In stark contrast to CD4+ and CD8+ T cells, the co-injection of non-transgenic DN T cells with T cell-depleted BM into a sublethally irradiated host ensured prolonged recipient survival in the absence of clinical signs of GVHD (He et al., 2007; Su et al., 2012; Figure 2B), indicating that DN T cells are not alloreactive nor pathogenic in this context. Here, CD4 is linked to graft versus host disease.