Pentostatin for treatment of steroid-refractory acute GVHD: a retrospective single-center analysis

Treatment of steroid-refractory graft versus host disease in children

Systemic steroids are still the first-line approach in acute graft-versus-host disease (aGvHD), and the backbone of chronic GvHD management. Refractoriness to steroid represent a major cause of morbidity and non-relapse mortality after hematopoietic stem cell transplantation (HSCT). In both backgrounds, several second-line immunosuppressive agents have been tested with variable results in terms of efficacy and toxicity. Solid evidence regarding these approaches is still lacking in the pediatric setting where results are mainly derived from adult experiences. Furthermore, the number of treated patients is limited and the incidence of acute and chronic GvHD is lower, resulting in a very heterogeneous approach to this complication by pediatric hematologists. Some conventional therapies and anti-cytokine monoclonal antibodies used in the adult setting have been evaluated in children. In recent years, the increasing understanding of the biological mechanisms underpinning the pathogenesis of GvHD justified the efforts toward the adoption of targeted therapies and non-pharmacologic approaches, with higher response rates and lower immunosuppressive effects. Moreover, many questions regarding the precise timing and setting in which to integrate these new approaches remain unanswered. This Review aims to critically explore the current evidence regarding novel approaches to treat SR-GvHD in pediatric HSCT recipients.

Vedolizumab for acute gastrointestinal graft-versus-host disease: A systematic review and meta-analysis

OBJECTIVE

To determine the safety and efficacy of vedolizumab for the prophylaxis and treatment of gastrointestinal involvement of acute graft-versus-host disease (GVHD) (GI-aGVHD).

METHODS

Literature search within PubMed, EMBASE, Web of Science, and Cochrane Library for observational studies and clinical trials that evaluated the effect of vedolizumab on GI-aGVHD was done through 17 May 2022. A bivariate and random-effect meta-analysis derived the pooled observational percentages and pooled risk ratios (RRs) from baseline of primary endpoints including overall response, complete response, mortality, and adverse events.

RESULTS

There was a total of 122 participants in eight eligible studies, including one study on the prophylactic use of vedolizumab and seven studies on vedolizumab for the treatment of GI-aGVHD. Of seven studies that reported details on baseline grades of GI-aGVHD, a total of 47 patients (47.95%) were of stage 4, 31 patients (31.63%) were of stage 3, 10 patients (10.2%) were of stage 2, and 10 patients (10.2%) were of stage 1. The use of vedolizumab for the treatment of GI-aGVHD yielded a significantly improved objective response rate (ORR) at 14 days (pooled ORR = 60.53%, pooled RR = 14.14, 95% CI: 2.95-67.71), 28 days (pooled ORR = 50%, RR = 7.36, 95% CI = 2.14-25.37), and 12 months (pooled ORR = 76.92%, RR = 13.66, 95% CI = 3.5-53.35) from baseline. Likewise, the use of vedolizumab was followed by a significantly improved complete response (CR) at 12 months (pooled CR = 27.27%, RR = 5.50, 95% CI = 1.01-29.95), yet the CR at 14 days and 28 days did not reach statistical significance. Fifty-seven out of 87 (pooled overall survival, OS = 34.5%) and 46 out of 65 (pooled OS = 29.2%) patients expired at 6 and 12 months after the use of vedolizumab, respectively. Prophylactic use of vedolizumab was not associated with any specific type of reported adverse events, while patients with GI-aGVHD on vedolizumab presented with significantly increased risks of adverse events including infections (RR = 7.55) and impaired metabolism or nutritional complications (RR = 9.00). All analyses were of a low heterogeneity (all I-squares = 0%).

CONCLUSION

Vedolizumab was safe and effective for the prophylaxis and management of early grade GI-aGVHD. More clinical evidence is warranted to validate these findings.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=345584, identifier CRD42022345584.

