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

Research advances on short-chain fatty acids in gastrointestinal acute graft-versus-host disease

Gastrointestinal acute graft-versus-host disease (GI-aGVHD) is a severe early complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT). It has been shown that the intestinal microbiota plays a critical role in this process. As metabolites of the intestinal microbiota, short-chain fatty acids (SCFAs) are vital for maintaining the host-microbiota symbiotic equilibrium. This article provides an overview of the protective effect of SCFAs in the gastrointestinal tract, emphasizes their association with GI-aGVHD, and explores relevant research progress in prevention and treatment research.

The Microbiome and Pediatric Transplantation

The microbial communities that inhabit our bodies have been increasingly linked to host physiology and pathophysiology. This microbiome, through its role in colonization resistance, influences the risk of infections after transplantation, including those caused by multidrug-resistant organisms. In addition, through both direct interactions with the host immune system and via the production of metabolites that impact local and systemic immunity, the microbiome plays an important role in the establishment of immune tolerance after transplantation, and conversely, in the development of graft-versus-host disease and graft rejection. This review offers a comprehensive overview of the evidence for the role of the microbiome in hematopoietic cell and solid organ transplant complications, drivers of microbiome shift during transplantation, and the potential of microbiome-based therapies to improve pediatric transplantation outcomes.

Gut microbiota, microbiota-derived metabolites, and graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation is one of the most effective treatment strategies for leukemia, lymphoma, and other hematologic malignancies. However, graft-versus-host disease (GVHD) can significantly reduce the survival rate and quality of life of patients after transplantation, and is therefore the greatest obstacle to transplantation. The recent development of new technologies, including high-throughput sequencing, metabolomics, and others, has facilitated great progress in understanding the complex interactions between gut microbiota, microbiota-derived metabolites, and the host. Of these interactions, the relationship between gut microbiota, microbial-associated metabolites, and GVHD has been most intensively researched. Studies have shown that GVHD patients often suffer from gut microbiota dysbiosis, which mainly manifests as decreased microbial diversity and changes in microbial composition and microbiota-derived metabolites, both of which are significant predictors of poor prognosis in GVHD patients. Therefore, the purpose of this review is to summarize what is known regarding changes in gut microbiota and microbiota-derived metabolites in GVHD, their relationship to GVHD prognosis, and corresponding clinical strategies designed to prevent microbial dysregulation and facilitate treatment of GVHD.

Use of complementary and alternative medicine in children affected by oncologic, neurologic and liver diseases: a narrative review

Complementary and alternative medicine (CAM) consist of a broad group of restorative resources often linked to existing local cultures and established health care systems and are also increasingly used in children with some serious illnesses. In this narrative review, we examine the epidemiology of the use, efficacy, and safety of complementary and alternative medicine in pediatric oncology, neurology, and hepatology. We searched for relevant articles published in Pubmed evaluating CAM use and its efficacy in safety in children affected by oncologic, neurologic and liver diseases. CAM is used to improve the success of conventional therapies, but also to alleviate the pain, discomfort, and suffering resulting from the diseases and their treatment, which are often associated with a significant burden of adverse effects. CAM use must be evaluated in children with neurological, oncological and liver diseases.

The Critical Exploration into Current Evidence behind the Role of the Nutritional Support in Adult Patients Who Undergo Haematogenic Stem Cell Transplantation

Haematopoietic stem cell transplantation (HSCT) is a treatment option for many haematological conditions in patients of all ages. Nutritional support is important at each stage of treatment, but particular nutritional needs and dictated support occur during the preparatory (conditioning regimen) and post-transplant periods. Patients may require nutritional treatment by the enteral or parenteral route. The quantitative and qualitative composition of meals may change. Vitamin requirements, including vitamin D and vitamin C, might also be different. An adequately composed diet, adapted to the needs of the patient, may influence the occurrence of complications such as graft-versus-host disease (GvHD), gastrointestinal disorders, infections, and reduced survival time. Haematological diseases as well as transplantation can negatively affect the intestinal flora, with negative consequences in the form of mucosal inflammation and disorders of a functional nature. Currently, aspects related to nutrition are crucial in the care of patients after HSCT, and numerous studies, including randomized trials on these aspects, are being conducted. This study serves the critical analysis of current scientific evidence regarding nutritional support for patients after HSCT.

From support to therapy: rethinking the role of nutrition in acute graft-versus-host disease

Allogeneic Hematopoietic stem cell transplantation (HSCT) offers a potential cure for patients with hematologic malignancies. Unfortunately, graft-versus-host disease (GVHD) remains a major obstacle to the greater success of this treatment. Despite intensive research efforts over the past several decades, GVHD is still a major cause of morbidity and mortality in patients receiving allogeneic HSCT. The genetic disparity between donor and recipient is the primary factor that dictates the extent of alloimmune response and the severity of acute GVHD (aGVHD). However, some nongenetic factors are also actively involved in GVHD pathogenesis. Thus, identifying host factors that can be readily modified to reduce GVHD risk is of important clinical significance. We are particularly interested in the potential role of nutrition, as a nongenetic factor, in the etiology and management of aGVHD. In this article, we summarize recent findings regarding how different routes of nutritional support and various dietary factors affect aGVHD. Since diet is one of the most important factors that shape gut microbiota, we also provide evidence for a potential link between certain nutrients and gut microbiota in recipients of allogeneic HSCT. We propose a shifting role of nutrition from support to therapy in GVHD by targeting gut microbiota.

Gut microbiota intervention by pre and probiotics can induce regulatory T cells and reduce the risk of severe acute GVHD following allogeneic hematopoietic stem cell transplantation

BACKGROUND

Acute graft-versus-host disease (aGVHD) is one of the leading causes of limitation and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Numerous studies have shown that changes in the gut microbiome diversity increased post-transplant problems, including the occurrence of aGVHD. Probiotics and prebiotics can reconstitute the gut microbiota and thus increase bacterial metabolites such as short-chain fatty acids (SCFAs) that have immunomodulatory effects preventing aGVHD in recipients of allo-HSCTs.

METHODS/STUDY DESIGN

We conducted a pilot randomized clinical trial to investigate whether oral synbiotics are associated with the prevention or reduction in occurrence/severity and mitigate complications of aGVHD following allo-HSCT. A commercially available synbiotic mixture containing high levels of 7 safe bacterial strains plus fructo-oligosaccharides as a prebiotic was administered to allo-HSCT recipients. Out of 40 allo-HSCT patients, 20 received daily a synbiotic 21 days prior to transplantation (days -21 to day 0). In contrast, in the control group 20 recipients of allo-HSCT did not receive a symbiotic therapy.

