The biology of graft-versus-host disease: experimental systems instructing clinical practice. Blood. 2014;124:354-362. [PMID: 24914137 DOI: 10.1182/blood-2014-02-514745]

Simple, Rapid, Reproducible and Biomarker-Validated Clinical Grading System for Murine Models of Xenogeneic Graft-Versus-Host Disease

Experiment models of xenogeneic graft-versus-host disease (xeno-GVHD), in which human immune cells are injected into immunodeficient mice, are increasingly used to study human immune cell behavior in vivo and to test therapeutic approaches. Today, the main, and more commonly accepted clinical parameters used to characterize xeno-GVHD are weight loss and mortality. These criteria do not provide an accurate and subtle assessment of the disease intensity, nor do they reflect the great variability of xeno-GVHD, which depends on the donor. Relying on previous work in which we described an original clinical grading system for assessing GVHD in mice, we propose an adaptation of this system for xeno-GVHD models. This simple, solid, and reproducible scoring system of xeno-GVHD is constituted of the binary (yes or no) evaluation of 4 easy-to-evaluate parameters that reflect the complexity of the disease without the need to sacrifice the mice. This scoring system is consistent with the gold standard histological grading of human GVHD and with numerous biomarkers characteristic of the disease. We propose this new clinical grading system to evaluate and compare the results obtained with a common tool, regardless of the experimenters and laboratories where the experiments would have been carried out and whatever the therapeutic strategy evaluated.

Macrophages in graft-versus-host disease (GVHD): dual roles as therapeutic tools and targets

Graft-versus-host disease remains one of the most formidable barriers to the complete success of hematopoietic stem cell transplantation that has emerged as the curative approach for many hematopoietic malignancies because it affects quality of life and overall survival. Macrophages are among the important members of the immune system, which perform dual roles in GVHD as both therapeutic tools and targets. This review epitomizes the multifunctional role of macrophages in the pathophysiology of both acute and chronic GVHD. Macrophages play an important role in the early phase of GVHD because of their recruitment and infiltration into target organs. Furthermore, they polarize into two functionally different phenotypes, including M1 and M2. In the case of acute GVHD, most macrophages express the M1 phenotype characterized by the production of pro-inflammatory cytokines that contribute to tissue damage. In contrast, in chronic GVHD, macrophages tend toward the M2 phenotype associated with the repair of tissues and fibrosis. A critical balance among these phenotypes is central to the course and severity of GVHD. Further interactions of macrophages with other lymphocytes such as T cells, B cells, and fibroblast further determine the course of GVHD. Macrophage interaction associated with alloreactive T cells promotes inflammation. This is therefore important in inducing injuries of tissues during acute GVHD. Interaction of macrophages, B cell, fibroblast, and CD4+ T cells promotes fibrosis during chronic GVHD and, hence, the subsequent dysfunction of organs. These are some insights, while several challenges remain. First, the impact of the dominant cytokines in GVHD on the polarization of macrophages is incompletely characterized and sometimes controversial. Second, the development of targeted therapies able to modulate macrophage function without systemic side effects remains an area of ongoing investigation. Future directions involve the exploration of macrophage-targeted therapies, including small molecules, antibodies, and nanotechnology, which modulate macrophage behavior and improve patient outcomes. This underlines the fact that a profound understanding of the dual role of macrophages in GVHD is essential for developing new and more effective therapeutic strategies. Targeting macrophages might represent one avenue for decreasing the incidence and severity of GVHD and improving the success and safety of HSCT.

Improving bench-to-bedside translation for acute graft-versus-host disease models

The transplantation of allogeneic hematopoietic stem cells is a potentially curative treatment for hematological malignancies, inherited blood disorders and immune deficiencies. Unfortunately, 30-50% of patients receiving allogeneic hematopoietic stem cells will develop a potentially life-threatening inflammatory disease called acute graft-versus-host disease (aGVHD). In patients with aGVHD, graft-associated T cells, which typically target the skin, intestinal tract and liver, can also damage the lungs and lymphoid tissue. Damage to lymphoid tissue creates prolonged immunodeficiency that markedly increases the risk of infections and bleeding, resulting in considerable morbidity and mortality. Although mouse models of aGVHD have been instrumental to our understanding of this condition's pathogenesis, translation of preclinical data into new and more effective treatments for human disease has been limited for reasons that remain to be fully understood. However, evidence suggests that factors associated with mouse models of aGVHD likely contribute to these unsatisfactory results. In this Review, we identify and discuss the specific factors inherent to mouse models of aGVHD that may limit the translation of preclinical data to patient treatment, and suggest how to improve the translatability of these models.

Chemokine receptors are required for effector T-cell trafficking to GVHD tissues but not to bone marrow

ABSTRACT

In allogeneic hematopoietic stem cell transplantation (allo-SCT), alloreactive donor T cells mediate the graft-versus-leukemia effect but also attack nonhematopoietic tissues, causing graft-versus-host disease (GVHD). Reducing alloreactive T-cell trafficking to GVHD target tissues while allowing their access to bone marrow (BM) and spleen, major sites of malignant hematopoiesis, is a rational strategy for reducing the GVHD risk when using alloreactive T cells as a therapeutic. Here, we show that effector T-cell (Teff) entry into BM and spleen in unmanipulated mice and in mice that received transplantation without alloreactive T cells is augmented by pertussis toxin (PTX)-sensitive chemokine receptor signaling. However, unexpectedly, in the presence of a GVH response, chemokines no longer draw T cells into BM and spleen but remain critical for their recruitment to GVHD target tissues. Consistent with this, PTX-treated Teff cells were as efficacious as untreated T cells in killing leukemia cells in BM and spleen in mice with a concurrent GVHD response. These results suggest a strategy to improve the safety of alloreactive T-cell therapeutics in treating leukemias in the context of an allo-SCT.

Clinicopathologic Effects of Xenogeneic GvHD Induced by Adoptively Transferred Human-Derived T Cells in Severely Immunodeficient Mice

BACKGROUND

Xenogeneic graft-versus-host disease (xGvHD) is an inevitable confounder of preclinical evaluation of adoptive immunotherapies on tumor-bearing immunodeficient mouse models. This study was designed to appraise the clinical and histopathological effects caused by xGvHD in severely immunodeficient mice considering the T cell dosage.

METHODS

Fifty NOG mice underwent intraperitoneal injection of three different doses of human-derived total T cells, a high dose of CD8+T cells, or vehicle (as control). Clinical and histopathological status of the study subjects were evaluated and compared according to scoring systems.

RESULTS

In mice receiving higher doses of total T cells, the clinical severity of xGvHD was greater. However, recipients of CD8+T cells developed none to mild xGvHD manifestations. Higher doses of T cells were associated with poorer outcomes including premature death and more severe histopathologic damages. Greater CD3+T cell tissue engraftment (immunohistochemical CD3 positivity) was associated with more severe xGvHD-induced histopathological damages. Clinical xGvHD scores were significantly correlated with histopathological xGvHD scores in total and in each tissue. Mice with severe cutaneous symptoms had higher scores of xGvHD-induced histopathologic changes in the skin. Lethargy was associated with higher histopathological scores in the lungs, liver and spleen.

CONCLUSION

In preclinical evaluations, lower doses of T cell-based therapies are associated with milder xGvHD. Development of xGvHD may be averted by the use of CD4+T cell-depleted grafts. Histopathological and clinical scoring systems for evaluating xGvHD are significantly correlated. The lungs and liver are reliable organs for histopathological assessment and scoring of xGvHD.

Local administration of myeloid-derived suppressor cells prevents progression of immune-mediated dry eye disease

Myeloid derived suppressor cells (MDSCs) are a heterogenous population of immature hematopoietic precursors with known immunoregulatory functions. The immunosuppressive role of MDSCs has been highlighted in several inflammatory ophthalmic disorders; however, their therapeutic application in suppressing the immune-mediated changes in dry eye disease (DED) has not been studied. We observed significant reduction in antigen presenting cell (APC) frequencies and their maturation in the presence of MDSCs. Moreover, co-culturing MDSCs with T helper 17 cells (Th17) resulted in reduced Th17 frequencies and their IL-17 expression. On the contrary, MDSCs maintained regulatory T cell frequencies and enhanced their function in-vitro. Furthermore, we delineated the role of interleukin-10 (IL-10) secreted by MDSCs in their immunoregulatory functions. We confirmed these results by flow cytometry analysis and observed that treatment with MDSCs in DED mice effectively suppressed the maturation of APCs, pathogenic Th17 response, and maintained Treg function and significantly ameliorated the disease. The results in this study highlight the potential therapeutic application of MDSCs in treating refractory DED.

Graft-versus-leukaemia immunity is retained following treatment with post-transplant cyclophosphamide alone or combined with tocilizumab in humanised mice

Objectives

Donor haematopoietic stem cell transplantation treats leukaemia by inducing graft-versus-leukaemia (GVL) immunity. However, this benefit is often mitigated by graft-versus-host disease (GVHD), which is reduced by post-transplant cyclophosphamide (PTCy) alone or combined with tocilizumab (TOC) in humanised mice. This study established a preclinical humanised mouse model of GVL and investigated whether PTCy alone or combined with TOC impacts GVL immunity.

Methods

NOD-scid-IL2Rγnull mice were injected with 2 × 107 human peripheral blood mononuclear cells (hPBMCs) on day 0 and with 1 × 106 THP-1 acute myeloid leukaemia cells on day 14. In subsequent experiments, mice were also injected with PTCy (33 mg kg-1) or Dulbecco's phosphate buffered saline (PBS) on days 3 and 4, alone or combined with TOC or control antibody (25 mg kg-1) twice weekly for 28 days. Clinical signs of disease were monitored until day 42.

