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

Allogenic stem cell transplant-associated acute graft versus host disease: a computational drug discovery text mining approach using oral and gut microbiome signatures

PURPOSE

Acute graft versus host disease (aGVHD) is a major cause of non-relapse morbidity and mortality post-allogenic hematopoietic stem cell transplant (HSCT). Using conventional literature search and computational approaches, our objective was to identify oral and gut bacterial species associated with aGVHD, potentially affecting drug treatment via lipopolysaccharide (LPS) pathways.

METHODS

Medline, PubMed, PubMed Central, and Google Scholar were searched using MeSH terms. The top 100 hits per database were curated, and 25 research articles were selected to examine oral and gut microbiomes associated with health, HSCT, and aGVHD. Literature search validation, aGVHD drug targets, and microbial metabolic pathway identification were completed using BioReader, MACADAM, KEGG, and STRING programs.

RESULTS

Our review determined that (1) oral genera Rothia, Solobacterium, and Veillonella were identified in HSCT patients' stool and associated with aGVHD; (2) shifts in gut enterococci profiles were determined in HSCT-associated aGVHD; (3) gut microbiome dysbiosis prior or during HSCT and lower Shannon diversity index at time of HSCT were also associated with increased risk of aGVHD and transplant related death; and (4) Coriobacteriaceae family was negatively correlated with gut aGVHD, whereas Eubacterium limosum was associated with decreased risk of chronic GVHD relapse. Additionally, we identified molecular pathways related to TLR4/ LPS, including candidate aGVHD drug targets, impacted by oral and gut bacterial taxa.

CONCLUSION

Reduced microbial diversity reflects higher severity and mortality rate in HSCT patients with aGVHD. Multi-omics approaches to decipher oral and gut microbiome associations will be critical for developing aGVHD preventive therapies.

Differential regulation of claudin-2 and claudin-15 expression in children and adults with malabsorptive disease

Intestinal Na+-nutrient cotransport depends on claudin-2 and claudin-15 mediated Na+ recycling. Expression of these proteins is coordinately regulated during postnatal development. While expression of claudin-2 and claudin-15 has been studied in inflammatory bowel disease (IBD) and celiac disease (CD), it has not been assessed in other malabsorptive diseases, and no reports have compared expression in children and adults. We used quantitative immunofluorescence microscopy to assess claudin-2 and claudin-15 expression in duodenal biopsies from children and adults with malabsorptive disease and healthy controls. Consistent with previous work in rodents, claudin-2 expression in healthy children was markedly greater, and claudin-15 expression was less, than that in adults. Claudin-2 expression was increased in adults with CD and downregulated in children with graft-versus-host disease (GVHD). In contrast, claudin-15 expression was reduced in adults with GVHD and common variable immunodeficiency (CVID). These data show that one of the two Na+/water pore-forming claudins is upregulated in CD and downregulated in GVHD and CVID. The specific claudin whose expression changes, however, reflects the age of the patient (child or adult). We conclude that contributions of claudin-2 and claudin-15 to pathophysiology of and responses to diarrhea in children and adults with GVHD and CVID differ from those in CD and IBD.

