The bone marrow produces stem cells. Some stem cells circulate in the blood stream. Also, some stem cells reside in fat cells giving rise to adipose (fat cell) derived stem cell therapy.
Any procedure that is used to extract a component from the blood is called an apheresis. An apheresis is used to obtain stem cells from blood. The procedure is called an apheresis whether the harvesting of stem cells is done from the blood of the circulatory system or the blood from the bone marrow.
When healthy stems cells from a donor are used to replace damaged or destroyed stem cells, the procedure is called an allogeneic transplant.
A transplant replacing stem cells with one's own stem cells is an autologous transplant. This is done when chemotherapy or radiation damages the stem cells.
In apheresis, whole blood is separated into its components, the stem cells are extracted, and the other blood components are returned to the donor during the apheresis process.
The links below provide more detailed information about stem cell harvesting:
Children's Hospital of Philadelphia
Download