In vitro stimulation with irradiated allogeneic cells stimulated the production of IFNγ in both T cell populations (Figure 1C), and blockade of PD-1/PD-L1 interaction significantly increased the amount of cytokine produced, confirming that T cell-mediated GVHD is regulated by PD-1 (Figure 1C). The gene discussed is PDCD1; the disease is graft versus host disease.