In this issue of Blood, Hazenberg and Spits provide a detailed overview of human innate lymphoid cell (ILC) subsets and their development and distribution throughout the human body, discussing these cells in the context of human disease. In the same issue, Munneke et al for the first time link ILCs to human hematopoietic malignancies by identifying a clear correlation between the presence of activated ILCs after induction chemotherapy and the absence of acute graft-versus-host disease (GVHD) development following subsequent hematopoietic stem cell transplantation (HSCT).1,2