Hematopoietic Cell Transplantation, Version 2.2020, NCCN Clinical Practice Guidelines in Oncology

Hematopoietic cell transplantation (HCT) involves the infusion of hematopoietic progenitor cells into patients with hematologic disorders with the goal of re-establishing normal hematopoietic and immune function. HCT is classified as autologous or allogeneic based on the origin of hematopoietic cells. Autologous HCT uses the patient's own cells while allogeneic HCT uses hematopoietic cells from a human leukocyte antigen-compatible donor. Allogeneic HCT is a potentially curative treatment option for patients with certain types of hematologic malignancies, and autologous HCT is primarily used to support patients undergoing high-dose chemotherapy. Advances in HCT methods and supportive care in recent decades have led to improved survival after HCT; however, disease relapse and posttransplant complications still commonly occur in both autologous and allogeneic HCT recipients. Allogeneic HCT recipients may also develop acute and/or chronic graft-versus-host disease (GVHD), which results in immune-mediated cellular injury of several organs. The NCCN Guidelines for Hematopoietic Cell Transplantation focus on recommendations for pretransplant recipient evaluation and the management of GVHD in adult patients with malignant disease.

Retrospective single center analysis of outcome, risk factors and therapy in steroid refractory graft-versus-host disease after allogeneic hematopoietic cell transplantation

Acute and chronic graft-vs.-host disease (aGvHD and cGvHD) are major complications after allogeneic hematopoietic cell transplantation (HCT) leading to substantial morbidity and mortality. This retrospective single-center study analyzes incidence, therapy, and outcome of GvHD in n = 721 patients ≥18 years having received allogeneic HCT 2004-2013 with a special focus on steroid refractory GvHD. Acute (n = 355/49.2%) and chronic (n = 269/37.3%) GvHD were mainly treated by steroids in first-line therapy. The proportion of steroid refractory aGvHD and cGvHD was 35.7% and 31.4%, respectively. As there is no standard therapy for steroid refractory GvHD, a range of different agents was used. In aGvHD, the overall response rate (ORR) of steroid refractory GvHD to second-line treatment was 27.4%. Mycophenolate mofetil (MMF) and mTOR inhibitors led to superior response rates (ORR 50.0% and 53.3%, respectively). In steroid refractory cGvHD therapy, ORR was 44.4%. Use of calcineurin inhibitors (CNI; n = 11/45.5%), MMF (n = 18/50.0%), mTOR inhibitors (n = 10/60.0%), and extracorporeal photophoresis (ECP; n = 16/56.3%) showed ORR above average. Targeted therapies lead to responses in 7.7% (n = 13). This data may help to improve the design of future prospective clinical studies in GvHD.

Safety and Effectiveness of Vedolizumab in Patients with Steroid-Refractory Gastrointestinal Acute Graft-versus-Host Disease: A Retrospective Record Review

Allogeneic hematopoietic cell transplantation (allo-HCT) can be curative in patients with hematologic malignancies but carries a significant risk of graft-versus-host disease (GVHD). There are no standard treatments for steroid-refractory (SR) gastrointestinal (GI) acute GVHD (aGVHD). This multicenter, international, retrospective medical record review aimed to evaluate the off-label use of vedolizumab, a gut-selective immunomodulator, for treating SR GI aGVHD. Data were collected from patients' medical records; criteria for extraction included no more than 1 allo-HCT and at least 1 dose of vedolizumab as treatment for SR GI aGVHD (ie, stage 1 to 4 GI aGVHD following ≥1 previous treatment regimen(s) containing ≥1 mg/kg methylprednisolone or equivalent). Descriptive analyses of response rate, overall survival (OS), and serious adverse effects (SAEs) were performed. Twenty-nine patients were identified from 7 sites who had received 1 to 10 doses of vedolizumab 300 mg i.v. (median 3 doses) as treatment for SR GI aGVHD. The overall response rate at 6 to 10 weeks after vedolizumab initiation was 64%, and OS at 6 months was 54%. There were 29 SAEs, including 12 infections; 3 SAEs were considered possibly related to vedolizumab, 2 of which were infections. Thirteen SAEs were fatal, 1 of which was possibly vedolizumab-related. There were 8 nonserious infections and 1 serious infection with confirmed GI origin in 8 patients; there was no apparent pattern in the timing of these infections relative to the initiation of vedolizumab treatment. Further data on the efficacy and safety of vedolizumab in this setting from prospective trials are needed.

