IL22 and graft versus host disease: Although the limited data available are suggestive of Th22 participation toward allograft rejection, conflicting studies exist, attributing regulatory function to IL-22 in experimental GvHD mouse models.78 In clinical patients with steroid-refractory GvHD, complete responders to extracorporeal photopheresis demonstrated increased Th22 cell frequencies, whereas Th22 cells were decreased in nonresponders,79 indicating a potential regulatory role.