Finding a Donor
Before a child undergoes the HSCT, a donor must be found. Finding the right donor can take several weeks or months. The reason it can take so long to find a donor is because the donor must match, or come close to matching, a child’s proteins called human leukocyte antigen, or HLA. The HLA proteins on the cells helps determine which cells belong to a person’s body, and which cells don’t belong to a person’s body.
If the HLA of the donor is matching to a child’s HLA, then the new immune cells put into the child’s body will stay alive and thrive. If the HLA of the donor is not matching the HLA of the child, then the new immune cells put into the child’s body may have a higher chance of being rejected or fighting the cells in the child’s body.
Sibling Matched Donor
The best stem cell donor for a child with SCID is an HLA matched sibling. The sibling must have the same mother and father as the child with SCID. Full biological siblings of children with SCID have a 25% chance of being a perfect match, so families may need to look elsewhere for a donor.
Unrelated Matched Donor
Another stem cell source is an unrelated HLA matched donor. These are individuals who are donors with no family connection to the child. These donors volunteer to provide their stem cells.
People who are willing to donate their stem cells are placed on an anonymous list called a registry. Doctors examine the registry and look for donor types that match the child’s HLA. If the donor stem cells match the child’s in HLA, then those cells can be requested for use in the HSCT.
When a sibling HLA matched donor or an unrelated HLA matched donor cannot be found, then another option for stem cells is a haploidentical family match. This is a half-matched donor who is usually a parent but can be a sibling or even an aunt, uncle or cousin.
Umbilical Cord Blood Donor
Another option for a source of stem cells is umbilical cord blood. Umbilical cord blood is sometimes donated by a mother after she has a child. The blood comes from the umbilical cord of her child and contains hematopoietic stem cells. The blood is frozen and kept in repositories for donation. The cord blood, which typically comes from an unrelated individual, could be a match for a child with SCID.