A prospective study on serum Cytokeratin (CK)-18 and CK18 fragments as biomarkers of acute hepato-intestinal GVHD

Apoptotic intestinal crypt cells are pathognomonic of acute intestinal graft versus host disease (GVHD). Serum levels of the apoptotic degradation product cytokeratin-18 fragments (CK18F) were associated with acute hepato-intestinal GVHD. Here we present a prospective clinical observational trial (NCT00935324) investigating serum levels of total CK18 (tCK18) and apoptotic CK18F to predict imminent acute hepato-intestinal GVHD and response to treatment. Total (t)CK18 and CK18F kinetics were measured before transplantation and in weekly intervals thereafter. In total 109 patients were enrolled. Acute hepato-intestinal GVHD grade I-IV was suspected in 36 patients (33%) at a median of 56 days post-transplant, 12 of these patients developed steroid-refractory GVHD. Both tCK18 and apoptotic CK18F increased at GVHD onset, and distinguished patients with suspected acute hepato-intestinal GVHD who were negative in intestinal histology. In patients with clinical acute hepato-intestinal GVHD, tCK18 significantly raised already 7-14 days before symptom onset. In receiver operator characteristics, areas under the curve at GVHD onset were 0.927 (p < 0.001) for tCK18 and 0.875 (p < 0.001) for apoptotic CK18F for patients with proven hepato-intestinal acute GVHD. This prospective study validates CK18F and highlights tCK18 as specific biomarkers suitable for improving prediction and diagnosis of suspected imminent and clinically manifest acute hepato-intestinal GVHD.

Pentostatin therapy for steroid-refractory acute graft versus host disease: identifying those who may benefit

We report outcomes of 60 patients with steroid-refractory (SR)-aGVHD treated with pentostatin. Almost half (47%) of patients had grade 4 GVHD-22% had stage 3-4 liver GVHD and 51% had stage 3-4 lower gastrointestinal tract (LGI) GVHD. Patients received a median of 3 courses (range, 1-9) of pentostatin. Day 28 overall response rate (ORR) was 33% (n = 20) (complete response 18% (n = 11), partial response 15% (n = 9)). Non-relapse mortality was 72% (95% confidence interval (CI) 61-84%) and overall survival (OS) was 21% (95% CI 12-32%) at 18 months. On univariate analysis, age >60 years (HR 1.9, 95% CI 1.01-3.7, p = 0.045) and presence of liver GVHD (HR 1.9, 95% CI 1.9, 95% CI 1.5-3.3, p = 0.03) were significant predictors of poor OS while patients with LGI GVHD had superior OS than those without (HR 0.4, 95% CI 0.2-0.8, p = 0.01). On stratified analysis, patients <60 years with isolated LGI GVHD had the best outcomes with an ORR of 48% and OS of 42% at 18 months. Among older patients, OS was 14% in those with isolated LGI aGVHD and 0% in others. Pentostatin remains a viable treatment option for SR-aGVHD, especially in patients 60 years or younger with isolated LGI involvement.

Pilot study of lithium to restore intestinal barrier function in severe graft-versus-host disease

Severe intestinal graft-vs-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT) causes mucosal ulceration and induces innate and adaptive immune responses that amplify and perpetuate GVHD and the associated barrier dysfunction. Pharmacological agents to target mucosal barrier dysfunction in GVHD are needed. We hypothesized that induction of Wnt signaling by lithium, an inhibitor of glycogen synthase kinase (GSK3), would potentiate intestinal crypt proliferation and mucosal repair and that inhibition of GSK3 in inflammatory cells would attenuate the deregulated inflammatory response to mucosal injury. We conducted an observational pilot study to provide data for the potential design of a randomized study of lithium. Twenty patients with steroid refractory intestinal GVHD meeting enrollment criteria were given oral lithium carbonate. GVHD was otherwise treated per current practice, including 2 mg/kg per day of prednisone equivalent. Seventeen patients had extensive mucosal denudation (extreme endoscopic grade 3) in the duodenum or colon. We observed that 8 of 12 patients (67%) had a complete remission (CR) of GVHD and survived more than 1 year (median 5 years) when lithium administration was started promptly within 3 days of endoscopic diagnosis of denuded mucosa. When lithium was started promptly and less than 7 days from salvage therapy for refractory GVHD, 8 of 10 patients (80%) had a CR and survived more than 1 year. In perspective, a review of 1447 consecutive adult HCT patients in the preceding 6 years at our cancer center showed 0% one-year survival in 27 patients with stage 3-4 intestinal GVHD and grade 3 endoscopic appearance in the duodenum or colon. Toxicities included fatigue, somnolence, confusion or blunted affect in 50% of the patients. The favorable outcomes in patients who received prompt lithium therapy appear to support the future conduct of a randomized study of lithium for management of severe GVHD with extensive mucosal injury.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00408681.

