How can a tool traditionally used to match transplant recipients to organ donors now help guide care for cancer and autoimmune disease? Human leukocyte antigens (HLAs) are markers on our cells that help the immune system identify “self” from “non-self.” For decades, they’ve been essential for matching organ donors and recipients and lowering the risk of organ rejection. Now, those same markers are being leveraged to inform more precise treatment decisions, support safer drug development and help