“To the best of our knowledge, we present the first evidence of an association between pretransplantation lower gut microbiota diversity and poorer outcome in children undergoing allo-HSCT,” the authors report, in research published in the journal Blood. “Our findings underscore the importance of pre-transplant gut microbiota diversity and compositional structure in influencing allo-HSCT-related clinical outcomes in the pediatric setting.”
While allogeneic hematopoietic stem cell transplantation (allo-HSCT) can be potentially curative of hematologic malignancies, the stem cell transplantation process can wreak havoc on gut microbiota, because of factors including the conditioning regimen, antibiotic exposure, and dietary changes.
Specifically, the process can cause a substantial decrease in necessary alpha diversity and a potential expansion of possibly pathogenic bacteria.
While poor gut microbiota diversity has been linked to higher mortality in adult patients receiving allo-HSCT, research on the effects in pediatric patients is lacking.
“The gut microbiota of children differs from adults’ one, and this accounts for the need for specific pediatric studies on the gut microbiota-to–allo-HSCT relationship,” the authors write.
For the multicenter study, first author Riccardo Masetti, MD, PhD, of the department of pediatric oncology and hematology at the University of Bologna, Italy, and colleagues analyzed the gut microbiota diversity of 90 pediatric allo-HSCT recipients at four centers in Italy and one in Poland, stratifying the patients into groups of higher and lower diversity pretransplantation and again at the time of neutrophil engraftment.
Overall, gut microbiota diversity significantly declined from before allo-HSCT to afterward, at the time of neutrophil engraftment (P < .0001), with lower diversity observed in patients 3 years of age or younger.
With a median follow-up of 52 months, compared with the lower diversity group, those with higher diversity prior to transplantation had a significantly higher probability of overall survival (hazard ratio, 0.26; P = .011), after adjustment for age, graft source, donor type, intensity of conditioning regimen, center, and type of disease, with estimated overall survival at 52 months after allo-HSCT of 88.9% for the higher diversity group and 62.7% for the lower diversity group.
The cumulative incidence of grade II-IV acute GvHD was significantly lower for the higher diversity group versus lower diversity (20.0 versus 44.4, respectively; P = .017), as were the incidence rates of grade III-IV acute GvHD (2.2 versus 20.0; P = .007).
There were, however, no significant differences between the low and high diversity gut microbiota groups in relapse-free survival (P = .091).
The higher diversity group notably had higher relative abundances of potentially health-related bacterial families, including Ruminococcaceae and Oscillospiraceae, while the lower diversity group showed an overabundance of Enterococcaceae and Enterobacteriaceae.
Of note, the results differ from those observed in adults, among whom gut microbiota diversity before as well as after transplantation has been significantly associated with transplant outcomes, whereas with children, the association was limited to diversity prior to transplant.
In general, children have significantly lower diversity of gut microbiota than adults, with varying functional properties, and microbiota that is more easily modified by environmental factors, with larger changes occurring upon exposure to external stressors, the authors explain.
“Considering these different ecological properties compared to adults, we hypothesize that allo-HSCT–induced dysbiosis in the pediatric setting may imply loss of age-related gut microbiota signatures, including alpha diversity, with high interpatient variability,” they say.
Characteristics that were associated with higher or lower gut microbiota diversity prior to allo-HSCT included the treating center, suggesting that the geographical region may affect the diversity and the type of antibiotic exposure prior to the transplant.
Limitations included that “we didn’t assess other pretransplant characteristics such as the type of chemotherapy received, or the lifestyle, and this should be addressed in future studies on larger cohorts,” Dr. Masetti said in an interview.
While lengthy delays in screening of samples are barriers in the use of the gut microbiome as a tool in clinical practice, he noted that clinicians can take key measures to improve the microbiota.
“[Preventive measures] include the avoidance of unnecessary antibiotic treatment, which has a detrimental effect on the microbiota,” he said. “Moreover, some dietary changes may promote microbiota health.”
In addition, key measures can be taken during the allo-HSCT to preserve the microbiota, he added.
“In our center, we use enteral nutrition with a nasogastric tube rather than parenteral nutrition, which helps the microbiota to recover faster,” Dr. Masetti explained. “Moreover, other interventional measures such as fecal microbiota transplantation or the use of probiotics are under testing.”
“In particular, our data emphasize the importance of an overall healthy network, rather than the abundance of specific families or genera, in preventing complications and unfavorable outcomes.”
Commenting on the study, Robert Jenq, MD, an assistant professor in the departments of genomic medicine and stem cell transplantation and cellular therapy at the University of Texas M.D. Anderson Cancer Center, Houston, noted that with the growing evidence of the effects of poor gut microbiota diversity on clinical outcomes, multiple early-phase clinical trials are being conducted to test various strategies to prevent or treat gut injury.
“I’m not aware of any one approach that has shown enough promise to warrant being tested in multicenter studies yet, but it’s still a bit early,” Dr. Jenq said.“In the meantime, discontinuing or de-escalating antibiotics when medically safe, and encouraging patients to eat as much as they’re able to is a reasonable recommendation.”
Dr. Jenq added that, with most of the data on the issue being retrospective, a causative role has not been established, and “the finding of an association between the gut microbiota composition and survival, while interesting and provocative, does not provide evidence that intervening on the gut microbiota will lead to a clinical benefit.”
“I’m hopeful that randomized clinical trials will eventually demonstrate that we can protect or restore the gut microbiota, and this will lead to substantial clinical benefits, but this remains to be seen,” he said.
The authors had no disclosures to report. Dr. Jenq is an advisor for Seres Therapeutics, Prolacta Biosciences, and MaaT Pharma.