The primacy of the gastrointestinal tract as a target organ of acute graft-versus-host disease: rationale for the use of cytokine shields in allogeneic bone marrow transplantation

Hematopoietic cell transplantation and cellular therapeutics in the treatment of childhood malignancies

Hematopoietic cell transplantation (HCT) represents the most common and effective form of immunotherapy for childhood malignancies. The role of the graft-versus-leukemia effect in allogeneic HCT has been well established in childhood malignancies, but is also associated with short-term and long-term morbidity. HCT may be ineffective in some settings at obtaining control of the malignancy, and as such, cannot be used as a universal cancer immunotherapy. Novel therapies using dendritic cell vaccinations, tumor-infiltrating lymphocytes, and chimeric antigen receptor T cells are being evaluated as potential adjuvants to HCT.

Associations between gastrointestinal toxicity, micro RNA and cytokine production in patients undergoing myeloablative allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a procedure with a high risk of treatment related mortality. The primary aim of the present study was to examine associations between markers of gastrointestinal toxicity, markers of systemic inflammation, and plasma levels of microRNA (miRNA) -155 and -146a during the first month after HSCT. The secondary aim was to characterize the impact of the toxic-inflammatory response on the function of circulating leukocytes during immune recovery. Thirty HSCT patients were included. Gastrointestinal injury was monitored by toxicity scores, lactulose-mannitol test and plasma citrulline, as a measure of the enterocyte population. Nadir of citrulline and maximum of oral toxicity scores, intestinal permeability, CRP and plasma levels of IL-6 and IL-10 was seen at day +7 post-HSCT. miRNA-155 and mi-RNA-146a showed an inverse relation with significantly elevated miRNA-155 and decreased miRNA-146a levels, from day 0 to day +28 compared with pre-conditioning levels. Citrulline levels below the median at day +7 were associated with higher spontaneous production of IL-6 and TNF-α as well as higher in vitro stimulated production of IL-17A at day +21. This study is the first to demonstrate that toxic responses to chemotherapy are accompanied by differential regulation of miRNAs with opposing effects on immune regulation. We find that a proinflammatory miRNA profile is sustained during the first three weeks after the transplantation, indicating that these miRNAs may play a role in the regulation of the inflammatory environment during immune reconstitution after HSCT.

A prognostic score for acute graft-versus-host disease based on biomarkers: a multicentre study

BACKGROUND

Graft-versus-host disease (GVHD) is the major cause of non-relapse mortality after allogeneic haemopoietic stem-cell transplantation (SCT). The severity of symptoms at the onset of GVHD does not accurately define risk, and thus most patients are treated alike with high dose systemic corticosteroids. We aimed to define clinically meaningful risk strata for patients with newly diagnosed acute GVHD using plasma biomarkers.

METHODS

Between April 13, 2000, and May 7, 2013, we prospectively collected plasma from 492 SCT patients with newly diagnosed acute GVHD and randomly assigned (2:1) using a random number generator, conditional on the final two datasets having the same median day of onset, into training (n=328) and test (n=164) sets. We used the concentrations of three recently validated biomarkers (TNFR1, ST2, and Reg3α) to create an algorithm that computed the probability of non-relapse mortality 6 months after GVHD onset for individual patients in the training set alone. We rank ordered the probabilities and identified thresholds that created three distinct non-relapse mortality scores. We evaluated the algorithm in the test set, and again in an independent validation set of an additional 300 patients who underwent stem cell transplant and were enrolled on multicentre clinical trials of primary therapy for acute GVHD.

FINDINGS

In all three datasets (training, test, and validation), the cumulative incidence of 6-month non-relapse mortality significantly increased as the Ann Arbor GVHD score increased. In the multicentre validation set, scores were 8% (95% CI 3-16) for score 1, 27% (20-34) for score 2, and 46% (33-58) for score 3 (p<0·0001). Conversely, the response to primary GVHD treatment within 28 days decreased as the GVHD score increased 86% for score 1, 67% for score 2, and 46% for score 3 in the multicentre validation set, p<0·0001).

INTERPRETATION

Biomarker-based scores can be used to guide risk-adapted therapy at the onset of acute GVHD. High risk patients with a score of 3 are candidates for intensive primary therapy, while low risk patients with a score of 1 are candidates for rapid tapers of systemic steroid therapy.

FUNDING

The National Cancer Institute, the National Heart, Lung, and Blood Institute, the National Institute of Allergy and Infectious Diseases, the Doris Duke Charitable Fund, the American Cancer Society, and the Judith Devries Fund.

A radio-resistant perforin-expressing lymphoid population controls allogeneic T cell engraftment, activation, and onset of graft-versus-host disease in mice

Immunosuppressive pretransplantation conditioning is essential for donor cell engraftment in allogeneic bone marrow transplantation (BMT). The role of residual postconditioning recipient immunity in determining engraftment is poorly understood. We examined the role of recipient perforin in the kinetics of donor cell engraftment. MHC-mismatched BMT mouse models demonstrated that both the rate and proportion of donor lymphoid cell engraftment and expansion of effector memory donor T cells in both spleen and BM were significantly increased within 5 to 7 days post-BMT in perforin-deficient (pfn(-/-)) recipients, compared with wild-type. In wild-type recipients, depletion of natural killer (NK) cells before BMT enhanced donor lymphoid cell engraftment to that seen in pfn(-/-) recipients. This demonstrated that a perforin-dependent, NK-mediated, host-versus-graft (HVG) effect limits the rate of donor engraftment and T cell activation. Radiation-resistant natural killer T (NKT) cells survived in the BM of lethally irradiated mice and may drive NK cell activation, resulting in the HVG effect. Furthermore, reduced pretransplant irradiation doses in pfn(-/-) recipients permitted long-term donor lymphoid cell engraftment. These findings suggest that suppression of perforin activity or selective depletion of recipient NK cells before BMT could be used to improve donor stem cell engraftment, in turn allowing for the reduction of pretransplant conditioning.

