Stem cell mobilization with G-CSF induces type 17 differentiation and promotes scleroderma. Blood. 2010;116:819-828. [PMID: 20435882 DOI: 10.1182/blood-2009-11-256495]

Calcineurin inhibition rescues alloantigen-specific central memory T cell subsets that promote chronic GVHD

Calcineurin inhibitors (CNIs) constitute the backbone of modern acute graft-versus-host disease (aGVHD) prophylaxis regimens but have limited efficacy in the prevention and treatment of chronic GVHD (cGVHD). We investigated the effect of CNIs on immune tolerance after stem cell transplantation with discovery-based single-cell gene expression and T cell receptor (TCR) assays of clonal immunity in tandem with traditional protein-based approaches and preclinical modeling. While cyclosporin and tacrolimus suppressed the clonal expansion of CD8+ T cells during GVHD, alloreactive CD4+ T cell clusters were preferentially expanded. Moreover, CNIs mediated reversible dose-dependent suppression of T cell activation and all stages of donor T cell exhaustion. Critically, CNIs promoted the expansion of both polyclonal and TCR-specific alloreactive central memory CD4+ T cells (TCM) with high self-renewal capacity that mediated cGVHD following drug withdrawal. In contrast to posttransplant cyclophosphamide (PT-Cy), CSA was ineffective in eliminating IL-17A-secreting alloreactive T cell clones that play an important role in the pathogenesis of cGVHD. Collectively, we have shown that, although CNIs attenuate aGVHD, they paradoxically rescue alloantigen-specific TCM, especially within the CD4+ compartment in lymphoid and GVHD target tissues, thus predisposing patients to cGVHD. These data provide further evidence to caution against CNI-based immune suppression without concurrent approaches that eliminate alloreactive T cell clones.

Two-Part Phase 1 Study to Evaluate the Taste Profile of Novel Belumosudil Oral Suspensions and Assess the Relative Bioavailability and Food Effect of the Selected Belumosudil Oral Suspension Compared With Oral Tablet Reference in Healthy Male Participants

Belumosudil is a selective rho-associated coiled-coil-containing protein kinase 2 inhibitor in clinical use for the treatment of chronic graft-versus-host disease. The current tablet formulation may be inappropriate for children or adults with dysphagia and/or upper gastrointestinal manifestations of chronic graft-versus-host disease. This study (NCT04735822) assessed the taste and palatability of oral suspensions of belumosudil, evaluated the relative bioavailability of an oral suspension versus the tablet formulation, and characterized the effect of food on the pharmacokinetics of an oral suspension. Addition of sweetener and/or flavor vehicle improved the taste. Relative bioavailability of 200-mg doses of the oral suspension and tablet in the fed state was similar for belumosudil and its metabolites (KD025m1 and KD025m2), but absorption was faster with the oral suspension (median time to maximum concentration: 2 vs 3 hours). Administration of the oral suspension with food increased exposure compared with fasted administration, with maximum observed concentration being increased by 16% and area under the concentration-time curve from time 0 to the last measurable concentration (AUC0-last) by 19%. Safety and tolerability were consistent with the known safety profile of belumosudil. These results may support administration of a 200-mg belumosudil oral suspension with or without food.

Regulatory T cells suppress myeloma-specific immunity during autologous stem cell mobilization and transplantation

ABSTRACT

Autologous stem cell transplantation (ASCT) is the standard of care consolidation therapy for eligible patients with myeloma but most patients eventually progress, an event associated with features of immune escape. Novel approaches to enhance antimyeloma immunity after ASCT represent a major unmet need. Here, we demonstrate that patient-mobilized stem cell grafts contain high numbers of effector CD8 T cells and immunosuppressive regulatory T cells (Tregs). We showed that bone marrow (BM)-residing T cells are efficiently mobilized during stem cell mobilization (SCM) and hypothesized that mobilized and highly suppressive BM-derived Tregs might limit antimyeloma immunity during SCM. Thus, we performed ASCT in a preclinical myeloma model with or without stringent Treg depletion during SCM. Treg depletion generated SCM grafts containing polyfunctional CD8 T effector memory cells, which dramatically enhanced myeloma control after ASCT. Thus, we explored clinically tractable translational approaches to mimic this scenario. Antibody-based approaches resulted in only partial Treg depletion and were inadequate to recapitulate this effect. In contrast, a synthetic interleukin-2 (IL-2)/IL-15 mimetic that stimulates the IL-2 receptor on CD8 T cells without binding to the high-affinity IL-2Ra used by Tregs efficiently expanded polyfunctional CD8 T cells in mobilized grafts and protected recipients from myeloma progression after ASCT. We confirmed that Treg depletion during stem cell mobilization can mitigate constraints on tumor immunity and result in profound myeloma control after ASCT. Direct and selective cytokine signaling of CD8 T cells can recapitulate this effect and represent a clinically testable strategy to improve responses after ASCT.

CSF-1R inhibitor PLX3397 attenuates peripheral and brain chronic GVHD and improves functional outcomes in mice

Graft-versus-host disease (GVHD) is a serious complication of otherwise curative allogeneic haematopoietic stem cell transplants. Chronic GVHD induces pathological changes in peripheral organs as well as the brain and is a frequent cause of late morbidity and death after bone-marrow transplantation. In the periphery, bone-marrow-derived macrophages are key drivers of pathology, but recent evidence suggests that these cells also infiltrate into cGVHD-affected brains. Microglia are also persistently activated in the cGVHD-affected brain. To understand the involvement of these myeloid cell populations in the development and/or progression of cGVHD pathology, we here utilized the blood-brain-barrier permeable colony stimulating factor-1 receptor (CSF-1R) inhibitor PLX3397 (pexidartinib) at varying doses to pharmacologically deplete both cell types. We demonstrate that PLX3397 treatment during the development of cGVHD (i.e., 30 days post-transplant) improves disease symptoms, reducing both the clinical scores and histopathology of multiple cGVHD target organs, including the sequestration of T cells in cGVHD-affected skin tissue. Cognitive impairments associated with cGVHD and neuroinflammation were also attenuated by PLX3397 treatment. PLX3397 treatment prior to the onset of cGVHD (i.e., immediately post-transplant) did not change in clinical scores or histopathology. Overall, our data demonstrate significant benefits of using PLX3397 for the treatment of cGVHD and associated organ pathologies in both the periphery and brain, highlighting the therapeutic potential of pexidartinib for this condition.

Chronic GvHD NIH Consensus Project Biology Task Force: evolving path to personalized treatment of chronic GvHD

Chronic graft-versus-host disease (cGvHD) remains a prominent barrier to allogeneic hematopoietic stem cell transplantion as the leading cause of nonrelapse mortality and significant morbidity. Tremendous progress has been achieved in both the understanding of pathophysiology and the development of new therapies for cGvHD. Although our field has historically approached treatment from an empiric position, research performed at the bedside and bench has elucidated some of the complex pathophysiology of cGvHD. From the clinical perspective, there is significant variability of disease manifestations between individual patients, pointing to diverse biological underpinnings. Capitalizing on progress made to date, the field is now focused on establishing personalized approaches to treatment. The intent of this article is to concisely review recent knowledge gained and formulate a path toward patient-specific cGvHD therapy.

Ruxolitinib as the first post-steroid treatment for acute and chronic graft-versus-host disease

INTRODUCTION

Acute and chronic graft-versus-host disease (GvHD) are potentially life-threatening complications occurring after allogeneic stem cell transplantation (allo-HSCT). Although steroids represent the first-line treatment for both conditions, in those patients who do not adequately benefit from steroid therapy, standardized treatment algorithms are lacking. In recent years, ruxolitinib has emerged as the most promising agent for the second-line therapy of steroid-refractory (SR)-GvHD.

