The Microbiome and Hematopoietic Cell Transplantation: Past, Present, and Future

Gut microbial dysbiosis in the pathogenesis of leukemia: an immune-based perspective

Leukemias are a set of clonal hematopoietic malignant diseases that develop in the bone marrow. Several factors influence leukemia development and progression. Among these, the gut microbiota is a major factor influencing a wide array of its processes. The gut microbial composition is linked to the risk of tumor development and the host's ability to respond to treatment, mostly due to the immune-modulatory effects of their metabolites. Despite such strong evidence, its role in the development of hematologic malignancies still requires attention of investigators worldwide. In this review, we make an effort to discuss the role of host gut microbiota-immune crosstalk in leukemia development and progression. Additionally, we highlight certain recently developed strategies to modify the gut microbial composition that may help to overcome dysbiosis in leukemia patients in the near future.

Blood and guts: how the intestinal microbiome shapes hematopoiesis and treatment of hematologic disease

ABSTRACT

Over the past 10 years, there has been a marked increase in recognition of the interplay between the intestinal microbiome and the hematopoietic system. Despite their apparent distance in the body, a large literature now supports the relevance of the normal intestinal microbiota to steady-state blood production, affecting both hematopoietic stem and progenitor cells as well as differentiated immune cells. Microbial metabolites enter the circulation where they can trigger cytokine signaling that influences hematopoiesis. Furthermore, the state of the microbiome is now recognized to affect outcomes from hematopoietic stem cell transplant, immunotherapy, and cellular therapies for hematologic malignancies. Here we review the mechanisms by which microbiotas influence hematopoiesis in development and adulthood as well as the avenues by which microbiotas are thought to impact stem cell transplant engraftment, graft-versus-host disease, and efficacy of cell and immunotherapies. We highlight areas of future research that may lead to reduced adverse effects of antibiotic use and improved outcomes for patients with hematologic conditions.

Non-Graft-versus-Host Disease Enterocolitis Following Cord Blood Transplantation is Real, with Poorly Understood Pathophysiology, and Requires Distinct Management, with Eventual Resolution without Immune Suppression

Enterocolitis is common after cord blood transplantation (CBT) and a specific, non-graft-versus-host disease (GVHD) entity with specific histopathologic features ("cord colitis") has been described in some cases in selected series. Immune suppression is not without risk, and we have used it only when biopsy features are consistent with classical GVHD. In the absence of biopsy features of classical GVHD, our management of intestinal failure has been supportive, and we have withdrawn immune suppression to allow immune reconstitution and better prevent relapse of malignant disease and reduce infectious complications. We evaluated our approach over an 11-year period in a retrospective study of all patients at our large pediatric CBT center who experienced intestinal failure necessitating endoscopy and biopsy in the post-CBT period. We conducted a blinded histopathologic review of gastrointestinal (GI) biopsy specimens from all patients who had undergone GI endoscopy for intestinal failure in the post-CBT period. Patient records were evaluated to determine clinical HSCT course and outcome data, including mortality, relapse, and infection, as well as the duration of immune suppression and parenteral nutrition. Out of 144 patients who underwent CBT during the study period, 25 (17%) experienced intestinal failure requiring endoscopy. Thirteen patients were diagnosed with acute GVHD after blinded review of biopsy specimens, and 12 patients had non-GVHD enterocolitis. Management in the absence of GVHD on GI biopsy is supportive, with withdrawal of immune suppression in patients with malignant disease and continuing in accordance with institutional practice in those with nonmalignant disease. Compared with the GVHD cohort, the non-GVHD enterocolitis cohort had superior overall survival (91% versus 41%; P = .04) and a shorter duration of immune suppression (mean, 112 days versus 180 days; P = .049), reflecting these different management approaches. These results demonstrate that different histopathologic findings in those with intestinal failure after CBT likely indicates a different etiology from GVHD and mandates a different clinical management strategy to achieve optimal clinical outcomes.

Lipocalin-2 expression identifies an intestinal regulatory neutrophil population during acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT), for which therapeutic options are limited. Strategies to promote intestinal tissue tolerance during aGVHD may improve patient outcomes. Using single-cell RNA sequencing, we identified a lipocalin-2 (LCN2)-expressing neutrophil population in mice with intestinal aGVHD. Transfer of LCN2-overexpressing neutrophils or treatment with recombinant LCN2 reduced aGVHD severity, whereas the lack of epithelial or hematopoietic LCN2 enhanced aGVHD severity and caused microbiome alterations. Mechanistically, LCN2 induced insulin-like growth factor 1 receptor (IGF-1R) signaling in macrophages through the LCN2 receptor SLC22A17, which increased interleukin-10 (IL-10) production and reduced major histocompatibility complex class II (MHCII) expression. Transfer of LCN2-pretreated macrophages reduced aGVHD severity but did not reduce graft-versus-leukemia effects. Furthermore, LCN2 expression correlated with IL-10 expression in intestinal biopsies in multiple cohorts of patients with aGVHD, and LCN2 induced IGF-1R signaling in human macrophages. Collectively, we identified a LCN2-expressing intestinal neutrophil population that reduced aGVHD severity by decreasing MHCII expression and increasing IL-10 production in macrophages. This work provides the foundation for administration of LCN2 as a therapeutic approach for aGVHD.

The Role of the Gut Microbiome in Hematological Cancers

Humans are in a complex symbiotic relationship with a wide range of microbial organisms, including bacteria, viruses, and fungi. The evolution and composition of the human microbiome can be an indicator of how it may affect human health and susceptibility to diseases. Microbiome alteration, termed as dysbiosis, has been linked to the pathogenesis and progression of hematological cancers. A variety of mechanisms, including epithelial barrier disruption, local chronic inflammation response trigger, antigen dis-sequestration, and molecular mimicry, have been proposed to be associated with gut microbiota. Dysbiosis may be induced or worsened by cancer therapies (such as chemotherapy and/or hematopoietic stem cell transplantation) or infection. The use of antibiotics during treatment may also promote dysbiosis, with possible long-term consequences. The aim of this review is to provide a succinct summary of the current knowledge describing the role of the microbiome in hematological cancers, as well as its influence on their therapies. Modulation of the gut microbiome, involving modifying the composition of the beneficial microorganisms in the management and treatment of hematological cancers is also discussed. Additionally discussed are the latest developments in modeling approaches and tools used for computational analyses, interpretation and better understanding of the gut microbiome data.

Restrictive Versus Permissive Use of Broad-spectrum Antibiotics in Patients Receiving Allogeneic Stem Cell Transplantation and With Early Fever Due to Cytokine Release Syndrome: Evidence for Beneficial Microbiota Protection Without Increase in Infectious Complications

BACKGROUND

Intestinal microbiome contributes to the pathophysiology of acute gastrointestinal (GI) graft-versus-host disease (GvHD) and loss of microbiome diversity influences the outcome of patients after allogeneic stem cell transplantation (SCT). Systemic broad-spectrum antibiotics have been identified as a major cause of early intestinal dysbiosis.

METHODS

In 2017, our transplant unit at the university hospital in Regensburg changed the antibiotic strategy from a permissive way with initiation of antibiotics in all patients with neutropenic fever independent of the underlying cause and risk to a restrictive use in cases with high likelihood of cytokine release syndrome (eg, after anti-thymocyte globulin [ATG] therapy). We analyzed clinical data and microbiome parameters obtained 7 days after allogeneic SCT from 188 patients with ATG therapy transplanted in 2015/2016 (permissive cohort, n = 101) and 2918/2019 (restrictive cohort, n = 87).

