The role of chemokines in mediating graft versus host disease: opportunities for novel therapeutics

Influence of Housing Temperature and Genetic Diversity on Allogeneic T Cell-Induced Tissue Damage in Mice

The objective of this study was to determine how housing temperature and genetic diversity affect the onset and severity of allogeneic T cell-induced tissue damage in mice subjected to reduced intensity conditioning (RIC). We found that adoptive transfer of allogeneic CD4+ T cells from inbred donors into sub-lethally irradiated inbred recipients (I→I) housed at standard housing temperatures (ST; 22-24 °C) induced extensive BM and spleen damage in the absence of injury to any other tissue. Although engraftment of T cells in RIC-treated mice housed at their thermo-neutral temperature (TNT; 30-32 °C) also developed similar BM and spleen damage, their survival was markedly and significantly increased when compared to their ST counterparts. In contrast, the adoptive transfer of allogeneic T cells into RIC-treated outbred CD1 recipients failed to induce disease in any tissue at ST or TNT. The lack of tissue damage was not due to defects in donor T cell trafficking to BM or spleen but was associated with the presence of large numbers of B cells and myeloid cells within these tissues that are known to contain immunosuppressive regulatory B cells and myeloid-derived suppressor cells. These data demonstrate, for the first time, that housing temperature affects the survival of RIC-treated I→I mice and that RIC-conditioned outbred mice are resistant to allogeneic T cell-induced BM and spleen damage.

Enforced gut homing of murine regulatory T cells reduces early graft-versus-host disease severity

Damage to the gastrointestinal tract following allogeneic hematopoietic stem cell transplantation is a significant contributor to the severity and perpetuation of graft-versus-host disease. In preclinical models and clinical trials, we showed that infusing high numbers of regulatory T cells reduces graft-versus-host disease incidence. Despite no change in in vitro suppressive function, transfer of ex vivo expanded regulatory T cells transduced to overexpress G protein-coupled receptor 15 or C-C motif chemokine receptor 9, specific homing receptors for colon or small intestine, respectively, lessened graft-versus-host disease severity in mice. Increased regulatory T cell frequency and retention within the gastrointestinal tissues of mice that received gut homing T cells correlated with lower inflammation and gut damage early post-transplant, decreased graft-versus-host disease severity, and prolonged survival compared with those receiving control transduced regulatory T cells. These data provide evidence that enforced targeting of ex vivo expanded regulatory T cells to the gastrointestinal tract diminishes gut injury and is associated with decreased graft-versus-host disease severity.

The chemerin/CMKLR1 axis regulates intestinal graft-versus-host disease

Gastrointestinal graft-versus-host disease (GvHD) is a major cause of mortality and morbidity following allogeneic bone marrow transplantation (allo-BMT). Chemerin is a chemotactic protein that recruits leukocytes to inflamed tissues by interacting with ChemR23/CMKLR1, a chemotactic receptor expressed by leukocytes, including macrophages. During acute GvHD, chemerin plasma levels were strongly increased in allo-BM-transplanted mice. The role of the chemerin/CMKLR1 axis in GvHD was investigated using Cmklr1-KO mice. WT mice transplanted with an allogeneic graft from Cmklr1-KO donors (t-KO) had worse survival and more severe GvHD. Histological analysis demonstrated that the gastrointestinal tract was the organ mostly affected by GvHD in t-KO mice. The severe colitis of t-KO mice was characterized by massive neutrophil infiltration and tissue damage associated with bacterial translocation and exacerbated inflammation. Similarly, Cmklr1-KO recipient mice showed increased intestinal pathology in both allogeneic transplant and dextran sulfate sodium-induced colitis. Notably, the adoptive transfer of WT monocytes into t-KO mice mitigated GvHD manifestations by decreasing gut inflammation and T cell activation. In patients, higher chemerin serum levels were predictive of GvHD development. Overall, these results suggest that CMKLR1/chemerin may be a protective pathway for the control of intestinal inflammation and tissue damage in GvHD.

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.

Mycophenolate Mofetil: A Friend or a Foe with PTCy and Tacrolimus Prophylaxis in HLA-Matched donors?

