Flagellin, a TLR5 agonist, reduces graft-versus-host disease in allogeneic hematopoietic stem cell transplantation recipients while enhancing antiviral immunity

Rapamycin immunomodulation utilizes time-dependent alterations of lymph node architecture, leukocyte trafficking, and gut microbiome

Transplant recipients require lifelong, multimodal immunosuppression to prevent rejection by reducing alloreactive immunity. Rapamycin is known to modulate adaptive and innate immunity, but its full mechanism remains incompletely understood. We investigated the understudied effects of rapamycin on lymph node (LN) architecture, leukocyte trafficking, and gut microbiome and metabolism after 3 (early), 7 (intermediate), and 30 (late) days of rapamycin treatment. Rapamycin significantly reduced CD4+ T cells, CD8+ T cells, and Tregs in peripheral LNs, mesenteric LNs, and spleen. Rapamycin induced early proinflammation transition to protolerogenic status by modulating the LN laminin α4/α5 expression ratios (La4/La5) through LN stromal cells, laminin α5 expression, and adjustment of Treg numbers and distribution. Additionally, rapamycin shifted the Bacteroides/Firmicutes ratio and increased amino acid bioavailability in the gut lumen. These effects were evident by 7 days and became most pronounced by 30 days in naive mice, with changes as early as 3 days in allogeneic splenocyte-stimulated mice. These findings reveal what we believe to be a novel mechanism of rapamycin action through time-dependent modulation of LN architecture and gut microbiome, which orchestrates changes in immune cell trafficking, providing a framework for understanding and optimizing immunosuppressive therapies.

The intestinal microbiota and cellular therapy: implications for impact and mechanisms

ABSTRACT

The microbiota, comprising bacteria, fungi, and viruses residing within our bodies, functions as a key modulator in host health and states, including immune responses. Studies have linked microbiota and microbiota-derived metabolites to immune cell functions. In this review, we probe the complex relationship between the human microbiota and clinical outcomes of cellular therapies that leverage immune cells to fight various cancers. With a particular emphasis on hematopoietic cell transplantation and chimeric antigen receptor T-cell therapy, we explore the potential mechanisms underpinning this interaction. We also highlight the interventional applications of the microbiota in cellular therapy while outlining future research directions in the field.

Early Immunomodulatory Program Triggered by Protolerogenic Bifidobacterium pseudolongum Drives Cardiac Transplant Outcomes

BACKGROUND

Despite ongoing improvements to regimens preventing allograft rejection, most cardiac and other organ grafts eventually succumb to chronic vasculopathy, interstitial fibrosis, or endothelial changes, and eventually graft failure. The events leading to chronic rejection are still poorly understood and the gut microbiota is a known driving force in immune dysfunction. We previously showed that gut microbiota dysbiosis profoundly influences the outcome of vascularized cardiac allografts and subsequently identified biomarker species associated with these differential graft outcomes.

METHODS

In this study, we further detailed the multifaceted immunomodulatory properties of protolerogenic and proinflammatory bacterial species over time, using our clinically relevant model of allogenic heart transplantation.

RESULTS

In addition to tracing longitudinal changes in the recipient gut microbiome over time, we observed that Bifidobacterium pseudolongum induced an early anti-inflammatory phenotype within 7 d, whereas Desulfovibrio desulfuricans resulted in a proinflammatory phenotype, defined by alterations in leukocyte distribution and lymph node (LN) structure. Indeed, in vitro results showed that B pseudolongum and D desulfuricans acted directly on primary innate immune cells. However, by 40 d after treatment, these 2 bacterial strains were associated with mixed effects in their impact on LN architecture and immune cell composition and loss of colonization within gut microbiota, despite protection of allografts from inflammation with B pseudolongum treatment.

CONCLUSIONS

These dynamic effects suggest a critical role for early microbiota-triggered immunologic events such as innate immune cell engagement, T-cell differentiation, and LN architectural changes in the subsequent modulation of protolerant versus proinflammatory immune responses in organ transplant recipients.

Current Advances in Graft-versus-host Disease After Intestinal Transplantation

Graft-versus-host disease (GvHD) remains a potentially fatal complication following intestinal transplant (ITx). Over the past decade, advances in the understanding of the pathophysiology of this complex immunological phenomenon have led to the reassessment of the host systemic immune response and have created a gateway for novel preventive and therapeutic strategies. Although sufficient evidence dictates the use of corticosteroids as a first-line option, the treatment for refractory disease remains contentious and lacks a standardized therapeutic approach. Timely diagnosis remains crucial, and the advent of chimerism detection and immunological biomarkers have transformed the identification, prognostication, and potential for survival after GvHD in ITx. The objectives of the following review aim to discuss the clinical and diagnostic features, pathophysiology, advances in immune biomarkers, as well as therapeutic opportunities in the prevention and treatment of GvHD in ITx.

Association of polymorphous light eruption with NOD-2 and TLR-5 gene polymorphisms

BACKGROUND

Polymorphous light eruption (PLE) is a common, immunologically mediated, photosensitive skin disease. After ultraviolet-B (UV-B) irradiation, patients with PLE show reduced Langerhans cell (LC) depletion in the epidermis, which results in a non-suppressive microenvironment in the skin. Interestingly, severe acute graft-versus-host-disease (aGvHD) occurred in stem cell transplanted patients that showed no or incomplete depletion of LCs after UVB-irradiation. Genetic variation in nucleotide-binding oligomerization domain 2 (NOD-2) and toll-like receptor 5 (TLR-5) genes also confers susceptibility to aGvHD.