AREAS COVERED

This review will summarize the biological properties and the mechanistic aspects that justify the therapeutic role of ruxolitinib in GvHD. In addition, current treatment options for SR-GvHD will be briefly discussed. Finally, results of the most relevant clinical trials on the use of ruxolitinib for SR-GvHD will be analyzed, with a particular focus on two phase-III randomized trials in which ruxolitinib demonstrated its superiority in comparison with the best available therapy.

EXPERT OPINION

Ruxolitinib has considerably improved the outcome of patients with SR-acute/chronic-GvHD and should be regarded as the standard-of-care option when corticosteroids fail or cannot be tapered. Nevertheless, a number of questions still remain unanswered and significant room for improvement exists. Additional observations derived from a longer follow-up will certainly increase our expertise in the management of this powerful therapy.

Tocilizumab increases regulatory T cells, reduces natural killer cells and delays graft-versus-host disease development in humanized mice treated with post-transplant cyclophosphamide

Graft-versus-host disease (GVHD) is a life-threatening complication following donor hematopoietic stem cell transplantation, where donor T cells damage host tissues. This study investigated the effect of tocilizumab (TOC) combined with post-transplant cyclophosphamide (PTCy) on immune cell engraftment and GVHD development in a humanized mouse model. NOD-scid-IL2Rγ^null (NSG) mice were injected intraperitoneally with 2 × 10⁷ human (h) peripheral blood mononuclear cells and cyclophosphamide (33 mg kg^-1 ) or saline on days 3 and 4, then TOC or control antibody (0.5 mg mouse^-1 ) twice weekly for 28 days. Mice were monitored for clinical signs of GVHD for either 28 or 70 days. Spleens and livers were assessed for human leukocyte subsets, and serum cytokines and tissue histology were analyzed. In the short-term model (day 28), liver and lung damage were reduced in PTCy + TOC compared with control mice. All groups showed similar splenic hCD45⁺ leukocyte engraftment (55-60%); however, PTCy + TOC mice demonstrated significantly increased (1.5-2-fold) splenic regulatory T cells. Serum human interferon gamma was significantly reduced in PTCy + TOC compared with control mice. Long-term (day 70), prolonged survival was similar in PTCy + TOC (median survival time, > 70 days) and PTCy mice (median survival time, 56 days). GVHD onset was significantly delayed in PTCy + TOC, compared with TOC or control mice. Notably, natural killer cells were reduced (77.5%) in TOC and PTCy + TOC mice. Overall, combining PTCy with TOC increases regulatory T cells and reduces clinical signs of early GVHD, but does not improve long-term survival compared with PTCy alone.

Mocravimod, a S1P receptor modulator, increases T cell counts in bone marrow biopsies from patients undergoing allogeneic hematopoietic stem cell transplantation

Graft-versus-leukemia (GvL) effects are critical to prevent relapses after allogeneic hematopoietic cell transplantation (allo-HCT). However, the success of allo-HCT is limited by graft-versus-host disease (GvHD). Both, CD4⁺ and CD8⁺ T cells contribute to GvHD and GvL. The sphingosine-1-phosphate receptor (S1PR) signaling plays a crucial role in lymphocyte trafficking. Mocravimod is an S1PR modulator and its administration leads to blocking lymphocyte egress from lymphoid organs. We hypothesized that this applies to the bone marrow (BM) too, and analyzed BM biopsies from the clinical study with mocravimod (phase I trial in allo-HCT patients; NCT01830010) by immunohistochemical staining for CD3, CD4, CD8, TIA1, FoxP3, PD1, T-Bet, GATA3, and ROR-γt to identify and quantify T cell subsets in situ. Allo-HCT patients without receiving mocravimod were used as controls. BM from 9 patients in the mocravimod group and 10 patients in the control group were examined. CD3⁺ T cells were found to accumulate in the BM of mocravimod-treated patients compared to controls, both on day 30 and 90 post-transplant. The effect was stronger for CD4⁺ T cells, than CD8⁺ T cells, which is in line with data from murine studies showing that CD4⁺ T cells are more sensitive to mocravimod treatment than CD8⁺ T cells. Clinically-relevant acute GvHD events (grade II-IV) were slightly lower, but comparable to controls when mocravimod was administered. Taken together, data are supportive of mocravimod's mode of action and bring additional evidence of fewer relapses for allo-HCT patients treated with S1PR modulators.

T helper 17 and regulatory T-cell profile and graft-versus-host disease after allogeneic hematopoietic stem cell transplantation in pediatric patients with beta-thalassemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment option for hereditary hemoglobin disorders, such as beta-thalassemia; However, this procedure is not without constraints, mainly engendering complications such as acute graft-versus-host disease (aGvHD), chronic GvHD (cGvHD), and susceptibility to infections. The clinical outcomes of allo-HSCT are highly dependant on the quality and quantity of T-cell subsets reconstitution. Following the allo-HSCT of six pediatric patients afflicted with beta-thalassemia, their mononuclear cells were isolated, and then cultured with a combination of phorbol myristate acetate (PMA)/ionomycin and Brefeldin A. The content of CD4 T-cell subsets, including T helper 17 (Th17) cells and regulatory T cells (Tregs), were determined by specific conjugated-monoclonal antibodies three and six months post-HSCT. An increased frequency of total CD4 T-cells, Tregs and Th17 cells was observed at day 90 and 180 after allo-HSCT, albeit the numbers were still lower than that of our healthy controls. In patients who developed cGvHD, a lower Th17/Treg ratio was observed, owing it to a decreased proportion of Th17 cells. In conclusion, creating balance between Th17 and Treg subsets may prevent acute and chronic GvHD in patients after allo-HSCT.

TIGIT inhibition and lenalidomide synergistically promote antimyeloma immune responses after stem cell transplantation in mice

Autologous stem cell transplantation (ASCT) with subsequent lenalidomide maintenance is standard consolidation therapy for multiple myeloma, and a subset of patients achieve durable progression-free survival that is suggestive of long-term immune control. Nonetheless, most patients ultimately relapse, suggesting immune escape. TIGIT appears to be a potent inhibitor of myeloma-specific immunity and represents a promising new checkpoint target. Here we demonstrate high expression of TIGIT on activated CD8+ T cells in mobilized peripheral blood stem cell grafts from patients with myeloma. To guide clinical application of TIGIT inhibition, we evaluated identical anti-TIGIT antibodies that do or do not engage FcγR and demonstrated that anti-TIGIT activity is dependent on FcγR binding. We subsequently used CRBN mice to investigate the efficacy of anti-TIGIT in combination with lenalidomide maintenance after transplantation. Notably, the combination of anti-TIGIT with lenalidomide provided synergistic, CD8+ T cell-dependent, antimyeloma efficacy. Analysis of bone marrow (BM) CD8+ T cells demonstrated that combination therapy suppressed T cell exhaustion, enhanced effector function, and expanded central memory subsets. Importantly, these immune phenotypes were specific to the BM tumor microenvironment. Collectively, these data provide a logical rationale for combining TIGIT inhibition with immunomodulatory drugs to prevent myeloma progression after ASCT.

