Arya Majumder would have celebrated his 19th birthday last month. Instead he died of cancer in 2010, his condition exacerbated by a scarcity of bone-marrow donors. Arya’s father later recounted how the loss of his only child “took away my very heart and soul, and triggered the collapse of my 23-year-old marriage.”

Other families may be spared the same life-upending sorrow because last week the Department of Health and Human Services withdrew a proposed Obama-era regulation that would have prohibited compensation for bone-marrow...