Probiotic effects on experimental graft-versus-host disease: let them eat yogurt

The Influence of the Gut Microbiome on Cancer, Immunity, and Cancer Immunotherapy

The microbiome is receiving significant attention given its influence on a host of human diseases including cancer. Its role in response to cancer treatment is becoming increasingly apparent, with evidence suggesting that modulating the gut microbiome may affect responses to numerous forms of cancer therapy. A working knowledge of the microbiome is vital as we move forward in this age of precision medicine, and an understanding of the microbiome's influence on immune responses and cancer is key. It is also important to understand factors influencing the gut microbiome and strategies to manipulate the microbiome to augment therapeutic responses.

Variability of nutritional practices in peritransplant period after allogeneic hematopoietic stem cell transplantation: a survey by the Complications and Quality of Life Working Party of the EBMT

Recommendations on screening and nutritional support for patients undergoing hematopoietic stem cell transplantation (HSCT) have been presented by international nutritional societies, but nutritional practices remain poorly standardized. Following the general policy of the European Society for Blood and Marrow Transplantation (EBMT) to standardize transplantation procedures, the Complications and Quality of Life Working Party and Nursing Research Group carried out a survey among all EBMT centers about their current nutritional practices. The aim of this study was to better understand current practices, differences from available guidelines, and possible barriers for recommended nutritional therapy. Responses from 90 centers (19%) from 23 countries were received. We observed a marked variability in nutritional care between EBMT centers and a substantial lack of standardized operating procedures in screening patients for malnutrition and management of gastrointestinal GVHD. Furthermore, our study confirmed neutropenic diet as standard of care in most centers as well a preference for parenteral nutritional support over enteral. On the basis of these findings, future EBMT efforts will focus on better implementation of international nutritional guidelines into clinical practice.

Changes in intestinal microbiota and their effects on allogeneic stem cell transplantation

The human intestinal microbiota is essential for microbial homeostasis, regulation of metabolism, and intestinal immune tolerance. Rapidly evolving understanding of the importance of the microbiota implicates changes in the composition and function of intestinal microbial communities in an assortment of systemic conditions. Complications following allogeneic stem cell transplant now join the ever-expanding list of pathologic states regulated by intestinal microbiota. Dysbiosis, or disruption of the normal ecology of this microbiome, has been directly implicated in the pathogenesis of entities such as Clostridium difficile infections, graft-versus-host disease (GVHD), and most recently disease relapse, all of which are major causes of morbidity and mortality in patients undergoing allogeneic stem cell transplant. In this review, we elucidate the key origins of microbiotic alterations and discuss how dysbiosis influences complications following allogeneic stem cell transplant. Our emerging understanding of the importance of a balanced and diverse intestinal microbiota is prompting investigation into the appropriate treatment of dysbiosis, reliable and early detection of such, and ultimately its prevention in patients to improve the outcome following allogeneic hematopoietic stem cell transplant.

Colonization with multidrug-resistant bacteria increases the risk of complications and a fatal outcome after allogeneic hematopoietic cell transplantation

Composition of the gut microbiota seems to influence early complications of allogeneic hematopoietic cell transplantation (HCT) such as bacterial infections and acute graft-versus-host disease (GVHD). In this study, we assessed the impact of colonization with multidrug-resistant bacteria (MDRB) prior to HCT and the use of antibiotics against anaerobic bacteria on the outcomes of HCT. We retrospectively analyzed the data of 120 patients who underwent HCT for hematologic disorders between 2012 and 2014. Fifty-one (42.5%) patients were colonized with MDRB and 39 (32.5%) had infections caused by MDRB. Prior colonization was significantly correlated with MDRB infections (P < 0.001), especially bacteremia (P = 0.038). A higher incidence of MDRB infections was observed in patients with acute (P = 0.014) or chronic (P = 0.002) GVHD and in patients aged > 40 years (P = 0.002). Colonization had a negative impact on overall survival (OS) after HCT (64 vs. 47% at 24 months; P = 0.034) and infection-associated mortality (P < 0.001). Use of metronidazole was correlated with an increased incidence of acute GVHD (P < 0.001) and lower OS (P = 0.002). Patients colonized with MDRB are more susceptible to life-threatening infections. Colonization with virulent flora is the most probable source of neutropenic infection; therefore, information about prior positive colonization should be crucial for the selection of empiric antibiotic therapy. The use of metronidazole, affecting the biodiversity of the intestinal microbiome, seems to have a significant impact on OS and acute GVHD.

The Mycobiome: Impact on Health and Disease States

The term "microbiome" refers to microorganisms (microbiota) and their genomes (metagenome) coexisting with their hosts. Some researchers coined the term "second genome" to underscore the importance of the microbiota and its collective metagenome on their host's health and/or disease. It is now undeniable that the commensal fungal microorganisms, alongside the other components of the microbiota, play a central role in association with the human host. In recognition, projects were launched nationally and internationally to unify efforts to characterize the microbiome and elucidate the functional role of the microbiota and the mechanism(s) by which these organisms and their metabolites (metabolome) may affect health and disease states. In this article, we will highlight the role of the fungal community as an indispensable component of the microbiome.

