Increased serum levels of high-mobility group box 1 protein in patients who developed acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Inflammasomes: potential therapeutic targets in hematopoietic stem cell transplantation

The realm of hematopoietic stem cell transplantation (HSCT) has witnessed remarkable advancements in elevating the cure and survival rates for patients with both malignant and non-malignant hematologic diseases. Nevertheless, a considerable number of patients continue to face challenges, including transplant-related complications, infection, graft failure, and mortality. Inflammasomes, the multi-protein complexes of the innate immune system, respond to various danger signals by releasing inflammatory cytokines and even mediating cell death. While moderate activation of inflammasomes is essential for immune defense and homeostasis maintenance, excessive activation precipitates inflammatory damage. The intricate interplay between HSCT and inflammasomes arises from their pivotal roles in immune responses and inflammation. This review examines the molecular architecture and composition of various types of inflammasomes, highlighting their activation and effector mechanisms within the context of the HSCT process and its associated complications. Additionally, we summarize the therapeutic implications of targeting inflammasomes and related factors in HSCT.

Association of High Mobility Group Box-Protein 1 and Platelet Microparticles in Patients After Hematopoietic Stem Cell Transplantation

Thrombotic complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT) significantly impact transplant outcomes. We focused on high mobility group box-protein (HMGB)1, one causative agent of thrombotic lesions in allo-HSCT, and investigated its association with platelets. We statistically analyzed available data from 172 patients with hematopoietic malignancies receiving allo-HSCT. A significant enhancement of monocyte-chemotactant protein-1, HMGB1, and platelet-derived microparticle (PDMP) levels was observed at day 0 after transplantation as compared to pre-transplantation. Multivariate analysis of the association among HMGB1 and 16 factors on day 0 revealed a significant correlation of HMGB1 levels with thrombin-antithrombin complex, interleukin-6, and PDMPs. High mobility group box-protein 1-induced procoagulant platelet induction and PDMP generation were performed in vitro using healthy platelets. High mobility group box-protein 1-induced PDMP generation was suppressed by toll-like receptor inhibitors and recombinant thrombomodulin. These results suggest that HMGB1 contributes to platelet activation in patients after allo-HSCT and is associated with PDMP-related thrombotic complications.

High mobility group box 1 (HMGB1): a pivotal regulator of hematopoietic malignancies

High mobility group box 1 (HMGB1) is a nonhistone chromatin-associated protein that has been widely reported to play a pivotal role in the pathogenesis of hematopoietic malignancies. As a representative damage-associated molecular pattern (DAMP), HMGB1 normally exists inside cells but can be secreted into the extracellular environment through passive or active release. Extracellular HMGB1 binds with several different receptors and interactors to mediate the proliferation, differentiation, mobilization, and senescence of hematopoietic stem cells (HSCs). HMGB1 is also involved in the formation of the inflammatory bone marrow (BM) microenvironment by activating proinflammatory signaling pathways. Moreover, HMGB1-dependent autophagy induces chemotherapy resistance in leukemia and multiple myeloma. In this review, we systematically summarize the emerging roles of HMGB1 in carcinogenesis, progression, prognosis, and potential clinical applications in different hematopoietic malignancies. In summary, targeting the regulation of HMGB1 activity in HSCs and the BM microenvironment is highly beneficial in the diagnosis and treatment of various hematopoietic malignancies.

Altered homeostatic regulation of innate and adaptive immunity in lower gastrointestinal tract GVHD pathogenesis

Lower gastrointestinal (GI) tract graft-versus-host disease (GVHD) is the predominant cause of morbidity and mortality from GVHD after allogeneic stem cell transplantation. Recent data indicate that lower GI tract GVHD is a complicated process mediated by donor/host antigenic disparities. This process is exacerbated by significant changes to the microbiome, and innate and adaptive immune responses that are critical to the induction of disease, persistence of inflammation, and a lack of response to therapy. Here, we discuss new insights into the biology of lower GI tract GVHD and focus on intrinsic pathways and regulatory mechanisms crucial to normal intestinal function. We then describe multiple instances in which these homeostatic mechanisms are altered by donor T cells or conditioning therapy, resulting in exacerbation of GVHD. We also discuss data suggesting that some of these mechanisms produce biomarkers that could be informative as to the severity of GVHD and its response to therapy. Finally, novel therapies that might restore homeostasis in the GI tract during GVHD are highlighted.

Danger Signals and Graft-versus-host Disease: Current Understanding and Future Perspectives

Graft-versus-host response after allogeneic hematopoietic stem cell transplantation (allo-HCT) represents one of the most intense inflammatory responses observed in humans. Host conditioning facilitates engraftment of donor cells, but the tissue injury caused from it primes the critical first steps in the development of acute graft-versus-host disease (GVHD). Tissue injuries release pro-inflammatory cytokines (such as TNF-α, IL-1β, and IL-6) through widespread stimulation of pattern recognition receptors (PRRs) by the release of danger stimuli, such as damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). DAMPs and PAMPs function as potent stimulators for host and donor-derived antigen presenting cells (APCs) that in turn activate and amplify the responses of alloreactive donor T cells. Emerging data also point towards a role for suppression of DAMP induced inflammation by the APCs and donor T cells in mitigating GVHD severity. In this review, we summarize the current understanding on the role of danger stimuli, such as the DAMPs and PAMPs, in GVHD.

