stem cell transplantation?
Stem cell is a primitive cell in the body that can evolve into various types of specialized cells. It can also make more stem cells and thus continuously regenerate the pool for stem cells.
Stem cell transplantation is a process in which stem cells from a donor are injected into a patient to regenerate into required specialized cells.
hematopoietic stem cells (HSC)?
Hematopoietic stem cells (HSC) are cells that give rise to the lymphocytes, other blood cells and other cells of the immune system. Infusion of HSC into a donor is called as hematopoietic stem cell transplantation (HSCT).
What is the
difference between stem cell transplantation and bone marrow transplantation?
Traditionally, stem cells were obtained from bone marrow and these stem cells from a donor were infused into a patient. This is called as bone marrow transplantation. Now-a-days stem cells can be obtained from blood or from the umbilical cord (cord blood) at time of birth.
For which diseases stem cell transplantation can be done?
Several genetic diseases such as inborn errors of metabolism, primary immunodeficiencies such as severe combined immune deficiency (SCID), Wiskott-Aldrich syndrome (WAS), Hyper IgM syndrome (HIGM) and chronic granulomatous disease are treated with HSCT. In addition, diseases such as thalassemia and leukemia can also be cured by HSCT. These stem cells then replace the cells deficient in the enzyme causing disease with normal cells.
What are the
pre-requisites when doing hematopoietic stem cell transplantation?
One of the first pre-requisite is finding a donor whose tissue matches that of the patient. This is determined by doing histocompatibility antigens (HLA) in both donor and recipient and checking for 100% match. HLA antigens of each person are unique and a chance of getting a 100% match is 1 in a million. People who are closely related (like brothers and sisters) share many genes and have HLA antigens very similar to each other. Thus each sibling has 25% chance of having 100% match. If an HLA identical matched sibling donor is not available, then suitable donor can be determined from registries of individuals who have volunteered to serve as bone marrow donors.
What happens if a 100% HLA matched donor is not available?
There have been instances where many patients have successfully undergone transplantation using donors that were not fully matched. Success rate is not that high as 100% matched transplant and successful transplantation decreases as degree of mismatch between patient and donor increases.
Also, the donor's mature T-lymphocytes can be removed from the stem cells before infusing them so that rejection rates decrease. Usually unmatched donors are the parents as they share one-half of the HLA antigens of their child.
How is bone marrow transplantation done?
Bone marrow from the donor is removed from the hip bone by a needle and syringe. About 10 ml of marrow is taken from each puncture site. (If more is taken, the marrow gets diluted with blood). Maximum amount of marrow taken depends on the weight of the recipient. Usually only a few punctures are needed if the recipient is a baby but in adult recipient, over 100 punctures may be required in the donor.
Due to the ability of stem cells to regenerate the donor does not get depleted bone marrow.
The marrow removed from the donor is then filtered to remove any small particles of bone and then placed in a sterile plastic bag and injected into the recipient into a vein in same manner as blood transfusion. In case of cord blood, the amount of stem cells are small as only small quantity of cord blood is obtained, there may not be sufficient number of stem cells to treat larger children.
What are the
complications of a hematopoietic stem cell transplantation ?
The recipient's immune system may treat the donor's marrow as foreign, react against it and reject it. Thus one problem of a stem cell transplant is rejection. Thus most patients who receive hematopoietic stem cell transplantation undergo chemotherapy and/or radiation therapy in order to suppress their immune system to prevent rejection. The recipient thus also becomes susceptible to infections as the patient's immunity is down.
Another problem that may be seen with stem cell transplantation is that the donor marrow which contains T-lymphocytes may recognize the patient's tissues as foreign and attack it. This is known as graft versus host disease (GVHD).