Donor plasmacytoid dendritic cells limit graft-versus-host disease through vasoactive intestinal polypeptide expression

Vasoactive intestinal polypeptide (VIP), an anti-inflammatory neuropeptide with pleiotropic cardiovascular effects, induces differentiation of hematopoietic stem cells into regulatory dendritic cells that limit graft-versus-host disease (GVHD) in allogeneic hematopoietic stem cell transplant (HSCT) recipients. We have previously shown that donor plasmacytoid dendritic cells (pDCs) in bone marrow (BM) donor grafts limit the pathogenesis of GVHD. In this current study we show that murine and human pDCs express VIP, and that VIP-expressing pDCs limit T-cell activation and expansion using both in vivo and in vitro model systems. Using T cells or pDCs from transgenic luciferase+ donors in murine bone marrow transplantation (BMT), we show similar homing patterns of donor pDCs and T cells to the major sites for alloactivation of donor T cells: spleen and gut. Cotransplanting VIP-knockout (KO) pDCs with hematopoietic stem cells and T cells in major histocompatibility complex mismatched allogeneic BMT led to lower survival, higher GVHD scores, and more colon crypt cell apoptosis than transplanting wild-type pDCs. BMT recipients of VIP-KO pDCs had more T helper 1 polarized T cells, and higher plasma levels of granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-α than recipients of wild-type pDCs. T cells from VIP-KO pDC recipients had increasing levels of bhlhe40 transcripts during the first 2 weeks posttransplant, and higher levels of CyclophilinA/Ppia transcripts at day 15 compared with T cells from recipients of wild-type pDCs. Collectively, these data indicate paracrine VIP synthesis by donor pDCs limits pathogenic T-cell inflammation, supporting a novel mechanism by which donor immune cells regulate T-cell activation and GVHD in allogeneic BMT.

SGK1, a Critical Regulator of Immune Modulation and Fibrosis and a Potential Therapeutic Target in Chronic Graft-Versus-Host Disease

Patients with severe chronic graft-versus-host disease (cGVHD) always experience debilitating tissue injury and have poorer quality of life and shorter survival time. The early stage of cGVHD is characterized by inflammation, which eventually leads to extensive tissue fibrosis in various organs, such as skin and lung, eventually inducing scleroderma-like changes and bronchiolitis obliterans syndrome. Here we review the functions of serum/glucocorticoid regulated kinase 1 (SGK1), a hub molecule in multiple signal transduction pathways and cell phosphorylation cascades, which has important roles in cell proliferation and ion channel regulation, and its relevance in cGVHD. SGK1 phosphorylates the ubiquitin ligase, NEDD4, and induces Th cells to differentiate into Th17 and Th2 phenotypes, hinders Treg development, and promotes inflammatory fibrosis. Phosphorylation of NEDD4 by SGK1 also leads to up-regulation of the transcription factor SMAD2/3, thereby amplifying the fibrosis-promoting effect of TGF-β. SGK1 also up-regulates the inflammatory transcription factor, nuclear factor-κB (NF-κB), which in turn stimulates the expression of multiple inflammatory mediators, including connective tissue growth factor. Overexpression of SGK1 has been observed in various fibrotic diseases, including pulmonary fibrosis, diabetic renal fibrosis, liver cirrhosis, hypertensive cardiac fibrosis, peritoneal fibrosis, and Crohn’s disease. In addition, SGK1 inhibitors can attenuate, or even reverse, the effect of fibrosis, and may be used to treat inflammatory conditions and/or fibrotic diseases, such as cGVHD, in the future.

Phase 1 Studies to Evaluate the Food Effect and Relative Bioavailability of Tablet and Capsule Formulations of Belumosudil in Healthy Adult Subjects

Belumosudil is a selective Rho-associated coiled-coil containing protein kinase 2 inhibitor. A capsule formulation was used during early clinical development of belumosudil; it was later replaced by a tablet formulation, which mimicked the capsule's release properties and facilitated manufacturing scalability. To assess belumosudil's pharmacokinetics, including potential food effects, and evaluate the relative bioavailability of the 2 formulations, 2 phase 1 clinical trials were conducted. Administration of both belumosudil tablets and capsules with food increased exposure ≈2× as compared to the fasted state and delayed time to maximum concentration by 0.5 hour, indicating a decrease in the rate but increase in the extent of absorption with fed administration. Relative bioavailability was slightly higher when belumosudil was administered as tablets vs capsules, although the difference was not clinically meaningful. Safety and tolerability were generally consistent with the known safety profile of belumosudil. The results of these studies support administration of belumosudil with food.

A Phase 1 Pharmacokinetic Drug Interaction Study of Belumosudil Coadministered With CYP3A4 Inhibitors and Inducers and Proton Pump Inhibitors

Belumosudil is a selective Rho-associated protein kinase 2 inhibitor. Inhibition of Rho-associated protein kinase 2 has emerged as a promising treatment for chronic graft-versus-host disease by restoring immune homeostasis and reducing fibrosis. In vitro assessments have suggested that metabolism of belumosudil is primarily dependent on cytochrome P450 (CYP) 3A4 activity and that the solubility of belumosudil is pH dependent. As such, this 2-part clinical drug-drug interaction study was conducted to assess the effect of itraconazole (a strong CYP3A4 inhibitor), rifampicin (a strong CYP3A4 inducer), rabeprazole, and omeprazole (both proton pump inhibitors) on the pharmacokinetics of belumosudil. No clinically relevant change in belumosudil exposure was observed following a 200-mg single oral dose of belumosudil with itraconazole; however, exposure of main metabolite, KD025m2, was decreased. Consistent with the proposed metabolic pathway of belumosudil, the strong CYP3A4 inducer rifampicin significantly decreased exposure of belumosudil and KD025m2 and increased KD025m1 exposure. When a 200-mg single oral dose of belumosudil was coadministered with both rabeprazole and omeprazole, parent and metabolite exposures were largely reduced, suggesting that belumosudil dosage should be increased when given with PPIs. Administration of belumosudil with and without perpetrator drugs was safe, and no notable adverse events were reported.

Absolute Bioavailability, Mass Balance, and Metabolic Profiling Assessment of [14 C]-Belumosudil in Healthy Men: A Phase 1, Open-Label, 2-Part Study

Belumosudil is a selective Rho-associated coiled-coil containing protein kinase 2 (ROCK2) inhibitor. ROCK2 has been shown to drive proinflammatory response and fibrosis that occurs with chronic graft-versus-host disease; therefore, inhibition of ROCK2 has emerged as a therapeutic target for chronic graft-versus-host disease. In this phase 1 two-part study, the pharmacokinetics, mass balance, and metabolic profile of belumosudil were evaluated after single doses of unlabeled belumosudil oral tablets (200 mg), radiolabeled belumosudil intravenous (IV) microtracer infusions (100 μg), and radiolabeled oral capsules (200 mg). Absolute bioavailability based on area under the plasma concentration-time curve from time 0 to infinity for the oral dose/area under the plasma concentration-time curve from time 0 to infinity for the IV dose was calculated as 63.7%. Radiolabeled IV microtracer dosing demonstrated a low extraction ratio and distribution of belumosudil into tissues. The majority of total radioactivity was recovered in feces, with minimal amounts recovered in urine, suggesting minimal renal elimination of belumosudil. In addition to parent and main metabolite KD025m2, metabolites identified in plasma included the phase 2 metabolites O-dealkylated belumosudil sulfate and belumosudil glucuronide. These metabolites (with the exception of the glucuronide) in addition to monohydroxy-belumosudil, and belumosudil diol were identified in feces. No metabolites in urine accounted for >10% of the radioactive dose.

Expression of transforming growth factor β pathway components in chronic graft-versus-host disease after allogeneic hematopoietic cell transplantation

Chronic graft-versus-host disease (cGvHD), an immunological complication of allogeneic cell transplantation, is the principal cause of non-relapse mortality and morbidity. Even though advances have been made in understanding the pathophysiology of this disorder, many questions remain. We sought to evaluate gene expression of transforming growth factor β (TGF-β) pathway components, through quantitative RT-PCR and PCR array, in patients with cGvHD with different disease activity. We observed an upregulation of SMAD3, BMP2, CDKN1A, IL6, and TGF-β2 genes in the clinical tolerance group, which had never developed cGvHD, or which had been withdrawn from all immunosuppressive treatments (IST) for at least 1 year. In addition, SMAD5 gene upregulation was observed in cGvHD patients undergoing IST, and ordinal regression showed a correlation between SMAD5 expression and disease severity. Our data support the evidence of the important role of TGF-β effects in the pathological process of cGvHD.

