Antimicrobial and immunosuppressive therapy during HSCT results in loss of microbial diversity and injury to the intestinal epithelium which are risk factors for iGVHD. Indole, produced by the metabolism of phenylalanine by Enterobacteriaceae and some anaerobes, is a major quorum sensing signal that inhibits pathogenic bacterial injury and strengthens the intestinal epithelium mucosal barrier.
Fecal indole concentrations were measured in stools from healthy volunteers (HV) without a history of antibiotic exposure, use of immunosuppressants or recent travel (n=18), HSCT recipients at the time of conditioning (n=21) and patients with biopsy proven iGVHD (n=10) using a colorimetric assay. Fecal bacterial DNA from 13 HSCT and 6 iGVHD individuals was isolated and 16S rDNAV4 PCR sequencing performed using an IlluminaMiSeq 2x250 platform.
Comparison of indole concentrations amongst the 3 groups showed a significant difference between HV & HSCT (3498 vs. 812 μM; p=0.0001), HSCT & iGVHD (812 vs. 233μM; p=0.02), and HV & iGVHD (3498 vs 233 μM; p=0.0001). Fecal microbiome comparative analysis showed a lower number of operational taxonomic units in patients with iGVHD compared to HSCT at the time of conditioning with dominance of Lactobacillus, Streptococcus, Citrobacter and Enterococcus in patients with GVHD. Whereas Bacteroides, Escherichia, Shigella were the major species identified in patients without GVHD.
Figure 1. Phylogenetic microbial diversity in patients with iGVHD and in patients at the time of conditioning for HSCT
Figure 2. Dot plot graph representing the fecal indole concentrations measured in three groups of subjects (iGVHD, HV and Transplant patients at baseline). +++ Represents median values and ---- Error bars.
When compared to HV and to HSCT recipients at the time of conditioning, fecal indole levels of patients with iGVHD were decreased. Low indole concentrations in iGVHD correlated with the loss of microbial diversity, particularly with the loss of Escherichia-Shigella and Bacteroides species. Fecal indole may be of use in the early identification of patients at risk for HSCT related iGVHD. Prospective studies that evaluate the microbiome shifts in diversity, indole and other tryptophan metabolites in patients at risk for HSCT related iGVHD are in progress.
A. Alousi, None
E. Shpall, None
S. Shelburne, None
J. Petrosino, None
K. Rezvani, None
N. J. Ajami, None
N. Ghosh, None
L. Carlin, None
R. Chemaly, None