Increased reactive oxygen species and exhaustion of quiescent CD34-positive bone marrow cells may contribute to poor graft function after allotransplants

Cigarette smoke impairs the hematopoietic supportive property of mesenchymal stem cells via the production of reactive oxygen species and NLRP3 activation

BACKGROUND

Mesenchymal stem cells (MSCs) play important roles in tissue homeostasis by providing a supportive microenvironmental niche for the hematopoietic system. Cigarette smoking induces systemic abnormalities, including an impeded recovery process after hematopoietic stem cell transplantation. However, the role of cigarette smoking-mediated alterations in MSC niche function have not been investigated.

METHODS

In the present study, we investigated whether exposure to cigarette smoking extract (CSE) disrupts the hematopoietic niche function of MSCs, and pathways impacted. To investigate the effects on bone marrow (BM)-derived MSCs and support of hematopoietic stem and progenitor cells (HSPCs), mice were repeatedly infused with the CSE named 3R4F, and hematopoietic stem and progenitor cells (HSPCs) supporting function was determined. The impact of 3R4F on MSCs at cellular level were screened by bulk-RNA sequencing and subsequently validated through qRT-PCR. Specific inhibitors were treated to verify the ROS or NLRP3-specific effects, and the cells were then transplanted into the animal model or subjected to coculture with HSPCs.

RESULTS

Both direct ex vivo and systemic in vivo MSC exposure to 3R4F resulted in impaired engraftment in a humanized mouse model. Furthermore, transcriptomic profile analysis showed significantly upregulated signaling pathways related to reactive oxygen species (ROS), inflammation, and aging in 3R4F-treated MSCs. Notably, ingenuity pathway analysis revealed the activation of NLRP3 inflammasome signaling pathway in 3R4F-treated MSCs, and pretreatment with the NLRP3 inhibitor MCC950 rescued the HSPC-supporting ability of 3R4F-treated MSCs.

CONCLUSION

In conclusion, these findings indicate that exposure to CSE reduces HSPCs supportive function of MSCs by inducing robust ROS production and subsequent NLRP3 activation.

Definitions, incidence and outcome of poor graft function after hematopoietic cell transplantation: A systematic review and meta-analysis

Poor graft function (PGF) after allogeneic hematopoietic stem cell transplantation (HCT) is a serious complication with high morbidity and mortality. The reported incidence of PGF, its risk factors and outcome vary substantially between studies. This variability may be explained by heterogeneity in patient cohorts and HCT strategies, differences in the underlying causes of cytopenia, as well as by differences in PGF definition. In this systematic review and meta-analysis, we provide an overview of the various PGF definitions used and determined the impact of this variability on the reported incidence and outcome. We searched MEDLINE, EMBASE and Web of Science up to July 2022, for any study on PGF in HCT recipients. We performed random-effect meta-analyses for incidence and outcome and subgroup analyses based on different PGF criteria. Among 69 included studies (14.265 HCT recipients), we found 63 different PGF definitions, using various combinations of 11 common criteria. The median incidence of PGF was 7% (IQR: 5-11%, 22 cohorts). The pooled survival of PGF patients was 53% (95% CI: 45-61%, 23 cohorts). The most commonly reported risk factors associated with PGF were history of cytomegalovirus infection and prior graft-versus-host disease. Incidence was lower in studies with strict cytopenic cutoffs, while survival was lower for primary compared to secondary PGF. This work indicates that a standardized, quantitative definition of PGF is needed to facilitate clinical guideline development and to advance scientific progress.

The nuclear factor erythroid 2-related factor 2 agonist tert-butylhydroquinone improves bone marrow mesenchymal stromal cell function in prolonged isolated thrombocytopenia after allogeneic haematopoietic stem cell transplantation

Prolonged isolated thrombocytopenia (PT) is a life-threatening comorbidity associated with allogeneic haematopoietic stem cell transplantation (allo-HSCT). Our previous study indicated that dysfunctional bone marrow mesenchymal stromal cells (BM MSCs) played a role in PT pathogenesis and that reactive oxygen species (ROS) accumulation was related to BM MSC senescence and apoptosis. However, the mechanism of the increase in ROS levels in the BM MSCs of PT patients is unknown. In the current case-control study, we investigated whether nuclear factor erythroid 2-related factor 2 (NRF2), which is a central regulator of the cellular anti-oxidant response that can clear ROS in human BM MSCs, was associated with PT after allo-HSCT. We evaluated whether an NRF2 agonist (tert-butylhydroquinone, TBHQ) could enhance BM MSCs from PT patients in vitro. We found that BM MSCs from PT patients exhibited increased ROS levels and reduced NRF2 expression. Multivariate analysis showed that low NRF2 expression was an independent risk factor for primary PT [p = 0.032, Odds ratio (OR) 0.868, 95% confidence interval (CI) 0.764-0.988]. In-vitro treatment with TBHQ improved the quantity and function of BM MSCs from PT patients by downregulating ROS levels and rescued the impaired BM MSC support of megakaryocytopoiesis. In conclusion, these results suggested that NRF2 downregulation in human BM MSCs might be involved in the pathogenesis of PT after allo-HSCT and that BM MSC impairment could be improved by NRF2 agonist in vitro. Although further validation is needed, our data indicate that NRF2 agonists might be a potential therapeutic approach for PT patients after allo-HSCT.

