Background: Although Enterococcus domination has been extensively evaluated in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT), the prevalence and clinical implications of other dominant genera remain poorly understood. Objective: In this study, we sought to determine the dynamics, predictors and clinical implications of intestinal domination in Brazilian patients undergoing allo-HSCT. Methods: In a prospective study of four Brazilian centers, fecal specimens were collected longitudinally prior to allo-HSCT until six months post-transplantation. To identify intestinal domination, we performed 16S rRNA gene sequencing using the Illumina platform. We then evaluated the impact of intestinal domination on overall survival and acute Graft-versus-Host-Disease (aGvHD) incidence. Finally, to identify predictors of intestinal domination, we performed a logistic regression model. Results: A total of 192 fecal specimens were collected from 69 patients. No significant changes in alpha or beta diversity were observed over the course of allo-HSCT. Among the 192 specimens, 131 (68%) presented intestinal domination. The top four dominant genera were Bacteroides, Akkermansia, Phascolarctobacterium, and Escherichia-Shigella. No significant associations were found between domination by these genera and either overall survival or aGvHD incidence. Furthermore, no patient-level characteristics, including age, sex, underlying disease, conditioning regimen, or stem cell source, reliably predicted intestinal domination. Conclusions: Our findings reveal a unique intestinal domination fingerprint in Brazilian patients and highlight the importance of geographic context in interpreting microbiota–outcome associations in allo-HSCT settings.

In patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT), emerging evidence suggests that the oral microbiota may serve as a predictive biomarker. We conducted a systematic review to provide a critical overview of oral microbiota research in the allo-HSCT setting. We searched PubMed, Embase, and Web of Science from inception to December 2025 to identify studies assessing the oral microbiota in allo-HSCT settings. We included all articles reporting detailed data on the oral microbiota in this context and conducted a qualitative synthesis. Risk of bias was assessed using the JBI critical appraisal tools. From 8160 initially identified records, 35 studies evaluating the oral microbiota in 1964 allo-HSCT patients were included. Of these, 27 studies (77%) assessed temporal oral microbiota dynamics and reported dysbiosis in the early post-transplantation period, followed by gradual recovery. Additionally, 27 studies (77%) evaluated the prognostic value of the oral microbiota, identifying associations with key clinical outcomes such as oral mucositis, overall survival, and graft-versus-host disease. Finally, substantial methodological heterogeneity was observed across studies, including differences in sampling techniques, sampling timepoints, and analytical strategies. This systematic review highlights the prognostic and therapeutic potential of the oral microbiota in allo-HSCT and underscores the need for standardized methodologies.

Background: Although Enterococcus domination has been extensively evaluated in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT), the prevalence and clinical implications of other dominant genera remain poorly understood. Objective: In this study, we sought to determine the dynamics, predictors and clinical implications of intestinal domination in Brazilian patients undergoing allo-HSCT. Methods: In a prospective study of four Brazilian centers, fecal specimens were collected longitudinally from prior to allo-HSCT to six months after. To identify intestinal domination, we performed 16S rRNA gene sequencing using Illumina platform. We then evaluated the impact of intestinal domination on overall survival and acute graft versus host disease (aGvHD) incidence. Finally, to identify predictors of intestinal domination, we performed a logistic regression model. Results: A total of 192 fecal specimens were collected from 69 patients. Among these specimens, 131 (68%) had intestinal domination. The top four dominant genera were Bacteroides, Akkermansia, Phascolarctobacterium, and Escherichia-Shigella. No significant association was identified between intestinal domination by these genera and overall survival and aGvHD incidence. Additionally, we identified that no patient-level characteristic reliably predicts intestinal domination. Conclusion: Our findings suggest that the prognostic significance of intestinal domination may vary according to the dominant genera and to the population being evaluated.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important therapeutic strategy for hematological malignancies and other diseases but remains associated with substantial morbidity and mortality. Although microbial dominance has been extensively investigated in the gut microbiota, its dynamics and clinical implications in the oral microbiota remain poorly understood. In this prospective multicenter study, longitudinal oral mucosal samples were collected from pre-conditioning to six months post-transplantation in Brazilian patients undergoing allo-HSCT, and microbiota composition was assessed by 16S rRNA gene sequencing. Associations between oral dominance and death within D+180, disease relapse, and acute graft-versus-host disease (aGvHD) were evaluated using competing-risk methods, while predictors of oral dominance were assessed using mixed-effects logistic regression. Among 90 patients, 244 oral samples were analyzed. Alpha diversity significantly decreased during the first 30 days post-allo-HSCT compared with healthy controls. Oral dominance occurred in 87.8% of patients, with Streptococcus, Veillonella, and Rothia being the most frequent dominant genera. Streptococcus dominance was associated with a higher cumulative incidence of moderate-to-severe aGvHD, whereas Rothia dominance was associated with a higher cumulative incidence of disease relapse. These findings demonstrate substantial oral microbiota disruption during allo-HSCT and suggest that specific taxonomic patterns may be associated with clinically relevant transplant outcomes.

The role of zonulin as a biomarker of intestinal permeability in the allogeneic hematopoietic stem cell transplantation (allo-HSCT) setting remains poorly understood. In this study, we aimed to evaluate serum zonulin dynamics, identify its predictors, and assess its prognostic significance in patients undergoing allo-HSCT. This multicenter, prospective cohort study was conducted across four Brazilian hospitals. Eligible participants were patients aged ≥12 years who provided at least one blood sample during the allo-HSCT course. A control group of 15 healthy adult individuals was also included. Serum zonulin levels were quantified using enzyme-linked immunosorbent assay multiple times over the allo-HSCT course. Outcomes included acute graft-versus-host disease, overall survival, and bloodstream infections. A total of 477 blood samples were collected from 140 patients. Compared with the control group, zonulin levels were persistently elevated at all evaluated time points throughout the allo-HSCT course. However, no significant differences were observed among the different time points assessed during transplantation. No clinical or transplantation-related characteristics were identified as significant predictors of elevated zonulin levels. Finally, zonulin did not demonstrate prognostic value for allo-HSCT-related outcomes. Future studies should investigate whether other intestinal permeability biomarkers have prognostic relevance in the allo-HSCT setting.