A new study 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.

HCT is a procedure in which a patient receives blood-forming stem cells from a genetically similar donor.

This approach is often used to treat aggressive blood cancers, but it can be associated with severe complications such as graft-versus-host disease (GVHD), a serious and potentially life-threatening complication that occurs when the donated immune cells attack the patient’s cells as foreign tissue.

Although the study is observational and doesn’t show cause and effect, the results suggest that it may be possible to reduce patients’ risk of complications by taking steps to improve the health of their gut microbiota before beginning HCT, according to researchers.

The billions of bacteria and other microbes that live on and within our bodies play an important role in maintaining healthy bodily functions.

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.

“Before we approve patients to receive a transplant, we do many tests to make sure all of their organs are in good working order,” said lead study author Jonathan U. Peled, MD, PhD, of Memorial Sloan Kettering Cancer Centre.

“In the future, we envision that the health of the gut microbiota - which some have called the ‘forgotten organ’ - may become part of this whole-body evaluation.

It might also be possible to intervene and repair the microbiota in the pre-transplantation period.”

Source: ASH