While the activation of human T cells in the xeno-GVHD model is a useful model, it does not address potential cellular interactions between the activated T cells and other cell populations that are absent or present at very low frequencies (B cells, dendritic cells, Natural Killer cells, and myeloid cells) in PBMC reconstituted NSG mice and which may play a role in the upregulation of Foxp3 expression by Tconv cells. Here, FOXP3 is linked to graft versus host disease.