Technically the first bone marrow transplant took place in Cooperstown, NY. But — for those without an identical twin on hand — UW research did revolutionize the process when UW professor Fritz Bach performed the first successful matched human bone marrow transplant in 1968 at UW Children’s Hospital. Matched human refers to human leukocyte antigens (HLA), or markers, that your immune system uses to see which cells belong in your body and which don’t. When incompatible cells enter the body, the body begins to attack them, leading to dangerous and often lethal outcomes. Since someone’s identical twin was guaranteed to be genetically compatible, most transplants only occurred between twins. Bach developed the mixed lymphocyte culture test, to act as a surrogate HLA compatibility marker. Using this test, Bach performed what was essentially a test-tube transplant, taking white blood cells of patients and combining them with donor cells. If no reaction occurred, the procedure could safely be performed. So, Bach didn’t perform the first bone marrow transplant, but his test broadened the field of viable donors and drastically decreased the chances of lethal rejections. Today, any donor and recipient pair, regardless of familial relation, can be tested for compatibility.