Results

Mice with hPBMCs from three different donors and THP-1 cells showed similar survival, clinical score and weight loss. hCD33+ leukaemia cells were minimal in mice reconstituted with hPBMCs from two donors but present in mice with hPBMCs from a third donor, suggesting donor-specific GVL responses. hPBMC-injected mice treated with PTCy alone or combined with TOC (PTCy + TOC) demonstrated prolonged survival compared to control mice. PTCy alone and PTCy + TOC-treated mice with hPBMCs showed minimal hepatic hCD33+ leukaemia cells, indicating sustained GVL immunity. Further, the combination of PTCy + TOC reduced histological damage in the lung and liver.

Conclusion

Collectively, this research demonstrates that PTCy alone or combined with TOC impairs GVHD without compromising GVL immunity.

Post-Transplant Cyclophosphamide Combined with Brilliant Blue G Reduces Graft-versus-Host Disease without Compromising Graft-versus-Leukaemia Immunity in Humanised Mice

Allogeneic haematopoietic stem cell transplantation (HSCT) leads to the establishment of graft-versus-leukaemia (GVL) immunity, but in many cases also results in the development of graft-versus-host disease (GVHD). This study aimed to determine if P2X7 antagonism using Brilliant Blue G (BBG) could improve the beneficial effects of post-transplant cyclophosphamide (PTCy) in a humanised mouse model of GVHD, without comprising GVL immunity. NOD.Cg-Prkdcscid Il2rgtm1Wjl (NSG) mice were injected with human peripheral blood mononuclear cells (PBMCs) (Day 0), then with cyclophosphamide (33 mg/kg) on Days 3 and 4, and with BBG (50 mg/kg) (or saline) on Days 0-10. PTCy with BBG reduced clinical GVHD development like that of PTCy alone. However, histological analysis revealed that the combined treatment reduced liver GVHD to a greater extent than PTCy alone. Flow cytometric analyses revealed that this reduction in liver GVHD by PTCy with BBG corresponded to an increase in human splenic CD39+ Tregs and a decrease in human serum interferon-γ concentrations. In additional experiments, humanised NSG mice, following combined treatment, were injected with human THP-1 acute myeloid leukaemia cells on Day 14. Flow cytometric analyses of liver CD33+ THP-1 cells showed that PTCy with BBG did not mitigate GVL immunity. In summary, PTCy combined with BBG can reduce GVHD without compromising GVL immunity. Future studies investigating P2X7 antagonism in combination with PTCy may lead to the development of novel treatments that more effectively reduce GVHD in allogeneic HSCT patients without promoting leukaemia relapse.

Understanding the Needs and Lived Experiences of Patients With Graft-Versus-Host Disease: Real-World European Public Social Media Listening Study

BACKGROUND

Graft-versus-host disease (GVHD) is the major cause of short- and long-term morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Treatment options beyond corticosteroid therapy remain limited, and prolonged treatment often leads to impaired quality of life (QoL). A better understanding of the needs and experiences of patients with GVHD is required to improve patient care.

OBJECTIVE

The aim of this study is to explore different social media (SM) channels for gathering and analyzing the needs and experiences of patients and other stakeholders across 14 European countries.

METHODS

We conducted a retrospective analysis of SM data from the public domain. The Talkwalker social analytics tool collected data from open-access forums, blogs, and various social networking sites using predefined search strings. The raw data set derived from the aggregator tool was automatically screened for the relevancy of posts, generating the curated data set that was manually reviewed to identify posts that fell within the predefined inclusion and exclusion criteria. This final data set was then used for the deep-dive analysis.

RESULTS

A total of 9016 posts relating to GVHD were identified between April 2019 and April 2021. Deduplication and relevancy checks resulted in 325 insightful posts, with Twitter contributing 250 (77%) posts; blogs, 49 (15%) posts; forums, 13 (4%) posts; Facebook, 7 (2%) posts; and Instagram and YouTube, 4 (1%) posts. Patients with GVHD were the primary stakeholders, contributing 63% of all SM posts. In 234 posts, treatment was the most discussed stage of the patient journey (68%), followed by symptoms (33%), and diagnosis and tests (21%). Among treatment-related posts (n=159), steroid therapy was most frequently reported (54/159, 34%). Posts relating to treatment features (n=110) identified efficacy (45/110, 41%), side effects (38/110, 35%), and frequency and dosage (32/110, 29%), as the most frequently discussed features. Symptoms associated with GVHD were described in 24% (77/325) of posts, including skin-related conditions (49/77, 64%), dry eyes or vision change (13/77, 17%), pain and cramps (16/77, 21%), and fatigue or muscle weakness (12/77, 16%). The impacts of GVHD on QoL were discussed in 51% (165/325) of all posts, with the emotional, physical and functional, social, and financial impacts mentioned in 69% (114/165), 50% (82/165), 5% (8/165), and 2% (3/165) of these posts, respectively. Unmet needs were reported by patients or caregivers in 24% (77/325) of analyzed conversations, with treatment-related side effects being the most common (35/77, 45%) among these posts.

CONCLUSIONS

SM listening is a useful tool to identify medical needs. Treatment of GVHD, including treatment-related side effects, as well as its emotional and physical impact on QoL, are the major topics that GVHD stakeholders mention on SM. We encourage a structured discussion of these topics in interactions between health care providers and patients with GVHD.

TRIAL REGISTRATION

Not applicable.

Acute Myeloid Leukemia Causes T Cell Exhaustion and Depletion in a Humanized Graft-versus-Leukemia Model

Allogeneic hematopoietic stem cell transplantation (alloSCT) is, in many clinical settings, the only curative treatment for acute myeloid leukemia (AML). The clinical benefit of alloSCT greatly relies on the graft-versus-leukemia (GVL) effect. However, AML relapse remains the top cause of posttransplant death; this highlights the urgent need to enhance GVL. Studies of human GVL have been hindered by the lack of optimal clinically relevant models. In this article, we report, the successful establishment of a novel (to our knowledge) humanized GVL model system by transplanting clinically paired donor PBMCs and patient AML into MHC class I/II knockout NSG mice. We observed significantly reduced leukemia growth in humanized mice compared with mice that received AML alone, demonstrating a functional GVL effect. Using this model system, we studied human GVL responses against human AML cells in vivo and discovered that AML induced T cell depletion, likely because of increased T cell apoptosis. In addition, AML caused T cell exhaustion manifested by upregulation of inhibitory receptors, increased expression of exhaustion-related transcription factors, and decreased T cell function. Importantly, combined blockade of human T cell-inhibitory pathways effectively reduced leukemia burden and reinvigorated CD8 T cell function in this model system. These data, generated in a highly clinically relevant humanized GVL model, not only demonstrate AML-induced inhibition of alloreactive T cells but also identify promising therapeutic strategies targeting T cell depletion and exhaustion for overcoming GVL failure and treating AML relapse after alloSCT.

Defining a TCF1-expressing progenitor allogeneic CD8+ T cell subset in acute graft-versus-host disease

Graft-versus-host disease (GvHD) is a severe complication of hematopoietic stem cell transplantation driven by activated allogeneic T cells. Here, we identify a distinct subset of T cell factor-1 (TCF1)+ CD8+ T cells in mouse allogeneic and xenogeneic transplant models of acute GvHD. These TCF1+ cells exhibit distinct characteristics compared to TCF1- cells, including lower expression of inhibitory receptors and higher expression of costimulatory molecules. Notably, the TCF1+ subset displays exclusive proliferative potential and could differentiate into TCF1- effector cells upon antigenic stimulation. Pathway analyses support the role of TCF1+ and TCF1- subsets as resource cells and effector cells, respectively. Furthermore, the TCF1+ CD8+ T cell subset is primarily present in the spleen and exhibits a resident phenotype. These findings provide insight into the differentiation of allogeneic and xenogeneic CD8+ T cells and have implications for the development of immunotherapeutic strategies targeting acute GvHD.

Immunotherapy in hematologic malignancies: achievements, challenges and future prospects

The immune-cell origin of hematologic malignancies provides a unique avenue for the understanding of both the mechanisms of immune responsiveness and immune escape, which has accelerated the progress of immunotherapy. Several categories of immunotherapies have been developed and are being further evaluated in clinical trials for the treatment of blood cancers, including stem cell transplantation, immune checkpoint inhibitors, antigen-targeted antibodies, antibody-drug conjugates, tumor vaccines, and adoptive cell therapies. These immunotherapies have shown the potential to induce long-term remission in refractory or relapsed patients and have led to a paradigm shift in cancer treatment with great clinical success. Different immunotherapeutic approaches have their advantages but also shortcomings that need to be addressed. To provide clinicians with timely information on these revolutionary therapeutic approaches, the comprehensive review provides historical perspectives on the applications and clinical considerations of the immunotherapy. Here, we first outline the recent advances that have been made in the understanding of the various categories of immunotherapies in the treatment of hematologic malignancies. We further discuss the specific mechanisms of action, summarize the clinical trials and outcomes of immunotherapies in hematologic malignancies, as well as the adverse effects and toxicity management and then provide novel insights into challenges and future directions.