Adapted from the haploidentical literature, post-transplantation cyclophosphamide (PTCy) is increasingly being used with HLA-matched donors, generally with a calcineurin inhibitor, such as tacrolimus (Tac) with or without mycophenolate mofetil (MMF). Owing to its immunosuppressive, potentially antitumor, and antimicrobial properties, MMF is an attractive drug; however, it remains unclear how much benefit is gained when used with PTCy/Tac. To assess that, we compared PTCy/Tac (n=242) to PTCy/Tac/MMF (n= 144) in recipients of HLA-matched donors. In multivariate analysis, the PTCy/Tac/MMF group had a significantly higher risk of grade II-IV acute graft-versus-host disease (GVHD; hazard ratio (HR) 2.1, 95% confidence interval (CI) 1.6-2.8, p<0.001), and steroid-refractory/dependent acute GVHD (HR 4.8, 95% CI 2.4-9.6, p<0.001), yet a significantly lower risk of relapse (HR 0.5, 95% CI, 0.3-0.9, p=0.009) and better progression-free survival (PFS; HR 0.7, 95% CI 0.5-0.9, p=0.04). There was no difference in the risk of grade III-IV acute GVHD, chronic GVHD, non-relapse mortality, or overall survival. MMF was associated with prolonged neutrophil engraftment by 2 days, and a higher risk of bacterial infections. In an exploratory stool microbiome analysis (n=16), we noted a higher relative abundance of β-glucuronidase-producing bacteria in the MMF group, which may have a role in the pathogenesis of MMF-related GVHD. Our data suggest that the addition of MMF to PTCy/Tac for HLA-matched donor HCT does not provide any advantage for GVHD prevention. Further studies are needed to decipher this mechanism, and understand its role with PTCy-based prophylaxis.

LPSlow-Macrophages Alleviate the Outcome of Graft-Versus-Host Disease Without Aggravating Lymphoma Growth in Mice

Despite significant therapeutic advances, graft-versus-host disease (GvHD) remains the main life-threatening complication following allogeneic hematopoietic stem cell transplantation. The pathogenesis of GvHD is dominated by a dysregulated allogeneic immune response that drives fibrosis and autoimmunity in chronic forms. A multitude of cell therapy approaches, including infusion of myeloid cells, has been proposed to prevent GvHD through tolerance induction but yielded variable results. Myeloid cells like macrophages can be reprogrammed to develop adaptive-like features following antigenic challenge to reinforce or inhibit a subsequent immune response; a phenomenon termed ‘trained immunity’. Here we report that, whereas LPS^low-trained macrophages elicit a suppressor effect on allogeneic T cell proliferation and function in vitro in an IL-10-dependent manner, Bacille Calmette et Guérin (BCG)-trained macrophages exert an opposite effect. In a murine model of sclerodermatous chronic GvHD, LPS^low-trained macrophages attenuate clinical signs of GvHD with significant effects on T cell phenotype and function, autoantibodies production, and tissue fibrosis. Furthermore, infusion of LPS^low-macrophages significantly improves survival in mice with acute GvHD. Importantly, we also provide evidence that LPS^low-macrophages do not accelerate A20-lymphoma tumor growth, which is significantly reduced upon transfer of BCG-macrophages. Collectively, these data indicate that macrophages can be trained to significantly inhibit in vitro and in vivo allo-reactive T cell proliferation without exhibiting pro-tumoral effect, thereby opening the way to promising clinical applications.

Regulatory Dendritic Cells Induced by Bendamustine Are Associated With Enhanced Flt3 Expression and Alloreactive T-Cell Death

The growth factor Flt3 ligand (Flt3L) is central to dendritic cell (DC) homeostasis and development, controlling survival and expansion by binding to Flt3 receptor tyrosine kinase on the surface of DCs. In the context of hematopoietic cell transplantation, Flt3L has been found to suppress graft-versus-host disease (GvHD), specifically via host DCs. We previously reported that the pre-transplant conditioning regimen consisting of bendamustine (BEN) and total body irradiation (TBI) results in significantly reduced GvHD compared to cyclophosphamide (CY)+TBI. Pre-transplant BEN+TBI conditioning was also associated with greater Flt3 expression among host DCs and an accumulation of pre-cDC1s. Here, we demonstrate that exposure to BEN increases Flt3 expression on both murine bone marrow-derived DCs (BMDCs) and human monocyte-derived DCs (moDCs). BEN favors development of murine plasmacytoid DCs, pre-cDC1s, and cDC2s. While humans do not have an identifiable equivalent to murine pre-cDC1s, exposure to BEN resulted in decreased plasmacytoid DCs and increased cDC2s. BEN exposure and heightened Flt3 signaling are associated with a distinct regulatory phenotype, with increased PD-L1 expression and decreased ICOS-L expression. BMDCs exposed to BEN exhibit diminished pro-inflammatory cytokine response to LPS and induce robust proliferation of alloreactive T-cells. These proliferative alloreactive T-cells expressed greater levels of PD-1 and underwent increased programmed cell death as the concentration of BEN exposure increased. Alloreactive CD4⁺ T-cell death may be attributable to pre-cDC1s and provides a potential mechanism by which BEN+TBI conditioning limits GvHD and yields T-cells tolerant to host antigen.

