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

Sustained-release of SOD from multivesicular liposomes accelerated the colonic mucosal healing of colitis mice by inhibiting oxidative stress

Oxidative stress has long been known as a pathogenic factor of ulcerative colitis. Superoxide dismutase (SOD) has been demonstrated to mitigate gut mucosal injury via combating oxidative stress. Herein, we developed SOD-loaded multivesicular liposomes (S-MVLs) as sustained-release depot for ulcerative colitis treatment. S-MVLs were spherical honeycomb-like particles with average particle size of 27.3 ± 5.4 μm and encapsulating efficiency of 78.7 ± 2.6 %. Moreover, the two-phase release profiles of SOD from S-MVLs were exhibited, that was, the burst release phase within 4 h and the sustained-release phase within 96 h. After intraperitoneally injecting S-MVLs, in situ retention time of SOD at bowel cavity extended by 4-fold in comparison with SOD solution. In vitro cells experiment showed that S-MVLs had the protective effect on LPS-treated RAW 264.7 cells via scavenging ROS and inhibiting pro-inflammatory cytokines production. S-MVLs ameliorated the body weight loss, DAI score and the colon shortening of colitis mice. Meanwhile, the colonic morphology and the epithelial barrier of colitis mice were effectively recovered after S-MVLs treatment. The therapeutic mechanism might be associated with polymerizing M1 macrophages to M2 phenotypes and alleviating oxidative stress. Collectively, multivesicular liposomes might be a promising sustained-release depot of SOD for ulcerative colitis treatments.

Time-Dependent Shifts in Intestinal Bacteriome, Klebsiella Colonization and Incidence of Antibiotic-Resistance Genes after Allogeneic Hematopoietic Stem Cell Transplantation

Dose-intensive cytostatic therapy and antibiotic treatment in allogeneic hematopoietic stem cell transplantation (allo-HSCT) cause severe abnormalities in a composition of gut microbiota as well as the emergence of antibiotic resistance. The data on the longitudinal recovery of major bacterial phyla and the expansion of genes associated with antibiotic resistance are limited. We collected regular stool samples during the first year after allo-HSCT from 12 adult patients with oncohematological disorders after allo-HSCT and performed 16SrRNA sequencing, multiplex PCR, conventional bacteriology and CHROMagar testing. We observed a decline in Shannon microbiota diversity index as early as day 0 of allo-HSCT (p = 0.034) before any administration of antibiotics, which persisted up to 1 year after transplantation, when the Shannon index returned to pre-transplant levels (p = 0.91). The study confirmed the previously shown decline in Bacillota (Firmicutes) genera and the expansion of E. coli/Shigella, Klebsiella and Enterococci. The recovery of Firmicutes was slower than that of other phyla and occurred only a year post-transplant. A positive correlation was observed between the expansion of E. coli/Shigella genera and blaKPC, blaCTX-M-1 and blaTEM (p < 0.001), Klebsiella spp. and blaOXA-48-like, blaNDM, blaCTX-M-1, blaTEM, and blaSHV (p < 0.001), Pseudomonas spp. and blaNDM (p = 0.002), Enterococcus spp. and blaOXA-48-like, blaNDM, blaCTX-M-1, blaSHV (p < 0.01). The correlation was observed between the expansion of Enterobacterales and and carbapenemase-positive CHROMagar samples (p < 0.001). Samples positive for carbapenem-resitant bacteria were at their maximum levels on day +30, and were gradually diminishing one year after allo-HSCT. From day +30 to +60, all isolated K. pneumoniae strains in fecal samples proved to be resistant to the main antibiotic groups (carbapenems, aminoglycosides, fluoroquinolones, third-generation cephalosporins). One year after HSCT, we documented the spontaneous decolonization of K. pneumoniae. The sensitivity of molecular biology techniques in the search for total and antibiotic-resistant Klebsiella seems to be superior to common bacteriological cultures. Future studies should be focused on searching for novel approaches to the efficient reconstitution and/or maintenance of strictly anaerobic microbiota in oncological patients.

Microbiota dictate T cell clonal selection to augment graft-versus-host disease after stem cell transplantation

Allogeneic T cell expansion is the primary determinant of graft-versus-host disease (GVHD), and current dogma dictates that this is driven by histocompatibility antigen disparities between donor and recipient. This paradigm represents a closed genetic system within which donor T cells interact with peptide-major histocompatibility complexes (MHCs), though clonal interrogation remains challenging due to the sparseness of the T cell repertoire. We developed a Bayesian model using donor and recipient T cell receptor (TCR) frequencies in murine stem cell transplant systems to define limited common expansion of T cell clones across genetically identical donor-recipient pairs. A subset of donor CD4+ T cell clonotypes differentially expanded in identical recipients and were microbiota dependent. Microbiota-specific T cells augmented GVHD lethality and could target microbial antigens presented by gastrointestinal epithelium during an alloreactive response. The microbiota serves as a source of cognate antigens that contribute to clonotypic T cell expansion and the induction of GVHD independent of donor-recipient genetics.

The Promise of Precision Nutrition for Modulation of the Gut Microbiota as a Novel Therapeutic Approach to Acute Graft-versus-host Disease

Acute graft-versus-host disease (aGVHD) is a severe side effect of allogeneic hematopoietic stem cell transplantation (aHSCT) that has complex phenotypes and often unpredictable outcomes. The current management is not always able to prevent aGVHD. A neglected actor in the management of aGVHD is the gut microbiota. Gut microbiota dysbiosis after aHSCT is caused by many factors and may contribute to the development of aGVHD. Diet and nutritional status modify the gut microbiota and a wide range of products are now available to manipulate the gut microbiota (pro-, pre-, and postbiotics). New investigations are testing the effect of probiotics and nutritional supplements in both animal models and human studies, with encouraging results. In this review, we summarize the most recent literature about the probiotics and nutritional factors able to modulate the gut microbiota and we discuss the future perspective in developing new integrative therapeutic approaches to reducing the risk of graft-versus-host disease in patients undergoing aHSCT.