T Cell Subsets in Graft Versus Host Disease and Graft Versus Tumor

Allogeneic hematopoietic cell transplantation (allo-HCT) is an essential therapeutic modality for patients with hematological malignancies and other blood disorders. Unfortunately, acute graft-versus-host disease (aGVHD) remains a major source of morbidity and mortality following allo-HCT, which limits its use in a broader spectrum of patients. Chronic graft-versus-host disease (cGVHD) also remains the most common long-term complication of allo-HCT, occurring in reportedly 30-70% of patients surviving more than 100 days. Chronic GVHD is also the leading cause of non-relapse mortality (NRM) occurring more than 2 years after HCT for malignant disease. Graft versus tumor (GVT) is a major component of the overall beneficial effects of allogeneic HCT in the treatment of hematological malignancies. Better understanding of GVHD pathogenesis is important to identify new therapeutic targets for GVHD prevention and therapy. Emerging data suggest opposing roles for different T cell subsets, e.g., IFN-γ producing CD4+ and CD8+ T cells (Th1 and Tc1), IL-4 producing T cells (Th2 and Tc2), IL-17 producing T cells (Th17 and Tc17), IL-9 producing T cells (Th9 and Tc9), IL-22 producing T cells (Th22), T follicular helper cells (Tfh), regulatory T-cells (Treg) and tissue resident memory T cells (Trm) in GVHD and GVT etiology. In this review, we first summarize the general description of the cytokine signals that promote the differentiation of T cell subsets and the roles of these T cell subsets in the pathogenesis of GVHD. Next, we extensively explore preclinical findings of T cell subsets in both GVHD/GVT animal models and humans. Finally, we address recent findings about the roles of T-cell subsets in clinical GVHD and current strategies to modulate T-cell differentiation for treating and preventing GVHD in patients. Further exploring and outlining the immune biology of T-cell differentiation in GVHD that will provide more therapeutic options for maintaining success of allo-HCT.

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.

ROCK2, a critical regulator of immune modulation and fibrosis has emerged as a therapeutic target in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is an immune-mediated disorder characterized by chronic inflammation and fibrosis. Rho-associated coiled-coil-containing protein kinases (ROCKs) are key coordinators of tissue response to injury, regulating multiple functions, such as gene expression and cell migration, proliferation and survival. Relevant to cGVHD and autoimmunity, only the ROCK2 isoform drives a pro-inflammatory type 17 helper T (Th17) cell response. Moreover, ROCK2 inhibition shifts the Th17/regulatory T (Treg) cell balance toward Treg cells and restores immune homeostasis in animal models of autoimmunity and cGVHD. Furthermore, the selective inhibition of ROCK2 by belumosudil reduces fibrosis by downregulating both transforming growth factor-β signaling and profibrotic gene expression, thereby impeding the creation of focal adhesions. Consistent with its anti-inflammatory and antifibrotic activities, belumosudil has demonstrated efficacy in clinical studies, resulting in an overall response rate of >70% in patients with cGVHD who failed 2 to 5 prior lines of systemic therapy. In summary, selective ROCK2 inhibition has emerged as a promising novel therapeutic approach for treating cGVHD and other immunologic diseases with unique mechanisms of action, targeting both immune imbalance and detrimental fibrotic responses.

Glucose oxidase induces mobilization of long-term repopulating hematopoietic cells in mice

Hematopoietic stem progenitor cells (HSPCs) mobilized to peripheral blood, rather than those remaining in the bone marrow (BM), are commonly used as stem cell source in the clinic. As reactive oxygen species (ROS) are suggested as mediator of HSPC mobilization, we examined the impacts of glucose oxidase (GO) on peripheral mobilization of BM HSPCs and the associated mechanisms. Intravenous injection of GO induced HSPC mobilization even by single treatment, and the GO‐mobilized cells maintained their long‐term reconstituting and differentiating potentials in conditioned recipients. GO‐injected mice lived a normal life without adverse effects such as stem cell senescence, hematopoietic disorders, and blood parameter alteration. The mobilization effect of GO was even evident in animal models showing poor mobilization, such as old, 5‐fluorouracil‐treated, or alendronate‐treated mice. Importantly, combined injection of GO with granulocyte colony‐stimulating factor (G‐CSF) and/or AMD3100 enhanced more greatly HSPC mobilization than did G‐CSF, AMD3100, or both. The GO‐stimulated HSPC mobilization was almost completely attenuated by n‐acetyl‐L‐cysteine treatment. Collectively, our results not only highlight the potential role of GO in HSPC mobilization via ROS signaling, but also provide a GO‐based new strategy to improve HSPC mobilization in poorly mobilizing allogeneic or autologous donors via combination with G‐CSF and/or AMD3100.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: IV. The 2020 Highly morbid forms report

Chronic graft-versus-host disease (GVHD) can be associated with significant morbidity, in part because of nonreversible fibrosis, which impacts physical functioning (eye, skin, lung manifestations) and mortality (lung, gastrointestinal manifestations). Progress in preventing severe morbidity and mortality associated with chronic GVHD is limited by a complex and incompletely understood disease biology and a lack of prognostic biomarkers. Likewise, treatment advances for highly morbid manifestations remain hindered by the absence of effective organ-specific approaches targeting "irreversible" fibrotic sequelae and difficulties in conducting clinical trials in a heterogeneous disease with small patient numbers. The purpose of this document is to identify current gaps, to outline a roadmap of research goals for highly morbid forms of chronic GVHD including advanced skin sclerosis, fasciitis, lung, ocular and gastrointestinal involvement, and to propose strategies for effective trial design. The working group made the following recommendations: (1) Phenotype chronic GVHD clinically and biologically in future cohorts, to describe the incidence, prognostic factors, mechanisms of organ damage, and clinical evolution of highly morbid conditions including long-term effects in children; (2) Conduct longitudinal multicenter studies with common definitions and research sample collections; (3) Develop new approaches for early identification and treatment of highly morbid forms of chronic GVHD, especially biologically targeted treatments, with a special focus on fibrotic changes; and (4) Establish primary endpoints for clinical trials addressing each highly morbid manifestation in relationship to the time point of intervention (early versus late). Alternative endpoints, such as lack of progression and improvement in physical functioning or quality of life, may be suitable for clinical trials in patients with highly morbid manifestations. Finally, new approaches for objective response assessment and exploration of novel trial designs for small populations are required.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: IIb. The 2020 Preemptive Therapy Working Group Report

Chronic graft-versus-host disease (GVHD) commonly occurs after allogeneic hematopoietic cell transplantation (HCT) despite standard prophylactic immune suppression. Intensified universal prophylaxis approaches are effective but risk possible overtreatment and may interfere with the graft-versus-malignancy immune response. Here we summarize conceptual and practical considerations regarding preemptive therapy of chronic GVHD, namely interventions applied after HCT based on evidence that the risk of developing chronic GVHD is higher than previously appreciated. This risk may be anticipated by clinical factors or risk assignment biomarkers or may be indicated by early signs and symptoms of chronic GVHD that do not fully meet National Institutes of Health diagnostic criteria. However, truly preemptive, individualized, and targeted chronic GVHD therapies currently do not exist. In this report, we (1) review current knowledge regarding clinical risk factors for chronic GVHD, (2) review what is known about chronic GVHD risk assignment biomarkers, (3) examine how chronic GVHD pathogenesis intersects with available targeted therapeutic agents, and (4) summarize considerations for preemptive therapy for chronic GVHD, emphasizing trial development, including trial design and statistical considerations. We conclude that robust risk assignment models that accurately predict chronic GVHD after HCT and early-phase preemptive therapy trials represent the most urgent priorities for advancing this novel area of research.