Targeting SLP76:ITK interaction separates GVHD from GVL in allo-HSCT

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for hematological malignancies, due to graft-versus-leukemia (GVL) activity mediated by alloreactive donor T cells. However, graft-versus-host disease (GVHD) is also mediated by these cells. Here, we assessed the effect of attenuating TCR-mediated SLP76:ITK interaction in GVL vs. GVHD effects after allo-HSCT. CD8+ and CD4+ donor T cells from mice expressing a Y145F mutation in SLP-76 did not cause GVHD but preserved GVL effects against B-ALL cells. SLP76Y145FKI CD8+ and CD4+ donor T cells also showed less inflammatory cytokine production and migration to GVHD target organs. We developed a novel peptide to specifically inhibit SLP76:ITK interactions, resulting in decreased phosphorylation of PLCγ1 and ERK, decreased cytokine production in human T cells, and separation of GVHD from GVL effects. Altogether, our data suggest that inhibiting SLP76:ITK interaction could be a therapeutic strategy to separate GVHD from GVL effects after allo-HSCT treatment.

Ruxolitinib Inhibits IFNγ Licensing of Human Bone Marrow Derived Mesenchymal Stromal Cells

Ruxolitinib is a JAK2/JAK1 inhibitor that blocks the inflammatory JAK-STAT signaling pathway. Ruxolitinib has been demonstrated to be effective in the treatment of steroid-resistant acute graft-versus-host disease (GVHD). Ruxolitinib's effect on inflammatory cells of hematopoietic origin is known. However, its effect on nonhematopoietic cell types with immune-modulating and antigen-presenting cell competency plausibly involved in pathogenesis of GVHD has not been explored. Mesenchymal stromal cells (MSCs) are CD45^- nonhematopoietic cells of the bone marrow with immune modulatory functions in vivo. MSCs' immunobiology largely depends on their responsiveness to IFNγ. We aimed to define the effect of ruxolitinib on the immunobiology of MSCs that are modulated by IFNγ. Human bone marrow derived MSCs, peripheral blood mononuclear cells (PBMCs), and primary bone marrow aspirates were analyzed for their sensitivity to ruxolitinib-mediated blocking of IFNγ-induced STAT-1 phosphorylation and downstream effector molecules, utilizing Western blot, flow cytometry, secretome analysis, and phosflow techniques. IFNγ-induced cytostatic effects on MSCs are reversed by ruxolitinib. Ruxolitinib inhibits IFNγ and secretome of activated peripheral PBMC-induced STAT-1 phosphorylation on human bone marrow derived MSCs. In addition, ruxolitinib inhibits IFNγ-induced pro-GVHD pathways on MSCs, which includes HLAABC(MHCI), HLADR(MHCII), CX3CL1, and CCL2. IFNγ-induced immunosuppressive molecules IDO and PDL-1 were also inhibited by ruxolitinib on MSCs. Comparative analysis with PBMCs has demonstrated that MSCs are as equal as to HLADR⁺ PBMC populations in responding to ruxolitinib-mediated inhibition of IFNγ-induced STAT-1 phosphorylation. Ex vivo analysis of human marrow aspirates has demonstrated that ruxolitinib blocks IFNγ-induced STAT-1 phosphorylation in CD45^+/-HLADR^+/- populations at different levels, which is depending on their sensitivity to IFNγ responsiveness. These results inform the hypothesis that ruxolitinib's immune-modulatory effects in vivo may pharmacologically involve marrow and tissue-resident MSCs. Ruxolitinib affects the immunobiology of MSCs equivalent to professional HLADR⁺ antigen presenting cells, which collectively mitigate GVHD.

Biomarkers for acute and chronic graft versus host disease: state of the art

INTRODUCTION

Despite significant advances in treatment and prevention, graft-versus-host disease (GVHD) still represents the main cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Thus, considerable research efforts have been made to find and validate reliable biomarkers for diagnosis, prognosis, and risk stratification of GVHD.

AREAS COVERED

In this review the most recent evidences on different types of biomarkers studied for GVHD, such as genetic, plasmatic, cellular markers, and those associated with microbiome, were summarized. A comprehensive search of peer-review literature was performed in PubMed including meta-analysis, preclinical and clinical trials, using the terms: cellular and plasma biomarkers, graft-versus-host disease, cytokines, and allogeneic hematopoietic stem cell transplantation.

EXPERT OPINION

In the near future, several validated biomarkers will be available to help clinicians in the diagnosis of GVHD, the identification of patients at high risk of GVHD development and in patients' stratification according to its severity. Then, immunosuppressive treatment could be tailored to each patient's real needs. However, more efforts are needed to achieve this goal. Although most of the proposed biomarkers currently lack validation with large-scale clinical data, their study led to improved knowledge of the biological basis of GVHD, and ultimately to implementation of GHVD treatment.