The immunologic and hematopoietic profiles of mesenchymal stem cells derived from different sections of human umbilical cord

Mesenchymal stem cells (MSCs) have been widely used in allogeneic stem cell transplantation. We compared immunologic and hematopoietic characteristics of MSCs derived from whole human umbilical cord (UC), as well as from different sections of UCs, including the amniotic membrane (AM), Wharton's jelly (WJ), and umbilical vessel (UV). Cell phenotypes were examined by flow cytometry. Lymphocyte transformation test and mixed lymphocyte reaction were performed to evaluate the immuno-modulatory activity of MSCs derived from UCs. The mRNA expression of cytokines was detected by real-time polymerase chain reaction. Hematopoietic function was studied by co-culturing MSCs with CD34(+) cells isolated from cord blood. Our results showed that MSCs separated from these four different sections including UC, WJ, UV, and AM had similar biological characteristics. All of the MSCs had multi-lineage differentiation ability and were able to differentiate into osteoblasts, adipocytes, and chondrocytes. The MSCs also inhibited the proliferation of allogeneic T cells in a dose-dependent manner. The relative mRNA expression of cytokines was examined, and the results showed that UCMSCs had higher interleukin-6 (IL6), IL11, stem cell factor, and FLT3 expression than MSCs derived from specific sections of UCs. CD34(+) cells had high propagation efficiencies when co-cultured with MSCs derived from different sections of UCs, among which UCMSCs are the most efficient feeding layer. Our study demonstrated that MSCs could be isolated from whole UC or specific sections of UC with similar immunomodulation and hematopoiesis supporting characteristics.

Feasible outcomes of T cell-replete haploidentical stem cell transplantation with reduced-intensity conditioning in patients with myelodysplastic syndrome

Even with the recent optimization of haploidentical stem cell transplantation (SCT), its role for patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia evolving from MDS (sAML) should be validated. We analyzed the outcomes of consecutive 60 patients with MDS or sAML who received T cell-replete haploidentical SCT after reduced-intensity conditioning with fludarabine, busulfan, and rabbit antithymocyte globuline ± 800 cGy total body irradiation. Patients achieved a rapid neutrophil engraftment after a median of 12 days (range, 8 to 23) and an early immune reconstitution without high incidences of acute graft-versus-host disease (GVHD) II to IV and chronic GVHD (36.7% and 48.3%, respectively). After a median follow-up of 4 years, incidence of relapse and nonrelapse mortality and rate of overall survival and disease-free survival was 34.8%, 23.3%, 46.8%, and 41.9%, respectively. In multivariate analysis, the disease status at peak was a significant predictor for relapse (lower-risk MDS versus higher-risk MDS or sAML; hazard ratio [HR], 5.69; 95% confidence interval [CI], 1.45 to 22.29; P = .013) and disease-free survival (HR, 4.44; 95% CI, 1.14 to 17.34; P = .032). Chronic GVHD was an additional significant predictor for relapse (no versus yes; HR, 2.87; 95% CI, 1.03 to 7.51; P = .043). Our T cell-replete haploidentical SCT may be a feasible option for patients with MDS and sAML without conventional donors.

Association between NOD2 single nucleotide polymorphisms and Grade III-IV acute graft-versus-host disease: A meta-analysis

Objectives The effects of NOD2 single nucleotide polymorphisms (SNPs) on Grade III-IV acute graft-versus-host disease (aGVHD) risk are somewhat contradictory in different studies. The aim of the meta-analysis was to clarify the effects of NOD2 SNPs on the incidence of Grade III-IV aGVHD. Methods We searched PubMed, EMBASE, Web of SCIENCE, WanFang and Chinese National Knowledge Infrastructure (CNKI) databases to collect eligible publications. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the association between NOD2 polymorphisms and Grade III-IV aGVHD risk. Results A total of nine studies from eight publications met the inclusion criteria and were included in this meta-analysis. Patient NOD2 SNPs were not associated with aGVHD risk. A tendency of higher risk to develop Grade III-IV aGVHD was found in patients with pairs NOD2 SNPs. Subgroup analyses showed that pairs NOD2 SNPs were associated with Grade III-IV aGVHD in the Caucasian population and in identical sibling donors (IS), but not in matched unrelated donors (MUD). In patients who received hematopoietic stem cell transplantation (HSCT) with T-cell depletion and gut decontamination, there was still an association between pairs NOD2 SNPs and Grade III-IV aGVHD risk. Conclusions Our meta-analysis suggests that pairs NOD2 SNPs, not patient NOD2 SNPs, may be associated with Grade III-IV aGVHD risk, especially in the Caucasian population. It is also indicated that in pairs NOD2 polymorphisms group, patients who receive HSCT from IS may experience higher risk of Grade III-IV aGVHD.

Comparison of reduced-intensity and myeloablative conditioning regimens for allogeneic hematopoietic stem cell transplantation in patients with acute myeloid leukemia and acute lymphoblastic leukemia: a meta-analysis

Currently, the indications to perform reduced-intensity conditioning allogeneic hematopoietic stem cell transplant (RIC-HCT) are based on data derived mainly from large registry and single-centre retrospective studies. Thus, at the present time, there is limited direct evidence supporting the current practice in selecting patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) for RIC versus myeloablative conditioning (MAC) transplants. To determine the relationship between dose intensity of conditioning regimen and survival outcomes after allografting in AML/ALL patients, we performed a meta-analysis of 23 clinical trials reported between 1990 and 2013 involving 15,258 adult patients that compare survival outcomes after RIC-HCT versus MAC-HCT. RIC-HCT resulted in comparable <2-year and 2-6 year overall survival (OS) rates post-transplantation even though the RIC-HCT recipients were older and had more active disease than MAC-HCT recipients. The 2-6 year progression-free survival (PFS), nonrelapse mortality, acute graft-versus-host disease (GvHD) and chronic GvHD rates were reduced after RIC-HCT, but relapse rate was increased. Similar outcomes were observed regardless of disease type and status at transplantation. Odds ratio for all outcomes remained comparable with or without performing separate analyses for the year of HCT and for retrospective versus prospective studies. Among RIC-HCT recipients, survival rates were superior if patients were in CR at transplantation. Significant inter-study heterogeneity for aGvHD data and publication bias for PFS data were observed. This meta-analysis showed no OS benefit of MAC-HCT over RIC-HCT across the entire cohort of patients suggesting that RIC-HCT could be an effective therapeutic option for AML/ALL patients who are ineligible for MAC-HCT and CR status is preferred before RIC-HCT.

