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Research in stem cell transplants

Stem cell transplant replaces a person’s blood-forming (hematopoietic) stem cells. It is used when stem cells or the bone marrow has been damaged by chemotherapy drugs, radiation therapy or disease (such as cancer). The new stem cells make healthy blood cells.

Stem cell transplants have changed in the past 20 years. Researchers are studying ways to make stem cell transplants safer and more effective.

Blood and bone marrow stem cell transplants

Most stem cell transplants use stem cells taken from the blood instead of the bone marrow. The reason is that more stem cells can be taken from blood circulating in the body (called peripheral blood) than from bone marrow. Also, it’s easier for donors to give peripheral blood stem cells than bone marrow. Another reason that peripheral blood stem cell transplants are more common is that the recipient’s blood cell count usually recovers faster than with a bone marrow transplant.

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Reduced-intensity allogeneic transplants

An allogeneic stem cell transplant takes blood or bone marrow from a donor (usually a first-degree relative) and gives it to a recipient. Researchers are studying a new, experimental procedure called a reduced-intensity allogeneic transplant. It is similar to an allogeneic transplant as it uses stem cells from a matched donor. This transplant uses lower doses of chemotherapy or radiation therapy that don’t completely destroy the recipient’s bone marrow so blood cell counts don’t drop as low as they do in standard stem cell transplants. For this reason, there is a lower risk of complications.

A reduced-intensity allogeneic transplant is also called:

  • mini-allotransplant
  • mini-transplant
  • non-myeloablative transplant
  • mixed chimerism transplant

Reduced-intensity allogeneic transplants tend to work better when cancer is present in small amounts or is growing slowly (low-grade). Researchers are looking at ways to improve outcomes with this treatment because reduced-intensity allogeneic transplants are linked with a higher risk of recurrence than standard stem cell transplants. They are also studying reduced-intensity allogeneic transplants for people who may not be able to tolerate a standard stem cell transplant, such as those with certain health conditions and older people.

Researchers are also looking at using reduced-intensity allogeneic transplants after an autologous transplant. An autologous stem cell transplant uses a person’s own blood or bone marrow. It is collected and then stored and later given back to the same person. Giving an autologous transplant before the reduced-intensity allogeneic transplant can help lower the amount of cancer in the body. A lower dose of chemotherapy given before the reduced-intensity allogeneic transplant may then still work well and allow a person to have the benefit of the graft-versus-leukemia or graft-versus-tumour effect of the allogeneic transplant.

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Cord blood transplants

Cord blood transplants are linked with a lower risk of graft-versus-host disease (GVHD). Cord blood transplants are most often used when the person doesn’t have a matched sibling and an unrelated donor can’t be found.

Stem cells can be removed from the blood of the placenta and the umbilical cord of a newborn. This cord blood can be banked and stored for the family’s own use later, or it can be donated to a blood bank. In Canada, there are a few cord blood banks or programs that collect and store cord blood.

Research using cord blood transplants includes studying how stem cells from cord blood can be appropriately used and who would be most suited for this procedure. The amount of blood taken from the umbilical cord is small (50–100 mL). This means there are a limited number of stem cells available for transplant (less than 10% of the number given in a typical stem cell transplant). For this reason, cord blood transplants are mostly studied in children and small adults. Researchers are also looking for ways to use cord blood in larger adults, such as by boosting the number of stem cells in cord blood before they are transplanted.

Researchers are also using cord blood from 2 newborns (dual cord blood transplant) and using cord blood in reduced-intensity allogeneic transplants (mini-transplants).

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Tandem transplants

A tandem transplant is also called a double autologous transplant. A tandem transplant means that 2 autologous transplants are given in a row. The recipient is given 2 courses of high-dose chemotherapy. Each dose is followed by a stem cell transplant.

Stem cells are collected before the first high-dose chemotherapy treatment. Half of the stem cells are used for each transplant. The 2 courses of chemotherapy are usually given within 6 months. The second course of chemotherapy will not be given until the person recovers from the first transplant.

Tandem transplants are used to treat some types of cancer but researchers are still trying to decide when it is best to give the transplant and who will benefit most from it. They are also studying tandem transplants to see if they can help lower the risk that the cancer will come back, or recur.

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New ways of preparing for and managing transplants

Research is trying to find the best ways to prepare a person for conditioning treatment and transplant. Studies are researching:

  • different growth or colony-stimulating factors to activate stem cell production and speed up bone marrow recovery
  • improved conditioning procedures such as different chemotherapy drugs and targeted therapy drugs, or using radioimmunotherapy (a treatment that uses a monoclonal antibody attached to a radioactive substance to deliver radiation to cancer cells)
  • better ways to prevent and treat potential side effects of stem cell transplants such as infection, sore mouth (mucositis) and GVHD
  • better ways to “clean” (purge) stem cells to remove any remaining cancer cells before they are given back to the person in an autologous stem cell transplant
  • how to improve treatments that are given after a stem cell transplant (called maintenance therapy) to help prevent relapse

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Using mismatched donors

A donor’s stem cells need to match the recipient’s as closely as possible to improve the chance of a successful stem cell transplant and to lower the risk of complications. Human leukocyte antigen (HLA) typing makes sure that the donor and recipient are closely matched. At least 6–10 specific antigens need to match. A person has the best chance of finding a match from one of their relatives, with the greatest likelihood for a match being a blood-related sibling.

Researchers are studying transplants between partially matched relatives because the chance of finding a complete match is quite low.

Find out more about HLA typing.

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Stem cell transplants for different types of cancer

Researchers are studying the effectiveness of stem cell transplants for cancers that are not normally treated with stem cell transplants. These cancers include:

  • breast cancer
  • kidney cancer
  • ovarian cancer
  • lung cancer
  • colon cancer
  • metastatic cancer

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Encouraging non-Caucasians to donate stem cells

A person who gets a stem cell transplant has the best chance of finding a donor match if the donor is from the same ethnic background. Currently, most stem cells are donated by Caucasians. Some organizations are encouraging non-Caucasians to participate in donor programs so that people with different ethnic backgrounds have a better chance of finding a good match.

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graft-versus-tumour

The response of immune cells in transplanted blood or bone marrow against the cancer cells present in the recipient.

graft-versus-host disease (GVHD)

A condition that might happen after a stem cell transplant. Healthy stem cells from a donor (called the graft) attack a recipient’s (receiver’s) cells (called the host). The graft cells see the host cells as foreign and start to destroy them. Symptoms include jaundice, rash or blisters on the skin, dry mouth or dry eyes.

monoclonal antibody

A substance that can find and bind to a particular target molecule (antigen) on a cancer cell.

Monoclonal antibodies can interfere with a cell’s function or can be used to carry drugs, toxins or radioactive material directly to a tumour.

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