Toll-Like Receptor Stimulation by MicroRNAs in Acute Graft-vs.-Host Disease

Acute graft-vs.-host disease (aGVHD) is a frequent complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT), accounting for substantial morbidity and mortality associated with this treatment modality. The pathogenesis of aGVHD involves a complex cascade of humoral and cellular interactions in which donor T cells target HLA mismatched host tissues, causing tissue injury through secretion of pro-inflammatory cytokines and induction of direct cytotoxicity. Toll-like receptors (TLRs) are key components of the innate immune system that recognize endogenous danger-associated molecular patterns (DAMPs) and exogenous pathogen-associated molecular patterns (PAMPs). Patients receiving conditioning chemotherapy and/or whole-body irradiation prior to all-HSCT are prone to gastrointestinal damage and translocation of microbiota across compromised intestinal epithelium, resulting in release of PAMPs and DAMPs. These “danger signals” play critical roles in disease pathogenesis by both initiating and propagating aGVHD through dendritic cell maturation and alloreactive T cell responses. There are 10–15 TLRs identified in mammalian species, a subset of which recognize single-stranded RNA (ssRNA) and serve as a key component of viral immunity. Recently, ssRNAs other than those of viral origin have been investigated as potential ligands of TLRs. MicroRNAs (miRs) are short (19–24 nt) non-coding RNAs that play critical roles in a variety of diseases. While traditionally miRs post-translationally modulate gene expression, non-canonical functions such as regulating TLR stimulation by acting as TLR ligands have been described. Here, we review the role of TLRs in aGVHD pathogenesis, the function of miRs in TLR stimulation, and the recent literature describing miRs as TLR ligands in aGVHD.

Toll-like Receptor 4 Single-Nucleotide Polymorphisms and Heart Transplant Rejection

BACKGROUND

Transplant rejection is one of the major problems after heart transplantation (HTx). The aim of the study was to find possible links between chosen single-nucleotide polymorphisms (SNPs) of Toll-like receptor 4 (TLR4) and heart transplant rejection.

MATERIAL AND METHODS

Blood samples were taken from 24 patients subjected to HTx between 2010 and 2016 at the Clinic of Cardiac Surgery and Transplantation and under the control of I Clinic of Cardiology. All the patients were permanently controlled and had therapeutic levels of immunosuppressants in their blood. Their DNA was isolated and analyzed using the high-resolution melting method according to the Toll-like receptor 4 SNPs rs10983755 A/G, rs4986791 C/T, rs4986790 A/G, rs10759932 C/T, rs1927911 C/T, rs11536889 C/G, and rs12377632 C/T. The analysis of the clinical data of biopsies according to International Society for Heart and Lung Transplantation classification was derived from the patients' medical history, divided into two groups: 0-1b and 2-4. A statistical analysis was then performed.

RESULTS

The results obtained showed no association between analyzed SNPs and rejection. For rs10983755 A/G, P = .85; rs4986791 C/T, rs4986790 A/G, and rs1927911 C/T had P = .35; and rs10759932 C/T, rs11536889 C/G, and rs12377632 C/T had P = 1.

CONCLUSIONS

No association between the SNPs rs10983755 A/G, rs4986791 C/T, rs4986790 A/G, rs10759932 C/T, rs1927911 C/T, rs11536889 C/G, and rs12377632 C/T and heart transplant rejection was found, but further investigation is suggested for TLR4 SNPs with P < .5.

Genetic polymorphism related to monocyte-macrophage function is associated with graft-versus-host disease

Despite detailed human leukocyte antigen (HLA) matching and modern immunosuppressive therapy, severe graft-versus-host disease (GvHD) remains a major hurdle for successful allogeneic hematopoietic stem cell transplantation (HSCT). As the genetic diversity in GvHD complicates the systematic discovery of associated variants across populations, we studied 122 GvHD-associated single nucleotide polymorphisms (SNPs) in 492 HLA-matched sibling HSCT donor-recipient pairs from Finland and Spain. The association between these candidate SNPs and grade III–IV acute GvHD and extensive chronic GvHD was assessed. The functional effects of the variants were determined using expression and cytokine quantitative trait loci (QTL) database analyses. Clear heterogeneity was observed in the associated markers between the two populations. Interestingly, the majority of markers, such as those annotated to IL1, IL23R, TLR9, TNF, and NOD2 genes, are related to the immunological response by monocytes-macrophages to microbes, a step that precedes GvHD as a result of intestinal lesions. Furthermore, cytokine QTL analysis showed that the GvHD-associated markers regulate IL1β, IFNγ, and IL6 responses. These results support a crucial role for the anti-microbial response in GvHD risk. Furthermore, despite apparent heterogeneity in the genetic markers associated with GvHD, it was possible to identify a biological pathway shared by most markers in both populations.

