Interestingly, we observed in our system an increased ratio of splenic donor regulatory T cells (Treg) to total donor conventional CD4+ and CD8+ T cells (Tcon) in the presence of NK cells, suggesting a differential susceptibility of Treg and Tcon to NK cell-mediated cell lysis leading to an immune-regulatory environment that eventually contributes to GvHD suppression (37). Here, CD4 is linked to graft versus host disease.