Modeling human gastrointestinal inflammatory diseases using microphysiological culture systems

Gastrointestinal illnesses are a significant health burden for the US population, with 40 million office visits each year for gastrointestinal complaints and nearly 250,000 deaths. Acute and chronic inflammations are a common element of many gastrointestinal diseases. Inflammatory processes may be initiated by a chemical injury (acid reflux in the esophagus), an infectious agent (Helicobacter pylori infection in the stomach), autoimmune processes (graft versus host disease after bone marrow transplantation), or idiopathic (as in the case of inflammatory bowel diseases). Inflammation in these settings can contribute to acute complaints (pain, bleeding, obstruction, and diarrhea) as well as chronic sequelae including strictures and cancer. Research into the pathophysiology of these conditions has been limited by the availability of primary human tissues or appropriate animal models that attempt to physiologically model the human disease. With the many recent advances in tissue engineering and primary human cell culture systems, it is conceivable that these approaches can be adapted to develop novel human ex vivo systems that incorporate many human cell types to recapitulate in vivo growth and differentiation in inflammatory microphysiological environments. Such an advance in technology would improve our understanding of human disease progression and enhance our ability to test for disease prevention strategies and novel therapeutics. We will review current models for the inflammatory and immunological aspects of Barrett's esophagus, acute graft versus host disease, and inflammatory bowel disease and explore recent advances in culture methodologies that make these novel microphysiological research systems possible.

Donor CD4 T cells trigger costimulation blockade-resistant donor bone marrow rejection through bystander activation requiring IL-6

Bone marrow (BM) transplantation under costimulation blockade induces chimerism and tolerance. Cotransplantation of donor T cells (contained in substantial numbers in mobilized peripheral blood stem cells and donor lymphocyte infusions) together with donor BM paradoxically triggers rejection of donor BM through undefined mechanisms. Here, nonmyeloablatively irradiated C57BL/6 recipients simultaneously received donor BM (BALB/c) and donor T cells under costimulation blockade (anti-CD154 and CTLA4Ig). Donor CD4, but not CD8 cells, triggered natural killer-independent donor BM rejection which was associated with increased production of IL-6, interferon gamma (IFN-γ) and IL-17A. BM rejection was prevented through neutralization of IL-6, but not of IFN-γ or IL-17A. IL-6 counteracted the antiproliferative effect of anti-CD154 in vitro. Rapamycin and anti-lymphocyte function-associated antigen 1 negated this effect of IL-6 in vitro and prevented BM rejection in vivo. Simultaneous cotransplantation of (BALB/cxB6)F1, recipient or irradiated donor CD4 cells, or late transfer of donor CD4 cells did not lead to BM rejection, whereas cotransplantation of third party CD4 cells did. Transferred donor CD4 cells became activated, rapidly underwent apoptosis and triggered activation and proliferation of recipient T cells. Collectively, these results provide evidence that donor T cells recognizing the recipient as allogeneic lead to the release of IL-6, which abolishes the effect of anti-CD154, triggering donor BM rejection through bystander activation.

The role of pattern-recognition receptors in graft-versus-host disease and graft-versus-leukemia after allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only treatment with curative potential for certain aggressive hematopoietic malignancies. Its success is limited by acute graft-versus-host disease (GVHD), a life-threatening complication that occurs when allo-reactive donor T cells attack recipient organs. There is growing evidence that microbes and innate pattern-recognition receptors (PRRs) such as toll-like receptors (TLR) and nod-like receptors (NLR) are critically involved in the pathogenesis of acute GVHD. Currently, a widely accepted model postulates that intensive chemotherapy and/or total-body irradiation during pre-transplant conditioning results in tissue damage and a loss of epithelial barrier function. Subsequent translocation of bacterial components as well as release of endogenous danger molecules stimulate PRRs of host antigen-presenting cells to trigger the production of pro-inflammatory cytokines (cytokine storm) that modulate T cell allo-reactivity against host tissues, but eventually also the beneficial graft-versus-leukemia (GVL) effect. Given the limitations of existing immunosuppressive therapies, a better understanding of the molecular mechanisms that govern GVHD versus GVL is urgently needed. This may ultimately allow to design modulators, which protect from GvHD but preserve donor T-cell attack on hematologic malignancies. Here, we will briefly summarize current knowledge about the role of innate immunity in the pathogenesis of GVHD and GVL following allo-HSCT.

Modulation of lymphocyte subpopulations by extracorporeal photopheresis in patients with acute graft-versus-host disease or graft rejection

Extracorporeal photopheresis (ECP) constitutes a promising treatment for patients with steroid-refractory acute graft-versus-host disease (aGvHD) after allogeneic stem cell transplantation and for patients with graft rejection after solid organ transplantation (SOT). There is an increasing body of evidence that modulation of lymphocyte subsets might play a crucial role in the mechanism of action in ECP. We therefore analyzed immunological effects concomitantly with clinical findings in patients under ECP therapy using multicolor flow cytometry. In a patient with steroid-refractory aGvHD and a patient with progressive bronchiolitis obliterans syndrome (BOS) after double-lung transplantation, clinical responses to ECP therapy were paralleled by an increase of CD4 + CD25hiFoxP3 + regulatory T cells and a decrease of T(EMRA) (CD3 + CD8+ CD45RA+ CD62L+ effector memory T) cells as well as of natural killer (NK)T cells. In summary, immunomonitoring of T cell subsets can elucidate the mechanism of action in ECP.

The biology of graft-versus-host disease: experimental systems instructing clinical practice

The last 6 decades have seen major advances in the understanding of immunologic diseases, driven by preclinical animal models. Indeed, bone marrow transplantation (BMT) has its genesis in rodent models dating back to the 1950s. Allogeneic BMT and its major complication, graft-versus-host disease (GVHD), represent a paradigm for the translation of preclinical concepts into clinical practice. The appreciation that GVHD can be thought of as a stepwise escalation in immune activation characterized by eventual massive target tissue apoptosis has allowed the design of rational approaches to better manage patients. Here, we describe the pathophysiology of GVHD as defined in preclinical models, focusing on the successes and failures of this research to instruct and translate clinical practice. We also provide a commentary on the limitations of these models so that they may be better appreciated and addressed in future studies. Notable preclinical successes include the definition of modern immune suppression, reductions in conditioning intensity, posttransplant cyclophosphamide, and the promotion of regulatory T-cell reconstitution. New strategies including naïve T-cell depletion, focused cytokine and chemokine inhibition, and the blockade of costimulation now also appear highly promising and very likely to translate into patients in the near future.