OBJECTIVES

We hypothesized that PLE is associated with genetic variation in the NOD-2 and TLR-5 genes.

METHODS

We investigated single nucleotid polymorphisms (SNPs) of NOD-2 (R702W, G908R, 3020Cins) and TLR-5 (A592S, P616L, N392STOP) in skin biopsies of PLE-patients (n=143) and in healthy controls (n=104) using restriction fragment-length polymorphism analysis.

RESULTS

The frequency of NOD-2 alleles with the SNP R702W was significantly higher in PLE than in controls (31.8% vs 6.3%; p<0.0001), and homozygous carriers of this mutation were more common in PLE (27.9% vs 0%; p<0.0001). For SNP 3020Cins, the allele frequency (7.3% vs 0.7%; p=0.0025) and the number of heterozygotes (14.7% vs 1.3%; p=0.0019) were higher in PLE. The frequency of alleles with the N392STOP SNP of the TLR5 gene, which is associated with a truncated, non-functional receptor, was significantly higher in PLE (21% vs 5%; 7% vs 1% homozygotes, 28% vs 8% heterozygotes; p<0.0001). The other SNPs did not differ significantly.

CONCLUSIONS

This study yielded a high frequency of functional SNPs in the NOD-2 and TLR-5 genes in PLE. The same SNPs are associated with aGvHD and there are similarities in the reaction of LCs after UVB-irradiation between aGvHD and PLE. This leads to the hypothesis that PLE-patients may be more susceptible to developing GvHD after stem-cell transplantation, an assumption that needs to be investigated further.

Challenges and opportunities targeting mechanisms of epithelial injury and recovery in acute intestinal graft-versus-host disease

Despite advances in immunosuppressive prophylaxis and overall supportive care, gastrointestinal (GI) graft-versus-host disease (GVHD) remains a major, lethal side effect after allogeneic hematopoietic stem cell transplantation (allo-HSCT). It has become increasingly clear that the intestinal epithelium, in addition to being a target of transplant-related toxicity and GVHD, plays an important role in the onset of GVHD. Over the last two decades, increased understanding of the epithelial constituents and their microenvironment has led to the development of novel prophylactic and therapeutic interventions, with the potential to protect the intestinal epithelium from GVHD-associated damage and promote its recovery following insult. In this review, we will discuss intestinal epithelial injury and the role of the intestinal epithelium in GVHD pathogenesis. In addition, we will highlight possible approaches to protect the GI tract from damage posttransplant and to stimulate epithelial regeneration, in order to promote intestinal recovery. Combined treatment modalities integrating immunomodulation, epithelial protection, and induction of regeneration may hold the key to unlocking mucosal recovery and optimizing therapy for acute intestinal GVHD.

Effects of four different adjuvants separately combined with Aeromonas veronii inactivated vaccine on haematoimmunological state, enzymatic activity, inflammatory response and disease resistance in crucian carp

The purpose of the current study was to explore the immunomodulatory effects of different adjuvants combined with inactivated vaccines under Aeromonas veronii TH0426 infection in crucian carp. This study explored the best conditions for A. veronii as an inactivated vaccine, and included an animal safety test. Furthermore, we expressed the flagellin FlaA of the A. veronii TH0426 strain for use as an adjuvant supplemented in the diet. Crucian carp were fed 12 different experimental diets for 35 days, including the administration of 10 different adjuvants and inactivated vaccine combinations (50% aluminum hydroxide gel and inactivated vaccine combination, and inactivated vaccine with 20%, 30%, or 50% glucan, astragalus polysaccharide or flagellin), inactivated vaccine alone, and PBS control without adjuvant and inactivated vaccine. After the 42 day feeding trials, the fish were challenged with A. veronii TH0426, and the survival rate over 14 days was recorded. In addition, flagellin FlaA can be expressed normally in large amounts. All experimental groups produced higher levels of IgM serum titres than the control group in the different feeding cycles. Moreover, the activity of serum ACP, AKP, SOD, and LZM, and the expression of inflammatory factors were significantly increased in the experimental groups compared with the control group. The results of qRT-PCR analysis showed that the transcription levels of the IL-10, IL-1β, IFN-γ and TNF-α genes in heart, liver, spleen and kidney tissues were significantly enhanced by adjuvant treatment, indicating that the addition of adjuvants can significantly promote the body's inflammatory response. In addition, the phagocytic activity of leukocytes in each adjuvant treated group was significantly enhanced compared to that in the groups without adjuvant. After the A. veronii challenge, the survival rate of all adjuvant-treated groups was significantly higher than that of the control group, and the 50% flagellin adjuvant group had the highest rate of 78.37%. Overall, our findings strongly indicate that adjuvants not only significantly improve the body's immunity, but also exhibit a strong anti-infection ability. Importantly, this work provides a new perspective for the prevention and control of aquaculture diseases.

Roles of the intestinal microbiota and microbial metabolites in acute GVHD

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is one of the most curative strategies for the treatment of many hematologic malignancies and diseases. However, acute graft-versus-host disease (GVHD) limits the success of allo-HSCT. The prevention and treatment of acute GVHD is the key issue for improving the efficacy of allo-HSCT and has become a research hotspot. The intestine is the primary organ targeted by acute GVHD, and the intestinal microbiota is critical for maintaining the homeostasis of the intestinal microenvironment and the immune response. Many studies have demonstrated the close association between the intestinal microbiota and the pathogenesis of acute GVHD. Furthermore, dysbiosis of the microbiota, which manifests as alterations in the diversity and composition of the intestinal microbiota, and alterations of microbial metabolites are pronounced in acute GVHD and associated with poor patient prognosis. The microbiota interacts with the host directly via microbial surface antigens or microbiota-derived metabolites to regulate intestinal homeostasis and the immune response. Therefore, intervention strategies targeting the intestinal microbiota, including antibiotics, prebiotics, probiotics, postbiotics and fecal microbiota transplantation (FMT), are potential new treatment options for acute GVHD. In this review, we discuss the alterations and roles of the intestinal microbiota and its metabolites in acute GVHD, as well as interventions targeting microbiota for the prevention and treatment of acute GVHD.