RESULTS

Restrictive antibiotic treatment postponed the beginning of antibiotic administration from 1.4 ± 7.6 days prior to 1.7 ± 5.5 days after SCT (P = .01) and significantly reduced the duration of antibiotic administration by 5.8 days (P < .001) without increase in infectious complications. Furthermore, we observed beneficial effects of the restrictive strategy compared with the permissive way on microbiome diversity (urinary 3-indoxylsulfate, P = .01; Shannon and Simpson indices, P < .001) and species abundance 7 days post-transplant as well as a positive trend toward a reduced incidence of severe GI GvHD (P = .1).

CONCLUSIONS

Our data indicate that microbiota protection can be achieved by a more careful selection of neutropenic patients qualifying for antibiotic treatment during allogeneic SCT without increased risk of infectious complications.

Feasibility of a dietary intervention to modify gut microbial metabolism in patients with hematopoietic stem cell transplantation

Evaluation of the impact of dietary intervention on gastrointestinal microbiota and metabolites after allogeneic hematopoietic stem cell transplantation (HCT) is lacking. We conducted a feasibility study as the first of a two-phase trial. Ten adults received resistant potato starch (RPS) daily from day -7 to day 100. The primary objective was to test the feasibility of RPS and its effect on intestinal microbiome and metabolites, including the short-chain fatty acid butyrate. Feasibility met the preset goal of 60% or more, adhering to 70% or more doses; fecal butyrate levels were significantly higher when participants were on RPS than when they were not (P < 0.0001). An exploratory objective was to evaluate plasma metabolites. We observed longitudinal changes in plasma metabolites compared to baseline, which were independent of RPS (P < 0.0001). However, in recipients of RPS, the dominant plasma metabolites were more stable compared to historical controls with significant difference at engraftment (P < 0.05). These results indicate that RPS in recipients of allogeneic HCT is feasible; in this study, it was associated with significant alterations in intestinal and plasma metabolites. A phase 2 trial examining the effect of RPS on graft-versus-host disease in recipients of allogeneic HCT is underway. ClinicalTrials.gov registration: NCT02763033 .

Updates in hematopoietic cell transplant and cellular therapies that enhance the risk for opportunistic infections

BACKGROUND

Infectious disease physicians may be asked to evaluate and manage a variety of infections in immunocompromised hosts undergoing hematopoietic cell transplant (HCT) and cellular therapies. Over the last decade, several advances in cellular therapy have occurred, with implications for the types of infectious complications that may be seen.

AIMS

The purpose of this review is to update the infectious disease physician on newer advances in HCT and cellular therapy, including haploidentical transplant, expanding indications for transplant in older individuals and children, and chimeric antigen receptor T-cells. We will review how these advances might influence infectious disease complications following HCT. We will also provide a perspective that infectious disease physicians can use to evaluate the degree of immune suppression in an individual patient to help determine the type of infections that may be encountered.

The gut microbiome: an important factor influencing therapy for pediatric acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most prevalent form of pediatric leukemia. The gut microbiome (GM) is crucial for proper nutrition, immunity, and biological conflict. Since the relationship between ALL and GM is bidirectional, ALL occurrence and treatment are closely related to GM destruction and the development of impaired immunity. Studies have discovered significant GM alterations in patients with ALL, including decreased diversity, that are likely directly caused by the development of ALL. Chemotherapy, antibiotic therapy, and hematopoietic stem cell transplantation (HSCT) are the mainstays of treatment for pediatric ALL. These approaches affect the composition, diversity, and abundance of intestinal microorganisms, which in turn affects therapeutic efficiency and can cause a variety of complications. Modulating the GM can aid the recovery of patients with ALL. This article discusses the various treatment modalities for pediatric ALL and their corresponding effects on the GM, as well as the changes in the GM that occur in children with ALL from diagnosis to treatment. Gaining a greater understanding of the link between ALL and the GM is expected to help improve treatment for pediatric ALL in the future.

Sarcopenia and gut microbiota alterations in patients with hematological diseases before and after hematopoietic stem cell transplantation

Objective

The aim of this study was to investigate the prevalence of sarcopenia (SP) and its relationship with gut microbiota alterations in patients with hematological diseases before and after hematopoietic stem cell transplantation (HSCT).

Methods

A total of 108 patients with various hematological disorders were selected from Peking University People's Hospital. SP was screened and diagnosed based on the 2019 Asian Sarcopenia Diagnosis Strategy. Physical measurements and fecal samples were collected, and 16S rRNA gene sequencing was conducted. Alpha and beta diversity analyses were performed to evaluate gut microbiota composition and diversity.

Results

After HSCT, significant decreases in calf circumference and body mass index (BMI) were observed, accompanied by a decline in physical function. Gut microbiota analyses revealed significant differences in the relative abundance of Enterococcus, Bacteroides, Blautia and Dorea species before and after HSCT (P<0.05). Before HSCT, sarcopenic patients had lower Dorea levels and higher Phascolarctobacterium levels than non-sarcopenia patients (P<0.01). After HSCT, no significant differences in species abundance were observed. Alpha diversity analysis showed significant differences in species diversity among the groups, with the highest diversity in the post-HSCT 90-day group and the lowest in the post-HSCT 30-day group. Beta diversity analysis revealed significant differences in species composition between pre- and post-HSCT time points but not between SP groups. Linear discriminant analysis effect size (LEfSe) identified Alistipes, Rikenellaceae, Alistipes putredinis, Prevotellaceae defectiva and Blautia coccoides as biomarkers for the pre-HSCT sarcopenia group. Functional predictions showed significant differences in anaerobic, biofilm-forming and oxidative stress-tolerant functions among the groups (P<0.05).

Conclusions

This study demonstrated a significant decline in physical function after HSCT and identified potential gut microbiota biomarkers and functional alterations associated with SP in patients with hematological disorders. Further research is needed to explore the underlying mechanisms and potential therapeutic targets.

After Bone Marrow Transplantation, the Cell-Intrinsic Th2 Pathway Promotes Recipient T Lymphocyte Survival and Regulates Graft-versus-Host Disease

Recipient T cells can aggravate or regulate lethal and devastating graft-versus-host disease (GVHD) after bone marrow transplantation (BMT). In this context, we have shown before that intestinal immune conditioning with helminths is associated with survival of recipient T cells and Th2 pathway-dependent regulation of GVHD. We investigated the mechanism of survival of recipient T cells and their contribution to GVHD pathogenesis in this helminth infection and BMT model after myeloablative preparation with total body irradiation in mice. Our results indicate that the helminth-induced Th2 pathway directly promotes the survival of recipient T cells after total body irradiation. Th2 cells also directly stimulate recipient T cells to produce TGF-β, which is required to regulate donor T cell-mediated immune attack of GVHD and can thereby contribute to recipient T cell survival after BMT. Moreover, we show that recipient T cells, conditioned to produce Th2 cytokines and TGF-β after helminth infection, are fundamentally necessary for GVHD regulation. Taken together, reprogrammed or immune-conditioned recipient T cells after helminth infection are crucial elements of Th2- and TGF-β-dependent regulation of GVHD after BMT, and their survival is dependent on cell-intrinsic Th2 signaling.