Inhibition of plasmin attenuates murine acute graft-versus-host disease mortality by suppressing the matrix metalloproteinase-9-dependent inflammatory cytokine storm and effector cell trafficking

The systemic inflammatory response observed during acute graft-versus-host disease (aGVHD) is driven by proinflammatory cytokines, a 'cytokine storm'. The function of plasmin in regulating the inflammatory response is not fully understood, and its role in the development of aGVHD remains unresolved. Here we show that plasmin is activated during the early phase of aGVHD in mice, and its activation correlated with aGVHD severity in humans. Pharmacological plasmin inhibition protected against aGVHD-associated lethality in mice. Mechanistically, plasmin inhibition impaired the infiltration of inflammatory cells, the release of membrane-associated proinflammatory cytokines including tumor necrosis factor-α (TNF-α) and Fas-ligand directly, or indirectly via matrix metalloproteinases (MMPs) and alters monocyte chemoattractant protein-1 (MCP-1) signaling. We propose that plasmin and potentially MMP-9 inhibition offers a novel therapeutic strategy to control the deadly cytokine storm in patients with aGVHD, thereby preventing tissue destruction.

Treatment with a rho kinase inhibitor improves survival from graft-versus-host disease in mice after MHC-haploidentical hematopoietic cell transplantation

Acute graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic cell transplantation (HCT) and the main cause of nonrelapse mortality during the first 100 days post-transplant. Although GVHD can be prevented by extensive removal of mature donor T cells from the donor hematopoietic stem cell population, doing so eliminates any potential allogeneic graft-versus-tumor (GVT) effect also mediated by donor T cells and results in unacceptable rates of cancer relapse. One potential solution to this problem of separating GVHD development from a GVT response is to prevent T cell-mediated GVHD in the intestinal tract (IT) while preserving systemic antihost alloreactivity of donor T cells that target residual tumor cells expressing host alloantigens. We examined the ability of the anti-inflammatory rho kinase inhibitor, fasudil, given orally and intraperitoneally, to prevent GVHD in a C3H → B6C3F1 mouse model of MHC-haploidentical bone marrow transplantation. Fasudil-treated recipients of anti-thy-1 mAb + C' treated bone marrow (ATBM) cells plus T cells had a 73% 90-day survival compared with 25% among untreated ATBM + T cell recipients (P < .0001). Severe initial weight loss was similar in the 2 groups, but less diarrhea was observed among treated animals, and fasudil-treated survivors recovered more weight than untreated survivors. Skin inflammation occurred and resolved between weeks 2 and 8 with similar severity and kinetics in both treated and untreated surviving animals, indicating persistent alloreactivity. Day 10 post-transplantation splenocytes from fasudil-treated mice, containing mature donor T cells, and day 98 splenocytes, containing mature donor and de novo thymus-derived T cells, exhibited alloreactivity against host parental antigens, as assessed by in vitro IFN-γ production and rounds of allostimulated proliferation, respectively. These data support the idea that targeted treatment of the IT with rho kinase inhibitors can ameliorate lethal GVHD while preserving systemic alloreactivity. The results also suggest that similar mechanisms of IT-specific tolerance or resistance to GVHD operate in fasudil-treated and untreated long-term survivors of allogeneic ATBM + T cells.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Oral complications in hematopoietic stem cell recipients: the role of inflammation

Hematopoietic stem cell transplantation (HSCT) is widely used as a potentially curative treatment for patients with various hematological malignancies, bone marrow failure syndromes, and congenital immune deficiencies. The prevalence of oral complications in both autologous and allogeneic HSCT recipients remains high, despite advances in transplant medicine and in supportive care. Frequently encountered oral complications include mucositis, infections, oral dryness, taste changes, and graft versus host disease in allogeneic HSCT. Oral complications are associated with substantial morbidity and in some cases with increased mortality and may significantly affect quality of life, even many years after HSCT. Inflammatory processes are key in the pathobiology of most oral complications in HSCT recipients. This review article will discuss frequently encountered oral complications associated with HSCT focusing on the inflammatory pathways and inflammatory mediators involved in their pathogenesis.

PIAS3 suppresses acute graft-versus-host disease by modulating effector T and B cell subsets through inhibition of STAT3 activation

Graft-versus-host disease (GVHD) caused by transplanted donor T cells remains the major obstacle of allogeneic bone marrow transplantation (BMT). Previous reports have suggested that IL-17-producing helper T (Th17) cells mediate the development of acute GVHD (aGVHD). Protein inhibitor of activated STAT3 (PIAS) inhibits the activity of the transcription factor STAT3, which is a pivotal transcription factor for Th17 differentiation. To elucidate whether PIAS3 could inhibit the development of aGVHD, pcDNA-PIAS3 or mock vector was administered in a murine model of aGVHD by intramuscular injection and subsequent electroporation. The results demonstrated that PIAS3 overexpression by pcDNA-vector administration significantly attenuated the clinical severity and histopathological severities of aGHVD involving the skin, liver, intestine, and lung. Additionally, the STAT3 activities in aGVHD target organs were suppressed by PIAS3 overexpression. Furthermore, phosphorylated (p) STAT3 activity in the spleen was profoundly attenuated in PIAS3-overexpressing GVHD mice. Interestingly, flow cytometric analysis demonstrated that the populations of CD21(high)CD23(low) marginal zone B cells were dramatically expanded in PIAS3-overexpressing mice. PIAS3-induced inhibition of aGVHD was largely related to the downregulation of Th1 and Th17 and the upregulation of Th2 and Treg populations. Both populations of pSTAT3(Tyr705)-expressing Th17 cells and B cells were significantly reduced in the spleens of PIAS3-overexpressing mice, whereas pSTAT5 activity was increased. In addition to CD4(+)CD25(+)Foxp3(+) Treg cells, the populations of CD8(+)CD25(+)Foxp3(+) Treg cells were also expanded by treatment with PIAS3. These data suggest the therapeutic potential of PIAS3 in the development of aGVHD through reciprocal regulation of Th17/Treg lineages.

Relative defects in mucosal immunity predict acute graft-versus-host disease

Impairment of gut mucosal immunity by the transplant process could facilitate translocation of commensal bacteria and thereby augment the graft-versus-host response. To begin to assess the influence of gut mucosal immunity on the development of acute graft-versus-host disease (GVHD), we conducted a prospective study in 24 pediatric allogeneic hematopoietic cell transplant recipients, assessing 4 fecal markers of mucosal immunity: calprotectin, soluble CD8 (sCD8), soluble intracellular adhesion molecule 1, and β-defensin-2. Stool samples were collected prospectively on transplant days 0, +5, +10, and +15 and analyzed by ELISA. Lower levels on day +5 (calprotectin and β-defensin-2) and day +10 (calprotectin, β-defensin-2, and sCD8) were associated with subsequent acute GVHD. The most striking difference was with calprotectin on day +10. Patients with levels below 424 mg/kg had an incidence of 77.8%, whereas those with levels above this threshold had a cumulative incidence of 0% (P = .002). Relative defects in gut mucosal immunity may be important in the pathogenesis of acute GVHD.

