Umbilical cord blood transplantation has become the principal type of transplant, now beyond more than bone marrow. First performed in Paris in 1988, it is no longer considered experimental in any setting.

These days, the use of umbilical cord blood is "routine." It comes as a single plastic bag of blood, which is fed painlessly through a tube in the patient's chest.

Called a Hickman catheter, the tube rests near the collar bone; the other end inserts directly into the right ventricle of the heart. A small amount of umbilical cord blood is infused quickly and quietly into the patient.

The blood that is transferred into the patient's body contains remarkable "seeds'' for making new healthy blood.

These "seeds," known as hematopoietic stem and progenitor cells, are found in the blood of every newborn baby's umbilical cord and placenta. Traditionally, these birth by-products have been discarded.

Once in the bloodstream, the stem cells migrate to the patient's bone marrow. This is where they must lodge, then "engraft" and grow to replenish the bone marrow and blood. They are replacing diseased marrow and blood destroyed by extremely high doses of chemotherapy and radiation. But in addition, cord blood contains immune cells that target and kill residual cancer. It's not just the chemotherapy and radiation, but the cord blood itself that cures the patient.

The migration and engraftment process takes about two to four weeks. After they have been accepted by the body—or "engrafted," in the language of transplant experts—their real work begins. Over the next 100 days, the stem cells will literally rebuild the blood, bit by bit— and continue to do so for a lifetime.

And this is the true marvel of umbilical cord blood: Stem cells can turn into lots of different kinds of blood cells.

For example, they can turn into erythrocytes (red cells) for carrying oxygen to body tissues and leukocytes (white blood cells) for fighting infection. While the stem cells are the same as those from bone marrow, it is the accompanying immune system that is vastly different. The umbilical cord blood immune system is immature, or "naive," where the adult immune system is mature.

Bone marrow stem cells can turn into different kinds of blood cells, too. But there are two main drawbacks to bone marrow, which is why doctors, patients and families are increasingly turning to umbilical cord blood instead of bone marrow.

The first is that cord blood is more easily and readily obtained. It takes an average of only seven days to donate a cord blood unit. Bone marrow donation, on the other hand, takes three to four months on average. And even when identified, 30 percent of the time the donor is not available at the time needed.

The second is that cord blood appears to be more readily accepted by the body, thus reducing the chance of graft-versus-host disease (GVHD), a condition where the donor's immune cells try to reject the patient. Al though the complication can occur with cord blood, it has been proven over and over again that the risk of GVHD is much lower and more readily treatable even when it does occur.