PRF1 and graft versus host disease: Such a STAT6-mediated preservation of GVT response without causing severe, lethal acute GVHD also contributes to our understanding of how the conditioning of the donor T cells with IL18 can preserve GVT response without causing GVHD because previous studies have shown that IL18 conditioning regulates GVHD in a STAT6-dependent manner [36], and the same conditioning proceeds via the perforin pathway to preserve GVT immunity [37].