Inflammatory cytokines, such as IL-1 [3], IL-2 [4], TNF-α [4] and IFN-γ [5], are elevated after allogeneic HSCT and perpetuate GVHD through direct cytotoxic effects on host tissues and by priming and activating immune effector cells [6]. The gene discussed is IFNG; the disease is graft versus host disease.