Last year, Caroline Hysmith became a stem cell donor for her dad, Timothy. She was only 15 at the time.

As part of his leukemia treatment, Timothy participated in a clinical trial at MD Anderson that tested the use of stem cells from “half-matched” donors – those who match half of a patient’s tissue type. This type of transplant, called “haploidentical,” is performed when full matches cannot be found. Research has shown that half-match...