Fecal Microbiota Transplantation for Acute Graft-versus-Host Disease After Allogeneic Hematopoietic Cell Transplantation: Expanding the Horizon into Pediatrics

The microbiome plays a vital role in maintaining homeostasis of the intestinal microenvironment and immune response in allogeneic hematopoietic cell transplantation (HCT) recipients. Disruption of the intestinal microbiome has been associated with the development of acute graft-versus-host disease (GVHD) of the lower GI tract and worse survival. Fecal microbiota transplantation (FMT) can achieve clinical responses in refractory GVHD, establishing the promise of microbiome-directed interventions in this population. While most data about microbial changes in HCT recipients have been generated from the adult population, children with refractory GVHD represent an important group that may benefit from FMT. In this review, we first highlight characteristics that distinguish the pediatric intestinal microbiome from adults. Subsequently, we explore multiple clinical factors that warrant careful consideration to optimize the application of FMT and other microbiome-directed therapeutics to children.

Longitudinal relationship between the gut microbiota variation and diversity and gut graft-versus-host disease (GVHD) following pediatric allogeneic hematopoietic cell transplantation (HCT) - Case series

Allogeneic Hematopoietic Cell Transplantation (HCT) offers children with life-threatening diseases a chance at survival. Complications from graft-versus-host disease (GVHD, Stages 0-4) represent a significant cause of morbidity and mortality which has been recently associated with gut dysbiosis the adult HCT population. Here, our objective was to conduct a prospective, longitudinal cohort study in nine pediatric allogeneic HCT participants by collecting longitudinally post-HCT stool specimens up to 1 year. Stool microbiota analyses showed that allogeneic HCT and antibiotic therapy lead to acute shifts in the diversity of the gut microbiota with those experiencing stages 3-4 gut GVHD having significantly greater microbiota variation over time when compared to control participants (p = 0.007). Pre-HCT microbiota diversity trended towards an inverse relationship with gut microbiota stability over time, however, this did not reach statistical significance (p = 0.05). Future large prospective studies are necessary to elucidate the mechanisms underlying these dynamic changes in the gut microbiota following pediatric allogeneic HCT.

Pathophysiology of gastrointestinal acute graft-versus-host disease and the potential role of glucagon-like peptide 2

Acute graft-versus-host disease (aGVHD) is a life-threatening complication after allogeneic haematopoietic cell transplantation, with gastrointestinal (GI) tract involvement (GI aGVHD) being one of the leading causes of morbidity and mortality. Whilst systemic steroids are the standard first-line treatment for aGVHD, approximately 50% of patients become steroid refractory (SR), which is associated with poor outcomes. Existing options for SR-GVHD are limited, and there is a significant unmet need for new non-immunosuppressive treatment approaches in patients with GI aGVHD. Here, we review newer concepts in the pathogenesis of GI aGVHD and present the evidence for the role of glucagon-like peptide 2 (GLP-2) in maintaining and protecting GI epithelial cells, including the enterocytes, intestinal stem cells and Paneth cells, which are direct targets of aGVHD. Finally, we discuss the therapeutic rationale for GLP-2 treatment as a tissue regeneration approach and the potential use of the novel GLP-2 analogue apraglutide as an adjunctive treatment for GI aGVHD.

A unique immune signature in blood separates therapy-refractory from therapy-responsive acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is an immune cell‒driven, potentially lethal complication of allogeneic hematopoietic stem cell transplantation affecting diverse organs, including the skin, liver, and gastrointestinal (GI) tract. We applied mass cytometry (CyTOF) to dissect circulating myeloid and lymphoid cells in children with severe (grade III-IV) aGVHD treated with immune suppressive drugs alone (first-line therapy) or in combination with mesenchymal stromal cells (MSCs; second-line therapy). These results were compared with CyTOF data generated in children who underwent transplantation with no aGVHD or age-matched healthy control participants. Onset of aGVHD was associated with the appearance of CD11b+CD163+ myeloid cells in the blood and accumulation in the skin and GI tract. Distinct T-cell populations, including TCRγδ+ cells, expressing activation markers and chemokine receptors guiding homing to the skin and GI tract were found in the same blood samples. CXCR3+ T cells released inflammation-promoting factors after overnight stimulation. These results indicate that lymphoid and myeloid compartments are triggered at aGVHD onset. Immunoglobulin M (IgM) presumably class switched, plasmablasts, and 2 distinct CD11b- dendritic cell subsets were other prominent immune populations found early during the course of aGVHD in patients refractory to both first- and second-line (MSC-based) therapy. In these nonresponding patients, effector and regulatory T cells with skin- or gut-homing receptors also remained proportionally high over time, whereas their frequencies declined in therapy responders. Our results underscore the additive value of high-dimensional immune cell profiling for clinical response evaluation, which may assist timely decision-making in the management of severe aGVHD.

Perturbation of the gut microbiome and association with outcomes following autologous stem cell transplantation in patients with multiple myeloma

The gut microbiome is an important feature of host immunity with associations to hematologic malignancies and cellular therapy. We evaluated the gut microbiome and dietary intake in patients with multiple myeloma undergoing autologous stem cell transplantation. Thirty patients were enrolled, and samples were collected at four timepoints: pre-transplant, engraftment, day +100 (D + 100), and 9-12 months post-transplant. Microbiome analysis demonstrated a loss of alpha diversity at the engraftment timepoint driven by decreases in Blautia, Ruminococcus, and Faecalibacterium genera and related to intravenous antibiotic exposure. Higher fiber intake was associated with increased relative abundance of Blautia at the pre-transplant timepoint. Lower alpha diversity at engraftment was associated with a partial response to therapy compared with complete response (CR) or very good partial response (VGPR) (CR/VGPR vs. PR, p < 0.05). We conclude that loss of bacterial diversity at engraftment may be associated with impaired response to stem cell transplantation in multiple myeloma.

Quantification of Tryptophan, Indole, and Indoxyl Sulfate in Urine Using Liquid Chromatography-Tandem Mass Spectrometry

Having a diverse gut microbiota has been correlated with the short- and long-term success of allogeneic stem cell transplantation. Intestinal bacteria metabolize the amino acid tryptophan to indole. Indole is further oxidized and sulfonated in the liver to 3-indoxyl sulfate (3-IS), which is then excreted in urine. Urinary 3-IS is a potential biomarker for intestinal health and an early predictor of successful stem cell transplantation. We describe a rapid method for quantifying tryptophan, indole, and 3-indoxyl sulfate in urine specimens, in which urine samples are diluted with a formic acid solution and deuterated internal standards, and then injected on LC-MS/MS for analysis.

The Impact of Human Microbiotas in Hematopoietic Stem Cell and Organ Transplantation

The human microbiota heavily influences most vital aspects of human physiology including organ transplantation outcomes and transplant rejection risk. A variety of organ transplantation scenarios such as lung and heart transplantation as well as hematopoietic stem cell transplantation is heavily influenced by the human microbiotas. The human microbiota refers to a rich, diverse, and complex ecosystem of bacteria, fungi, archaea, helminths, protozoans, parasites, and viruses. Research accumulating over the past decade has established the existence of complex cross-species, cross-kingdom interactions between the residents of the various human microbiotas and the human body. Since the gut microbiota is the densest, most popular, and most studied human microbiota, the impact of other human microbiotas such as the oral, lung, urinary, and genital microbiotas is often overshadowed. However, these microbiotas also provide critical and unique insights pertaining to transplantation success, rejection risk, and overall host health, across multiple different transplantation scenarios. Organ transplantation as well as the pre-, peri-, and post-transplant pharmacological regimens patients undergo is known to adversely impact the microbiotas, thereby increasing the risk of adverse patient outcomes. Over the past decade, holistic approaches to post-transplant patient care such as the administration of clinical and dietary interventions aiming at restoring deranged microbiota community structures have been gaining momentum. Examples of these include prebiotic and probiotic administration, fecal microbial transplantation, and bacteriophage-mediated multidrug-resistant bacterial decolonization. This review will discuss these perspectives and explore the role of different human microbiotas in the context of various transplantation scenarios.

