When a couple has a child with a disease that requires a bone marrow transplant, they learn that the optimal source of cells needed for transplant is a human leukocyte antigen (HLA)-matched sibling. Donor cells need to be HLA-matched to the affected child to avoid rejection of the transplanted cells (a reaction called graft vs. host disease). Many children do not have a matching sibling, so their physicians look for an unrelated donor through the bone marrow registry and cord blood registry.
Some couples have undertaken a pregnancy in the hope of having a child who is an HLA match to their affected child. With each pregnancy, these couples have a 20 percent chance of conceiving a child who is an HLA match to their affected child.
An alternative allows couples to use in vitro fertilization (IVF) with preimplantation genetic diagnosis to identify embryos that are an HLA match and only use those embryos to establish pregnancy.
PGD Process for HLA Matching
A couple and their affected child undergo blood tests to determine whether the preimplantation genetic diagnosis process will be feasible. If these tests show that PGD is possible, the parents will undergo an IVF cycle to form embryos. Genetic analysis is then performed on cells from each embryo prior to transfer into the woman’s uterus. The embryo is biopsied on the third day of its development when the embryo has approximately 6-8 cells. One or two cells are taken from the embryo. The embryo is incubated until testing is complete.
The techniques used in PGD for HLA matching compares the mother’s DNA and father’s DNA to that of the affected child. It is necessary that both parents are the biological parents of the affected child. If non-paternity or non-maternity is discovered, pursuit of an HLA-matched embryo will not be successful.
It is expected that the cord blood from the matched sibling will be used for transplantation. Because the cord blood sample may fall short of the required number of cells for transplantation we expect that 70 percent of cord bloods may need supplementation with other progenitor cell sources such as bone marrow or peripheral blood stem cells.