Impact of iron overload on poor graft function after allo-HSCT in a patient with transfusion-dependent low-risk MDS: A case report and literature review

RATIONALE

Poor graft function (PGF) occurs in 5% to 27% of allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is associated with high life-threatening complications. The etiology of PGF is complex and multifactorial, and iron overload (IOL) is considered as a predictive factor.

PATIENT CONCERN

A 45-years-old woman who was diagnosed as low-risk myelodysplastic syndrome in 2012 has been transfusion dependent and developed severe IOL.

DIAGNOSES

Due to transfusion dependency and also ineffective erythropoiesis, this patient was diagnosed as IOL and developed PGF after allo-HSCT.

INTERVENTIONS

Deferasirox (20mg/kg/d) was administered regularly after allo-HSCT for 2 years.

OUTCOMES

Hematopoiesis was gradually recovered during iron chelation therapy treatment after allo-HSCT and PGF was reverted.

LESSONS

IOL, as a prognostic factor for PGF, is a common problem in Transfusion dependent myelodysplastic syndrome patients undergoing HSCT. IOL issues should be considered at the time of diagnosis and throughout the treatment course for patients who are potential candidates for HSCT.

Recent Advancements in Poor Graft Function Following Hematopoietic Stem Cell Transplantation

Poor graft function (PGF) is a life-threatening complication that occurs after transplantation and has a poor prognosis. With the rapid development of haploidentical hematopoietic stem cell transplantation, the pathogenesis of PGF has become an important issue. Studies of the pathogenesis of PGF have resulted in some success in CD34⁺-selected stem cell boosting. Mesenchymal stem cells, N-acetyl-l-cysteine, and eltrombopag have also been investigated as therapeutic strategies for PGF. However, predicting and preventing PGF remains challenging. Here, we propose that the seed, soil, and insect theories of aplastic anemia also apply to PGF; CD34⁺ cells are compared to seeds; the bone marrow microenvironment to soil; and virus infection, iron overload, and donor-specific anti-human leukocyte antigen antibodies to insects. From this perspective, we summarize the available information on the common risk factors of PGF, focusing on its potential mechanism. In addition, the safety and efficacy of new strategies for treating PGF are discussed to provide a foundation for preventing and treating this complex clinical problem.

The Incidence, Outcomes, and Risk Factors of Secondary Poor Graft Function in Haploidentical Hematopoietic Stem Cell Transplantation for Acquired Aplastic Anemia

Secondary poor graft function (sPGF) increases the risk of life-threatening complications after hematopoietic stem cell transplantation (HSCT). The incidence, clinical outcomes, and risk factors of sPGF have not been elucidated in haploidentical (haplo-) HSCT for acquired aplastic anemia (AA) patients. We retrospectively reviewed 423 consecutive AA patients who underwent haplo-HSCT between January 2006 and December 2020 and report a 3-year cumulative incidence of 4.62% (95% confidence interval [CI]: 3.92%-10.23%) of sPGF. While no primary PGF occurred. The median time to sPGF was 121 days (range 30-626 days) after transplantation. To clarify the risk factors for sPGF, 17 sPGF cases and 382 without PGF were further analyzed. Compared to patients without PGF, the 2-year overall survival was significantly poorer for sPGF patients (67.7% vs 90.8%, p =.002). Twelve sPGF patients were alive until the last follow-up, and 7 achieved transfusion independency. The multivariable analyses revealed that later neutrophil engraftment (OR 2.819, p=.049) and a history of refractory cytomegalovirus viremia (OR=7.038, p=.002) post-transplantation were associated with sPGF. There was weak evidence that a history of grade 3-4 acute graft-versus-host disease increased the risk of sPGF (p=.063). We advocated better post-transplantation strategies to balance the risk of immunosuppression and viral reactivation for haplo-HSCT in AA patients.