Tissue-specific features of the T cell repertoire after allogeneic hematopoietic cell transplantation in human and mouse

T cells are the central drivers of many inflammatory diseases, but the repertoire of tissue-resident T cells at sites of pathology in human organs remains poorly understood. We examined the site-specificity of T cell receptor (TCR) repertoires across tissues (5 to 18 tissues per patient) in prospectively collected autopsies of patients with and without graft-versus-host disease (GVHD), a potentially lethal tissue-targeting complication of allogeneic hematopoietic cell transplantation, and in mouse models of GVHD. Anatomic similarity between tissues was a key determinant of TCR repertoire composition within patients, independent of disease or transplant status. The T cells recovered from peripheral blood and spleens in patients and mice captured a limited portion of the TCR repertoire detected in tissues. Whereas few T cell clones were shared across patients, motif-based clustering revealed shared repertoire signatures across patients in a tissue-specific fashion. T cells at disease sites had a tissue-resident phenotype and were of donor origin based on single-cell chimerism analysis. These data demonstrate the complex composition of T cell populations that persist in human tissues at the end stage of an inflammatory disorder after lymphocyte-directed therapy. These findings also underscore the importance of studying T cell in tissues rather than blood for tissue-based pathologies and suggest the tissue-specific nature of both the endogenous and posttransplant T cell landscape.

The delicate balance of graft versus leukemia and graft versus host disease after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

The curative basis of allogeneic hematopoietic stem cell transplantation (HSCT) relies in part upon the graft versus leukemia (GvL) effect, whereby donor immune cells recognize and eliminate recipient malignant cells. However, alloreactivity of donor cells against recipient tissues may also be deleterious. Chronic graft versus host disease (cGvHD) is an immunologic phenomenon wherein alloreactive donor T cells aberrantly react against host tissues, leading to damaging inflammatory symptoms.

AREAS COVERED

Here, we discuss biological insights into GvL and cGvHD and strategies to balance the prevention of GvHD with maintenance of GvL in modern HSCT.

EXPERT OPINION/COMMENTARY

Relapse remains the leading cause of mortality after HSCT with rates as high as 40% for some diseases. GvHD is a major cause of morbidity after HSCT, occurring in up to half of patients and responsible for 15-20% of deaths after HSCT. Intriguingly, the development of chronic GvHD may be linked to lower relapse rates after HSCT, suggesting that GvL and GvHD may be complementary sides of the immunologic foundation of HSCT. The ability to fine tune the balance of GvL and GvHD will lead to improvements in survival, relapse rates, and quality of life for patients undergoing HSCT.

Assessment of therapeutic role of mesenchymal stromal cells in mouse models of graft-versus-host disease using cryo-imaging

Insights regarding the biodistribution and homing of mesenchymal stromal cells (MSCs), as well as their interaction with alloreactive T-cells are critical for understanding how MSCs can regulate graft-versus-host disease (GVHD) following allogeneic (allo) bone marrow transplantation (BMT). We developed novel assays based on 3D, microscopic, cryo-imaging of whole-mouse-sized volumes to assess the therapeutic potential of human MSCs using an established mouse GVHD model. Following infusion, we quantitatively tracked fluorescently labeled, donor-derived, T-cells and third party MSCs in BMT recipients using multispectral cryo-imaging. Specific MSC homing sites were identified in the marginal zones in the spleen and the lymph nodes, where we believe MSC immunomodulation takes place. The number of MSCs found in spleen of the allo BMT recipients was about 200% more than that observed in the syngeneic group. To more carefully define the effects MSCs had on T cell activation and expansion, we developed novel T-cell proliferation assays including secondary lymphoid organ (SLO) enlargement and Carboxyfluoescein succinimidyl ester (CFSE) dilution. As anticipated, significant SLO volume enlargement and CFSE dilution was observed in allo but not syn BMT recipients due to rapid proliferation and expansion of labeled T-cells. MSC treatment markedly attenuated CFSE dilution and volume enlargement of SLO. These assays confirm evidence of potent, in vivo, immunomodulatory properties of MSC following allo BMT. Our innovative platform includes novel methods for tracking cells of interest as well as assessing therapeutic function of MSCs during GVHD induction. Our results support the use of MSCs treatment or prevention of GVHD and illuminate the wider adoption of MSCs as a standard medicinal cell therapy.

Extracorporeal photopheresis for the treatment of chronic graft versus host disease

OBJECTIVES

Chronic graft versus host disease (chronic GVHD) still remains the leading cause of late morbidity and mortality for allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients. In this retrospective study, 53 consecutive allo-HSCT patients with chronic GVHD refractory to corticosteroids were treated with extracorporeal photopheresis (ECP).

METHODS

This study was performed as a retrospective single-center study. Medical records of a total of 59 patients treated with ECP for chronic GVHD were reviewed.

RESULTS

Best organ responses to ECP were observed in skin, mouth mucosa, eyes and liver. Overall response rate (ORR) to ECP was 81.2% (CR 17% and PR 64.2%). Overall survival (OS) was 84.9% and 36.7%, at 1 and 3 years, respectively. Female sex appears to have an advantage on ORR. Patients achieving ORR were able to maintain their responses with a prolonged continuation of treatments for +6 and +12 months indicating the benefits of longer ECP treatment.

DISCUSSION

We found that patients with chronic GVHD who were treated with ECP for 12 months or longer had a higher response rate. Our findings in line with the data reported previously suggest that patients responding to ECP should continue longer therapy schedules to achieve a better and sustained response. In our cohort, long-term ECP therapy was safe and well-tolerated with no significant adverse effects. Best responses were observed in the patients with skin, eye, liver and oral involvement. The ECP procedure offers the advantage relative to the problems with typical immunosuppressive agents. The female sex appeared to have an advantage based on the cumulative probability of the OR after ECP for chronic GVHD.

Dendritic cell-derived IL-27 p28 regulates T cell program in pathogenicity and alleviates acute graft-versus-host disease

Interleukin 27 (IL-27), a heterodimeric cytokine composed of Epstein-Barr virus-induced 3 and p28, is a pleiotropic cytokine with both pro-and anti-inflammatory properties. However, the precise role of IL-27 in acute graft-versus-host disease is not yet fully understood. In this study, utilizing mice with IL-27 p28 deficiency in dendritic cells (DCs), we demonstrated that IL-27 p28 deficiency resulted in impaired Treg cell function and enhanced effector T cell responses, corresponding to aggravated aGVHD in mice. In addition, using single-cell RNA sequencing, we found that loss of IL-27 p28 impaired Treg cell generation and promoted IL-1R2⁺TIGIT⁺ pathogenic CD4⁺ T cells in the thymus at a steady state. Mechanistically, IL-27 p28 deficiency promoted STAT1 phosphorylation and Th1 cell responses, leading to the inhibition of Treg cell differentiation and function. Finally, patients with high levels of IL-27 p28 in serum showed a substantially decreased occurrence of grade II-IV aGVHD and more favorable overall survival than those with low levels of IL-27 p28. Thus, our results suggest a protective role of DC-derived IL-27 p28 in the pathogenesis of aGVHD through modulation of the Treg/Teff cell balance during thymic development. IL-27 p28 may be a valuable marker for predicting aGVHD development after transplantation in humans.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Multiomics Analysis Identifies SOCS1 as Restraining T Cell Activation and Preventing Graft-Versus-Host Disease

Graft-versus-host disease (GVHD) is a major life-threatening complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Inflammatory signaling pathways promote T-cell activation and are involved in the pathogenesis of GVHD. Suppressor of cytokine signaling 1 (SOCS1) is a critical negative regulator for several inflammatory cytokines. However, its regulatory role in T-cell activation and GVHD has not been elucidated. Multiomics analysis of the transcriptome and chromatin structure of granulocyte-colony-stimulating-factor (G-CSF)-administered hyporesponsive T cells from healthy donors reveal that G-CSF upregulates SOCS1 by reorganizing the chromatin structure around the SOCS1 locus. Parallel in vitro and in vivo analyses demonstrate that SOCS1 is critical for restraining T cell activation. Loss of Socs1 in T cells exacerbates GVHD pathogenesis and diminishes the protective role of G-CSF in GVHD mouse models. Further analysis shows that SOCS1 inhibits T cell activation not only by inhibiting the colony-stimulating-factor 3 receptor (CSF3R)/Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway, but also by restraining activation of the inflammasome signaling pathway. Moreover, high expression of SOCS1 in T cells from patients correlates with low acute GVHD occurrence after HSCT. Overall, these findings identify that SOCS1 is critical for inhibiting T cell activation and represents a potential target for the attenuation of GVHD.

A Promising Insight: The Potential Influence and Therapeutic Value of the Gut Microbiota in GI GVHD

Allogeneic hematopoietic cell transplantation (allo-HSCT) is a reconstruction process of hematopoietic and immune functions that can be curative in patients with hematologic malignancies, but it carries risks of graft-versus-host disease (GVHD), thrombotic microangiopathy (TMA), Epstein–Barr virus (EBV) infection, cytomegalovirus infection, secondary hemophagocytic lymphohistiocytosis (sHLH), macrophage activation syndrome (MAS), bronchiolitis obliterans, and posterior reversible encephalopathy syndrome (PRES). Gastrointestinal graft-versus-host disease (GI GVHD), a common complication of allo-HSCT, is one of the leading causes of transplant-related death because of its high treatment difficulty, which is affected by preimplantation, antibiotic use, dietary changes, and intestinal inflammation. At present, human trials and animal studies have proven that a decrease in intestinal bacterial diversity is associated with the occurrence of GI GVHD. Metabolites produced by intestinal bacteria, such as lipopolysaccharides, short-chain fatty acids, and secondary bile acids, can affect the development of GVHD through direct or indirect interactions with immune cells. The targeted damage of GVHD on intestinal stem cells (ISCs) and Paneth cells results in intestinal dysbiosis or dysbacteriosis. Based on the effect of microbiota metabolites on the gastrointestinal tract, the clinical treatment of GI GVHD can be further optimized. In this review, we describe the mechanisms of GI GVHD and the damage it causes to intestinal cells and we summarize recent studies on the relationship between intestinal microbiota and GVHD in the gastrointestinal tract, highlighting the role of intestinal microbiota metabolites in GI GVHD. We hope to elucidate strategies for immunomodulatory combined microbiota targeting in the clinical treatment of GI GVHD.

