Allogeneic stem cell transplants involve collecting stem cells from a donor and transferring them into the bloodstream of someone whose stem cells have been damaged or destroyed.

There are many diseases, both cancerous and noncancerous, that can be treated with allogeneic stem cell transplants. Some examples include blood cancers, blood conditions, and immune disorders.

Allogeneic stem cell transplants are sometimes called bone marrow transplants or simply stem cell transplants, depending on the source of the cells.

Most allogeneic stem cell transplants use cells taken from the bloodstream of a healthy donor, but the cells can also be taken directly from a donor’s bone marrow or from donated umbilical cord blood.

If your own stem cells are collected and then returned to your body, this is a different procedure called an autologous stem cell transplant.

Keep reading to learn more about what’s involved in an allogeneic stem cell transplant, how it can help, and who’s a good candidate for the procedure.

Stem cell transplants replace damaged blood stem cells with healthy ones. Blood (hematopoietic) stem cells are produced in your bone marrow, which is the soft tissue inside of your bones. These are stem cells that can develop into:

  • red blood cells, which carry oxygen in your blood
  • white blood cells, which fight infections
  • platelets, which help your blood clot

The stem cells in your bone marrow produce billions of new blood cells every single day. This process is critical to the proper functioning of your blood and your immune system. If your bone marrow isn’t producing enough blood cells, you may benefit from a transplant.

In order to prepare your body for a transplant, doctors will need to destroy your existing diseased stem cells and weaken your immune system so that you don’t reject the transplant. This requires a process called “conditioning,” which involves high doses of chemotherapy and sometimes radiation.

When a stem cell transplant is successful, the donated stem cells start making healthy blood cells. This process is called engraftment. A successful transplant will also help reset your immune system, triggering it to fight off any remaining cancer cells.

The graft vs. tumor effect

In an allogeneic stem cell transplant, the transplanted cells are called a graft. The graft contains immune cells from your donor’s immune system.

Sometimes, these immune cells recognize malignant cells in your body and attack them. The graft can help your body fight cancerous tumors and cancer cells in your blood.

Not everyone is a good candidate for an allogeneic stem cell transplant. The conditioning process, which typically involves high doses of chemotherapy, can be very difficult on the body.

People who are older or in poorer health may not be able to tolerate the difficult conditioning process. This is also true of people whose organs aren’t functioning properly.

Doctors will make sure that your most essential systems are functioning properly. This includes the following systems:

You must also be psychologically prepared to undergo not just the procedure, but the extensive follow-up care as well.

You can expect to remain in the hospital for several weeks after an allogeneic stem cell transplant. You may also need to be in isolation for an extended period of time. Your immune system could take a year or longer to reach maturity.

Your doctor will be able to explain your specific risks in greater detail.

Before receiving an allogeneic stem cell transplant, you’ll need to go through a conditioning process. Sometimes called myeloablation, this regimen typically consists of high dose chemotherapy, whole body radiation therapy, or both.

The conditioning process is intended to destroy cancerous and diseased cells. It purposefully damages your own bone marrow and blood stem cells. The process makes it easier for the donor cells to enter your bone marrow and start functioning as if they were your own.

Conditioning comes with all of the risks that normally accompany chemotherapy or radiation therapy, including the destruction of your immune system. This is a calculated risk, though, because it reduces the chances that your body will reject the transplant.

The conditioning process usually takes about a week, and you can expect to stay in the hospital throughout that time.

The intense conditioning process necessary for a stem cell transplant can be too dangerous for some people. In such cases, reduced-intensity conditioning may be an option.

Reduced-intensity conditioning, sometimes called a reduced-toxicity regimen, still uses chemotherapy or radiation therapy, but the doses are lower. This means your own immune system won’t be destroyed.

This may sound good, but it increases the likelihood that your body will reject the transplant. For this reason, the reduced-intensity conditioning process sometimes includes immunosuppressant medications.

The use of allogeneic stem cell transplants has been on the rise with older adults over the last decade. This has led to wider adoption of reduced-intensity conditioning regimens.

However, not everyone is a good candidate for this type of treatment. Candidacy is somewhat dependent on how well you’re matched to your donor and what condition the transplant is treating.

