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Stem cell transplant, bone marrow transplant: what's the difference?

A life saving procedure, bone marrow transplants are a type of stem cell transplant used to treat a variety of conditions including multiple myeloma, leukemia, lymphoma, aplastic anemia, sickle cell anemia, thalassemia and disseminated metastatic disease. But what exactly is a bone marrow transplant and how does it work? In essence, a bone marrow transplant involves killing the cancerous cells, jumpstarting the immune system, and then transplanting new cancer-free immature cells. These immature cells then mature into blood cells including the cells that constitute the immune system. The first step in the transplant process involves harvesting the cells.

What is harvesting?

Harvesting signifies obtaining and preparing the cells for transplantation. The cells are harvested differently depending on their origin. They may originate from the bone marrow, hence the name bone marrow transplant, the peripheral blood stream, or umbilical cord blood. All of these cells are stem cells. A hematopoeitic stem cell transplant is, thus, the general term for a transplant involving non-cancerous immature pluripotent cells, whilst a bone marrow transplant refers to specifically stem cell transplants that originate in the bone marrow.

The cells may come from the patient or from another person deemed a match.

  • An autologous stem cell transplant is a transplant involving cells arising from the same patient.

  • An allogeneic transplant signifies a transplant from the same species but not the same person. A detailed examination is performed to verify that the allogeneic transplant is an appropriate match.

Bone marrow cells are obtained from the pelvic bone or sometimes, but less commonly, the sternum through a needle aspiration. Peripheral blood stem cells, which stem from the bloodstream, are harvested through apharesis, a process that involves encouraging the proliferation of stem cells in the bloodstream and then subsequently drawing blood. Obtained from the umbilical cord, umbilical cord blood stem cells are pooled, and depending on the size of the recipient, sometimes, multiple umbilical cords are needed to make up just one transplant. In all of these processes, the medium is filtered and processed, and the cells are cryopreserved.

What is conditioning?

After the cells are harvested, the next phase is called 'conditioning.' Killing the cancer cells, 'conditioning' often involves total body irradiation (TBI) and high dose chemotherapy.

Then what?

The new cancer-free cells are then transplanted. what happens after conditioning?

Known as day 0, the transplant day is the day at which the new cells are infused through a central line. At this point, the blood cell counts are low. They will begin to increase, however, once engraftment occurs.

What's engraftment?

Engraftment indicates that the new blood cells have started growing and proliferating. Infused through a central line, engraftment usually begins as early as two to three weeks after receiving a bone marrow or peripheral blood cells. For patients who receive cord blood transplants, engraftment may take as long as six weeks to begin. Often, engraftment may be measured by an ANC of at least 0.5 k/mm3 for three consecutive days and a platelet count of at least 20,000 cells/mm3.

Then what?

After engraftment, blood cells continue to proliferate and the immune system continues to get stronger. Nonethless, patients are at a high risk for developing complications at this time, and during this recovery period, patients are often monitored and treated in the hospital.

Okay, are there any oral side effects associated with stem cell transplants?

Yes. There are oral manifestations associated with bone marrow and stem cell transplants.

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