Low-Dose 5-Aza and DZnep Alleviate Acute Graft-Versus-Host Disease With Less Side Effects Through Altering T-Cell Differentiation

Objective

Previous studies showed that hypomethylating agents (HMAs) could alleviate acute graft-versus-host disease (aGvHD), but affect engraftment after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The combination of two different HMAs in lower doses might overcome this problem. This study aimed to evaluate the treatment effect of the combination of two HMAs—azacitidine (5-Aza) and histone H3K27 methyltransferase inhibitor 3-deazaneplanocin (DZNep)—for the prophylaxis of aGvHD after allo-HSCT and to explore the possible mechanisms.

Methods

We first optimized the concentrations of individual and combinational 5-Aza and DZNep treatments to ensure no obvious toxicities on activated T cells by evaluating T-cell proliferation, viability, and differentiation. A mouse model of aGvHD was then established to assess the prophylactic efficacy of 5-Aza, DZNep, and their combination on aGvHD. The immunomodulatory effect on T cells and the hematopoietic reconstruction were assessed. Additionally, RNA sequencing (RNA-seq) was performed to identify the underlying molecular mechanisms.

Results

Compared with single treatments, the in vitro application of 5-Aza with DZNep could more powerfully reduce the production of T helper type 1 (Th1)/T cytotoxic type 1 (Tc1) cells and increase the production of regulatory T cells (Tregs). In an allo-HSCT mouse model, in vivo administration of 5-Aza with DZNep could enhance the prophylactic effect for aGvHD compared with single agents. The mechanism study demonstrated that the combination of 5-Aza and DZNep in vivo had an enhanced effect to inhibit the production of Th1/Tc1, increase the proportions of Th2/Tc2, and induce the differentiation of Tregs as in vitro. RNA-seq analysis revealed the cytokine and chemokine pathways as one mechanism for the alleviation of aGvHD with the combination of 5-Aza and DZNep.

Conclusion

The combination of 5-Aza and DZNep could enhance the prophylactic effect for aGvHD by influencing donor T-cell differentiation through affecting cytokine and chemokine pathways. This study shed light on the effectively prophylactic measure for aGvHD using different epigenetic agent combinations.

A novel clinically relevant graft-versus-leukemia model in humanized mice

The prognosis for acute myeloid leukemia (AML) relapse post allogeneic hematopoietic stem cell transplantation (alloSCT) is dismal. Novel effective treatment is urgently needed. Clinical benefit of alloSCT greatly relies on the graft-versus-leukemia (GVL) effect. The mechanisms that mediate immune escape of leukemia (thus causing GVL failure) remain poorly understood. Studies of human GVL have been hindered by the lack of optimal clinically relevant models. Here, using our large, longitudinal clinical tissue bank that include AML cells and G-CSF mobilized donor hematopoietic stem cells (HSCs), we successfully established a novel GVL model in humanized mice. Donor HSCs were injected into immune-deficient NOD-Cg-Prkdcscid IL2rgtm1Wjl /SzJ (NSG) mice to build humanized mice. Immune reconstitution in these mice recapitulated some clinical scenario in the patient who received the corresponding HSCs. Allogeneic but HLA partially matched patient-derived AML cells were successfully engrafted in these humanized mice. Importantly, we observed a significantly reduced (yet incomplete elimination of) leukemia growth in humanized mice compared with that in control NSG mice, demonstrating a functional (but defective) GVL effect. Thus, for the first time, we established a novel humanized mouse model that can be used for studying human GVL responses against human AML cells in vivo. This novel clinically relevant model provides a valuable platform for investigating the mechanisms of human GVL and development of effective leukemia treatments.

Beneficial outcomes and epidemiologics of atypical electrophoretic profiles arising after allogeneic hematopoietic stem cell transplantation for myeloid malignancies

PURPOSE OF THE STUDY

Atypical serum protein electrophoresis (SPE) profiles may arise in patients who received allogeneic hematopoietic stem cell transplantation (allo-HSCT), but little is known about their clinical significance. Atypical SPE combine either monoclonal and oligoclonal components, suspected on SPE and confirmed by immunofixation. The aim of the study is to analyze the incidence, the etiology and the clinical significance of atypical SPE profiles in patients who received allo-HSCT.

PATIENTS AND METHODS

This retrospective study enrolled 117 patients with myeloid malignancies who received an allo-HSCT between 2012 and 2018. We excluded patients with lymphoid malignancies or multiple myeloma, patients presenting atypical electrophoresis prior to transplantation and patients who died within 100 days post-transplant.

RESULTS

Atypical SPE occurred in 42.7% of patients. The cumulative incidence of atypical profiles was significantly higher in patients with acute Graft Versus Host Disease (GVHD, p = 0.019) and in patients with Cytomegalovirus (CMV) reactivation (p = 0.0017). We observed for the first time that atypical SPE profiles mostly occurred in patients transplanted from a CMV+ donor (p = 0.031). CMV reactivation preceded the occurrence of atypical SPE in the majority of patients. We show that atypical SPE delay the relapse of the underlying malignant disease (486 vs 189 days, p = 0.006), and significantly improve overall survival (OS; 33.1 months vs 28.3 months, p = 0.049). In both univariate and multivariate analyzes, the presence of an atypical SPE is the only factor that significantly improves OS.

CONCLUSIONS

The occurrence of atypical SPE profiles after allo-HSCT may reflect an adapted post-transplant immune response leading to favourable outcomes.

Roles of the intestinal microbiota and microbial metabolites in acute GVHD

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is one of the most curative strategies for the treatment of many hematologic malignancies and diseases. However, acute graft-versus-host disease (GVHD) limits the success of allo-HSCT. The prevention and treatment of acute GVHD is the key issue for improving the efficacy of allo-HSCT and has become a research hotspot. The intestine is the primary organ targeted by acute GVHD, and the intestinal microbiota is critical for maintaining the homeostasis of the intestinal microenvironment and the immune response. Many studies have demonstrated the close association between the intestinal microbiota and the pathogenesis of acute GVHD. Furthermore, dysbiosis of the microbiota, which manifests as alterations in the diversity and composition of the intestinal microbiota, and alterations of microbial metabolites are pronounced in acute GVHD and associated with poor patient prognosis. The microbiota interacts with the host directly via microbial surface antigens or microbiota-derived metabolites to regulate intestinal homeostasis and the immune response. Therefore, intervention strategies targeting the intestinal microbiota, including antibiotics, prebiotics, probiotics, postbiotics and fecal microbiota transplantation (FMT), are potential new treatment options for acute GVHD. In this review, we discuss the alterations and roles of the intestinal microbiota and its metabolites in acute GVHD, as well as interventions targeting microbiota for the prevention and treatment of acute GVHD.

Emerging Bone Marrow Microenvironment-Driven Mechanisms of Drug Resistance in Acute Myeloid Leukemia: Tangle or Chance?

Simple Summary

Despite high rates of remission obtained with conventional chemotherapy, the persistence of leukemic cells after treatments, eventually exiting in disease relapse, remains the main challenge in acute myeloid leukemia (AML). Increasing evidence indicates that, besides AML cell mutations, stromal and immune cells, as leukemic microenvironment components, may protect AML cells from therapies. Here, we will recapitulate emerging bone marrow (BM) microenvironment-dependent mechanisms of therapy resistance. The understanding of these processes will help find new drug combinations and conceive novel and more effective treatments.

Abstract

Acute myeloid leukemia (AML) has been considered for a long time exclusively driven by critical mutations in hematopoietic stem cells. Recently, the contribution of further players, such as stromal and immune bone marrow (BM) microenvironment components, to AML onset and progression has been pointed out. In particular, mesenchymal stromal cells (MSCs) steadily remodel the leukemic niche, not only favoring leukemic cell growth and development but also tuning their responsiveness to treatments. The list of mechanisms driven by MSCs to promote a leukemia drug-resistant phenotype has progressively expanded. Moreover, the relative proportion and the activation status of immune cells in the BM leukemic microenvironment may vary by influencing their reactivity against leukemic cells. In that, the capacity of the stroma to re-program immune cells, thus promoting and/or hampering therapeutic efficacy, is emerging as a crucial aspect in AML biology, adding an extra layer of complexity. Current treatments for AML have mainly focused on eradicating leukemia cells, with little consideration for the leukemia-damaged BM niche. Increasing evidence on the contribution of stromal and immune cells in response to therapy underscores the need to hold the mutual interplay, which takes place in the BM. A careful dissection of these interactions will help provide novel applications for drugs already under experimentation and open a wide array of opportunities for new drug discovery.