Gut Microbiome Suffers from Hematopoietic Stem Cell Transplantation in Childhood and Its Characteristics Are Positively Associated with Intra-Hospital Physical Exercise

Gut microbiome impairment is a serious side effect of cancer treatment. The aim of this study was to identify the effects of hematopoietic stem cell transplantation (HSCT) treatment on gut microbiota composition in children with acute lymphoblastic leukemia (ALL). Fecal microbiotas were categorized using specific primers targeting the V1-V3 region of 16S rDNA in eligible pediatric ALL patients after HSCT (n = 16) and in healthy controls (Ctrl, n = 13). An intra-hospital exercise program was also organized for child patients during HSCT treatment. Significant differences in gut microbiota composition were observed between ALL HSCT and Ctrl with further negative effects. Plasma C-reactive protein correlated positively with the pathogenic bacteria Enterococcus spp. and negatively with beneficial bacteria Butyriccocus spp. or Akkermansia spp., respectively (rs = 0.511, p = 0.05; rs = -0.541, p = 0.04; rs = -0.738, p = 0.02). Bacterial alpha diversity correlated with the exercise training characteristics. Therefore, specific changes in the microbiota of children were associated with systemic inflammation or the ability to exercise physically during HSCT treatment.

Financial incentives to increase stool collection rates for microbiome studies in adult bone marrow transplant patients

INTRODUCTION

In order to study the role of the microbiome in hematopoietic stem cell transplantation (HCT), researchers collect stool samples from patients at various time points throughout HCT. However, stool collection requires active subject participation and may be limited by patient reluctance to handling stool.

METHODS

We performed a prospective study on the impact of financial incentives on stool collection rates. The intervention group consisted of allogeneic HCT patients from 05/2017-05/2018 who were compensated with a $10 gas gift card for each stool sample. The intervention group was compared to a historical control group of allogeneic HCT patients from 11/2016-05/2017 who provided stool samples before the incentive was implemented. To control for possible changes in collections over time, we also compared a contemporaneous control group of autologous HCT patients from 05/2017-05/2018 with a historical control group of autologous HCT patients from 11/2016-05/2017; neither autologous HCT group was compensated. The collection rate was defined as the number of samples provided divided by the number of time points we attempted to obtain stool.

RESULTS

There were 35 allogeneic HCT patients in the intervention group, 19 allogeneic HCT patients in the historical control group, 142 autologous HCT patients in the contemporaneous control group (that did not receive a financial incentive), and 75 autologous HCT patients in the historical control group. Allogeneic HCT patients in the intervention group had significantly higher average overall collection rates when compared to the historical control group allogeneic HCT patients (80% vs 37%, p<0.0001). There were no significant differences in overall average collection rates between the autologous HCT patients in the contemporaneous control and historical control groups (36% vs 32%, p = 0.2760).

CONCLUSION

Our results demonstrate that a modest incentive can significantly increase collection rates. These results may help to inform the design of future studies involving stool collection.

Bone marrow transplantation induces changes in the gut microbiota that chronically increase the cytokine response pattern of splenocytes

Bone marrow transplantation (BMT) involves conditioning regimens which acutely induce side effects, including systemic inflammation, intestinal damage and shifts in the gut microbial composition, some of which may persist chronically. As the gut microbiota affect systemic immune responses, we aimed to investigate whether, post-BMT, the peripheral immune system is modulated as a direct consequence of alterations in the gut microbiota. We show that 24 weeks post-BMT, splenocytes but not peritoneal macrophages display increased cytokine response patterns upon ex-vivo stimulation with various pathogens as compared to untreated controls. The pattern of BMT-induced cytokine responses was transferred to splenocytes, and not to peritoneal macrophages, of healthy controls via co-housing and transferred to germfree mice via transplantation of cecum content. Thus, BMT induces changes in gut microbiota that in their turn increase cytokine responsiveness of splenocytes. Thus, BMT establishes a dominant microbiota that attenuates normalization of the immune-response.

The Role of the Crosstalk Between Gut Microbiota and Immune Cells in the Pathogenesis and Treatment of Multiple Myeloma

Around 10% of all hematologic malignancies are classified as multiple myeloma (MM), the second most common malignancy within that group. Although massive progress in developing of new drugs against MM has been made in recent years, MM is still an incurable disease, and every patient eventually has relapse refractory to any known treatment. That is why further and non-conventional research elucidating the role of new factors in MM pathogenesis is needed, facilitating discoveries of the new drugs. One of these factors is the gut microbiota, whose role in health and disease is still being explored. This review presents the continuous changes in the gut microbiota composition during our whole life with a particular focus on its impact on our immune system. Additionally, it mainly focuses on the chronic antigenic stimulation of B-cells as the leading mechanism responsible for MM promotion. The sophisticated interactions between microorganisms colonizing our gut, immune cells (dendritic cells, macrophages, neutrophils, T/B cells, plasma cells), and intestinal epithelial cells will be shown. That article summarizes the current knowledge about the initiation of MM cells, emphasizing the role of microorganisms in that process.

Circulating microbial content in myeloid malignancy patients is associated with disease subtypes and patient outcomes

Although recent work has described the microbiome in solid tumors, microbial content in hematological malignancies is not well-characterized. Here we analyze existing deep DNA sequence data from the blood and bone marrow of 1870 patients with myeloid malignancies, along with healthy controls, for bacterial, fungal, and viral content. After strict quality filtering, we find evidence for dysbiosis in disease cases, and distinct microbial signatures among disease subtypes. We also find that microbial content is associated with host gene mutations and with myeloblast cell percentages. In patients with low-risk myelodysplastic syndrome, we provide evidence that Epstein-Barr virus status refines risk stratification into more precise categories than the current standard. Motivated by these observations, we construct machine-learning classifiers that can discriminate among disease subtypes based solely on bacterial content. Our study highlights the association between the circulating microbiome and patient outcome, and its relationship with disease subtype.

Rare transmission of commensal and pathogenic bacteria in the gut microbiome of hospitalized adults

Bacterial bloodstream infections are a major cause of morbidity and mortality among patients undergoing hematopoietic cell transplantation (HCT). Although previous research has demonstrated that pathogens may translocate from the gut microbiome into the bloodstream to cause infections, the mechanisms by which HCT patients acquire pathogens in their microbiome have not yet been described. Here, we use linked-read and short-read metagenomic sequencing to analyze 401 stool samples collected from 149 adults undergoing HCT and hospitalized in the same unit over three years, many of whom were roommates. We use metagenomic assembly and strain-specific comparison methods to search for high-identity bacterial strains, which may indicate transmission between the gut microbiomes of patients. Overall, the microbiomes of patients who share time and space in the hospital do not converge in taxonomic composition. However, we do observe six pairs of patients who harbor identical or nearly identical strains of the pathogen Enterococcus faecium, or the gut commensals Akkermansia muciniphila and Hungatella hathewayi. These shared strains may result from direct transmission between patients who shared a room and bathroom, acquisition from a common hospital source, or transmission from an unsampled intermediate. We also identify multiple patients with identical strains of species commonly found in commercial probiotics, including Lactobacillus rhamnosus and Streptococcus thermophilus. In summary, our findings indicate that sharing of identical pathogens between the gut microbiomes of multiple patients is a rare phenomenon. Furthermore, the observed potential transmission of commensal, immunomodulatory microbes suggests that exposure to other humans may contribute to microbiome reassembly post-HCT.

