To ensure that the lack of GVHD was not related to an increase in CD4+CD25+ regulatory T cells (Tregs), they performed additional experiments in which they depleted Tregs before a T-cell infusion and observed that the Treg-depleted naïve T cells still caused GVHD whereas the Treg-depleted memory T cells did not. This evidence concerns the gene CD4 and graft versus host disease.