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The diversity of bacteria in the gastrointestinal tract of patients receiving stem cell transplants may be a predictor of post-transplant survival, according to a study available online ahead of print in BloodDOI: 10.1182/blood-2014-02-554725.

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Previous studies have shown that the intensive treatment given to individuals receiving a stem cell transplant from a healthy donor can destroy a significant portion of the recipients' gut microbiota and reduce its overall diversity. Disturbances of the gut microbiota have been shown to be correlated with post-transplant complications such as bloodstream infections and graft-versus-host disease.


"While the link between gut microbiota and complications in allogeneic stem cell transplantation [SCT] has been previously established, until this point it has remained unclear whether the gut bacteria of transplant recipients could predict their survival," said the study's senior author, Ying Taur, MD, MPH, of Lucille Castori Center for Microbes, Inflammation, and Cancer at Memorial Sloan Kettering Cancer Center. "This study sought to further explore the potential connection between transplantation, gut bacteria, and overall survival."


To better understand the association between post-transplant microbiota and patient outcomes, he and his colleagues collected fecal specimens from 80 patients undergoing allogeneic SCT and sequenced each sample's bacterial DNA. Specimens were collected within seven days of engraftment, the point at which transplanted blood-forming cells start to grow and make healthy cells in the recipient and the point at which the team speculated that microbiota diversity would be greatest following pre-transplant conditioning, they explained.


Patient outcomes were compared based on the diversity of microbiota in their specimens, grouped into categories of high, intermediate, and low microbiota diversity. At time of stem cell engraftment, 34 patients (42.5%) were observed to have low gut microbiota diversity, 20 (25%) had intermediate diversity, and 26 (32.5%) had high diversity. The analysis continued for up to three years or until death or last follow-up.


A strong connection was found between post-transplant gut microbiota diversity and outcomes, with overall survival rates of 36, 60, and 67 percent among the low-, intermediate-, and high-diversity groups, respectively. Furthermore, the researchers noted, diversity was particularly associated with transplant-related outcomes: Patients with low microbiota diversity were approximately five times more likely to die of transplant-related causes within the follow-up period than those with more diverse gut bacteria.


"These results further underscore the significance of the gut microbiota in allogeneic stem cell transplant. A major question is whether we can improve outcomes by preserving diversity within the gut microbiota," Taur said in a news release.


"One possible strategy is to find ways to perform transplants in a manner that minimizes damage to the gut microbiota. Another approach would be to replenish the gut with beneficial microbes that are lost after this procedure is performed. We hope that this study will inspire additional research that will further examine the role and importance of the gut microbiota to stem cell transplant outcome."