Clinical features, pathophysiology, and therapy of poor graft function post-allogeneic stem cell transplantation

Poor graft function (PGF), defined by the presence of multilineage cytopenias in the presence of 100% donor chimerism, is a serious complication of allogeneic stem cell transplant (alloSCT). Inducers or potentiators of alloimmunity such as cytomegalovirus reactivation and graft-versus-host disease are associated with the development of PGF, however, more clinical studies are required to establish further risk factors and describe outcomes of PGF. The pathophysiology of PGF can be conceptualized as dysfunction related to the number or productivity of the stem cell compartment, defects in bone marrow microenvironment components such as mesenchymal stromal cells and endothelial cells, or immunological suppression of post-alloSCT hematopoiesis. Treatment strategies focused on improving stem cell number and function and microenvironment support of hematopoiesis have been attempted with variable success. There has been limited use of immune manipulation as a therapeutic strategy, but emerging therapies hold promise. This review details the current understanding of the causes of PGF and methods of treatment to provide a framework for clinicians managing this complex problem.

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.

Research advances on haploidentical hematopoietic stem cell transplantation in the treatment of severe aplastic anemia in children

Haploidentical hematopoietic stem cell transplantation is a recommended alternative therapy for children with severe aplastic anemia who lack a human leukocyte antigen (HLA)-identical sibling donor and do not respond well to immunosuppressive therapy; however, due to non-identical HLA, the patients may have donor-specific anti-HLA antibody, which may lead to a relatively high incidence rate of poor graft function. Compared with HLA-identical transplantation, conditioning regimen for haploidentical transplantation still needs to be explored. This article reviews the detection and treatment of donor-specific anti-HLA antibody, the selection of conditioning regimen, and the mechanism and treatment of poor graft function in haploidentical hematopoietic stem cell transplantation.

Overcoming graft failure after haploidentical transplantation: Is this a possibility?

Allogeneic hematopoietic stem cell transplantation (allo-HSCT), including haploidentical HSCT (haplo-HSCT), is a potentially curative treatment for several hematologic disorders. However, the occurrence of poor graft function (PGF) can lead to mortality. Advances in the use of novel conditioning regimens and strategies to improve engraftment while reducing PGF, are expected to improve outcomes. This review has examined recent evidence that will provide insights into reducing graft failure in haplo-HSCT.

β3-Adrenoreceptors as ROS Balancer in Hematopoietic Stem Cell Transplantation

In the last decades, the therapeutic potential of hematopoietic stem cell transplantation (HSCT) has acquired a primary role in the management of a broad spectrum of diseases including cancer, hematologic conditions, immune system dysregulations, and inborn errors of metabolism. The different types of HSCT, autologous and allogeneic, include risks of severe complications including acute and chronic graft-versus-host disease (GvHD) complications, hepatic veno-occlusive disease, lung injury, and infections. Despite being a dangerous procedure, it improved patient survival. Hence, its use was extended to treat autoimmune diseases, metabolic disorders, malignant infantile disorders, and hereditary skeletal dysplasia. HSCT is performed to restore or treat various congenital conditions in which immunologic functions are compromised, for instance, by chemo- and radiotherapy, and involves the administration of hematopoietic stem cells (HSCs) in patients with depleted or dysfunctional bone marrow (BM). Since HSCs biology is tightly regulated by oxidative stress (OS), the control of reactive oxygen species (ROS) levels is important to maintain their self-renewal capacity. In quiescent HSCs, low ROS levels are essential for stemness maintenance; however, physiological ROS levels promote HSC proliferation and differentiation. High ROS levels are mainly involved in short-term repopulation, whereas low ROS levels are associated with long-term repopulating ability. In this review, we aim summarize the current state of knowledge about the role of β3-adrenoreceptors (β3-ARs) in regulating HSCs redox homeostasis. β3-ARs play a major role in regulating stromal cell differentiation, and the antagonist SR59230A promotes differentiation of different progenitor cells in hematopoietic tumors, suggesting that β3-ARs agonism and antagonism could be exploited for clinical benefit.

Mito-managing ROS & redox to reboot the immune system: Tapping mitochondria & redox management to extend the reach of hematopoietic stem cell transplantation

Hematopoietic stem cells (HSCs) are responsible for life-long production of blood and immune cells. HSC transplantation (HSCT) is the original cell therapy which can cure hematological disorders but also has the potential to treat other diseases if technical and safety barriers are overcome. To maintain homeostatic hematopoiesis or to restore hematopoiesis during transplantation HSCs must perform both self-renewal, replication of themselves, and differentiation, generation of mature blood and immune cells. These are just two of the cell fate choices HSCs have; the transitional phases where HSCs undergo these cell fate decisions are regulated by reduction-oxidation (redox) signaling, mitochondrial activity, and cellular metabolism. Recent studies revealed that mitochondria, a key source of redox signaling components, are central to HSC cell fate decisions. Here we highlight how mitochondria serve as hubs in HSCs to manage redox signaling and metabolism and thus guide HSC fate choices. We focus on how mitochondrial activity is modulated by their clearance, biogenesis, dynamics, distribution, and quality control in HSCs. We also note how modulating mitochondria in HSCs can help overcome technical barriers limiting further use of HSCT.