Preclinical evaluation of JAK1/2 inhibition by ruxolitinib in a murine model of chronic graft-versus-host disease

The objective of this study was to examine the therapeutic effect of ruxolitinib, an orally administered selective Janus kinase (JAK) 1/2 inhibitor, on chronic graft-versus-host disease (cGVHD) using a murine model of sclerodermatous GVHD (scl-GVHD). Compared with scl-GVHD controls, ruxolitinib-treated recipients had scl-GVHD of significantly attenuated clinical and pathological severity in the skin and decreased frequencies of effector cells, CD4⁺ T cells, and CD11b⁺ macrophage/monocytes. Regulatory CD4⁺ Foxp3⁺ T cells were expanded whereas interferon-γ (IFN-γ)-producing CD4⁺ T cells were significantly decreased in ruxolitinib-treated recipients. Ruxolitinib suppressed not only the production of IFN-γ from CD4⁺ T cells and monocyte chemoattractant protein 1 (MCP-1) from CD11b⁺ macrophage/monocytes, but also the proliferation of these cells in vitro. Levels of both cytokines (IFN-γ and MCP-1) were also reduced in the spleen and skin of ruxolitinib-treated recipients in vivo. IFN-γ-induced MCP-1 production and migration of RAW 264.7 cells, a macrophage cell line, were inhibited by ruxolitinib. However, supplementation with MCP-1 restored this effect of ruxolitinib. In addition, blocking JAK-STAT signaling using ruxolitinib reduced the activation of STAT1 in stimulated immune effector cells. Taken together, these results suggest that ruxolitinib can prevent scl-GVHD by suppressing IFN-γ produced by T cells and MCP-1 expression in macrophage/monocytes via inhibition of JAK-STAT signaling.

Signaling through the type 2 cannabinoid receptor regulates the severity of acute and chronic graft-versus-host disease

Graft-versus-host disease (GVHD) pathophysiology is a complex interplay between cells that comprise the adaptive and innate arms of the immune system. Effective prophylactic strategies are therefore contingent upon approaches that address contributions from both immune cell compartments. In the current study, we examined the role of the type 2 cannabinoid receptor (CB2R), which is expressed on nearly all immune cells, and demonstrated that absence of the CB2R on donor CD4+ or CD8+ T cells or administration of a selective CB2R pharmacological antagonist exacerbated acute GVHD lethality. This was accompanied primarily by the expansion of proinflammatory CD8+ T cells, indicating that constitutive CB2R expression on T cells preferentially regulated CD8+ T-cell alloreactivity. Using a novel CB2ReGFP reporter mouse, we observed significant loss of CB2R expression on T cells, but not macrophages, during acute GVHD, indicative of differential alterations in receptor expression under inflammatory conditions. Therapeutic targeting of the CB2R with the agonists Δ9-tetrahydrocannabinol (THC) and JWH-133 revealed that only THC mitigated lethal T cell-mediated acute GVHD. Conversely, only JWH-133 was effective in a sclerodermatous chronic GVHD model where macrophages contributed to disease biology. In vitro, both THC and JWH-133 induced arrestin recruitment and extracellular regulated kinase phosphorylation via CB2R, but THC had no effect on CB2R-mediated inhibition of adenylyl cyclase. This study shows that the CB2R plays a critical role in the regulation of GVHD and suggests that effective therapeutic targeting is dependent upon agonist signaling characteristics and receptor selectivity in conjunction with the composition of pathogenic immune effector cells.

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.

Current Concepts and Advances in Graft-Versus-Host Disease Immunology

Worldwide, each year over 30,000 patients undergo an allogeneic hema-topoietic stem cell transplantation with the intent to cure high-risk hematologic malignancy, immunodeficiency, metabolic disease, or a life-threatening bone marrow failure syndrome. Despite substantial advances in donor selection and conditioning regimens and greater availability of allograft sources, transplant recipients still endure the morbidity and mortality of graft-versus-host disease (GVHD). Herein, we identify key aspects of acute and chronic GVHD pathophysiology, including host/donor cell effectors, gut dysbiosis, immune system and cytokine imbalance, and the interface between inflammation and tissue fibrosis. In particular, we also summarize the translational application of this heightened understanding of immune dysregulation in the design of novel therapies to prevent and treat GVHD.

Potential Novel Biomarkers in Chronic Graft-Versus-Host Disease

Prognostic, diagnostic or predictive biomarkers are urgently needed for assessment of chronic graft-versus-host disease (cGvHD), a major risk for patients undergoing allogeneic hematopoietic stem cell transplantation. The main goal of this review generated within the COST Action EUROGRAFT "Integrated European Network on Chronic Graft Versus Host Disease" was to identify potential novel biomarkers for cGvHD besides the widely accepted molecular and cellular biomarkers. Thus, the focus was on cellular biomarkers, alloantibodies, glycomics, endothelial derived particles, extracellular vesicles, microbiome, epigenetic and neurologic changes in cGvHD patients. Both host-reactive antibodies in general, and particularly alloantibodies have been associated with cGvHD and require further consideration. Glycans attached to IgG modulate its activity and represent a promising predictive and/or stratification biomarker for cGVHD. Furthermore, epigenetic changes such as microRNAs and DNA methylation represent potential biomarkers for monitoring cGvHD patients and novel targets for developing new treatment approaches. Finally, the microbiome likely affects the pathophysiology of cGvHD; bacterial strains as well as microbial metabolites could display potential biomarkers for dysbiosis and risk for the development of cGvHD. In summary, although there are no validated biomarkers currently available for clinical use to better inform on the diagnosis, prognosis or prediction of outcome for cGvHD, many novel sources of potential markers have shown promise and warrant further investigation using well characterized, multi-center patient cohorts.

Contrasting Immunopathogenic and Therapeutic Roles of Granulocyte Colony-Stimulating Factor in Cancer

Tumor cells are particularly adept at exploiting the immunosuppressive potential of neutrophils as a strategy to achieve uncontrolled proliferation and spread. Recruitment of neutrophils, particularly those of an immature phenotype, known as granulocytic myeloid-derived suppressor cells, is achieved via the production of tumor-derived granulocyte colony-stimulating factor (G-CSF) and neutrophil-selective chemokines. This is not the only mechanism by which G-CSF contributes to tumor-mediated immunosuppression. In this context, the G-CSF receptor is expressed on various cells of the adaptive and innate immune systems and is associated with induction of T cell polarization towards the Th2 and regulatory T cell (Treg) phenotypes. In contrast to the potentially adverse effects of sustained, endogenous production of G-CSF by tumor cells, stringently controlled prophylactic administration of recombinant (r) G-CSF is now a widely practiced strategy in medical oncology to prevent, and in some cases treat, chemotherapy-induced severe neutropenia. Following an overview of the synthesis, structure and function of G-CSF and its receptor, the remainder of this review is focused on: (i) effects of G-CSF on the cells of the adaptive and innate immune systems; (ii) mechanisms by which this cytokine promotes tumor progression and invasion; and (iii) current clinical applications and potential risks of the use of rG-CSF in medical oncology.

The microbe-derived short-chain fatty acids butyrate and propionate are associated with protection from chronic GVHD

Studies of the relationship between the gastrointestinal microbiota and outcomes in allogeneic hematopoietic stem cell transplantation (allo-HCT) have thus far largely focused on early complications, predominantly infection and acute graft-versus-host disease (GVHD). We examined the potential relationship of the microbiome with chronic GVHD (cGVHD) by analyzing stool and plasma samples collected late after allo-HCT using a case-control study design. We found lower circulating concentrations of the microbe-derived short-chain fatty acids (SCFAs) propionate and butyrate in day 100 plasma samples from patients who developed cGVHD, compared with those who remained free of this complication, in the initial case-control cohort of transplant patients and in a further cross-sectional cohort from an independent transplant center. An additional cross-sectional patient cohort from a third transplant center was analyzed; however, serum (rather than plasma) was available, and the differences in SCFAs observed in the plasma samples were not recapitulated. In sum, our findings from the primary case-control cohort and 1 of 2 cross-sectional cohorts explored suggest that the gastrointestinal microbiome may exert immunomodulatory effects in allo-HCT patients at least in part due to control of systemic concentrations of microbe-derived SCFAs.

