Lactose drives Enterococcus expansion to promote graft-versus-host disease

Lactose can fuel GVHD Allogeneic hematopoietic cell transplantation (allo-HCT) is used to treat certain hematopoietic malignancies, but patients have a risk of developing graft-versus-host disease (GVHD). Stein-Thoeringer et al. performed a large-scale analysis of more than 1300 patients treated with allo-HCT across four clinical centers (see the Perspective by Zitvogel and Kroemer). High levels of bacteria from the Enterococcus genus were associated with greater incidence of GVHD and mortality. Lactose appears to provide a substrate for Enterococcus growth, and patients with a lactose-malabsorption genotype had a greater abundance of Enterococcus. A lactose-free diet limited Enterococcus growth, reduced the severity of GVHD, and improved survival in gnotobiotic mouse models. Science , this issue p. 1143 ; see also p. 1077