R-Spondin1 expands Paneth cells and prevents dysbiosis induced by graft-versus-host disease

The intestinal microbial ecosystem is actively regulated by Paneth cell-derived antimicrobial peptides such as α-defensins. Various disorders, including graft-versus-host disease (GVHD), disrupt Paneth cell functions, resulting in unfavorably altered intestinal microbiota (dysbiosis), which further accelerates the underlying diseases. Current strategies to restore the gut ecosystem are bacteriotherapy such as fecal microbiota transplantation and probiotics, and no physiological approach has been developed so far. In this study, we demonstrate a novel approach to restore gut microbial ecology by Wnt agonist R-Spondin1 (R-Spo1) or recombinant α-defensin in mice. R-Spo1 stimulates intestinal stem cells to differentiate to Paneth cells and enhances luminal secretion of α-defensins. Administration of R-Spo1 or recombinant α-defensin prevents GVHD-mediated dysbiosis, thus representing a novel and physiological approach at modifying the gut ecosystem to restore intestinal homeostasis and host-microbiota cross talk toward therapeutic benefits.

Complementary and Integrative Medicine in Hematologic Malignancies: Questions and Challenges

Hematologic malignancies represent 9.7% of all cancers, making them the fourth most common type of cancer in the United States. The aggressive and complex treatments administered in hematologic malignancies result in a high burden of psychological needs. Complementary and integrative medicine (CIM) is becoming one of the options that patients use to address their distress during and after cancer treatments. It is not clear whether appropriate CIM can relieve distress in patients affected by these malignancies. This review covers the potential benefits of CIM as relates to nutrition, nutritional supplements, exercise, circadian rhythm, methods for reducing distress during bone marrow aspiration, massage therapy, and acupuncture, in treating patients with hematological malignancies. This review may provide a framework to enhance patient-doctor dialogue regarding CIM use in hematologic malignancies.

Associations between acute gastrointestinal GvHD and the baseline gut microbiota of allogeneic hematopoietic stem cell transplant recipients and donors

Growing evidence suggests that host-microbiota interactions influence GvHD risk following allogeneic hematopoietic stem cell transplant. However, little is known about the influence of the transplant recipient's pre-conditioning microbiota nor the influence of the transplant donor's microbiota. Our study examines associations between acute gastrointestinal GvHD (agGvHD) and 16S rRNA fecal bacterial profiles in a prospective cohort of N=57 recipients before preparative conditioning, as well as N=22 of their paired HLA-matched sibling donors. On average, recipients had lower fecal bacterial diversity (P=0.0002) and different phylogenetic membership (UniFrac P=0.001) than the healthy transplant donors. Recipients with lower phylogenetic diversity had higher overall mortality rates (hazard ratio=0.37, P=0.008), but no statistically significant difference in agGvHD risk. In contrast, high bacterial donor diversity was associated with decreased agGvHD risk (odds ratio=0.12, P=0.038). Further investigation is warranted as to whether selection of hematopoietic stem cell transplant donors with high gut microbiota diversity and/or other specific compositional attributes may reduce agGvHD incidence, and by what mechanisms.

Role of the intestinal mucosa in acute gastrointestinal GVHD

Intestinal graft-versus-host disease (GVHD) remains a significant obstacle to the success of allogeneic hematopoietic cell transplantation. The intestinal mucosa comprises the inner lining of the intestinal tract and maintains close proximity with commensal microbes that reside within the intestinal lumen. Recent advances have significantly improved our understanding of the interactions between the intestinal mucosa and the enteric microbiota. Changes in host mucosal tissue and commensals posttransplant have been actively investigated, and provocative insights into mucosal immunity and the enteric microbiota are now being translated into clinical trials of novel approaches for preventing and treating acute GVHD. In this review, we summarize recent findings related to aspects of the intestinal mucosa during acute GVHD.

Altered homeostatic regulation of innate and adaptive immunity in lower gastrointestinal tract GVHD pathogenesis

Lower gastrointestinal (GI) tract graft-versus-host disease (GVHD) is the predominant cause of morbidity and mortality from GVHD after allogeneic stem cell transplantation. Recent data indicate that lower GI tract GVHD is a complicated process mediated by donor/host antigenic disparities. This process is exacerbated by significant changes to the microbiome, and innate and adaptive immune responses that are critical to the induction of disease, persistence of inflammation, and a lack of response to therapy. Here, we discuss new insights into the biology of lower GI tract GVHD and focus on intrinsic pathways and regulatory mechanisms crucial to normal intestinal function. We then describe multiple instances in which these homeostatic mechanisms are altered by donor T cells or conditioning therapy, resulting in exacerbation of GVHD. We also discuss data suggesting that some of these mechanisms produce biomarkers that could be informative as to the severity of GVHD and its response to therapy. Finally, novel therapies that might restore homeostasis in the GI tract during GVHD are highlighted.