Synergistic effect of the TLR5 agonist CBLB502 and its downstream effector IL-22 against liver injury

The toll-like receptor 5 (TLR5) agonist, CBLB502/Entolimod, is a peptide derived from bacterial flagellin and has been shown to protect against radiation-induced tissue damage in animal models. Here we investigated the protective mechanism of CBLB502 in the liver using models of ischemia-reperfusion injury and concanavalin A (ConA) induced immuno-hepatitis. We report that pretreatment of mice with CBLB502 provoked a concomitant activation of NF-κB and STAT3 signaling in the liver and reduced hepatic damage in both models. To understand the underlying mechanism, we screened for cytokines in the serum of CBLB502 treated animals and detected high levels of IL-22. There was no transcriptional upregulation of IL-22 in the liver, rather it was found in extrahepatic tissues, mainly the colon, mesenteric lymph nodes (MLN), and spleen. RNA-seq analysis on isolated hepatocytes demonstrated that the concomitant activation of NF-κB signaling by CBLB502 and STAT3 signaling by IL-22 produced a synergistic cytoprotective transcriptional signature. In IL-22 knockout mice, the loss of IL-22 resulted in a decrease of hepatic STAT3 activation, a reduction in the cytoprotective signature, and a loss of hepatoprotection following ischemia-reperfusion-induced liver injury. Taken together, these findings suggest that CBLB502 protects the liver by increasing hepatocyte resistance to acute liver injury through the cooperation of TLR5-NF-κB and IL-22-STAT3 signaling pathways.

The Butyrogenic and Lactic Bacteria of the Gut Microbiota Determine the Outcome of Allogenic Hematopoietic Cell Transplant

Graft versus host disease (GVHD) is a post-transplant pathology in which donor-derived T cells present in the Peyer's patches target the cell-surface alloantigens of the recipient, causing host tissue damages. Therefore, the GVHD has long been considered only a purely immunological process whose prevention requires an immunosuppressive treatment. However, since the early 2010s, the impact of gut microbiota on GVHD has received increased attention. Both a surprising fall in gut microbiota diversity and a shift toward Enterobacteriaceae were described in this disease. Recently, unexpected results were reported that further link GVHD with changes in bacterial composition in the gut and disruption of intestinal epithelial tight junctions leading to abnormal intestinal barrier permeability. Patients receiving allogenic hematopoietic stem cell transplant (allo-HCT) as treatment of hematologic malignancies showed a decrease of the overall diversity of the gut microbiota that affects Clostridia and Blautia spp. and a predominance of lactic acid bacteria (LAB) of the Enterococcus genus, in particular the lactose auxotroph Enterococcus faecium. The reduced microbiota diversity (likely including Actinobacteria, such as Bifidobacterium adolescentis that cross feed butyrogenic bacteria) deprives the butyrogenic bacteria (such as Roseburia intestinalis or Eubacterium) of their capacity to metabolize acetate to butyrate. Indeed, administration of butyrate protects against the GVHD. Here, we review the data highlighting the possible link between GVHD and lactase defect, accumulation of lactose in the gut lumen, reduction of Reg3 antimicrobial peptides, narrower enzyme equipment of bacteria that predominate post-transplant, proliferation of En. faecium that use lactose as metabolic fuels, induction of innate and adaptive immune response against these bacteria which maintains an inflammatory process, elevated expression of myosin light chain kinase 210 (MLCK210) and subsequent disruption of intestinal barrier, and translocation of microbial products (lactate) or transmigration of LAB within the liver. The analysis of data from the literature confirms that the gut microbiota plays a major role in the GVHD. Moreover, the most recent publications uncover that the LAB, butyrogenic bacteria and bacterial cross feeding were the missing pieces in the puzzle. This opens new bacteria-based strategies in the treatment of GVHD.

Virotherapy as Potential Adjunct Therapy for Graft-Vs-Host Disease

PURPOSE OF REVIEW

This review discusses the pathophysiology, risk factors, and the advances in the prevention or treatment of graft-vs-host disease (GvHD) by exploiting adjunct virotherapy. In addition, nonviral adjunct therapeutic options for the prevention of GvHD in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT) are discussed. The role of oncolytic viruses to treat different HSCT-eligible hematological cancers is also considered and correlated with the issue of GvHD in the context of allo-HSCT.

RECENT FINDINGS

Emerging therapies focused on the prevention or treatment of GvHD include the use of regulatory T cells (Tregs), mesenchymal stem cells (MSCs), microbiome manipulation, B cell inhibitors, among others. Our lab and others have reported that an oncolytic DNA virus from the Poxviridae family, called myxoma virus (MYXV), not only exhibits oncolytic activity against various hematologic malignancies like multiple myeloma (MM) or acute myeloid leukemia (AML) but also, in addition, ex vivo MYXV treatment of human allogeneic-bone marrow transplants (allo-BMT), or allo-peripheral blood mononuclear cell (allo-PBMC) transplants can abrogate GvHD in xenografted mice without impairing graft-vs-tumor (GvT) effects against residual cancer. To date, this is the first and the only oncolytic virus with a dual potential of mediating oncolysis against a residual cancer target and also inhibiting or preventing GvHD following allo-HSCT.

