Peripheral Stem Cell Transplants
There are two types of peripheral stem cell transplants (commonly referred to as bone marrow transplants) - autologous (where your own cells are used) and allogeneic (where a donor is required). In fact, for the majority of the autologous transplants, cells that are collected from a patient’s blood are used instead of bone marrow.
In an autologous transplant, very high doses of chemotherapy or radiation are used to kill the tumor cells in a patient’s body. The levels of therapy required to kill these tumor cells are often five to ten times higher than regular chemotherapy doses, which unfortunately also results in the death of the healthy cells that live in the bone marrow.
Cells in the bone marrow contain all of the important blood stem cells that have the ability to form all blood types. These include red blood cells that carry oxygen, white blood cells that treat infection and platelets that prevent bleeding. In addition, these stem cells are able to form themselves so that theoretically, a single cell could reproduce the entire bone marrow after it is damaged. This may also be referred to as a stem cell rescue or stem cell support, and in this situation the important treatment for the cancer is the high doses of chemotherapy. The stem cells are given back to the patient after the therapy is completed, allowing the “rescue” of the marrow. This form of therapy enables the patient to receive the required high doses of chemotherapy or radiation.
It is important to note that these stem cells are not the ones that you often hear about in the news. These are largely limited to producing only the blood type cells listed above. Although they reside in the bone marrow, they are rarely collected from the marrow itself. Instead, we use the knowledge that after chemotherapy and certain medicines, the stem cells move into the blood stream. We can then collect the cells from the blood stream, before treatment, to be used later after the high doses of chemotherapy are given.
The second major type of transplant, an allogeneic transplant, also typically involves very high doses of chemotherapy or radiation to kill the underlying cancer cells. In this situation, cells are collected from a donor and then given back to the patient. These cells can also be collected from the blood stream or bone marrow, and in some cases, from the umbilical cord blood. When these donor cells grow to form the new blood stem cells, they retain some of the characteristics of the original donor. This is a true transplant of the blood and immune system from donor to patient.