RESULTS

Within first 100 days of observation, the incidence of severe (grade III/IV) aGVHD in the a synbiotic-therapy group was 0% (0 out of 20 patients), whereas it was 25% (5 out of 20 patients) in the control group (P = 0.047). The median percentage of CD4 + CD25 + Foxp3+ regulatory T cells (Tregs) among CD4+ lymphocytes on day 28 after HSCT in the synbiotic group was higher (2.54%) than in control group (1.73%; P = 0.01). There was no difference in Treg cells on day 7 after HSCT between two groups. However, the median percentage and the absolute count of Tregs in patients who experience aGVHD was significantly lower on days 7 and 28 after HSCT (both P < 0.05). The overall 12-month survival (OS) rate was higher (90%) in the symbiotic-treated patients than in the control group (75%), but the difference was not statistically significant (P = 0.234).

CONCLUSION

Our preliminary findings suggest that synbiotic intake before and during the conditioning regimen of allo-HSCT patients may lead to a reduction in the incidence and severity of aGVHD through the induction of CD4 + CD25 + Foxp3+ regulatory T cells, thus contributing to the improvement of transplant outcomes. Much larger studies are needed to confirm our observations.

Anti-E. coli Immunoglobulin Yolk (IgY): Reduction of pathogen receptors and inflammation factors could be caused by decrease in E. coli load

Graft versus host disease (GVHD) remains the major cause of morbidity and mortality after allogeneic stem cell transplantation, especially for intestinal GVHD, as steroid resistant GVHD results in high mortality. For this reason, new treatments of GVHD are needed. One approach is the reduction of pathogenic bacteria using anti-E. coli Immunoglobulin Yolk (IgY). In a haploidentical murine model, B6D2F1 mice conditioned with total body irradiation (TBI), received bone marrow cells (BM) and splenocytes (SC) from either syngeneic (Syn = B6D2F1) or allogeneic (Allo = C57BL/6) donors. Following this, animals received from day -2 until day +28 chow contained IgY or control chow. Thereafter the incidence and severity of aGVHD, the cytokines, chemokines, IDO1 and different pathogen-recognition receptors (PRR) were analyzed and compared to control animals (received chow without IgY). We found that animals receiving chow with IgY antibody showed reduced GVHD severity compared to control animals. On day28 after alloBMT, IDO, NOD2, TLR2, TLR4 and the inflammatory chemokine CCL3, were reduced in the colon and correlated with a significant decrease in E. coli bacteria. In summary chow containing chicken antibodies (IgY) improved GVHD via decrease in bacterial load of E coli conducting to reduction of pathogen receptors (NOD2, TLR2 and 4), IDO, chemokines and cytokines.

The Microbiome and Its Impact on Allogeneic Hematopoietic Cell Transplantation

ABSTRACT

Allogeneic hematopoietic cell transplantation (alloHCT) is a standard curative therapy for a variety of benign and malignant hematological diseases. Previously, patients who underwent alloHCT were at high risk for complications with potentially life-threatening toxicities, including a variety of opportunistic infections as well as acute and chronic manifestations of graft-versus-host disease (GVHD), where the transplanted immune system can produce inflammatory damage to the patient. With recent advances, including newer conditioning regimens, advances in viral and fungal infection prophylaxis, and novel GVHD prophylactic and treatment strategies, improvements in clinical outcomes have steadily improved. One modality with great potential that has yet to be fully realized is targeting the microbiome to further improve clinical outcomes.In recent years, the intestinal microbiota, which includes bacteria, fungi, viruses, and other microbes that reside within the intestinal tract, has become established as a potent modulator of alloHCT outcomes. The composition of intestinal bacteria, in particular, has been found in large multicenter prospective studies to be strongly associated with GVHD, treatment-related mortality, and overall survival. Murine studies have demonstrated a causal relationship between intestinal microbiota injury and aggravated GVHD, and more recently, clinical interventional studies of repleting the intestinal microbiota with fecal microbiota transplantation have emerged as effective therapies for GVHD. How the composition of the intestinal bacterial microbiota, which is often highly variable in alloHCT patients, can modulate GVHD and other outcomes is not fully understood. Recent studies, however, have begun to make substantial headway, including identifying particular bacterial subsets and/or bacterial-derived metabolites that can mediate harm or benefit. Here, the authors review recent studies that have improved our mechanistic understanding of the relationship between the microbiota and alloHCT outcomes, as well as studies that are beginning to establish strategies to modulate the microbiota with the hope of optimizing clinical outcomes.

Allogeneic hematopoietic cell transplantation, the microbiome, and graft-versus-host disease

Many patients with hematological malignancies, such as acute myeloid leukemia, receive an allogeneic hematopoietic cell transplantation (HCT) to cure their underlying condition. Allogeneic HCT recipients are exposed to various elements during the pre-, peri- and post-transplant period that can disrupt intestinal microbiota, including chemo- and radiotherapy, antibiotics, and dietary changes. The dysbiotic post-HCT microbiome is characterized by low fecal microbial diversity, loss of anaerobic commensals, and intestinal domination, particularly by Enterococcus species, and is associated with poor transplant outcomes. Graft-versus-host disease (GvHD) is a frequent complication of allogeneic HCT caused by immunologic disparity between donor and host cells and results in tissue damage and inflammation. Microbiota injury is particularly pronounced in allogeneic HCT recipients who go on to develop GvHD. At present, manipulation of the microbiome for example, via dietary interventions, antibiotic stewardship, prebiotics, probiotics, or fecal microbiota transplantation, is widely being explored to prevent or treat gastrointestinal GvHD. This review discusses current insights into the role of the microbiome in GvHD pathogenesis and summarizes interventions to prevent and treat microbiota injury.

The interplay between anticancer challenges and the microbial communities from the gut

Cancer being an increasing burden on human health, the use of anticancer drugs has risen over the last decades. The physiological effects of these drugs are not only perceived by the host's cells but also by the microbial cells it harbors as commensals, notably the gut microbiota. Since the early '50 s, the cytotoxicity of anticancer chemotherapy was evaluated on bacteria revealing some antimicrobial activities that result in an established perturbation of the gut microbiota. This perturbation can affect the host's health through dysbiosis, which can lead to multiple complications, but has also been shown to have a direct effect on the treatment efficiency.We, therefore, conducted a review of literature focusing on this triangular relationship involving the microbial communities from the gut, the host's disease, and the anticancer treatment. We focused specifically on the antimicrobial effects of anticancer chemotherapy, their impact on mutagenesis in bacteria, and the perspectives of using bacteria-based tools to help in the diagnostic and treatment of cancer.