Gut microbiota and acute graft-versus-host disease

Although allogeneic stem cell transplantation (allo-SCT) is a potentially curative treatment for various hematological diseases, acute graft-versus-host disease (GVHD) is a major cause of morbidity and mortality, and its management is clinically important. Advances in biological techniques have led to great progress in understanding the complex interactions between the host and the gut microbiota. The gut microbiota clearly modulates the immune response and is associated with the pathogenesis of various disorders. Also in allo-SCT, both preclinical and clinical results indicate that the gut microbiota is closely associated with the development of acute GVHD and transplant outcomes. These results led to the idea that improvement in quantitative and/or qualitative abnormalities of microbiota (dysbiosis) may be a new treatment strategy for acute GVHD. Evaluations of therapies targeting the gut microbiota such as probiotics or fecal microbiota transplantation have just begun. Furthermore, intervention in the gut microbiota with a nutritional approach including prebiotics, postbiotics, and antibiotics selection may also be another promising treatment option for acute GVHD.

Lactobacillus rhamnosus GG probiotic enteric regimen does not appreciably alter the gut microbiome or provide protection against GVHD after allogeneic hematopoietic stem cell transplantation

Graft-versus-host disease (GVHD) is a major adverse effect associated with allogeneic stem cell transplant. Previous studies in mice indicated that administration of the probiotic Lactobacillus rhamnosus GG can reduce the incidence of GVHD after hematopoietic stem cell transplant. Here we report results from the first randomized probiotic enteric regimen trial in which allogenic hematopoietic stem cell patients were supplemented with Lactobacillus rhamnosus GG. Gut microbiome analysis confirmed a previously reported gut microbiome association with GVHD. However, the clinical trial was terminated when interim analysis did not detect an appreciable probiotic-related change in the gut microbiome or incidence of GVHD. Additional studies are necessary to determine whether probiotics can alter the incidence of GVHD after allogeneic stem cell transplant.

The intestinal microbiota in allogeneic hematopoietic cell transplant and graft-versus-host disease

Hematopoietic cell transplantation (HCT) is a critical treatment of patients with high-risk hematopoietic malignancies, hematological deficiencies, and other immune diseases. In allogeneic HCT (allo-HCT), donor-derived T cells recognize host tissues as foreign, causing graft-versus-host disease (GVHD) which is a main contributor to morbidity and mortality. The intestine is one of the organs most severely affected by GVHD and research has recently highlighted the importance of bacteria, particularly the gut microbiota, in HCT outcome and in GVHD development. Loss of intestinal bacterial diversity is common during the course of HCT and is associated with GVHD development and treatment with broad-spectrum antibiotics. Loss of intestinal diversity and outgrowth of opportunistic pathogens belonging to the phylum Proteobacteria and Enterococcus genus have also been linked to increased treatment-related mortality including GVHD, infections, and organ failure after allo-HCT. Experimental studies in allo-HCT animal models have shown some promising results for prebiotic and probiotic strategies as prophylaxis or treatment of GVHD. Continuous research will be important to define the relation of cause and effect for these associations between microbiota features and HCT outcomes. Importantly, studies focused on geographic and cultural differences in intestinal microbiota are necessary to define applicability of new strategies targeting the intestinal microbiota.

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.

Intestinal dysbiosis and allogeneic hematopoietic progenitor cell transplantation

The intestinal microbiota is a diverse and dynamic ecosystem that is increasingly understood to play a vital role in human health. Hematopoietic stem cell transplant recipients undergo prolonged exposure to antimicrobials, chemotherapeutic agents, and immunosuppressants, resulting in profound shifts in the gut microbiome. A growing body of research has revealed the ways in which these microbiologic shifts shape immune modulation, affecting susceptibility to infections and graft-versus-host disease, the two major post-transplant complications in this population. As transplant medicine becomes increasingly personalized, the potential for microbiome-modulating treatments holds immense potential. Strategies to preserve the intestinal microbiota, including targeted antibiotics, prebiotics and probiotics, and fecal microbiota transplant could mitigate some of the microbiologic shifts in stem cell transplant recipients, and reduce the incidence of peri-transplant morbidity and mortality.

Role of the intestinal mucosa in acute gastrointestinal GVHD

Intestinal graft-versus-host disease (GVHD) remains a significant obstacle to the success of allogeneic hematopoietic cell transplantation. The intestinal mucosa comprises the inner lining of the intestinal tract and maintains close proximity with commensal microbes that reside within the intestinal lumen. Recent advances have significantly improved our understanding of the interactions between the intestinal mucosa and the enteric microbiota. Changes in host mucosal tissue and commensals posttransplant have been actively investigated, and provocative insights into mucosal immunity and the enteric microbiota are now being translated into clinical trials of novel approaches for preventing and treating acute GVHD. In this review, we summarize recent findings related to aspects of the intestinal mucosa during acute GVHD.

