Lastly, NSG mice, engrafted with human fetal thymus and liver and CD34+ stem cells isolated from the same fetal tissue one day from birth (NSG-1d), were shown to be highly susceptible to infection by HTLV-1 and demonstrated rapid polyclonal proliferation and infiltration of CD4+CD25+ T-cells to vital organs, weight loss and death [31]. Here, CD4 is linked to infection.