A new study from Memorial Sloan Kettering Cancer Center presented at ASH 2018 in San Diego reports the likelihood of complications from a hematopoietic cell transplantation (HCT) is higher if a patient has lower diversity of microbes residing in the gut before beginning the transplantation process.

While previous research has shown a similar relationship between outcomes and gut microbial composition shortly after transplantation, this new study suggests that the association starts even before patients begin transplantation. The study, conducted in the United States, Europe and Japan, found patients set to undergo HCT had gut microbiota that was 1.7- to 2.5-fold lower in diversity compared to healthy volunteers.

The microbial communities in the majority of the patients’ guts went on to be dominated by a single bacterial species. The study compared stool samples from nearly 1,000 patients undergoing allogeneic HCT to those of healthy volunteers.While microbial composition, which depends to some extent on diet and environment, showed some variation from place to place, the diversity and types of microbes found in the stool of transplant patients in all countries was markedly different from those of the healthy volunteers.

Further analysis showed this low diversity was associated with lower calorie intake, the use of broad-spectrum antibiotics, and the use of higher-intensity conditioning drugs to clear cancer cells from the body before transplantation. Patients with the lowest microbial diversity showed lower overall survival and a higher risk for GVHD.