Recruitment of CD8(+) T cells into bone marrow might explain the suppression of megakaryocyte apoptosis through high expression of CX3CR1(+) in prolonged isolated thrombocytopenia after allogeneic hematopoietic stem cell transplantation

The role of immune cells settled in the bone marrow on adult hematopoietic stem cells

Certain immune cells, including neutrophils, macrophages, dendritic cells, B cells, Breg cells, CD4+ T cells, CD8+ T cells, and Treg cells, establish enduring residency within the bone marrow. Their distinctive interactions with hematopoiesis and the bone marrow microenvironment are becoming increasingly recognized alongside their multifaceted immune functions. These cells play a dual role in shaping hematopoiesis. They directly influence the quiescence, self-renewal, and multi-lineage differentiation of hematopoietic stem and progenitor cells through either direct cell-to-cell interactions or the secretion of various factors known for their immunological functions. Additionally, they actively engage with the cellular constituents of the bone marrow niche, particularly mesenchymal stem cells, endothelial cells, osteoblasts, and osteoclasts, to promote their survival and contribute to tissue repair, thereby fostering a supportive environment for hematopoietic stem and progenitor cells. Importantly, these bone marrow immune cells function synergistically, both locally and functionally, rather than in isolation. In summary, immune cells residing in the bone marrow are pivotal components of a sophisticated network of regulating hematopoiesis.

HDAC3 single-nucleotide polymorphism rs2530223 is associated with increased susceptibility and severity of primary immune thrombocytopenia

INTRODUCTION

Primary immune thrombocytopenia (ITP) is an autoimmune hemorrhagic disorder characterized by a low platelet count and increased risk of bleeding. We previously reported that low-dose chidamide, a histone deacetylase (HDAC) inhibitor, restores immune tolerance in patients with ITP. This study aimed to evaluate the association of a single-nucleotide polymorphism (SNP) rs2530223 in the HDAC3 gene with susceptibility to ITP and its clinical features.

METHODS

Patients with ITP and age-matched healthy participants were recruited for this case-control study. Genotyping of the HDAC3 rs2530223 polymorphism was performed using MassARRAY platform.

RESULTS

Individuals with T allele of HDAC3 rs2530223 exhibited a 1.472-fold increased risk of ITP susceptibility (OR 1.472; 95% CI 1.100-1.969; p = .009), while ones with the TT genotype under the codominant and recessive models, and the TC/TT genotypes under the dominant model all revealed increased risk of ITP susceptibility (dominant odds ratio[OR] 1.965; 95% CI: 1.046-3.656; p = .036; codominant OR 2.264; 95% CI 1.175-4.360; p = .015; and recessive OR 1.512; 95% CI 1.028-2.224; p = .036, respectively). Regarding platelet counts in ITP patients, we observed that the TC/TT genotypes exhibited a 3.932-fold increased risk for platelet (PLT) <30 × 10⁹ /L (OR 3.932; 95% CI 1.426-10.842; p = .008).

CONCLUSION

This study indicates that HDAC3 rs2530223 may be an important genetic factor related to ITP susceptibility and platelet count in ITP patients, providing new perspectives on disease progression, new therapeutic targets, and severity prediction.

M2 macrophages, but not M1 macrophages, support megakaryopoiesis by upregulating PI3K-AKT pathway activity

Dysfunctional megakaryopoiesis hampers platelet production, which is closely associated with thrombocytopenia (PT). Macrophages (MФs) are crucial cellular components in the bone marrow (BM) microenvironment. However, the specific effects of M1 MФs or M2 MФs on regulating megakaryocytes (MKs) are largely unknown. In the current study, aberrant BM-M1/M2 MФ polarization, characterized by increased M1 MФs and decreased M2 MФs and accompanied by impaired megakaryopoiesis-supporting abilities, was found in patients with PT post-allotransplant. RNA-seq and western blot analysis showed that the PI3K-AKT pathway was downregulated in the BM MФs of PT patients. Moreover, in vitro treatment with PI3K-AKT activators restored the impaired megakaryopoiesis-supporting ability of MФs from PT patients. Furthermore, we found M1 MФs suppress, whereas M2 MФs support MK maturation and platelet formation in humans. Chemical inhibition of PI3K-AKT pathway reduced megakaryopoiesis-supporting ability of M2 MФs, as indicated by decreased MK count, colony-forming unit number, high-ploidy distribution, and platelet count. Importantly, genetic knockdown of the PI3K-AKT pathway impaired the megakaryopoiesis-supporting ability of MФs both in vitro and in a MФ-specific PI3K-knockdown murine model, indicating a critical role of PI3K-AKT pathway in regulating the megakaryopoiesis-supporting ability of M2 MФs. Furthermore, our preliminary data indicated that TGF-β released by M2 MФs may facilitate megakaryopoiesis through upregulation of the JAK2/STAT5 and MAPK/ERK pathways in MKs. Taken together, our data reveal that M1 and M2 MФs have opposing effects on MKs in a PI3K-AKT pathway-dependent manner, which may lead to new insights into the pathogenesis of thrombocytopenia and provide a potential therapeutic strategy to promote megakaryopoiesis.