Expansion of IL-17A-secreting CD8+ mucosa-associated invariant T cells in peripheral blood following stem cell mobilization

Stem cell mobilization with G-CSF promotes IL-17A secretion by donor CD8+ MAIT cells. Tbet and RORγt coexpression identifies potential IL-17A–secreting proinflammatory populations after allogeneic stem cell transplantation.

The primacy of gastrointestinal tract antigen-presenting cells in lethal graft-versus-host disease

Allogeneic stem cell transplantation is a cornerstone of curative therapy for high-risk and/or advanced hematological malignancies but remains limited by graft-versus-host disease (GVHD). GVHD is initiated by the interaction between recipient antigen-presenting cells (APCs) and donor T cells, culminating in T-cell differentiation along pathogenic type-1 and type-17 paradigms at the expense of tolerogenic regulatory T-cell patterns. Type-1 and type-17 T cells secrete cytokines (eg, granulocyte-macrophage colony-stimulating factor and interferon-γ) critical to the cytokine storm that amplifies expansion of donor APCs and their alloantigen presentation. It has become increasingly clear that pathogenic donor T-cell differentiation is initiated by both professional recipient APCs (eg, dendritic cells [DCs]) and nonprofessional APCs (eg, epithelial and mesenchymal cells), particularly within the gastrointestinal (GI) tract. In the immediate peritransplantation period, these APCs are profoundly modified by pathogen-associated molecular pattern (PAMP)/damage-associated molecular pattern (DAMP) signals derived from conditioning and intestinal microbiota. Subsequently, donor DCs in the GI tract are activated by DAMP/PAMP signals in the colon that gain access to the lamina propria once the mucosal barrier mucosa is compromised by GVHD. This results in donor DC expansion and alloantigen presentation in the colon and subsequent migration into the mesenteric lymph nodes. Here, new donor T cells are primed, expanded, differentiated, and imprinted with gut-homing integrins permissive of migration into the damaged GI tract, resulting in the lethal feed-forward cascade of GVHD. These new insights into our understanding of the cellular and molecular factors initiating GVHD, both spatially and temporally, give rise to a number of logical therapeutic targets, focusing on the inhibition of APC function in the GI tract.

IL-6 dysregulation originates in dendritic cells and mediates graft-versus-host disease via classical signaling

Graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (alloSCT) is characterized by interleukin-6 (IL-6) dysregulation. IL-6 can mediate effects via various pathways, including classical, trans, and cluster signaling. Given the recent availability of agents that differentially inhibit these discrete signaling cascades, understanding the source and signaling and cellular targets of this cytokine is paramount to inform the design of clinical studies. Here we demonstrate that IL-6 secretion from recipient dendritic cells (DCs) initiates the systemic dysregulation of this cytokine. Inhibition of DC-driven classical signaling after targeted IL-6 receptor (IL-6R) deletion in T cells eliminated pathogenic donor Th17/Th22 cell differentiation and resulted in long-term survival. After engraftment, donor DCs assume the same role, maintaining classical IL-6 signaling-dependent GVHD responses. Surprisingly, cluster signaling was not active after transplantation, whereas inhibition of trans signaling with soluble gp130Fc promoted severe, chronic cutaneous GVHD. The latter was a result of exaggerated polyfunctional Th22-cell expansion that was reversed by IL-22 deletion or IL-6R inhibition. Importantly, inhibition of IL-6 classical signaling did not impair the graft-versus-leukemia effect. Together, these data highlight IL-6 classical signaling and downstream Th17/Th22 differentiation as important therapeutic targets after alloSCT.

Interleukin-10 mediated immune regulation after stem cell transplantation: Mechanisms and implications for therapeutic intervention

Interleukin-10 (IL-10) is a multi-faceted anti-inflammatory cytokine which plays an essential role in immune tolerance. Indeed, deficiency of IL-10 or its receptor results in aberrant immune responses that lead to immunopathology. Graft-versus-host disease (GVHD) is the limiting complication of allogeneic stem cell transplantation (SCT) and results from an imbalance in pathological versus regulatory immune networks. A number of immune cells exert their immunomodulatory role through secretion of IL-10 or induction of IL-10-secreting cells after SCT. Type-1 regulatory T cells (Tr1 cells) and FoxP3⁺ regulatory T cells (T_regs) are predominant sources of IL-10 after SCT and the critical role of this cytokine in preventing GVHD is now established. Recently, intriguing interactions among IL-10, immune cells, commensal microbes and host tissues in the gastrointestinal (GI) tract and other barrier surfaces have been uncovered. We now understand that IL-10 secretion is dynamically modulated by the availability of antigen, co-stimulatory signals, cytokines, commensal microbes and their metabolites in the microenvironment. In this review, we provide an overview of the control of IL-10 secretion and signaling after SCT and the therapeutic interventions, with a focus on Tr1 cells.

Modeling Chronic Graft-versus-Host Disease in MHC-Matched Mouse Strains: Genetics, Graft Composition, and Tissue Targets

Graft-versus-host disease (GVHD) remains a major complication of allogeneic hematopoietic cell transplantation. Acute GVHD (aGVHD) results from direct damage by donor T cells, whereas the biology of chronic GVHD (cGVHD) with its autoimmune-like manifestations remains poorly understood, mainly because of the paucity of representative preclinical models. We examined over an extended time period 7 MHC-matched, minor antigen-mismatched mouse models for development of cGVHD. Development and manifestations of cGVHD were determined by a combination of MHC allele type and recipient strain, with BALB recipients being the most susceptible. The C57BL/6 into BALB.B combination most closely modeled the human syndrome. In this strain combination moderate aGVHD was observed and BALB.B survivors developed overt cGVHD at 6 to 12 months affecting eyes, skin, and liver. Naïve CD4⁺ cells caused this syndrome as no significant pathology was induced by grafts composed of purified hematopoietic stem cells (HSCs) or HSC plus effector memory CD4⁺ or CD8⁺ cells. Furthermore, co-transferred naïve and effector memory CD4⁺ T cells demonstrated differential homing patterns and locations of persistence. No clear association with donor Th17 cells and the phenotype of aGVHD or cGVHD was observed in this model. Donor CD4⁺ cells caused injury to medullary thymic epithelial cells, a key population responsible for negative T cell selection, suggesting that impaired thymic selection was an underlying cause of the cGVHD syndrome. In conclusion, we report for the first time that the C57BL/6 into BALB.B combination is a representative model of cGVHD that evolves from immunologic events during the early post-transplant period.

Adoptive T Cell Therapy Following Haploidentical Hematopoietic Stem Cell Transplantation

Delayed immune reconstitution and the consequently high rates of leukemia relapse and infectious complications are the main limitations of haploidentical hematopoietic stem cell transplantation. Donor T cell addback can accelerate immune reconstitution but the therapeutic window between graft-vs.-host disease and protective immunity is very narrow in the haploidentical transplant setting. Hence, strategies to improve the safety and efficacy of adoptive T cell transfer are particularly relevant in this setting. Adoptive T cell transfer strategies in haploidentical transplantation include the use of antigen-specific T cells, allodepletion and alloanergy induction, immune modulation by the co-infusion of regulatory cell populations, and the use of safety switch gene-modified T cells. Whilst common principles apply, there are features that are unique to haploidentical transplantation, where HLA-mismatching directly impacts on immune reconstitution, and shared vs. non-shared HLA-allele can be an important consideration in antigen-specific T cell therapy. This review will also present an update on safety switch gene-modified T cells, which can be conditionally deleted in the event of severe graft- vs.-host disease or other adverse events. Herpes Virus Simplex Thymidine Kinase (HSVtk) and inducible caspase-9 (iCasp9) are safety switches that have undergone multicenter studies in haploidentical transplantation with encouraging results. These gene-modified cells, which are trackable long-term, have also provided important insights on the fate of adoptively transferred T cells. In this review, we will discuss the biology of post-transplant T cell immune reconstitution and the impact of HLA-mismatching, and the different cellular therapy strategies that can help accelerate T cell immune reconstitution after haploidentical transplantation.