SUMMARY

This review discusses how oncolytic virotherapy can be applied as a potential adjunct therapy for the potential treatment of GvHD. In addition, we highlight major emerging nonviral therapies currently studied for the treatment or prevention of GvHD. We also review the emerging oncolytic virotherapies against different hematological cancers currently eligible for allo-HSCT and highlight the potential role of the oncolytic virus MYXV to decrease GvHD while maintaining or enhancing the positive benefits of GvT.

Gut microbiota-dependent modulation of innate immunity and lymph node remodeling affects cardiac allograft outcomes

We hypothesized that the gut microbiota influences survival of murine cardiac allografts through modulation of immunity. Antibiotic pretreated mice received vascularized cardiac allografts and fecal microbiota transfer (FMT), along with tacrolimus immunosuppression. FMT source samples were from normal, pregnant (immune suppressed), or spontaneously colitic (inflammation) mice. Bifidobacterium pseudolongum (B. pseudolongum) in pregnant FMT recipients was associated with prolonged allograft survival and lower inflammation and fibrosis, while normal or colitic FMT resulted in inferior survival and worse histology. Transfer of B. pseudolongum alone resulted in reduced inflammation and fibrosis. Stimulation of DC and macrophage lines with B. pseudolongum induced the antiinflammatory cytokine IL-10 and homeostatic chemokine CCL19 but induced lesser amounts of the proinflammatory cytokines TNFα and IL-6. In contrast, LPS and Desulfovibrio desulfuricans (D. desulfuricans), more abundant in colitic FMT, induced a more inflammatory cytokine response. Analysis of mesenteric and peripheral lymph node structure showed that B. pseudolongum gavage resulted in a higher laminin α4/α5 ratio in the lymph node cortical ridge, indicative of a suppressive environment, while D. desulfuricans resulted in a lower laminin α4/α5 ratio, supportive of inflammation. Discrete gut bacterial species alter immunity and may predict graft outcomes through stimulation of myeloid cells and shifts in lymph node structure and permissiveness.

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.

PD-1 and CTLA-4 up regulation on donor T cells is insufficient to prevent GvHD in allo-HSCT recipients

The expression of checkpoint blockade molecules PD-1, PD-L1, CTLA-4, and foxp3+CD25+CD4+ T cells (Tregs) regulate donor T cell activation and graft-vs-host disease (GvHD) in allogeneic hematopoietic stem cell transplant (allo-HSCT). Detailed kinetics of PD-1-, CTLA-4-, and PD-L1 expression on donor and host cells in GvHD target organs have not been well studied. Using an established GvHD model of allo-HSCT (B6 → CB6F1), we noted transient increases of PD-1- and CTLA-4-expressing donor CD4+ and CD8+ T cells on day 10 post transplant in spleens of allo-HSCT recipients compared with syngeneic HSCT (syn-HSCT) recipients. In contrast, expression of PD-1- and CTLA-4 on donor T cells was persistently increased in bone marrow (BM) of allo-HSCT recipients compared with syn-HSCT recipients. Similar differential patterns of donor T cell immune response were observed in a minor histocompatibility (miHA) mismatched transplant model of GvHD. Despite higher PD-1 and CTLA-4 expression in BM, numbers of foxp3+ T cells and Tregs were much lower in allo-HSCT recipients compared with syn-HSCT recipients. PD-L1-expressing host cells were markedly decreased concomitant with elimination of residual host hematopoietic elements in spleens of allo-HSCT recipients. Allo-HSCT recipients lacking PD-L1 rapidly developed increased serum inflammatory cytokines and lethal acute GvHD compared with wild-type (WT) B6 allo-HSCT recipients. These data suggest that increased expression of checkpoint blockade molecules PD-1 and CTLA-4 on donor T cells is not sufficient to prevent GvHD, and that cooperation between checkpoint blockade signaling by host cells and donor Tregs is necessary to limit GvHD in allo-HSCT recipients.

TLR5 signaling in murine bone marrow induces hematopoietic progenitor cell proliferation and aids survival from radiation

Administration of the bacterial protein flagellin to mice activates innate immune signaling that protects against an array of challenges, including ionizing radiation. Herein, we define the underlying mechanism for this protection. We report that flagellin treatment induces proliferation and mobilization of bone marrow cells that aid survival following irradiation. Specifically, treatment of mice or bone marrow cells ex vivo with flagellin induced Toll-like receptor 5 (TLR5)-dependent and NOD-like receptor C4-independent proliferation of Lin^-Sca-1⁺Kit⁺ (LSK) cells, which includes both hematopoietic stem cells that provide long-term repopulation (LTR) and multipotent progenitor cells (MPPs) that transiently proliferate and differentiate into a range of blood cell types. TLR5 expression on bone marrow cells was necessary and sufficient for flagellin-induced LSK proliferation. Flagellin treatment stimulated LSK proliferation by inducing a 10-fold increase in type 3 MPP (MPP3) without a concomitant increase in LTR cells. Cotransfer of 5 × 10³ fluorescence-activated cell sorted flagellin-induced MPP3 cells along with 1 × 10⁵ whole bone marrow cells to lethally irradiated mice revealed that such cells predominantly repopulated the neutrophil compartment for up to 4 week, and dramatically increased the survival rate of the bone marrow transplantation procedure. Hence, we propose the administration of MPP3 cells, elicited by flagellin, as a novel approach to prevent life-threatening neutropenia that can accompany bone marrow transplant and other myeloablative therapeutic procedures.