Metagenomic analysis of the stool microbiome in patients receiving allogeneic stem cell transplantation: loss of diversity is associated with use of systemic antibiotics and more pronounced in gastrointestinal graft-versus-host disease

Next-generation sequencing of the hypervariable V3 region of the 16s rRNA gene isolated from serial stool specimens collected from 31 patients receiving allogeneic stem cell transplantation (SCT) was performed to elucidate variations in the composition of the intestinal microbiome in the course of allogeneic SCT. Metagenomic analysis was complemented by strain-specific enterococcal PCR and indirect assessment of bacterial load by liquid chromatography-tandem mass spectrometry of urinary indoxyl sulfate. At the time of admission, patients showed a predominance of commensal bacteria. After transplantation, a relative shift toward enterococci was observed, which was more pronounced under antibiotic prophylaxis and treatment of neutropenic infections. The shift was particularly prominent in patients that developed subsequently or suffered from active gastrointestinal (GI) graft-versus-host disease (GVHD). The mean proportion of enterococci in post-transplant stool specimens was 21% in patients who did not develop GI GVHD as compared with 46% in those that subsequently developed GI GVHD and 74% at the time of active GVHD. Enterococcal PCR confirmed predominance of Enterococcus faecium or both E. faecium and Enterococcus faecalis in these specimens. As a consequence of the loss of bacterial diversity, mean urinary indoxyl sulfate levels dropped from 42.5 ± 11 μmol/L to 11.8 ± 2.8 μmol/L in all post-transplant samples and to 3.5 ± 3 μmol/L in samples from patients with active GVHD. Our study reveals major microbiome shifts in the course of allogeneic SCT that occur in the period of antibiotic treatment but are more prominent in association with GI GVHD. Our data indicate early microbiome shifts and a loss of diversity of the intestinal microbiome that may affect intestinal inflammation in the setting of allogeneic SCT.

IL-1β and TLR4 signaling are involved in the aggravated murine acute graft-versus-host disease caused by delayed bortezomib administration

It was shown that the proteasome inhibitor, bortezomib, administered immediately following allogeneic bone marrow transplantation resulted in marked inhibition of acute graft-versus-host disease (aGVHD), with retention of graft-versus-tumor effects. However, continuous bortezomib administration resulted in significant acceleration of graft-versus-host disease-dependent morbidity. We carried out studies to dissect the mechanisms of aggravated aGVHD caused by delayed bortezomib administration. First, we demonstrated that IL-1β was critically involved, and the subsequent aGVHD could be alleviated by IL-1β blockade. Bortezomib treatment after dendritic cell (DC) activation resulted in drastically elevated IL-1β production, whereas bortezomib treatment before DC activation inhibited IL-1β production, suggesting that the timing of bortezomib administration significantly affected IL-1β production by DCs. We further demonstrated that delayed administration of bortezomib accelerated aGVHD through TLR4 signaling. Because the LPS levels were much lower with reduced-intensity conditioning compared with high-dose irradiation, the accelerated graft-versus-host disease-dependent morbidity with delayed bortezomib administration could be rescued by reduced-intensity conditioning. Our studies suggested that TLR4 pathway activation and delayed bortezomib administration amplified the production of IL-1β and other inflammatory cytokines, which resulted in accelerated aGVHD-dependent morbidity. These results indicated that decreased toxicity of continuous bortezomib administration could be achieved by reduced-intensity conditioning or by inhibiting IL-1β.

Host programmed death ligand 1 is dominant over programmed death ligand 2 expression in regulating graft-versus-host disease lethality

Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, play an important role in the maintenance of peripheral tolerance. We explored the role of PD-1 ligands in regulating graft-versus-host disease (GVHD). Both PD-L1 and PD-L2 expression were upregulated in the spleen, liver, colon, and ileum of GVHD mice. Whereas PD-L2 expression was limited to hematopoietic cells, hematopoietic and endothelial cells expressed PD-L1. PD-1/PD-L1, but not PD-1/PD-L2, blockade markedly accelerated GVHD-induced lethality. Chimera studies suggest that PD-L1 expression on host parenchymal cells is more critical than hematopoietic cells in regulating acute GVHD. Rapid mortality onset in PD-L1-deficient hosts was associated with increased gut T-cell homing and loss of intestinal epithelial integrity, along with increased donor T-cell proliferation, activation, Th1 cytokine production, and reduced apoptosis. Bioenergetics profile analysis of proliferating alloreactive donor T-cells demonstrated increased aerobic glycolysis and oxidative phosphorylation in PD-L1-deficient hosts. Donor T-cells exhibited a hyperpolarized mitochondrial membrane potential, increased superoxide production, and increased expression of a glucose transporter in PD-L1-deficient hosts. Taken together, these data provide new insight into the differential roles of host PD-L1 and PD-L2 and their associated cellular and metabolic mechanisms controlling acute GVHD.

Dissection of the human multipotent adult progenitor cell secretome by proteomic analysis

Multipotent adult progenitor cells (MAPCs) are adult adherent stromal stem cells currently being assessed in acute graft versus host disease clinical trials with demonstrated immunomodulatory capabilities and the potential to ameliorate detrimental autoimmune and inflammation-related processes. Our previous studies documented that MAPCs secrete factors that play a role in regulating T-cell activity. Here we expand our studies using a proteomics approach to characterize and quantify MAPC secretome components secreted over 72 hours in vitro under steady-state conditions and in the presence of the inflammatory triggers interferon-γ and lipopolysaccharide, or a tolerogenic CD74 ligand, RTL1000. MAPCs differentially responded to each of the tested stimuli, secreting molecules that regulate the biological activity of the extracellular matrix (ECM), including proteins that make up the ECM itself, proteins that regulate its construction/deconstruction, and proteins that serve to attach and detach growth factors from ECM components for redistribution upon appropriate stimulation. MAPCs secreted a wide array of proteases, some detectable in their zymogen forms. MAPCs also secreted protease inhibitors that would regulate protease activity. MAPCs secreted chemokines and cytokines that could provide molecular guidance cues to various cell types, including neutrophils, macrophages, and T cells. In addition, MAPCs secreted factors involved in maintenance of a homeostatic environment, regulating such diverse programs as innate immunity, angiogenesis/angiostasis, targeted delivery of growth factors, and the matrix-metalloprotease cascade.