Diverse Activity of IL-17+ Cells in Chronic Skin and Mucosa Graft-Versus-Host Disease

Excessive inflammatory environment in a course of chronic graft-versus-host disease (cGvHD) is associated with T-cell trafficking into inflamed tissues. This study focused on the identification of IL-17-producing cells in the tissue biopsies of cGvHD patients. Forty-one biopsy specimens of cGvHD lesions of the skin (n = 27), gastrointestinal tract (n = 9) and oral mucosa (n = 5), examined in 24 patients, were morphologically defined according to the NIH criteria and analyzed for the presence of cellular infiltrations including: IL-17⁺, FOXP3⁺ and CCR6⁺ cells. IL-17⁺ cells were identified in 26/27 skin and in all gut and oral mucosa biopsies, being more frequent in mucosa lesions than in the skin (11/14 vs 14/26, respectively; NS: not significant). Double staining documented that CD138⁺/IL-17⁺ cells were commonly seen in the gut than in the skin (5/8 vs 3/11, respectively; NS). In the skin, cells expressing trafficking receptor CCR6⁺ were more frequent than IL-17⁺ cells compared to the mucosa (23/26 vs 2/13, respectively; p < 0.0001). CCR6 was present on a majority of IL-17⁺ cells in all examined skin biopsies but only in 6 out of 11 digestive tract biopsies (p = 0.0112). FOXP3⁺ cells were identified only in five patients (with mild lesions) at least in one biopsy. In this study group, results documented that local expansion of IL-17-producing cells in the digestive tract correlate with moderate and severe clinical symptoms of cGvHD, in contrast to the skin, where IL-17⁺ cells are rather scarcely present (p = 0.0301) and the course of cGvHD is slowly progressing with final organ deterioration.

Targeting PI3Kδ function for amelioration of murine chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is a leading cause of morbidity and mortality following allotransplant. Activated donor effector T cells can differentiate into pathogenic T helper (Th)-17 cells and germinal center (GC)-promoting T follicular helper (Tfh) cells, resulting in cGVHD. Phosphoinositide-3-kinase-δ (PI3Kδ), a lipid kinase, is critical for activated T cell survival, proliferation, differentiation, and metabolism. We demonstrate PI3Kδ activity in donor T cells that become Tfh cells is required for cGVHD in a nonsclerodermatous multiorgan system disease model that includes bronchiolitis obliterans (BO), dependent upon GC B cells, Tfhs, and counterbalanced by T follicular regulatory cells, each requiring PI3Kδ signaling for function and survival. Although B cells rely on PI3Kδ pathway signaling and GC formation is disrupted resulting in a substantial decrease in Ig production, PI3Kδ kinase-dead mutant donor bone marrow-derived GC B cells still supported BO cGVHD generation. A PI3Kδ-specific inhibitor, compound GS-649443, that has superior potency to idelalisib while maintaining selectivity, reduced cGVHD in mice with active disease. In a Th1-dependent and Th17-associated scleroderma model, GS-649443 effectively treated mice with active cGVHD. These data provide a foundation for clinical trials of US Food and Drug Administration (FDA)-approved PI3Kδ inhibitors for cGVHD therapy in patients.

Interleukin-17 pathways in systemic sclerosis-associated fibrosis

Fibrosis is unregulated tissue repair that may cause impairment of organ function, especially in end-organ damage. Systemic sclerosis (SSc) is the prototype systemic fibrosing disorder. Classical targets for fibrosis in SSc like transforming growth factor Beta (TGF-β), Interleukin-6 (IL-6), and multiple tyrosine kinases, have not yielded therapeutic benefit. There is multitude of evidence from across different tissues like the heart, lung, skin, liver, colon, and, to some extent, the kidney, that interleukin-17 (IL-17) and its downstream pathways are strongly associated with the initiation and propagation of fibrosis. Data from scleroderma patients, as well as from animal models of SSc, mirror these findings. Interestingly, hitherto unknown to be related to IL-17, newer molecules like Programmed Death-protein1 (PD-1), the phosphatase SHP2, along with known signal transducers like signal transducer and activator of transcription (STAT3), have been recently shown to be involved in the pathogenesis of fibrosis. Related molecules include the intracellular signalling molecules Ras/Erk, mammalian target organ of rapamycin (mTOR), and complement components. The biology of these pathways has not yet been fully elucidated to predict regulatory mechanisms, redundancies, and potential off-target effects. All these need to be better understood in the context of each other, in an effort to arrive at the optimal target to modulate fibrosis.

Achievement of Tolerance Induction to Prevent Acute Graft-vs.-Host Disease

Acute graft-vs.-host disease (GVHD) limits the efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT), a main therapy to treat various hematological disorders. Despite rapid progress in understanding GVHD pathogenesis, broad immunosuppressive agents are most often used to prevent and remain the first line of therapy to treat GVHD. Strategies enhancing immune tolerance in allo-HSCT would permit reductions in immunosuppressant use and their associated undesirable side effects. In this review, we discuss the mechanisms responsible for GVHD and advancement in strategies to achieve immune balance and tolerance thereby avoiding GVHD and its complications.

B cells in chronic graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (alloHCT) is the definitive therapy for numerous otherwise incurable hematologic malignancies and non-malignant diseases. The genetic disparity between donor and recipient both underpins therapeutic effects and confers donor immune system-mediated damage in the recipient, called graft-versus-host disease (GVHD). Chronic GVHD (cGVHD) is a major cause of late post-transplant morbidity and mortality. B cells have a substantiated role in cGVHD pathogenesis, as first demonstrated by clinical response to the anti-CD20 monoclonal antibody, rituximab. Initiation of CD20 blockade is met at times with limited therapeutic success that has been associated with altered peripheral B cell homeostasis and excess B Cell Activating Factor of the TNF family (BAFF). Increased BAFF to B cell ratios are associated with the presence of circulating, constitutively activated B cells in patients with cGVHD. These cGVHD patient B cells have increased survival capacity and signal through both BAFF-associated and B Cell Receptor (BCR) signaling pathways. Proximal BCR signaling molecules, Syk and BTK, appear to be hyper-activated in cGVHD B cells and can be targeted with small molecule inhibitors. Murine studies have confirmed roles for Syk and BTK in development of cGVHD. Emerging evidence has prompted investigation of several small molecule inhibitors in an attempt to restore B cell homeostasis and potentially target rare, pathologic B cell populations.

