REPORTING FROM THE 2018 BMT TANDEM MEETINGS
SALT LAKE CITY (FRONTLINE MEDICAL NEWS) – A multicenter study confirmed that diversity of gut microbiota is associated with better survival after allogeneic hematopoietic cell transplantation (HCT), while low diversity and the predominance of pathogenic bacteria are linked to graft versus host disease (GVHD).
Lower calorie intake and exposure to broad-spectrum antibiotics were both associated with lower diversity, the study found.
“One of the striking findings early on was this association between diversity in the gut and overall survival,” said Jonathan Peled, MD, PhD, noting that his research group also saw that high gut diversity was associated with lower rates of GVHD-related mortality.
“The first question that I want to ask today is ‘Are the patterns of microbiota injury that have been described in single-center studies and their association with clinical outcomes consistent across geography?’” Dr. Peled said during a top abstracts session at the combined annual meetings of the Center for International Blood & Marrow Transplant Research and the American Society for Blood and Marrow Transplantation.
To answer this, Dr. Peled and his associates at Memorial Sloan Kettering Cancer Center (MSKCC), New York, teamed up with a research group at Duke University, Durham, N.C., and with investigators in Regensburg, Germany. The international group devised a study that would use centralized sequencing and analysis to examine patient fecal samples from all three centers.
In all, 5,310 samples were obtained from 1,034 HCT patients. MSKCC contributed most of the samples (n = 908, 87.8%), with Regensburg contributing 79 (7.6%) and Duke contributing 47 (4.5%).
The most common malignancies treated were acute myeloid leukemia, myelodysplastic syndrome, and non-Hodgkin lymphoma. The balance of graft sources and conditioning intensity varied between centers, but overall, more than three-quarters of grafts were from peripheral blood stem cells and just over half of patients received myeloablative conditioning.
The centralized microbiota profiling involved extracting bacterial DNA, and then using polymerase chain reaction to amplify 16sRNA for sequencing and subsequent taxonomic identification.
“Samples can be segregated into clusters according to microbiota composition,” said Dr. Peled, a medical oncologist at MSKCC. The investigators used an algorithm called t-distributed stochastic neighbor embedding, or tSNE, to help detect patterns in microbiota composition and diversity before and throughout the HCT process. Visualizations using tSNE allow for two-dimensional representations of complicated associations and interrelatedness in data.
“Color-coded by diversity and time, we see that these early samples tend to be more diverse,” in the tSNE analyses, Dr. Peled said. The later clusters, he said, show evidence of lower diversity and injury.
Individual samples can also be coded in a way that shows clusters by abundance of various bacterial taxa, Dr. Peled said. “The early, diverse cluster tends to be dominated, or filled, by anaerobic commensals such as Firmicutes and Clostridia, which we and others have found are associated with good outcomes after transplant.”
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.
Patients at both MSKCC and Regensburg had a better chance of overall survival if they had high intestinal microbial diversity around the period of neutrophil engraftment, as seen in a sample collected within 7 days of post-HCT day 14. At MSKCC, data for 651 patients showed a statistically significant association (P = .006); this finding was reproduced at Regensburg, which also saw a significant association (P = .015) for the 59 patients studied, Dr. Peled reported.
Increased treatment-related mortality was seen for patients who had low microbial diversity following neutrophil engraftment as well. Of 372 MSKCC patients who had samples available 7-50 days after engraftment, high diversity was associated with better overall survival, and with lower treatment-related mortality (P = .03 for both).
Dr. Peled and his collaborators also divided patients into quartiles by amount of biodiversity. They found that comparing the highest to the lowest biodiversity quartile showed significantly overall survival benefits for the highest-diversity group (P = .007).
The problem starts before transplant, Dr. Peled explained. The researchers found that compared with healthy controls at MSKCC and data from the Human Microbiome Project, HCT patients entered their transplant with significantly less gut biodiversity.
The second question to be addressed is “What are the key environmental determinants of intestinal microbiota composition?” said Dr. Peled.
“Peri-HCT exposure to broad-spectrum antibiotics is associated with lower intestinal microbial diversity,” he said. For 5,936 samples taken from 976 patients receiving allogeneic HCT, the most significant difference in diversity between those with and without broad-spectrum antibiotic exposure was seen at day 15 post transplant (P = .008).
Higher calorie intake was also associated with greater diversity (P less than .001). Higher dietary fiber intake was associated with higher abundance of Blautia, a genus considered to be a healthy commensal microorganism, Dr. Peled said.
“Conditioning intensity is associated with the magnitude of diversity loss, and with distinct microbiome configurations,” said Dr. Peled. Using 4,311 samples from 908 patients, a myeloablative conditioning regimen (n = 508) was associated with significantly less diversity when compared with reduced intensity (n = 316) and nonmyeloablative regimens (n = 84; P =.002 and P less than .001, respectively).
To answer a third question – What is the natural history of recovery from microbiota injury after HCT? – the investigators looked at trends over time for 28 allogeneic HCT recipients. With a total of 294 samples for analysis, Dr. Peled and his group found that “diversity increases, but often to a configuration distinct from the pre-HCT state.” It took some patients nearly a year to return to their pretransplant level of diversity.
Patients in the subset of those who go on to develop lower gastrointestinal GVHD have an intestinal microbiota composition that is distinct from those patients whose GVHD exclusively involved the upper gastrointestinal tract, the skin, or the liver (P = .019), Dr. Peled said.
He and his team are currently enrolling patients for a phase 2 randomized clinical trial ( NCT03078010 ) that will explore strategies to deescalate the use of broad-spectrum antibiotics for febrile neutropenia in patients with allogeneic HCT. The trial will randomize patients to receive either piperacillin-tazobactam, the current standard of care at MSKCC, or cefepime with deescalation to aztreonam with vancomycin, the microbiota-sparing strategy. The trial will examine the abundance of Clostridiales and Blautia species, gut biodiversity, the rate of GVHD, bacteremia, and survival rates.
The research presented was funded by the Parker Institute for Cancer Immunotherapy, the Sawiris Foundation, Empire Clinical Research Investigator Program, and Seres Therapeutics. Dr. Peled reported that he has intellectual property rights and research funding through Seres Therapeutics
SOURCE: Peled J et al. 2018 BMT Tandem Meetings, Abstract 3 .