Soluble GARP has potent antiinflammatory and immunomodulatory impact on human CD4+ T cells

GARP efficiently represses proliferation of naïve and resting CD4+ T cells and is involved in the induction of adaptive regulatory T cells. In vivo, GARP prevents T cell–mediated destructive inflammation in a preclinical humanized mouse model of GVHD.

Reciprocal expression of enteric antimicrobial proteins in intestinal graft-versus-host disease

We recently demonstrated that expression of α-defensins, the major antimicrobial peptides produced by Paneth cells, was severely suppressed in mice with graft-versus-host disease (GVHD). In this study, we found that antibacterial lectin, regenerating islet-derived IIIγ (RegIIIγ) was upregulated in villous enterocytes, thus demonstrating the reciprocal control of enteric antimicrobial proteins in GVHD. Upregulation of RegIIIγ was mediated by a mechanism independent upon radiation-induced intestinal tract damage. MyD88-mediated signaling in intestinal epithelium was required for RegIIIγ upregulation in GVHD and antibiotic therapy downregulated RegIIIγ expression. These results suggest that MyD88-mediated sensing of the intestinal microbes disregulated in GVHD induces RegIIIγ upregulation in GVHD and argue a role for RegIIIγ in the pathogenesis of GVHD.

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

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

In vivo activation of transferred regulatory T cells specific for third-party exogenous antigen controls GVH disease in mice

Treg cells hold enormous promise for therapeutic application in GVH disease, a lethal complication of allogeneic HSC transplantation. Mouse studies showed that donor‐derived recipient‐specific Treg (rsTreg) cells are far more efficient than polyclonal Treg cells in suppressing GVH disease. However, clinical grade preparations of rsTreg cells carries the risk of containing significant numbers of highly pathogenic recipient‐specific effector T cells. We hypothesized that an alternative approach using Treg cells specific for an exogenous (i.e. nondonor, nonrecipient) Ag (exoTreg cells) can overcome this risk by taking advantage of the bystander suppressive effect of Treg cells. For this, we used a murine model for aggressive GVH disease. We expanded ex vivo exoTreg cells that are primed against the HY Ag, which is only expressed in males. ExoTreg cells supressed GVH disease as efficiently as rsTreg cells in recipient male mice. We also applied this strategy in female mice that do not express this Ag. While exoTreg cells were not effective in female recipients when applied alone, providing the cognate HY Ag in vivo along side effectively activated exoTreg cells and completely abrogated GVH disease, establishing a targeted on/off system to provide a suppressive effect on alloreactive effector T cells.

Inhibiting retinoic acid signaling ameliorates graft-versus-host disease by modifying T-cell differentiation and intestinal migration

Graft-versus-host disease (GVHD) is a critical complication after allogeneic bone marrow transplantation. During GVHD, donor T cells are activated by host antigen-presenting cells and differentiate into T-effector cells (Teffs) that migrate to GVHD target organs. However, local environmental factors influencing Teff differentiation and migration are largely unknown. Vitamin A metabolism within the intestine produces retinoic acid, which contributes to intestinal homeostasis and tolerance induction. Here, we show that the expression and function of vitamin A-metabolizing enzymes were increased in the intestine and mesenteric lymph nodes in mice with active GVHD. Moreover, transgenic donor T cells expressing a retinoic acid receptor (RAR) response element luciferase reporter responded to increased vitamin A metabolites in GVHD-affected organs. Increasing RAR signaling accelerated GVHD lethality, whereas donor T cells expressing a dominant-negative RARα (dnRARα) showed markedly diminished lethality. The dnRARα transgenic T cells showed reduced Th1 differentiation and α4β7 and CCR9 expression associated with poor intestinal migration, low GVHD pathology, and reduced intestinal permeability, primarily via CD4(+) T cells. The inhibition of RAR signaling augmented donor-induced Treg generation and expansion in vivo, while preserving graft-versus-leukemia effects. Together, these results suggested that reagents blunting donor T-cell RAR signaling may possess therapeutic anti-GVHD properties.

Advances in the treatment of acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (HSCT) has been widely used for the treatment of hematologic malignant and non-malignant hematologic diseases and other diseases. However, acute graft-versus-host disease (GVHD) is a life-threatening complication of allogeneic transplantation. Acute GVHD may occur in 30% of transplant recipients, which is a syndrome of erythematous skin eruption, cholestatic liver disease and intestinal dysfunction, resulting from the activation of donor T lymphocytes by host antigen-presenting cells, resulting in an immune-mediated inflammatory response. Recent scientific advances in the understanding of the pathogenesis involved in the development of acute GVHD and clinical investigation have provided more effective therapeutic strategies for acute GVHD. This review focuses on major scientific and clinical advances in the treatment of acute GVHD.

Low Paneth cell numbers at onset of gastrointestinal graft-versus-host disease identify patients at high risk for nonrelapse mortality

Acute graft-versus-host disease (GVHD) of the gastrointestinal (GI) tract is an often lethal complication of allogeneic hematopoietic cell transplant. Clinical severity correlates with outcomes, but histopathologic grading is primarily used to confirm the clinical diagnosis. One barrier to using histopathologic grading to predict clinical outcomes is inter-grader variability among transplant centers. Recent experimental models have shown that the loss of Paneth cells, which are located in the small intestine and help regulate the GI microbiome by secreting antimicrobial peptides, correlates with clinical GVHD severity. Because Paneth cells are easy to identify and quantify by light microscopy, we evaluated the mean number of Paneth cells per high-powered field (hpf) in 116 duodenal biopsies obtained at diagnosis of GI GVHD at 2 different centers with their clinical outcomes. Paneth cell counts were reproducible between centers (r(2) = 0.81; P < .0001). Lower numbers of Paneth cells at diagnosis correlated with clinically more severe GI GVHD (P < .0001) and less likelihood of response to GVHD treatment (P < .0001). A threshold of 4 Paneth cells per hpf stratified patients according to nonrelapse mortality (28% vs 56%; P = .004). We conclude that the enumeration of duodenal Paneth cells is a readily available index of disease severity that provides important information regarding GVHD prognosis.