Here, Siranosian et al. provide evidence for rare transmission of commensal and pathogenic bacteria between the microbiomes of hospitalized adults, with important factors being roommate overlap and exposure to broad-spectrum antibiotics.

Intestinal mycobiota composition and changes in children with thalassemia who underwent allogeneic hematopoietic stem cell transplantation

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) alters the diversity of the intestinal bacterial microbiota. This study aimed to evaluate human mycobiota composition pre-HSCT and post-HSCT in children with thalassemia.

METHOD

Ten children with thalassemia undergoing allogeneic HSCT were enrolled. The stool samples were collected before the transplantation regimen, before the transplant day, and +15, +30 days, and three months after transplantation. Stool samples were also collected from the donor and the patient's caregivers. Gut mycobiota composition was evaluated with metagenomic analysis.

RESULTS

Pretransplant mycobiota of children with thalassemia (the predominant genus was Saccharomyces, 64.1%) has been shown to approximate the diverse mycobiota compositions of healthy adult donors but becomes altered (lower diversity) following transplant procedures. Three months after HSCT, phyla Ascomycota and Basidiomycota were 83.4% and 15.6%, respectively. The predominant species were Saccaharomyces_uc and Saccharomyces cerevisiae (phylum Ascomycota); we also observed Malassezia restricta and Malassezia globosa (phylum Basidiomycota) (∼13%). On day 90 after HSCT, we observed 65.3% M. restricta and 18.4% M. globosa predominance at the species level in a four-year-old boy with acute graft-versus-host disease (GVHD) (skin and gut involvement) 19 days after transplantation included.

CONCLUSION

The mycobiota composition of children with thalassemia altered after HSCT. We observed Malassezia predominance in a child with GVHD. Further studies in children with GVHD will identify this situation.

A longitudinal population-based study of predictors of mortality from bloodstream infections in Calgary, Alberta, Canada

Aim: To study the predictors of mortality from nine major pathogens causing approximately 70% of cases over a 7-year period. Materials & methods: A population-based surveillance cohort of all adult and pediatric patients in the Calgary Zone with an initial episode of bloodstream infections (BSI). Results: The 1-year mortality was 29.2% among 9524 patients (5164 males [54%]). Incidence rates for BSI increased annually to 119.7/100,000 persons by 2016. Distinct survival curves were found for each specific pathogen. Age, comorbidity burden and infecting organism were significantly associated with increased hazard of death. No relationship occurred between the time to positivity for blood cultures and overall mortality. Conclusion: BSI has a high mortality, but overall survival depends on underlying host health and the type of pathogen acquired.

GPR Expression in Intestinal Biopsies From SCT Patients Is Upregulated in GvHD and Is Suppressed by Broad-Spectrum Antibiotics

Microbiota can exert immunomodulatory effects by short-chain fatty acids (SCFA) in experimental models of graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-SCT). Therefore we aimed to analyze the expression of SCFAs sensing G-protein coupled receptor GPR109A and GPR43 by quantitative PCR in 338 gastrointestinal (GI) biopsies obtained from 199 adult patients undergoing allo-SCT and assessed the interaction of GPR with FOXP3 expression and regulatory T cell infiltrates. GPR expression was strongly upregulated in patients with stage II-IV GvHD (p=0.000 for GPR109A, p=0.01 for GPR43) and at the onset of GvHD (p 0.000 for GPR109A, p=0.006 for GPR43) and correlated strongly with FOXP3 and NLRP3 expression. The use of broad-spectrum antibiotics (Abx) drastically suppressed GPR expression as well as FOXP3 expression in patients’ gut biopsies (p=0.000 for GPRs, FOXP3 mRNA and FOXP3+ cellular infiltrates). Logistic regression analysis revealed treatment with Abx as an independent factor associated with GPR and FOXP3 loss. The upregulation of GPRs was evident only in the absence of Abx (p=0.001 for GPR109A, p=0.014 for GPR43) at GvHD onset. Thus, GPR expression seems to be upregulated in the presence of commensal bacteria and associates with infiltration of FOXP3+ T regs, suggesting a protective, regenerative immunomodulatory response. However, Abx, which has been shown to induce dysbiosis, interferes with this protective response.

Fecal Microbiota Transplant Mitigates Adverse Outcomes Seen in Patients Colonized With Multidrug-Resistant Organisms Undergoing Allogeneic Hematopoietic Cell Transplantation

The gut microbiome can be adversely affected by chemotherapy and antibiotics prior to hematopoietic cell transplantation (HCT). This affects graft success and increases susceptibility to multidrug-resistant organism (MDRO) colonization and infection. We performed an initial retrospective analysis of our use of fecal microbiota transplantation (FMT) from healthy donors as therapy for MDRO-colonized patients with hematological malignancy. FMT was performed on eight MDRO-colonized patients pre-HCT (FMT-MDRO group), and outcomes compared with 11 MDRO colonized HCT patients from the same period. At 12 months, survival was significantly higher in the FMT-MDRO group (70% versus 36% p = 0.044). Post-HCT, fewer FMT-MDRO patients required intensive care (0% versus 46%, P = 0.045) or experienced fever (0.29 versus 0.11 days, P = 0.027). Intestinal MDRO decolonization occurred in 25% of FMT-MDRO patients versus 11% non-FMT MDRO patients. Despite the significant differences and statistically comparable patient/transplant characteristics, as the sample size was small, a matched-pair analysis between both groups to non-MDRO colonized control cohorts (2:1 matching) was performed. At 12 months, the MDRO group who did not have an FMT had significantly lower survival (36.4% versus 61.9% respectively, p=0.012), and higher non relapse mortality (NRM; 60.2% versus 16.7% respectively, p=0.009) than their paired non-MDRO-colonized cohort. Conversely, there was no difference in survival (70% versus 43.4%, p=0.14) or NRM (12.5% versus 31.2% respectively, p=0.24) between the FMT-MDRO group and their paired non-MDRO cohort. Collectively, these data suggest that negative clinical outcomes, including mortality associated with MDRO colonization, may be ameliorated by pre-HCT FMT, even in the absence of intestinal MDRO decolonization. Further work is needed to explore this observed benefit.

The Pathophysiology and Treatment of Graft-Versus-Host Disease: Lessons Learnt From Animal Models

Allogeneic hematopoietic cell transplantation (HCT) is a curative treatment for hematologic malignancies, bone marrow failure syndromes, and inherited immunodeficiencies and metabolic diseases. Graft-versus-host disease (GVHD) is the major life-threatening complication after allogeneic HCT. New insights into the pathophysiology of GVHD garnered from our understanding of the immunological pathways within animal models have been pivotal in driving new therapeutic paradigms in the clinic. Successful clinical translations include histocompatibility matching, GVHD prophylaxis using cyclosporine and methotrexate, posttransplant cyclophosphamide, and the use of broad kinase inhibitors that inhibit cytokine signaling (e.g. ruxolitinib). New approaches focus on naïve T cell depletion, targeted cytokine modulation and the inhibition of co-stimulation. This review highlights the use of animal transplantation models to guide new therapeutic principles.

