title: Gut Microbiota As Potential Non-Invasive Biomarker For Kidney Graft Rejection
Creators: name: Visconti, Vanessa
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024

description: Background: Kidney graft rejection still represents the major cause of graft loss in kidney transplant recipients. Increasing evidences have demonstrated the link between gut microbiota alterations and allograft outcome, mostly attributable to the bidirectional relationship between gut microbiome and systemic immune system activation’s profile. Purpose of this study was to characterize the gut microbiota of kidney transplant recipients with and without allograft rejection (AR) in order to identify a specific microbial fingerprint associated with rejection. We also aimed to define a bacterial genomic biomarker for rejection, which characterisation could lead to the etablishment of a non-invasive method for the diagnosis of AR, thus preventing patient’s exposure to possible complications related to renal graft biopsy. Furthermore, we intented to perform a predictional functional analysis in order to hipotetise functional implications of the different microbial compositions between the two groups. Methods: We enrolled a total of 76 patients, of which 66 were suitable for completing the clinical trial. Into this prospective cohort trial involving adult kidney transplant recipients with and without AR, fecal bacterial composition was characterized using 16S rRNA gene sequencing of the V4 hypervariable region, and taxonomy was assigned after amplicon sequence variants (ASV) clustering. Results: Gut microbial composition of recipients with AR was characterised by lower richness, especially pronounced when comparing alpha diversity metrics of patients with cronic active T cellular mediated rejection to controls (Chao1 index p-value= 0.025 and ACE index p-value= 0.02). PERMANOVA analysis based on Aitchison distance, Bray-Curtis dissimilarity and Jaccard distance revealed differences in the microbial beta-diversity between controls and patients with AR with an adjusted p-value respectively of p = 0.01, p=0.021 and p= 0.022. Use of proton pump inhibitors did not significantly influenced the gut microbial composition of the cohorts. We identified a gut microbial fingerprint for each of our study cohorts, where the control group was characterised by a significant enrichment of anti-inflammatory taxa, while the rejection group by bacteria well known for their role in chronic inflammation. We also identified group-specific ASVs able to distinguish patients with AR from controls as non-invasive biomarkers. A 5-ASVs-combination was able to identify controls with a sensitivity of 86%, a specificity of 100%, a negative predictive value of 88%, and a positive predictive value of 100%, while a 7-ASVs-combination was able to recognise with a sensitivity of 90% patients with rejection, ruling out 100% of controls, with a positive predictive value of 100% and a negative predictive value of 91%. Lastly, PICRUSt 2.0 analysis, used to predict metagenomic functions, revealed that the control group was characterised by higher abundance of metabolic genes, including enzymes involved in the bacterial processing of SCFAs, in the electron transport chain and in the heat shock response. Conclusions: Our results lay the foundations for validating promising non-invasive biomarker based on gut bacterial genome to identify patients with AR in a larger cohort of patients. If confirmed, it would have a relevant clinical impact in the field of transplantation. Whether the different bacterial fingerprint between the two groups is a co-cause or consequence of AR remains an open question, which we believe is worth to be clarified through a clinical follow-up study. Lastly, the different predicted functional profiles of the two cohorts are a starting point to further explore the metagenomic profile of gut bacteria of patients with AR.