Elusive CD8+ T cells that transiently secrete interleukin (IL)-17 cause graft-versus-host disease (GVHD) but do not contribute to beneficial graft-versus-leukemia (GVL) responses, as reported by Gartlan et al in this issue of Blood. 1 GVHD remains a lethal and morbid complication of allogeneic bone marrow transplantation, but GVHD is tightly linked to beneficial GVL effects, and removal of donor T cells that cause GVHD also diminish GVL, leading to greater relapse after bone marrow transplantation (BMT). This elegant paper from the laboratory of Geoffrey Hill has identified a rare “night fury” T-cell subset that causes much pain with no gain, a finding that may take us one large step closer to the long sought after goal of separating GVL and GVHD.