The Potential Roles of Mucosa-Associated Invariant T Cells in the Pathogenesis of Gut Graft-Versus-Host Disease After Hematopoietic Stem Cell Transplantation

Gut acute graft-versus-host disease (aGVHD) is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is associated with high mortality. Mucosa-associated invariant T (MAIT) cells are a group of innate-like T cells enriched in the intestine that can be activated by riboflavin metabolites from various microorganisms. However, little is known about the function or mechanism of action of MAIT cells in the occurrence of gut aGVHD in humans. In our study, multiparameter flow cytometry (FCM) was used to evaluate the number of MAIT cells and functional cytokines. 16S V34 region amplicon sequencing analysis was used to analyze the intestinal flora of transplant patients. In vitro stimulation and coculture assays were used to study the activation and function of MAIT cells. The number and distribution of MAIT cells in intestinal tissues were analyzed by immunofluorescence technology. Our study showed that the number and frequency of MAIT cells in infused grafts in gut aGVHD patients were lower than those in no-gut aGVHD patients. Recipients with a high number of MAITs in infused grafts had a higher abundance of intestinal flora in the early posttransplantation period (+14 days). At the onset of gut aGVHD, the number of MAIT cells decreased in peripheral blood, and the activation marker CD69, chemokine receptors CXCR3 and CXCR4, and transcription factors Rorγt and T-bet tended to increase. Furthermore, when gut aGVHD occurred, the proportion of MAIT17 was higher than that of MAIT1. The abundance of intestinal flora with non-riboflavin metabolic pathways tended to increase in gut aGVHD patients. MAIT cells secreted more granzyme B, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ under the interleukin (IL)-12/IL-18 stimulation [non-T-cell receptor (TCR) signal] and secreted most of the IL-17 under the cluster of differentiation (CD)3/CD28 stimulation (TCR signal). MAIT cells inhibited the proliferation of CD4+ T cells in vitro. In conclusion, the lower number of MAIT cells in infused grafts was related to the higher incidence of gut aGVHD, and the number of MAIT cells in grafts may affect the composition of the intestinal flora of recipients early after transplantation. The flora of the riboflavin metabolism pathway activated MAIT cells and promoted the expression of intestinal protective factors to affect the occurrence of gut aGVHD in humans.

Keeping an 'eye' on ocular GVHD

Ocular graft versus host disease (GVHD) is a common manifestation in patients undergoing allogeneic haematopoietic stem cell transplantation (allo-HSCT). Ocular GVHD affects approximately 10% of patients with acute GVHD and more than 50% of patients with chronic GVHD. Symptoms of dry eye disease are one of the clinical hallmarks of ocular GVHD, and inflammatory changes to the ocular surface, cornea, conjunctiva, eyelids and lacrimal glands have been observed. Less commonly, the posterior segment of the eye is involved in the form of microvascular retinopathy, scleritis or intraretinal and vitreous haemorrhage. Although ocular GVHD does not usually result in permanent visual loss, it often impairs the patient's quality of life and activities of daily living. Regular and more consistent ocular assessment of allo-HSCT patients, including screening prior to transplantation will allow for the earlier detection and treatment of ocular complications associated with GVHD and potentially prevent more severe outcomes. The implementation of additional screening including corneal endothelial cell density assessment and non-invasive analysis of tear biomarkers may be valuable additions to current clinical testing and assist in better detection and clinical intervention in patients with GVHD. This review describes the clinical features, diagnostic criteria and clinical scoring of ocular GVHD, as well as current treatment strategies and potential ophthalmic screening tools for common ocular complications. Further, we describe the clinical and histopathological features of ocular GVHD in preclinical mouse models.

Outcome of allogeneic hematopoietic stem cell transplant recipients admitted to the intensive care unit with a focus on haploidentical graft and sequential conditioning regimen: results of a retrospective study

Haploidentical transplantation has extended the availability of allogeneic hematopoietic stem cell transplant (alloHCT) to almost all patients. Sequential conditioning regimens have been proposed for the treatment of hematological active disease. Whether these new transplantation procedures affect the prognosis of critically ill alloHCT recipients remains unknown. We evaluated this question in a retrospective study including consecutive alloHCT patients admitted to the intensive care unit of a tertiary academic center from 2010 to 2017. During the study period, 412 alloHCTs were performed and 110 (27%) patients-median age 55 (36-64) years-were admitted to ICU in a median time of 58.5 (14-245) days after alloHCT. Twenty-nine (26%) patients had received a haploidentical graft and 34 (31%) a sequential conditioning. Median SOFA score was 9 (6-11). Invasive mechanical ventilation (MV) was required in 61 (55%) patients. Fifty-six (51%) patients died in the hospital. Independent factors associated with in-hospital mortality were as follows: MV (OR=8.44 [95% CI 3.30-23.19], p<0.001), delta SOFA between day 3 and day 1 (OR=1.60 [95% CI 1.31-2.05], p<0.0001), and sequential conditioning (OR=3.7 [95% CI 1.14-12.92], p=0.033). Sequential conditioning was also independently associated with decreased overall survival (HR=1.86 [95% CI 1.05-3.31], p=0.03). Other independent factors associated with reduced overall survival were HCT-specific comorbidity index ≥2 (HR=1.76 [95% CI 1.10-2.84], p=0.02), acute GVHD grade ≥2 (HR=1.88 [95% CI 1.14-3.10], p=0.01), MV (HR=2.37 [95% CI 1.38-4.07, p=0.002), and vasopressors (HR=2.21 [95% CI 1.38-3.54], p=0.001). Haploidentical transplantation did not affect outcome. Larger multicenter studies are warranted to confirm these results.

Donor-derived M2 macrophages attenuate GVHD after allogeneic hematopoietic stem cell transplantation

Introduction

Graft‐versus‐host disease (GVHD) is frequent and fatal complication following allogeneic hematopoietic stem cell transplantation (HSCT) and characteristically involves skin, gut, and liver. Macrophages promote tissue regeneration and mediate immunomodulation. Macrophages are divided into two different phenotypes, classically activated M1 (pro‐inflammatory or immune‐reactive macrophages) and alternatively activated M2 (anti‐inflammatory or immune‐suppressive macrophages). The anti‐inflammatory effect of M2 macrophage led us to test its effect in the pathophysiology of GVHD.

Methods

GVHD was induced in lethally irradiated BALB/c mice. M2 macrophages derived from donor bone marrow (BM) were administered intravenously, while controls received donor BM‐mononuclear cells and splenocytes. Animals were monitored for clinical GVHD and analyzed.

Results

We confirmed that administering donor BM‐derived M2 macrophages attenuated GVHD severity and prolonged survival after HSCT. Moreover, donor BM‐derived M2 macrophages significantly suppressed donor T cell proliferation by cell‐to‐cell contact in vitro.

Conclusions

We showed the protective effects of donor‐derived M2 macrophages on GVHD and improved survival in a model of HSCT. Our data suggest that donor‐derived M2 macrophages offer the potential for cell‐based therapy to treat GVHD.

The Pathophysiology and Treatment of Graft-Versus-Host Disease: Lessons Learnt From Animal Models

Allogeneic hematopoietic cell transplantation (HCT) is a curative treatment for hematologic malignancies, bone marrow failure syndromes, and inherited immunodeficiencies and metabolic diseases. Graft-versus-host disease (GVHD) is the major life-threatening complication after allogeneic HCT. New insights into the pathophysiology of GVHD garnered from our understanding of the immunological pathways within animal models have been pivotal in driving new therapeutic paradigms in the clinic. Successful clinical translations include histocompatibility matching, GVHD prophylaxis using cyclosporine and methotrexate, posttransplant cyclophosphamide, and the use of broad kinase inhibitors that inhibit cytokine signaling (e.g. ruxolitinib). New approaches focus on naïve T cell depletion, targeted cytokine modulation and the inhibition of co-stimulation. This review highlights the use of animal transplantation models to guide new therapeutic principles.

CD11c participates in triggering acute graft-versus-host disease during bone marrow transplantation

CD11c is a canonical dendritic cell (DC) marker with poorly defined functions in the immune system. Here, we found that blocking CD11c on human peripheral blood mononuclear cell‐derived DCs (MoDCs) inhibited the proliferation of CD4⁺ T cells and the differentiation into IFN‐γ‐producing T helper 1 (Th1) cells, which were critical in acute graft‐versus‐host disease (aGVHD) pathogenesis. Using allogeneic bone marrow transplantation (allo‐BMT) murine models, we consistently found that CD11c‐deficient recipient mice had alleviated aGVHD symptoms for the decreased IFN‐γ‐expressing CD4⁺ Th1 cells and CD8⁺ T cells. Transcriptional analysis showed that CD11c participated in several immune regulation functions including maintaining antigen presentation of APCs. CD11c‐deficient bone marrow‐derived DCs (BMDCs) impaired the antigen presentation function in coculture assay. Mechanistically, CD11c interacted with MHCII and Hsp90 and participated in the phosphorylation of Akt and Erk1/2 in DCs after multiple inflammatory stimulations. Therefore, CD11c played crucial roles in triggering aGVHD and might serve as a potential target for the prevention and treatment of aGVHD.

Update in clinical and mouse microbiota research in allogeneic haematopoietic cell transplantation

PURPOSE OF REVIEW

The intestinal microbiota plays a critical role in intestinal homeostasis and immune regulation and has been recognized as a predictor of clinical outcome in patients undergoing allogeneic haematopoietic cell transplantation (allo-HCT) and specifically a determinant of the severity of graft-versus-host disease (GVHD) in mouse models. As GVHD is the most important cause of nonrelapse mortality (NRM) after allo-HCT, understanding the mechanisms by which modifying the microbiota may prevent or decrease the severity of GVHD would represent an important advance.