TLR/MyD88-mediated Innate Immunity in Intestinal Graft-versus-Host Disease

Graft-versus-host disease (GHVD) is a severe complication after allogeneic hematopoietic stem cell transplantation. The degree of inflammation in the gastrointestinal tract, a major GVHD target organ, correlates with the disease severity. Intestinal inflammation is initiated by epithelial damage caused by pre-conditioning irradiation. In combination with damages caused by donor-derived T cells, such damage disrupts the epithelial barrier and exposes innate immune cells to pathogenic and commensal intestinal bacteria, which release ligands for Toll-like receptors (TLRs). Dysbiosis of intestinal microbiota and signaling through the TLR/myeloid differentiation primary response gene 88 (MyD88) pathways contribute to the development of intestinal GVHD. Understanding the changes in the microbial flora and the roles of TLR signaling in intestinal GVHD will facilitate the development of preventative and therapeutic strategies.

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.

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.

Non-HLA genomics: does it have a role in predicting haematopoietic stem cell transplantation outcome?

Haematopoietic stem cell transplantation (HSCT) remains the only cure for many haematological neoplasms; however, the mortality rate remains high, at around 30-80%. Complications after HSCT include relapse, graft-versus-host disease, graft rejection and infection. High-resolution HLA matching has improved survival in HSCT over recent years; however, GVHD still remains a serious complication. Single nucleotide polymorphisms (SNPS) within genes that are involved with an individual's capability to mount an immune response to infectious pathogens, residual leukaemia, alloantigens or genes involved in drug metabolism have been studied for their association with HSCT outcome. Indeed, over the last 15 years, several groups, including ourselves, have demonstrated that non-HLA gene polymorphisms can be predictive of HSCT outcome. Can genetic characteristics of the patient and donor be used in the future to tailor HSCT protocols and determine GVHD prophylaxis? This review summarizes some of the recent SNP association studies in HSCT and highlights some of the disparities therein, discussing the integral problems of performing genetic association studies on diseases with complex outcomes using heterogeneous cohorts. The review will comment on recent genomewide association studies (GWAS) and discuss their relevance in this field, and it will also comment on recent meta-analysis combining GWAS studies with other studies such as gene expression micro array data in the field of autoimmune disease and solid organ transplantation. It will mention possible novel candidate gene polymorphisms, for example SNPS in microRNAs. In addition, it will discuss some of the inherent problems associated with gene association studies including the GRIPs (genetic risk prediction studies) recommendations. In summary, this review will assess the usefulness of non-HLA genomic studies in HSCT with regard to predicting outcome and modifying therapy.

Recipient NK cell inactivation and intestinal barrier loss are required for MHC-matched graft-versus-host disease

Previous studies have shown a correlation between pretransplant conditioning intensity, intestinal barrier loss, and graft-versus-host disease (GVHD) severity. However, because irradiation and other forms of pretransplant conditioning have pleiotropic effects, the precise role of intestinal barrier loss in GVHD pathogenesis remains unclear. We developed GVHD models that allowed us to isolate the specific contributions of distinct pretransplant variables. Intestinal damage was required for the induction of minor mismatch [major histocompatibility complex (MHC)-matched] GVHD, but was not necessary for major mismatch GVHD, demonstrating fundamental pathogenic distinctions between these forms of disease. Moreover, recipient natural killer (NK) cells prevented minor mismatch GVHD by limiting expansion and target organ infiltration of alloreactive T cells via a perforin-dependent mechanism, revealing an immunoregulatory function of MHC-matched recipient NK cells in GVHD. Minor mismatch GVHD required MyD88-mediated Toll-like receptor 4 (TLR4) signaling on donor cells, and intestinal damage could be bypassed by parenteral lipopolysaccharide (LPS) administration, indicating a critical role for the influx of bacterial components triggered by intestinal barrier loss. In all, the data demonstrate that pretransplant conditioning plays a dual role in promoting minor mismatch GVHD by both depleting recipient NK cells and inducing intestinal barrier loss.

