Low diversity of gut microbiota in the early phase of post-bone marrow transplantation increases the risk of chronic graft-versus-host disease

Oral inflammation and microbiome dysbiosis exacerbate chronic graft-versus-host disease

ABSTRACT

The oral microbiota, second in abundance to the gut, is implicated in chronic systemic diseases, but its specific role in graft-versus-host disease (GVHD) pathogenesis has been unclear. Our study finds that mucositis-induced oral dysbiosis in patients after hematopoietic cell transplantation (HCT) associated with increased chronic GVHD (cGVHD), even in patients receiving posttransplant cyclophosphamide. In murine HCT models, oral dysbiosis caused by bilateral molar ligatures exacerbated cGVHD and increased bacterial load in the oral cavity and gut, with Enterococcaceae significantly increasing in both organs. In this model, the migration of Enterococcaceae to cervical lymph nodes both before and after transplantation activated antigen-presenting cells, thereby promoting the expansion of donor-derived inflammatory T cells. Based on these results, we hypothesize that pathogenic bacteria increase in the oral cavity might not only exacerbate local inflammation but also enhance systemic inflammation throughout the HCT course. Additionally, these bacteria translocated to the gut and formed ectopic colonies, further amplifying systemic inflammation. Furthermore, interventions targeting the oral microbiome mitigated murine cGVHD. Collectively, our findings highlight the importance of oral dysbiosis in cGVHD and suggest that modulation of the oral microbiome during transplantation may be an effective approach for preventing or treating cGVHD.

The association of intestinal microbiota diversity and outcomes of allogeneic hematopoietic cell transplantation: a systematic review and meta-analysis

Growing evidence suggests that highly intestinal microbiota diversity modulates host inflammation and promotes immune tolerance. Several studies have reported that patients undergoing allo-HSCT have experienced microbiota disruption that is characterized by expansion of potentially pathogenic bacteria and loss of microbiota diversity. Thus, the primary aim of this meta-analysis was to determine the association of intestinal microbiota diversity and outcomes after allo-HSCT, and the secondary aim was to analyze the associations of some specific microbiota abundances with the outcomes of allo-HSCT. Electronic databases of Pubmed, Embase, Web of Science, and Cochrane Library were searched from inception to August 2023, and 17 studies were found eligible. The pooled estimate suggested that higher intestinal microbiota diversity was significantly associated with overall survival (OS) benefit (HR = 0.66, 95% CI: 0.55-0.78), as well as decreased risk of transplant-related mortality (HR = 0.56, 95% CI: 0.41-0.76), and lower incidence of grade II-IV aGVHD (HR = 0.41, 95% CI: 0.27-0.63). Furthermore, higher abundance of Clostridiales was associated with a superior OS (HR = 0.40, 95% CI: 0.18-0.87), while higher abundance of Enterococcus (HR = 2.03, 95% CI: 1.55-2.65), γ-proteobacteria (HR = 2.82, 95% CI: 1.53-5.20), and Candida (HR = 3.80, 95% CI: 1.32-10.94) was an adverse prognostic factor for OS. Overall, this meta-analysis highlights the protective role of higher intestinal microbiota diversity on outcomes after allo-HSCT during both pre-transplant and post-transplant periods. Some specific microbiota can be useful in the identification of patients at risk of mortality, offering new tools for individualized pre-emptive or therapeutic strategies to improve allo-HSCT outcomes.

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.