Host-microbe interactions and outcomes in multiple myeloma and hematopoietic stem cell transplantation

Microbiota are essential to normal immune development and there is growing recognition of its importance to human health and disease and deepening understanding of the complexity of host-microbe interactions in the human gut and other tissues. Commensal microbes not only can influence host immunity locally through impacts of bioactive microbial metabolites and direct interactions with epithelial cells and innate immune receptors but also can exert systemic immunomodulatory effects via impacts on host immune cells capable of trafficking beyond the gut. Emerging data suggest microbiota influence the development of multiple myeloma (MM), a malignancy of the immune system derived from immunoglobulin-producing bone marrow plasma cells, through the promotion of inflammation. Superior treatment outcomes for MM correlate with a higher abundance of commensal microbiota capable of influencing inflammatory responses through the production of butyrate. In patients with hematologic malignancies, higher levels of diversity of the gut microbiota correlate with superior outcomes after hematopoietic stem cell transplantation. Correlative data support the impact of commensal microbiota on survival, risk of infection, disease relapse, and graft-versus-host disease (GVHD) after transplant. In this review, we will discuss the current understanding of the role of host-microbe interactions and the inflammatory tumor microenvironment of multiple myeloma, discuss data describing the key role of microbiota in hematopoietic stem cell transplantation for treatment of hematologic malignancies, and highlight several possible concepts for interventions directed at the gut microbiota to influence treatment outcomes.

FK506 and Lactobacillus acidophilus ameliorate acute graft-versus-host disease by modulating the T helper 17/regulatory T-cell balance

Background

Graft-versus-host disease (GvHD) is a critical complication after allogeneic hematopoietic stem cell transplantation (HSCT). The immunosuppressants given to patients undergoing allogeneic HSCT disturb the microbiome and the host immune system, potentially leading to dysbiosis and inflammation, and may affect immune function and bone marrow transplantation. The intestinal microbiome is a target for the development of novel therapies for GvHD. Lactobacillus species are widely used supplements to induce production of antimicrobial and anti-inflammatory factors.

Methods

We determined the effect of the combination of Lactobacillus acidophilus and FK506 on GvHD following major histocompatibility complex-mismatched bone marrow transplantation.

Results

The combination treatment suppressed IFN-γ and IL-17-producing T cell differentiation, but increased Foxp3⁺Treg differentiation and IL-10 production. Also, the combination treatment and combination treated-induced Treg cells modulated the proliferation of murine alloreactive T cells in vitro. Additionally, the combination treatment upregulated Treg-related genes—Nt5e, Foxp3, Ikzf2, Nrp1 and Itgb8—in murine CD4⁺-T cells. The combination treatment also alleviated GvHD clinically and histopathologically by controlling the effector T cell and Treg balance in vivo. Moreover, the combination treatment decreased Th17 differentiation significantly and significantly upregulated Foxp3 and IL-10 expression in peripheral blood mononuclear cells from healthy controls and liver transplantation (LT) patients.

Conclusions

Therefore, the combination of L. acidophilus and FK506 is effective and safe for patients undergoing allogeneic hematopoietic stem cell transplantation.

Berberine ameliorates aGVHD by gut microbiota remodelling, TLR4 signalling suppression and colonic barrier repairment for NLRP3 inflammasome inhibition

Berberine (BBR), an isoquinoline alkaloid, is used to treat gastrointestinal disorders as an herbal medicine in China. The aim of this study was to investigate the anti‐inflammatory activities of BBR in a mouse model with acute graft‐versus‐host disease (aGVHD). Mice were intravenously injected with bone marrow cells from donors combined with splenocytes to develop aGVHD. The body weight, survival rate and clinical scores were monitored. Then the levels of inflammatory cytokines, histological changes (lung, liver and colon), colonic mucosal barrier and gut microbiota were analysed. Moreover, the toll‐like receptor 4 (TLR4)/myeloid differentiation primary response gene 88 (Myd88)/nuclear factor‐κB signalling pathway, NLRP3 inflammasome and its cytokines’ expressions were determined. The results showed that the gavage of BBR lessened GVHD‐induced weight loss, high mortality and clinical scores, inhibited inflammation and target organs damages and prevented GVHD‐indued colonic barrier damage. Additionally, BBR modulated gut microbiota, suppressed the activation of the TLR4 signaling pathway and inhibited NLRP3 inflammasome and its cytokine release. This study indicated that BBR might be a potential therapy for aGVHD through NLRP3 inflammasome inhibition.

Microbiota-targeted therapies in inflammation resolution

Gut microbiota has been shown to systemically shape the immunological landscape, modulate homeostasis and play a role in both health and disease. Dysbiosis of gut microbiota promotes inflammation and contributes to the pathogenesis of several major disorders in gastrointestinal tract, metabolic, neurological and respiratory diseases. Much effort is now focused on understanding host-microbes interactions and new microbiota-targeted therapies are deeply investigated as a means to restore health or prevent disease. This review details the immunoregulatory role of the gut microbiota in health and disease and discusses the most recent strategies in manipulating individual patient's microbiota for the management and prevention of inflammatory conditions.

Roles of the intestinal microbiota and microbial metabolites in acute GVHD

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

Retinoic Acid Signaling Modulates Recipient Gut Barrier Integrity and Microbiota After Allogeneic Hematopoietic Stem Cell Transplantation in Mice

Graft-versus-host disease (GVHD) remains a major complication after allogeneic hematopoietic stem cell transplantation (HSCT). An impaired intestinal epithelial barrier is an important component of GVHD pathogenesis. However, contributing host factors that modulate mucosal barrier integrity during GVHD are poorly defined. We hypothesized that vitamin A and retinoic acid (RA) exert positive impacts on maintaining intestinal barrier function after HSCT, thus preventing or dampening GVHD severity. Unexpectedly, we found that exogenous RA increased intestinal permeability of recipient mice after allogeneic HSCT. Serum bacterial endotoxin levels were significantly higher in GVHD mice fed a vitamin A-high (VAH) diet compared to those fed a vitamin A-normal (VAN) diet, indicating a more compromised intestinal barrier function. Furthermore, VAH mice showed more severe lung GVHD with increased donor T cell infiltration in this tissue and died significantly faster than VAN recipients. 16S rRNA sequencing of fecal samples revealed significant differences in the diversity and composition of gut microbiota between VAN and VAH transplant recipients. Collectively, we show that retinoic acid signaling may negatively impact intestinal barrier function during GVHD. Mild vitamin A supplementation is associated with increased lung GVHD and more profound gut dysbiosis. Micronutrients such as vitamin A could modulate complications of allogeneic HSCT, which may be mediated by shaping gut microbiota.