Pathogenesis of acute graft-versus-host disease: from intestinal microbiota alterations to donor T cell activation

Acute graft-versus-host disease (aGVHD) is a major life-threatening complication of allogeneic haematopoietic cell transplantation (allo-HCT). Here we discuss the aGVHD pathophysiology initiated by multiple signals that cause alloreactive T-cell activation. The outcome of such donor T-cell activation is influenced by T-cell receptor-signal strength, anatomical location, co-stimulatory/co-inhibitory signals and differentiation stage (naive, effector/memory) of T-cells. Additionally, cross-priming of T cells to antigens expressed by pathogens can contribute to aGVHD-mediated tissue injury. In addition to the properties of donor T-cell activation, highly specialized tissue resident cell types, such as innate lymphoid cells, antigen-presenting cells, immune regulatory cells and various intestinal cell populations are critically involved in aGVHD pathogenesis. The role of the thymus and secondary lymphoid tissue injury, non-haematopoietic cells, intestinal microflora, cytokines, chemokines, microRNAs, metabolites and kinases in aGVHD pathophysiology will be highlighted. Acute GVHD pathogenic mechanisms will be connected to novel therapeutic approaches under development for, and tested in, the clinic.

Gut microbiota and hematopoietic stem cell transplantation: where do we stand?

Advances in biological techniques have potentiated great progresses in understanding the interaction between human beings and the ∼10 to 100 trillion microbes living in their gastrointestinal tract: gut microbiota (GM). In this review, we describe recent emerging data on the role of GM in hematopoietic stem cell transplantation, with a focus on immunomodulatory properties in the immune system recovery and the impact in the development of the main complications, as GvHD and infections.

The Gut Microbiota and Immune System Relationship in Human Graft-versus-Host Disease

Gut microbiota has gained increasing interest in the pathogenesis of immune-related diseases. In this context, graft-versus-host disease is a condition characterized by an immune response which frequently complicates and limits the outcomes of hematopoietic stem cell transplantations. Past studies, carried mostly in animals, already supported a relationship between gut microbiota and graft-versus-host disease. However, the possible mechanisms underlying this connection remain elusory. Moreover, strategies to prevent graft-versus-host disease are of great interest as well as the potential role of gut microbiota modulation. We reviewed the role of gut microbiota in the development of immune system and its involvement in the graft-versus-host disease, focusing on data available on humans.

Potential protective effect of Helicobacter pylori on the development of gastrointestinal GvHD

Previous reports ascribe a modulating capacity of the immune response to Helicobacter pylori (HP). Our hypothesis was to demonstrate in a prospective study that HP infection could have a protective effect against development of gastrointestinal GvHD in patients receiving allogeneic hematopoietic cell transplantation (HCT). Presence of HP before transplant was determined using C(13) urea breath test. Seventy-nine patients receiving an allogeneic HCT were included and 93.7% of them received PBSC; in 51.9%, the donor was unrelated. Acute gastrointestinal GvHD was diagnosed in 51.9% (n=41). In the multivariable analysis, HP infection was associated with a lower frequency of gastrointestinal GvHD (odds ratio (OR)=0.19 (95% confidence interval (CI): 0.05-0.67); in contrast, an unrelated donor was associated with a higher frequency of gastrointestinal GvHD (odds ratio=5.4 (95% confidence interval: 1.6-18.2). One year overall survival (OS) was 74%. In the multivariate Cox proportional-hazards regression analysis, stages 0-II gastrointestinal GvHD (hazards ratio (HR)=0.19), reduced intensity conditioning (HR=0.04) and tacrolimus-sirolimus GvHD prophylaxis (HR=0.06) were all associated with a better OS. In summary, HP infection could have a role in decreasing gastrointestinal GvHD in patients receiving allogeneic HCT from peripheral blood including related and unrelated donors.

Intestinal microbiota sustains inflammation and autoimmunity induced by hypomorphic RAG defects

Rigoni et al. report that hypomorphic Rag2^R229Q mutation is associated with altered microbiota composition and defects in the gut–blood barrier and suggest that intestinal microbes may play a critical role in the distinctive immune dysregulation of Omenn syndrome.