Evaluation of risk factors for and subsequent mortality from poor graft function (PGF) post allogeneic stem cell transplantation

Poor Graft Function (PGF) is defined by multi-lineage cytopenias with complete donor chimerism post allogeneic transplantation, Risk factors for and subsequent mortality from PGF were assessed in our transplant cohort. Non-sibling donor [OR 1.97; 95% CI 1.02-3.70], ICU admission [OR 5.28; 95% CI 2.29-11.88] or blood culture positivity within the first 30 days [OR 1.67; 95% CI 1.07-2.62], grade III-IV acute graft vs host disease (GVHD) [OR 4.082; 95% CI 2.31-7.16] and CMV viremia [OR 2.43; 95% CI 1.53-3.88] and were significantly associated with development of PGF. PGF patients without count recovery had a 2 year OS of 6%. Severe GVHD, thrombocytopenia and anemia portended inferior survival and were used to develop a prognostic score for mortality from PGF. This analysis identifies risk factors predictive of PGF and poor survival in those without recovery.

Protection of hematopoietic stem cells from stress-induced exhaustion and aging

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) are defined by their ability to self-renew and differentiate to replenish all blood lineages throughout adult life. Under homeostasis, the majority of HSCs are quiescent, and few stem cells are cycling to sustain hematopoiesis. However, HSCs can be induced to proliferate and differentiate in response to stress signals produced during infection, inflammation, chemotherapy, radiation, bone marrow transplantation, and aging. Recent evidence suggests that acute and chronic stress impact the number and function of HSCs including their ability to repopulate and produce mature cells. This review will focus on how chronic stress affects HSC biology and methods to mitigate HSC loss during chronic hematopoietic stress.

RECENT FINDINGS

Quiescent HSCs exit dormancy, divide, and differentiate to maintain steady-state hematopoiesis. Under conditions of acute stress including infection or blood loss some HSCs are pushed into division by cytokines and proinflammatory stimuli to differentiate and provide needed myeloid and erythroid cells to protect and reconstitute the host; after which, hematopoiesis returns to steady-state with minimal loss of HSC function. However, under conditions of chronic stress including serial bone marrow transplantation (BMT), chronic inflammation, and genotoxic stress (chemotherapy) and aging, HSCs are continuously induced to proliferate and undergo accelerated exhaustion. Recent evidence demonstrates that ablation of inhibitor of DNA binding 1 (Id1) gene can protect HSCs from exhaustion during chronic proliferative stress by promoting HSC quiescence.

SUMMARY

Increasing our understanding of the molecular processes that protect HSCs from chronic proliferative stress could lead to therapeutic opportunities to prevent accelerated HSC exhaustion during physiological stress, genotoxic stress, BMT, and aging.

Rescue treatment with eltrombopag in refractory cytopenias after allogeneic stem cell transplantation

Background:

Patients with post-transplant cytopenias due to poor graft function or primary engraftment failure show poor prognosis with a high mortality rate mainly because of graft versus host disease (GVHD), infection and/or bleeding. Treatment options are scarce and a CD34+ stem cell boost or a second bone marrow transplantation may be required to restore adequate haematopoiesis.

Methods:

In the present study patients with primary engraftment failure (n = 1) and refractory poor graft function (n = 11) were treated with eltrombopag in a single centre. The reason for eltrombopag treatment was trilineage cytopenia in six patients, bilineage cytopenia in three patients and single lineage cytopenia in three patients. Eltrombopag was initiated at a median of 214 (range: 120–877) days after haematopoietic stem cell transplantation (HCST) and administered for a median time of 114 (range: 12 days to >490) days. In 8/12 patients eltrombopag was introduced at a dose of 75 mg/day and then increased to 150 mg/day after 1 week; 1 patient was given 50 mg eltrombopag per day, and 3 patients received 75 mg daily.

Results:

In 10/12 patients eltrombopag significantly enhanced blood count values and patients became transfusion independent. Once stable haematological response was obtained, treatment was tapered until final discontinuation in 9/10 responding patients. No grade 3 or 4 toxicities were observed. At time of last follow up, 3/12 patients were dead, 2 due to disease relapse, 1 due to GVHD and pneumonia. All patients except one maintained their complete response and remain transfusion independent at a median of 858 (range: 429–1119) days.

Conclusion:

These preliminary data confirm that eltrombopag is able to rescue multilineage haematopoiesis in patients with treatment-refractory cytopenias after allogeneic HSCT.