Targeting the Complement Alternative Pathway Permits Graft Versus Leukemia Activity while Preventing Graft Versus Host Disease

PURPOSE

Application of allogeneic hematopoietic cell transplantation (allo-HCT) for patients with hematologic disorders is limited by the development of GVHD. Separation of GVHD and graft-versus-leukemia (GVL) remains a great challenge in the field. We investigated the contribution of individual pathways involved in the complement cascade in GVH and GVL responses to identify specific targets by which to separate these two processes.

EXPERIMENTAL DESIGN

We used multiple preclinical murine and human-to-mouse xenograft models involving allo-HCT recipients lacking components of the alternative pathway (AP) or classical pathway (CP)/lectin pathway (LP) to dissect the role of each individual pathway in GVHD pathogenesis and the GVL effect. For translational purposes, we used the AP-specific complement inhibitor, CR2-fH, which localizes in injured target organs to allow specific blockade of complement activation at sites of inflammation.

RESULTS

Complement deposition was evident in intestines of mice and patients with GVHD. In a preclinical setting, ablation of the AP, but not the CP/LP, significantly improved GVHD outcomes. Complement activation through the AP in host hematopoietic cells, and specifically dendritic cells (DC), was required for GVHD progression. AP deficiency in recipients decreased donor T-cell migration and Th1/Th2 differentiation, while increasing the generation of regulatory T cells. This was because of decreased activation and stimulatory activity of recipient DCs in GVHD target organs. Treatment with CR2-fH effectively prevented GVHD while preserving GVL activity.

CONCLUSIONS

This study highlights the AP as a new therapeutic target to prevent GVHD and tumor relapse after allo-HCT. Targeting the AP by CR2-fH represents a promising therapeutic approach for GVHD treatment.

CCL1 blockade alleviates human mesenchymal stem cell (hMSC)-induced pulmonary fibrosis in a murine sclerodermatous graft-versus-host disease (Scl-GVHD) model

Background

Human chronic graft-versus-host disease (CGVHD) shares clinical characteristics with a murine sclerodermatous GVHD (Scl-GVHD, B10.D2 → BALB/c) model that is characterized by skin and lung fibrosis. In this study, bone marrow- or adipose tissue-derived human mesenchymal stem cells (hMSCs) were injected into the Scl-GVHD mice to address their therapeutic effect on CGVHD.

Methods

Lethally irradiated BALB/c mice were transplanted with B10.D2 T cell-depleted bone marrow with or without spleen cells to generate Scl-GVHD. hMSCs were intravenously treated on days 3, 5, and 7 post-transplantation, and the control antibody or CCL1 blocking antibody was subcutaneously injected according to the same schedule as the hMSCs. Fourteen days after transplantation, the recipient mice were sacrificed, and their skin and lungs were analyzed.

Results

After the early injection of hMSCs after transplantation, the clinical and pathological severity of Scl-GVHD in the skin was significantly attenuated, whereas the pathological score was exacerbated in the lungs. hMSCs had migrated into the lungs, but not into the skin. CD11b monocyte/macrophages and CD4 T cells were markedly decreased in skin tissues, whereas there was an early recruitment of CD11b cells, and subsequently increased infiltration of CD4 T cells, in the lungs. Importantly, hMSCs persistently upregulated the expression of CCL1 in the lungs, but not in the skin. Concurrent treatment of hMSCs with a CCL1-blocking antibody alleviated the severity of the lung histopathology score and fibrosis with the preservation of the cutaneous protective effect against CGVHD. Infiltration of CD3 T cells and CD68 macrophages and upregulation of chemokines were also decreased in lung tissues, along with the recruitment of eosinophils and tissue IgE expression. In the skin, chemokine expression was further reduced after CCL1 blockade.

Conclusions

These data demonstrate that despite a protective effect against Scl-GVHD in the skin, administration of hMSCs exacerbated lung fibrosis associated with eosinophilia and airway inflammation through persistent CCL1 upregulation. CCL1 blockade offers a potential treatment of pulmonary complications induced after treatment with hMSCs.

Predictive value of serum protein levels in patients with advanced non-small cell lung cancer treated with nivolumab

BACKGROUND

Although programmed cell death-ligand-1 (PD-L1) expression in tumor tissue has been established as predictive biomarker for the anti-programmed cell death-1 (PD-1) antibody treatment of non-small-cell lung cancer (NSCLC), additional biomarkers are critically needed. We evaluated serum proteins relevant to immune checkpoint blockade in patients with NSCLC treated with nivolumab to identify novel non-invasive predictive biomarkers.