Toll-like receptor 5 signaling restrains T-cell/natural killer T-cell activation and protects against concanavalin A-induced hepatic injury

Toll-like receptor-5 (TLR5) signaling regulates the immune privileged status of the liver and is involved in hepatic immune disorders. However, the role of TLR5 has not yet been investigated in experimental models of concanavalin A (Con A)-mediated liver injury. Here, we show that TLR5 is highly up-regulated in the hepatic mononuclear cells of mice during Con A-induced hepatitis. Increased mortality and liver histopathology of TLR5-deficient mice correlated with excessive production of proinflammatory cytokines, suggesting that TLR5 knockout mice were more susceptible to Con A-induced hepatitis. We also report that administration of CBLB502, an exogenous TLR5 agonist, substantially alleviated Con A-mediated hepatitis in wild-type mice as shown by increased survival rates, reduced aminotransferase and proinflammatory cytokine production, impaired lymphocyte infiltration, and ameliorated hepatocyte necrosis and/or apoptosis. Mechanistic studies revealed that CBLB502 acts as a negative regulator in limiting T-cell/natural killer T-cell activity and cytokine production in the Con A-hepatitis model. Bone marrow transplantation experiments showed that TLR5 in bone marrow-derived cells contributed to the hepatoprotective efficacy of CBLB502 against Con A-induced liver injury. Moreover, interleukin-6 elevation induced by CBLB502 is an important protective factor against Con A-induced liver injury. In addition, we demonstrate that CBLB502 suppresses α-galactosylceramide-induced natural killer T cell-dependent inflammatory liver injury.

CONCLUSION

The TLR5 signaling pathway plays an important role in T cell-mediated hepatic injury and may be exploited for therapeutic treatment of inflammatory liver diseases. (Hepatology 2017;65:2059-2073).

The gastrointestinal tract: properties and role in allogeneic hematopoietic stem cell transplantation

INTRODUCTION

The GI-tract is a major target for both the intensive chemo and/or radiotherapy conditioning as well as for GVHD and therefore is closely associated with transplant outcome. Apart from being a target, the GI-tract is also a mediator and therefore is also a key player of the pathogenetic process following allogeneic transplantation. Areas covered: The intestinal homeostasis is regulated through complicated interactions between the key players of this process which are the intestinal epithelium, the intestinal immune system, and the intestinal microbiota. A brief description of these elements, based on published english-language articles in PubMed, as well as their role during the process of allo-HSCT is discussed in this review. Expert commentary: Data on GI-tract properties suggest a central role for the intestine in regulation of immunity, both in healthy - steady state conditions and in pathological states such as during allo-HSCT. Given the fact that in the allogeneic transplant setting severe complications such as infections and GVHD are limiting this treatment modality, understanding the mechanisms that mediate intestinal homeostasis could lead to new preventive methods and improved outcomes.

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.

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.

Regulatory T-cell impairment in cystic fibrosis patients with chronic pseudomonas infection

RATIONALE

Patients with cystic fibrosis (CF) lung disease have chronic airway inflammation driven by disrupted balance of T-cell (Th17 and Th2) responses. Regulatory T cells (Tregs) dampen T-cell activation, but their role in CF is incompletely understood.

OBJECTIVES

To characterize numbers, function, and clinical impact of Tregs in CF lung disease.

METHODS

Tregs were quantified in peripheral blood and airway samples from patients with CF and from lung disease control patients without CF and healthy control subjects. The role of Pseudomonas aeruginosa and CF transmembrane conductance regulator (CFTR) in Treg regulation was analyzed by using in vitro and murine in vivo models.

MEASUREMENTS AND MAIN RESULTS

Tregs were decreased in peripheral blood and airways of patients with CF compared with healthy controls or lung disease patients without CF and correlated positively with lung function parameters. Patients with CF with chronic P. aeruginosa infection had lower Tregs compared with patients with CF without P. aeruginosa infection. Genetic knockout, pharmacological inhibition, and P. aeruginosa infection studies showed that both P. aeruginosa and CFTR contributed to Treg dysregulation in CF. Functionally, Tregs from patients with CF or from Cftr(-/-) mice were impaired in suppressing conventional T cells, an effect that was enhanced by P. aeruginosa infection. The loss of Tregs in CF affected memory, but not naive Tregs, and manifested gradually with disease progression.

CONCLUSIONS

Patients with CF who have chronic P. aeruginosa infection show an age-dependent, quantitative, and qualitative impairment of Tregs. Modulation of Tregs represents a novel strategy to rebalance T-cell responses, dampen inflammation, and ultimately improve outcomes for patients with infective CF lung disease.

A GMCSF and IL7 fusion cytokine leads to functional thymic-dependent T-cell regeneration in age-associated immune deficiency

The competence of cellular immunity depends on a diverse T-cell receptor (TCR) repertoire arising from thymic output. Normal thymopoiesis arises from marrow-derived CD3(-)CD4(-)CD8(-) triple-negative T-cell progenitors (TN), which develop into mature single-positive (SP) CD4 or CD8 T cells after expressing both CD4 and CD8 (double-positive, DP) transiently, leading to de novo T-cell production. Interleukin-7 (IL7) is a singularly important common γ-chain IL involved in normal thymic development. Our previous work has demonstrated that γc cytokines fused with granulocyte-macrophage colony stimulating factor (GMCSF) at the N-terminus acquire unheralded biological properties. Therefore, to enhance thymopoiesis, we developed a novel biopharmaceutical based on the fusion of GMCSF and IL7, hereafter GIFT7. Systemic administration of GIFT7 leads to cortical thymic hyperplasia including the specific expansion of CD44(int)CD25(-) double-negative 1 (DN1) thymic progenitors. During murine cytomegalovirus (mCMV) infection of aged animals, GIFT7-mediated neo-thymopoiesis led to increased absolute numbers of viral-specific CD8(+) T cell. Our work demonstrated that thymic precursors can be therapeutically repopulated and its reconstitution leads to meaningful central and peripheral T-cell neogenesis, correcting immune dysfunction arising from age-associated thymic atrophy.