Gut Microbiome Modulation and Faecal Microbiota Transplantation Following Allogenic Hematopoietic Stem Cell Transplantation

Nowadays, allogenic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy that is mainly recommended for hematologic malignancies. However, complications (such as graft-versus-host disease, mucositis, disease relapse, and infections) associated with the HSCT procedure contribute to the development of gut microbiota imbalance, gut-barrier disruption, and increased intestinal permeability. In the present narrative review, the crosstalk between gut microbiota products and intestinal homeostasis is discussed. Notably, gut-microbiota-related aspects have an impact on patients' clinical outcomes and overall survival. In accordance with the most recent published data, gut microbiota is crucial for the treatment effectiveness of many diseases, not only gastrointestinal cancers but also hematologic malignancies. Therefore, it is necessary to indicate a therapeutic method allowing to modulate gut microbiota in HSCT recipients. Currently, fecal microbiota transplantation (FMT) is the most innovative method used to alter/restore gut microbiota composition, as well as modulate its activity. Despite the fact that some previous data have shown promising results, the knowledge regarding FMT in HSCT is still strongly limited, except for the treatment of Clostridium difficile infection. Additionally, administration of prebiotics, probiotics, synbiotics, and postbiotics can also modify gut microbiota; however, this strategy should be considered carefully due to the high risk of fungemia/septicemia (especially in case of fungal probiotics).

The post-hematopoietic cell transplantation microbiome: relationships with transplant outcome and potential therapeutic targets

Microbiota injury occurs in many patients undergoing allogeneic hematopoietic cell transplantation, likely as a consequence of conditioning regimens involving chemo- and radiotherapy, the widespread use of both prophylactic and therapeutic antibiotics, and profound dietary changes during the peri-transplant period. Peri-transplant dysbiosis is characterized by a decrease in bacterial diversity, loss of commensal bacteria and single-taxon domination (e.g., with Enterococcal strains). Clinically, deviation of the post-transplant microbiota from a normal, high-diversity, healthy state has been associated with increased risk of bacteremia, development of graft-versus-host disease and decreases in overall survival. A number of recent clinical trials have attempted to target the microbiota in allogeneic hematopoietic cell transplantation patients via dietary interventions, selection of therapeutic antibiotics, administration of pre- or pro-biotics, or by performing fecal microbiota transplantation. These strategies have yielded promising results but the mechanisms by which these interventions influence transplant-related complications remain largely unknown. In this review we summarize the current approaches to targeting the microbiota, discuss potential underlying mechanisms and highlight the key outstanding areas that require further investigation in order to advance microbiota- targeting therapies.

Interplay Between the Intestinal Microbiota and Acute Graft-Versus-Host Disease: Experimental Evidence and Clinical Significance

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for many hematological disorders and autoimmune diseases, but acute graft-versus-host disease (aGVHD) has remained a major obstacle that limits allo-HSCT and exhibits a daunting mortality rate. The gastrointestinal system is among the most common sites affected by aGVHD. Experimental advances in the field of intestinal microbiota research enhanced our understanding - not only of the quantity and diversity of intestinal microbiota - but also their association with homeostasis of the immune system and disease pathogenesis, including that of aGVHD. Meanwhile, ever-growing clinical evidence suggest that the intestinal microbiota is dysregulated in patients who develop aGVHD and that the imbalance may affect clinical outcomes, indicating a potential predictive role for microbiota dysregulation in aGVHD severity and prognosis. The current animal and human studies investigating the intestinal microbiota in aGVHD and the understanding of the influence and management of the microbiota in the clinic are reviewed herein. Taken together, monitoring and remodeling the intestinal microecology following allo-HSCT may provide us with promising avenues for diagnosing, preventing or treating aGVHD in the clinic.

Probiotics in Cancer

In recent years, the consumption of over-the-counter probiotics to promote health has grown rapidly worldwide and become an independent industry. In medicine, various studies have demonstrated that probiotics can help improve the immune system and intestinal health. They are usually safe, but in some rare cases, they may cause concerning adverse reactions. Although the use of probiotics has been widely popularized in the public, the results of many probiotic clinical trials are contradictory. Particularly in cancer patients, the feasibility of probiotic management providing benefits by targeting cancer and lessening anticancer side effects requires further investigation. This review summarizes the interactions between probiotics and the host as well as current knowledge on the pros and cons of utilizing probiotics in cancer patients.

Immunonutritional support as an important part of multidisciplinary anti-cancer therapy

Immunonutrition is one of the most important parts of nutritional treatment in patients with cancer. There are studies which confirm positive effects of using immunonutrition (arginine, glutamine, omega-3 fatty acids, nucleotides, pre- and probiotics) among others on the reduction of the pro-inflammatory cytokines concentrations, shortening of the hospital stay and improvement of the nutritional status. Arginine takes part not only in wound healing process, but also it improves body’s immunity and reduces the incidence of infections. Glutamine reduces the incidence of acute grade 2 and 3 esophagitis and improves quality of life of gastric cancer patients. Omega 3-fatty acids have the ability to inhibit the activity of NF-κB. They also reduce the symptoms of graft-versus-host disease in patients undergoing hematopoietic cell transplantation. Nucleotides support the regeneration of intestinal villi. Probiotics play many roles, mainly inhibit the process of carcinogenesis, reduce the incidence of diarrhea and modify intestinal microbiome. However, there are studies indicating the lack of advantages of using immunonutrition compared to standard nutrition. Currently, there is no clear evidence for the use of formulae enriched with immunonutrients versus standard oral nutritional supplements exclusively in the preoperative period. This review summarizes the current knowledge about the role of immunonutrition in supporting treatment of cancer diseases.

The role of microbiota in allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is commonly performed to treat a variety of benign and malignant hematological diseases. Acute graft-versus-host disease (GVHD) is a major life-threatening complication that often occurs following allo-HSCT. Recently, improvements in methods to characterize the microbiota have led to a greater appreciation for how frequently and profoundly an alteration in microbial composition, or dysbiosis, can occur in allo-HSCT recipients to better decipher the complex interplay between microbiota and allo-HSCT outcomes.

AREAS COVERED

This article reviews the current knowledge of the microbiota's impact on allo-HSCT outcomes, including effects of microbiota-derived metabolites, and crosstalk between commensals and the allogeneic immune response. This article also summarizes the effects of HSCT and transplant-related procedures on microbiota, and recent developments in interventional strategies.

