Improved outcome of hematopoietic SCT in patients with homozygous gene variant of Toll-like receptor 9

Genetic variants associated with inflammatory bowel disease and gut graft-versus-host disease

An IBD-associated locus tagged by rs1260326 is associated with gut GVHD after allogeneic HCT.

Genetic variation in anti-inflammatory activity mediated by FNDC4 within this locus could account for the association with gut GVHD.

Previous studies have identified genetic variants associated with inflammatory bowel disease (IBD). We tested the hypothesis that some of these variants are also associated with the risk of moderate to severe gut graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT). Associations were evaluated initially in a discovery cohort of 1980 HCT recipients of European ancestry with HLA-matched related or unrelated donors. Associations discovered in this cohort were tested for replication in a separate cohort of 1294 HCT recipients. Among the 296 single-nucleotide polymorphisms and 26 HLA alleles tested, we found that the recipient rs1260326 homozygous T allele in GCKR was associated with a higher risk of stage 2 to 4 gut GVHD. No other candidate variants were associated with stage 2 to 4 gut GVHD. The rs1260326 variant resides in an IBD-associated locus containing FNDC4, a gene that encodes a secreted anti-inflammatory factor that dampens macrophage activity and improves colitis in mice. Our results suggest that targeting inflammatory macrophages with recombinant FNDC4 offers an attractive avenue of clinical investigation for management of IBD and gut GVHD.

Targeting Toll-Like Receptors for Cancer Therapy

The immune system encompasses a broad array of defense mechanisms against foreign threats, including invading pathogens and transformed neoplastic cells. Toll-like receptors (TLRs) are critically involved in innate immunity, serving as pattern recognition receptors whose stimulation leads to additional innate and adaptive immune responses. Malignant cells exploit the natural immunomodulatory functions of TLRs, expressed mainly by infiltrating immune cells but also aberrantly by tumor cells, to foster their survival, invasion, and evasion of anti-tumor immune responses. An extensive body of research has demonstrated context-specific roles for TLR activation in different malignancies, promoting disease progression in certain instances while limiting cancer growth in others. Despite these conflicting roles, TLR agonists have established therapeutic benefits as anti-cancer agents that activate immune cells in the tumor microenvironment and facilitate the expression of cytokines that allow for infiltration of anti-tumor lymphocytes and the suppression of oncogenic signaling pathways. This review focuses on the clinical application of TLR agonists for cancer treatment. We also highlight agents that are undergoing development in clinical trials, including investigations of TLR agonists in combination with other immunotherapies.

The ex vivo toll-like receptor 7 tolerance induction in donor lymphocytes prevents murine acute graft-versus-host disease

BACKGROUND AIMS

Acute graft-versus-host disease (aGVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation, mediated by alloreactive donor T cells. Toll-like receptors (TLRs), a family of conserved pattern-recognition receptors (PRRs), represent key players in donors' T-cell activation during aGVHD; however, a regulatory, tolerogenic role for certain TLRs has been recognized in a different context. We investigated whether the ex vivo-induced TLR-2,-4,-7 tolerance in donor cells could prevent alloreactivity in a mismatched transplantation model.

METHODS

TLR-2,-4,-7 tolerance was induced in mouse splenocytes, after stimulation with low doses of corresponding ligands. Cellular and molecular changes of the TLR-tolerant splenocytes and purified T cells were assessed by immunophenotypic and gene expression analyses. Incidence of aGVHD was evaluated by the clinical score and survival as well as histopathology of target tissues.

RESULTS

Only the R848-induced TLR7 tolerance prevented aGVHD. The TLR7 ligand-induced tolerance lasted for a critical post-transplant period and was associated with distinct cellular and molecular signatures characterized by induction of regulatory T cells, reduced alloreactivity and balanced regulation of inflammatory signaling and innate immune responses. The TLR7-tolerant T cells preserved the immunological memory and generated in vitro virus-specific T cells upon antigen stimulation. The anti-aGVHD tolerization effect was direct and specific to TLR7 and required the receptor-ligand interaction; TLR7^-/- T cells isolated from B6 TLR7^-/- mice presented a distinct gene expression profile but failed to prevent aGVHD.

