Alterations in the gut microbial composition is common during hematopoietic stem cell transplantation (HSCT), and is associated with the development of graft-versus-host disease (GvHD). Florent Malard, MD, PhD, from Hôpital Saint-Antoine, Paris, France, discusses the promises of the Phase II ODYSEE trial (NCT02928523) investigating the use of autologous fecal microbiota transplantation (AFMT) in gut-predominant steroid refractory GvHD patients. Speaking at the European Society for Blood and Marrow Transplantation (EBMT) 2019 Annual Meeting, held in Frankfurt, Germany, Dr Malard stresses how using fecal microbiota from a pool of donors can result in high bacterial diversity and successful intestinal recolonization in patients.