Promising role of reduced-toxicity hematopoietic stem cell transplantation (PART-I)

Allogeneic hematopoietic stem cell transplantation (HSCT) remains a potential curative option for many patients with hematological malignancies (HM). However, the high rate of transplantation-related mortality (TRM) restricted the use of standard myeloablative HSCT to a minority of young and fit patients. Over the past few years, it has become evident that the alloreactivity of the immunocompetent donor cells mediated anti-malignancy effects independent of the action of high dose chemoradiotherapy. The use of reduced intensity conditioning (RIC) regimens has allowed a graft-versus-malignancy (GvM) effect to be exploited in patients who were previously ineligible for HSCT on the grounds of age and comorbidity. Retrospective analysis showed that RIC has been associated with lower TRM but a higher relapse rate leading to similar intermediate term overall and progression-free survivals when compared to standard myeloablative HSCT. However, the long term antitumor effect of this approach is less well established. Prospective studies are ongoing to define which patients might most benefit from reduced toxicity stem cell transplant (RT-SCT) and which transplant protocols are suitable for the different types of HM. The advent of RT-SCT permits the delivery of a potentially curative GvM effect to the majority of patients with HM whose outcome with conventional chemotherapy would be dismal. Remaining challenges include development of effective strategies to reduce relapse rates by augmenting GvM effects without increasing toxicity.

Rifaximin for preventing acute graft-versus-host disease: impact on plasma markers of inflammation and T-cell activation

In murine allogeneic hematopoietic cell transplantation models, inhibiting bacterial translocation stemming from conditioning-induced damage to the gut mucosa abrogates inflammatory stimulation of donor T cells, preventing acute graft-versus-host disease (AGVHD). We conducted a phase I trial to begin testing the hypothesis that rifaximin, a broadly acting oral antibiotic, would reduce systemic inflammation and T-cell activation. We administered rifaximin to 20 adolescents and younger adults (day -10 through day +30) receiving intensive conditioning. We measured the plasma level of interleukin-6, as a marker of conditioning-induced inflammation, and the levels of soluble tumor necrosis factor receptor-1 and soluble interleukin-2 receptor, as surrogate markers of AGVHD. We formed a historical control group (n=24), from a previous study of biomarkers in AGVHD. The increase in the treatment group's mean interleukin-6 level from baseline to day 0 was 73% less than that in the control group (P=0.006). The increase from baseline to day 15 in the treatment group's mean soluble tumor necrosis factor-1 and soluble interleukin-2 receptor levels was similar to the control group. Incidences of grade 2 to 4 AGVHD also did not differ. This suggests that rifaximin may abrogate bacterial translocation and resultant inflammation, but in alternative donor transplants this does not prevent downstream activation of donor T cells.

Interleukin 11 expression in the normal canine eye

OBJECTIVES

The purpose of this study was to characterize the expression of interleukin-11 (IL-11), a cytokine with anti-inflammatory, cytoprotective, and immune-modulating characteristics, in the canine eye.

PROCEDURES

Normal canine eyes were collected from clinically healthy dogs that had been euthanized for reasons unrelated to this study. The distribution of IL-11 expression in the different ocular layers was evaluated by immunofluorescence (eight eyes). Expression levels were quantified (based on fluorescence intensity) using pixel density analysis. Primary cell cultures were derived from all three corneal cell layers. IL-11 mRNA expression was assessed in these cultures using quantitative RT-PCR before and after treatment with TGF-β1, a known inducer of IL-11 expression. IL-11 protein expression was also assessed in the media of these cells by Western blot analysis.

RESULTS

IL-11 protein was detected in the corneal epithelium, keratocytes, and the corneal endothelium of the normal canine eyes examined using immunofluorescence. Baseline IL-11 mRNA expression was noted in the corneal epithelium, fibroblasts, and endothelium using quantitative RT-PCR. Treatment of canine corneal cell lines with TGF-β1 resulted in statistically significant increases in IL-11 expression in the corneal epithelium, endothelial and fibroblast cell lines with strongest induction noted in the fibroblasts and endothelium.

CONCLUSION

This is the first description of IL-11 expression in the canine eye. The protein and mRNA appear to be constitutively present throughout all layers of the cornea and are increased by TGF-β1, a cytokine important in ocular inflammation and disease.

Endothelial and epithelial barriers in graft-versus-host disease

Endothelial and epithelial cells form selectively permeable barriers that separate tissue compartments. These cells coordinate movement between the lumen and tissue via the transcellular and paracellular pathways. The primary determinant of paracellular permeability is the tight junction, which forms an apical belt-like structure around endothelial and epithelial cells. This chapter discusses endothelial and epithelial barriers in graft-versus-host disease after allogeneic bone marrow transplantation, with a focus on the tight junction and its role in regulating paracellular permeability. Recent studies suggest that in graft-versus-host disease, pathological increases in paracellular permeability, or barrier dysfunction, are initiated by pretransplant conditioning and sustained by alloreactive cells and the proinflammatory milieu. The intestinal epithelium is a significant focus, as it is a target organ of graft-versus-host disease, and the mechanisms of barrier regulation in intestinal epithelium have been well characterized. Finally, we propose a model that incorporates endothelial and epithelial barrier dysfunction in graft-versus-host disease and discuss modulating barrier properties as a therapeutic approach.

A critical role for the retinoic acid signaling pathway in the pathophysiology of gastrointestinal graft-versus-host disease

Damage to the gastrointestinal tract during graft-versus-host disease (GVHD) is one of the major causes of morbidity and mortality in allogeneic hematopoietic stem cell transplant (HSCT) recipients. In the current study, we identified a critical role for the retinoic acid (RA) signaling pathway in the induction and propagation of gastrointestinal GVHD. The administration of exogenous RA significantly increased expression of the gut-homing molecules, CCR9 and α4β7, on donor T cells in mesenteric lymph nodes, and augmented the accumulation of proinflammatory CD4(+) and CD8(+) T cells within the gut mucosa, leading to a selective exacerbation of colonic GVHD and increased overall mortality. Conversely, depletion of RA in recipient mice by vitamin A deprivation resulted in a dramatic reduction of gut-homing molecule expression on donor T cells after HSCT. Significantly, absence of the RA receptor-α on donor T cells markedly attenuated the ability of these cells to cause lethal GVHD. This observation was attributable to a significant reduction in pathological damage within the colon. These findings identify an organ-specific role for RA in GVHD and provide evidence that blockade of the RA signaling pathway may represent a novel strategy for mitigating the severity of colonic GVHD.