PATIENTS AND METHODS

Patients with advanced NSCLC, who had failed at least one prior chemotherapy regimen, received nivolumab monotherapy (3 mg/kg, Q2W) until progressive disease (PD) or unacceptable toxicity was observed. Blood samples were collected at baseline and week 4. Fifty-seven serum protein levels were quantified with a Milliplex MAP assay. The associations of both clinical benefit (CB) and the onset of immune related adverse events (irAEs) with serum proteins levels were evaluated.

RESULTS

Thirty-eight patients with advanced NSCLC were enrolled in the study, with 38 and 32 paired serum samples at baseline and week 4 being available for efficacy analysis and irAE analysis, respectively. In durable CB (DCB) patients compared with non-DCB patients, the baseline serum levels of BMP-9 were significantly higher, whereas the follistatin, IL-8, IP-10, and TNF-α levels were significantly lower. In irAE patients compared with non-irAE patients the serum levels of G-CSF and RANTES at week 4 were significantly higher, whereas the levels of leptin were significantly lower. A multivariate analysis revealed that follistatin and IP-10 were statistically associated with DCB (p < 0.05) and RANTES was associated with irAE onset (p < 0.05). In a subset of irAE-developed patients, RANTES levels decreased after steroid administration, supporting its involvement in irAE.

CONCLUSION

Serum proteins have the potential to be predictive markers for DCB and irAEs onset in patients with NSCLC treated with nivolumab. In addition, antitumor activity and irAEs may not be regulated by the same mechanisms.

Complement C3a and C5a receptors promote GVHD by suppressing mitophagy in recipient dendritic cells

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic cell transplantation (HCT). DCs play critical roles in GVHD induction. Modulating autophagy represents a promising therapeutic strategy for the treatment of immunological diseases. Complement receptors C3aR/C5aR expressed on DCs regulate immune responses by translating extracellular signals into intracellular activity. In the current study, we found that C3aR/C5aR deficiency enhanced ceramide-dependent lethal mitophagy (CDLM) in DCs. Cotransfer of host-type C3aR-/-/C5aR-/- DCs in the recipients significantly improved GVHD outcome after allogeneic HCT, primarily through enhancing CDLM in DCs. C3aR/C5aR deficiency in the host hematopoietic compartment significantly reduced GVHD severity via impairing Th1 differentiation and donor T cell glycolytic activity while enhancing Treg generation. Prophylactic treatment with C3aR/C5aR antagonists effectively alleviated GVHD while maintaining the graft-versus-leukemia (GVL) effect. Altogether, we demonstrate that inhibiting C3aR/C5aR induces lethal mitophagy in DCs, which represents a potential therapeutic approach to control GVHD while preserving the GVL effect.

MicroRNA-155 Modulates Acute Graft-versus-Host Disease by Impacting T Cell Expansion, Migration, and Effector Function

MicroRNA-155 (miR-155) is a small noncoding RNA critical for the regulation of inflammation as well as innate and adaptive immune responses. MiR-155 has been shown to be dysregulated in both donor and recipient immune cells during acute graft-versus-host disease (aGVHD). We previously reported that miR-155 is upregulated in donor T cells of mice and humans with aGVHD and that mice receiving miR-155-deficient (miR155^-/-) splenocytes had markedly reduced aGVHD. However, molecular mechanisms by which miR-155 modulates T cell function in aGVHD have not been fully investigated. We identify that miR-155 expression in both donor CD8⁺ T cells and conventional CD4⁺ CD25^- T cells is pivotal for aGVHD pathogenesis. Using murine aGVHD transplant experiments, we show that miR-155 strongly impacts alloreactive T cell expansion through multiple distinct mechanisms, modulating proliferation in CD8⁺ donor T cells and promoting exhaustion in donor CD4⁺ T cells in both the spleen and colon. Additionally, miR-155 drives a proinflammatory Th1 phenotype in donor T cells in these two sites, and miR-155^-/- donor T cells are polarized toward an IL-4-producing Th2 phenotype. We further demonstrate that miR-155 expression in donor T cells regulates CCR5 and CXCR4 chemokine-dependent migration. Notably, we show that miR-155 expression is crucial for donor T cell infiltration into multiple target organs. These findings provide further understanding of the role of miR-155 in modulating aGVHD through T cell expansion, effector cytokine production, and migration.

Graft versus Host Disease: From Basic Pathogenic Principles to DNA Damage Response and Cellular Senescence

Graft versus host disease (GVHD), a severe immunogenic complication of allogeneic hematopoietic stem cell transplantation (HSCT), represents the most frequent cause of transplant-related mortality (TRM). Despite a huge progress in HSCT techniques and posttransplant care, GVHD remains a significant obstacle in successful HSCT outcome. This review presents a complex summary of GVHD pathogenesis with focus on references considering basic biological processes such as DNA damage response and cellular senescence.

