What is a Stem Cell?
Blood cells are formed in the hollow of the bones in a soft gel like substance called bone marrow. The cells in the bone marrow are called stem cells and these are pluripotent, that is, they have the ability to develop into any type of cells. So stem cells are are undifferentiated cells that can develop into the required type of cells.
Differentiation is the process where cells develop different organelles (parts of a cell are called organelles) to accommodate the different functions of that cell and this process is called hematopoiesis.
Bone Marrow or Stem cell transplantation:
Stem cell transplant as the name suggests involves the replacement of old and affected stem cells by new healthy ones. Certain cancers and other conditions affect the hematopoietic stem cells from developing normally and in such cases, a stem cell transplant is needed.
Stem cell and bone marrow transplantation refer to the same process by which blood cancer is treated. Previously it was more commonly known as bone marrow transplant involved the stem cells being collected from the bone marrow. Now stem cells are collected from the blood instead of bone marrow and is called stem cell transplantation usually.
Types of stem cell transplantation:
There are two main types of stem cell transplantation which are as follows:
- Autologous transplantation:
In autologous transplant, the stem cells from the patient himself/herself are collected. This is followed by a strong dose of chemotherapy or even radiation therapy. Once the rest period after the treatment is complete, the collected stem cells are retrieved and introduced back into the body intravenously. The stem cells reach the bone marrow in about 24 hours where they start growing and multiplying.
- Allogeneic transplantation:
In allogeneic transplantation, the stem cells of another person are used for the transplantation. It is important to find an exact match for this, as there are proteins called antigens that need to match to those of the donor to avoid complications. Siblings of the patient are most likely to be the best match, if not, a close family member may work too. In case a likely donor is not found in the patient’s circle, the closest match is found from the available donor list.
Factors to consider for the type of transplantation:
The following are a few factors taken into consideration when deciding the type of stem cell transplantation.
- The patient’s diagnosis: In case of ALL (Acute Lymphocytic Leukemia), MDS (Myelodysplastic Syndrome) etc, the chances of relapse is high or the blood cells are affected too much to be used for autologous transplant.
- Sufficiency stem cells: If sufficient number of stem cells cannot be collected from the patient’s body, then allogeneic transplant is the only choice.
- Age: Allogeneic stem cell transplant is more likely to be successful in younger patients than in older ones. This is because older patients are likely to have complicated conditions, the overall effect of chemotherapy and/or radiation therapy can cause too many side effects and a general decrease in body tolerance.
- Availability of donor: This is an important factor to take into consideration to choose the type of transplantation is the availability of donor. Improper match leads to severe complications.
Before undergoing stem cell transplantation, the patient is given pretreatment or conditioning treatment where high dosage of chemotherapy or radiotherapy is given for the following reasons:
- To eliminate any diseased cells that might remain at the time of stem cell collection
- To eliminate white blood cells that can attack the developing stem cells especially in case of marrow failure
- To decrease the risk of immune cells rejecting the transplant cells (in case of allogeneic transplant)
As chemotherapy or radiation therapy is a part of the transplantation process, many side effects of those treatments can be seen in this treatment method too. The most serious side effect are infections and GVHD which will be discussed in detail after the common side effects.
Immediate side effects:
These are likely to last for the initial one to two weeks of transplant.
- Nausea and vomiting
- Mouth Sores
- Easy bruising and slow clotting of blood due to decrease in platelet count.
- Anemia due to decrease in RBC count.
Long term side effects:
These side effects can develop months or even years after the transplantation process
- Early menopause in women
- Risk of developing other cancers
Due to pretreatment, the immunity of the body is severely low during the process. The bacteria, virus and other germs that normally do not affect the body, cause infections in this stage. While the white blood cells recover within two weeks of treatment, the immune system never completely recovers from the treatment.
Graft versus Host Disease (GVHD):
The risk of GVHD is the most serious side effect of stem cell transplantation which occurs in case of allogeneic transplantation. In this condition the the new stem cells attack the body. The T cells of the donated stem cells view the host (patient’s) cells as foreign and attack them. Normally T cells do not attack our own body cells as they recognise the proteins called Human Leukocyte Antigens (HLA) of our body.
This is why close matching is necessary for allogeneic transplantation. Higher the matching, lesser is the risk of developing GVHD though it can develop even in case of 100% match. Doctors will prescribe medication in case of GVHD to help support the immune system. There are two types of GVHD- Acute and Chronic.
Frequent checkups and tests are required post treatment to ensure that the bone marrow is functioning properly and there are no threatening side effects or complications. The follow up care is different for the first three months and post that period.
First 3 months:
Check up are scheduled with frequency ranging from daily to once every two weeks depending on the patient’s condition until blood cell counts are back to optimum levels. Frequent blood count tests, medication to help fight infections, immunosuppressant drugs in case of allogeneic transplant, blood transfusions if needed, etc can be expected. Acute GVHD is likely to develop is this period.
After 3 months:
After three months, a follow up schedule is given depending on the patient’s response to treatment and recovery. If no complications arise, the frequency of check ups is decreased as the risk decreases. General health and bone marrow check ups are done during this period. By the end of first year, the stem cells are expected to be fully functional and produce healthy blood cells. Vaccines commonly given during childhood may be given again about one to two years after treatment.