Activation of Innate Immunity in Graft-versus-Host Disease: Implications for Novel Targets?

Acute graft-versus-host disease (GvHD) is mediated by alloreactive donor-derived T cells with a suitable T cell receptor recognizing recipient major histocompatibility complex or minor histocompatibility antigens. However, the process of T cell activation and tissue injury sensing is also dependent on innate immune cells and non-hematopoietic cells. Different cell types of the innate immune system have the ability to sense danger-associated and pathogen-associated molecular patterns via pattern recognition receptors which can be transmembrane Toll-like receptors or cytoplasmic nucleotide-binding oligomerization domain-like receptors. Infectious stimuli include bacterial, viral, and fungal components, while non-infectious stimuli can be components derived from damaged cells or extracellular matrix. A better understanding of the complex sensing and effector mechanisms of innate immune cells in GvHD may help to improve preventive and therapeutic strategies in GvHD.

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.

In vivo Toll-like receptor 5 (TLR5) imaging with radiolabeled anti-TLR5 monoclonal antibody in rapamycin-treated mouse allogeneic skin transplantation model

BACKGROUND

In organ transplantation, increasing evidence, both in experimental and human studies, indicates that Toll-like receptor (TLR) activation is involved in the innate immune recognition of allograft. TLR5, the only protein recognition receptor of TLRs, is indicated potentially to be the immune regulation target. This study was designed to determine whether TLR5 could be a biomarker for in vivo allograft visualization, after immunosuppressant rapamycin treatment, using radiolabeled sodium iodide ((131) I)-anti-TLR5 monoclonal antibody (mAb).

METHODS

BALB/c mice were transplanted with C57BL/6 skin, with/without rapamycin treatment (the rapamycin-treated group and the phosphate buffered saline [PBS]-rejection group, respectively). In vivo dynamic whole-body phosphor-autoradiography and ex vivo biodistribution studies were conducted after (131) I-anti-TLR5 mAb injection.

RESULTS

Dynamic phosphor-autoradiography imaging showed clear graft localization from 12 h onward. At 72 h after injection, graft uptake quantified from images was higher for the rapamycin-treated group (26,448 ± 904 digital light units [DLU]/mm(2) ), compared with the PBS-treated allo-rejection group (9176 ± 576 DLU/mm(2) ). Treatment with anti-TLR5 mAb inhibited graft uptake. Organ biodistribution study reflected the same tendency, and (131) I-anti-TLR5 mAb uptake reached a maximum of 12.05 ± 1.86 %ID/g (percent injected dose per gram) at 1 h, and graft-to-native skin ratio reached 8.10 ± 0.10 %ID/g at 72 h after injection in rapamycin-treated grafts.

CONCLUSION

Radiolabeled anti-TLR5 mAb showed higher uptake in allo-treated grafts compared with allo-rejection grafts, which was proved by non-invasive dynamic phosphor-autoradiography imaging, and invasive ex vivo biodistribution. Radiolabeled anti-TLR5 mAb is a new tracer for non-invasive in vivo imaging of TLR5 in rapamycin-treated allograft.

Non-invasive imaging of allogeneic transplanted skin graft by 131I-anti-TLR5 mAb

Although ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake can be used for the non-invasive detection and monitoring of allograft rejection by activated leucocytes, this non-specific accumulation is easily impaired by immunosuppressants. Our aim was to evaluate a ¹³¹I-radiolabelled anti-Toll-like receptor 5 (TLR5) mAb for non-invasive in vivo graft visualization and quantification in allogeneic transplantation mice model, compared with the non-specific radiotracer ¹⁸F-FDG under using of immunosuppressant. Labelling, binding, and stability studies were performed. BALB/c mice transplanted with C57BL/6 skin grafts, with or without rapamycin treatment (named as allo-treated group or allo-rejection group), were injected with ¹³¹I-anti-TLR5 mAb, ¹⁸F-FDG, or mouse isotype ¹³¹I-IgG, respectively. Whole-body phosphor-autoradiography and ex vivo biodistribution studies were obtained. Whole-body phosphor-autoradiography showed ¹³¹I-anti-TLR5 mAb uptake into organs that were well perfused with blood at 1 hr and showed clear graft images from 12 hrs onwards. The ¹³¹I-anti-TLR5 mAb had significantly higher graft uptake and target-to-non-target ratio in the allo-treated group, as determined by semi-quantification of phosphor-autoradiography images; these results were consistent with ex vivo biodistribution studies. However, high ¹⁸F-FDG uptake was not observed in the allo-treated group. The highest allograft-skin-to-native-skin ratio (A:N) of ¹³¹I-anti-TLR5 mAb uptake was significantly higher than the ratio for ¹⁸F-FDG (7.68 versus 1.16, respectively). ¹³¹I-anti-TLR5 mAb uptake in the grafts significantly correlated with TLR5 expression in the allograft area. The accumulation of ¹³¹I-IgG was comparable in both groups. We conclude that radiolabelled anti-TLR5 mAb is capable of detecting allograft with high target specificity after treatment with the immunosuppressive drug rapamycin.