Omenn syndrome (OS) is caused by hypomorphic Rag mutations and characterized by a profound immunodeficiency associated with autoimmune-like manifestations. Both in humans and mice, OS is mediated by oligoclonal activated T and B cells. The role of microbial signals in disease pathogenesis is debated. Here, we show that Rag2^R229Q knock-in mice developed an inflammatory bowel disease affecting both the small bowel and colon. Lymphocytes were sufficient for disease induction, as intestinal CD4 T cells with a Th1/Th17 phenotype reproduced the pathological picture when transplanted into immunocompromised hosts. Moreover, oral tolerance was impaired in Rag2^R229Q mice, and transfer of wild-type (WT) regulatory T cells ameliorated bowel inflammation. Mucosal immunoglobulin A (IgA) deficiency in the gut resulted in enhanced absorption of microbial products and altered composition of commensal communities. The Rag2^R229Q microbiota further contributed to the immunopathology because its transplant into WT recipients promoted Th1/Th17 immune response. Consistently, long-term dosing of broad-spectrum antibiotics (ABXs) in Rag2^R229Q mice ameliorated intestinal and systemic autoimmunity by diminishing the frequency of mucosal and circulating gut-tropic CCR9⁺ Th1 and Th17 T cells. Remarkably, serum hyper-IgE, a hallmark of the disease, was also normalized by ABX treatment. These results indicate that intestinal microbes may play a critical role in the distinctive immune dysregulation of OS.

Microbiota Manipulation With Prebiotics and Probiotics in Patients Undergoing Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is a potentially life-saving therapy that often comes at the cost of complications such as graft-versus-host disease and post-transplant infections. With improved technology to understand the ecosystem of microorganisms (viruses, bacteria, fungi, and microeukaryotes) that make up the gut microbiota, there is increasing evidence of the microbiota's contribution to the development of post-transplant complications. Antibiotics have traditionally been the mainstay of microbiota-altering therapies available to physicians. Recently, interest is increasing in the use of prebiotics and probiotics to support the development and sustainability of a healthier microbiota. In this review, we will describe the evidence for the use of prebiotics and probiotics in combating microbiota dysbiosis and explore the ways in which they may be used in future research to potentially improve clinical outcomes and decrease rates of graft-versus-host disease (GVHD) and post-transplant infection.

Understanding Luminal Microorganisms and Their Potential Effectiveness in Treating Intestinal Inflammation

The human intestine contains 10¹⁴ bacteria, which outnumber the mammalian cells 10-fold. Certain other commensal or infectious agents, like helminthic parasites, become members of this microbial ecosystem, especially in populations living under less hygienic conditions. Intestinal microbes, also called the microbiome or microbiota, shape the host immune reactivity to self and nonself throughout life. Changes in microbiome composition may impair the maturation of immune regulatory pathways and predispose the host to develop various forms of inflammatory disorders, like Crohn's disease or ulcerative colitis. The microbiome is also critical to successful transplantation of organs or grafts. After allogeneic hematopoietic stem cell transplantation, when the new donor cells, such as T lymphocytes learn to discriminate "the new self from nonself" in the transplant recipient, they need healthy microbiota-derived signals to preserve the immune homeostasis. Restoring microbiota through intestinal delivery of bacterial strains, helminths, fecal microbiota transplantation, or stool substitutes have the potential to improve and correct aberrant immune reactivity in various disorders.

Prebiotic and Probiotic Regulation of Bone Health: Role of the Intestine and its Microbiome

Recent advances in our understanding of how the intestinal microbiome contributes to health and disease have generated great interest in developing strategies for modulating the abundance of microbes and/or their activity to improve overall human health and prevent pathologies such as osteoporosis. Bone is an organ that the gut has long been known to regulate through absorption of calcium, the key bone mineral. However, it is clear that modulation of the gut and its microbiome can affect bone density and strength in a variety of animal models (zebrafish, rodents, chicken) and humans. This is demonstrated in studies ablating the microbiome through antibiotic treatment or using germ-free mouse conditions as well as in studies modulating the microbiome activity and composition through prebiotic and/or probiotic treatment. This review will discuss recent developments in this new and exciting area.

The safety and feasibility of probiotics in children and adolescents undergoing hematopoietic cell transplantation

Hematopoietic cell transplantation (HCT) has become a standard treatment for many adult and pediatric conditions. Emerging evidence suggests that perturbations in the microbiota diversity increase recipients' susceptibilities to gut-mediated conditions such as diarrhea, infection and acute GvHD. Probiotics preserve the microbiota and may minimize the risk of developing a gut-mediated condition; however, their safety has not been evaluated in the setting of HCT. We evaluated the safety and feasibility of the probiotic, Lactobacillus plantarum (LBP), in children and adolescents undergoing allogeneic HCT. Participants received once-daily supplementation with LBP beginning on day -8 or -7 and continued until day +14. Outcomes were compliance with daily administration and incidence of LBP bacteremia. Administration of LBP was feasible with 97% (30/31, 95% confidence interval (CI) 83-100%) of children receiving at least 50% of the probiotic dose (median 97%; range 50-100%). We did not observe any case of LBP bacteremia (0% (0/30) with 95% CI 0-12%). There were not any unexpected adverse events related to LBP. Our study provides preliminary evidence that administration of LBP is safe and feasible in children and adolescents undergoing HCT. Future steps include the conduct of an approved randomized, controlled trial through Children's Oncology Group.