Microbiota long-term dynamics and prediction of acute graft-versus-host disease in pediatric allogeneic stem cell transplantation

BACKGROUND

Patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) exhibit changes in their gut microbiota and are experiencing a range of complications, including acute graft-versus-host disease (aGvHD). It is unknown if, when, and under which conditions a re-establishment of microbial and immunological homeostasis occurs. It is also unclear whether microbiota long-term dynamics occur at other body sites than the gut such as the mouth or nose. Moreover, it is not known whether the patients' microbiota prior to HSCT holds clues to whether the patient would suffer from severe complications subsequent to HSCT. Here, we take a holobiont perspective and performed an integrated host-microbiota analysis of the gut, oral, and nasal microbiota in 29 children undergoing allo-HSCT.

RESULTS

The bacterial diversity decreased in the gut, nose, and mouth during the first month and reconstituted again 1-3 months after allo-HSCT. The microbial community composition traversed three phases over 1 year. Distinct taxa discriminated the microbiota temporally at all three body sides, including Enterococcus spp., Lactobacillus spp., and Blautia spp. in the gut. Of note, certain microbial taxa appeared already changed in the patients prior to allo-HSCT as compared with healthy children. Acute GvHD occurring after allo-HSCT could be predicted from the microbiota composition at all three body sites prior to HSCT. The reconstitution of CD4⁺ T cells, T_H17, and B cells was associated with distinct taxa of the gut, oral, and nasal microbiota.

CONCLUSIONS

This study reveals for the first time bacteria in the mouth and nose that may predict aGvHD. Monitoring of the microbiota at different body sites in HSCT patients and particularly through involvement of samples prior to transplantation may be of prognostic value and could assist in guiding personalized treatment strategies. The identification of distinct bacteria that have a potential to predict post-transplant aGvHD might provide opportunities for an improved preventive clinical management, including a modulation of microbiomes. The host-microbiota associations shared between several body sites might also support an implementation of more feasible oral and nasal swab sampling-based analyses. Altogether, the findings suggest that the microbiota and host factors together could provide actionable information to guiding precision medicine. Video Abstract.

Fecal microbiota transfer for refractory intestinal graft-versus-host disease - Experience from two German tertiary centers

RATIONALE

Steroid refractory graft-vs-host disease (sr-GvHD) represents a challenging complication after allogeneic hematopoietic cell transplantation (allo-HCT). Intestinal microbiota (IM) diversity and dysbiosis were identified as influencing factors for the development of acute GvHD. Fecal microbiota transfer (FMT) is hypothesized to restore IM dysbiosis, but there is limited knowledge about the significance of FMT in the treatment of sr-GvHD.

OBJECTIVES

We studied the effects of FMT on sr-GvHD in allo-HCT patients from two German tertiary clinical centers (n = 11 patients; period: March 2017 until July 2019). To assess safety and clinical efficacy, we analyzed clinical data pre- and post-FMT (day -14 to +30 relative to FMT). Moreover, IM were analyzed in donor samples and in a subset of patients pre- and post-FMT by 16S rRNA sequencing.

RESULTS

Post-FMT, we observed no intervention-associated, systemic inflammatory responses and only minor side effects (5/11 patients: abdominal pain and transformation of peristalsis-each 3/11 and vomiting-1/11). Stool frequencies and volumes were significantly reduced [pre- vs post-FMT (d14): P < .05, respectively] as well as clear attenuation regarding both grading and staging of sr-GvHD was present upon FMT. Moreover, IM analyses revealed an increase of alpha diversity as well as a compositional shifts toward the donor post-FMT.

CONCLUSIONS

In our study, we observed positive effects on sr-GVHD after FMT without the occurrence of major adverse events. Although these findings are in line with published data on beneficial effects of FMT in sr-GvHD, further randomized clinical studies are urgently needed to better define the clinical validity including mode of action.

Update in clinical and mouse microbiota research in allogeneic haematopoietic cell transplantation

PURPOSE OF REVIEW

The intestinal microbiota plays a critical role in intestinal homeostasis and immune regulation and has been recognized as a predictor of clinical outcome in patients undergoing allogeneic haematopoietic cell transplantation (allo-HCT) and specifically a determinant of the severity of graft-versus-host disease (GVHD) in mouse models. As GVHD is the most important cause of nonrelapse mortality (NRM) after allo-HCT, understanding the mechanisms by which modifying the microbiota may prevent or decrease the severity of GVHD would represent an important advance.

RECENT FINDINGS

Microbiota injury was observed globally and higher diversity at peri-engraftment was associated with lower mortality. Lactose is a dietary factor that promotes post-allo-HCT Enterococcus expansion, which is itself associated with mortality from GVHD in patients and exacerbates GVHD in mice. Bacterial and fungal bloodstream infections are preceded by intestinal colonization with a corresponding organism, supporting the gut as a source for many bloodstream infections. Metabolomic profiling studies showed that GVHD is associated with changes in faecal and plasma microbiota-derived molecules.

SUMMARY

In this review, we highlight some of the most recent and important findings in clinical and mouse microbiota research, as it relates to allo-HCT. Many of these are already being translated into clinical trials that have the potential to change future practice in the care of patients.

Impact of pre-transplant use of antibiotics on the graft-versus-host disease in adult patients with hematological malignancies

OBJECTIVES

Changes in fecal microbiota affect the incidence and extent of graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). Most patients with hematological malignancies receive antibiotics for the treatment of febrile neutropenia prior to allogeneic HSCT, and pre-transplant use of antibiotics may influence the fecal microbiota and GVHD.

METHODS

We retrospectively analysed consecutive adult patients with hematological malignancies who received allogeneic HSCT at Chungnam National University Hospital between 2007 and 2018. Pre-transplant use of antibiotics was defined as the use of antibiotics before conditioning chemotherapy.

RESULTS

This study included 131 patients with a median age of 46 (range, 18-71) years: 76 (58%) patients were AML, 28 (21.4%) with ALL, 23 (17.6%) with MDS, and 4 (3.1%) with CML. All patients received calcineurin inhibitors with short-course methotrexate for GVHD prophylaxis. A total of 31 (23.7%) patients received anti-thymocyte globulin. All patients received antibiotics prior to HSCT: 70 (53.4%) patients received glycopeptide, 114 (87.0%) received cefepime, 87 (66.4%) received piperacillin/tazobactam, and 51 (38.9%) received carbapenem. Patients who received glycopeptide had more frequently extensive chronic GVHD (cGVHD) than those who did not (51.1% vs. 28.1% at 5 years) and had more frequently cGVHD of the lung (34.8% vs. 15.8% at 5 years). Pre-transplant use of glycopeptide did not affect the overall survival (OS) or GVHD- and relapse-free survival (GRFS) (median OS; 49 months in glycopeptide group vs. not reached in non-glycopeptide group, p=0.475; median GRFS; 9 months in glycopeptide group vs. 16 months in non-glycopeptide group, p=0.092).

CONCLUSION

Pre-transplant use of glycopeptide tends to increase the incidence of extensive cGVHD.

Fecal microbiota transplantation in the treatment of intestinal steroid-resistant graft-versus-host disease: two case reports and a review of the literature

Acute graft-versus-host disease (aGvHD) reduces the efficiency and safety of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In recent years, attempts have been made to transplant fecal microbiota from healthy donors to treat intestinal GvHD. This study presented two cases of patients undergoing allo-HSCT who were later selected for fecal microbiota transplantation (FMT). In the first patient, FMT resulted in the complete resolution of symptoms, whereas therapeutic efficacy was not achieved in the second patient. FMT eliminated drug-resistant pathogens, namely very drug-resistant Enterococcus spp., but not multidrug-resistant Acinetobacter baumannii or Candida spp. Further research is needed, particularly on the safety of FMT in patients with intestinal steroid-resistant GvHD and on the distant impact of transplanted microflora on the outcomes of allo-HSCT. FMT appears promising for the treatment of patients with steroid-resistant GvHD.