DISCUSSION

We propose an effective and clinically applicable ex vivo approach for aGVHD prevention through a transient and reversible immune reprogramming exerted by TLR7-tolerant donor lymphocytes.

Functional Toll-Like Receptor 9 Expression and CXCR3 Ligand Release in Pulmonary Sarcoidosis

Sarcoidosis is a granulomatous disease characterized by a T-helper type 1 (Th1) cell-dominated alveolitis. As a role of bacteria in the pathogenesis of sarcoidosis has been discussed, Toll-like receptors (TLRs) may be involved in the initiation of a first immune reaction. We analyzed expression and functional relevance of several TLRs in bronchoalveolar lavage (BAL) cells from patients with pulmonary sarcoidosis. In parallel, we determined the release of C-X-C motif chemokine 9 (CXCL9), CXCL10, and CXCL11 by BAL cells from patients with pulmonary sarcoidosis. Nucleotide-binding oligomerization domain-containing protein (NOD) 1 and 2, TLR2, TLR6, and TLR9 expression by BAL cells was analyzed by real-time RT-PCR and cell surface expression by flow cytometry. Chemokine release was measured in BAL cell culture supernatants by ELISA. We found increased TLR9 mRNA expression in patients with sarcoidosis with chest X-ray type I and II and TLR9 protein expression in BAL cells from patients with chest X-ray type II and III. Stimulation with CpG nucleotides increased CXCL10 release by BAL cells from patients with sarcoidosis type II significantly compared with control subjects or other patients with sarcoidosis. In contrast, no increase in TNF, IL-12p40, or CXCL8 was detected. Spontaneous release of CXCL10, but not CXCL9 or CXCL11, by cultured BAL cells was also highest in cells from patients with chest X-ray type II. We found a significant association between TLR9 expression and CD4⁺ lymphocytes in BAL. Our data demonstrate that TLR9 ligands may contribute to the immunopathogenesis of sarcoidosis via induction of CXCL10 release in the alveolar macrophages.

Sensing danger: toll-like receptors and outcome in allogeneic hematopoietic stem cell transplantation

Pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs) play key roles in initiating innate and adaptive immune responses. Based mainly on animal studies there is growing evidence to suggest that TLRs are involved in the development of chemotherapy-induced mucositis and in the propagation of graft versus host reactions as well as graft versus tumor effects in allogeneic hematopoietic stem cell transplantation (HSCT). In this review we discuss these findings along with the emerging, although still preliminary, clinical evidence, that points to a role of PRRs in determining the outcome of HSCT and new therapeutic perspectives that may be related to this development.

Danger Signals and Graft-versus-host Disease: Current Understanding and Future Perspectives

Graft-versus-host response after allogeneic hematopoietic stem cell transplantation (allo-HCT) represents one of the most intense inflammatory responses observed in humans. Host conditioning facilitates engraftment of donor cells, but the tissue injury caused from it primes the critical first steps in the development of acute graft-versus-host disease (GVHD). Tissue injuries release pro-inflammatory cytokines (such as TNF-α, IL-1β, and IL-6) through widespread stimulation of pattern recognition receptors (PRRs) by the release of danger stimuli, such as damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). DAMPs and PAMPs function as potent stimulators for host and donor-derived antigen presenting cells (APCs) that in turn activate and amplify the responses of alloreactive donor T cells. Emerging data also point towards a role for suppression of DAMP induced inflammation by the APCs and donor T cells in mitigating GVHD severity. In this review, we summarize the current understanding on the role of danger stimuli, such as the DAMPs and PAMPs, in GVHD.

