Story by: Kim Huston on September 5, 2019
A haploidentical transplant is a special type of allogeneic blood and marrow transplant used to treat children with blood-related cancer and disorders, for whom a conventional stem cell donor cannot be found.
In an allogeneic transplant, a child’s unhealthy blood-forming stem cells are replaced with a donor’s healthy blood-forming stem cells. For the transplant to be successful, a good match is needed between the tissue types of the donor and the patient. In a conventional transplant, if a matched donor cannot be found for the patient, a transplant may not be possible. Haploidentical transplant is a breakthrough treatment type that makes blood or marrow transplant possible for nearly every patient who needs one by expanding the pool of potential donors.
For decades, many childrenwho needed a blood or marrow transplant were unable to get one, because suitable transplant donors could not be found. This was due to the fact that suitable donors needed to have identical tissue types — usually from a sibling. Tissue type is based on human leukocyte antigen (HLA) proteins on the surface of cells. HLA tells the immune system which cells are healthy and can be left alone and which are sick and/or foreign and need to be removed.
A child’s sibling has a 25% chance of being a perfect HLA-matched donor for the child. Other siblings or the parents may have only half of their HLA proteins matched to the child. They are called “haploidentical,” or half-matched, potential donors. In the past, the use of haploidentical donors in transplants carried a very high risk of the development of graft failure or graft-versus-host disease (GVHD). GVHD is a serious complication that happens when a transplant recipient’s immune system attacks the healthy donor tissue.
During the early 2000s, researchers looked to solve the issue of haploidentical transplantation. The researchers developed a modified treatment plan for haploidentical transplants that has dramatically cut down on the risk for complications. This modification leads to significantly improved clinical outcomes associated with haploidentical transplants and makes it possible for parents, siblings, and possibly aunts, uncles, half-siblings and grandparents, to be potential donors. In addition, a haploidentical transplant can be performed sooner than with unrelated donor transplants, thus benefiting patients who need a transplant quickly because of potential progression of the underlying disease.
Not all patients need a haploidentical transplant. A transplant physician will first test the blood to learn a child’s HLA type. The transplant team will then look for a donor who matches the child’s HLA type the closest, from a related or unrelated volunteer. If a HLA-matched donor cannot be found or a transplant is needed urgently, a haploidentical donor may be selected. The transplant team will consider all factors and review with the family whether a haploidentical transplant is the best treatment option.
For donors and recipients, a haploidentical transplant procedure is similar in most parts to other allogeneic transplant procedures. However, with a haploidentical transplant, after the infusion of the donor stem cells, the patient will receive an extra dose of a chemotherapy agent called cyclophosphamide, which will help to reboot the immune system and decrease the number of active donor T-cells that can attack the patient’s tissues and cause GVHD. The patient then will be monitored closely to prevent the development of GVHD.
Children with various conditions can be treated with a haploidentical bone marrow transplant, including:
In addition to other forms of blood and marrow transplant, haploidentical transplant is available at Norton Children’s Cancer Institute for the appropriate patients. Norton Children’s Cancer Institute is affiliated with the University of Louisville and, since 1993, has been home to the Hanna Catherine Evans Bone Marrow Transplant Program, the region’s only blood and marrow transplant program dedicated to helping kids.
Norton Children’s Hospital is a member of the Pediatric Blood & Marrow Transplant Consortium and the Blood and Marrow Transplant Clinical Trials Network, and is accredited by the Foundation for the Accreditation of Cellular Therapy for high-quality care provided to transplant patients. A dedicated team of well-trained blood and marrow transplant clinicians and other specialists work closely with families to provide comprehensive care to patients who may need a haploidentical transplant.