Cord Blood: Reduced Intensity Transplants
A typical stem cell transplant, whether using cord blood or bone marrow grafts, involves a preparative or conditioning regimen that is often intense and can be fatal in some cases. This pre-transplant procedure involves intense chemotherapy and radiation treatment, which is aimed at destroying diseased cells (such as cancer cells) as well as the patient’s immune system so as to prevent a patient who is undergoing a stem cell transplant from rejecting the donor stem cells in the system.
This typical stem cell preparative regimen is also known as myeloablation. Through stem cell research, doctors have developed the reduced intensity transplant to minimize the effects and potential risks that are sometimes associated with umbilical cord blood and bone marrow transplants. These types of stem cell transplants are sometimes referred to as non-myeloablative transplants or mini-transplants.
The Stem Cell Transplant Procedure
The preparative regimen for a stem cell transplant using the reduced intensity procedure is not aimed at destroying many diseased cells and therefore uses low doses of chemotherapy and sometimes radiation therapy. This merely weakens, instead of destroying, the patient’s immune system so that the body does not reject the foreign donor stem cells and result in graft-versus-host-disease (GVHD).
The stem cells used in a reduced intensity transplant must come from a donor source such as a family member, unrelated donor, or a cord blood unit. This procedure is thus an allogeneic transplant. The donor cells (the graft) then develop a new immune system to attack diseased cells.
Because the patient’s immune system is not destroyed, as it would be during a standard stem cell transplant, both the patient’s immune system as well as the donor system co-exist in mixed chimerism for the first 6 to 12 weeks following the transplant. After this period, the donor immune system takes over in the form of full chimerism and begins to attack the diseased cells in a process known as the graft-versus-leukemia effect or the graft-versus-tumor effect.
Benefits of Reduced Intensity Transplants
This type of stem cell transplant is better suited to treat certain patients suffering from specific illnesses. Patients who typically benefit from this procedure are those whose systems cannot tolerate the standard transplant procedures and include the following:
- older patients
- patients with weak organs including those with heart disease or lung dysfunction, or whose organs have been damaged due to previous treatments or infections
- patients who had one or more previous transplants
- patients with immune deficiencies or bone marrow failure as a result of congenital neutropenia, thrombocytopenia or aplastic anemia
- patients with pre-leukemia syndromes such as myelodysplastic syndrome and monosomy 7
- patients in the first remission stage of acute myeloid leukemia (AML) or in the chronic stage of myeloid leukemia (CML)
- patients with metabolic disorders such as Hurler’s disease and metachromatic or adrenal leukodystrophy
- patients with acute leukemia
- other patients who cannot tolerate a standard procedure due to disease stage or overall health
Currently, a reduced intensity stem cell transplant can help treat diseases including the following:
- chronic and acute myelogenous leukemia
- Non-Hodgkin's lymphoma
- multiple myeloma
- renal cell cancer
Speak to your doctor or health care provider about available transplant options for your particular case.
Disadvantages of Reduced Intensity Transplants
A reduced-intensity transplant may not be effective in treating fast growing diseases or progressive stages of certain diseases, such as leukemia in its blast stage. Some of the risks associated with this type of stem cell transplant include the following:
- infection remains a serious transplant risk; however, this risk is lower for reduced intensity transplants
- GVHD. The risk of graft-versus-host-disease following a mini transplant is not well understood. Some studies have shown it to be higher, while others have shown opposing results. Nonetheless, the transplant patient will be given anti GVHD drugs following the procedure, and will be closely monitored to prevent this complication.
- chemotherapy-associated risks, which are lower in these cases
- disease relapse is at a higher risk following reduced intensity transplants
In some cases, the donor immune system cells fail to take over the patient’s cells and do not achieve full chimerism. As a result, a doctor may recommend a decreased dose of anti-GVHD drugs to give the immune cells a better chance to grow. Doctors may also administer more of the donor’s T cells in a process known as donor lymphocyte infusion (DLI). The extra T cells may help destroy the diseased cells. In some cases, even a mixed chimerism may be sufficient in destroying a patient’s diseased cells.
Further stem cell research is being conducted in order to better understand all of the risks and benefits of a reduced intensity transplant.