Kim and coworkers reported that GITR stimulation converted chronic to active GvHD, ameliorated disease symptoms, and affected survival in (C57BL/6xDBA/2)F1 mice with chronic GvHD upon transfer of DBA/2 parental cells, and this was due to modulation of effector T cells [20, 64]. The gene discussed is TNFRSF18; the disease is graft versus host disease.