Therapeutic targets and emerging treatment options in gastrointestinal acute graft-versus-host disease

Introduction

Graft-versus-host disease (GVHD) continues to be the major lethal complication of allogeneic hematopoietic stem cell transplantation (HCT) but the standard of care, high dose steroids, has not changed in 40 years. Approximately 50% of GVHD patients will develop steroid refractory disease, typically involving the gastrointestinal (GI) tract, which has a very poor prognosis. Newly developed GVHD biomarker-based risk scores provide the first opportunity to treat patients at the onset of symptoms according to risk of steroid failure. Furthermore, improvements in our understanding of the pathobiology of GVHD, its different signaling pathways, involved cytokines, and the role of post-translational and epigenetic modifications, has identified new therapeutic targets for clinical trials.

Areas covered

This manuscript summarizes the pathophysiology, diagnosis, staging, current and new targeted therapies for GVHD, with an emphasis on GI GVHD. A literature search on PubMed was undertaken and the most relevant references included.

Expert Opinion

The standard treatment for GVHD, high dose steroids, offers less than optimal outcomes as well as significant toxicities. Better treatments, especially for GI GVHD, are needed to reduce non-relapse mortality after allogeneic HCT. The identification of high risk patients through a biomarker-defined scoring system offers a personalized approach to a disease that still requires significant research attention.

Improved Treatment-Related Mortality and Overall Survival of Patients with Grade IV Acute GVHD in the Modern Years

The impact of advances in supportive care and hematopoietic stem cell transplantation (HSCT) practices on the outcomes of patients who develop grade III or IV acute graft-versus-host disease (GVHD) is unknown. We performed a retrospective analysis of 427 patients with overall grade III or IV acute GVHD treated at 2 partner institutions between 1997 and 2012. We compared treatment-related mortality (TRM) and overall survival (OS) in 2 cohorts based on the year of transplantation, 1997 to 2006 (n = 222) and 2007 to 2012 (n = 205), using multivariate analysis, adjusting for significant patient-, disease-, and transplantation-related factors. Recipient age, reduced-intensity conditioning, unrelated donor, and peripheral blood stem cell grafts in the patients with grade III or IV acute GVHD increased over time. In the unadjusted analysis, 12-month OS increased over time (30% in 1997 to 2006 versus 42% in 2007 to 2012; P = .003) reflecting a decrease in TRM (58% in 1997 to 2006 versus 38% in 2007 to 2012; P = .0002), and an increase in PFS (29% in 1997 to 2006 versus 43% in 2007 to 2012; P = .002). On multivariate analysis, the period of transplantation remained a significant predictor for OS (hazard ratio [HR], 0.71; 95% confidence interval [CI], 0.54 to 0.94; P = .02), progression-free survival (PFS) (HR, 0.70; 95% CI, 0.52 to 0.94; P = .02), and TRM (HR, 0.57; 95% CI, 0.39 to 0.82; P = .002). In subgroup analysis, these differences were observed mainly in patients with grade IV acute GVHD. The outcomes of patients who develop overall grade III or IV acute GVHD after allogeneic HSCT has improved over time, with lower TRM and improved OS. This improvement in outcomes was seen primarily in patients with grade IV acute GVHD.

Limited benefit of pentostatin salvage therapy for steroid-refractory grade III-IV acute graft-versus-host disease

Corticosteroid-refractory (SR) acute graft-versus-host disease (aGVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. Multiple agents have been evaluated in this setting, but the benefit of pentostatin has not been described well. We report a single-center experience of pentostatin salvage therapy for SR aGVHD. Fifteen patients received pentostatin for SR aGVHD from March 2005 till March 2010 after failure to respond to methylprednisolone ≥ 2 mg/kg/d for at least seven d. All patients had grade III-IV aGVHD prior to pentostatin therapy. Thirteen (87%), 10 (67%), and six (40%) patients had gastrointestinal (GI), skin, and liver involvement of aGVHD, respectively. Pentostatin was given at a median of 33 d after steroid therapy initiation. The dose of pentostatin was 1.4 mg/m(2) daily for three d, repeated every two wk. Eight (53%) patients also received additional therapies. Complete responses were noted in two patients (both in skin). However, one patient relapsed and did not respond to additional salvage treatment. Partial responses were seen in three patients. Fourteen died of GVHD-related causes. This study suggested that pentostatin is of limited benefit in the treatment for SR grade III-IV aGVHD.