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.

Acute graft-versus-host disease: a bench-to-bedside update

Over the past 5 years, many novel approaches to early diagnosis, prevention, and treatment of acute graft-versus-host disease (aGVHD) have been translated from the bench to the bedside. In this review, we highlight recent discoveries in the context of current aGVHD care. The most significant innovations that have already reached the clinic are prophylaxis strategies based upon a refinement of our understanding of key sensors, effectors, suppressors of the immune alloreactive response, and the resultant tissue damage from the aGVHD inflammatory cascade. In the near future, aGVHD prevention and treatment will likely involve multiple modalities, including small molecules regulating immunologic checkpoints, enhancement of suppressor cytokines and cellular subsets, modulation of the microbiota, graft manipulation, and other donor-based prophylaxis strategies. Despite long-term efforts, major challenges in treatment of established aGVHD still remain. Resolution of inflammation and facilitation of rapid immune reconstitution in those with only a limited response to corticosteroids is a research arena that remains rife with opportunity and urgent clinical need.

Recombinant TLR5 agonist CBLB502 promotes NK cell-mediated anti-CMV immunity in mice

Prior work using allogeneic bone marrow transplantation (allo-BMT) models showed that peritransplant administration of flagellin, a toll-like receptor 5 (TLR5) agonist protected murine allo-BMT recipients from CMV infection while limiting graft-vs-host disease (GvHD). However, the mechanism by which flagellin-TLR5 interaction promotes anti-CMV immunity was not defined. Here, we investigated the anti-CMV immunity of NK cells in C57BL/6 (B6) mice treated with a highly purified cGMP grade recombinant flagellin variant CBLB502 (rflagellin) followed by murine CMV (mCMV) infection. A single dose of rflagellin administered to mice between 48 to 72 hours prior to MCMV infection resulted in optimal protection from mCMV lethality. Anti-mCMV immunity in rflagellin-treated mice correlated with a significantly reduced liver viral load and increased numbers of Ly49H+ and Ly49D+ activated cytotoxic NK cells. Additionally, the increased anti-mCMV immunity of NK cells was directly correlated with increased numbers of IFN-γ, granzyme B- and CD107a producing NK cells following mCMV infection. rFlagellin-induced anti-mCMV immunity was TLR5-dependent as rflagellin-treated TLR5 KO mice had ∼10-fold increased liver viral load compared with rflagellin-treated WT B6 mice. However, the increased anti-mCMV immunity of NK cells in rflagellin-treated mice is regulated indirectly as mouse NK cells do not express TLR5. Collectively, these data suggest that rflagellin treatment indirectly leads to activation of NK cells, which may be an important adjunct benefit of administering rflagellin in allo-BMT recipients.

rFliC prolongs allograft survival in association with the activation of recipient Tregs in a TLR5-dependent manner

Allorejection remains an obstacle for successful organ transplantation. Although different types of immunosuppressive agents are effective for controlling rejection and prolonging graft survival, drug treatment is limited because of side effects and toxicity. Therefore, it is necessary and urgent to identify new candidate drugs for inducing allotolerance. Recently, it has been reported that bacterial flagellin induces the immunosuppressive activity of regulatory T cells (Tregs) in humans in vitro. In the present study, we analyzed the effects of recombinant flagellin (rFliC) on allograft survival and explored the underlying mechanisms associated with the activation of recipient Tregs in a murine skin allotransplantation model. The results showed that rFliC administration (3 mg/kg, once per day for 3 days, i.p.) prolonged allograft survival (mean survival time: 18.4±1.1 days) compared to the control group (10±0.7 days, P<0.01). Additionally, higher positive expression of Toll-like receptor 5 (TLR5) was detected within the allograft administered with rFliC. The frequency of CD4(+)CD25(+)Foxp3(+) Tregs; the expression of Treg-related factors TLR5, Foxp3, TGF-β1 and IL-10; and the proliferation and suppression of Tregs were increased following rFliC administration compared to the control. Moreover, the increased expression of tolerance-related molecules and the proliferation of Tregs induced by rFliC were attenuated by an anti-TLR5 blocking antibody both in vivo and in vitro. In conclusion, rFliC administration prolongs the survival of allografts, which is associated with the activation of recipient Tregs in a TLR5-dependent manner. rFliC may be a new candidate for anti-allorejection therapy.

Flagellin induces antibody responses through a TLR5- and inflammasome-independent pathway

Flagellin is a potent immunogen that activates the innate immune system via TLR5 and Naip5/6, and generates strong T and B cell responses. The adaptor protein MyD88 is critical for signaling by TLR5, as well as IL-1Rs and IL-18Rs, major downstream mediators of the Naip5/6 Nlrc4-inflammasome. In this study, we define roles of known flagellin receptors and MyD88 in Ab responses generated toward flagellin. We used mice genetically deficient in flagellin recognition pathways to characterize innate immune components that regulate isotype-specific Ab responses. Using purified flagellin from Salmonella, we dissected the contribution of innate flagellin recognition pathways to promote Ab responses toward flagellin and coadministered OVA in C57BL/6 mice. We demonstrate IgG2c responses toward flagellin were TLR5 and inflammasome dependent; IgG1 was the dominant isotype and partially TLR5 and inflammasome dependent. Our data indicate a substantial flagellin-specific IgG1 response was induced through a TLR5-, inflammasome-, and MyD88-independent pathway. IgA anti-FliC responses were TLR5 and MyD88 dependent and caspase-1 independent. Unlike C57BL/6 mice, flagellin-immunized A/J mice induced codominant IgG1 and IgG2a responses. Furthermore, MyD88-independent, flagellin-induced Ab responses were even more pronounced in A/J MyD88(-/-) mice, and IgA anti-FliC responses were suppressed by MyD88. Flagellin also worked as an adjuvant toward coadministered OVA, but it only promoted IgG1 anti-OVA responses. Our results demonstrate that a novel pathway for flagellin recognition contributes to Ab production. Characterization of this pathway will be useful for understanding immunity to flagellin and the rationale design of flagellin-based vaccines.

