To date, Janus-head roles taken by Th17 and associated cytokines such as IL-17A and IL-22 during acute GVHD have been documented [14] In one study, IL-17A deficiency led to disease reduction [15], whereas another study showed that the absence of IL-17A- secreting cells exacerbated GVHD [16]. The gene discussed is IL17A; the disease is acute graft versus host disease.