Advances in the understanding of poor graft function following allogeneic hematopoietic stem-cell transplantation

Poor graft function (PGF) following allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is a life-threatening complication and is characterized by bilineage or trilineage blood cell deficiency and hypoplastic marrow with full chimerism. With the rapid development of allo-HSCT, especially haploidentical-HSCT, PGF has become a growing concern. The most common risk factors illustrated by recent studies include low dose of infused CD34+ cells, donor-specific antibody, cytomegalovirus infection, graft versus host disease (GVHD), iron overload and splenomegaly, among others. Because of the poor prognosis of PGF, it is crucial to uncover the underlying mechanism, which remains elusive. Recent studies have suggested that the bone marrow microenvironment may play an important role in the pathogenesis of PGF. Deficiency and dysfunction of endothelial cells and mesenchymal stem cells, elevated reactive oxygen species (ROS) levels, and immune abnormalities are believed to contribute to PGF. In this review, we also discuss recent clinical trials that evaluate the safety and efficacy of new strategies in patients with PGF. CD34+-selected stem-cell boost (SCB) is effective with an acceptable incidence of GVHD, despite the need for a second donation. Alternative strategies including the applications of mesenchymal stem cells, N-acetyl-l-cysteine (NAC), and eltrombopag have shown favorable outcomes, but further large-scale studies are needed due to the small sample sizes of the recent clinical trials.

Eltrombopag treatment promotes platelet recovery and reduces platelet transfusion for patients with post-transplantation thrombocytopenia

Post-transplantation thrombocytopenia (PT) is a common and severe complication which usually leads to poor prognosis. Eltrombopag (EPAG), a novel oral thrombopoietin (TPO) receptor agonist, has shown promising effects in thrombocytopenia due to immune thrombocytopenic purpura (ITP) and refractory severe aplastic anemia (rSAA), while the effectiveness of EPAG for PT patients still needs to be evaluated. A total of 32 PT patients receiving EPAG were retrospectively analyzed between September 2017 and July 2019, including 15 patients with poor graft function (PGF) and 17 patients with secondary failure of platelet recovery (SFPR). To date, 21 (65.6%) patients achieved overall recovery (OR) and 14 (43.8%) patients achieved complete recovery (CR). Among responders, 18 (85.7%) patients discontinued or tapered the drug and 16 (76.2%) patients successfully maintained their best response. During the EPAG treatment, responders received much lower median platelet transfusion units than non-responders (11 vs. 95, P < 0.001). After a median follow-up time of 364 days (range, 24-842), the overall survival in these patients was 78.1% (100% for responders and 36.4% for non-responders, P < 0.001). In the univariate and multivariate analysis, PGF was identified as the independent risk factor for OR (P = 0.041, HR = 5.333). Megakaryocyte (Megk) amounts (P = 0.025, HR = 14.638) and splenomegaly (P = 0.042, HR = 11.278) were identified as independent risk factors for CR. Besides, PGF patients tended to take a longer time to achieve PR and CR than SFPR patients. In conclusion, our data suggest that EPAG can promote platelet recovery and reduce platelet transfusion in PT patients.

Autophagy in endothelial cells regulates their haematopoiesis-supporting ability

Background

Endothelial cells (ECs) function as an instructive platform to support haematopoietic stem cell (HSC) homeostasis. Our recent studies found that impaired bone marrow (BM) ECs are responsible for the defective haematopoiesis in patients with poor graft function (PGF), which is characterised by pancytopenia post-allotransplant. Although activated autophagy was reported to benefit ECs, whether EC autophagy plays a critical role in supporting HSCs and its effect on PGF patients post-allotransplant remain unclear.

Methods

To evaluate whether the autophagy status of ECs modulates their ability to support haematopoiesis, human umbilical vein endothelial cells (HUVECs) and primary BM ECs derived from healthy donors were subjected to knockdown or overexpression of Beclin-1 (an autophagy-related protein). Moreover, BM ECs derived from PGF patients were studied.

Findings

Beclin-1 knockdown significantly reduced the haematopoiesis-supporting ability of ECs by suppressing autophagy, which could be restored by activating autophagy via Beclin-1 upregulation. Moreover, autophagy positively regulated haematopoiesis-related genes in HUVECs. Subsequently, a prospective case-control study demonstrated that defective autophagy reduced Beclin-1 expression and the colony-forming unit (CFU) plating efficiency in BM ECs from PGF patients compared to matched patients with good graft function. Rapamycin, an autophagy activator, quantitatively and functionally improved BM ECs from PGF patients in vitro and enhanced their ability to support HSCs by activating the Beclin-1 pathway.

Interpretation

Our results suggest that the autophagy status of ECs modulates their ability to support haematopoiesis by regulating the Beclin-1 pathway. Defective autophagy in BM ECs may be involved in the pathogenesis of PGF post-allotransplant. Rapamycin provides a promising therapeutic approach for PGF patients.

Funding

Please see funding sources.