Ibrutinib for chronic graft-versus-host disease after failure of prior therapy

Chronic graft-versus-host disease (cGVHD) is a serious complication of allogeneic stem cell transplantation with few effective options available after failure of corticosteroids. B and T cells play a role in the pathophysiology of cGVHD. Ibrutinib inhibits Bruton tyrosine kinase in B cells and interleukin-2-inducible T-cell kinase in T cells. In preclinical models, ibrutinib reduced severity of cGVHD. This multicenter, open-label study evaluated the safety and efficacy of ibrutinib in patients with active cGVHD with inadequate response to corticosteroid-containing therapies. Forty-two patients who had failed 1 to 3 prior treatments received ibrutinib (420 mg) daily until cGVHD progression. The primary efficacy end point was cGVHD response based on 2005 National Institutes of Health criteria. At a median follow-up of 13.9 months, best overall response was 67%; 71% of responders showed a sustained response for ≥20 weeks. Responses were observed across involved organs evaluated. Most patients with multiple cGVHD organ involvement had a multiorgan response. Median corticosteroid dose in responders decreased from 0.29 mg/kg per day at baseline to 0.12 mg/kg per day at week 49; 5 responders discontinued corticosteroids. The most common adverse events were fatigue, diarrhea, muscle spasms, nausea, and bruising. Plasma levels of soluble factors associated with inflammation, fibrosis, and cGVHD significantly decreased over time with ibrutinib. Ibrutinib resulted in clinically meaningful responses with acceptable safety in patients with ≥1 prior treatments for cGVHD. Based on these results, ibrutinib was approved in the United States for treatment of adult patients with cGVHD after failure of 1 or more lines of systemic therapy. This trial was registered at www.clinicaltrials.gov as #NCT02195869.

Endothelial damage is aggravated in acute GvHD and could predict its development

The aim of the present study was to explore whether there is enhanced endothelial dysfunction in patients developing acute GvHD (aGvHD) after allogeneic hematopoietic cell transplantation (allo-HCT) and to identify biomarkers with predictive and/or diagnostic value. In in vitro experiments, endothelial cells (ECs) were exposed to serum from patients with (aGvHD, n=31) and without (NoGvHD, n=13) aGvHD, to evaluate changes in surface adhesion receptors, the reactivity of the extracellular matrix by measuring the presence of Von Willebrand factor (VWF) and platelet adhesion, and the activation of intracellular signaling proteins. Plasma levels of VWF, ADAMTS-13, TNF receptor 1 (TNFR1), soluble vascular cell adhesion molecule 1 and soluble intercellular adhesion molecule 1 were also measured. In vitro results showed a more marked proinflammatory and prothrombotic phenotype in ECs in association with aGvHD. Regarding circulating biomarkers, levels of VWF and TNFR1 above an optimal cutoff score, taken independently or combined, at day 7 after allo-HCT, would be able to positively predict that around 90% of patients will develop aGvHD. Our results demonstrate that endothelial damage is aggravated in those allo-HCT recipients developing aGvHD, and that VWF and TNFR1 are promising predictive aGvHD biomarkers. These findings could contribute to improve the understanding of the pathophysiology of aGvHD.

CXCR5-Overexpressing Mesenchymal Stromal Cells Exhibit Enhanced Homing and Can Decrease Contact Hypersensitivity

Mesenchymal stromal cells (MSCs) can modulate inflammation and contribute to tissue regeneration and, thus, have emerged as a promising option for cell-based therapy. However, the ability of MSCs to migrate to injured tissues still needs to be improved. In this study, we investigated whether genetically engineered MSCs could exhibit increased migratory properties and improved therapeutic efficacy. Using a mouse model of contact hypersensitivity (CHS), chemokine gene expression screening revealed that CXCL13 changed most significantly in injured tissue. Unfortunately, MSCs hardly express the corresponding receptor, CXCR5. Thus, CXCR5-overexpressing MSCs (MSC^CXCR5) were generated that retained their abilities of proliferation, differentiation, and immunomodulation. Furthermore, MSC^CXCR5 showed significantly increased migrating ability toward CXCL13. Importantly, systemic infusion of MSC^CXCR5 dramatically suppressed CHS in mice, as evidenced by decreased levels of inflammatory cell infiltration and pro-inflammatory cytokine production. Numerous MSC^CXCR5 migrated into inflamed ears, localized with T cells, inhibited T cell proliferation, promoted T cell apoptosis, and suppressed the production of T cell-derived pro-inflammatory factors. Collectively, these findings demonstrate that CXCR5 overexpression increases the ability of MSCs to respond to migratory stimuli and highly intensifies their immunomodulatory effects in vivo. This strategy for enhancing targeted stem/progenitor cell homing may improve the efficacy of MSC-based therapies.