Reduced-intensity regimens may be more effective than traditional conditioning in treating some diseases, but more research is still needed.

A potential stem cell donor has to have a similar genetic profile to you so that your body doesn’t reject the transplant.

Close family members are most likely to match. Siblings, specifically, have a 1 in 4 chance of being a match. Identical twins, however, may not make good donor donors. This is because their cells are too similar and they may share genetic defects.

If no close family members are a match or able to donate, there are donor programs available to help match potential donors with those in need of stem cells.

Additionally, it’s now possible to extract stem cells from umbilical cord blood. Umbilical cords can be donated for this purpose at the time of birth. One umbilical cord is unlikely to have enough stem cells for an adult transplant recipient, so cord blood from several donors may be used together.

During the conditioning process you’ll need to receive a lot of medications. A tube, called a central line, is often inserted into your chest to make this quicker and easier. The tube will be left in after conditioning to be used for the transplant.

You might need to spend a couple days recovering from conditioning before the transplant.

When it’s time for the transplant, the stem cells will be passed into your body using the existing tube. It won’t feel much different than having medication go in. It doesn’t hurt, and you’ll be awake throughout the procedure, which usually takes a couple of hours.

After conditioning, the risks from stem cell transplant primarily come from your reduced immune response. You’ll be at higher risk of infection from things like viruses and bacteria.

You might need to take medication to help you fight off infections. You can also expect to remain in a clean environment in the hospital until your immune system starts to replenish.

Graft-versus-host disease (GVHD) is a potential complication that you might face after an allogeneic stem cell transplant. This is when the graft, or the donated cells, attacks your body because it identifies it as foreign.

GVHD is common, occurring up to 50 percent of the time when the donor is a sibling. It can be very serious, or even fatal.

Some of the factors that increase the likelihood of GVHD include:

  • greater degree of donor mismatch
  • older age of donor or recipient
  • less intensive conditioning regimens

After the transplant, you’ll have a severely reduced number of red and white blood cells and platelets.

Until your cell counts are back within a healthy range you may need to take medication to prevent and treat infections. This could take as long as a year or two.

Fevers can happen. It’s important that you contact your transplant care team any time you get a fever.

You might also need one or more blood transfusions during this time. You should expect to take additional drugs to prevent GVHD as well. This may include a combination of cyclosporine and methotrexate for several months after the transplant.

You could feel a range of emotions, too, that include everything from joy to depression.

Doctors will monitor you with blood tests and follow up visits. These visits will be frequent at the beginning, perhaps daily, but will become less frequent at your doctor’s discretion.

1. What conditions are treated with allogeneic stem cell transplant?

Some diseases treated with allogeneic stem cell transplants include:

Research is still ongoing for the treatment of the following diseases using allogeneic stem cell transplants:

2. What is the survival rate of allogeneic stem cell transplants?

Many people who undergo allogeneic stem cell transplants have other conditions, such as cancer, which makes the question complex. Infections and graft vs. host disease are the main complications of the procedure.

But the risks of a transplant varies depending on the type of disease being treated and how well the donor and recipient are matched.

3. Is stem cell transplant a major surgery?

A stem cell transplant is a very intensive process, but there is no surgical intervention. The transplanted cells are administered through an IV line in your chest.

Between chemotherapy and recovery, the entire process can take a couple of weeks. But the infusion itself only takes a few hours.

It should be painless, so you’ll be awake and won’t need anesthesia.

4. What happens if a stem cell transplant fails?

You can sometimes try a second transplant, but this is highly dependent on your individual situation and your overall health. Many times, if the transplant fails your doctor will recommend exploring other treatment options.

An allogeneic stem cell transplant is one where the stem cells come from a donor other than yourself. The donor’s stem cells will be infused into your body intravenously.

Before the transplant, you’ll need to undergo conditioning with intensive chemotherapy, radiation therapy, or both. In some circumstances, a reduced-intensity conditioning process may be considered.

Close family members are often the best match for a donor, but you could also match with a stranger through a donor registry.

Potential complications include graft vs. host disease and the overall risks associated with a weakened immune system.