Definition

A term used to describe a tissue donor whose HLA tissue type partially matches (usually 50%) the HLA tissue type of a person receiving a stem cell or organ transplant. HLAs are a set of cell surface markers found on a person’s cells and tissues that play an important role in the body’s immune response to foreign substances. Before someone receives a transplant, their HLA tissue type will be matched with that of a potential donor. A haploidentical donor, such as a parent, child, or sibling, may be used in a stem cell or organ transplant when a fully or closely matched donor is not available.