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.

Reduced β2-GPI is associated with increased platelet aggregation and activation in patients with prolonged isolated thrombocytopenia after allo-HSCT

We aimed to measure platelet function and its relationship with β2-GPI in prolonged isolated thrombocytopenia (PT) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Fifty-six patients with PT and 60 allo-HSCT recipients without PT (non-PT controls) were enrolled. Platelet aggregation and activation, β2-GPI and anti-β2-GPI antibody levels, vWF antigen, and vWF activity were analyzed. The effect of β2-GPI on platelet aggregation was also measured ex vivo. Results showed that ADP-induced platelet aggregation significantly increased (39%±7.5% vs. 23%±8.5%, P=0.032), and the platelet expression of both CD62p (33.6%±11.6% vs. 8.5%±3.5%, P<0.001) and PAC-1 (42.4%±7.6% vs. 6.8%±2.2%, P<0.001) was significantly higher in patients with PT than in those without PT. Significantly lower β2-GPI levels (164.2±12 μg mL^-1 vs. 234.2±16 μg mL^-1, P<0.001), higher anti-β2-GPI IgG levels (1.78±0.46 U mL^-1 vs. 0.94±0.39 U mL^-1, P<0.001), and increased vWF activity (133.06%±30.50% vs. 102.17%±25.90%, P<0.001) were observed in patients with PT than in those without PT. Both ADP-induced platelet aggregation (n=116, r²=-0.5042, P<0.001) and vWF activity (n=116, r²=-0.2872, P<0.001) were negatively correlated with β2-GPI levels. In summary, our data suggested that platelet aggregation and activation were significantly higher in patients with PT than in those without PT, which might be associated with reduced β2-GPI levels. The reduced β2-GPI levels might be due to the existence of anti-β2-GPI IgG.

Interferon-Gamma-Mediated Osteoimmunology

Osteoimmunology is the interdiscipline that focuses on the relationship between the skeletal and immune systems. They are interconnected by shared signal pathways and cytokines. Interferon-gamma (IFN-γ) plays important roles in immune responses and bone metabolism. IFN-γ enhances macrophage activation and antigen presentation. It regulates antiviral and antibacterial immunity as well as signal transduction. IFN-γ can promote osteoblast differentiation and inhibit bone marrow adipocyte formation. IFN-γ plays dual role in osteoclasts depending on its stage. Furthermore, IFN-γ is an important pathogenetic factor in some immune-mediated bone diseases including rheumatoid arthritis, postmenopausal osteoporosis, and acquired immunodeficiency syndrome. This review will discuss the contradictory findings of IFN-γ in osteoimmunology and its clinical application potential.

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.

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.

Donor-Specific Anti-Human Leukocyte Antigen Antibodies Predict Prolonged Isolated Thrombocytopenia and Inferior Outcomes of Haploidentical Hematopoietic Stem Cell Transplantation

Prolonged isolated thrombocytopenia (PT) after allogeneic stem cell transplantation (allo-SCT) has a great impact on transplant outcome. In this study, we performed a retrospective analysis to investigate the association of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) with PT in 394 patients who underwent unmanipulated haploidentical blood and marrow transplantation (HBMT). For HLA antibody positive samples with a median fluorescent intensity (MFI) > 500, DSAs were further examined. A total of 390 patients (99.0%) achieved sustained myeloid engraftment. Of the 394 cases tested, 45 (11.4%) were DSA positive. The cumulative incidence of PT in this cohort of patients was 9.9 ± 1.5%. The incidence of PT was higher in patients with a MFI ≥ 1000 compared with those with a MFI < 1000 (16.8 ± 6.4% versus 7.4 ± 1.4%, P = 0.05). Multivariate analysis showed that the presence of DSAs (MFI ≥ 1000) was correlated to PT (hazard ratio (HR) 3.262; 95% confidence interval (CI), 1.339-7.946; P = 0.009) and transplant-related mortality (HR 2.320; 95% CI, 1.169-4.426; P = 0.044). Our results, for the first time, suggest an association of DSAs with PT after unmanipulated HBMT. It would help screen out the suitable donor and guide intervention. This indicated that DSAs should be incorporated in the algorithm for unmanipulated HBMT.

High-dose corticosteroid associated with catheter-related thrombosis after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients are at an increased risk of thrombotic complications, most of which are catheter-related and present a substantial challenge. The incidence of CRT varies considerably depending on clinical factors. However, the underlying pathogenesis and risk factors remain unclear.

METHODS

We performed a retrospective nested case-control study in patients following allo-HSCT. Thrombotic episodes were diagnosed based on the clinical suspicion of the physician (pain, swelling, etc.) with subsequent CVC or PICC thrombosis confirmed via duplex ultrasound. Cases with CRT and controls were matched for time of HSCT, age at HSCT, donor source and type of insertion (CVCs or PICC).