EXPERT OPINION

A growing body of literature indicates that the composition of the intestinal microbiota can function as a predictive biomarker for the risk and severity of acute GVHD, as well as overall survival, in patients undergoing allo-HSCT. Mechanisms underpinning these associations, however, are not well understood, and clinical strategies that modulate the microbiome to improve outcomes have yet to be fully developed. There is an unmet need to determine mechanisms to improve the efficacy of allo-HSCT.

The emerging roles of the gut microbiome in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is used for the treatment of hematologic cancers and disorders. However, graft-versus-host disease (GVHD) in which the donor immune cells attack the genetically-disparate recipient is a significant cause of morbidity. Acute GVHD is an inflammatory condition and the gastrointestinal system is a major organ affected but is also tied to beneficial graft-versus-tumor (GVT) effects. There is increasing interest on the role of the microbiome on immune function as well as on cancer progression and immunotherapy outcomes. However, there are still significant unanswered questions on the role the microbiome plays in GVHD progression or how to exploit the microbiome in GVHD prevention or treatment. In this review, concepts of HSCT with the focus on GVHD pathogenesis as well as issues in preclinical models used to study GVHD will be discussed with an emphasis on the impact of the microbiome. Factors affecting the microbiome and GVHD outcome such as obesity are also examined. The bridging of preclinical models and clinical outcomes in relation to the role of the microbiome will also be discussed along with possibilities for therapeutic exploitation.

Targeting the gut microbiome: An emerging trend in hematopoietic stem cell transplantation

Mounting evidence has demonstrated the critical role of the gut microbiome in different cancer treatment modalities showing intensive crosstalk between microbiota and the host immune system. In cancer patients receiving hematopoietic stem cell transplantation (HSCT), conditioning regimens including chemotherapy, radiotherapy, and immunosuppressive therapy, as well as antimicrobial prophylaxis, result in intestinal barrier disruption and massive changes in microbiota composition. According to clinical studies, a drastic loss of microbial diversity during HSCT is associated with enhanced pro-inflammatory immune response and an increased risk of transplant-related complications such as graft-versus-host disease (GvHD) and mortality. In this review, we outline the current understanding of the role of microbiota diversity in the patient response to cancer therapies and highlight the impact of changes in the gut microbiome on clinical outcomes in post-HSCT patients. Moreover, the therapeutic implications of microbiota modulation by probiotics, prebiotics, and fecal microbiota transplantation (FMT) in hematologic cancer patients receiving HSCT are discussed.

Risk Factors and Outcome of C. difficile Infection after Hematopoietic Stem Cell Transplantation

Patients who undergo hematopoietic stem cell transplants (HSCT) are at major risk of C. difficile (CD) infection (CDI), the most common cause of nosocomial diarrhea. We conducted a retrospective study, which enrolled 481 patients who underwent autologous (220) or allogeneic HSCT (261) in a 5-year period, with the aim of identifying the incidence, risk factors and outcome of CDI between the start of conditioning and 100 days after HSCT. The overall cumulative incidence of CDI based upon clinical evidence was 5.4% (95% CI, 3.7% to 7.8%), without any significant difference between the two types of procedures. The median time between HSCT and CDI diagnosis was 12 days. Out of 26 patients, 19 (73%) with clinical and symptomatic evidence of CDI were positive also for enzymatic or molecular detection of toxigenic CD; in particular, in 5 out of 26 patients (19%) CD binary toxin was also detected. CDI diagnoses significantly increased in the period 2018-2019, since the introduction in the microbiology lab unit of the two-step diagnostic test based on GDH immunoenzymatic detection and toxin B/binary toxin/027 ribotype detection by real-time PCR. Via multivariate analysis, abdominal surgery within 10 years before HSCT (p = 0.002), antibiotic therapy within two months before HSCT (p = 0.000), HCV infection (p = 0.023) and occurrence of bacterial or fungal infections up to 100 days after HSCT (p = 0.003) were significantly associated with a higher risk of CDI development. The 26 patients were treated with first-line vancomycin (24) or fidaxomicine (2) and only 2 patients needed a second-line treatment, due to the persistence of stool positivity. No significant relationship was identified between CDI and the development of acute graft versus host disease (GVHD) after allogeneic HSCT. At a median follow-up of 25 months (range 1-65), the cumulative incidence of transplant related mortality (TRM) was 16.6% (95% CI 11.7% to 22.4%) and the 3-year overall survival (OS) was 67.0% (95% CI 61.9% to 71.6%). The development of CDI had no significant impact on TRM and OS, which were significantly impaired in the multivariate analysis by gastrointestinal and urogenital comorbidities, severe GVHD, previous infections or hospitalization within two months before HSCT, active disease at transplant and occurrence of infections after HSCT. We conclude that 20% of all episodes of diarrhea occurring up to 100 days after HSCT were related to toxigenic CD infection. Patients with a history of previous abdominal surgery or HCV infection, or those who had received broad spectrum parenteral antibacterial therapy were at major risk for CDI development. CDIs were successfully treated with vancomycin or fidaxomicin after auto-HSCT as well as after allo-HSCT.

How to Make an Immune System and a Foreign Host Quickly Cohabit in Peace? The Challenge of Acute Graft-Versus-Host Disease Prevention After Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) has been used as cellular immunotherapy against hematological cancers for more than six decades. Its therapeutic efficacy relies on the cytoreductive effects of the conditioning regimen but also on potent graft-versus-tumor (GVT) reactions mediated by donor-derived immune cells. However, beneficial GVT effects may be counterbalanced by acute GVHD (aGVHD), a systemic syndrome in which donor immune cells attack healthy tissues of the recipient, resulting in severe inflammatory lesions mainly of the skin, gut, and liver. Despite standard prophylaxis regimens, aGVHD still occurs in approximately 20–50% of alloHCT recipients and remains a leading cause of transplant-related mortality. Over the past two decades, advances in the understanding its pathophysiology have helped to redefine aGVHD reactions and clinical presentations as well as developing novel strategies to optimize its prevention. In this review, we provide a brief overview of current knowledge on aGVHD immunopathology and discuss current approaches and novel strategies being developed and evaluated in clinical trials for aGVHD prevention. Optimal prophylaxis of aGVHD would prevent the development of clinically significant aGVHD, while preserving sufficient immune responsiveness to maintain beneficial GVT effects and immune defenses against pathogens.

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.

Bidirectional interaction between intestinal microbiome and cancer: opportunities for therapeutic interventions

Gut microbiota composition influences the balance between human health and disease. Increasing evidence suggests the involvement of microbial factors in regulating cancer development, progression, and therapeutic response. Distinct microbial species have been implicated in modulating gut environment and architecture that affects cancer therapy outcomes. While some microbial species offer enhanced cancer therapy response, others diminish cancer treatment efficacy. In addition, use of antibiotics, often to minimize infection risks in cancer, causes intestinal dysbiosis and proves detrimental. In this review we discuss the role of gut microbiota in cancer development and therapy. We also provide insights into future strategies to manipulate the microbiome and gut epithelial barrier to augment therapeutic responses while minimizing toxicity or infection risks.

