogeneic hematopoietic stem cell transplantation-an old complication with new insights☆

Poor graft function (PGF), characterized by pancytopenia, is a life-threatening complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). PGF has become a growing obstacle that contributes to high morbidity and mortality after allo-HSCT, especially with the increasing use of haploidentical allo-HSCT, and clinical management 81870139, is challenging. Emerging evidence demonstrates that the bone marrow (BM) microenvironment plays a crucial role in maintaining and regulating hematopoiesis. Recent prospective case-control studies demonstrated that impaired BM microenvironments are involved in the pathogenesis of PGF. Moreover, in vitro treatment with N-acetyl-L-cysteine, a reactive oxygen species scavenger, could enhance the defective hematopoietic stem cells by repairing the dysfunctional BM microenvironment of PGF patients. Consequently, a better understanding of the pathogenesis of PGF may guide effective therapy and eventually improve the prognosis of allo-HSCT. Here, based on new insights into the BM microenvironment in PGF patients, we provide an overview of the pathogenesis and promising treatment strategies for PGF patients.

N-acetyl-L-cysteine improves bone marrow endothelial progenitor cells in prolonged isolated thrombocytopenia patients post allogeneic hematopoietic stem cell transplantation

Prolonged isolated thrombocytopenia (PT) is a serious complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). According to murine studies, endothelial progenitor cells (EPCs) play a crucial role in the regulation of hematopoiesis and thrombopoiesis in the bone marrow (BM) microenvironment. We previously showed that the reduced frequency of BM EPCs was an independent risk factor for the occurrence of PT following allo-HSCT. However, the functional role of BM EPCs and methods to improve the impaired BM EPCs in PT patients are unknown. In the current case-control study, we investigated whether the BM EPCs in PT patients differed from those in good graft function patients. Moreover, we evaluated whether N-acetyl-L-cysteine (NAC, a reactive oxygen species [ROS] scavenger) could enhance BM EPCs from PT patients in vitro and in vivo. The PT patients exhibited dysfunctional BM EPCs characterized by high levels of ROS and apoptosis and decreased migration and angiogenesis capabilities. In vitro treatment with NAC improved the quantity and function of the BM EPCs cultivated from the PT patients by downregulating the p38 MAPK pathway and rescued the impaired BM EPCs to support megakaryocytopoiesis. Furthermore, according to the results of a preliminary clinical study, NAC is safe and effective in PT patients. In summary, these results suggested that the reduced and dysfunctional BM EPCs are involved in the occurrence of PT. The defective BM EPCs in the PT patients can be quantitatively and functionally improved by NAC, indicating that NAC is a promising therapeutic approach for PT patients following allo-HSCT.

Evaluation of blood vessel injury, oxidative stress and circulating inflammatory factors in an L-NAME-induced preeclampsia-like rat model

Preeclampsia is a pregnancy-specific disease characterized by hypertension as well as proteinuria after the 20th week of pregnancy. Animal models are effective tools for studying the pathogenesis, diagnostic criteria and treatment methods of preeclampsia. The present study sought to establish and evaluate a preeclampsia-like Sprague Dawley (SD) rat model using N-nitro-L-arginine methyl ester (L-NAME). Rats were randomly assigned to 7 groups (n=10 in each): Control rats and rats treated with low-dose L-NAME (40 mg/kg body weight/day) starting from gestational day (GD) 9, medium-L-NAME (75 mg/kg body weight/day) starting from GD 9 (9D ML group), high-dose L-NAME (125 mg/kg body weight/day) starting from GD 9, low-dose L-NAME starting from GD 10, medium-dose L-NAME starting from GD 10 and high-dose L-NAME starting from GD 10. Blood pressure (BP), 24-h proteinuria, fetal intrauterine growth, histopathological changes, the plasma soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PLGF) ratio and cytokine levels were evaluated. Elevated BP, increased urinary albumin excretion, severe endotheliosis, mesangial expansion and increased sFlt-1/PLGF ratios were observed in the experimental groups compared with the control group (P<0.05), particularly in the 9D ML group. The results of the present study may optimize the conditions of the previously established L-NAME-induced preeclampsia SD rat model and aid further study into the pathogenesis of preeclampsia.

N-acetyl-L-cysteine improves mesenchymal stem cell function in prolonged isolated thrombocytopenia post-allotransplant

Prolonged isolated thrombocytopenia (PT) is a serious complication of allogeneic haematopoietic stem cell transplantation (allo-HSCT). Murine studies and in vitro experiments suggest that mesenchymal stem cells (MSCs) can, not only to support haematopoiesis, but also preferentially support megakaryocytopoiesis in bone marrow (BM). However, little is known about the quantity and function of BM MSCs in PT patients. In a case-control study, we found that BM MSCs from PT patients exhibited significantly reduced proliferative capacities, increased reactive oxygen species and senescence. Antioxidant (N-acetyl-L-cysteine, NAC) treatment in vitro not only quantitatively and functionally improved BM MSCs derived from PT patients through down-regulation of the p38 (also termed MAPK14) and p53 (also termed TP53) pathways but also partially rescued the impaired ability of BM MSCs to support megakaryocytopoiesis. Subsequently, a pilot study showed that the overall response of NAC treatment was obtained in 7 of the enrolled PT patients (N = 10) without significant side effects. Taken together, the results indicated that dysfunctional BM MSCs played a role in the pathogenesis of PT and the impaired BM MSCs could be improved by NAC in vitro. Although requiring further validation, our data indicate that NAC might be a potential therapeutic approach for PT patients after allo-HSCT.