Ocular graft-versus-host disease

PURPOSE OF REVIEW

This review was carried out to study the frequency, and severity of ocular surface involvement at the setting of allogeneic hematopoietic stem cell transplantation and subsequent graft-versus-host disease (GVHD) and evaluate the clinical outcomes of newer treatments.

RECENT FINDINGS

Ocular involvement has been reported in 60-90% of patients with chronic GVHD. Although dry eye is the most frequent finding occurring in the great majority of patients (up to 90%), posterior segment complications are also not infrequent, seen in 12.8% of patients after bone marrow transplantation. Anti-inflammatory treatments particularly T-cell suppressants seem to have a beneficial effect in managing GVHD. Corticoteroids, calcineurin inhibitors, such as cyclosporine and tacrolimus, as well as antifibrotic agents such as tranilast are available options for topical application. Cyclosporine ophthalmic drop seems to be a well tolerated and effective treatment modality; favorable results have been demonstrated with increased dosage.

SUMMARY

GVHD is an increasingly frequent cause of ocular surface morbidity with the potential of visual loss from corneal involvement. Early diagnosis and aggressive local as well as systemic treatment can be vision saving.

The central nervous system is a target of acute graft versus host disease in mice

Despite significant advances in prevention and management, graft versus host disease (GVHD) is still a leading complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although skin, gut, liver, thymus, and lung are GVHD targets, neurological complications (NC) have also been reported following allo-HSCT. We demonstrate that the central nervous system (CNS) can be a direct target of alloreactive T cells following allo-HSCT in mice. We found significant infiltration of the CNS with donor T lymphocytes and cell death of neurons and neuroglia in allo-HSCT recipients with GVHD. We also found that allo-HSCT recipients with GVHD had deficits in spatial learning/memory and demonstrated increased anxious behavior. These findings highlight CNS sensitivity to damage caused by alloreactive donor T cells and represent the first characterization of target cell subsets and NC during GVHD. Therefore, these clinically relevant studies offer a novel and rational explanation for the well-described neurological symptoms observed after allo-HSCT.

Mesenchymal stem cells as cellular immunotherapeutics in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment option in hematopoietic disorders, immunodeficiencies and leukemia. To date graft-versus-host disease (GvHD) represents a life-threatening complication even if associated with beneficial antileukemic reactivity. GvHD is the clinical manifestation of donor cells reacting against host tissue. Because of their ability to facilitate endogenous repair and to attenuate inflammation, MSC have evolved as a highly attractive cellular therapeutic in allo-HSCT. Here we report on the clinical experience in the use of MSC to enhance engraftment and prevent and treat acute and chronic GvHD. In early clinical trials, MSC have shown considerable benefit in the setting of manifest GvHD. These encouraging results warrant further exploration.

Advances in predicting acute GVHD

Acute graft-versus-host disease (GVHD) is a leading cause of non-relapse mortality following allogeneic haematopoietic cell transplantation. Attempts to improve treatment response in clinically-established GVHD have not improved overall survival, often due to the increased risk of infectious complications. Alternative approaches to decrease GVHD-related morbidity and mortality have focused on the ability to predict GVHD prior to clinical manifestation in an effort to provide an opportunity to abort GVHD development, and to gain new insights into GVHD pathophysiology. This review outlines the research efforts to date that have identified clinical and laboratory-based factors that are predictive of acute GVHD and describes future directions in developing algorithms that will improve the ability to predict the development of clinically relevant GVHD.

Nonalloreactive T cells prevent donor lymphocyte infusion-induced graft-versus-host disease by controlling microbial stimuli

In mice, graft-versus-host reactions, associated with powerful graft-versus-tumor effects, can be achieved without graft-versus-host disease (GVHD) by delayed administration of donor lymphocyte infusions (DLI) to established mixed chimeras. However, GVHD sometimes occurs after DLI in established mixed chimeric patients. In contrast to mice, in which T cell recovery from the thymus occurs prior to DLI administration, human T cell reconstitution following T cell-depleted hematopoietic cell transplantation is slow, resulting in lymphopenia at the time of DLI. We demonstrate in this study that T cell lymphopenia is an independent risk factor for GVHD following DLI in the absence of known inflammatory stimuli. DLI-induced GVHD was prevented in lymphopenic recipients by prior administration of a small number of nonalloreactive polyclonal T cells, insufficient to prevent lymphopenia-associated expansion of subsequently administered T cells, through a regulatory T cell-independent mechanism. GVHD was not inhibited by T cells with irrelevant specificity. Moreover, administration of antibiotics reduced the severity of GVHD in lymphopenic hosts. Accumulation of DLI-derived effector T cells and host hematopoietic cell elimination were markedly diminished by regulatory T cell-depleted, nonalloreactive T cells. Finally, thymectomized mixed chimeras showed increased GVHD following delayed DLI. Collectively, our data demonstrate that in the absence of known conditioning-induced inflammatory stimuli, T cell lymphopenia is a risk factor for GVHD in mixed chimeras receiving delayed DLI. Our data suggest that the predisposition to GVHD can at least in part be explained by the presence of occult inflammatory stimuli due to the absence of T cells to control microbial infections.

Toll-like receptor gene polymorphisms confer susceptibility to graft-versus-host disease in allogenic hematopoietic stem cell transplantation

Graft-versus-host disease (GvHD) is a major complication in hematopoietic stem cell transplantation (HSCT). The immune response against gut microbes is thought to be an important factor in the beginning of GvHD. Toll-like receptors (TLR) recognize molecular structures of microbes and viruses and play central part in the innate immunity. We studied whether genetic variation in the TLR1, TLR2, TLR4, TLR5, TLR6 and TLR10 genes confers susceptibility to GvHD in 305 human leucocyte antigen-identical sibling donor HSCT's performed in a single Finnish centre. The results showed that the genetic markers rs4833079 (P = 0.035) in TLR1, rs4837656 (P = 0.032) and rs17582214 (P = 0.029) in TLR4, rs10737416 (P = 0.048) in TLR5, rs6531656 (P = 0.035) in TLR6, and rs337629 (P = 0.005) in TLR10 were associated with the occurrence of acute GvHD. Interestingly, two markers in the TLR5 gene, rs2800230 (P = 0.010) and rs2800237 (P = 0.017), were associated with chronic GvHD. These results indicate that many genes of the TLR system are involved in the overall genetic risk for GvHD and emphasize the role of innate immunity in GvHD.