Microbiome-intestine cross talk during acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-SCT) offers cure for a variety of conditions, in particular, but not limited to, hematologic malignancies. However, it can be associated with life-threatening complications, including graft-versus-host disease (GVHD) and infections, which are factors limiting its widespread use. Technical advances in the field of microbiome research have allowed for a better understanding of the microbial flora of the human intestine, as well as dissection of their interactions with the host immune system in allo-SCT and posttransplant complications. There is growing evidence that the commensal microbiome is frequently dysregulated following allo-SCT and that this dysbiosis can predispose to adverse clinical outcomes, especially including acute intestinal GVHD and reduced overall survival. In this review, we discuss the interactions between the microbiome and the components of the immune system that play a major role in the pathways leading to the inflammatory state of acute intestinal GVHD. We also discuss the microbiome-centered strategies that have been devised or are actively being investigated to improve the outcomes of allo-SCT patients in regard to acute intestinal GVHD.

Nutritional traditional and complementary medicine strategies in pediatric cancer: A narrative review

Traditional and complementary medicine (T&CM) strategies are commonly used by pediatric cancer patients. Nutritional approaches to T&CM include bioactive compounds, supplements, and herbs as well as dietary approaches. Pediatric cancer patients and their families commonly request and use nutritional T&CM strategies. We review the potential risks and benefits of nutritional T&CM use in pediatric cancer care and provide an overview of some commonly used and requested supplements, including probiotics, antioxidants, cannabinoids, vitamins, turmeric, mistletoe, Carica papaya, and others. We also discuss the role of specific diets such as the ketogenic diet, caloric restriction diets, whole-food diets, and immune modulating diets. There is a growing body of evidence to support the use of some T&CM agents for the supportive care of children with cancer. However, further study is needed into these agents and approaches. Open communication with families about T&CM use is critical.

The Impact of Antibiotic-Mediated Modification of the Intestinal Microbiome on Outcomes of Allogeneic Hematopoietic Cell Transplantation: Systematic Review and Meta-Analysis

Accumulating evidence points toward a protective role of intestinal microbiota diversity in allogeneic hematopoietic cell transplantation (allo-HCT). The purpose of this systematic review and meta-analysis is to determine the effect of antibiotic-mediated disruption of microbiota on main allo-HCT outcomes (graft-versus-host disease [GVHD], treatment-related mortality [TRM], overall survival [OS]). Following literature search, 2 reviewers screened eligible studies and assessed risk of bias (RoB). Meta-analysis was performed using Review Manager Software. Among 443 screened references, 18 were eligible for meta-analysis. In studies with genomic markers, grade II to IV acute GVHD was significantly reduced in patients not receiving gut decontamination (GD) (odds ratio [OR], 1.56; 95% confidence interval [CI], 1.20 to 2.04). In subgroup analysis, prophylaxis with systemic antibiotics conferred an increased risk of acute GVHD (OR, 1.65; 95% CI, 1.08 to 2.53). When we incorporated RoB, we found a positive correlation of intestinal GVHD with GD (OR, 1.77; 95% CI, 1.29 to 2.44). Patients with higher microbiota diversity presented increased OS (risk ratio [RR], 1.58; 95% CI, 1.19 to 2.09) and lower TRM (RR, 0.45; 95% CI, 0.26 to 0.76). Our findings confirm that GD and prophylaxis with systemic antibiotics increase acute and intestinal GVHD. Importantly, our meta-analysis was the first to show a significant effect of microbiota diversity on TRM and OS.

Brazilian Nutritional Consensus in Hematopoietic Stem Cell Transplantation: Graft- versus -host disease

The Brazilian Consensus on Nutrition in Hematopoietic Stem Cell Transplantation: Graft- versus -host disease was approved by Sociedade Brasileira de Transplante de Medula Óssea , with the participation of 26 Brazilian hematopoietic stem cell transplantation centers. It describes the main nutritional protocols in cases of Graft- versus -host disease, the main complication of hematopoietic stem cell transplantation.

Microbiome Anomalies in Allogeneic Hematopoietic Cell Transplantation

The microbiome is an integrated part of the human body that can modulate a variety of disease processes and affect prognosis, treatment response, complications, and outcomes. The importance of allogeneic hematopoietic cell transplantation in cancer treatment has resulted in extensive investigations on the interaction between the microbiome and this treatment modality. These investigations are beginning to lead to clinical trials of microbiome-targeted interventions. Here we review some of these discoveries and describe strategies being investigated to manipulate the microbiome for favorable outcomes, such as the proper selection and timing of antibiotics, type of diet and route of administration, probiotics, prebiotics, and fecal microbiota transplantation.

Inducción de tolerancia por vía oral en trasplante de órganos y tejidos. Revisión de la Literatura

Introducción. La tolerancia oral es la supresión de la respuesta inmune a antígenos administrados con anterioridad por vía oral; su inducción tiene el propósito de evitar el uso de fármacos inmunosupresores, los cuales, dado que son poco específicos a antígenos, vuelven al huésped más susceptible de contraer infecciones y desarrollar neoplasias.Objetivos. Realizar una revisión de la literatura sobre los referentes teóricos más relevantes de la inducción de a tolerancia oral en lo que respecta al trasplante de órganos y tejidos para demostrar que el uso de esta alternativa terapéutica es viable en pacientes trasplantados.Materiales y métodos. Se realizó una revisión de la literatura en PubMed, MEDLINE, LILACS y Embase mediante la siguiente estrategia de búsqueda: periodo de publicación: sin límites; idiomas: Inglés y Español; tipo de artículos: estudios caso-control, revisiones sistemáticas y de la literatura; términos de búsqueda: “T-Lymphocytes, Regulatory”, “Autoimmunity”, Immunosuppression”, “Immune system” and “Immune Tolerance”, y sus equivalentes en español.Resultados. La búsqueda inicial arrojó 719 registros, sin embargo solo 99 abordaban la inducción de la tolerancia oral. Una vez los registros duplicados y los artículos sin acceso a texto completo fueron removidos, se incluyeron 72 estudios en la revisión.Conclusiones. La administración oral de antígenos es una opción efectiva para inducir tolerancia inmunológica en pacientes trasplantados (modelos murinos), pues elimina los efectos adversos que conlleva la terapia inmunosupresora actualmente utilizada.