Gut microbiota and allogeneic transplantation

The latest high-throughput sequencing technologies show that there are more than 1000 types of microbiota in the human gut. These microbes are not only important to maintain human health, but also closely related to the occurrence and development of various diseases. With the development of transplantation technologies, allogeneic transplantation has become an effective therapy for a variety of end-stage diseases. However, complications after transplantation still restrict its further development. Post-transplantation complications are closely associated with a host's immune system. There is also an interaction between a person's gut microbiota and immune system. Recently, animal and human studies have shown that gut microbial populations and diversity are altered after allogeneic transplantations, such as liver transplantation (LT), small bowel transplantation (SBT), kidney transplantation (KT) and hematopoietic stem cell transplantation (HTCT). Moreover, when complications, such as infection, rejection and graft versus host disease (GVHD) occur, gut microbial populations and diversity present a significant dysbiosis. Several animal and clinical studies have demonstrated that taking probiotics and prebiotics can effectively regulate gut microbiota and reduce the incidence of complications after transplantation. However, the role of intestinal decontamination in allogeneic transplantation is controversial. This paper reviews gut microbial status after transplantation and its relationship with complications. The role of intervention methods, including antibiotics, probiotics and prebiotics, in complications after transplantation are also discussed. Further research in this new field needs to determine the definite relationship between gut microbial dysbiosis and complications after transplantation. Additionally, further research examining gut microbial intervention methods to ameliorate complications after transplantation is warranted. A better understanding of the relationship between gut microbiota and complications after allogeneic transplantation may make gut microbiota as a therapeutic target in the future.

Immunosuppression and probiotics: are they effective and safe?

This opinion statement discusses indications, efficacy and safety of probiotics in immunosuppressed patients. The best evidence available is for the prophylaxis of infections in patients after liver transplantation and for patients with liver cirrhosis. For other organ transplantations and for bone marrow transplantation the efficacy of probiotic interventions has not been proven yet, but in these patient groups safety is a concern. Also in critically ill patients, the data on efficacy are inconclusive and safety is a concern. In HIV patients and patients after major surgery, probiotic bacteria seem to be safe since there are no associations with increased risks of side effects.

Intestinal Blautia Is Associated with Reduced Death from Graft-versus-Host Disease

The relationship between intestinal microbiota composition and acute graft-versus-host disease (GVHD) after allogeneic blood/marrow transplantation (allo-BMT) is not well understood. Intestinal bacteria have long been thought to contribute to GVHD pathophysiology, but recent animal studies in nontransplant settings have found that anti-inflammatory effects are mediated by certain subpopulations of intestinal commensals. Hypothesizing that a more nuanced relationship may exist between the intestinal bacteria and GVHD, we evaluated the fecal bacterial composition of 64 patients 12 days after BMT. We found that increased bacterial diversity was associated with reduced GVHD-related mortality. Furthermore, harboring increased amounts of bacteria belonging to the genus Blautia was associated with reduced GVHD lethality in this cohort and was confirmed in another independent cohort of 51 patients from the same institution. Blautia abundance was also associated with improved overall survival. We evaluated the abundance of Blautia with respect to clinical factors and found that loss of Blautia was associated with treatment with antibiotics that inhibit anaerobic bacteria and receiving total parenteral nutrition for longer durations. We conclude that increased abundance of commensal bacteria belonging to the Blautia genus is associated with reduced lethal GVHD and improved overall survival.

The Role of Intestinal Microbiota in Acute Graft-versus-Host Disease

The mammalian intestinal microbiota is a complex ecosystem that plays an important role in host immune responses. Recent studies have demonstrated that alterations in intestinal microbiota composition are linked to multiple inflammatory diseases in humans, including acute graft-versus-host disease (aGVHD). aGVHD is one of the major obstacles in allogeneic hematopoietic stem cell transplantation (allo-HSCT), characterized by tissue damage in the gastrointestinal (GI) tract, liver, lung, and skin. Here, we review the current understanding of the role of intestinal microbiota in the control of immune responses during aGVHD. Additionally, the possibility of using probiotic strains for potential treatment or prevention of aGVHD will be discussed.

Intestinal microbiota-related effects on graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an increasingly important treatment for conditions including hematopoietic malignancies and inherited hematopoietic disorders, and is considered to be the most effective form of tumor immunotherapy available to date. However, graft-versus-host disease (GVHD) remains a major source of morbidity and mortality following allo-HSCT, and understanding the mechanisms of GVHD has been highlighted as a key research priority. During development of GVHD, activation of various immune cells, especially donor T cells, leads to damage of target organs including skin, liver, hematopoietic system, and of particular clinical importance, gut. In addition to histocompatibility complex differences between the donor and recipient, pretransplant conditioning with chemotherapy and irradiation also contributes to GVHD by damaging the gut, resulting in systemic exposure to microbial products normally confined to the intestinal lumen. The intestinal microbiota is a modulator of gastrointestinal immune homeostasis. It also promotes the maintenance of epithelial cells. Recent reports provide growing evidence of the impact of intestinal microbiota on GVHD pathophysiology. This review summarizes current knowledge of changes and effects of intestinal microbiota in the setting of allo-HSCT. We will also discuss potential future strategies of intestinal microbiota manipulation that might be advantageous in decreasing allo-HSCT-related morbidity and mortality.