Reactive Oxygen Species and Nrf2: Functional and Transcriptional Regulators of Hematopoiesis

Hematopoietic stem cells (HSCs) are characterized by self-renewal and multilineage differentiation potentials. Although they play a central role in hematopoietic homeostasis and bone marrow (BM) transplantation, they are affected by multiple environmental factors in the BM. Here, we review the effects of reactive oxygen species (ROS) and Nrf2 on HSC function and BM transplantation. HSCs reside in the hypoxic microenvironment of BM, and ROS play an important role in HSPC regulation. Recently, an extraphysiologic oxygen shock/stress phenomenon was identified in human cord blood HSCs collected under ambient air conditions. Moreover, Nrf2 has been recently recognized as a master transcriptional factor that regulates multiple antioxidant enzymes. Since several years, the role of Nrf2 in hematopoiesis has been extensively studied, which has functional similarities of cellular oxygen sensor hypoxia-inducible factor-1 as transcriptional factors. Increasing evidence has revealed that abnormally elevated ROS production due to factors such as genetic defects, aging, and ionizing radiation unexceptionally resulted in lethal impairment of HSC function and hematopoiesis. Both experimental and clinical studies have identified elevated ROS levels as a major culprit of ineffective BM transplantation. Lastly, we discuss the possibility of using small molecule antioxidants, such as N-acetyl cysteine, resveratrol, and curcumin, to augment HSC function and improve the therapeutic efficacy of BM transplantation. Further research on the function of ROS levels and improving the efficacy of BM transplantation may have a great potential for broad clinical applications of HSCs.

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.

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.

Reactive oxygen species in haematopoiesis: leukaemic cells take a walk on the wild side

Oxidative stress is related to ageing and degenerative diseases, including cancer. However, a moderate amount of reactive oxygen species (ROS) is required for the regulation of cellular signalling and gene expression. A low level of ROS is important for maintaining quiescence and the differentiation potential of haematopoietic stem cells (HSCs), whereas the level of ROS increases during haematopoietic differentiation; thus, suggesting the importance of redox signalling in haematopoiesis. Here, we will analyse the importance of ROS for haematopoiesis and include evidence showing that cells from leukaemia patients live under oxidative stress. The potential sources of ROS will be described. Finally, the level of oxidative stress in leukaemic cells can also be harnessed for therapeutic purposes. In this regard, the reliance of front-line anti-leukaemia chemotherapeutics on increased levels of ROS for their mechanism of action, as well as the active search for novel compounds that modulate the redox state of leukaemic cells, will be analysed.

Dysfunctional Bone Marrow Mesenchymal Stem Cells in Patients with Poor Graft Function after Allogeneic Hematopoietic Stem Cell Transplantation

Poor graft function (PGF) is a life-threatening complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is characterized by defective hematopoiesis. Mesenchymal stem cells (MSCs) have been shown to support hematopoiesis, but little is known about the role of MSCs in the pathogenesis of PGF. In the current prospective case-control study, we evaluated whether the number and function of bone marrow (BM) MSCs in PGF patients differed from those in good graft function (GGF) patients. We found that BM MSCs from PGF patients expanded more slowly and appeared flattened and larger, exhibiting more apoptosis and senescence than MSCs from GGF patients. Furthermore, increased intracellular reactive oxygen species, p-p53, and p21 (but not p38) levels were detected in MSCs from PGF patients. Moreover, the ability of MSCs to sustain hematopoiesis was significantly reduced in PGF patients, as evaluated by cell number, apoptosis, and the colony-forming unit-plating efficiency of CD34⁺ cells. In summary, the biologic characteristics of PGF MSCs are different from those of GGF MSCs, and the in vitro hematopoiesis-supporting ability of PGF MSCs is significantly lower. Although requiring further validation, our study indicates that reduced and dysfunctional BM MSCs may contribute to deficient hematopoiesis in PGF patients. Therefore, improvement of BM MSCs may represent a promising therapeutic approach for PGF patients after allo-HSCT.

Expression of Intracellular Reactive Oxygen Species in Hematopoietic Stem Cells Correlates with Time to Neutrophil and Platelet Engraftment in Patients Undergoing Autologous Bone Marrow Transplantation

