Bone marrow transplantation - Online Science Notes

Bone marrow is the soft, fatty tissue inside our bones which consists of stem cells that produce different blood cells.
A procedure in which bone marrow that is diseased or damaged is replaced with healthy bone marrow is called bone marrow transplantation.
It is one of the methods of combating disorders of blood-forming tissues such as aplastic anemia, leukemia and lymphoma.
The purpose of bone marrow transplantation is to introduce normal blood cells into the bloodstream of the patient.
To ensure a high degree of compatibility between donor and recipient, so that the recipient will not reject the donated marrow, physicians try to match six tissue factors called human leukocyte antigens (HLA).
Before the transplant, chemotherapy, radiation, or both may be given. At this time, and for a period following the transplantation, the patient is vulnerable because the immune system is compromised.This may be done in 2 ways:
- Ablative (myeloablative) treatment:
  - High-dose chemotherapy, radiation, or both are given to kill any cancer cells.
  - This also kills all healthy bone marrow that remains, and allows new stem cells to grow in the bone marrow.
- Reduced intensity treatment:
  - This is also called a mini transplant.
  - Lower doses of chemotherapy and radiation are given before a transplant which allows older people, and those with other health problems to have a transplant.

Procedure:

The patient is treated before the transplantation with high doses of radiation and/or chemotherapy to remove all cells from the bone marrow.
About 500-700 ml of bone marrow from a compatible donor (preferably a twin or sibling) is aspirated (removed by suction) from the donor’s pelvic bones (usually from the iliac crest).
A large hypodermic needle is attached to the syringe for this process.
Only a small incision is necessary to aspirate the bone marrow, which is always to be done by an expert.
Donor stem cells can be collected in two ways:
- Bone marrow harvest:
  - This minor surgery is done under general anesthesia.
  - The bone marrow is removed from the back of both hip bones.
  - The amount of marrow removed depends on the weight of the person who is receiving it.
- Leukapheresis:
  - First, the donor is given several days of shots to help stem cells move from the bone marrow into the blood.
  - Blood is removed from the donor through an IV line.
  - The part of white blood cells that contains stem cells is then separated in a machine and removed to be later given to the recipient.
  - The red blood cells are returned to the donor.
The removed marrow is mixed with an anticoagulant (heparin) and then filtered.
The filtration separates the donor’s T-cells, which would otherwise encourage rejection of the marrow by the recipient.
The recipient receives the donor’s marrow through an intravenous infusion (just like blood transfusion).
Two units of donor’s blood, which were removed during two sessions about a week before the transplantation, are transfused back into the donor to replace the blood aspirated along with the marrow.
There are three kinds of bone marrow transplants:
- Autologous bone marrow transplant:
  - Stem cells are removed from our body before we receive high-dose chemotherapy or radiation treatment.
  - The stem cells are stored in a freezer. After high-dose chemotherapy or radiation treatments, our stems cells are put back in our body to make normal blood cells. This is called a rescue transplant.
- Allogeneic bone marrow transplant:
  - Stem cells are removed from another person, called a donor.
  - Most times, the donor’s genes must at least partly match our genes (twins, siblings).
  - A brother or sister is most likely to be a good match. Sometimes parents, children, and other relatives are good matches.
  - Special tests are done to see if a donor is a good match for us.
  - People who are not related to us, yet still match, may act donors.
- Umbilical cord blood transplant:
  - This is a type of allogeneic transplant.
  - Stem cells are removed from a newborn baby’s umbilical cord right after birth.
  - The stem cells are frozen and stored until they are needed for a transplant.
  - Umbilical cord blood cells are very immature so there is less of a need for perfect matching.
The success of bone marrow transplantation isn’t assured fully until the reseeding of the marrow with healthy cells is established.