Types of stem cell transplants for treating cancer

In a typical stem cell transplant for cancer very high doses of chemo are used, often along with radiation therapy, to try to destroy all the cancer cells. 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 who gives the stem cells.

These stem cells come from you alone. 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. To find out more about that process, please see the section Whats it like to donate stem cells? 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. When you donate your own stem cells you dont have to worry about the graft attacking your body (graft-versus-host disease) or about getting a new infection from another person. But there can still be graft failure, and autologous transplants cant produce the graft-versus-cancer" effect.

This kind of transplant is mainly used to treat certain leukemias, lymphomas, and multiple myeloma. Its 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.

A possible disadvantage of an autologous transplant is that cancer cells may be picked up along with the stem cells and then put back into your body later. Another disadvantage is that your immune system is still the same as before when your stem cells engraft. The cancer cells were able to grow despite your immune cells before, and may be able to do so again.

To prevent this, doctors may give you anti-cancer drugs or treat your stem cells in other ways to reduce the number of cancer cells that may be present. Some centers treat the stem cells to try to remove any cancer cells before they are given back to the patient. This is sometimes called purging. It isnt clear that this really helps, as it has not yet been proven to reduce the risk of cancer coming back (recurrence).

A possible downside of purging is that some normal stem cells can be lost during this process, causing the patient to take longer to begin making normal blood cells, and have unsafe levels of white blood cells or platelets for a longer time. This could increase the risk of infections or bleeding problems.

One popular method now is to give the stem cells without treating them. Then, after transplant, the patient gets a medicine to get rid of cancer cells that may be in the body. This is called in vivo purging. Rituximab (Rituxan), a monoclonal antibody drug, may be used for this in certain lymphomas and leukemias, and other drugs are being tested. The need to remove cancer cells from transplants or transplant patients and the best way to do it is being researched.

Doing 2 autologous transplants in a row is known as a tandem transplant or a double autologous transplant. In this type of 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 most often used to treat multiple myeloma and advanced testicular cancer, but doctors do not always agree that these are really better than a single transplant for certain cancers. Because this involves 2 transplants, the risk of serious outcomes is higher than for a single transplant. Tandem transplants are still being studied to find out when they might be best used.

Sometimes an autologous transplant followed by an allogeneic transplant might also be called a tandem transplant (see Mini-transplants in the section Allogeneic stem cell transplants).

In the most common type of allogeneic transplant, the stem cells come from a donor whose tissue type closely matches the patients. (This is discussed later under HLA matching in the section called Donor matching for allogeneic transplant.) The best donor is a close family member, usually a brother or sister. If you do not have a good match in your family, a donor might be found in the general public through a national registry. This is sometimes called a MUD (matched unrelated donor) transplant. Transplants with a MUD are usually riskier than those with a relative who is a good match.

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, such as using cord blood from 2 donors.

Pros of allogeneic stem cell transplant: 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 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.

Cons to allogeneic stem cell transplants: The transplant, also known as the graft, might not take that is, the donor cells could die or be destroyed by the patients body before settling in the bone marrow. Another risk is that the immune cells from the donor may not just attack the cancer cells they could attack healthy cells in the patients body. This is called 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, multiple myeloma, myelodysplastic syndrome, and other bone marrow disorders such as aplastic anemia.

For some people, age or certain health conditions 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 thats 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 might 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 along with 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 patients 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 patients own bone marrow cells. These new cells can then develop an immune response to the cancer and help kill off the patients cancer cells the graft-versus-cancer effect.

One advantage of a mini-transplant is the lower doses of chemotherapy (chemo) and/or radiation. And because the stem cells arent all killed, blood cell counts dont 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 arent strong enough for a standard allogeneic stem cell transplant. Rarely, it may 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, although side effects from chemo and radiation may be less than those from a standard allogeneic transplant, the risk of graft-versus-host disease is not.

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

Studies have looked at using an allogeneic mini-transplant after an autologous transplant. This is another type of tandem transplant (see Tandem transplants under Autologous transplant) 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.

This is a special kind of allogeneic transplant that can only be used when the recipient has an identical sibling (twin or triplet) who can donate someone who will 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 because the new immune system is so much like the recipients immune system, there is no graft-versus-cancer effect, either. 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).

Some centers are doing half-match (haploidentical) transplants for people who dont have closely matching family members. This technique is most often used in children, usually with a parent as the donor, though a child can also donate to a parent. Half of the HLA factors will match perfectly, and the other half typically dont match at all, so the procedure requires a special way to get rid of a certain white blood cells that can cause graft-versus-host disease. Its still rarely done, but its being studied in a few centers in the United States. Researchers are continuing to learn new ways to make haploidentical transplants more successful.

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Types of stem cell transplants for treating cancer