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.

The Gut Microbiota in Causation, Detection, and Treatment of Cancer

The gut microbiota has emerged as an important consideration in clinical oncology. The role of the microbiome in cancer extends beyond causation and cancer risk. It is now known that the microbiome not only acts at a local epithelial level in the gut but also modifies immune responses within intestinal and extraintestinal tumors. Microbial signaling influences the clinical course of cancer including the efficacy, bioavailability, and toxicity of chemotherapeutic and immunotherapy agents. This has focused research on microbiota profiling in different cancer states with an aim of developing prognostic biomarkers of risk. The potential value of microbiome manipulation with live biotherapeutics or microbial transplantation has also become a realistic consideration. Maintenance of microbial diversity in patients with cancer is a variable challenge given the modifying influences of the tumor itself, chemotherapy, nutritional status, and sporadic antimicrobial therapy. Here, we address current evidence for the role of the microbiome in cancer therapy.

Considering the Supraorganism: Harnessing the Gut Microbiome for Cancer Prevention, Detection, and Treatment

Although causal relationships between specific microbes and cancer are well recognized, a growing body of evidence suggests that the broader community of gut microbes may influence cancer risk, provide diagnostic insight, shape clinical course, and impact treatment success in the gastrointestinal tract and beyond. In this issue, Murphy et al. reviewed evidence for the role of the microbiome in clinical oncology. Given that the gut microbiome may be modified by treatments ranging from diet and live biotherapeutics to microbial transplantation, microbiome-directed therapies hold tremendous promise for personalized therapies and improved treatment outcomes.

The gut microbiota and graft-versus-host disease

Graft-versus-host disease (GvHD) is a common complication of hematopoietic cell transplantation that negatively impacts quality of life in recipients and can be fatal. Animal experiments and human studies provide compelling evidence that the gut microbiota is associated with risk of GvHD, but the nature of this relationship remains unclear. If the gut microbiota is a driver of GvHD pathogenesis, then manipulation of the gut microbiota offers one promising avenue for preventing or treating this common condition, and antibiotic stewardship efforts in transplantation may help preserve the indigenous microbiota and modulate immune responses to benefit the host.

Impact of the microbiome on cancer progression and response to anti-cancer therapies

Humans are a colonized with trillions of commensal microorganisms which exert a profound effect on normal host physiology and immune function through an abundance of genetic and metabolic by-products. Although the commensal microbiome has beneficial functions to host physiology, perturbations of the composition of the commensal microbiome or the homeostatic mucosal environment can lead to the induction of immune pathology and systemic inflammation. In the context of cancer progression or response to immune therapy, this inflammation can be detrimental, resulting in tumor growth and the promotion of immune suppression. On the other hand, significant associations have been identified whereby certain commensal microorganisms are able to enhance T cell function or are required for tumor control in cancer patients treated with certain immune therapies and chemotherapies. The focus of this chapter is to highlight the role of the commensal microbiome during tumor progression and in response to immune therapies.

Safety of Probiotics Among High-Risk Pediatric Hematopoietic Stem Cell Transplant Recipients

INTRODUCTION

Increased diversity of the intestinal microbiome has been significantly associated with lower mortality after hematopoietic stem cell transplant (HSCT). Probiotics, such as Lactobacillus species with defined probiotic potential, may have beneficial properties including restoration of commensal species to the intestinal tract, anti-microbial effects, and healing of the intestinal mucosa. However, the use of probiotics in immune-compromised patients raises concerns, specifically regarding the risk for possible Lactobacillus bacteremia. Risk of bacteremia is an even greater concern in HSCT patients with breakdown of mucosal barriers, specifically patients with Clostridium difficile infection (CDI) or gastrointestinal graft-versus-host disease (GVHD). Minimal data have been reported on the safety of probiotics in these high-risk HSCT populations.

METHODS

We performed a retrospective study of allogeneic HSCT recipients at our institution between 2011 and 2016, and identified 14 patients (median age 7 years) prescribed probiotics, 10 of whom received probiotics prior to day 100 after HSCT.

RESULTS

Eight of ten patients were diagnosed with acute GVHD, four of whom (40%) specifically had acute GVHD involving the gastrointestinal tract. Five patients (50%) on probiotics prior to day 100 were diagnosed with CDI (median onset at day 13 post-transplant). There were no cases of Lactobacillus bacteremia, including in patients with GVHD or CDI.

CONCLUSION

This small case series supports the safe use of probiotics in a high-risk population of pediatric HSCT patients with compromised intestinal mucosal integrity. Further studies are needed to determine if probiotics have benefit in preventing and treating gastrointestinal GVHD or CDI.

Microbiome: An Emerging New Frontier in Graft-Versus-Host Disease

Hematopoietic cell transplantation is an intensive therapy used to treat high-risk hematological malignant disorders and other life-threatening hematological and genetic diseases. Graft-versus-host disease (GVHD) presents a barrier to its wider application. A conditioning regimen and medications given to patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HCT) are capable of disturbing the homeostatic crosstalk between the microbiome and the host immune system and of leading to dysbiosis. Intestinal inflammation in the context of GVHD is associated with loss in microbial diversity that could serve as an independent predictor of mortality. Successful gastrointestinal decontamination using high doses of non-absorbable antibiotics likely affect allo-HCT outcomes leading to significantly less acute GVHD (aGVHD). Butyrate-producing Clostridia directly result in the increased presence of regulatory T cells in the gut, which are protective in GVHD development. Beyond the microbiome, Candida, a member of the mycobiome, colonization in the gut has been considered as a risk factor in pathophysiology of aGVHD and reduction in GVHD is observed with antifungal prophylaxis with fluconazole. Reduced number of goblet cells and Paneth cells have been shown to associate with GVHD and has a significant impact on the micro- and mycobiome density and their composition. Lower levels of 3-indoxyl sulfate at initial stages after allo-HCT are related with worse GVHD outcomes and increased mortality. Increased understanding of the vital role of the gut microbiome in GVHD can give directions to move the field towards the development of improved innovative approaches for preventing or treating GVHD following allo-HCT.

