Canine bone marrow transplantation is the replacement of damaged bone marrow with normal stem cells. It allows veterinary oncologists to treat blood cell cancers such as lymphoma and leukemia with the most aggressive treatments possible. They can administer high dose chemotherapy or more commonly a total body irradiation high enough to kill cancer cells that may be resistant to chemotherapy or residing in locations in the body where chemotherapy cannot reach. Standard chemotherapy alone strives to achieve remission (patient shows no evidence of cancer and is unaffected by it) and extend length and quality of life. For some dogs, bone marrow transplantation after chemotherapy may be an option. Bone marrow transplantation as an adjunct to chemotherapy strives to achieve a cure.
There are two main types of transplantation:
Allogenic transplantation takes compatible stem cells from one patient and gives them to another.
- Autologous transplantation removes the dog's own stem cells, which are then put back into the dog. These stem cells were historically taken from the bone marrow, requiring a painful and invasive procedure. Today, they are obtained directly from the blood. Therefore, this procedure is now more accurately termed Hematopoietic Stem Cell Transplantation (HCT). Allogenic transplantation is possible, but due to a lack of a national animal registry for stem cell donors, most transplantations in dogs are autologous.
How Is Autologous Transplantation Performed?
The patient will first undergo a battery of tests to determine physical capability for undergoing the transplant procedure. This testing will also provide the veterinary oncologist with information that will help tell when the patient is in complete remission from the disease and able to undergo the transplantation process, which is outlined below:
Consolidation Chemotherapy: Once in remission, your pet will receive a single high dose of a chemotherapeutic agent. This treatment, termed consolidation, clears any remaining cancerous cells from the blood stream, where the stem cells will be collected.
Stem Cell Mobilization: After your pet's white blood cells and platelets have recovered, additional testing will ensure that no other diseases or signs of cancer are present. Your pet will then receive twice daily injections at home of a medication that promotes white blood cell proliferation, as well as oral antibiotics to help remove bacteria from the intestinal tract. In six days, your pet will be ready to undergo stem cell collection, called apheresis.
Apheresis: Your pet will be sedated or anesthetized in order to remain completely still during the collection procedure, which can take four to six hours. Intravenous catheters are placed and stem cells for transplantation are filtered out of your pet's blood. The rest of your dog's blood is returned.
Transplantation: Patients undergo total body irradiation (TBI) 24 hours after apheresis in order to eradicate any remaining cancer cells. However, this destroys all normal white blood cells, as well. Therefore, immediately after radiation, the healthy stem cells collected from your pet the previous day are re-infused (transplanted) back into your pet intravenously.
Recovery: During the next 10 to 14 days following transplantation, dogs will be hospitalized in a dedicated clean environment where they can be protected from harmful bacteria and viruses. During this time their irradiated white cells and platelets will die and eventually be replaced by the transplanted stem cells. Patients receive 24-hour care and observation during their stay. This is the most critical aspect of transplantation because complications (hemorrhage, infection, or complications due to radiation), although rare, may occur.
Follow-up: If successful, further cancer therapy will not be required. However, to make certain a cure has occurred, your veterinarian will schedule regular follow-up appointments for physical examination and testing.
Who Is A Candidate For BMT?
Any dog with lymphoma is a potential candidate for transplantation. However, depending on the specific type of lymphoma, ability to obtain a remission, age, weight, and the presence of other concurrent diseases, some patients will be better candidates than others. Dogs with other types of blood cell cancers such as leukemia may also qualify. However, for these patients a matching stem cell donor (near relative of patient with DNA that is nearly identical) will be necessary as a successful outcome will almost always require that an allogenic transplantation is performed. Whether or not your pet is a candidate for transplantation should be carefully discussed with your veterinarian early in the course of therapy.
Can a BMT be performed in cats?
Although it is possible to perform hematopoietic stem cell transplantation in cats, due to their small size and an inability to precisely detect low levels of cancer cells in their blood, transplantations are not often recommended.