Hematopoietic stem cell transplant

A hematopoietic stem cell transplant is what many people know as a bone marrow transplant. Bone marrow is the center of your bones, and it's packed with hematopoietic stem cells, the cells that give rise to all the different kinds of blood cells. When the marrow isn't working well or has run out of these cells, the transplant gives the person healthy stem cells.

Before the transplant comes a very intense treatment: high doses of chemotherapy, which are very powerful drugs, and sometimes radiation. That treatment destroys the stem cells that were in the marrow. Then the new ones arrive. They go in through a vein, travel through the blood to the marrow, settle into the space that was cleared, and start making new blood cells. It's like replanting a garden: you clear the soil, put in new plants, they take root in the same spot, and the garden starts producing again.

These cells can come from the same person, in which case the transplant is called autologous, or from someone else, a donor, in which case it's called allogeneic. In leukemia, a cancer that affects the blood cells, a transplant from a donor can do something more. The donor's white blood cells, which are part of the body's defenses, can attack any cancer that's left behind. This is called the graft-versus-tumor effect: the graft is the donor's cells, and the tumor is the cancer that was left.