RECENT FINDINGS

Microbiota injury was observed globally and higher diversity at peri-engraftment was associated with lower mortality. Lactose is a dietary factor that promotes post-allo-HCT Enterococcus expansion, which is itself associated with mortality from GVHD in patients and exacerbates GVHD in mice. Bacterial and fungal bloodstream infections are preceded by intestinal colonization with a corresponding organism, supporting the gut as a source for many bloodstream infections. Metabolomic profiling studies showed that GVHD is associated with changes in faecal and plasma microbiota-derived molecules.

SUMMARY

In this review, we highlight some of the most recent and important findings in clinical and mouse microbiota research, as it relates to allo-HCT. Many of these are already being translated into clinical trials that have the potential to change future practice in the care of patients.

Effect of Human or Mouse IL-7 on the Homeostasis of Porcine T Lymphocytes

Due to the inconsistent fluctuation of blood supply for transfusion, much attention has been paid to the development of artificial blood using other animals. Although mini-pigs are candidate animals, contamination of mini-pig T cells in artificial blood may cause a major safety concern. Therefore, it is important to analyze the cross-reactivity of IL-7, the major survival factor for T lymphocytes, between human, mouse, and mini-pig. Thus, we compared the protein sequences of IL-7 and found that porcine IL-7 was evolutionarily different from human IL-7. We also observed that when porcine T cells were cultured with either human or mouse IL-7, these cells did not increase the survival or proliferation compared to negative controls. These results suggest that porcine T cells do not recognize human or mouse IL-7 as their survival factor.

Post-transplant cyclophosphamide limits reactive donor T cells and delays the development of graft-versus-host disease in a humanized mouse model

Graft-versus-host disease (GVHD) is a major complication of allogeneic haematopoietic stem cell transplantation (allo-HSCT) that develops when donor T cells in the graft become reactive against the host. Post-transplant cyclophosphamide (PTCy) is increasingly used in mismatched allo-HSCT, but how PTCy impacts donor T cells and reduces GVHD is unclear. This study aimed to determine the effect of PTCy on reactive human donor T cells and GVHD development in a preclinical humanized mouse model. Immunodeficient NOD-scid-IL2Rγ^null mice were injected intraperitoneally (i.p.) with 20 × 10⁶ human peripheral blood mononuclear cells stained with carboxyfluorescein succinimidyl ester (CFSE) (day 0). Mice were subsequently injected (i.p.) with PTCy (33 mg kg^-1 ) (PTCy-mice) or saline (saline-mice) (days 3 and 4). Mice were assessed for T-cell depletion on day 6 and monitored for GVHD for up to 10 weeks. Flow cytometric analysis of livers at day 6 revealed lower proportions of reactive (CFSE^low ) human (h) CD3⁺ T cells in PTCy-mice compared with saline-mice. Over 10 weeks, PTCy-mice showed reduced weight loss and clinical GVHD, with prolonged survival and reduced histological liver GVHD compared with saline-mice. PTCy-mice also demonstrated increased splenic hCD4⁺ :hCD8⁺ T-cell ratios and reduced splenic Tregs (hCD4⁺  hCD25⁺  hCD127^lo ) compared with saline-mice. This study demonstrates that PTCy reduces GVHD in a preclinical humanized mouse model. This corresponded to depletion of reactive human donor T cells, but fewer human Tregs.

A phase 3 double-blind study of the addition of tocilizumab vs placebo to cyclosporin/methotrexate GVHD prophylaxis

We determined the efficacy of tocilizumab (TCZ) in preventing grade 2-4 acute graft-versus-host disease (aGVHD) in patients with acute leukemia or myelodysplasia undergoing matched sibling donor (MSD) or volunteer unrelated donor (VUD) allogeneic stem cell transplantation after myeloablative or reduced-intensity conditioning across 5 Australian centers. A total of 145 patients (50 MSD, 95 VUD) were randomly assigned to placebo or TCZ on day -1. All patients received T-cell-replete peripheral blood stem cell grafts and graft-versus-host disease (GVHD) prophylaxis with cyclosporin/methotrexate. A planned substudy analyzed the VUD cohort. With a median follow-up of 746 days, the incidence of grade 2-4 aGVHD at day 100 for the entire cohort was 36% for placebo vs 27% for TCZ (hazard ratio [HR], 0.69; 95% confidence interval [CI], 0.38-1.26; P = .23) and 45% vs 32% (HR, 0.61; 95% CI, 0.31-1.22; P = .16) for the VUD subgroup. The incidence of grade 2-4 aGVHD at day 180 for the entire cohort was 40% for placebo vs 29% for TCZ (HR, 0.68; 95% CI, 0.38-1.22; P = .19) and 48% vs 32% (HR, 0.59; 95% CI, 0.30-1.16; P = .13) for the VUD subgroup. Reductions in aGVHD were predominantly in grade 2 disease. For the entire cohort, transplant-related mortality occurred in 8% vs 11% of placebo-treated vs TCZ-treated patients, respectively (P = .56), and overall survival was 79% vs 71% (P = .27). Median day to neutrophil and platelet engraftment was delayed by 2 to 3 days in TCZ-treated patients, whereas liver toxicity and infectious complications were similar between groups. In this phase 3 randomized double-blind trial, TCZ showed nonsignificant trends toward reduced incidence of grade 2-4 aGVHD in recipients from HLA-matched VUDs but no improvements in long term-survival.

Functional Contributions of Antigen Presenting Cells in Chronic Graft-Versus-Host Disease

Chronic graft-versus-host disease (cGVHD) is one of the most common reasons of late non-relapse morbidity and mortality of patients with allogeneic hematopoietic stem cell transplantation (allo-HSCT). While acute GVHD is considered driven by a pathogenic T cell dominant mechanism, the pathogenesis of cGVHD is much complicated and involves participation of a variety of immune cells other than pathogenic T cells. Existing studies have revealed that antigen presenting cells (APCs) play crucial roles in the pathophysiology of cGVHD. APCs could not only present auto- and alloantigens to prime and activate pathogenic T cells, but also directly mediate the pathogenesis of cGVHD via multiple mechanisms including infiltration into tissues/organs, production of inflammatory cytokines as well as auto- and alloantibodies. The studies of this field have led to several therapies targeting different APCs with promising results. This review will focus on the important roles of APCs and their contributions in the pathophysiology of cGVHD after allo-HSCT.

5-Aminolevulinic acid combined with sodium ferrous citrate (5-ALA/SFC) ameliorated liver injury in a murine acute graft-versus-host disease model by reducing inflammation responses through PGC1-α activation

Acute graft-versus-host disease (aGvHD) remains lethal as a life-threatening complication after allogeneic hematopoietic stem cell transplantation (HSCT). Inflammatory responses play an important role in aGvHD. 5-Aminolevulinic acid combined with sodium ferrous citrate (5-ALA/SFC) has been widely reported to have a major effect on the anti-inflammatory response; however, these effects in aGvHD models have never been reported. In this study, a murine aGvHD model was developed by transferring spleen cells from donor B6/N (H-2kb) mice into recipient B6D2F1 (H-2kb/d) mice. In addition to evaluating manifestations in aGvHD mice, we analyzed the serum ALT/AST levels, liver pathological changes, infiltrating cells and mRNA expression of inflammation-related cytokines and chemokines. 5-ALA/SFC treatment significantly ameliorated liver injury due to aGvHD and decreased the population of liver-infiltrating T cells, resulting in a reduced expression of pro-inflammatory cytokines and chemokines. Furthermore, the mRNA expression proliferator-activated receptor-γcoactivator (PGC-1α) was enhanced, which might explain why 5-ALA/SFC treatment downregulates inflammatory signaling pathways. Our results indicated that 5-ALA/SFC can ameliorate liver injury induced by aGvHD through the activation of PGC-1α and modulation of the liver mRNA expression of inflammatory-related cytokines and chemokines. This may be a novel strategy for treating this disease.

Graft-versus-host disease prophylaxis: Pathophysiology-based review on current approaches and future directions

Graft-versus-host disease (GvHD) was first described in 1959, since then major efforts have been made in order to understand its physiopathology and animal models have played a key role. Three steps, involving different pathways, have been recognised in either acute and chronic GvHD, identifying them as two distinct entities. In order to reduce GvHD incidence and severity, prophylactic measures were added to transplant protocols. The combination of a calcineurin inhibitor (CNI) plus an antimetabolite remains the standard of care. Better knowledge of GvHD pathophysiology has moved this field forward and nowadays different drugs are being used on a daily basis. Improving GvHD prophylaxis is a major goal as it would translate into less non-relapse mortality and better overall survival. As compared to CNI plus methotrexate the combination of CNI plus mycophenolate mophetil (MMF) allows us to obtain similar results in terms of GvHD incidence but a lower toxicity rate in terms of neutropenia or mucositis. The use of ATG has been related to a lower risk of acute and chronic GvHD in prospective randomized trials as well as the use of posttransplant Cyclophosphamide, with no or marginal impact on overall survival but with an improvement in GvHD-relapse free survival (GRFS). The use of sirolimus has been related to a lower risk of acute GvHD and significantly influenced overall survival in one prospective randomized trial. Other prospective trials have evaluated the use of receptors such as CCR5 or α4β7 to avoid T-cells trafficking into GvHD target organs, cytokine blockers or immune check point agonists. Also, epigenetic modifiers have shown promising results in phase II trials. Attention should be paid to graft-versus-leukemia, infections and immune recovery before bringing new prophylactic strategies to clinical practice. Although the list of novel agents for GvHD prophylaxis is growing, randomized trials are still lacking for many of them.

