Fucosylation by α-1,3-fucosyltransferase-VI enzyme on ex vivo–expanded Tregs forming the sialyl Lewis X moiety (sLeX) on P-selectin glycoprotein ligand-1 (A) is a strategy to improve in vivo trafficking and persistence in GVHD target tissues (B), leading to a balance in favor of Tregs instead of allogeneic T effector (Teff) cells and to improved survival in treated mice (C).