Reactive oxygen species (ROS) play important roles in hematopoiesis and regulate the self-renewal, migration, and myeloid differentiation of hematopoietic stem cells (HSCs). This study was conducted to determine whether ROS levels in donor HSCs correlate with neutrophil and platelet engraftment in patients after bone marrow transplantation. Cryopreserved HSC samples from 51 patients who underwent autologous transplantation were studied. Levels of intracellular ROS were assessed by flow cytometry using 2',7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) in the CD45⁺/CD34⁺ HSC population. Colony forming unit assays were performed on HSCs isolated from the ROS^high and ROS^low populations to assess the differentiation potential of these 2 cell subsets. Distinct populations of ROS^high and ROS^low cells were evident in all patient samples. The median percentage of ROS^high expressing HSCs in the study cohort was 75.8% (range, 2% to 95.2%). A significant correlation was identified between the percentage of ROS^high stem cells present in the hematopoietic progenitor cells collected by apheresis product infused and the time to neutrophil engraftment (P < .001, r = -.54), as well as time to plt20, plt50, and plt100 (P < 0.001; r = -.55, -.59, and -.56 respectively). The dose of CD34⁺/ROS^high/kg infused also inversely correlated with a shorter time to neutrophil engraftment; time to engraftment for patients receiving > or ≤3 × 10⁶ cells/kg was 11.5 days (range, 9 to 23) versus 14 days (range, 10 to 28), respectively (P = .02). The dose of ROS^high HSCs delivered did not correlate with platelet engraftment. Collectively, these data suggest that the dose of ROS^high stem cells delivered to patients may predict time to neutrophil engraftment after autologous transplantation.

Atorvastatin enhances bone marrow endothelial cell function in corticosteroid-resistant immune thrombocytopenia patients

Impaired BM EPCs were found in corticosteroid-resistant ITP patients. Atorvastatin improved BM EPC quantity and function, representing a novel therapy approach for corticosteroid-resistant ITP patients.

Update on current research into haploidentical hematopoietic stem cell transplantation

INTRODUCTION

Haploidentical stem cell transplantation (Haplo-SCT) is currently a suitable alternative worldwide for patients with hematological diseases, who lack human leukocyte antigen (HLA)-matched siblings or unrelated donors. Areas covered: This review summarizes the advancements in Haplo-SCT in recent years, primarily focusing on the global trends of haploidentical allograft, the comparison of outcomes between Haplo-SCT and other transplantation modalities, strategies for improving clinical outcomes, including donor selection, hematopoietic reconstitution promotion, and graft-versus-host disease, and relapse prevention/management, as well as the expanded indications of Haplo-SCT, such as severe aplastic anemia, myeloma and lymphoma. Expert commentary: Haploidentical allografts, including granulocyte colony-stimulating factor-based protocol and a post-transplant cyclophosphamide-based protocol, have been the mainstream strategy for Haplo-SCT. However, there are many unanswered questions in this field.

Replication stress in hematopoietic stem cells in mouse and man

Life-long blood regeneration relies on a rare population of self-renewing hematopoietic stem cells (HSCs). These cells' nearly unlimited self-renewal potential and lifetime persistence in the body signifies the need for tight control of their genome integrity. Their quiescent state, tightly linked with low metabolic activity, is one of the main strategies employed by HSCs to preserve an intact genome. On the other hand, HSCs need to be able to quickly respond to increased blood demands and rapidly increase their cellular output in order to fight infection-associated inflammation or extensive blood loss. This increase in proliferation rate, however, comes at the price of exposing HSCs to DNA damage inevitably associated with the process of DNA replication. Any interference with normal replication fork progression leads to a specialized molecular response termed replication stress (RS). Importantly, increased levels of RS are a hallmark feature of aged HSCs, where an accumulating body of evidence points to causative relationships between RS and the aging-associated impairment of the blood system's functional capacity. In this review, we present an overview of RS in HSCs focusing on its causes and consequences for the blood system of mice and men.

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.

Ruxolitinib/nilotinib cotreatment inhibits leukemia-propagating cells in Philadelphia chromosome-positive ALL

Background

As one of the major treatment obstacles in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ALL), relapse of Ph⁺ALL may result from the persistence of leukemia-propagating cells (LPCs). Research using a xenograft mouse assay recently determined that LPCs were enriched in the CD34⁺CD38⁻CD58⁻ fraction in human Ph⁺ALL. Additionally, a cohort study demonstrated that Ph⁺ALL patients with a LPCs phenotype at diagnosis exhibited a significantly higher cumulative incidence of relapse than those with the other cell phenotypes even with uniform front-line imatinib-based therapy pre- and post-allotransplant, thus highlighting the need for novel LPCs-based therapeutic strategies.

Methods

RNA sequencing (RNA-Seq) and real-time quantitative polymerase chain reaction (qRT-PCR) were performed to analyze the gene expression profiles of the sorted LPCs and other cell fractions from patients with de novo Ph⁺ALL. In order to assess the effects of the selective BCR–ABL and/or Janus kinase (JAK)2 inhibition therapy by the treatment with single agents or a combination of ruxolitinib and imatinib or nilotinib on Ph⁺ALL LPCs, drug-induced apoptosis of LPCs was investigated in vitro, as well as in vivo using sublethally irradiated and anti-CD122-conditioned NOD/SCID xenograft mouse assay. Moreover, western blot analyses were performed on the bone marrow cells harvested from the different groups of recipient mice.

