Administration of the small molecule P2X7 antagonist, BBG, in the same humanised mouse model as used here, revealed that P2X7 contributes to clinical and histological GVHD [20,21,22] but whether donor or host P2X7 or both species of this receptor contributed to GVHD progression could not be determined with this antagonist, which impairs both human and murine P2X7 [34]. This evidence concerns the gene P2RX7 and graft versus host disease.