Genetic Association of Hematopoietic Stem Cell Transplantation Outcome beyond Histocompatibility Genes

The outcome of hematopoietic stem cell transplantation (HSCT) is controlled by genetic factors among which the leukocyte antigen human leukocyte antigen (HLA) matching is most important. In addition, minor histocompatibility antigens and non-HLA gene polymorphisms in genes controlling immune responses are known to contribute to the risks associated with HSCT. Besides single-nucleotide polymorphisms (SNPs) in protein coding genes, SNPs in regulatory elements such as microRNAs (miRNAs) contribute to these genetic risks. However, genetic risks require for their realization the expression of the respective gene or miRNA. Thus, gene and miRNA expression studies may help to identify genes and SNPs that indeed affect the outcome of HSCT. In this review, we summarize gene expression profiling studies that were performed in recent years in both patients and animal models to identify genes regulated during HSCT. We discuss SNP–mRNA–miRNA regulatory networks and their contribution to the risks associated with HSCT in specific examples, including forkheadbox protein 3 and regulatory T cells, the role of the miR-155 and miR-146a regulatory network for graft-versus-host disease, and the function of MICA and its receptor NKG2D for the outcome of HSCT. These examples demonstrate how SNPs affect expression or function of proteins that modulate the alloimmune response and influence the outcome of HSCT. Specific miRNAs targeting these genes and directly affecting expression of mRNAs are identified. It might be valuable in the future to determine SNPs and to analyze miRNA and mRNA expression in parallel in cohorts of HSCT patients to further elucidate genetic risks of HSCT.

Recombinant IL-7/HGFβ hybrid cytokine separates acute graft-versus-host-disease from graft-versus-tumour activity by altering donor T cell trafficking

Given that donor T cells from a transplant contribute both the desired graft-versus-tumour (GVT) effect and detrimental graft-versus-host disease (GVHD), strategies to separate GVHD and GVT activity are a major clinical goal. We have previously demonstrated that in vivo administration of a recombinant (r)IL-7/HGFβ hybrid cytokine, consisting of interleukin-7 (IL-7, IL7) and the β-chain of hepatocyte growth factor (HGFβ), significantly inhibits the growth of cancer cells in murine tumour models. The antit-umour effect of rIL-7/HGFβ is related to a marked infiltration T cells in the tumour tissues. We have also shown that GVHD was not induced in rIL-7/HGFβ-treated T cell-depleted allogeneic haematopoietic stem cell transplantation (HSCT) recipients. We show here that, in T cell-replete allogeneic HSCT murine models, rIL-7/HGFβ attenuated acute GVHD (aGVHD), while promoting GVT activity. This was related to an alteration of donor T cell trafficking, with an increased infiltration of donor T cells into tumour tissues and the lympho-haematopoietic system but decreased number of the T cells in the GVHD target organs. Therefore, rIL-7/HGFβ may offer a new tool to alleviate aGVHD while prompting GVT, and to study the molecular regulation of T cell trafficking.

T-bet Promotes Acute Graft-versus-Host Disease by Regulating Recipient Hematopoietic Cells in Mice

Beyond its critical role in T cells, T-bet regulates the functions of APCs including dendritic cells and B cells, as well as NK cells. Given that recipient APCs are essential for priming allogeneic T cells and recipient NK or T cells are able to reject allogeneic donor cells, we evaluated the role of T-bet on the host in acute graft-versus-host disease (GVHD) using murine models of allogeneic bone marrow transplantation. T-bet(-/-) recipients developed significantly milder GVHD than their wild type counterparts in MHC-mismatched or CD4-dependent minor histocompatibility Ag-mismatched models. Allogeneic donor T cells, in particular, CD4 subset, significantly reduced IFN-γ production, proliferation and migration, and caused less injury in liver and gut of T-bet(-/-) recipients. We further observed that T-bet on recipient hematopoietic cells was primarily responsible for the donor T cell response and pathogenicity in GVHD. T-bet(-/-) dendritic cells expressed higher levels of Trail, whereas they produced lower levels of IFN-γ and IL-12/23 p40, as well as chemokine CXCL9, resulting in significantly higher levels of apoptosis, less priming, and infiltration of donor T cells. Meanwhile, NK cells in T-bet(-/-) hosts partially contribute to the decreased donor T cell proliferation. Furthermore, although T-bet on hematopoietic cells was required for GVHD development, it was largely dispensable for the graft-versus-leukemia effect. Taken together with our previous findings, we propose that T-bet is a potential therapeutic target for the control of GVHD through regulating donor T cells and recipient hematopoietic cells.