TLR stimulation of bone marrow lymphoid precursors from childhood acute leukemia modifies their differentiation potentials

Acute leukemias are the most frequent childhood malignancies worldwide and remain a leading cause of morbidity and mortality of relapsed patients. While remarkable progress has been made in characterizing genetic aberrations that may control these hematological disorders, it has also become clear that abnormalities in the bone marrow microenvironment might hit precursor cells and contribute to disease. However, responses of leukemic precursor cells to inflammatory conditions or microbial components upon infection are yet unexplored. Our previous work and increasing evidence indicate that Toll-like receptors (TLRs) in the earliest stages of lymphoid development in mice and humans provide an important mechanism for producing cells of the innate immune system. Using highly controlled co-culture systems, we now show that lymphoid precursors from leukemic bone marrow express TLRs and respond to their ligation by changing cell differentiation patterns. While no apparent contribution of TLR signals to tumor progression was recorded for any of the investigated diseases, the replenishment of innate cells was consistently promoted upon in vitro TLR exposure, suggesting that early recognition of pathogen-associated molecules might be implicated in the regulation of hematopoietic cell fate decisions in childhood acute leukemia.

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.

Antibodies against Marinobacter algicola and Salmonella typhimurium flagellins do not cross-neutralize TLR5 activation

Flagellins evoke strong innate and adaptive immune responses. These proteins may play a key role as radioprotectors, exert antitumoral activity in certain types of tumor and reduce graft-versus-host disease in allogeneic hematopoietic stem cell transplant recipients. Notwithstanding, flagellins are highly immunogenic, and repeated use leads to their neutralization by systemic antibodies. This neutralization is not prevented by using functional deleted flagellins. These observations led us to explore the possibility of preventing initial neutralization by means of another functional flagellin that does not belong to common pathogenic bacteria but that has the capacity to activate TLR5. Here we characterized the functional capacity of the two-phase Marinobacter algicola (MA)-derived flagellins (F and FR) as systemic and mucosal adjuvants and compared their performance with that of Salmonella typhimurium (STF) flagellins (FljB and FliC). We also report for the first time on the in vitro and in vivo capacity of various flagellins to trigger TLR5 activation in the presence of species-specific anti-flagellin antibodies, the cross-neutralization mediated by these antibodies, and the sequential use of these flagellins for TLR5 activation. Our results showed that MA flagellins behave in a similar way to STF ones, inducing pro-inflammatory cytokines (IL8, CCL20, CCL2) and evoking a strong in vivo antibody response against a model epitope. More importantly, MA flagellins were fully functional, in vitro or in vivo, in the presence of a high concentration of neutralizing anti-flagellin STF antibodies, and STF flagellin was not inhibited by neutralizing anti-flagellin MA antibodies. The use of active flagellins from distinct bacteria could be a useful approach to prevent systemic neutralization of this group of adjuvants and to facilitate the rational design of flagellin-based vaccines and/or other therapeutic treatments (against ischemia, acute renal failure, tumors, ionizing radiations and also to improve the outcome of bone marrow transplants).

A TLR5 agonist enhances CD8(+) T cell-mediated graft-versus-tumor effect without exacerbating graft-versus-host disease

Allogeneic hematopoietic cell transplantation is an established treatment for hematologic and nonhematologic malignancies. Donor-derived immune cells can identify and attack host tumor cells, producing a graft-versus-tumor (GVT) effect that is crucial to the effectiveness of the transplantation therapy. CBLB502 is a novel agonist for TLR5 derived from Salmonella flagellin. On the basis of TLR5-mediated immunomodulatory function, we examined the effect of CBLB502 on GVT activity. Using two tumor models that do not express TLR5, and thereby do not directly respond to CBLB502, we found that CBLB502 treatment significantly enhanced allogeneic CD8(+) T cell-mediated GVT activity, which was evidenced by decreased tumor burden and improved host survival. Importantly, histopathologic analyses showed that CBLB502 treatment did not exacerbate the moderate graft-versus-host disease condition caused by the allogeneic CD8(+) T cells. Moreover, mechanistic analyses showed that CBLB502 stimulates CD8(+) T cell proliferation and enhances their tumor killing activity mainly indirectly through a mechanism that involves the IL-12 signaling pathway and the CD11c(+) and CD11b(+) populations in the bone marrow cells. This study demonstrates a new beneficial effect of CBLB502, and suggests that TLR5-mediated immune modulation may be a promising approach to improve GVT immunity without exacerbating graft-versus-host disease.

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.

Advances in graft-versus-host disease biology and therapy

Allogeneic haematopoietic stem cell transplantation is used to treat a variety of disorders, but its efficacy is limited by the occurrence of graft-versus-host disease (GVHD). The past decade has brought impressive advances in our understanding of the role of stimulatory and suppressive elements of the adaptive and innate immune systems from both the donor and the host in GVHD pathogenesis. New insights from basic immunology, preclinical models and clinical studies have led to novel approaches for prevention and treatment. This Review highlights the recent advances in understanding the pathophysiology of GVHD and its treatment, with a focus on manipulations of the immune system that are amenable to clinical application.