GM dysbiosis in SOT recipients is mediated by the immune system through the SIgA response, with direct drug-mediated effects on fecal communities not observed in in vitro experiments.
Key Findings
Results
Pediatric solid organ transplant recipients exhibited confirmed compositional and functional dysbiosis compared to age-matched healthy controls.
Study included 48 pediatric SOT recipients (age 10.6 ± 4.7 years) receiving heart (n=11), kidney (n=10), or liver transplantation (n=27), compared to 16 age-matched healthy controls (HC).
Quantitative metagenomic analyses were used to assess gut microbiota composition and function.
Both compositional and functional dysbiosis were confirmed in SOT recipients across all three organ transplant types.
Results
The degree of gut microbiota dysbiosis in SOT recipients was associated with tacrolimus (TAC) levels.
Tacrolimus is a commonly used immunosuppressant in solid organ transplantation.
Higher tacrolimus levels correlated with greater degrees of dysbiosis in the gut microbiota.
This association suggests immunosuppression therapy plays a role in shaping gut microbiota composition in pediatric transplant recipients.
Results
SOT recipients exhibited higher secretory IgA (SIgA) levels than healthy controls, along with an increased percentage of bacteria targeted by SIgA.
SIgA sequencing was performed alongside quantitative metagenomic analyses in the same cohort of 48 SOT recipients and 16 HC.
SOT recipients showed not only elevated SIgA levels but also altered target spectra of SIgA-coated bacteria compared to healthy controls.
The increased percentage of SIgA-targeted bacteria indicates a broader or shifted immune targeting of gut microbiota in transplant recipients.
Results
Altered SIgA responses were associated with the degree of gut microbiota dysbiosis in SOT recipients.
Both the level of SIgA and the spectrum of bacteria targeted by SIgA were linked to dysbiosis severity.
This association was observed across the combined cohort of heart, kidney, and liver transplant recipients.
The findings suggest SIgA targeting alterations are not incidental but are linked to the extent of microbiota disruption.
Results
Direct drug-mediated effects of immunosuppressants on fecal microbial communities were not observed in in vitro experiments.
In vitro experiments were conducted to test whether immunosuppressive drugs directly alter gut microbial communities.
No direct drug-mediated effects on fecal communities were detected, suggesting immunosuppressants do not act directly on the microbiota.
This result supports the mechanistic model in which immunosuppression affects the gut microbiota indirectly through immune-mediated pathways rather than through direct antimicrobial activity.
Discussion
A mechanistic model was proposed suggesting that gut microbiota dysbiosis in SOT recipients is mediated by the immune system through the SIgA response.
The proposed model connects immunosuppression, gut microbiota composition, and SIgA-targeting as a causal pathway.
Immunosuppression is hypothesized to alter SIgA production or targeting, which in turn shapes the microbial community toward dysbiosis.
The model explains persisting long-term dysbiosis in SOT recipients as an immune-mediated rather than direct drug-mediated phenomenon.
This mechanistic framework is supported by the association between tacrolimus levels, SIgA alterations, and dysbiosis severity.
What This Means
This research suggests that children who receive solid organ transplants (heart, kidney, or liver) develop lasting imbalances in their gut bacteria, known as dysbiosis. The study followed 48 pediatric transplant recipients and 16 healthy children, analyzing both the gut bacteria and a specific immune protein called secretory IgA (SIgA), which normally helps protect the gut by tagging bacteria for immune surveillance. Transplant recipients had higher levels of SIgA than healthy children, and their SIgA was coating a broader and different set of bacteria than in healthy controls. The more disrupted a child's gut bacteria were, the more altered their SIgA response appeared to be.
Importantly, the study found that the immunosuppressant drug tacrolimus — taken by transplant recipients to prevent organ rejection — was associated with worse gut bacteria imbalance. However, when the researchers tested immunosuppressant drugs directly on gut bacteria samples in the laboratory, the drugs did not directly kill or change the bacteria. This suggests the drugs are not acting like antibiotics on the gut; instead, they appear to work indirectly by altering the immune system, which then changes how SIgA targets gut bacteria, ultimately leading to dysbiosis.
This research suggests that the persistent gut microbiota disruption seen in transplant recipients is driven by immune system changes — specifically altered SIgA responses — rather than by direct toxic effects of immunosuppressive drugs on gut bacteria. This distinction matters because it points toward the immune system as a potential target for interventions aimed at restoring healthier gut bacteria in transplant recipients, which could have implications for their long-term health and survival.
Schulze K, Goldschmidt I, Melk A, Boehne M, Woltemate S, Ballmaier M, et al.. (2026). Altered SIgA-targeting of gut microbiota is associated with long-term dysbiosis in pediatric solid organ transplant recipients.. Gut microbes. https://doi.org/10.1080/19490976.2026.2675078