To determine if the above paradigm is relevant to human GVHD, our groups have investigated the roles of purinergic signaling in Hu-PBMC-NSG mice using small molecule antagonists/agonists of purinergic molecules and PBMCs from human donors encoding natural variants of the P2RX7 and ENTPD1 genes (Figure 1). The gene discussed is ENTPD1; the disease is graft versus host disease.