Using stem cells from a donor, this method is used most often for:
Blood-related cancers (leukemia and lymphomas),
Bone marrow disorders (myelodysplastic syndrome and aplastic anemia),
Immune system disorders (reduce body’s ability to fight disease),
Metabolic disease (disrupt body’s ability to produce materials needed for life),
And other inherited (genetic) diseases.
If stem cells are taken from the bone marrow, the procedure is done under either general anesthesia, which puts the person to sleep, or local anesthesia, which causes loss of feeling. Only the bone marrow is collected or harvested from the hips. The bones are not removed or opened during the procedure. The amount of marrow needed is based on the weight of the transplant recipient, but it is usually one to two pints.
About 10 percent of the donor’s total bone marrow is harvested. Within a short time, the bone marrow will replenish itself. Side effects from the bone marrow harvest may be sore hips and mild anemia. Overall, there are few side effects. The surgery can be done as an outpatient procedure.
Stem cells taken from the bloodstream (peripheral blood stem cell transplant) is a less invasive option than bone marrow transplantation. The parent (or progenitor) cells are harvested via a collection catheter from the circulating blood instead of from the bone marrow. This procedure, called apheresis, is completed as an outpatient. The stem cells are collected, frozen, and stored for later use.
Allogeneic HSCT involves two people: the (healthy) donor and the (patient) recipient. Allogeneic HSC donors must have a tissue (HLA) type that matches the recipient. Matching is performed on the basis of variability at three or more loci of the (HLA) gene, and a perfect match at these loci is preferred. Even if there is a good match at these critical alleles, the recipient will require immunosuppressive medications to mitigate graft-versus-host disease. Allogeneic transplant donors may be related (usually a closely HLA matched sibling), syngeneic (a monozygotic or ‘identical’ twin of the patient – necessarily extremely rare since few patients have an identical twin, but offering a source of perfectly HLA matched stem cells) or unrelated (donor who is not related and found to have very close degree of HLA matching). A “savior sibling” may be intentionally selected by preimplantation genetic diagnosis in order to match a child both regarding HLA type and being free of any obvious inheritable disorder. Allogeneic transplants are also performed using umbilical cord blood as the source of stem cells. In general, by transplanting healthy stem cells to the recipient’s immune system, allogeneic HCSTs appear to improve chances for cure or long-term remission once the immediate transplant-related complications are resolved.
A compatible donor is found by doing additional HLA-testing from the blood of potential donors. The HLA genes fall in two categories (Type I and Type II). In general, mismatches of the Type-I genes (i.e. HLA-A, HLA-B, or HLA-C) increase the risk of graft rejection. A mismatch of an HLA Type II gene (i.e. HLA-DR, or HLA-DQB1) increases the risk of graft-versus-host disease. In addition a genetic mismatch as small as a single DNA base pair is significant so perfect matches require knowledge of the exact DNA sequence of these genes for both donor and recipient. Leading transplant centers currently perform testing for all five of these HLA genes before declaring that a donor and recipient are HLA-identical.