Toll-like receptor polymorphisms in allogeneic hematopoietic cell transplantation

To assess the impact of the genetic variation in toll-like receptors (TLRs) on outcome after allogeneic myeloablative conditioning hematopoietic cell transplantation (HCT), we investigated 29 single nucleotide polymorphisms across 10 TLRs in 816 patients and donors. Only donor genotype of TLR8 rs3764879, which is located on the X chromosome, was significantly associated with outcome at the Bonferroni-corrected level P ≤ .001. Male hemizygosity and female homozygosity for the minor allele were significantly associated with disease-free survival (hazard ratio [HR], 1.47 [95% confidence interval {CI}, 1.16 to 1.85]; P = .001). Further analysis stratified by donor sex due to confounding by sex was suggestive for associations with overall survival (male donor: HR, 1.41 [95% CI, 1.09 to 1.83], P = .010; female donor: HR, 2.78 [95% CI, 1.43 to 5.41], P = .003), disease-free survival (male donor: HR, 1.45 [95% CI, 1.12 to 1.87], P = .005; female donor: HR, 2.34 [95% CI, 1.18 to 4.65], P = .015), and treatment-related mortality (male donor: HR, 1.49 [95% CI, 1.09 to 2.04], P = .012; female donor: HR, 3.12 [95% CI, 1.44 to 6.74], P = .004). In conclusion, our findings suggest that the minor allele of TLR8 rs3764879 of the donor is associated with outcome after myeloablative conditioned allogeneic HCT.

Complete suppression of the gut microbiome prevents acute graft-versus-host disease following allogeneic bone marrow transplantation

The hypothesis that elimination of facultative and strict anaerobic microorganisms from the gastro-intestinal tract by antimicrobial drugs in the period of time around allogeneic bone marrow transplantation (BMT) prevents acute graft-versus-host disease (GVHD), was examined in a cohort of 112 children grafted between 1989 and 2002 for hematological malignancies. All patients received T-cell replete marrow from human leukocyte antigens (HLA) matched sibling donors under identical transplantation conditions. To eliminate microorganisms from the gastro-intestinal tract, total gastro-intestinal decontamination (GID) was applied by high doses of non-absorbable antimicrobial drugs while the graft recipient was maintained in strict protective isolation. About half of the children (51%) proved to be successfully decontaminated, and about half (49%) unsuccessfully. One recipient got acute GVHD in the first group and 8 in the second group (p = 0.013). The degree of success of total GID was decisive for the occurrence of acute GVHD, irrespective of the presence of other risk factors such as higher age of recipient and/or donor, female donor for male recipient and carriership or reactivation of herpesviruses. Our results demonstrate that successful total GID of the graft recipient prevents moderate to severe acute GVHD. We suppose that substantial translocation of gastro-intestinal microorganisms or parts of these, functioning as microbial-associated molecular patterns (MAMP's), triggering macrophages/dendritic cells via pattern recognizing receptors (PRR's) is prohibited. As a consequence the initiation and progression of an inflammatory process leading to acute GVHD is inhibited.

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.

The genetics of innate immunity sensors and human disease

Since their discovery, innate immunity microbial sensors have been increasingly studied and shown to play a critical role in innate responses to microbes in several experimental in vitro, ex vivo, and animal models. However, their role in the human response to infection in natural conditions has just started to be deciphered, by means of clinical studies of primary immunodeficiencies and epidemiological genetic studies. Here, we summarize the major findings concerning the genetic diversity of the various families of microbial sensors in humans, and of other molecules involved in the signaling pathways they trigger. Specifically, we review the genetic associations, revealed by both clinical and epidemiological genetics studies, of microbial sensors from five different families: Toll-like receptors, C-type lectin receptors, NOD-like receptors, RIG-I-like receptors, and cytosolic DNA sensors. In particular, we consider the relationships between variation at the genes encoding these molecules and susceptibility to and the severity of infectious diseases and other clinical conditions associated with immune dysfunction, including autoimmunity, inflammation, allergy, and cancer. Despite the fact that the genetic links between innate immunity sensors and human disorders remain still limited, human genetics studies are increasingly improving our understanding of the genuine functions of microbial sensors and downstream signaling molecules in the natural setting.

