In summary, the data reported by Ni et al. (58) suggested that the separation of GVL effects from GVHD could be ascribed to the PD-L1–mediated effect on CD8+ T cells depending on whether CD4+ T cells were present, the nature of the interacting partner expressed by CD8+ T cells, and the tissue microenvironment (Figure 1) (19, 21). The gene discussed is CD4; the disease is graft versus host disease.