While blood can be given to millions of people with the same blood type, stem cell donors and recipients are meticulously matched one-to-one.
Human Leukocyte Antigens (HLAs), which coat the surfaces of peripheral blood stem cells and most other cells, are the key to discovering a favorable match. These “markers” aid in the differentiation of cells from viruses, bacteria, and cancer.
Since HLA antigens (tissue types) are passed from one generation to the next, a match for stem cell donation is more likely to be found within a family group. Mostly, siblings from the same parents make the best matches.