High pre-transplant serum nitrate levels predict risk of acute steroid-refractory graft-versus-host disease in the absence of statin therapy

Steroid-refractory graft-versus-host disease is a life-threatening complication after allogeneic stem cell transplantation. Evidence is accumulating that steroid-refractory graft-versus-host disease is associated with endothelial distress. Endothelial cell homeostasis is regulated by nitric oxide, and serum nitrates are derived from nitric oxide synthase activity or dietary sources. In this retrospective study based on 417 patients allografted at our institution we investigated whether quantification of serum nitrates could predict steroid-refractory graft-versus-host disease. Elevated pre-transplant levels of serum nitrates (>26.5 μM) predicted steroid-refractory graft-versus-host disease (P=0.026) and non-relapse mortality (P=0.028), particularly in combination with high pre-transplant angiopoietin-2 levels (P=0.0007 and P=0.021, respectively). Multivariate analyses confirmed serum nitrates as independent predictors of steroid-refractory graft-versus-host disease and non-relapse mortality. Differences in serum nitrate levels did not correlate with serum levels of tumor necrosis factor or C-reactive protein or expression of inducible nitric oxide synthase in blood cells. Patients with high pre-transplant nitrate levels had significantly reduced rates of refractory graft-versus-host disease (P=0.031) when pravastatin was taken. In summary, patients at high risk of developing steroid-refractory graft-versus-host disease could be identified prior to transplantation by serum markers linked to endothelial cell function. Retrospectively, statin medication was associated with a reduced incidence of refractory graft-versus-host disease in this endothelial high-risk cohort.

Current practice in diagnosis and treatment of acute graft-versus-host disease: results from a survey among German-Austrian-Swiss hematopoietic stem cell transplant centers

To assess current clinical practice in diagnosis and treatment of acute graft-versus-host disease (aGVHD), we performed a survey among German, Austrian, and Swiss allogeneic hematopoietic stem cell transplantation (allo-HSCT) centers. Thirty-four of 72 contacted centers (47%) completed both the diagnostic and therapeutic sections of the survey, representing 65% of allo-HSCT activity within the participating countries in 2011. Three pediatric centers answered as requested only the diagnostic part of the survey. In the presence of diarrhea and decreased oral intake after engraftment, only 4 centers (12%) do not perform any endoscopy before the start of immunosuppressive treatment. In case of a skin rash with the differential diagnosis of drug reaction, only 12 centers (35%) perform a skin biopsy up front, whereas 19 do so after failure of systemic steroids. In the presence of rapidly increasing cholestasis occurring without any other signs of aGVHD, 11 centers (32%) perform a liver biopsy up front and 14 only after failure of steroid treatment, whereas 9 centers do not perform a liver biopsy at all. Twenty centers (59%) use a percutaneous approach, 12 a transvenous approach, and 1 mini-laparoscopy for liver biopsies. First-line treatment of cutaneous aGVHD stage 1 consists of topical treatment alone in 17 of 31 responding centers (61%), whereas isolated cutaneous aGVHD stage III is treated with systemic steroids (prednisolone below 0.5 mg/kg/day n = 2, 0.5 to 1.0 mg/kg/day n = 10, above 1.0 to 2.5 mg/kg/day n = 19) without or with topical agents (steroids n = 10; calcineurin inhibitors n = 3). In gastrointestinal manifestations of aGVHD, 9 centers (29%) add topical to systemic steroids, and 3 consider topical steroids as the only treatment for mild gastrointestinal and cutaneous aGVHD. The choice of agent for second-line treatment as well as the sequence of administration are extremely heterogeneous, most likely due to a lack of convincing data published. Most frequently used are mycophenolate mofetil (n = 14) and extracorporeal photopheresis (n = 10). Our survey also demonstrates that clinicians chose salvage therapies for steroid-refractory aGVHD based on their centers' own clinical experience.