Results

RNA-Seq and qRT-PCR demonstrated that JAK2 was more highly expressed in the sorted LPCs than in the other cell fractions in de novo Ph⁺ALL patients. Combination treatment with a selective JAK1/JAK2 inhibitor (ruxolitinib) and nilotinib more effectively eliminated LPCs than either therapy alone or both in vitro and in humanized Ph⁺ALL mice by reducing phospho-CrKL and phospho-JAK2 activities at the molecular level.

Conclusions

In summary, this pre-clinical study provides a scientific rationale for simultaneously targeting BCR–ABL and JAK2 activities as a promising anti-LPCs therapeutic approach for patients with de novo Ph⁺ALL.

DNA-damage response in hematopoietic stem cells: an evolutionary trade-off between blood regeneration and leukemia suppression

Self-renewing and multipotent hematopoietic stem cells (HSCs) maintain lifelong hematopoiesis. Their enormous regenerative potential coupled with lifetime persistence in the body, in contrast with the Progenitors, demand tight control of HSCs genome stability. Indeed, failure to accurately repair DNA damage in HSCs is associated with bone marrow failure and accelerated leukemogenesis. Recent observations exposed remarkable differences in several DNA-damage response (DDR) aspects between HSCs and Progenitors, especially in their DNA-repair capacities and susceptibility to apoptosis. Human HSCs in comparison with Progenitors exhibit delayed DNA double-strand break rejoining, persistent DDR signaling activation, higher sensitivity to the cytotoxic effects of ionizing radiation and attenuated expression of DNA-repair genes. Importantly, the distinct DDR of HSCs was also documented in mouse models. Nevertheless, physiological significance and the molecular basis of the HSCs-specific DDR features are only partially understood. Taking radiation-induced DDR as a paradigm, this review will focus on the current advances in understanding the role of cell-intrinsic DDR regulators and the cellular microenvironment in balancing stemness with genome stability. Pre-leukemia HSCs and clonal hematopoiesis evolvement will be discussed as an evolutionary compromise between the need for lifelong blood regeneration and DDR. Uniquely for this review, we outline the differences in HSCs-related DDR as highlighted by various experimental systems and attempt to provide their critical analysis.

Aberrant T cell responses in the bone marrow microenvironment of patients with poor graft function after allogeneic hematopoietic stem cell transplantation

Background

Poor graft function (PGF) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Nevertheless, whether abnormalities of T cell subsets in the bone marrow (BM) immune microenvironment, including Th17, Tc17, Th1, Tc1, Th2, Tc2 cells and regulatory T cells (Tregs), are involved in the pathogenesis of PGF remains unclear.

Methods

This prospective nested case–control study enrolled 20 patients with PGF, 40 matched patients with good graft function (GGF) after allo-HSCT, and 20 healthy donors (HD). Th17, Tc17, Th1, Tc1, Th2, Tc2 cells, Tregs and their subsets were analyzed by flow cytometry.

Results

A significantly higher proportion of stimulated CD4⁺ and CD8⁺ T cells that produced IL-17 (Th17 and Tc17) was found in the BM of PGF patients than in the BM of GGF patients and HD, whereas the percentages of Tregs in PGF patients were comparable to those in GGF patients and HD, resulting in a dramatically elevated ratio of Th17 cells/Tregs in the BM of PGF patients relative to those in GGF patients. Moreover, both CD4⁺ and CD8⁺ T cells were polarized towards a type 1 immune response in the BM of PGF patients.

Conclusions

The present study revealed that aberrant T cell responses in the BM immune microenvironment may be involved in the pathogenesis of PGF after allo-HSCT. These findings will facilitate the optimization of immune regulation strategies and improve the outcome of PGF patients post-allotransplant.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1159-y) contains supplementary material, which is available to authorized users.

Atorvastatin enhances endothelial cell function in posttransplant poor graft function

Dysfunctional BM EPCs were found in subjects with PGF postallotransplant. BM EPCs from subjects with PGF were enhanced by atorvastatin through downregulation of the p38 MAPK pathway.

Accumulation of DNA damage in the aged hematopoietic stem cell compartment

Aging is associated with loss of functional potential of multiple tissue systems, and there has been significant interest in understanding how tissue-specific cells contribute to this decline. DNA damage accumulation has been widely associated with aging in differentiated cell types. However, tissue-specific stem cells were once thought to be a geno-protected population, as damage accrued in a stem cell population has the potential to be inherited by differentiated progeny, as well as propagated within the stem cell compartment through self-renewal divisions. This review will discuss the evidence for DNA damage accumulation in the aged HSC compartment, potential drivers, and finally the consequences of the acquired damage.