Role of Toll-Like Receptor Signaling in the Pathogenesis of Graft-versus-Host Diseases

Graft-versus-host disease (GVHD) and infection are major complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and the leading causes of morbidity and mortality in HSCT patients. Recent work has demonstrated that the two complications are interdependent. GVHD occurs when allo-reactive donor T lymphocytes are activated by major histocompatibility antigens or minor histocompatibility antigens on host antigen-presenting cells (APCs), with the eventual attack of recipient tissues or organs. Activation of APCs is important for the priming of GVHD and is mediated by innate immune signaling pathways. Current evidence indicates that intestinal microbes and innate pattern-recognition receptors (PRRs) on host APCs, including both Toll-like receptors (TLRs) and nucleotide oligomerization domain (NOD)-like receptors (NLRs), are involved in the pathogenesis of GVHD. Patients undergoing chemotherapy and/or total body irradiation before allo-HSCT are susceptible to aggravated gastrointestinal epithelial cell damage and the subsequent translocation of bacterial components, followed by the release of endogenous dangerous molecules, termed pathogen-associated molecular patterns (PAMPs), which then activate the PRRs on host APCs to trigger local or systemic inflammatory responses that modulate T cell allo-reactivity against host tissues, which is equivalent to GVHD. In other words, infection can, to some extent, accelerate the progression of GVHD. Therefore, the intestinal flora's PAMPs can interact with TLRs to activate and mature APCs, subsequently activate donor T cells with the release of pro-inflammatory cytokines, and eventually, induce GVHD. In the present article, we summarize the current perspectives on the understanding of different TLR signaling pathways and their involvement in the occurrence of GVHD.

Intestinal barrier loss as a critical pathogenic link between inflammatory bowel disease and graft-versus-host disease

Compromised intestinal barrier function is a prominent feature of inflammatory bowel disease (IBD). However, links between intestinal barrier loss and disease extend much further, including documented associations with celiac disease, type I diabetes, rheumatoid arthritis, and multiple sclerosis. Intestinal barrier loss has also been proposed to have a critical role in the pathogenesis of graft-versus-host disease (GVHD), a serious, potentially fatal consequence of hematopoietic stem cell transplantation. Experimental evidence has begun to support this view, as barrier loss and its role in initiating and establishing a pathogenic inflammatory cycle in GVHD is emerging. Here we discuss similarities between IBD and GVHD, mechanisms of intestinal barrier loss in these diseases, and the crosstalk between barrier loss and the immune system, with a special focus on natural killer (NK) cells. Unanswered questions and future research directions on the topic are discussed along with implications for treatment.

Cytomegalovirus induces apoptosis in acute leukemia cells as a virus-versus-leukemia function

Cytomegalovirus (HCMV) reactivation occurs frequently after hematopoietic stem cell transplantation and is associated with an increased treatment-related mortality. Induction of apoptosis by HCMV is unusual because HCMV utilizes various strategies to prevent apoptosis in infected cells in order to delay cell death and maintain viral replication. Here we show that HCMV can infect the acute leukemia cell lines Kasumi-1 (AML) and SD-1 (BCR-ABL-positive ALL), which inhibited their proliferation and induced apoptosis in almost all cells after 14 days. Although HCMV induced a significant up-regulation of the anti-apoptotic gene cFLIP and the anti-stress gene Gadd45a, and simultaneously down-regulated the pro-apoptotic genes p53, Gadd45gamma in Kasumi-1 and SD-1 cells, we found that these anti-apoptotic mechanisms failed in HCMV-infected acute leukemia cells and apoptosis occurred via a caspase-dependent pathway. We conclude that HCMV can provide anti-leukemic effects in vitro. To determine if this phenomenon may be clinically relevant further investigations will be required.

Various forms of tissue damage and danger signals following hematopoietic stem-cell transplantation

Hematopoietic stem-cell transplantation (HSCT) is the most potent curative therapy for many malignant and non-malignant disorders. Unfortunately, a major complication of HSCT is graft-versus-host disease (GVHD), which is mediated by tissue damage resulting from the conditioning regimens before the transplantation and the alloreaction of dual immune components (activated donor T-cells and recipient’s antigen-presenting cells). This tissue damage leads to the release of alarmins and the triggering of pathogen-recognition receptors that activate the innate immune system and subsequently the adaptive immune system. Alarmins, which are of endogenous origin, together with the exogenous pathogen-associated molecular patterns (PAMPs) elicit similar responses of danger signals and represent the group of damage-associated molecular patterns (DAMPs). Effector cells of innate and adaptive immunity that are activated by PAMPs or alarmins can secrete other alarmins and amplify the immune responses. These complex interactions and loops between alarmins and PAMPs are particularly potent at inducing and then aggravating the GVHD reaction. In this review, we highlight the role of these tissue damaging molecules and their signaling pathways. Interestingly, some DAMPs and PAMPs are organ specific and GVHD-induced and have been shown to be interesting biomarkers. Some of these molecules may represent potential targets for novel therapeutic approaches.