Placenta-derived mesenchymal stem cells have an immunomodulatory effect that can control acute graft-versus-host disease in mice

BACKGROUND AND AIMS

Immunomodulatory properties of mesenchymal stem cells (MSCs) have been applied to reduce the incidence of graft-versus-host disease (GVHD) after hematopoietic stem cell transplantation (HSCT). Among the various sources of MSCs that have immunomodulatory effects in vitro, only placenta-derived MSCs (PD-MSCs) have not been evaluated in an in vivo model of GVHD. In this study, we investigated the immunomodulatory properties of PD-MSCs in vitro and evaluated their clinical potential for controlling GVHD in an animal model.

METHODS

A GVHD animal model was established by transplanting C57BL/6 donor bone marrow cells and spleen cells into lethally irradiated BALB/c recipient mice. To control GVHD, human PD-MSCs were transplanted into recipient mice (5 × 10(5) or 1 × 10(6) cells).

RESULTS

PD-MSCs suppressed mitogen-stimulated T cell proliferation in vitro in a dose-dependent manner. Moreover, PD-MSCs inhibited cytokine secretion (interleukin-12, tumor necrosis factor-α and interferon-γ) of activated T cells. In vivo, the survival rate in the PD-MSC group (transplanted with 1 × 10(6) cells) was higher than that in the control group and histological scores were low in the PD-MSC group.

CONCLUSION

We present the first evidence that human PD-MSCs can efficiently control GVHD in an HSCT in vivo model.

Endothelial vulnerability and endothelial damage are associated with risk of graft-versus-host disease and response to steroid treatment

There is accumulating evidence indicating that endothelial factors are involved in the pathogenesis of GVHD. We have recently shown that steroid-refractory, but not sensitive, GVHD is characterized by higher pretransplantation serum levels of angiopoetin-2 (ANG2), a hormone mediating endothelial vulnerability. To evaluate whether endothelial vulnerability is a risk factor for GVHD per se or becomes important only when noticeable GVHD is established, we measured ANG2 along with additional serum markers of endothelial stress, including soluble thrombomodulin (sTM), IL-8 (CXCL8), and hepatocyte growth factor (HGF), in patients with no, low-grade, or severe GVHD. Patients with refractory GVHD exhibited elevated serum levels of ANG2, sTM, HGF, and IL-8 posttransplantation compared with patients with sensitive GVHD and patients without GVHD. Pretransplantation ANG2 was the only growth factor correlated with the risk of refractoriness and mortality, and then only within the subset of patients who developed grade III-IV GVHD. In contrast, ANG2 was not predictive of GVHD or nonrelapse mortality (NRM) in patients with no GVHD or low-grade GVHD. These findings provide evidence that endothelial function plays an important role in the pathogenesis of steroid refractoriness in ongoing GVHD; however, endothelial vulnerability does not predict incidence of GVHD.

Steroid-refractory GVHD: T-cell attack within a vulnerable endothelial system

Acute graft-versus-host disease (GVHD) is a major complication of allogeneic stem cell transplantation (SCT) and can be readily controlled by systemic high-dose steroids in many patients. However, patients whose GVHD is refractory to this therapy have a poor prognosis. Refractory patients have ongoing end-organ damage despite effective immunosuppression with second-line regimens, suggesting pathomechanisms independent from the initiating T-cell attack. To explore whether endothelial damage might contribute to GVHD refractoriness and to study the role of angiopoietin-2 (ANG2) in this process, we have compared kinetics of T-cell activation markers and markers of endothelial dysfunction in the serum of patients with sensitive (n = 23) and refractory GVHD (n = 25). Longitudinal measurements of soluble FAS ligand along with other immune markers demonstrate that refractory patients are not exposed to an overwhelming or unresponsive T-cell attack. However, in contrast to sensitive GVHD, refractory GVHD was associated with rising thrombomodulin levels and high ANG2/ vascular endothelial-derived growth factor ratios. Patients with refractory GVHD showed significantly increased ANG2 levels already before SCT. These results suggest that endothelial cell vulnerability and dysfunction, rather than refractory T-cell activity, drives treatment refractoriness of GVHD and opens new avenues for prediction and control of this devastating condition.