Dr. Stephen Nimer
Director, Sylvester Comprehensive Cancer Center, Univ. of Miami
This year alone, about 19,000 stem cell transplants will be performed for cancer and related diseases in the United States. Over the last 30 years, the field of stem cell transplantation for cancer has provided not only hope, but cures on a consistent basis for many types of patients.
People often ask about the difference between current types of stem cell treatments, known as non-myeloablative transplants, and the conventional version of transplants. In conventional allogeneic transplants a patient is treated with preparative chemotherapy and/or radiation to kill as many cancer cells as possible and to suppress the immune system of the patient to allow the donor cells to grow. A non-myeloablative transplant aims to suppress the immune system just enough to allow engraftment of the donor cells to attack the cancer.
The follow-up question is then, with a non-myeloablative transplant, why don’t these stem cells attack the host, given that the host still has an immune system? What we understand now is that there is a battle that goes on between the immune cells of the host and the donor. We can create a very gentle, yet effective suppression of the immune system as long as we infuse a sufficient number of new immune cells.
Patients often wonder as to what type of donor they may need for a successful stem cell transplant. With an organ transplant, patients are given lifelong immune suppressive medications, thus the donor need not be related to the patient. However, when treating cancer, we do not want to give immunosuppressive therapy, and therefore you hope to find a donor who is closely related, but not necessarily identical to the patient. Thus, a brother or sister who is HLA matched is actually better, because the immune system that matures in the patient will have novel abilities to recognize and control the patient’s cancer.
Another amazing development in the past few years has been the use of cord blood stem cells for transplants. These stem cells are nearly the same as those that are in your bone marrow, but they are found in the cord blood at the time an infant is born. These cells are more immature than the cells that you get from bone marrow, especially in terms of their immune function, so that matching the donor with the patient is much easier. We refer to things like a 10/10 match when we take cells from an adult and transplant them. For cord blood transplants, we only need about 2/3 as strict a match as we need for adults. What this has done, in particular for minorities, is opened up the ability of curative therapies to be applied throughout the world. But the negative side of using cord blood in a transplant is that it often takes 12 to 18 months for the immune system to come in quite robustly, leaving the patient at risk for infections for a longer period of time. A lot of the research now is to identify how to strengthen the immune system of cord blood transplant recipients once the process has started. The results are looking better, especially for pediatric patients.