RESULTS

During the 8-year period, catheters were placed in 2896 patients, with a total of 40 patients (1.38%) developed CRT, among which 11 were associated with CVCs and 29 were associated with PICCs. The median duration from catheter insertion to thrombosis was 97days. Despite reports of an association between thrombosis and infection, central line-associated bloodstream infection was comparable between groups. No significant differences were noted in terms of primary disease, donor type, conditioning regimen or catheter type between the cases and controls. A multivariate regression analysis identified high-dose corticosteroids as independent risk factors for the development of CRT. CRT seems to negatively affect prognosis in allo-HSCT patients.

CONCLUSION

In conclusion, we demonstrate that the use of high-dose corticosteroids is correlated with the onset of CRT. However, the efficacy and safety of thromboprophylaxis in this population require further investigation.

Controlled, Randomized, Open-Label Trial of Risk-Stratified Corticosteroid Prevention of Acute Graft-Versus-Host Disease After Haploidentical Transplantation

PURPOSE

This study evaluated whether a prophylaxis strategy directed by the graft-versus-host disease (GVHD) biomarker might reduce the 100-day incidence of acute GVHD grades II to IV.

PATIENTS AND METHODS

This controlled, open-label, randomized trial included 228 patients who underwent haploidentical transplantation. On the basis of bone marrow allogeneic graft CD4:CD8 ratios, patients were categorized as low risk (n = 83; group A) or high risk (n = 145). Patients at high risk were randomly assigned to either receive (n = 72; group B) or not receive (n = 73; group C) low-dose corticosteroid prophylaxis.

RESULTS

The incidence in group B was 21% (95% CI, 11% to 31%) compared with 26% (95% CI, 16%to 36%; P = .43) in group A and 48% (95% CI, 32% to 60%; P < .001) in group C. Low-dose corticosteroid prophylaxis was significantly associated with a relatively low risk of acute GVHD grades II to IV (hazard ratio, 0.66; 95% CI, 0.49 to 0.89; P = .007) and rapid platelet recovery (hazard ratio, 0.30; 95% CI, 0.23 to 0.47; P < .001). The incidence of moderate-to-severe chronic GVHD in group B (21%) was lower than that in both group A (50%; P = .025) and group C (36%; P = .066). The 100-day corticosteroid doses were 205 ± 111 mg in group B, 229 ± 149 mg in group A (P = .256), and 286.54 ± 259.67 mg in group C (P = .016). Compared with group C, group B showed significantly lower incidences of femoral head necrosis (P = .034) and hypertension (P = .015). Infection rates were comparable among these groups.

CONCLUSION

Our results suggest that risk stratification-directed, low-dose corticosteroid prophylaxis significantly decreased the incidence of acute GVHD grades II to IV, accelerated platelet recovery, and reduced adverse events without increasing infections.

Desialylation is associated with apoptosis and phagocytosis of platelets in patients with prolonged isolated thrombocytopenia after allo-HSCT

BACKGROUND

Prolonged isolated thrombocytopenia (PT) is a frequent complication in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT), and it is associated with an adverse prognosis. In this study, we hypothesized that desialylation on platelet surfaces was associated with PT after allo-HSCT. The mechanisms participating in this process may include NEU1 translocation, platelet apoptosis, and phagocytosis by macrophages.

METHODS

PT was defined as a peripheral platelet count less than 100 × 10(9)/L without sustained anemia or leukopenia for more than 3 months after allo-HSCT. 34 patients were identified consecutively from a cohort of 255 patients who underwent allo-HSCT for hematologic malignancies between May and October 2014 at Peking University Institute of Hematology. Desialylation, enzyme expression, and phagocytosis were detected using flow cytometry, immunofluorescence, RT-PCR, Western blot, and so on.

RESULTS

Platelets from the PT patients had significantly fewer sialic acids (P = .001) and increased β-galactose exposure indicative of desialylation on the surface (P = .042), and serum from the PT patients showed a higher sialic acid concentration (8.400 ± 0.2209 μmol/L, P < .001). The sialidase NEU1 was over-expressed from mRNA to protein levels, and its catalytic activity was increased in platelets from the PT patients. Desialylation of GPIbα in the PT patients was correlated with changes in 14-3-3ζ distribution, which, relative to Bad activation, modulated the expression of Bcl-2 family proteins, depolarized the inner membrane of the mitochondria, and initiated the intrinsic mitochondria-dependent pathway of apoptosis. Macrophages derived from the THP-1 cell line preferred to phagocytize desialylated platelets from the PT patients in vitro. We also revealed that oseltamivir (400 μmol/L) could inhibit 50 % of the sialidase activity on platelets and could protect 20 % of platelets from phagocytosis in vitro.

CONCLUSIONS

Desialylation of platelets was associated with platelet apoptosis and phagocytosis, whereas oseltamivir could reduce platelet destruction in the periphery, indicating a potential novel treatment for PT after allo-HSCT.