Intestinal permeability in patients undergoing stem cell transplantation correlates with systemic acute phase responses and dysbiosis

Intestinal permeability may correlate with adverse outcomes during hematopoietic stem cell transplantation (HSCT), but longitudinal quantification with traditional oral mannitol and lactulose is not feasible in HSCT recipients because of mucositis and diarrhea. A modified lactulose:rhamnose (LR) assay is validated in children with environmental enteritis. Our study objective was to quantify peri-HSCT intestinal permeability changes using the modified LR assay. The LR assay was administered before transplant, at day +7 and +30 to 80 pediatric and young adult patients who received allogeneic HSCT. Lactulose and rhamnose were detected using urine mass spectrometry and expressed as an L:R ratio. Metagenomic shotgun sequencing of stool for microbiome analyses and enzyme-linked immunosorbent assay analyses of plasma lipopolysaccharide binding protein (LBP), ST2, REG3α, claudin1, occludin, and intestinal alkaline phosphatase were performed at the same timepoints. L:R ratios were increased at day +7 but returned to baseline at day +30 in most patients (P = .014). Conditioning regimen intensity did not affect the trajectory of L:R (P = .39). Baseline L:R ratios did not vary with diagnosis. L:R correlated with LBP levels (r2 = 0.208; P = .0014). High L:R ratios were associated with lower microbiome diversity (P = .035), loss of anaerobic organisms (P = .020), and higher plasma LBP (P = .0014). No adverse gastrointestinal effects occurred because of LR. Intestinal permeability as measured through L:R ratios after allogeneic HSCT correlates with intestinal dysbiosis and elevated plasma LBP. The LR assay is well-tolerated and may identify transplant recipients who are more likely to experience adverse outcomes.

Conditioning Regimens are Associated with Distinct Patterns of Microbiota Injury in Allogeneic Hematopoietic Cell Transplantation

PURPOSE

The gut microbiota is subject to multiple insults in allogeneic hematopoietic cell transplantation (allo-HCT) recipients. We hypothesized that preparative conditioning regimens contribute to microbiota perturbation in allo-HCT.

EXPERIMENTAL DESIGN

This was a retrospective study that evaluated the relationship between conditioning regimens exposure in 1,188 allo-HCT recipients and the gut microbiome. Stool samples collected from 20 days before transplantation up to 30 days after were profiled using 16S rRNA sequencing. Microbiota injury was quantified by changes in α-diversity.

RESULTS

We identified distinct patterns of microbiota injury that varied by conditioning regimen. Diversity loss was graded into three levels of conditioning-associated microbiota injury (CMBI) in a multivariable model that included antibiotic exposures. High-intensity regimens, such as total body irradiation (TBI)-thiotepa-cyclophosphamide, were associated with the greatest injury (CMBI III). In contrast, the nonmyeloablative regimen fludarabine-cyclophosphamide with low-dose TBI (Flu/Cy/TBI200) had a low-grade injury (CMBI I). The risk of acute GVHD correlated with CMBI degree. Pretransplant microbial compositions were best preserved with Flu/Cy/TBI200, whereas other regimens were associated with loss of commensal bacteria and expansion of Enterococcus.

CONCLUSIONS

Our findings support an interaction between conditioning at the regimen level and the extent of microbiota injury.

The contribution of the intestinal microbiome to immune recovery after HCT

Allogenic hematopoietic stem-cell transplantation (allo-HCT) is a curative-intent immunotherapy for high-risk hematological malignancies and immune deficiencies. Allo-HCT carries a high risk of treatment-related mortality (TRM), largely due to infection or graft-versus-host disease (GVHD). Robust immune recovery is essential for optimal patient outcomes, given the immunologic graft-versus-leukemia effect prevents relapse, and functional innate and adaptive immunity are both needed for the prevention and control of infection. Most simply, we measure immune recovery by enumerating donor lymphocyte subsets in circulation. In functional terms, ideal immune recovery is more difficult to define, and current lab techniques are limited to the measurement of specific vaccine-responses or mitogens ex vivo. Clinically, poor immune function manifests as problematic infection with viral, bacterial and fungal organisms. Furthermore, the ideal recovering immune system is capable of exerting graft-versus-tumor effects to prevent relapse, and does not induce graft-versus-host disease. Large clinical observational studies have linked loss of diversity within the gut microbiome with adverse transplant outcomes including decreased overall survival and increased acute and chronic GVHD. Furthermore, the correlation between intestinal microbial communities and numeric lymphocyte recovery has now been reported using a number of approaches. Large sets of clinically available white blood cell count data, clinical flow cytometry of lymphocyte subsets and bespoke flow cytometry analyses designed to capture microbiota-specific T cells (e.g. Mucosal-associated invariant T cells, subsets of the gd T cells) have all been leveraged in an attempt to understand links between the microbiota and the recovering immune system in HCT patients. Additionally, preclinical studies suggest an immunomodulatory role for bacterial metabolites (including butyrate, secondary bile acids, and indole derivatives from tryptophan metabolism) in transplant outcomes, though further studies are needed to unravel mechanisms relevant to the post-HCT setting. An understanding of mechanistic relationships between the intestinal microbiome and post-transplant outcomes is necessary for reduction of risk associated with transplant, to inform prophylactic procedures, and ensure optimal immune reconstitution without alloreactivity. Here, we summarize the current understanding of the complex relationship between bacterial communities, their individual members, and the metabolites they produce with immune function in both the allo-HCT and steady-state setting.