P2RX7 and graft versus host disease: Prior to this study, targeting of P2X7 in pre‐clinical models of GVHD was restricted to five different small molecule P2X7 antagonists or an anti‐human P2X7 mAb,7, 8, 9, 10, 31, 37, 38, 39, 40 none of which is suitable for use in a clinical setting for GVHD, with the exception of stavudine.