Previous studies have reported that NOD-SCID IL2rγcnull mice reconstituted with human PBMCs without IL-2 remain free of GVHD symptoms for nearly 30 days after engraftment even with the transfer of up to 20×106 PBMCs [15] whereas, here with just 5×106 cells, all of the animals succumbed to the disease by 15–17 days ( Figure 4A). Here, IL2 is linked to graft versus host disease.