T-bet is critical for the development of acute graft-versus-host disease through controlling T cell differentiation and function

T-bet is a master regulator for IFN-γ production and Th1 differentiation. We evaluated the roles of T-bet and IFN-γ in T cell responses in acute graft-versus-host disease (GVHD) and found that T-bet(-/-) T cells induced significantly less GVHD compared with wild-type or IFN-γ(-/-) counterparts in both MHC-mismatched and MHC-matched but minor histocompatibility Ag-mismatched models driven by CD4 T cells. T-bet(-/-), but not IFN-γ(-/-), CD4 T cells had a markedly reduced ability to cause tissue damage in liver and gut. This distinct outcome is reflected by the differential gene expression on donor CD4 T cells deficient for T-bet or IFN-γ. At mRNA and protein levels, we defined several T-bet-dependent molecules that may account for the impaired ability of T-bet(-/-) T cells to migrate into target organs and to produce Th1-related cytokines. Moreover, these molecules were independent of either endogenous IFN-γ, such as CXCR3 and programmed death-1, or systematic IFN-γ, such as NKG2D, I-A(b), and granzyme B. Although both T-bet(-/-) and IFN-γ(-/-) CD4 T cells are prone to differentiate into Th17 cells, polarized Th17 cells deficient for T-bet but not for IFN-γ had a significantly reduced ability to cause GVHD. Finally, T-bet(-/-) T cells had a compromised graft-versus-leukemia effect, which could be essentially reversed by neutralization of IL-17 in the recipients. We conclude that T-bet is required for Th1 differentiation and migration, as well as for optimal function of Th17 cells. Thus, targeting T-bet or regulating its downstream effectors independent of IFN-γ may be a promising strategy to control GVHD in the clinic.

Diverse T-cell responses characterize the different manifestations of cutaneous graft-versus-host disease

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HCT) and can present in an acute (aGVHD), a chronic lichenoid (clGVHD), and a chronic sclerotic form (csGVHD). It is unclear whether similar or different pathomechanisms lead to these distinct clinical presentations. To address this issue, we collected lesional skin biopsies from aGVHD (n = 25), clGVHD (n = 17), and csGVHD (n = 7) patients as well as serial nonlesional biopsies from HCT recipients (prior to or post-HCT) (n = 14) and subjected them to phenotypic and functional analyses. Our results revealed striking differences between aGVHD and clGVHD. In aGVHD, we found a clear predominance of T helper (Th)2 cytokines/chemokines and, surprisingly, of interleukin (IL)-22 messenger RNA as well as an increase of IL-22-producing CD4(+) T cells. Thymic stromal lymphopoietin, a cytokine skewing the immune response toward a Th2 direction, was elevated at day 20 to 30 post-HCT in the skin of patients who later developed aGVHD. In sharp contrast to aGVHD, the immune response occurring in clGVHD showed a mixed Th1/Th17 signature with upregulated Th1/Th17 cytokine/chemokine transcripts and elevated numbers of interferon-γ- and IL-17-producing CD8(+) T cells. Our findings shed new light on the T-cell responses involved in the different manifestations of cutaneous GVHD and identify molecular signatures indicating the development of the disease.

Lithothamnion muelleri controls inflammatory responses, target organ injury and lethality associated with graft-versus-host disease in mice

Lithothamnion muelleri (Hapalidiaceae) is a marine red alga, which is a member of a group of algae with anti-inflammatory, antitumor, and immunomodulatory properties. The present study evaluated the effects of treatment with Lithothamnion muelleri extract (LM) in a model of acute graft-versus-host disease (GVHD), using a model of adoptive splenocyte transfer from C57BL/6 donors into B6D2F1 recipient mice. Mice treated with LM showed reduced clinical signs of disease and mortality when compared with untreated mice. LM-treated mice had reduced tissue injury, less bacterial translocation, and decreased levels of proinflammatory cytokines and chemokines (interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), chemokine (C-C motif) ligand 2 (CCL2), chemokine (C-C motif) ligand 3 (CCL3) and chemokine (C-C motif) ligand 5 (CCL5)). The polysaccharide-rich fraction derived from LM could inhibit leukocyte rolling and adhesion in intestinal venules, as assessed by intravital microscopy. LM treatment did not impair the beneficial effects of graft-versus-leukaemia (GVL). Altogether, our studies suggest that treatment with Lithothamnion muelleri has a potential therapeutic application in GVHD treatment.