The clinical role of the gut microbiome and fecal microbiota transplantation in allogeneic stem cell transplantation

Outcomes of allogeneic hematopoietic stem cell transplantation (allo- HSCT) have improved in the recent decade; however, infections and graft-versus-host disease remain two leading complications significantly contributing to early transplant-related mortality. In past years, the human intestinal microbial composition (microbiota) has been found to be associated with various disease states, including cancer, response to cancer immunotherapy and to modulate the gut innate and adaptive immune response. In the setting of allo-HSCT, the intestinal microbiota diversity and composition appear to have an impact on infection risk, mortality and overall survival. Microbial metabolites have been shown to contribute to the health and integrity of intestinal epithelial cells during inflammation, thus mitigating graft-versus-host disease in animal models. While the cause-andeffect relationship between the intestinal microbiota and transplant-associated complications has not yet been fully elucidated, the above findings have already resulted in the implementation of various interventions aiming to restore the intestinal microbiota diversity and composition. Among others, these interventions include the administration of fecal microbiota transplantation. The present review, based on published data, is intended to define the role of the latter approach in the setting of allo-HSCT.

The pulmonary metatranscriptome prior to pediatric HCT identifies post-HCT lung injury

Lung injury after pediatric allogeneic hematopoietic cell transplantation (HCT) is a common and disastrous complication that threatens long-term survival. To develop strategies to prevent lung injury, novel tools are needed to comprehensively assess lung health in HCT candidates. Therefore, this study analyzed biospecimens from 181 pediatric HCT candidates who underwent routine pre-HCT bronchoalveolar lavage (BAL) at the University Medical Center Utrecht between 2005 and 2016. BAL fluid underwent metatranscriptomic sequencing of microbial and human RNA, and unsupervised clustering and generalized linear models were used to associate microbiome gene expression data with the development of post-HCT lung injury. Microbe-gene correlations were validated using a geographically distinct cohort of 18 pediatric HCT candidates. The cumulative incidence of post-HCT lung injury varied significantly according to 4 pre-HCT pulmonary metatranscriptome clusters, with the highest incidence observed in children with pre-HCT viral enrichment and innate immune activation, as well as in children with profound microbial depletion and concomitant natural killer/T-cell activation (P < .001). In contrast, children with pre-HCT pulmonary metatranscriptomes containing diverse oropharyngeal taxa and lacking inflammation rarely developed post-HCT lung injury. In addition, activation of epithelial-epidermal differentiation, mucus production, and cellular adhesion were associated with fatal post-HCT lung injury. In a separate validation cohort, associations among pulmonary respiratory viral load, oropharyngeal taxa, and pulmonary gene expression were recapitulated; the association with post-HCT lung injury needs to be validated in an independent cohort. This analysis suggests that assessment of the pre-HCT BAL fluid may identify high-risk pediatric HCT candidates who may benefit from pathobiology-targeted interventions.

Recent insights into the role of the microbiome in malignant and benign hematologic diseases

Growing evidence suggests the impact of microbiome alteration, named dysbiosis, on the development of neoplasms, infections, inflammatory diseases, and immuno-mediated disorders. Regarding hematologic diseases, most data regard hematopoietic stem cell transplant (HSCT). In this review, we systematically evaluate the studies concerning microbiome in malignant and benign hematologic disorders beyond HSCT. A permissive microbiota is associated to the development of hematologic malignancies (including acute leukemia, lymphoma, and multiple myeloma), as well as of iron deficiency anemia, autoimmune cytopenias, and aplastic anemia. This happens through various mechanisms; chronic inflammatory triggering, epithelial barrier alteration, antigen dissequestration, and molecular mimicry. Hematologic therapies (chemo and immunosuppression) may induce/worsen dysbiosis and favour disease progression and infectious complications. Antibiotics may also induce dysbiosis with possible long-term consequences. Finally, novel target therapies are likely to alter microbiome, inducing gut inflammation (i.e. small molecules such as tyrosine-kinase-inhibitors) or enhancing host's immune system (as observed with CAR-T cells and checkpoint inhibitors).

Post-haematopoietic cell transplantation outcomes: why ST2 became a 'golden nugget' biomarker

Immunotherapies have emerged as highly promising approaches to treat cancer patients. Allogeneic haematopoietic cell transplantation (HCT) is the most validated tumour immunotherapy available to date but its clinical efficacy is limited by toxicities, such as graft-versus-host disease (GVHD) and treatment resistance leading to relapse. The problems with new cellular therapies and checkpoint inhibitors are similar. However, development of biomarkers post-HCT, particularly for toxicities, has taken off in the last decade and has expanded greatly. Thanks to the advances in genomics, transcriptomics, proteomics and cytomics technologies, blood biomarkers have been identified and validated in promising diagnostic tests, prognostic tests stratifying for future occurrence of GVHD, and predictive tests for responsiveness to GVHD therapy and non-relapse mortality. These biomarkers may facilitate timely and selective therapeutic intervention. This review outlines a path from biomarker discovery to first clinical correlation, focusing on soluble STimulation-2 (sST2) - the interleukin (IL)-33-decoy receptor - which is the most validated biomarker.

Fecal Microbiota Transplantation in Allogeneic Hematopoietic Stem Cell Transplantation Recipients: A Systematic Review

The disruption of gut microbiota eubiosis has been linked to major complications in allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients. Various strategies have been developed to reduce dysbiosis and related complications. Fecal microbiota transplantation (FMT) consists of the infusion of fecal matter from a healthy donor to restore impaired intestinal homeostasis, and could be applied in the allo-HSCT setting. We conducted a systematic review of studies addressing the use of FMT in allo-HSCT patients. In the 23 papers included in the qualitative synthesis, FMT was used for the treatment of recurrent Clostridioides difficile infections or as a therapeutic strategy for steroid-resistant gut aGvHD. FMT was also performed with a preventive aim (e.g., to decolonize from antibiotic-resistant bacteria). Additional knowledge on the biological mechanisms underlying clinical findings is needed in order to employ FMT in clinical practice. There is also concern regarding the administration of microbial consortia in immune-compromised patients with altered gut permeability. Therefore, the safety profile and efficacy of the procedure must be determined to better assess the role of FMT in allo-HSCT recipients.

Microbiome-Derived Metabolites in Allogeneic Hematopoietic Stem Cell Transplantation

The gut microbiome has emerged as a major character in the context of hematopoietic stem cell transplantation. The biology underpinning this relationship is still to be defined. Recently, mounting evidence has suggested a role for microbiome-derived metabolites in mediating crosstalk between intestinal microbial communities and the host. Some of these metabolites, such as fiber-derived short-chain fatty acids or amino acid-derived compounds, were found to have a role also in the transplant setting. New interesting data have been published on this topic, posing a new intriguing perspective on comprehension and treatment. This review provides an updated comprehensive overview of the available evidence in the field of gut microbiome-derived metabolites and hematopoietic stem cell transplantation.

