GVHD protection was due to the presence of alloreactive “licensed” NK cells capable of killing activated DCs (Figure 2), as supported by the requirement for Ly49 ligand-mismatch from otherwise MHC-matched donors for GVHD control [152, 156] and the fact that Ly49C silencing can induce NK cell alloreactivity [157]. Here, KLRA1P is linked to graft versus host disease.