Intestinal Microbiota Influence Immune Tolerance Post Allogeneic Hematopoietic Cell Transplantation and Intestinal GVHD

Under normal conditions our intestines are inhabited by trillions of diverse microorganisms composing the intestinal microbiota, which are mostly non-pathogenic anaerobic commensal bacteria vital for the maintenance of immune homeostasis. The composition and diversity of the intestinal microbiota can be disturbed by various factors including diet, antibiotics, and exposure to intestinal pathogens. Alterations of the intestinal microbiota contributes to many diseases including graft-vs.-host disease (GVHD), a life threatening complication that occurs after allogeneic hematopoietic cell transplantation (allo-HCT) caused by an allogeneic reaction of donor T cells against recipient target tissues. Intestinal GVHD is most difficult to treat and connected to a high mortality. Due to recent advances in high-throughput sequencing technology, composition of the microbiome during allo-HCT has been characterized, and some common patterns have been identified. Metabolites produced by intestinal bacteria were shown to promote intestinal tissue homeostasis and immune tolerance post-allo-HCT. In this review, we discuss the role of the intestinal microbiota and metabolites in the context of acute GVHD. Moreover, novel therapeutic approaches that aim at protecting or regenerating intestinal cell populations will be highlighted.

Combination Immunotherapy Development in Melanoma

Melanoma has been the most important cancer to drive immunotherapy development of solid tumors. Since 2010, immunotherapy has been revolutionized by the concept of breaking tolerance. It represents a major paradigm shift and marks the beginning of a new era. The impact of the first immune checkpoint inhibitors, anti-CTLA-4 and anti-PD-1/anti-PD-L1, is unprecedented. In 7 years, it transformed advanced-stage melanoma into a curable disease in over 50% of patients. Another major step has been the development of the combination of BRAF inhibitors plus MEK inhibitors in the treatment of BRAF-mutant melanomas. For the treatment of advanced disease, approvals were obtained for the immune checkpoint inhibitors ipilimumab (2011), nivolumab (2014), pembrolizumab (2014), the combination ipilimumab plus nivolumab (2015), and the oncolytic virus vaccine laherparepvec (2015). The combination dabrafenib plus trametinib for BRAF-mutant melanoma was approved in 2014, with similar success for other BRAF plus MEK inhibitor combinations. Because of its unique therapeutic index (high efficacy and low toxicity) anti-PD-1 agents (nivolumab and pembrolizumab) have now been placed at the center of practically all combination therapy development strategies in melanoma. Anti-PD-1 agents are the central molecule for combinations with a great variety of other immunotherapeutics such as immune checkpoint inhibitors, agonists, IDO inhibitors, macrophage polarizing agents, monoclonal antibodies, vaccines, targeted agents, chemotherapeutics, radiation therapy, and even microbiome modulators.

Advances in the understanding and management of mucositis during stem cell transplantation

PURPOSE OF REVIEW

Mucositis is a severe and common side effect of anticancer treatments, with an incidence of between 40 and 80% depending on the cytotoxic regimen used. The most profound mucositis burden is experienced during conditioning regimens for hematopoietic stem cell transplant (HSCT), where the use of highly mucotoxic agents with or without total body irradiation leads to serious damage throughout the alimentary tract. Currently, the assessment and management of both oral and gastrointestinal mucositis lack authoritative guideline, with recommendations only achieved in narrow clinical scenarios. This review provides a brief overview of current management guidelines for mucositis in both adult and pediatric patients receiving HSCT, highlights recent advances in mucositis prevention and discusses future research avenues.

RECENT FINDINGS

The Multinational Association of Supportive Care in Cancer and International Society for Oral Oncology (MASCC/ISOO) guidelines for the prevention of mucositis in HSCT are scarce, with low level laser therapy (photobiomodulation) and palifermin only recommended for oral mucositis. Loperamide and octreotide remain gold-standard for the treatment of diarrhea, despite poor efficacy. Although several interventions have been trialled in pediatric cohorts, no recommendations currently exist for children receiving high-dose chemotherapy or total body irradiation for HSCT.

SUMMARY

HSCT continues to be associated with mucositis, which impacts on patients' ability and willingness to receive engraftment, and worsens clinical outcome. Research into the prevention and treatment of mucositis in this setting remains limited, with an overwhelming amount of small, single-center studies that fail to achieve a sufficient level of evidence that warrant recommendation(s). As such, our ability to manage mucotoxic side effects of high-dose chemotherapy and irradiation is limited, particularly in children.

Gut microbiota injury in allogeneic haematopoietic stem cell transplantation

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is considered to be the strongest curative immunotherapy for various malignancies (primarily, but not limited to, haematologic malignancies). However, application of allo-HSCT is limited owing to its life-threatening major complications, such as graft-versus-host disease (GVHD), relapse and infections. Recent advances in large-scale DNA sequencing technology have facilitated rapid identification of the microorganisms that make up the microbiota and evaluation of their interactions with host immunity in various diseases, including cancer. This has resulted in renewed interest regarding the role of the intestinal flora in patients with haematopoietic malignancies who have received an allo-HSCT and in whether the microbiota affects clinical outcomes, including GVHD, relapse, infections and transplant-related mortality. In this Review, we discuss the potential role of intestinal microbiota in these major complications after allo-HSCT, summarize clinical trials evaluating the microbiota in patients who have received allo-HSCT and discuss how further studies of the microbiota could inform the development of strategies that improve outcomes of allo-HSCT.

Fecal Microbiota Transplantation in Patients With Blood Disorders Inhibits Gut Colonization With Antibiotic-Resistant Bacteria: Results of a Prospective, Single-Center Study

Background

Patients with blood disorders colonized with antibiotic-resistant bacteria (ARB) are prone to systemic infections that are difficult to treat. Reintroduction of commensal bacteria in a murine model of enterococcal colonization of the gut can lead to eradication of enterococci. We hypothesized that fecal microbiota transplantation (FMT) could be used to eradicate ARB in humans.

Methods

Participants colonized with ARB were treated with intraduodenal FMT according to a prospective protocol (NCT02461199). The primary endpoint was complete ARB decolonization at 1 month after FMT. Secondary endpoints included safety assessment and partial ARB decolonization. Microbiome sequencing was performed to investigate the influence of microbial composition of the transplanted material on the outcome of FMT.

Results

Twenty-five FMTs were performed in 20 participants (including 40% who had neutropenia) who were colonized by a median of 2 (range, 1-4) strains of ARB. The primary endpoint was reached in 15/25 (60%) of the FMTs and more frequently in cases in which there was no periprocedural use of antibiotics (79% vs 36%, P < .05). Among participants, 15/20 (75%) experienced complete ARB decolonization. There were no severe adverse events, and partial ARB decolonization was observed in 20/25 (80%) of the FMTs. The microbiota composition analysis revealed higher abundance of Barnesiella spp., Bacteroides, and Butyricimonas and greater bacterial richness in the fecal material, resulting in eradication of Klebsiella pneumoniae compared with nonresponders.

Conclusions

FMT in patients with blood disorders is safe and promotes eradication of ARB from the gastrointestinal tract.

Clinical Trials Registration

NCT02461199.