The role of danger signals and ectonucleotidases in acute graft-versus-host disease

Allogeneic hematopoietic cell transplantation (allo-HCT) represents the only curative treatment approach for many patients with benign or malignant diseases of the hematopoietic system. However, post-transplant morbidity and mortality are significantly increased by the development of acute graft-versus-host disease (GvHD). While alloreactive T cells act as the main cellular mediator of the GvH reaction, recent evidence suggests a critical role of the innate immune system in the early stages of GvHD initiation. Danger-associated molecular patterns released from the intracellular space as well as from the extracellular matrix activate antigen-presenting cells and set pro-inflammatory pathways in motion. This review gives an overview about danger signals representing therapeutic targets with a clinical perspective with a particular focus on extracellular nucleotides and ectonucleotidases.

Relationship between HMGB1 and PAI-1 after allogeneic hematopoietic stem cell transplantation

Background

Conditioning regimens including total body irradiation (TBI) or cyclophosphamide can mobilize high-mobility group box 1 (HMGB1) to peripheral blood. Additionally, increased plasminogen activator inhibitor (PAI)-1 levels are associated with post-allogeneic hematopoietic stem cell transplantation (aHSCT). However, changes to circulating levels of HMGB1 after aHSCT are poorly understood.

Materials and methods

The study cohort included 289 patients who underwent aHSCT at one of 25 institutions in Japan. We have investigated the relationship between HMGB1 and PAI-1 following aHSCT. A significant increase in HMGB1 levels occurred after conditioning treatment. Additionally, levels of HMGB1 at day 0 were significantly increased in TBI+ patients and cyclophosphamide/TBI patients.

Conclusion

Our data revealed that an increased level of HMGB1 at day 0 following aHSCT correlates with increased PAI-1 after aHSCT, which is consistent with previous reports. Increased HMGB1 at day 0 after a conditioning regimen may play a role in transplantation-associated coagulopathy following aHSCT, because PAI-1 can accelerate procoagulant activity.

Innate immune activation by tissue injury and cell death in the setting of hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) with donor lymphocyte infusion is the mainstay of treatment for many types of hematological malignancies, but the therapeutic effect and prevention of relapse is complicated by donor T-cell recognition and attack of host tissue in a process known as graft-versus-host disease (GvHD). Cytotoxic myeloablative conditioning regimens used prior to Allo-HSCT result in the release of endogenous innate immune activators that are increasingly recognized for their role in creating a pro-inflammatory milieu. This increased inflammatory state promotes allogeneic T-cell activation and the induction and perpetuation of GvHD. Here, we review the processes of cellular response to injury and cell death that are relevant following Allo-HSCT and present the current evidence for a causative role of a variety of endogenous innate immune activators in the mediation of sterile inflammation following Allo-HSCT. Finally, we discuss the potential therapeutic strategies that target the endogenous pathways of innate immune activation to decrease the incidence and severity of GvHD following Allo-HSCT.

Elevation of high-mobility group box 1 after clinical autologous islet transplantation and its inverse correlation with outcomes

A major problem after clinical autologous islet transplantation (AIT) is the difficulty in achieving insulin independence. To follow up on our demonstration in a murine model that high-mobility group box 1 (HMGB1) was released from islets and involved in early loss of transplanted islets, we tested the role of HMGB1 in clinical AIT. Serum HMGB1 levels from 15 AIT patients were significantly elevated during islet infusion (7.6 ± 1.2 ng/ml) and 24 h after infusion (8.0 ± 1.4 ng/ml) compared to admission levels (2.4 ± 0.6 ng/ml). The first elevation of HMGB1 was associated with islet damage, but the later elevation was not. The change in the HMGB1 level from admission to first peak (ΔHMGB1) was significantly higher in the AIT group (8.1 ± 1.1 ng/ml) than in the pancreatectomy-only control (2.2 ± 0.5 ng/ml) (p < 0.05). Circulating serum levels of soluble receptor for advanced glycation end products (sRAGE) were also elevated during islet infusion. In vitro studies demonstrated that damaged human islets released HMGB1 but not sRAGE. In terms of outcomes, the insulin-free group showed significantly lower ΔHMGB1 (5.2 ± 0.6 ng/ml) and higher ΔsRAGE (2.3 ± 0.6 ng/ml) than the insulin-dependent group (10.6 ± 1.9 ng/ml and 0.7 ± 0.2 ng/ml, respectively). The ΔHMGB1 correlated with the number of white blood cell, IP-10, EGF, and eotaxin. In conclusion, serum HMGB1 was elevated in AIT and could be associated with inflammatory reactions that deteriorate islet engraftment. Therefore, anti-HMGB1 therapy might be a candidate for further improving the outcomes of clinical AIT.