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.

Emerging Influence of the Intestinal Microbiota during Allogeneic Hematopoietic Cell Transplantation: Control the Gut and the Body Will Follow

The intestinal microbiota has many critical roles in maintaining gastrointestinal epithelial and gastrointestinal systemic immune homeostasis. This review provides insight into how allogeneic hematopoietic cell transplantation (HCT) and its associated complications and supportive care therapies affect the microbiota. Additionally, the review discusses how preservation and restoration of the microbiota might be advantageous in decreasing HCT-related morbidity and mortality.

Disease severity and mortality can be independently regulated in a mouse model of experimental graft versus host disease

Graft versus host disease (GVHD) is the major limitation of allogeneic hematopoietic stem cell transplantation (HSCT) presenting high mortality and morbidity rates. However, the exact cause of death is not completely understood and does not correlate with specific clinical and histological parameters of disease. Here we show, by using a semi-allogeneic mouse model of GVHD, that mortality and morbidity can be experimentally separated. We injected bone marrow-derived dendritic cells (BMDC) from NOD2/CARD15-deficient donors into semi-allogeneic irradiated chimaeras and observed that recipients were protected from death. However, no protection was observed regarding clinical or pathological scores up to 20 days after transplantation. Protection from death was associated with decreased bacterial translocation, faster hematologic recovery and epithelial integrity maintenance despite mononuclear infiltration at day 20 post-GVHD induction with no skew towards different T helper phenotypes. The protected mice recovered from aGVHD and progressively reached scores compatible with healthy animals. Altogether, our data indicate that severity and mortality can be separate events providing a model to study transplant-related mortality.

Integrative Therapy Use for Management of Side Effects and Toxicities Experienced by Pediatric Oncology Patients

Integrative Therapies (IT), otherwise known as Complementary and Alternative Medicine, are widely used among pediatric oncology patients, despite a paucity of available evidence. This review summarizes surveys that describe the prevalence of IT use by pediatric oncology patients, both during therapy and in survivorship, as well as the modalities being used. Additionally, the evidence that exists for specific treatments that appear to be efficacious in controlling specific symptoms is described. Finally, there are recommendations for practitioners on how to best counsel patients about IT use.

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.

Home care during neutropenia after allogeneic hematopoietic stem cell transplantation in children and adolescents is safe and may be more advantageous than isolation in hospital

After ASCT, children are isolated in hospital to prevent neutropenic infections. Patients living within two-h drive from the hospital were given the option of treatment at home after ASCT. Daily visits by an experienced nurse and phone calls from a physician from the unit were included in the protocol. We compared 29 children and adolescents treated at home with 58 matched hospital controls. The children spent a median time of 13 days at home (range 2-24 days) and 6 (0-35) days in hospital. The cumulative incidence of acute GVHD grades II-IV was 21% in the home-care children and 39% in the controls (p = 0.1). Chronic GVHD and probability of relapse were similar in the two groups. TRM at five yr was 11% in the home-care patients and 18% in the controls. Overall survival at three yr was 77% and 62%, respectively (p = 0.33). None of the patients died at home. Median costs were 38,748 euros in the home-care patients and 49,282 euros in those treated in the hospital (p = 0.2). We conclude that it is safe for children and adolescents to be treated at home during the pancytopenic phase after ASCT.

Possible implication of bacterial infection in acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Graft-versus-host disease (GVHD) is still one of the major causes of morbidity and mortality in allogeneic hematopoietic stem cell transplantation (HSCT). In the pathogenesis of acute GVHD, it has been established that donor-derived T-cells activated in the recipient play a major role in GVHD in initiation and maintenance within an inflammatory cascade. To reduce the risk of GVHD, intensification of GVHD prophylaxis like T-cell depletion is effective, but it inevitably increases the risk of infectious diseases and abrogates beneficial graft-versus-leukemia effects. Although various cytokines are considered to play an important role in the pathogenesis of GVHD, GVHD initiation is such a complex process that cannot be prevented by means of single inflammatory cytokine inhibition. Thus, efficient methods to control the whole inflammatory milieu both on cellular and humoral view are needed. In this context, infectious diseases can theoretically contribute to an elevation of inflammatory cytokines after allogeneic HSCT and activation of various subtypes of immune effector cells, which might in summary lead to an aggravation of acute GVHD. The appropriate treatments or prophylaxis of bacterial infection during the early phase after allogeneic HSCT might be beneficial to reduce not only infectious-related but also GVHD-related mortality. Here, we aim to review the literature addressing the interactions of bacterial infections and GVHD after allogeneic HSCT.

