Perforin inhibitors have been investigated in the context of hematopoieticstem cell transplantation, which is used to treat hematological cancersand nonmalignant disorders such as bone marrow failure and inheritedimmunodeficiency disorders.83,107,108 In the early stages, rejection of immunologically mismatched graftsis known to be driven by the recipient’s NK cells, which predominantlyuse the perforin/granule exocytosis pathway to kill the transplantedbone marrow stem cells. The gene discussed is PRF1; the disease is Bone marrow hypocellularity.