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.

A non-interventional study of the genetic polymorphisms of NOD2 associated with increased mortality in non-alcoholic liver transplant patients

Background

Infections after liver transplantation are the main cause of death in the first year. Recent reports indicate that NOD2 gene mutations increase the risk for inflammatory bowl disease and the severity of graft-versus-host disease in bone marrow transplant patients. Data on polymorphisms in liver transplant patients are sparse. We analyzed 13 single-nucleotide polymorphisms (SNPs) of 13 different gene variants including the SNPs of NOD2 genes from liver recipients. The aim of the study was to evaluate the impact of the SNPs on dialysis-dependent kidney failure, the incidence of infections and patient survival.

Methods

During a period of 20-months, 231 patients were recruited in this non-interventional, prospective study. Thirteen different SNPs and their impact on the patients’ survival, infection rate, and use of dialysis were assessed.

Results

NOD 2 wildtype genes were protective with respect to the survival of non-alcoholic, cirrhotic transplant patients (3 year survival: 66.8% wildtype vs. 42.6% gene mutation, p = 0.026). This effect was not observed in alcoholic transplant recipients.

The incidence of dialysis-dependent kidney failure and infection in the liver transplant patients was not influenced by NOD 2 gene polymorphisms. No effect was noted in the remaining 12 SNPs.

Patients with early allograft dysfunction experienced significantly more infections, required dialysis and had significantly worse survival.

In contrast, the donor-risk-index had no impact on the infection rate, use of dialysis or survival.

Conclusion

NOD2 gene variants seem to play a key role in non-alcoholic, liver transplant recipients. However these data should be validated in a larger cohort.

Donor TLR9 gene tagSNPs influence susceptibility to aGVHD and CMV reactivation in the allo-HSCT setting without polymorphisms in the TLR4 and NOD2 genes

Owing to ethnicity of the population, those best confirmed polymorphisms in the TLR (toll-like receptor)4 and NOD2 genes with significantly prognostic impact on allogeneic hematopoietic SCT (allo-HSCT) seem to be more applicable to Europeans and are nonpolymorphic in the Asian population. The influence of innate immunity gene polymorphisms on the outcomes of allo-HSCT in those populations has been questioned. We evaluated the influence of 10 candidate single nucleotide polymorphisms (SNPs) in the TLR1, TLR2, TLR3, TLR8 and TLR9 genes on the outcomes of allo-HSCT in a Chinese population including 138 pairs of patients and unrelated donors and a second cohort of 102 pairs of patients and HLA-identical sibling donors. We found that two tagSNPs in the TLR9 gene in the donor side, +1174 A/G (rs352139) and +1635 C/T (rs352140), influenced the risk of acute GVHD (aGVHD) and CMV reactivation. Furthermore, the presence of the susceptible haplotype (A-C) in donor may be an informative predicator of worse OS at 5 years compared with those with the G-C and G-T haplotypes (58% vs 82.9%, P=0.024). Our data suggested an unrecognized association between donor TLR9 tagSNPs and the risk of HSCT-related complications in a population without polymorphisms in the TLR4 and NOD2 genes.