T cell exhaustion and a failure in antigen presentation drive resistance to the graft-versus-leukemia effect

In hematopoietic cell transplants, alloreactive T cells mediate the graft-versus-leukemia (GVL) effect. However, leukemia relapse accounts for nearly half of deaths. Understanding GVL failure requires a system in which GVL-inducing T cells can be tracked. We used such a model wherein GVL is exclusively mediated by T cells that recognize the minor histocompatibility antigen H60. Here we report that GVL fails due to insufficient H60 presentation and T cell exhaustion. Leukemia-derived H60 is inefficiently cross-presented whereas direct T cell recognition of leukemia cells intensifies exhaustion. The anti-H60 response is augmented by H60-vaccination, an agonist αCD40 antibody (FGK45), and leukemia apoptosis. T cell exhaustion is marked by inhibitory molecule upregulation and the development of TOX+ and CD39-TCF-1+ cells. PD-1 blockade diminishes exhaustion and improves GVL, while blockade of Tim-3, TIGIT or LAG3 is ineffective. Of all interventions, FGK45 administration at the time of transplant is the most effective at improving memory and naïve T cell anti-H60 responses and GVL. Our studies define important causes of GVL failure and suggest strategies to overcome them.

Rapamycin-based graft-versus-host disease prophylaxis increases the immunosuppressivity of myeloid-derived suppressor cells without affecting T cells and anti-tumor cytotoxicity

The immunosuppressant rapamycin (RAPA) inhibits mammalian target of rapamycin (mTOR) functions and is applied after allogeneic bone marrow transplantation (BMT) to attenuate the development of graft‐versus‐host disease (GVHD), although the cellular targets of RAPA treatment are not well defined. Allogeneic T cells are the main drivers of GVHD, while immunoregulatory myeloid‐derived suppressor cells (MDSCs) were recently identified as potent disease inhibitors. In this study, we analyzed whether RAPA prevents the deleterious effects of allogeneic T cells or supports the immunosuppressive functions of MDSCs in a BMT model with major histocompatibility complex (MHC) classes I and II disparities. RAPA treatment efficiently attenuated clinical and histological GVHD and strongly decreased disease‐induced mortality. Although splenocyte numbers increased during RAPA treatment, the ratio of effector T cells to MDSCs was unaltered. However, RAPA treatment induced massive changes in the genomic landscape of MDSCs preferentially up‐regulating genes responsible for uptake or signal transduction of lipopeptides and lipoproteins. Most importantly, MDSCs from RAPA‐treated mice exhibited increased immunosuppressive potential, which was primarily inducible nitric oxide synthase (iNOS)‐dependent. Surprisingly, RAPA treatment had no impact on the genomic landscape of T cells, which was reflected by unchanged expression of activation and exhaustion markers and cytokine profiles in T cells from RAPA‐treated and untreated mice. Similarly, T cell cytotoxicity and the graft‐versus‐tumor effect were maintained as co‐transplanted tumor cells were efficiently eradicated, indicating that the immunosuppressant RAPA might be an attractive approach to strengthen the immunosuppressive function of MDSCs without affecting T cell immunity.

Increased P2X7 expression in the gastrointestinal tract and skin in a humanised mouse model of graft-versus-host disease

BACKGROUND

Allogeneic haematopoietic stem cell transplantation (HSCT) is a curative therapy for blood cancers; but results in the development of graft-versus-host disease (GVHD) in up to 70% of recipients. During GVHD, tissue damage results in ATP release into the extracellular compartment activating P2X7 on antigen-presenting cells, leading to the release of pro-inflammatory cytokines and subsequent activation of donor T cells. Therefore, the aim of the present study was to examine murine (m) P2rx7 and human (h) P2RX7 gene expression in GVHD target organs of humanised mice, and further characterise disease impact in these organs.

METHODS

NOD-scid IL2Rγnull (NSG) mice were injected with human peripheral blood mononuclear cells (hu-PBMC-NSG mice) or phosphate-buffered saline (PBS, control). Leucocytes were assessed by flow cytometry; gene expression was measured by quantitative polymerase chain reaction (qPCR), and tissue sections examined by histology.

RESULTS

Compared with control mice, hu-PBMC-NSG mice had increased mP2rx7 and mP2rx4 expression in the duodenum, ileum and skin. hP2RX7 was expressed in all tissues examined. hu-PBMC-NSG mice also displayed increased mReg3g expression in the duodenum and ileum, despite limited histological gut GVHD. hu-PBMC-NSG mice showed histological evidence of GVHD in the skin, liver and lung. Compared with control mice, hu-PBMC-NSG mice displayed increased ear swelling.

CONCLUSION

Combined data revealed that P2rx7 is up-regulated in gut and skin GVHD and that P2RX7 is present in target tissues of GVHD, corresponding to human leucocyte infiltration. Data also reveal increased mReg3g expression and ear swelling in hu-PBMC-NSG mice, offering new measurements of early-stage gut GVHD and skin GVHD, respectively.

In vivo dynamics of T cells and their interactions with dendritic cells in mouse cutaneous graft-versus-host disease

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality in allogeneic hematopoietic stem cell transplantation (alloSCT). By static microscopy, cutaneous GVHD lesions contain a mix of T cells and myeloid cells. We used 2-photon intravital microscopy to investigate the dynamics of CD4⁺ and CD8⁺ T cells and donor dendritic cells (DCs) in cutaneous GVHD lesions in an MHC-matched, multiple minor histocompatibility antigen-mismatched (miHA) model. The majority of CD4 and CD8 cells were stationary, and few cells entered and stopped or were stopped and left the imaged volumes. CD8 cells made TCR:MHCI-dependent interactions with CD11c⁺ cells, as measured by the durations that CD8 cells contacted MHCI⁺ vs MHCI^- DCs. The acute deletion of Langerin⁺CD103⁺ DCs, which were relatively rare, did not affect CD8 cell motility and DC contact times, indicating that Langerin^-CD103^- DCs provide stop signals to CD8 cells. CD4 cells, in contrast, had similar contact durations with MHCII⁺ and MHCII^- DCs. However, CD4 motility rapidly increased after the infusion of an MHCII-blocking antibody, indicating that TCR signaling actively suppressed CD4 movements. Many CD4 cells still were stationary after anti-MHCII antibody infusion, suggesting CD4 cell heterogeneity within the lesion. These data support a model of local GVHD maintenance within target tissues.

Restoration of Regulatory T-Cell Function in Dry Eye Disease by Antagonizing Substance P/Neurokinin-1 Receptor

Substance P (SP) is a tachykinin neuropeptide, implicated in the pathogenesis of various inflammatory conditions and a critical mediator in pain transmission. Recently, the role of SP was described in the pathogenesis of dry eye disease (DED) through its role in the maturation of antigen-presenting cells at the ocular surface after exposure to desiccating stress. However, the effect of SP on regulatory T cells (Tregs), which are functionally impaired in DED, remains unclear. This study examined the phenotypic and functional changes in Tregs in response to SP in DED. The in vitro cultures of normal Tregs in the presence of SP led to a significant reduction in both Treg frequencies and their suppressive function, which was prevented by the addition of an SP receptor (neurokinin-1 receptor) antagonist. Furthermore, in vivo treatment with the neurokinin-1 receptor antagonist in DED mice effectively restored Treg function, suppressed pathogenic T helper 17 response, and significantly ameliorated the disease. Our results show that a significant increase in SP levels promotes Treg dysfunction in DED, and blockade of SP effectively restores Treg function and suppresses DED severity.

Macrophage regulation of graft-vs-host disease

Hematopoietic stem cell transplantation has become a curative choice of many hematopoietic malignancy, but graft-vs-host disease (GVHD) has limited the survival quality and overall survival of hematopoietic stem cell transplantation. Understanding of the immune cells’ reaction in pathophysiology of GVHD has improved, but a review on the role of macrophages in GVHD is still absent. Studies have observed that macrophage infiltration is associated with GVHD occurrence and development. In this review, we summarize and analyze the role of macrophages in GVHD based on pathophysiology of acute and chronic GVHD, focusing on the macrophage recruitment and infiltration, macrophage polarization, macrophage secretion, and especially interaction of macrophages with other immune cells. We could conclude that macrophage recruitment and infiltration contribute to both acute and chronic GVHD. Based on distinguishing pathology of acute and chronic GVHD, macrophages tend to show a higher M1/M2 ratio in acute GVHD and a lower M1/M2 ratio in chronic GVHD. However, the influence of dominant cytokines in GVHD is controversial and inconsistent with macrophage polarization. In addition, interaction of macrophages with alloreactive T cells plays an important role in acute GVHD. Meanwhile, the interaction among macrophages, B cells, fibroblasts, and CD4+ T cells participates in chronic GVHD development.