Flt3L Treatment of Bone Marrow Donors Increases Graft Plasmacytoid Dendritic Cell Content and Improves Allogeneic Transplantation Outcomes

A higher number of donor plasmacytoid dendritic cells (pDCs) is associated with increased survival and reduced graft-versus-host disease (GVHD) in human recipients of unrelated donor bone marrow (BM) grafts, but not granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood grafts. We show that in murine models, donor BM pDCs are associated with increased survival and decreased GVHD compared with G-CSF-mobilized pDCs. To increase the content of pDCs in BM grafts, we studied the effect of FMS-like tyrosine kinase 3 ligand (Flt3L) treatment of murine BM donors on transplantation outcomes. Flt3L treatment (300 μg/kg/day) resulted in a schedule-dependent increase in the content of pDCs in the BM. Mice treated on days -4 and -1 had a >5-fold increase in pDC content without significant changes in numbers of HSCs, T cells, B cells, and natural killer cells in the BM graft. In an MHC-mismatched murine transplant model, recipients of Flt3L-treated T cell-depleted (TCD) BM (TCD F-BM) and cytokine-untreated T cells had increased survival and decreased GVHD scores with fewer Th1 and Th17 polarized T cells post-transplantation compared with recipients of equivalent numbers of untreated donor TCD BM and T cells. Gene array analyses of pDCs from Flt3L-treated human and murine donors showed up-regulation of adaptive immune pathways and immunoregulatory checkpoints compared with pDCs from untreated BM donors. Transplantation of TCD F-BM plus T cells resulted in no loss of the graft-versus-leukemia (GVL) effect compared with grafts from untreated donors in 2 murine GVL models. Thus, Flt3L treatment of BM donors is a novel method for increasing the pDC content in allografts, improving survival, and decreasing GVHD without diminishing the GVL effect.

In Vitro Th17-Polarized Human CD4+ T Cells Exacerbate Xenogeneic Graft-versus-Host Disease

Acute graft-versus-host disease (aGVHD) is a severe complication of allogeneic hematopoietic stem cell transplantation. The role of Th17 cells in its pathophysiology remains a matter of debate. In this study, we assessed whether enrichment of human peripheral blood mononuclear cells (PBMCs) with in vitro Th17-polarized CD4⁺ T cells would exacerbate xenogeneic GVHD (xGVHD) into NOD-scid IL-2Rγ null (NSG) mice. Naive human CD4⁺ T cells were stimulated under Th17-skewing conditions for 8 to 10 days and then coinjected in NSG mice with fresh PBMCs from the same donor. We observed that Th17-polarized cells engrafted and migrated toward xGVHD target organs. They also acquired a double-expressing IL-17A⁺IFNγ⁺ profile in vivo. Importantly, cotransfer of Th17-polarized cells (1 × 10⁶) with PBMCs (1 × 10⁶) exacerbated xGVHD compared with transplantation of PBMCs alone (2 × 10⁶). Furthermore, PBMC cotransfer with Th17-polarized cells was more potent for xGVHD induction than cotransfer with naive CD4⁺ T cells stimulated in nonpolarizing conditions (Th0 cells, 1 × 10⁶ + 1 × 10⁶ PBMCs) or with Th1-polarized cells (1 × 10⁶ + 1 × 10⁶ PBMCs). In summary, our results suggest that human Th17-polarized cells can cooperate with PBMCs and be pathogenic in the NSG xGVHD model.

Ex Vivo Generated Human Cord Blood Myeloid-Derived Suppressor Cells Attenuate Murine Chronic Graft-versus-Host Diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with anti-inflammatory activity, and expanded murine MDSCs are capable of attenuating preclinical acute graft-versus-host disease (aGVHD) severity. Two murine cGVHD models were used to evaluate the effectiveness of ex vivo cultured human cord blood (hCB) MDSCs in chronic GVHD (cGVHD). First, GVHD recipients surviving in a classic C57BL/6 into MHC-mismatched BALB/c aGVHD model developed cGVHD. Second, donor pretreatment with granulocyte colony-stimulating factor (G-CSF) induced cGVHD. hCB-MDSCs (1 × 10⁶) were intravenously injected to determine their preventive effects (on days 5, 7, 10, and 21) or therapeutic effects (on days 21, 28, and 35). In the first model the onset of clinical cutaneous cGVHD was significantly delayed in preventive hCB-MDSCs-treated allogeneic recipients. Pathologic scoring of target organs confirmed these clinical results. Importantly, thymic tissues of GVHD mice treated with hCB-MDSCs were less severely damaged, showing higher numbers of double (CD4 and CD8) positive T cells with reduced expansion of donor-type CD4 and CD8 T cells. Moreover, late infusion of hCB-MDSCs controlled the severity of established cGVHD that had occurred in control recipients. In the second model, cGVHD induced by G-CSF-mobilized stem cell graft was associated with promotion of Th 17 and Th 2 differentiation. hCB-MDSCs attenuated clinical and pathologic cGVHD severity. Increased production of IL-17 and more infiltration of T cells and macrophages in cGVHD mice were markedly reduced after hCB-MDSCs treatment. Importantly, Foxp3⁺ regulatory T cells and IFN-γ-producing T cells were expanded, whereas IL-17- and IL-4-producing T cells were decreased in allogeneic recipients of hCB-MDSCs. Taken together, these results showed that hCB-MDSCs have preclinical capability of attenuating cGVHD by preserving thymus function and regulating Th 17 signaling, suggesting a possible therapeutic strategy for clinical application.

Ruxolitinib protects skin stem cells and maintains skin homeostasis in murine graft-versus-host disease

Skin GVHD targets Lgr5+ HFSCs in association with impaired hair regeneration and wound healing. Topical ruxolitinib, unlike corticosteroids, protects Lgr5+ skin stem cells and maintains skin homeostasis in skin GVHD.

Unraveling the Mechanisms of Cutaneous Graft-Versus-Host Disease

The skin is the most common target organ affected by graft-versus-host disease (GVHD), with severity and response to therapy representing important predictors of patient survival. Although many of the initiating events in GVHD pathogenesis have been defined, less is known about why treatment resistance occurs or why there is often a permanent failure to restore tissue homeostasis. Emerging data suggest that the unique immune microenvironment in the skin is responsible for defining location- and context-specific mechanisms of injury that are distinct from those involved in other target organs. In this review, we address recent advances in our understanding of GVHD biology in the skin and outline the new research themes that will ultimately enable design of precision therapies.

A critical role for donor-derived IL-22 in cutaneous chronic GVHD

Graft-versus-host disease (GVHD) is the major cause of nonrelapse morbidity and mortality after allogeneic stem cell transplantation (allo-SCT). Prevention and treatment of GVHD remain inadequate and commonly lead to end-organ dysfunction and opportunistic infection. The role of interleukin (IL)-17 and IL-22 in GVHD remains uncertain, due to an apparent lack of lineage fidelity and variable and contextually determined protective and pathogenic effects. We demonstrate that donor T cell-derived IL-22 significantly exacerbates cutaneous chronic GVHD and that IL-22 is produced by highly inflammatory donor CD4+ T cells posttransplantation. IL-22 and IL-17A derive from both independent and overlapping lineages, defined as T helper (Th)22 and IL-22+ Th17 cells. Donor Th22 and IL-22+ Th17 cells share a similar IL-6-dependent developmental pathway, and while Th22 cells arise independently of the IL-22+ Th17 lineage, IL-17 signaling to donor Th22 directly promotes their development in allo-SCT. Importantly, while both IL-22 and IL-17 mediate skin GVHD, Th17-induced chronic GVHD can be attenuated by IL-22 inhibition in preclinical systems. In the clinic, high levels of both IL-17A and IL-22 expression are present in the skin of patients with GVHD after allo-SCT. Together, these data demonstrate a key role for donor-derived IL-22 in patients with chronic skin GVHD and confirm parallel but symbiotic developmental pathways of Th22 and Th17 differentiation.

Vitamin A–coupled liposomes containing siRNA against HSP47 ameliorate skin fibrosis in chronic graft-versus-host disease

HSP47+ myofibroblasts are accumulated in the fibrotic lesions of chronic GVHD and promote fibrosis in a CSF-1R+ macrophage-dependent manner. Vitamin A–coupled liposomes containing HSP47 siRNA abrogate HSP47 expression in myofibroblasts and ameliorate fibrosis in chronic GVHD.