Although these animals did experience mild weight loss as compared to animals that were transplanted with BM alone, all of the animals survived for reasons which at the moment are unclear, but are related to the production of IFN-γ by CIK cells, in addition to other Th1 cytokines such as tumor necrosis factor (TNF), as suggested by a subsequent paper by the same group of scientists [39] Indeed, CIK expanded from IFN-γ knock-out mice caused acute lethal GVHD [39]. The gene discussed is IFNG; the disease is graft versus host disease.