Prevention and management of carbapenem-resistant Enterobacteriaceae in haematopoietic cell transplantation

Carbapenem-resistant Enterobacteriaceae (CRE) infections are associated with high morbidity and mortality rates in haematopoietic cell transplantation (HCT) recipients. Factors like mucositis, neutropenia, prolonged hospital stay, and frequent use of prophylactic antimicrobials make HCT recipients especially susceptible to CRE infections. Low culture positivity rates, delay in microbiological diagnosis, and resistance to empirical antimicrobial therapy for febrile neutropenia are responsible for high mortality rates in HCT recipients infected with CRE. In this review we discuss the epidemiology, diagnosis, and management of CRE infections with particular emphasis on patients undergoing HCT. We emphasise the need for preventive strategies like multidisciplinary antimicrobial stewardship, and pre-emptive screening for CRE colonisation in prospective HCT patients as measures to mitigate the adverse impact of CRE on HCT outcomes. Newer diagnostic tests like polymerase chain reaction and matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF) assay that enable earlier and better identification of CRE isolates are discussed. Antimicrobial agents available against CRE, including newer agents like ceftazidime-avibactam and meropenem-vaborbactam, have been reviewed. We also discuss the data on promising experimental treatments against CRE: phage therapy and healthy donor faecal microbiota transplant. Finally, this review puts forth recommendations as per existing literature on diagnosis and management of CRE infections in blood and marrow transplant (BMT) unit.

Clinical effects and applications of the gut microbiome in hematologic malignancies

The gut microbiome and its effects on host immunity have exciting implications for cancer prognosis and therapy. Examples in allogeneic hematopoietic stem cell transplantation (allo-SCT) demonstrate the role of the gut microbiome as a biomarker for clinical outcomes, and animal models demonstrate how microbiota manipulation may augment therapeutic responses. There are multiple mechanisms that gut microbiota may have in affecting distant tumor environments, including control of cytokine release, dendritic cell activation, and T-cell lymphocyte stimulation. Recently, there has been a marked interest in understanding interactions between host and microbiome in hematologic malignancies. This review summarizes the current understanding of the gut microbiome and its impact on leukemia, lymphoma, multiple myeloma, and allo-SCT and highlights several broad methods for targeting the gut microbiome in therapeutic trials.

Broad-Spectrum Antibiotics and Risk of Graft-versus-Host Disease in Pediatric Patients Undergoing Transplantation for Acute Leukemia: Association of Carbapenem Use with the Risk of Acute Graft-versus-Host Disease

Variation in the gastrointestinal (GI) microbiota after hematopoietic cell transplantation (HCT) has been associated with acute graft-versus-host disease (aGVHD). Because antibiotics induce dysbiosis, we examined the association of broad-spectrum antibiotics with subsequent aGVHD risk in pediatric patients undergoing HCT for acute leukemia. We performed a retrospective analysis in a dataset merged from 2 sources: (1) the Center for International Blood and Marrow Transplant Research, an observational transplantation registry, and (2) the Pediatric Health Information Services, an administrative database from freestanding children's hospitals. We captured exposure to 3 classes of antibiotics used for empiric treatment of febrile neutropenia: (1) broad-spectrum cephalosporins, (2) antipseudomonal penicillins, and (3) carbapenems. The primary outcome was grade II-IV aGVHD; secondary outcomes were grade III-IV aGVHD and lower GI GVHD. The adjusted logistic regression model (full cohort) and time-to-event analysis (subcohort) included transplantation characteristics, GVHD risk factors, and adjunctive antibiotic exposures as covariates. The full cohort included 2550 patients at 36 centers; the subcohort included 1174 patients. In adjusted models, carbapenems were associated with an increased risk of grade II-IV aGVHD in the full cohort (adjusted odds ratio [aOR], 1.24; 95% confidence interval [CI], 1.02 to 1.51) and subcohort (sub hazard ratio [HR], 1.31; 95% CI, 0.99 to 1.72), as well as with an increased risk of grade III-IV aGVHD (subHR, 1.77; 95% CI, 1.25 to 2.52). Early carbapenem exposure (before day 0) especially impacted aGVHD risk. For antipseudomonal penicillins, the associations with aGVHD were in the direction of increased risk but were not statistically significant. There was no identified association between broad-spectrum cephalosporins and aGVHD. Carbapenems, more than other broad-spectrum antibiotics, should be used judiciously in pediatric HCT recipients to minimize aGVHD risk. Further research is needed to clarify the mechanism underlying this association.

Critical Care of Hematopoietic Stem Cell Transplant Patients

Life-threatening complications are frequent after hematopoietic stem cell transplant (HSCT), and optimum critical care is essential to ensuring good outcomes. The immunologic consequences of HSCT result in a markedly different host response to critical illness. Infection is the most common cause of critical illness but noninfectious complications are frequent. Respiratory failure or sepsis are the typical presentations but the sequelae of HSCT can affect nearly any organ system. Pattern recognition can facilitate anticipation and early intervention in post-HSCT critical illness. HSCT critical care is a multidisciplinary endeavor. Continued investigation and focus on process improvement will continue to improve outcomes.

Optimization of nutrition support practices early after hematopoietic cell transplantation

Nutrition support is often required during hematopoietic cell transplant (HCT) given the gastrointestinal toxicity that frequently precludes adequate protein-calorie intake. This article reviews the latest evidence for enteral versus parenteral nutrition in the adult and pediatric HCT population and addresses key considerations as well as barriers to implement this in practice. Registered Dietitian Nutritionists are key members of the interdisciplinary team to proactively manage enteral nutrition support to provide timely, adequate protein and calories to help prevent malnutrition, loss of lean body mass, and functional decline as well as provide evidence-based diet recommendations. This article also reviews emerging research supporting the role of luminal nutrients to maintain microbiotal diversity.

Microbiota modification in hematology: still at the bench or ready for the bedside?

Growing evidence suggests that human microbiota likely influence diverse processes including hematopoiesis, chemotherapy metabolism, and efficacy, as well as overall survival in patients with hematologic malignancies and other cancers. Both host genetic susceptibility and host-microbiota interactions may impact cancer risk and response to treatment; however, microbiota have the potential to be uniquely modifiable and accessible targets for treatment. Here, we focus on strategies to modify microbiota composition and function in patients with cancer. First, we evaluate the use of fecal microbiota transplant to restore microbial equilibrium following perturbation by antibiotics and chemotherapy, and as a treatment of complications of hematopoietic stem cell transplantation (HSCT), such as graft-versus-host disease and colonization with multidrug-resistant organisms. We then address the potential use of both probiotics and dietary prebiotic compounds in targeted modulation of the microbiota intended to improve outcomes in hematologic diseases. With each type of therapy, we highlight the role that abnormal, or dysbiotic, microbiota play in disease, treatment efficacy, and toxicity and evaluate their potential promise as emerging strategies for microbiota manipulation in patients with hematologic malignancies and in those undergoing HSCT.

Novel Biomarkers for Outcome After Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a well-established curative treatment for various malignant hematological diseases. However, its clinical success is substantially limited by major complications including graft-vs.-host disease (GVHD) and relapse of the underlying disease. Although these complications are known to lead to significant morbidity and mortality, standardized pathways for risk stratification of patients undergoing allo-HSCT are lacking. Recent advances in the development of diagnostic and prognostic tools have allowed the identification of biomarkers in order to predict outcome after allo-HSCT. This review will provide a summary of clinically relevant biomarkers that have been studied to predict the development of acute GVHD, the responsiveness of affected patients to immunosuppressive treatment and the risk of non-relapse mortality. Furthermore, biomarkers associated with increased risk of relapse and subsequent mortality will be discussed.