Early T Cell Activation Metrics Predict Graft-versus-Host Disease in a Humanized Mouse Model of Hematopoietic Stem Cell Transplantation

Acute graft-versus-host disease (GVHD) is a frequent complication of hematopoietic transplantation, yet patient risk stratification remains difficult, and prognostic biomarkers to guide early clinical interventions are lacking. We developed an approach to evaluate the potential of human T cells from hematopoietic grafts to produce GVHD. Nonconditioned NBSGW mice transplanted with titrated doses of human bone marrow developed GVHD that was characterized by widespread lymphocyte infiltration and organ pathology. Interestingly, GVHD was not an inevitable outcome in our system and was influenced by transplant dose, inflammatory status of the host, and type of graft. Mice that went on to develop GVHD showed signs of rapid proliferation in the human T cell population during the first 1-3 wk posttransplant and had elevated human IFN-γ in plasma that correlated negatively with the expansion of the human hematopoietic compartment. Furthermore, these early T cell activation metrics were predictive of GVHD onset 3-6 wk before phenotypic pathology. These results reveal an early window of susceptibility for pathological T cell activation following hematopoietic transplantation that is not simply determined by transient inflammation resulting from conditioning-associated damage and show that T cell parameters during this window can serve as prognostic biomarkers for risk of later GVHD development.

Comparison of Conventional Cyclophosphamide versus Fludarabine-Based Conditioning in High-Risk Aplastic Anemia Patients Undergoing Matched-Related Donor Transplantation

Allogeneic stem cell transplant for high-risk aplastic anemia (AA) yields inferior results using conventional cyclophosphamide (CY)-based conditioning. The use of fludarabine (Flu)-based regimens has resulted in improved outcomes in high-risk patients. Limited data are available comparing these two conditioning regimens in such patients. We retrospectively analyzed 192 high-risk patients undergoing matched-related donor transplantation from July 2001 to December 2018. The median age was 19.5 (2–52) years. Patients were divided into 2 groups, Cy²⁰⁰ anti-thymocyte globulin (ATG)²⁰ (Gp1 n = 79) or Flu^120–150 Cy^120–160 ATG²⁰ (Gp2 n = 113). The risk of graft failure was significantly higher in Gp1, and the majority occurred in patients with >2 risk factors (p = 0.02). The incidence of grade II-IV acute graft versus host disease (GVHD) and chronic GVHD was not significantly different between the two groups. The overall survival (OS) of the study cohort was 81.3 %, disease-free survival (DFS) 76.6 % and GVHD-free relapse-free survival (GRFS) was 64.1%. DFS and GRFS were significantly higher in Gp2 as compared to Gp1: DFS 84.1% versus 68.4 % (p = 0.02), GRFS 77.9% versus 54.4% (p = 0.01), respectively. We conclude that Flu-based conditioning is associated with superior OS, DFS and GRFS as compared to the conventional Cy-based regimen in high-risk AA.

Dissecting the biology of allogeneic HSCT to enhance the GvT effect whilst minimizing GvHD

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) was the first successful therapy for patients with haematological malignancies, predominantly owing to graft-versus-tumour (GvT) effects. Dramatic methodological changes, designed to expand eligibility for allo-HSCT to older patients and/or those with comorbidities, have led to the use of reduced-intensity conditioning regimens, in parallel with more aggressive immunosuppression to better control graft-versus-host disease (GvHD). Consequently, disease relapse has become the major cause of death following allo-HSCT. Hence, the prevention and treatment of relapse has come to the forefront and remains an unmet medical need. Despite >60 years of preclinical and clinical studies, the immunological requirements necessary to achieve GvT effects without promoting GvHD have not been fully established. Herein, we review learnings from preclinical modelling and clinical studies relating to the GvT effect, focusing on mechanisms of relapse and on immunomodulatory strategies that are being developed to overcome disease recurrence after both allo-HSCT and autologous HSCT. Emphasis is placed on discussing current knowledge and approaches predicated on the use of cell therapies, cytokines to augment immune responses and dual-purpose antibody therapies or other pharmacological agents that can control GvHD whilst simultaneously targeting cancer cells.

A single-nucleotide polymorphism in the human ENTPD1 gene encoding CD39 is associated with worsened graft-versus-host disease in a humanized mouse model

Regulatory T cells (Tregs) protect against graft-versus-host disease (GVHD), a life-threatening complication of allogeneic hematopoietic stem cell transplantation. The ectoenzyme CD39 is important for increasing the immunosuppressive function of Tregs. The rs10748643 (A → G) single-nucleotide polymorphism (SNP) in intron 1 of the human ENTPD1 gene is associated with increased proportions of CD39⁺ Tregs. This study aimed to determine whether the rs10748643 SNP corresponded to increased proportions of CD39⁺ Tregs in an Australian donor population, and whether this SNP influences clinical GVHD in a humanized mouse model. Donors were genotyped for the rs10748643 SNP by Sanger sequencing, and the proportion of CD39⁺ T cells in donor peripheral blood was determined by flow cytometry. Donors encoding the G allele (donors^AG/GG ) demonstrated higher proportions of CD39⁺ CD3⁺ CD4⁺ CD25⁺ CD127^lo Tregs, but not CD39⁺ CD3⁺ CD8⁺ T cells or CD39⁺ CD3⁺ CD4⁺ conventional T cells, compared with donors homozygous for the A allele (donors^AA ). NOD-SCID-IL2Rγ^null mice were injected with human peripheral blood mononuclear cells from either donors^AA (hCD39^AA mice) or donors^AG/GG (hCD39^AG/GG mice). hCD39^AG/GG mice demonstrated significantly greater weight loss and GVHD clinical scores, and significantly reduced survival, compared with hCD39^AA mice. hCD39^AG/GG mice showed significantly higher hCD4⁺ :hCD8⁺ T-cell ratios than hCD39^AA mice, but displayed similar proportions of CD3⁺ hCD4⁺ hCD25⁺ hCD127^lo Tregs and hCD39⁺ Tregs. However, the proportion of human Tregs corresponded to survival in hCD39^AA mice, but not in hCD39^AG/GG mice. This study demonstrates that donors encoding the G allele show higher percentages of CD39⁺ Tregs, but cause worsened GVHD in humanized mice compared with donors homozygous for the A allele.

Gastrointestinal peptides in children before and after hematopoietic stem cell transplantation

BACKGROUND

Gastrointestinal tract function and it's integrity are controlled by a number of peptides whose secretion is influenced by severe inflammation. In stomach the main regulatory peptide is ghrelin. For upper small intestine cholecystokinin and lower small intestine glucagon-like peptide- 1 are secreted, while fibroblast growth factor-21 is secreted by several organs, including the liver, pancreas, and adipose tissue [12]. Hematopoietic stem cell transplantation causes serious mucosal damage, which can reflect on this peptides.

METHODS

The aim of the study was to determine fasting plasma concentrations of ghrelin, cholecystokinin, glucagon- like peptide-1, and fibroblast growth factor-21, and their gene expressions, before and 6 months after hematopoietic stem cell transplantation.27 children were studied, control group included 26 healthy children.

RESULTS

Acute graft versus host disease was diagnosed in 11 patients (41%, n = 27). Median pre-transplantation concentrations of gastrointestinal peptides, as well as their gene expressions, were significantly lower in studied group compared with the control group. Only median of fibroblast growth factor-21 concentration was near-significantly higher before stem cell transplantation than in the control group. The post-hematopoietic transplant results revealed significantly higher concentrations of the studied peptides (except fibroblast growth factor-21) and respective gene expressions as compare to pre transplant results. Median glucagone like peptide-1 concentrations were significantly decreased in patients with features of acute graft versus host disease. Moreover, negative correlation between glucagone like peptide-1 concentrations and acute graft versus host disease severity was found.

CONCLUSIONS

Increased concentrations and gene expressions of gastrointestinal tract regulation peptides can be caused by stimulation of regeneration in the severe injured organ. Measurement of these parameters may be a useful method of assessment of severity of gastrointestinal tract complications of hematopoietic stem cell transplantation.

Tumor necrosis factor α in aGVHD patients contributed to the impairment of recipient bone marrow MSC stemness and deficiency of their hematopoiesis-promotion capacity

Background

Though accumulated evidence has demonstrated visceral organ involvement in acute graft-versus-host disease (aGVHD), how aGVHD influences the bone marrow (BM) niche and the reconstitution of hematopoiesis post-hematopoietic stem cell transplantation remains largely unknown.

Methods

In the current study, the cell morphology, immunophenotype, multi-differentiation capacity, self-renewal capacity, and hematopoiesis promotion of the MSCs from aGVHD and non-aGVHD patients were investigated. Additionally, the stemness and hematopoiesis-promoting property of healthy donor-derived MSCs were evaluated in the presence of BM supernatant from aGVHD patients. Mechanistically, antibodies targeting inflammatory cytokines involved in aGVHD were added into the MSC culture. Furthermore, a recombinant human tumor necrosis factor (TNF-α) receptor-Ig fusion protein (rhTNFR:Fc) was used to protect healthy donor-derived MSCs. Moreover, mRNA sequencing was performed to explore the underlying mechanisms.

Results

The aGVHD MSCs exhibited morphological and immunophenotypic characteristics that were similar to those of the non-aGVHD MSCs. However, the osteogenic and adipogenic activities of the aGVHD MSCs significantly decreased. Additionally, the colony formation capacity and the expression of self-renewal-related genes remarkably decreased in aGVHD MSCs. Further, the hematopoiesis-supporting capacity of aGVHD MSCs significantly reduced. The antibody neutralization results showed that TNF-α contributed to the impairment of MSC properties. Moreover, rhTNFR:Fc exhibited notable protective effects on MSCs in the aGVHD BM supernatants. The mRNA sequencing results indicated that the TNF-α pathway and the Toll-like receptor pathway may be activated by TNF-α.

Conclusions

Thus, our data demonstrate MSCs as cellular targets of aGVHD and suggest a potential role of TNF-α blockage in maintaining the BM niche of aGVHD patients.