Friday, October 25, 2013

Types of stem cell transplants for treating cancer

In a typical stem cell transplant very high doses of chemo are used, often along with radiation therapy, to try to destroy all of the cancer. This treatment also kills the stem cells in the bone marrow. Soon after treatment, stem cells are given to replace those that were destroyed. These stem cells are given into a vein, much like a blood transfusion. Over time they settle in the bone marrow and begin to grow and make healthy blood cells. This process is called engraftment.

There are 3 basic types of transplants. They are named based on where the stem cells come from.

Autologous (aw-tahl-uh-gus)—the cells come from you

Allogeneic (al-o-jen-NEE-ick or al-o-jen-NAY-ick)—the cells come from a matched related or unrelated donor

Syngeneic (sin-jen-NEE-ick or sin-jen-NAY-ick)—the cells come from your identical twin or triplet
Autologous stem cell transplant

In this type of transplant, your stem cells are taken before you get cancer treatment that destroys them. Your stem cells are removed, or harvested, from either your bone marrow or your blood and then frozen. After you get high doses of chemo and/or radiation the stem cells are thawed and given back to you.

One advantage of autologous stem cell transplant is that you are getting your own cells back. This means there is no risk that your immune system will reject the transplant or that the transplanted cells will attack or reject your body.

A possible disadvantage is that cancer cells may be harvested along with the stem cells and then put back into your body. To prevent this, doctors may give you anti-cancer drugs or treat your stem cells with other methods to reduce the number of cancer cells that may be present. (See the section, “Getting rid of cancer cells in autologous transplants.”) Another disadvantage is that you have the same immune system when your stem cells engraft. The cancer cells were able to grow in the presence of your immune cells before, and may be able to do so again.

This kind of transplant is mainly used to treat leukemias, lymphomas, and multiple myeloma. It’s sometimes used for other cancers, like testicular cancer and neuroblastoma, and certain cancers in children. Doctors are looking at how autologous transplants might be used to treat other diseases, too, like systemic sclerosis, multiple sclerosis, Crohn disease, and systemic lupus erythematosis.

Tandem transplants

A tandem transplant is also called a double autologous transplant. In a tandem transplant, the patient gets 2 courses of high-dose chemo, each followed by a transplant of their own stem cells. All of the stem cells needed are collected before the first high-dose chemo treatment, and half of them are used for each transplant. Most often both courses of chemo are given within 6 months, with the second one given after the patient recovers from the first one.

Tandem transplants are sometimes used to treat certain types of cancer, but doctors do not agree on when and how to use this type of transplant. For many people, the risk of serious outcomes is quite high. Tandem transplants are still being studied to find out when they might be best used.

Allogeneic stem cell transplant

In this type of transplant, the stem cells do not come from the patient, but from a donor whose tissue type closely matches the patient. (This is discussed later under “HLA matching” in the section called “Allogeneic transplant: The importance of a matched donor.”) The donor is often a family member, usually a brother or sister. If you do not have a good match in your family, a donor might be found from the general public through a national registry. This is sometimes called a MUD (matched unrelated donor) transplant.

Blood taken from the placenta and umbilical cord of newborns is a newer source of stem cells for allogeneic transplant. Called cord blood, this small volume of blood has a high number of stem cells that tend to multiply quickly. But the number of stem cells in a unit of cord blood is often too low for large adults, so this source of stem cells is limited to small adults and children. Doctors are now looking at different ways to use cord blood for transplant in larger adults.

An advantage of allogeneic stem cell transplant is that the donor stem cells make their own immune cells, which could help destroy any cancer cells that remain after high-dose treatment. This is called the graft-versus-cancer effect. Other possible advantages are that the donor can often be asked to donate more stem cells or even white blood cells if needed, and stem cells from healthy donors are free of cancer cells.

Still, there are many possible drawbacks to allogeneic stem cell transplants. The transplant, also known as the graft, might not take — that is, the donor cells may be more likely to die or be destroyed by the patient’s body before settling in the bone marrow. Another risk is that the immune cells from the donor can attack the patient’s body — a condition known as graft-versus-host disease (described in the section called “Problems that may come up shortly after transplant”). There is also a very small risk of certain infections from the donor cells, even though donors are tested before they donate. A higher risk comes from infections you have had, and which your immune system has under control. These infections often surface after allogeneic transplant because your immune system is held in check (suppressed) by medicines called immunosuppressive drugs. These infections can cause serious problems and even death.

Allogeneic transplant is most often used to treat certain types of leukemia, lymphomas, and other bone marrow disorders such as myelodysplasia.

Non-myeloablative or mini-transplants (allogeneic)

Some people have health conditions that would make it more risky to wipe out all of their bone marrow before a transplant. For those people, doctors can use a type of allogeneic transplant that’s sometimes called a mini-transplant. Compared with a standard allogeneic transplant, this one uses less chemo and/or radiation to get the patient ready for the transplant. Your doctor may refer to it as a non-myeloablative transplant or mention reduced-intensity conditioning (RIC). The idea here is to kill some of the cancer cells, some of the bone marrow, and suppress the immune system just enough to allow donor stem cells to settle in the bone marrow.

Unlike the standard allogeneic transplant, cells from both the donor and the patient exist together in the patient’s body for some time after a mini-transplant. But slowly, over the course of months, the donor cells take over the bone marrow and replace the patient’s own bone marrow cells. These new cells can then develop an immune response to the cancer and help kill off the patient’s cancer cells — the graft-versus-cancer effect.

One advantage of a mini-transplant is the lower doses of chemo and/or radiation. And because the stem cells aren’t all killed, blood cell counts don’t drop as low while waiting for the new stem cells to start making normal blood cells. This makes it especially useful in older patients and those with other health problems who aren’t strong enough for a standard allogeneic stem cell transplant. It may rarely be used in patients who have already had a transplant.

Mini-transplants treat some diseases better than others. They may not work well for patients with a lot of cancer in their body or those with fast-growing cancers. Also, the lowered immune response can still lead to graft-versus-host disease.

This procedure has only been used since the late 1990s and long-term patient outcomes are not yet clear. There are lower risks of complications, but the cancer may be more likely to relapse (come back). Ways to improve outcomes are still being studied.

Another future possibility is autologous transplant followed by an allogeneic mini-transplant. This is being tested in certain types of cancer, such as multiple myeloma. The autologous transplant can help decrease the amount of cancer present so that the lower doses of chemo given before the mini-transplant can work better. And the recipient still gets the benefit of the graft-versus-cancer effect of the allogeneic transplant.

Syngeneic stem cell transplant

This is a special kind of allogeneic transplant that can only be done when the recipient has an identical twin or identical triplet donor — someone who will always have the same tissue type. An advantage of syngeneic stem cell transplant is that graft-versus-host disease will not be a problem. There are no cancer cells in the transplant, either, as there would be in an autologous transplant. A disadvantage is that this type of transplant won’t help destroy any remaining cancer cells because the new immune system is so much like the recipient’s immune system. Every effort must be made to destroy all the cancer cells before the transplant is done to help keep the cancer from relapsing (coming back).

Last Medical Review: 08/23/2012
Last Revised: 10/24/2012


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