DLL1 and graft versus host disease: In terms of Notch ligands, Dll1 and Dll4 in the host accounted for all the effects of Notch signaling in GVHD, with a dominant role for Dll4 (Mochizuki et al., 2013; Tran et al., 2013; Chung et al., 2019; Perkey et al., 2020).