CD226 and graft versus host disease: NK cells have been implicated before in the suppression of GvHD by two mechanisms: either by direct killing of donor T cells, which are activated by alloantigens and may upregulate ligands for NK‐cell receptors DNAM‐1 and NKG2D 16, 17, or by killing host DCs hence inhibiting donor T‐cell proliferation 2.