The lower-diversity states seen later, after transplant, tend to be dominated by a variety of pathogenic bacteria, Dr. Peled said. These include Enterococcus and Proteobacteria, a phylum that includes Klebsiella and Escherichia coli species. This predominance has been associated with subsequent bacteremia, he said.
“Patients tend to enter transplant with a relatively diverse flora, and a frequent event in the posttransplant samples is domination by these pathobiomes,” Dr. Peled said. “In some cases, almost the entire composition of the gut is [composed] of a single species.” This loss of diversity and single-species domination was seen across the three geographically diverse research sites, he said.
This decimation of diversity is linked to poor transplant outcomes. In particular, Dr. Peled said, an enterococcus-dominated gut had previously been associated with higher risk for acute GVHD and with gastrointestinal GVHD.
Here, the multisite data showed that at Regensburg, higher enterococcus abundance on days 7-14 post HCT was associated with increased risk of GI GVHD. At MSKCC, enterococcus domination was associated with a hazard ratio of 1.4 for acute GVHD (P = .008). The MSKCC group used data from 503 patients, defining domination as at least 30% relative abundance in any sample from post-HCT days 7-21.