In an allogeneic transplant, the stem cells that replace the recipient’s diseased or cancerous cells come from a donor instead of using the recipient’s own cells.. The important thing is that donor genes should atleast partly match with the patient genes. There is a greater chance of genes matching if the donor is your sibling or parents (half matched).
Incase there is no matching donor available in the family, matching unrelated donors can be found through American, German, Indian and Australian registries.
In an allogeneic transplant, a matching donor’s stem cells are harvested using G-CSF and PBSCT. Normally a day care procedure, the donor’s blood is passed through an apheresis machine, the stem cells are harvested, processed and frozen for transplant at a later date. This process is called Apheresis.
Allogeneic transplants are used to cure leukemia, lymphomas, myelomas, sickle cell anemia and several other diseases.
To cancer cells are destroyed using high dose chemotherapy and radiation and post induction therapy, once the cancer is in remission, the donor’ s stem cells are transferred into the patients stem cells in the hope that the new cells will destroy the cancerous cells.
Chemotherapy and radiation may be done in two ways:
Myeloablative (ablative) Treatment: Patients are given chemotherapy and radiation to kill cancer cells. A very high dose of chemotherapy and radiation also kills healthy bone marrow. The donors stem cells allow new cells to replace the cancerous cells.
Mini Transplant or Reduced Intensity Treatment: Before actual transplant, the patient receives a lower doses of chemotherapy and radiation. This is usually carried out for older patient and patients who have health problems and may not be able to tolerate the high dose of radiation.
After chemotherapy and radiation, once there is no evidence of cancer cells, stem cells are delivered in the patients bloodstream. The new stem cells then start replicating and kill the diseased cells.
Post the induction or conditioning therapy, the patients blood counts may drop dramatically and that is normal. Discharge happens when the patient recovers his blood counts and develops some immunity.
As the stem cells belong to another person, some people develop a host vs graft disease, which means that the recipient’s body rejects donor cells.
To rejection at bay, the patient is kept on immune suppressants.
It may take from 6 months to an year to get the required immunity.
Doctor visits post a bone marrow transplant are a must to keep a check on blood counts and recovery.
Success of allogeneic bone marrow transplant often depends upon the match between the donor and recipient.