Pathogenesis of graft-versus-host disease: innate immunity amplifying acute alloimmune responses

In addition to reduced-intensity conditioning, which has expanded the eligibility for hematopoietic cell transplantation (HCT) to older patients, increased availability of alternative donors, including HLA-mismatched unrelated donors, has increased access to allogeneic HCT for more patients. However, acute graft-versus-host disease (GVHD) remains a lethal complication, even in HLA-matched donor-recipient pairs. The pathophysiology of GVHD depends on aspects of adaptive immunity and interactions between donor T-cells and host dendritic cells (DCs). Recent work has revealed that the role of other immune cells and endothelial cells and components of the innate immune response are also important. Tissue damage caused by the conditioning regimen leads to the release of exogenous and endogenous "danger signals". Exogenous danger signals called pathogen-associated molecular patterns and endogenous noninfectious molecules known as damage-associated molecular patterns (DAMPs) are responsible for initiating or amplifying acute GVHD by enhancing DC maturation and alloreactive T-cell responses. A significant association of innate immune receptor polymorphisms with outcomes, including GVHD severity, was observed in patients receiving allogeneic HCT. Understanding of the role of innate immunity in acute GVHD might offer new therapeutic approaches.

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.

Profile of toll-like receptors on peripheral blood cells in relation to acute graft-versus-host disease after allogeneic stem cell transplantation

Toll-like receptors (TLRs) play a key role in the cross-talk between the innate and adaptive immune systems. Previous studies investigating associations between certain TLRs and acute graft-versus-host disease (aGVHD) have reported contrasting results, and no studies relating aGVHD to the expression and function of all human TLRs together have been published to date. We prospectively evaluated the expression of 9 TLRs on T lymphocytes and monocytes by flow cytometry in relation to aGVHD in 34 patients. Induction of TNF-α, IL-4, IFN-γ, and monocyte chemotactic protein 1 on TLR activation was assessed by ELISA on cell supernatants. Nineteen patients developed aGVHD, at a median time of 28 days (range, 20-50 days) after transplantation. A 2-step multivariate analysis was performed using principal component analysis and multifactor analysis of variance. The levels of TLR-5 expression on monocytes and T lymphocytes were positively correlated to aGVHD (P = .01), whereas levels of TLR-1 and -9 were negative predictors (P = .03 and .01, respectively). This profile of TLR-1, -5, and -9 can promote an overall immunostimulatory/proinflammatory response. If our findings are confirmed by further studies, this TLR profile could be a useful biomarker of aGVHD.

Association analysis of the NOD2 gene with susceptibility to graft-versus-host disease in a Japanese population

Members of the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family participate in the innate immune system, exerting widespread effects on cytokine secretion, autophagy, and apoptosis. Recent studies in Caucasians revealed the association between mutants of NOD2, a member of the NLR family, and severity of acute graft-versus-host disease (GVHD). NOD2 polymorphism screening has been recommended for donor selection and risk assessment at bone marrow transplantation. To investigate whether NOD2 plays a role in the pathogenesis of GVHD in a Japanese population, we examined DNA from 142 bone marrow transplant patient/donor pairs to detect genetic variation in the NOD2 gene. No genetic variants of NOD2 were associated with the severity of acute GVHD in our patients. However, a weak association between a single nucleotide polymorphism in the NOD2 gene (R471C) and acute myeloid leukemia in the bone marrow patients (p = 0.029, odds ratio 4.08, 95% CI 1.22-13.67) was detected. This polymorphism was not prevalent in 479 Crohn's disease (CD) patients in Japan. These results suggest that, in the Japanese population, unlike the Caucasian, NOD2 is not a major contributor to susceptibility to severe acute GVHD.

The role of bacteria and pattern recognition receptors in GVHD

Graft-versus-Host Disease (GvHD) is the most serious complication of allogeneic stem cell transplantation (SCT) and results from an activation of donor lymphocytes by recipient antigen-presenting cells (APCs). For a long time, it has been postulated that the intestinal microflora and endotoxin exert a crucial step in this APC activation, as there is early and severe gastrointestinal damage induced by pretransplant conditioning. With the detailed description of pathogen-associated molecular patterns and pathogen recognition receptors single nucleotide polymorphisms of TLRs and especially NOD2 have been identified as potential risk factors of GvHD and transplant related complications thus further supporting the crucial role of innate immunity in SCT, related complications. Gastrointestinal decontamination and neutralization of endotoxin have been used to interfere with this early axis of activation with some success but more specific approaches of modulation of innate immunity are needed for further improvement of clinical outcome.