Immune activation and microbial translocation in liver disease progression in HIV/hepatitis co-infected patients: results from the Icona Foundation study

Background

We evaluated whether immune activation (IA) and microbial translocation (MT) might play a role in accelerating liver disease progression in HIV-HBV/HCV co-infected patients.

Methods

ART-naïve HIV/viral hepatitis co-infected patients from Icona with a CD4 cell count >200/μl and with a known date of prior HIV neg/pos tests and ≥1 plasma sample stored were included in the study. Plasma MT (LPS, sCD14) and IA (IL-6,TNFα) were measured using ELISA while activated CD8 + CD38 + HLA-DR + were measured by flow cytometry, with one measurement being performed for all patients and two measurements for a smaller group of subjects. The association between these biomarkers and the time to i) a single ALT >200 IU/l and ii) a Fib-4 >1.45 was also investigated. A standard survival analysis with robust standard errors was used for all evaluations. Follow-up was censored at patients’ last clinical follow-up.

Results

We studied 127 HIV-infected hepatitis viruses co-infected patients (118 HCV, 9 HBV). Overall median (IQR) CD4, VL, age were 596/μl (208–1303), 3.8 log₁₀cp/mL (3–4.3), 34 years (22–56). While heightened TNF-α was associated with a 13-fold increased risk of Fib-4 > 1.45 (RH 13.05, 95% CI 2.43-70; p = 0.003), markers of MT did not show an association with liver illness. Interestingly, higher sCD14 was associated with a decreased risk of Fib-4 > 1.45, independently of other biomarkers considered (RH 0.20, 95% CI 0.04-0,9; p = 0.04).

Conclusions

In HIV/hepatitis virus co-infected ART-naive patients, higher TNF-α plasma levels were associated with a 13-fold increase in the risk of progression to a Fib-4 >1.45, suggesting that the pro-inflammatory status in HIV infection might hasten the course of HCV. In view of the fact that sCD14 may hinder the interaction between LPS and the phagocyte membrane CD14, we herewith propose a model which aims to demonstrate that high sCD14 levels might contribute to shelter liver function through the down-regulation of the inflammatory cascade.

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

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

Oral combined therapy with probiotics and alloantigen induces B cell-dependent long-lasting specific tolerance

Allogeneic hematopietic stem cell transplantation (aHSCT) is widely used for the treatment of hematologic malignancies. Although aHSCT provides a good response against the malignant cells (graft-versus-leukemia [GVL]), it also leads to the development of graft-versus-host disease (GVHD), a severe disease with high mortality and morbidity rates. Therapy for GVHD is commonly based on nonspecific immunosupression of the transplanted recipient, resulting in the concomitant inhibition of the GVL effect. In this study, we propose an alternative approach to specifically suppress GVHD while sparing the GVL, based on oral treatment of transplant donors with recipient Ags, associated with the intake of probiotic Lactococcus lactis as tolerogenic adjuvant (combined therapy). We show that treatment of C57BL/6 donor mice with combined therapy before the transplant protects the recipients F1 (C57BL/6 × BAL/c) mice from clinical and pathological manifestations of disease, resulting in 100% survival rate. Importantly, the animals keep the immunological competence maintaining the GVL response as well as the response to third-party Ags. The protection is specific, long lasting and dependent on donor IL-10-sufficient B cells activity, which induces regulatory T cells in the host. These data suggest that combined therapy is a promising strategy for prevention of GVHD with preservation of GVL, opening new possibilities to treat human patients subjected to transplantation.

Bifidobacteria BbC50 Fermentation Products Induce Human Cd4+ Regulatory T Cells with Antigen-Specific Activation and Bystander Suppression

Probiotic bacteria have been shown to have health benefits in various situations (inflammation, allergy, infection). We previously showed that a bacteria-free fermentation product of Bifidobacterium breve C50 (BbC50sn) induced high IL-10 secretion by human dendritic cells. As IL-10 is a regulatory cytokine, the aim of the present study was to examine whether DCs cultured in the presence of BbC50sn could induce regulatory T cells in an allogeneic context. Purified CD4+CD25− human T cells were co-cultured with allogeneic BbC50sn-treated dendritic cells for 4 weeks. The T cell population (BbC50sn-T) was analysed both at phenotypical and functional [ability to inhibit a mixed lymphocyte reaction (MLR)] levels. We showed that T lymphocytes acquired phenotype characteristics of regulatory T cells after 4 weeks of co-culture with BbC50sn-DCs, and inhibited in vitro T lymphocyte proliferation and IFN-γ production in an MLR. Transwell experiments demonstrated that this suppressive activity was not T cell contact-dependent but probably mediated by a soluble factor. Although BbC50sn-T cells secreted significant amounts of IL-10 and TGF-β, their suppressive effect is most likely not mediated through these cytokines. This is, to our knowledge, the first demonstration of in vitro regulatory T cell induction by a bacteria-free fermentation product in an allogeneic context.