Toll-like receptors' pathway disturbances are associated with increased susceptibility to infections in humans

Toll-like receptors (TLRs) sense microbial products and play an important role in innate immunity. Currently, 11 members of TLRs have been identified in humans, with important function in host defense in early steps of the inflammatory response. TLRs are present in the plasma membrane (TLR1, TLR2, TLR4, TLR5, TLR6) and endosome (TLR3, TLR7, TLR8, TLR9) of leukocytes. TLRs and IL-1R are a family of receptors related to the innate immune response that contain an intracellular domain known as the Toll-IL-1R (TIR) domain that recruits the TIR-containing cytosolic adapters MyD88, TRIF, TIRAP and TRAM. The classical pathway results in the activation of both nuclear factor κB and MAPKs via the IRAK complex, with two active kinases (IRAK-1 and IRAK-4) and two non-catalytic subunits (IRAK-2 and IRAK-3/M). The classical pro-inflammatory TLR signaling pathway leads to the synthesis of inflammatory cytokines and chemokines, such as IL-1β, IL-6, IL-8, IL-12 and TNF-α. In humans, genetic defects have been identified that impair signaling of the TLR pathway and this may result in recurrent pyogenic infections, as well as virus and fungi infections. In this review, we discuss the main mechanisms of microbial recognition and the defects involving TLRs.

Role of non-HLA gene polymorphisms in graft-versus-host disease

A large number of reports have associated various non-HLA gene polymorphisms with the risk and severity of graft-versus-host disease (GVHD). To date, candidate gene studies and genome-wide association studies have been performed to investigate such non-HLA gene polymorphisms in relation to GVHD. Candidate gene studies are hypothesis-driven and cost-effective, whereas genome-wide association studies have the potential to discover new gene polymorphisms, including possible biomarkers and therapeutic targets. Some gene polymorphisms have the potential to affect protein function or gene expression, or to encode minor histocompatibility antigens. Non-HLA genotyping for genes influencing GVHD prior to transplantation should provide useful information that will facilitate choosing the donor, type of graft, conditioning treatment, and GVHD prophylaxis. However, attention should be paid to the need for validation studies and ethical issues.

Toll-like receptor polymorphisms, inflammatory and infectious diseases, allergies, and cancer

Toll-like receptors (TLRs) are germ-line-encoded innate immune sensors that recognize conserved microbial structures and host alarmins and signal expression of MHC proteins, costimulatory molecules, and inflammatory mediators by macrophages, neutrophils, dendritic cells, and other cell types. These processes activate immediate and early mechanisms of innate host defense, as well as initiate and orchestrate adaptive immune responses. Several single-nucleotide polymorphisms (SNPs) within the TLR genes have been associated with altered susceptibility to infectious, inflammatory, and allergic diseases, and have been found to play a role in tumorigenesis. Critical advances in our understanding of innate immune functions and genome-wide association studies (GWAS) have uncovered complex interactions of genetic polymorphisms within TLRs and environmental factors. However, conclusions obtained in the course of such analyses are restricted by limited power of many studies that is likely to explain controversial findings. Further, linkages to certain ethnic backgrounds, gender, and the presence of multigenic effects further complicate the interpretations of how the TLR SNPs affect immune responses. For many TLRs, the molecular mechanisms by which SNPs impact receptor functions remain unknown. In this review, I have summarized current knowledge about the TLR polymorphisms, their impact on TLR signaling, and associations with various inflammatory, infectious, allergic diseases and cancers, and discussed the directions of future scientific research.