Stem Cell Transplant for Children: Treatment, Donors & Success Rates
The conventional term “bone marrow transplant” has been replaced in recent years by the term “stem cell transplant.”
Stem cells of the blood system are cells that have the ability to divide and differentiate, and can therefore produce a new blood system in the transplant recipient’s body. In addition to bone marrow, which is the conventional source of stem cells, there are other sources such as the blood itself or umbilical cord blood.
Stem cell transplantation is currently considered an accepted treatment for a long list of malignant and non-malignant diseases.
Autologous stem cell transplantation in malignant diseases: This refers mainly to solid organ tumors such as certain brain tumors, disseminated neuroblastoma, relapse of Hodgkin or non-Hodgkin lymphomas, high-risk Ewing sarcoma, and more.
Pediatric leukemia and Bone marrow transplant
Usually, these serious diseases cannot be completely cured with conventional chemotherapy or radiation alone. Therefore, if the initial treatment results in a significant reduction in the tumor, high-dose chemotherapy can be combined at the end of the treatment. Such a dose may lead to the elimination of the last malignant cell in the body, but due to its toxicity, it will also lead to the irreversible destruction of the patient’s bone marrow cells, which are the most sensitive cells in the body. Therefore, a significant amount of these cells is collected at a relatively early stage of the treatments, preserved in a cryopreservation container, and returned to the patient’s body after he has received the high-dose chemotherapy.
Donor stem cell transplantation (Allogeneic) in malignant diseases: This transplantation is accepted in a number of diseases, such as high-risk acute lymphoblastic leukemia or those that do not respond to initial anti-leukemic therapy, early relapse of acute lymphoblastic leukemia, high-risk acute myeloid leukemia, myelodysplasia, chronic myeloid leukemia, and childhood chronic myelomonocytic leukemia.
The goals of the treatment that prepares for transplantation:
- To create a place (niche) in the patient’s bone marrow so that new cells can be taken up;
- To destroy remaining tumor cells;
- To suppress the recipient’s immune system so that it can take up foreign cells.
Childhood cancer treatment
The graft that is introduced into the patient’s body by transfusion contains stem cells that can create a new blood system in the patient’s body, as well as lymphocytes with effective immune capacity to eliminate leukemia cells remaining in the patient’s body in a non-cytotoxic but immunological way. This is the effect of graft versus leukemia, which is of great importance for the success of this therapeutic method.
The degree of compatibility in the tissue classification system that characterizes each of us is one of the most important factors for the success of the transplant. A mismatch can lead to rejection of the graft by the patient or to a situation in which the lymphocytes mentioned above in a positive context attack various organs in the patient’s body: graft versus host disease.
Donor stem cell transplantation in diseases with a deficiency in bone marrow products: This refers to acquired aplastic anemia, and hereditary diseases characterized by a deficiency or defect in cells that are normally produced in a normal bone marrow, such as immune system cells in congenital immunodeficiency disease, deficiency in blood system components such as thalassemia, sickle cell anemia, Fanconi anemia, white blood cell dysfunction, or storage diseases. During the transplant, the patient receives an infusion of stem cells from a healthy person. After preparation through chemotherapy and/or radiation, and after being absorbed into his diseased bone marrow, they will produce normal adult cells that will replace the defective adult cells. Transplants in hereditary diseases are characteristic mainly in children and not in adults.
Donor matching
When an allogeneic transplant is needed and there is no suitable donor from the family, an alternative donor must be found. This donor can be a family member such as a parent or sibling who is only partially compatible from the tissue classification system to the patient. Another option is to locate a donor from a pool of 7 million potential donors, most of whom are in the United States (there are also several pools in Israel), whose tissue classification system has been tested and who have expressed their willingness to be donors of stem cells if they are found to be reasonably compatible (the match is not “all or nothing” because several components of the tissue classification system are tested and there may be intermediate states of partial compatibility). Another alternative source of stem cells is umbilical cord blood. This blood, which is usually thrown away at the end of the birth process, with the placenta, contains stem cells with a high proliferative capacity (despite their relatively small number in the unit, they are able to fulfill a role as stem cells in a significantly greater number, compared to those in the bone marrow or blood of an adult). Currently, tens of thousands of units are available in global umbilical cord blood banks, and 2,500 transplants of this type have been performed to date. Because it is immunologically “naive”, an incompletely matched transplant can be performed without a significant increase in the rate of complications.
Despite the above, thanks to alternative donors, transplants from this source are still accompanied by high morbidity and mortality, and they require the accumulation of additional knowledge and great skill of the transplant center. A brother or sister who is compatible with the tissue classification system is still preferable as a potential donor.
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